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Perception without processing : J.J. Gibson's ecological approach Smart, Brent Maxwell 1988

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PERCEPTION WITHOUT PROCESSING: J . J . GIBSON'S ECOLOGICAL APPROACH By BRENT MAXWELL SMART B.A., The University of Calgary, 1983 A THESIS SUBMITTED IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF PHILOSOPHY  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA August 1988 .® Brent Maxwell Smart, 1988  In  presenting  degree freely  at  this  the  available  copying  of  department publication  thesis  in  partial  fulfilment  of  the  University  of  British  Columbia,  I  agree  for  this  thesis  or of  reference  by this  for  his thesis  and  scholarly  or for  her  Philosophy  of  T h e U n i v e r s i t y o f British Vancouver, Canada  Date  DE-6 (2/88)  August  l  f  1988  Columbia  I further  purposes  gain  shall  that  agree  may  representatives.  financial  permission.  Department  study.  requirements  It not  be  that  the  Library  permission  granted  is  by  understood be  for  allowed  an  advanced  shall for  the that  without  make  it  extensive  head  of  my  copying  or  my  written  Abstract The ecological movement in the psychology of perception, founded by James J . Gibson, hold that t r a d i t i o n a l approaches to perception are based upon c e r t a i n fundamental mistakes.  The chief one, ecological  t h e o r i s t s c l a i m , i s that perceptual information pickup consists of the a p p l i c a t i o n of c e r t a i n cognitive processes to sensory input which is not s p e c i f i c to features of organisms' environment.  Gibson's fundamental  claim i s t h a t perception does not require the processing of some form of sensory input.  In t h i s sense, the ecological approach i s said to be  a theory of d i r e c t perception. An important debate over the Gibsonian view concerns the question of whether or not perceptual information pickup without cognitive processing is a coherent n o t i o n .  Among the more recent w r i t e r s who claim  that the ecological view w i l l not work as i t stands are Jerry A. Fodor and Zenon W. Pylyshyn.  They claim, e s s e n t i a l l y , that Gibson's approach  has no means f o r accounting f o r i n t e n t i o n a l i t y .  Fodor and Pylyshyn  are answered by four prominent Gibsonians who claim such c r i t i c i s m s are u t t e r l y baseless.  These ecological t h e o r i s t s , Michael Turvey, Robert  Shaw, Edward Reed, and William Mace endeavour to show how t h e i r approach can indeed account f o r i n t e n t i o n a l i t y .  This debate between Fodor and  Pylyshyn on the one hand, and Turvey, Shaw, Reed, arid Mace on the other i s a perfect example of the kinds of misunderstandings that have arisen between Gibsonians and proponents of t r a d i t i o n a l  view.  In t h i s t h e s i s , I supply a d e t a i l e d description of Gibson's model  as i t r e l a t e s to the issue of how i n t e n t i o n a l i t y could survive perception without processing.  Fodor and Pylyshyn's understanding and assessment  of the Gibsonian position w i l l then be examined.  Although these defenders  of t r a d i t i o n a l views have, some important concerns,.they also seem not to have a proper grasp.of,:some Gibsonian concepts.  In p a r t i c u l a r ,  Fodor arid Pylyshyn have an unsatisfactory grasp of the notion of an invariant. There are more serious misunderstandings evident in the response to Fodor arid Pylyshyn given by Turvey et a l .  I point out that these  ecological t h e o r i s t s have d i f f i c u l t i e s with philosophical terms and theories they employ i n defense of Gibson.  As a r e s u l t of evident  confusions over notions of i n t e n s i o n , extension, and property, arid confusions over the nature of Fred I . Dretske's theory of natural laws and H i l l a r y Putnam's theory of natural kinds, Turvey et al do not manage to show how Gibson's approach could account f o r  intensionality.  I conclude by suggesting that the ecological approach nevertheless i s compatible with the idea,of analyzing perceptual information pickup in terms of behaviour, or d i s p o s i t i o n s t o behave.  On such an i n t e r -  p r e t a t i o n , the ecological approach is s i m i l a r in many important respects to the D.M. Armstrong's philosophical theory of perception.  The compar-  ison provides ecological t h e o r i s t s with a precedent as well as p h i l o sophical model t o c o n s u l t . i n order to better, understand the philosophical language and terminology.'-..On the other hand, the comparison with Armstrong provides philosophers of perception w i t h a means f o r approaching Gibson's view and the problems with which i t w i l l he confronted.  iv  Table of Contents ABSTRACT  ii  ACKNOWLEDGEMENT  v  Chapter I  1  (i) (ii) (iii) (iv)  •  2 6 11 21  II  26 (i) (ii) (iii) (iv)  •  III  26 28 35 44 48  (i) (ii)  48 64  IV  67 (i) (ii) (iii) (iv) (v)  67 70 71 77 80  V  89 (i)  89  (ii)  96  VI (i) (ii) (iii) (iv) SOURCES CITED  109  •  109 114 125 127 137  Acknowledgements I would l i k e to express my appreciation to Dr. Gary Wedeking and Dr. Steven S a v i t t f o r t h e i r considerable help in the development of my thesis t o p i c , and f o r the many hours they have spent c a r e f u l l y reading d r a f t s . I would also l i k e to thank my parents, Max and Sylvia Smart, and my wife Louise, f o r a l l t h e i r support, material and otherwise. F i n a l l y , I would l i k e to express my g r a t i t u d e to G.M. Grieg, professor of philosophy (emeritus) at the University of Calgary f o r a l l t h a t he taught me about philosophy. His unequalled dedication to his students w i l l be an example to me always.  Chapter One James J . Gibson's ecological approach to perception^'s an approach s t i l l very much undergoing refinement and hard c r i t i c a l s c r u t i n y .  Gibson  claims to have begun developing the theory s h o r t l y a f t e r the Second World War.  A number of well-known psychologists continue today to expound  Gibson's basic view and t o attempt to contribute more d e t a i l to  it.  Gibson's approach is taken by i t s founder and his followers to c o n s t i t u t e a new form of d i r e c t perceptual theory. i t is a v a r i e t y of d i r e c t realism.  Some even suggest that  A l l Gibsonians regard the outlook as.  r a d i c a l , as being an important divergence from v i r t u a l l y a l l previous perceptual t h e o r i e s .  A few of them have even speculated that the ecological  approach's supercession of p r i o r t r a d i t i o n a l views would amount to a 2  Kuhnian-style r e v o l u t i o n .  Others who are rather less i n d i s c r e t e in t h e i r  p r e d i c t i o n (Gibson being one of these) are nevertheless at pains to emphasize the alleged radical nature of t h e i r ideas.  Jerry A. Fodor and  Z.W. Pylyshyn believe there is a way of reading the ecological theory which reconciles i t with the "Establishment" (Fodor and Pylyshyn's term f o r t r a d i t i o n a l t h e o r i s t s ) , but go on t o note quite r i g h t l y t h a t Gibson does 3  not want his views i n t e r p r e t e d in such a c o n c i l i a t o r y fashion. This f i r s t chapter is one h a l f of an o u t l i n e of the ecological approach.  I w i l l endeavor t o introduce Gibson's view i n a very general way.  The emphasis w i l l be on his m o t i v a t i o n : of the Establishment and why.  what he believes are the mistakes  Detailed questions relevant to the p h i l o s -  ophical aspects of the Gibsonian Theory w i l l be dealt w i t h i n subsequent chapters.  2 (1) Gibson c i t e s f i v e important points over which his view d i f f e r s from 4  that which he regards as the t r a d i t i o n a l approach to perception : 1. The notion of perception i s conceived as the pickup of information. To perceive is t o pick up information about oneself or one's surroundings. 2. The categories of perception are reconceived. organisms perceive utility.  Gibson suggests that  t h e i r surroundings predominantly i n terms of  Organisms perceive t h e i r environment i n terms of what i t  affords. 3. There is a new view of the basis of perception (Gibson often r e f e r s to t h i s as "information f o r " perception).  This is Gibson's notion  of an " i n v a r i a n t " , or i n v a r i a n t s t r u c t u r e of ambient energy. 4. Perceptual systems are taken to be hierarchies of organs rather than i n d i v i d u a l organs or banks of receptors.  These sets of organs  function together in order to f a c i l i t a t e the pickup of information. 5. Perceptual systems must concurrently r e g i s t e r persistence and change in the f l u x of ambient energy to which each system is sensitive. 4) and 5) are relevant to the main issues w i t h which t h i s thesis w i l l be concerned although they are not c e n t r a l .  To the extent that they  require e l a b o r a t i o n , they w i l l be explained i n Chapter two.  Chapter two  w i l l deal f a r more with terminology of the ecological approach.  Much of  i t w i l l be devoted to 3) since the concept of an i n v a r i a n t is both a c r u c i a l and d i f f i c u l t idea of Gibson's.  As with 3 ) , 2) also pertains to a  showpiece, so to speak, of the ecological approach.  To explain what i t  means t o say that an organism perceives i t s environment in terms of requires an explanation of the notion of an "affordance".  utility  That w i l l be one  3  of the l a t e r tasks of t h i s chapter. F i r s t i t is necessary to expand and comment on 1 ) , however.  The  assertion from which Gibson's theory grows is t h a t to perceive is to pickup information.  For a number of reasons, the focus here w i l l mainly be on  visual perception.  Not least of these reasons is that Gibson's l a s t book,  i n which his new approach is most developed, is w r i t t e n e n t i r e l y about vision.  C l a r i t y of exposition is also f a c i l i t a t e d by thus constraining  discussion.  the  One should not, however, take the concentration on v i s i o n to be  a t a c i t assumption that an explanation of visual perception i s , with only terminological adjustments, a suitable account of the operations of other modalities. Gibson supposes there are always two d i f f e r e n t sorts of information available f o r pickup: about oneself.  information about the environment and information  These two v a r i e t i e s are correlated with his terms  "exteroception" (perception of the environment) and "proprioception" (perception of one's own body).  As one examines the ecological approach,  i t should become apparent that the two kinds of information pick up are very much interconnected.  The information one can pick up about one's own  surroundings i s p a r t i a l l y contingent upon proprioception.  Nevertheless, my  discussion w i l l be concentrated on exteroception since t h i s is the kind of perception which is t y p i c a l l y . o f i n t e r e s t i n the philosophy of perception. Thus, as i t is to be considered in subsequent chapters, perception w i l l mainly r e f e r to the pickup of information about the environment via visual systems. A very important point to make about Gibson's theory is that information pickup is an epistemic n o t i o n . pickup is epistemic perception.  Perceiving considered as information  Epistemic perception occurs when and only  when the process of perceiving y i e l d s knowing, b e l i e v i n g , j u d g i n g , or the l i k e ( t h a t i s , some kind of epistemic s t a t e ) .  I t is to be distinguished  4 from so-called "simple p e r c e i v i n g " , ^ which is not the a c q u i s i t i o n of some epistemic s t a t e .  The key difference between the two is t h a t p e r c e i v i n g , in  the epistemic sense, denotes an i n t e n t i o n a l r e l a t i o n whereas simple perceiving does not. I t is important to remember that Gibson's approach is an account of epistemic perception, because a large c r i t i c i s m of the ecological approach w i l l turn out to be that i t cannot explain the i n t e n t i o n a l component i n perceiving.  This c r i t i c i s m could only be a problem f o r a theory concerned  with epistemic perception.  Although in ordinary language i t is often  evident from the context whether an occurrence of the word "perceives" is being used in the simple or in the epistemic sense, the use w i l l be made e x p l i c i t throughout t h i s t h e s i s .  Any occurrences of "perceives" in the  simple sense w i l l be c l e a r l y indicated by some construction such as "(simple) perceives", or by s u b s t i t u t i n g "senses" f o r "perceives".  Otherwise, the  word should be taken i n the epistemic sense. F i n a l l y , the d i s t i n c t i o n between epistemic and simple perceiving is sometimes i d e n t i f i e d with the d i s t i n c t i o n between "perceiving things" and "perceiving t h a t " .  This is not quite accurate because epistemic perception  is any sort of perception which requires the perceiver to be i n some 8 epistemic (usually b e l i e f ) s t a t e .  "Perceiving a s " ,  t h a t " , i s a v a r i e t y of epistemic perception.  as well as "perceiving  These two notions d i f f e r both  grammatically and s u b s t a n t i v e l y . With respect to grammar, when "perceives t h a t " occurs i n a sentence, "perceives" acts as a bridge verb, taking a sentence as i t s grammatical object.  "Perceives as" takes a noun or noun phrase as i t s grammatical  object. Also, the t r u t h of "John perceives that there is a hawk overhead" ( f o r example) requires the embedded sentence, "there is a hawk overhead", to be  5  true.  However, "John perceives the thing overhead ( t h a t , i t ,  something...)  as a hawk" can be true even i f t h a t which John sees as a hawk is not a hawk at a l l .  There is an exception to t h i s general observation, though, whenever  the noun phrases occurring to the l e f t and to the r i g h t of "as" are e i t h e r the same, as in "perceives X as (qua) X", or e f f e c t i v e l y the same, as i n "perceives X as such". Both "perceiving as" and "perceiving t h a t " form r e f e r e n t i a l l y opaque contexts since both involve epistemic states of the perceiver.  With  reference to the previous example, suppose t h a t the very hawk John perceives is a r e d - t a i l e d hawk.  From the t r u t h of "John perceives t h a t there is a  hawk overhead", i t does not follow that John perceives t h a t there is a redt a i l e d hawk overhead.  S i m i l a r l y , from the f a c t that John perceives some-  thing as a hawk, i t does not follow t h a t John perceives i t as a r e d - t a i l e d hawk.  The difference in the l o c u t i o n s ' opacity is t h a t whereas "perceives  t h a t " does not guarantee t r u t h - preserving s u b s t i t u t i o n of codesignative terms anywhere to the r i g h t of the verb, "perceives as" r e s t r i c t s u t i o n only to the r i g h t of " a s " .  substit-  With the exception of the expressions  "perceives X as such" and "perceives X as X", noun phrases occurring to the l e f t of " a s " . The important substantive difference concerns the aforementioned difference in the t r u t h conditions of the expressions.  That i s , John can  perceive something as a hawk, but cannot perceive that there is a hawk when there are only ravens overhead.  I f one bases a theory of perception on the  notion of "perceiving t h a t " , then non-veridical perception must simply be regarded as f a i l u r e s to perceive.  I f one's perceptual theory is based on  the idea of "perceiving a s " , then non-veridical can be counted as misperc e p t i o n , but perception nonetheless.  9  6  I t i s not clear which notion of epistemic perception Gibson would adopt, p a r t l y because he is not completely decided on how to handle perceptual mistakes, and p a r t l y because he is not as careful about his terminology as would be p h i l o s o p h i c a l l y d e s i r a b l e .  Fodor and Pylyshyn  sometimes seem i n c l i n e d to categorize Gibson as holding a theory which analyzes perception i n terms of "perceiving t h a t " . ^ 1  However, Gibson's  discussion can be read very comfortably i n terms of "perceiving as".  My  discussion w i l l therefore make f a r greater use of the l a t t e r l o c u t i o n . (ii) I t must seem quite presumptuous of Gibsonians to claim t h a t v i r t u a l l y the e n t i r e community, past and present, of researchers in perception have been labouring under c e r t a i n mistaken assumptions.  This is especially true  since there is no systematic discussion in Gibson of various Establishment a l t e r n a t i v e s and how they p a r t i c u l a r l y exemplify the mistakes he suggests. As a r e s u l t , Gibson stands accused by some c r i t i c s , such as S. U l l m a n , * of 1  arguing s e l e c t i v e l y against proposed a l t e r n a t i v e s .  Although there is a  c e r t a i n force i n the complaint, the adequacy of Gibson's approach w i l l of course depend upon i t s own success in explaining the phenomena to which i t i s supposed to apply, rather than on the deficiencies of r i v a l s ( I am in no way suggesting that Ullman is unaware of t h i s ) .  I t is therefore not merely  presumptuous, but unnecessarily so, f o r Gibsonians to assert t h a t nearly the e n t i r e h i s t o r y of perceptual theory indulges i n the same basic e r r o r s . A l t e r n a t i v e l y , one can simply i d e n t i f y the general assumptions Gibson supposes philosophers and psychologists should abandon and take the Establishment theories to be whichever theories happen to subscribe to these. U l t i m a t e l y , Gibson must show that his own view succeeds i n avoiding the d i f f i c u l t i e s i n accounting f o r perception that he envisages ( w i t h o u t , of  7  course, r a i s i n g f u r t h e r ones). A f a i r l y general attempt of Gibson's to d i f f e r e n t i a t e between the t r a d i t i o n and his own view is as f o l l o w s : Up to the present time, theories of sense-perception have taken f o r granted that perception depends wholly on sensations that are s p e c i f i c to receptors. I have called these theories of sensation-based perception. The present theory asserts the p o s s i b i l i t y of perceptual experience without underlying sensory q u a l i t i e s that are s p e c i f i c to receptors, and I have called t h i s a theory of information-based perception.12 Now one reason t h a t Gibson i s accused of s e l e c t i v i t y is t h a t , i n s p i t e of his use of "sensation" and "sensory q u a l i t y " , he means to take aim at modern-day "information-processing" views as well as such t r a d i t i o n a l theories as those of Hermann von Helmholtz,  13  or even John Locke.  14  Gibson  takes the information-processing theories to be l i t t l e more than dressed-up versions of Lockean or Helmholtzian views: Not even the current theory that the inputs of the sensory channels are subject to "cognitive processing" w i l l do. The inputs are described in terms of information theory, but the processes are described in terms of old-fashioned mental acts: r e c o g n i t i o n , i n t e r p r e t a t i o n , inference, concepts, ideas, and storage and r e t r i e v a l of ideas. These are s t i l l the operations of the mind on the deliverances of the senses, and there are too many complexities e n t a i l e d in t h i s theory.15 In a s i m i l a r v e i n , Gibson complains about t h e o r i s t s who have taken computer analogies too much to heart: Adherents to the t r a d i t i o n a l theories of perception have recently been making the claim that what they assume is the processing of information in a modern sense of the term, not sensations, and that therefore they are not bound by the t r a d i t ional theories of perception. But i t seems to me that a l l they are doing is climbing on the l a t e s t bandwagon, the computer bandwagon, without reappraising the t r a d i t i o n a l assumption that perceiving is the processing of i n p u t s . ^ To put matters in the most neutral language possible, Gibson's objection is to the view that perceptual pickup of information is a matter of sensory/perceptual systems receiving meaningless input which is then  8 transformed i n t o information by cognitive processes that i n t e r p r e t i t .  The  conception of input Gibson purports to have in mind is "sensory or a f f e r e n t nerve i m p u l s e s . " ^  Elsewhere, however, Gibson's attack i s directed against  views on which the input would be called sense-data, sensations, visual or r e t i n a l images, or q u a l i t i e s or disturbances i n s e n s e - f i e l d s .  His c h i e f  concern is w i t h the idea of input being " s p e c i f i c to receptors" rather than t o features of one's surroundings (environment). The term " s p e c i f i c a t i o n " is a technical one on the ecological approach, one that is important in understanding the view.  In general, i f a sensory  input is uniquely associated with some state of the nervous system, then the input i s said to be s p e c i f i c t o t h a t state (Gibson has such a general notion of input t h a t i t is d i f f i c u l t to d e f i n e , but I take i t t h a t i t is something of which perceiving organisms may be c o g n i t i v e l y aware. about the notion of sensory input s h o r t l y ) .  More w i l l be said  In terms of the ecological  notion of " s p e c i f i c " , the t r a d i t i o n a l view amounts to the claim that a sensory input specifies a state of the nervous system or of the receptor. That i s , by obtaining i n p u t , a perceiving organism picks up information about some state of  itself.  One and the same kind of environmental phenomenon can bring about d i f f e r e n t states of one's nervous system and one and the same state may be brought about by d i f f e r e n t kinds of environmental phenomena.  Therefore, a  sensory input which is s p e c i f i c to a nervous system state w i l l only be s p e c i f i c t o such a s t a t e . some environmental f e a t u r e .  I t w i l l not also be uniquely associated with Any psychological theory of perception which  has some form of sensory input as i t s basis w i l l count as an Establishment theory f o r Gibson.  The ecological theory of s p e c i f i c a t i o n , as i t has been  explained by some of Gibson's supporters, w i l l receive more thorough,  9 c r i t i c a l treatment in l a t e r chapters.  The problems Gibson envisages f o r  r e c e p t o r - s p e c i f i c approaches to perception w i l l be described presently. Gibson claims t h a t sensation-based theories (theories based on sensory input that i s ) require a cognitive s t r u c t u r e capable of g e t t i n g information about one's environment out of the meaningless input.  Operations postulated  to explain how r e c e p t o r - s p e c i f i c input is transformed i n t o information about one's environment are the sorts of c o g n i t i v e , mental, or i n t e r n a l processes Gibson claims are not necessary f o r perception.  These processes f a l l in the  general area of inference and memory (storage and r e c a l l ) .  In l i s t i n g 18  operations he takes to be those invoked by sensation-based approaches, Gibson uses, i n addition to memory, the categories of " m e n t a l " , " s e m i l o g i c a l " , and "decoding operations".  Examples found under these headings range from  Kantian-style a p p l i c a t i o n of a p r i o r i categories of understanding, through deduction of features of the world via unconscious inference ( a t t r i b u t e d to Helmholtz), to the decoding of signals and use of perceptual cues. Language communication can be used as an analogy to i l l u s t r a t e the basic model of t r a d i t i o n a l approaches f o r Gibson.  A language, in the  general sense, consists of a set of symbols (physical signals) which has some i n t e r p r e t a t i o n . stage process.  A r e c e i v e r ' s being communicated t o is therefore a two-  A tokening (occurrence or use) of some of the symbols must  be detected by the receiver. input.  This is the correlate of reception of sensory  No information i s imparted to the receiver by the mere reception of  s i g n a l s , however.  I t s t i l l must have i n t e r p r e t a t i v e s k i l l s of c e r t a i n kinds  i n order to determine what the received input is supposed to convey. I n f e r e n t i a l processes are necessary, f o r example, i n order t o recognize a token as being one of a given type.  Also, depending on the complexity of  the system (and language) some symbols may be ambiguous.  Some function of  the receiver therefore must be to recognize the context in which a symbol occurs in order to determine which of several meanings the given token bears. F i n a l l y , any such system has to have some memory system so that stored knowledge of the r e l a t i o n s between symbols and what they denote can be r e c a l l e d at the appropriate time and applied to present i n p u t . Any perceptual theory conforming to the "sense-and-interpret" analogy constitutes a version of the t r a d i t i o n a l approach i n the sense Gibson means. While he and his followers e x h i b i t a broad suspicion of cognitive/mental processes i n p e r c e i v i n g , however, Gibson is most l u c i d and persistent i n his doubts about the role of memory.  His main conceptual concern pertains to  the notion that epistemic perception of one's environment is dependent upon previously acquired background knowledge, or concepts (innate or learned), and p r i o r sensory input.  Regarding sensation-based t h e o r i e s , Gibson notes  t h a t " A l l t h e o r i s t s seem to agree that past experience is brought to bear on the sensory i n p u t s , which means t h a t memories are somehow applied to 19 them.  C o n t r a r i l y , Gibson's own view is t h a t perceiving does not require  the a p p l i c a t i o n of memory t o i n p u t . Before i n d i c a t i n g the kinds of support Gibson c i t e s f o r his approach, a comment should be made on the status of sensory input.  Nowhere does  Gibson deny t h a t there are such things as visual sensations.  His view is  t h a t these simply do not f i g u r e in a cognitive theory of perception. Sensations, r a t h e r , are by-products of the physiological equipment with which organisms perceive.  In f a c t , f a r from being the basis of perception,  sensations are thought by Gibson to be a hindrance to i t .  He l i s t s the 20  obtrusion  of sensations on perception as a source of d e f i c i e n t perception.  For v i s i o n , the obtrusion would amount to a perceiver attending in an u n c h a r a c t e r i s t i c way t o a two-dimensional visual f i e l d rather than the threedimensional world.  Claiming they are i r r e l e v a n t to an account of perceptual  cognition  might well be the task Gibson plans f o r any notion of sensory i n p u t , although the s p e c i f i c reason need not always be the same.  In the case of  sensations or s i m i l a r " m e n t a l i s t i c " notions (sense-data, images in a visual f i e l d , f o r example), or even with regard to r e t i n a l images, i t is  fairly  plausible to suggest these are j u s t by-products rather than the basis or cause of perception.  Perhaps with other, physiological construals of i n p u t ,  such as nerve impulses or e x c i t a t i o n of receptor-banks, i t could be claimed t h a t , although these f i g u r e in the causation.of perception, they are part of a p h y s i o l o g i c a l , rather than a cognitive or psychological account of perceiving.  On Gibson's behalf one could say that a psychologist or  philosopher concerned with perception i s not expected to analyze perception in terms of neural impulses any more than he would be expected to analyze i t in terms of chemical reactions or the behavior of energy p a r t i c l e s . Making t h i s kind of point requires only the recognition of the existence of some hierarchy of levels of description and explanation in science.  Gibson  21 and his followers c l e a r l y do recognize some such hierarchy.  One should  therefore not be too quick to suppose Gibson denies the very existence of well-recognized psychological or physiological phenomena. (iii) Gibson states that his o r i g i n a l motivation f o r considering a d i f f e r e n t approach to perception is the r e s u l t of studies i n v o l v i n g the notion of depth-perception ( t h i s is a term, i n c i d e n t a l l y , that.Gibson t r i e s to avoid) in the 1940's.  The experiments were an attempt to apply psychological  theory concerning depth-perception to problems in a v i a t i o n and f l i g h t training.  An important i n i t i a l assumption apparently was t h a t depth-percep-  t i o n was based on the detection of cues in a f l a t (two-dimensional) field.  Gibson notes:  visual  The t r o u b l e was t h a t none of the tests based on cues f o r depth predicted the success or f a i l u r e of a student p i l o t , and none of the proposals f o r improving deptti perception by t r a i n i n g made i t any easier to learn to f l y . . . ^2 To t h i s he adds: I now say that there is information in ambient l i g h t f o r the perception of the layout of surfaces but not that there are cues or clues f o r the perception of depth. The t r a d i t i o n a l l i s t of cues is worthless i f perception does not begin w i t h a f l a t p i c t u r e . I t r i e d to reformulate the l i s t in 1950 as "gradients and steps of r e t i n a l s t i m u l a t i o n (Gibson, 1950b, pp. 1 3 7 f f ) . The hypothesis, of gradients was a good beginning, but the reformulation f a i l e d . Since Gibson f i r s t attempted t o develop a new approach to perception, he has suggested a number of problems f o r so-called Establishment views, including a v a r i e t y of experimental r e s u l t s which he takes to count against d i f f e r e n t versions.  The main general o b j e c t i o n s , though, continue to be founded on  the same theme underlying the foregoing quotes that the very basis f o r perception as i t is t r a d i t i o n a l l y conceived is deeply flawed and needs to be replaced.  This is often put, to repeat, by claiming that sensory input  is s p e c i f i c to receptors (states of a sensory or nervous system), rather than being s p e c i f i c to features of the environment.  Properties, o b j e c t s ,  events, processes, states of a f f a i r s may a l l be captured by the use of "features":  although Gibsonians take special i n t e r e s t i n the perception of  events, and of c e r t a i n kinds of p r o p e r t i e s , they are not as p a r t i c u l a r about t h e i r ontological commitments as a philosopher might be. To say t h a t input is not s p e c i f i c to environmental f e a t u r e s , i n Gibson's view, is to say t h a t with respect to the environment the input is meaningless.  Gibson objects to the notion that the pickup of information  (perceptual) awareness of what one's physical surroundings contains, must somehow be mentally derived or constructed from meaningless sensory input. The processes one needs to postulate i n order to explain how information i s gleaned from r e c e p t o r - s p e c i f i c i n p u t , Gibson t h i n k s , lead to too many  t h e o r e t i c a l complexities and/or p e r p l e x i t i e s .  He also suggests that per-  ception based on meaningless input is fundamentally flawed because i t requires possession of p r i o r knowledge or concepts i n order f o r a perceiving organism to process present input i n t o information. I f sensory input i s s p e c i f i c t o receptors, then a given input is supposed to be uniquely associated with some state of an organism's sensory or nervous system.  I t uniquely corresponds t o a kind of r e c e p t o r - s t a t e .  It  may or may not also be p e c u l i a r l y correlated with some feature of an organism's environment.  When a given kind of sensory input i§_ uniquely  associated with some environmental phenomenon, i t is a mere accident that is so r e l a t e d .  it  I t i s an accident in the sense that i t merely happens t h a t  only one sort of environmental phenomenon i s uniquely correlated with a c e r t a i n kind of sensory input and therefore to a p a r t i c u l a r state of the organism's nervous system. I f sensory input is s p e c i f i c to r e c e p t o r - s t a t e s , then changes of input w i l l correspond to changes i n these s t a t e s .  As is the case with associations  between given sensory input and environmental phenomena, there may or may not be c o r r e l a t i o n s between changes of input and changes (whether of a p a r t i c u l a r type or of d i f f e r e n t ones) i n features of one's environment. A l t e r a t i o n s in the frequency-mixture or d i r e c t i o n of the source of i l l u m i n a t i o n w i l l change the state of one's sensory system, as w i l l a l t e r i n g one's perspective ( p o s i t i o n r e l a t i v e to one's physical surroundings).  Some states  and changes of state of an organism's nervous system are the r e s u l t of physiological vagaries, connected e i t h e r i n d i r e c t l y or not at a l l to percept i o n of the environment (after-images and h a l l u c i n a t i o n s f o r instance). At the same t i m e , many of the a l t e r a t i o n s in the sensory portions of an organism's nervous system are the r e s u l t of changes i n i t s environment. Any perceptible event or process w i l l do as an example.  14 Since r e c e p t o r - s p e c i f i c input may or may not be uniquely associated with p a r t i c u l a r kinds of environmental phenomena, i t does not r e l i a b l y i n d i c a t e constituents of an organism's physical surroundings.  Similarly,  since change of input may or may not correspond to change i n the environment, i t is no consistent i n d i c a t o r f o r the occurrence of environmental transformations.  Gibson supposes that because sensory input is meaningless in t h i s  sense organisms must be endowed with c a p a b i l i t i e s f o r i n t e r p r e t a t i o n , means f o r adding to sensory i n p u t , that leads to some d i f f i c u l t A)  questions:  Given a theory on which input is not s p e c i f i c to features of the  environment, a p a r t i c u l a r sensory input could hardly be expected to be especially informative.  That i s , i t is more plausible to suppose on an  Establishment theory that information about one's surroundings is the r e s u l t of processing a series of inputs rather than i n d i v i d u a l ones.  Unless one  happens to be f i x a t i n g , a highly non-typical condition f o r an active organism, a series of visual inputs is going to consist of d i f f e r i n g i n d i v i d uals.  In s p i t e of the variable i n p u t , perceiving organisms (human ones at  l e a s t ) are aware of t h e i r environment as stable and unchanging.  Gibson  takes i t to be a mistake to t r y to explain t h i s phenomenon in terms of somehow applying mental processes, r e c a l l of past s i m i l a r occurrences, applying appropriate p r i o r knowledge (concepts) and the l i k e to the input in order t o derive awareness of unchanging features of one's physical surroundings. He w r i t e s : The century-old problem of why the world does not seem to move when the eyes move and the analogous problem of why the room does not appear to go around when one looks around are unnecessary. They only arise from the assumption that visual s t i m u l i andpVisual sensations are the elements of visual perception. Although the s o l u t i o n to the puzzle given by Gibson involves a good deal more than is indicated i n t h i s passage (a new notion of the c o n t r i b u -  t i o n of v i s i o n to proprioception and of the r e l a t i o n between proprioception and e x t e r o c e p t i o n ) , i t s resistance to r e s o l u t i o n in the past is c l e a r l y seen as r e s u l t i n g from the assumption t h a t perception is based on sensory inputs (visual sensation, i n t h i s case). B)  A puzzle closely related to how s t a b i l i t y , or nonchange, is perceived  i n the face of variable i n p u t s , i s t h a t of how an object is perceived as p e r s i s t i n g i n the face of variable input.  Any given kind of environmental  feature may be associated with an i n d e f i n i t e v a r i e t y of sensory input.  Some  part of an organism's sensory apparatus, then, must recognize any of an i n d e f i n i t e l y large s e t , or any of i n d e f i n i t e l y many sequences of input as r e l a t e d to some p a r t i c u l a r kind of environmental phenomenon.  To the extent  t h a t i t remains mysterious as to how a sensory system could perform t h i s t a s k , Gibson would regard the question of how large and variable sets of inputs manage to y i e l d awareness of the same, p e r s i s t i n g object as a problem the Establishment has yet to resolve.  This is a close kin to a problem 25  t h a t has troubled c e r t a i n philosophers  :  how can one recognize an object  as one and the same by obtaining d i f f e r e n t sense-impressions, sense-data, or the l i k e , belonging to i t ? C)  While these f i r s t two issues concern perception of p e r s i s t i n g features  of the environment, Gibson thinks the Establishment approach leads to complications in the perception of events (changing features) as w e l l . The r e g i s t e r i n g of a sequence of sensory input occurs over time.  The  input lasts only as long as the environment is constituted so as to cause the state of an organism's nervous system which is s p e c i f i e d by the input. According to Gibson's version of the t r a d i t i o n a l approach, as one perceives some progressive change in the condition of one's environment, there is a succession of sensory inputs as new states of the environment bring about  d i f f e r e n t , successive r e c e p t o r - s t a t e s .  An organism must therefore have some  complex s t o r a g e - r e c a l l - i n t e g r a t i o n system in order to r e t a i n and combine immediately past inputs with successive to bring about awareness o f an event. Without some memory process, there would be naught but the discrete r e g i s t e r i n g of i n d i v i d u a l i n p u t s .  Gibson apparently believes any such storage-  r e c a l l system would be f a r too cumbersome and that there is no coherent explanation of how i n d i v i d u a l sensory input could become "fused i n t o a scene" (or some c o r r e l a t e ) .  On the c o n t r a r y , he claims:  The simple f a c t is that perceiving is not focused down to the present item in a temporal s e r i e s . Animals and men perceive motions, events, episodes, and whole sequences. The doctrine of sensation-based perception requires the assumption that a succession of items can be grasped only i f the e a r l i e r ones are held over so as to be combined with l a t e r ones in a single composite. From t h i s comes the theory of t r a c e s , r e q u i r i n g that every percept lay down a t r a c e , that they accumulate, and that every trace be t h e o r e t i c a l l y able to r e i n s t a t e i t s proper, percept. This can be pushed to absurdity. I t is b e t t e r to assume that a succession o f items can be grasped without having to convert a l l o f them i n t o a simultaneous composite.'<Q The a l t e r n a t i v e Gibson alludes to in the l a s t sentence, as w i l l be discussed next chapter, is t o suppose there are c e r t a i n kinds of abstract properties called i n v a r i a n t s which are detectable by organisms' perceptual systems and which specify events and processes i n the environment. D)  The r e j e c t i o n of the idea that perception"is "focused down to the  present item in a temporal s e r i e s " is r e f l e c t e d as well i n what Gibson thinks about perception of that which is about to occur.  He adopts the  idea t h a t information pickup "slops over", so to speak, to include imminent events i n addition to those which have already occurred.  The conclusion  Gibson draws is the r e s u l t of experiments conducted by himself along with two colleagues  28  and l a t e r by W. S c h i f f .  29  An observer is placed close to a translucent screen upon which a small s i l h o u e t t e i s magnified r a p i d l y .  Observers, including a v a r i e t y of animals  used by S c h i f f i n the l a t e r study, apparently experience t h i s as rapid approach of a r i g i d object (as opposed, f o r instance, to enlargement or expansion of an e l a s t i c , non-approaching one).  That is to say, the  observer's behavior, when there is rapid magnification to the l i m i t (where the s u b j e c t ' s borders of the s i l h o u e t t e extend beyond the boundaries of f i e l d of view) indicates expectation of c o l l i s i o n .  The t e s t - s u b j e c t s 30  b l i n k e d , averted t h e i r eyes, cringed, and so f o r t h .  Gibsonians would  no doubt want t o make the general point that the consistency and speed of s u b j e c t ' s response, even among f a i r l y p r i m i t i v e creatures (crabs) tested by S c h i f f , would make an explanation in terms of processing s l i c e s of the expanding pattern and i n f e r r i n g " c o l l i s i o n " (an alleged t r a d i t i o n a l explan31 ation) quite implausible.  The conclusion Gibson draws which counts expli  c i t l y only against explanations of the behavior of the observers in terms of expectation, or inference, based on previous experience, is the f o l l o w i n The experiments of S c h i f f , Caviness, and Gibson (1962) and S c h i f f (1965) on o p t i c a l magnification of a s i l h o u e t t e in the f i e l d of view demonstrate t h a t "looming", the visual information f o r imminent c o l l i s i o n , is often detected by young animals who have never had painful encounters with an approaching object. They shrink away or b l i n k t h e i r eyes, or otherwise make p r o t e c t i v e responses without having any reason to "expect" c o l l i s i o n by reason of past experience. In t h i s case the visual nervous system is presumably attuned to the information at b i r t h . 3 2 Now Gibson is no more i n c l i n e d to accept a theory of perception which would explain the " c o l l i s i o n " experiments i n terms of expectations or i n f e r ences from some innate phenomenon, such as innate knowledge or concepts, than he is i n c l i n e d t o accept an e m p i r i c i s t view.  I t is not clear from the  previous quote whether Gibson would also consider these experiments as counting against the so-called n a t i v i s t version of the Establishment approach, though.  However, since he would c l e a r l y not consider the r e s u l t s  obtained by himself, S c h i f f , and Caviness as supporting some "innate ideas"  theory, there must be some d i s t i n c t i o n between such notions and that of "the attunement of perceptual systems at b i r t h " . distinction explicit.  Gibson never makes such a  Perhaps the d i s t i n c t i o n Gibson has in mind would be  that "attunement" of a perceptual system consists in an organism's being p h y s i o l o g i c a l l y structured so as t o pick up c e r t a i n kinds of information. To Gibson, t h i s would be d i s t i n c t from a theory which endows an organism, not w i t h a p a r t i c u l a r physiological makeup, but with the possession, p r i o r to b i r t h , of c e r t a i n information. E)  F i n a l l y , to take input s p e c i f i c to states of receptors as the basis  33 of perception is as Shaw, Turvey and Mace have put i t , to "the doctrine of i n t r a c t a b l e n o n - s p e c i f i c i t y " .  to subscribe  Since the postulated  input i s not uniquely associated with environmental f e a t u r e s , i t could only y i e l d information about the environment (be taken as an i n d i c a t o r of a parti c u l a r environmental type, say) i f i t were known what kind of thing under various circumstances produced the receptor s t a t e ( s ) specified by some input.  The conversion of sensory input i n t o information about one's envir-  onment therefore requires p r i o r possession of knowledge and/or concepts. Either the p r i o r knowledge required by an organism to pick up presently available information i s i t s e l f acquired or i t is innate. the former e m p i r i c i s t option produces a regress:  Taking  an organism cannot pick  up information about i t s environment without already having some other information about i t s environment that i t cannot pick up without s t i l l other i n f o r m a t i o n , and so on. postpones the problem.  Taking the l a t t e r , n a t i v i s t , horn only  By p o s t u l a t i n g c e r t a i n innate i n f o r m a t i o n , concepts,  p r i n c i p l e s of reason, or the l i k e , one can explain the o r i g i n of the information an i n d i v i d u a l organism possesses.  However, i t s t i l l remains to be  explained how the species t o which an organism belongs has come to possess  innate knowledge (and presumably how i t is passed on through successive generations).  The n a t i v i s t i s thus seen as encountering a problem at the  phylogenic level s i m i l a r to the one posed f o r the e m p i r i c i s t at the ontogenic l e v e l .  A present species member is said to have c e r t a i n information  i t acquired g e n e t i c a l l y .  I t s parents had the information to pass on because  they acquired g e n e t i c a l l y , and so on without end.  The n a t i v i s t view thus  makes the o r i g i n of our information as mysterious as the e m p i r i c i s t .  In  general terms, Gibson explains his version of the objection by saying: The e r r o r l i e s , i t seems to me, in assuming that e i t h e r innate ideas or acquired ideas must be applied to bare sensory inputs f o r perceiving to occur. The f a l l a c y is to assume that because inputs convey no knowledge they can somehow be made to y i e l d knowledge by "processing" them. Knowledge of the world must come from somewhere; the debate is over whether i t comes from stored knowledge, from innate knowledge, or from reason. But a l l three doctrines beg the question. Knowledge of the world cannot be explained by supposing that knowledge of the world already e x i s t s . A l l forms of 34 cognitive processing imply cognition so as to explain c o g n i t i o n . The d i f f i c u l t y Gibson sees, once again, is c l e a r l y directed at the assumption that perceiving is based on some form of meaningless input.  He  objects to any notion t h a t p r i o r knowledge, concepts, or some correlate is required to get f u r t h e r information from sensory input.  Thus Gibson writes  that " i f you agree to abandon the dogma that 'percepts without concepts are b l i n d , as Kant put i t , a deep t h e o r e t i c a l mess, a genuine quagmire, w i l l 1  35  dry up."  The problem posed f o r the Establishment here is assigned a  great deal of importance by a number of Gibsonians. There are a l t e r n a t i v e ways of s t a t i n g exactly what Gibson intends to r e j e c t , although they amount to much the same t h i n g .  One may say that he  rejects e i t h e r the necessity of p r i o r information or the necessity of cognitive/mental processing i n perception.  The r e j e c t i o n of processing  leaves no means f o r concepts or the l i k e to become e f f e c t i v e in perception. The r e j e c t i o n of p r i o r knowledge places serious r e s t r i c t i o n s on that f o r which cognitive processes could be used.  I t is not clear which point should  be given precedence but they converge on the same fundamental c r i t i c i s m of the Establishment:  the assumption that perceptual pickup of information  is based upon what Gibson would regard as meaningless i n p u t , input that does not specify features of an organism's environment, is a mistake.  Any  theory which accepts the assumption to which Gibson o b j e c t s , whatever the t h e o r e t i c a l language in which the view is couched, is an instance of what Gibson and his followers c a l l the t r a d i t i o n a l approach to perception (the Establishment view). Gibson's a l t e r n a t i v e is t o develop a new basis f o r perception on which the input is uniquely associated with p a r t i c u l a r features of an organism's environment, and on which the detection of such input by some perceptual system, by i t s e l f , constitutes the pick up of information.  Michael T.  Turvey, Robert E. Shaw, Edward S. Reed, and William M. Mace put the new assertion t h i s way: The fundamental hypothesis of the ecological approach t o v i s i o n , elaborated at great length by Gibson (1966, 1979) i s that o p t i c a l s t r u c t u r e specifies i t s environmental source and t h a t , t h e r e f o r e , mobile organisms with active visual systems t h a t can pick up t h i s information w i l l see t h e i r environments and s u i t a b l y adjust t h e i r a c t i v i t y , i f and when they detect that information (and only t h e n ) . Gibson himself expresses his fundamental view by saying that inform37 a t i o n is "simply a v a i l a b l e " , 38 "meanings" or "values".  or by claiming that organisms perceive  The sense in which the Gibsonian theory is  intended t o be a theory of d i r e c t perception is that the perceptual pickup of information does not require the mediation of cognitive processes, e s p e c i a l l y as would be used to apply p r i o r knowledge/concepts to sensory input:  when input is properly construed, i t s detection by perceptual  systems is the pickup of information.  (iv) Any d i r e c t theory of perception must be so with respect to some set of phenomena.  Gibson's view i s no exception.  Throughout t h i s discussion,  i t has been understood t h a t the ecological approach is a theory on which perceptual pickup of information about the environment is d i r e c t .  I have  a l s o , though not e x p l i c i t l y , roughly equated environments w i t h organisms' physical surroundings.  "Environment" is a technical notion of Gibson's,  however, and even though i t cannot be defined p r e c i s e l y , i t is important t o bring out points about the general c o n s t i t u t i o n of an environment. Philosophical debate concerning the immediacy of human perceptual connections t o things are most frequently concerned with these in r e l a t i o n to physical or material objects or some s i m i l a r n o t i o n , these being taken 39  as s u i t a b l e samples of the so-called external world.  The external world  could be thought of as c o n t a i n i n g , from some given t h e o r i s t ' s point of view, a l l that is m a t e r i a l :  physical o b j e c t s , events, processes, or states  of a f f a i r s of any size and s i t u a t e d anywhere w i t h i n the physical universe. Among the population of the e x t e r n a l , physical world is usually counted perceivers' bodies, although perceivers themselves are to be regarded as d i s t i n c t and not part of i t .  Gibson would not make such a d i s t i n c t i o n .  perceiving organism is part of i t s environment, on the one hand.  A  On the  o t h e r , when Gibson t a l k s about p r o p r i o c e p t i o n , he is not r e f e r r i n g to awareness of an ephemeral s e l f , a Cartesian t h i n k i n g thing which is d i s t i n c t from the physical organism t h a t moves through and i n t e r a c t s w i t h i t s onment.  envir-  S e l f - p e r c e p t i o n , in Gibsonian terms, involves awareness of the  states of one's own body and i t s r e l a t i o n s t o surrounding features of the environment.  Although environments include perceivers while the external world t y p i c a l l y does not, an environment is largely a subset of the external world.  I t is a place that supports l i f e , holds features necessary f o r org-  anisms of some kind to l i v e .  Put roughly, an environment consists of  "animal-relevant" features of the external world.  "External" or "physical"  world more closely resembles what Gibson means by "the world of physics". Gibson distinguishes the world of physics from an environment by w r i t i n g : The world of physics encompasses everything from atoms through t e r r e s t r i a l objects to galaxies. These things e x i s t at d i f f e r e n t levels of size that go to almost unimaginable extremes. The physical world of atoms and t h e i r ultimate p a r t i c l e s is measured at the level of m i l l i o n t h s of a m i l l i m e t e r and less. The astronomical world of stars and galaxies is measured at the level of l i g h t years and more. Neither of these extremes is an environment. The s i z e level at which the environment exists is the intermediate one that is measured in m i l l i m e t e r s and meters. The o r d i n a r y , f a m i l i a r things of earth are of t h i s size - - a c t u a l l y a narrow band r e l a t i v e to the f a r e x t r e m e s . ^ With respect to l i f e on t h i s planet, an environment consists of f a i r l y local physical phenomena.  The sun, other planets and more d i s t a n t astronom-  i c a l objects would a l l be excluded. is the notion of scale.  The most important point here, though  I t is very important to Gibson that perceiving  should be linked to what an organism must i n t e r a c t with in the physical regions i n which i t has grown up and in which i t s species has evolved.  In  general, animals i n t e r a c t with moderately s i z e d , tangible physical phenomena and therefore these are the kinds of t h i n g s , Gibson supposes, about which organisms ought t o be concerned with and suited f o r picking up information. What w i l l be said in subsequent chapters w i l l be said; bearing i n mind t h a t environmental phenomena, t h a t which we perceive™, consists of the "narrow band" of physical things with which organisms would t y p i c a l l y  interact.  The basic components of an environment, to be a l i t t l e more rigorous about Gibson's concept, are substances, surfaces, and a medium.  41  Gibson  postulates two environments f o r e a r t h . aquatic.  These are the t e r r e s t r i a l and the  For t e r r e s t r i a l animals (and i t is a species of these which is  obviously of the greatest i n t e r e s t ) , the medium is a i r .  The medium,  according to Gibson is "transparent" to perception, t e r r e s t r i a l organisms perceive things in and through i t .  I t permits locomotion.  The notions  of "substance" and "surface" are a p a i r because the surfaces of an environment are the surfaces of i t s substances.  Gibson defines "substance" very  generally as " s o l i d s and l i q u i d s that vary in composition and in resistance 42 to change."  In s h o r t , they are the tangible s t u f f of which the environ-  ment i s composed:  f l e s h , wood, g r a n i t e , and ( f o r the t e r r e s t r i a l  ment) water would a l l count as t y p i c a l examples.  environ-  Gibson characterizes  "surface" very g e n e r a l l y , saying that i t refers to the boundary between a substance and a medium.  Every substance has some surface.  These two  notions are v i t a l because the layout of surfaces and the nature of the substances to which they belong (sometimes j o i n t l y referred to as the e n v i r onment layout) are the terms in which Gibson organizes his account of visual perception.  Only structured l i g h t energy, as w i l l be explained next chapter  can be a source f o r the visual pickup of information.  The substances and  the surfaces make up the source of that which serves to provide l i g h t with the r e q u i s i t e s t r u c t u r e . The concept of an environment is s t i l l obviously f a i r l y general and i t seems destined to remain so.  There are plenty of examples, f o r instance, of  "poly-environmental animals", such as amphibians and c e r t a i n aquatic mammals that could cause trouble f o r any attempt to c l e a r l y individuate the Earth's two environments.  Also, some of Gibson's proponents use "environment" to  mean " h a b i t a t " , ^ which would c l e a r l y r e s u l t i n hundreds of environments on 4  Earth.  The main point t o bear in mind, though, is that Gibson wants to  confine his analysis of perception to the consideration of how i t allows the pickup of information about the places where an organism l i v e s and the phenomena i t must i n t e r a c t with there. This genuine i n t e r e s t in the ecological or evolutionary considerations i s p a r t i c u l a r l y clear i n the new categories of perception Gibson suggests. This r e f e r s to the second of the f i v e differences he claims between his approach and t h a t of the Establishment.  The essence of the claim is that  organisms perceive t h e i r environments p r i m a r i l y i n functional terms, or in terms of u t i l i t y .  The word " f u n c t i o n a l " here simply refers to t h a t which  the environment can do to and can do f o r organisms.  In Gibsonian terms,  organisms perceive environmental properties called "affordances".  Affordances  can be explained as f o l l o w s . Every animal has i n t e r e s t s and/or needs,, and a b i l i t i e s and v u l n e r a b i l i t i e s which determine how these can be f u l l f i l l e d .  These a b i l i t i e s and  l i m i t a t i o n s determine how an organism of some type could make use of i t s environment.  The s t r u c t u r e of the environment determines what there is to  be made use of by an animal, what actual opportunities there are f o r i t to use i t s a b i l i t i e s to s a t i s f y i t s needs (or f o r i t s v u l n e r a b i l i t i e s to lead i t to g r i e f ) .  This is t o consider the environment i n terms of that which i t  affords organisms. "Affordance" i s " a word Gibson coins to act as the substantive f o r the  44 verb "to a f f o r d " . onment.  An affordance is a- d i s p o s i t i o n a l property of the e n v i r -  The notion is most e a s i l y i l l u s t r a t e d by example (although i t  is  d i f f i c u l t to convey properly the g e n e r a l i t y of the notion t h i s way): ( r e l a t i v e to humans) a chef's knife affords c u t t i n g and also being cut.  A  rattlesnake affords being b i t t e n and poisoned, and also ( i t is alleged) eating.  R e l a t i v e l y l e v e l , s o l i d ground affords standing and walking.  Nelson  Goodman has w r i t t e n , with respect to d i s p o s i t i o n a l p r o p e r t i e s , t h a t an object  is f u l l of "threats and promises"  and t h i s can be used to give a good,  quick i l l u s t r a t i o n of affordances.  An affordance is a t h r e a t or promise  the substances and layout of surfaces of the environment hold f o r an organism ( f o l l o w i n g Goodman on another p o i n t , affordances are often indicated by Gibsonians by the a r t i f i c i a l addition of the s u f f i x e s " - i b l e " or " - a b l e " ) . Gibson sometimes puts t h i s by suggesting that affordances are values or 46 meanings. One of the most i n t r i g u i n g and unique aspects of the ecological approach to perception is Gibson's assertion that perception of affordances is the basic form of perception.  He takes the Establishment to be committed  to the primacy of "form p e r c e p t i o n " , perception in terms of manifest, sensible q u a l i t i e s .  C o n t r a r i l y , Gibson would deny that we recognize things  p r i m a r i l y as r e d , bulgy, heavy or the l i k e , claiming instead that things are p r i m a r i l y recognized as e d i b l e , h i d e - i n - a b l e , c u t - w i t h - a b l e ,  fall-off-  able, and so on. Thus Gibson holds t h a t the perceptual pickup of information only requires the detection of invariants by perceptual systems.  He also main-  tains t h a t the values or meanings of things ( r e l a t i v e to a perceiving organism) are the terms in which the environment is p r i m a r i l y perceived. The r e s u l t is a theory according to which i t is claimed t h a t things are d i r e c t l y perceived as having some meaning.  Gibson and his followers are  sometimes i n c l i n e d to put t h e i r point i n even more s t a r t l i n g terms: organisms " d i r e c t l y perceive" meanings.  Chapter Two The previous chapter began the task of e x p l i c a t i n g the Gibsonian theory of perception, explaining the f i r s t two of the f i v e essential differences Gibson sees between his own view and t r a d i t i o n a l approaches. The other three respects in which Gibson is supposed to d i f f e r from the Establishment is by: 3. suggesting a new basis f o r perception:  i n v a r i a n t s t r u c t u r e or  properties 4. taking perceptual systems to be overlapping hierarchies of organs 5. saying the function of perceptual systems involves the concurrent r e g i s t e r i n g of persistence and change This chapter w i l l continue the task which chapter one begins.  The  necessary d e t a i l w i l l be added to explain ( v i s u a l ) perceptual pickup of information through the notions of v i s u a l , or o p t i c arrays and i n v a r i a n t s . The foregoing points 3, 4, and 5 w i l l thereby be explained.  This chapter  w i l l conclude w i t h a discussion of Gibson's use of the term " i n f o r m a t i o n " . (1) In The Senses Considered as Perceptual Systems, Gibson i d e n t i f i e s perceptual systems*:  five  the basic o r i e n t i n g system, the auditory system, the  h a p t i c , the t a s t e - s m e l l , and the visual systems.  Each of these is s e n s i t i v e  to some form of energy (on a very l i b e r a l use of "energy").  The basic  o r i e n t i n g system is responsive to g r a v i t y and acceleration and the a u d i t o r y , system i s s e n s i t i v e to v i b r a t i o n s i n the medium, to give two examples.  The  only system to be elaborated here is the visual system, which is sensitive  to (stimulated by) l i g h t energy. Gibson says that t r a d i t i o n a l views hold that perceiving requires only the stimulation of receptors, or banks of receptors. passive senses.  He c a l l s these  These "passive" senses are a c t i v e only insofar as the  a c t i v i t y concerns the f i r i n g of neurons in the part of the brain to which the receptors are connected.  Perceptual systems, on the other hand, are  a c t i v e sets of organs designed to " o r i e n t , explore, i n v e s t i g a t e , a d j u s t , • •  optimize, resonate, e x t r a c t , and come to an e q u i l i b r i u m . "  2  I t is l e f t  l a r g e l y up to the reader to imagine precisely what i s entailed by these a c t i v i t i e s which is especially unfortunate in the case of " e x t r a c t i n g " or "resonating".  The detection of i n v a r i a n t s , which serves as Gibson's  replacement f o r the r e g i s t e r i n g of i n p u t , i s often described as e x t r a c t i o n of or resonating to an i n v a r i a n t by a perceptual system.  I t could only  have aided Gibson's case had he taken care to explain these a c t i v i t i e s of perceptual systems in some d e t a i l . The c o n s t i t u t i o n of the visual system is given in terms of  its  constituent organs and t h e i r adjustments: F i r s t , the l e n s , p u p i l , chamber, and r e t i n a comprise an organ. Second, the eye with i t s muscles in the o r b i t comprise an organ t h a t i s both s t a b i l i z e d and mobile. T h i r d , the two eyes in the head comprise a binocular organ. Fourth, the eyes in a mobile head t h a t can turn comprise an organ f o r the pickup of ambient i n f o r m a t i o n . F i f t h , the eyes in a head on a body c o n s t i t u t e a superordinate organ f o r information pickup over paths of locomot i o n . The adjustments of accomodation, i n t e n s i t y modulation, and dark adaptation go with the f i r s t l e v e l . The movements of compensation, f i x a t i o n , and scanning go with the second l e v e l . The movements of vergence and the pickup of d i s p a r i t y go w i t h the t h i r d l e v e l . The movements of the head, and of the body as a whole go w i t h the f o u r t h and f i f t h l e v e l s . 3  A l l of these adjustments, a c t i v i t i e s , and movements are undoubtedly important to the proper functioning of a visual system but only those r e lated to the l a s t two levels w i l l f i n d t h e i r way into the discussion of  invariants.  The adjustments of the eye-head system constitutes the pickup  of information by looking around.  The adjustments of the superordinate  organ of eyes in a mobile body c o n s t i t u t e the pickup of information through changing perspectives t h a t an organism takes on i t s environment. The c r u c i a l difference between a bank of receptors and a perceptual system is that the former i s incapable of the kinds of adjustments Gibson envisages f o r perceptual systems.  This difference captures the sense in  which receptors are said to be "passive".  Receptors merely r e g i s t e r  changing patterns of s t i m u l a t i o n and therefore do not comprise the " i n p u t output loops" of information pickup and adjustment t h a t are supposed to be comprised by Gibsonian perceptual systems.  There is no doubt, of course,  t h a t receptors and the regions of the brain to which they are connected are parts of perceptual systems.  I t is clear Gibson does not deny t h i s from 4  column three of his table mapping perceptual systems in Senses Considered. His point is j u s t that such sets of receptors, because they merely r e g i s t e r s t i m u l a t i o n , are not by themselves suited f o r the detection of i n v a r i a n t s . They can therefore only be parts of the systems required f o r the perceptual pickup of information. (ii) Once again, the form of energy to which the visual system is s e n s i t i v e is l i g h t .  However, t h i s is only to say t h a t the receptors contained i n the  organs of the visual system are stimulated by l i g h t energy.  Not a l l that  stimulates the visual system y i e l d s perception since, i n Gibson's terms, only s t r u c t u r e d , ambient l i g h t is a source of information. Ambient l i g h t surrounding a perceiving organism is described by Gibson as a "sea" or a " f l u x " of energy. visual or o p t i c array.  In ecological terms t h i s is known as the  "Ambient array" i s the general case f o r r e f e r r i n g to  any modality.  Since ambient l i g h t occurs in the absence of perceivers, thou'  Gibson defines " o p t i c array" more accurately and generally as the ambient l i g h t surrounding a "point of observation".  The s p e c i f i c use of "ambient  l i g h t " is to d i s t i n g u i s h between energy which is r e f l e c t e d by environmental surfaces and therefore is t y p i c a l l y s t r u c t u r e d , and radiant l i g h t , which is l i g h t from a source and i s never structured in Gibson's sense. "Point of observation" i t s e l f requires a l i t t l e explanation.  Gibson  says i t should be regarded as a place or p o s i t i o n , not as a point in some 5  geometric sense.  I t is q u i t e s i m i l a r to the concept of a s t a t i o n - p o i n t i n  perspective geometry except that a s t a t i o n - p o i n t is f i x e d .  Gibson intends  his notion of a point of observation to be a moving p o i n t .  Since any given  point can move i n r e l a t i o n to any other and since they need not be occupied by organisms, i t is quite d i f f i c u l t to imagine the terms in which these points of observation are supposed t o be i d e n t i f i e d or d i f f e r e n t i a t e d : perhaps i t is easier to envisage Gibson's conception i n terms of actual and possible perceivers, rather than i n terms of p o i n t s , places, or positions with no apparent co-ordinates. The two operative words i n the conception of the o p t i c array as the f l u x of l i g h t energy surrounding a point of observation are " s t r u c t u r e " and "surround".  An o p t i c array consists of i l l u m i n a t i o n , l i g h t t h a t has been  r e f l e c t e d by surfaces of the environmental layout. as i t is not homogenous.  I t is structured so long  An unstructured array could, f o r example, be  produced by t o t a l darkness, b l i n d i n g l y intense levels of i l l u m i n a t i o n , or by some d i f f u s i n g substance, such as a t h i c k f o g .  Leaving aside such excep-  t i o n s , an o p t i c array has two kinds of s t r u c t u r e :  " v a r i a n t " , which Gibson  sometimes refers to as "perspective s t r u c t u r e " , and "underlying i n v a r i a n t structure".  These two kinds and t h e i r i n t e r r e l a t i o n w i l l be made clear once  the functioning of the o p t i c array has been explained.  For structured ambient l i g h t to surround a point of observation, or to be "ambient at a p o i n t " , as Gibson sometimes puts i t , i s explained when he w r i t e s : To be ambient, an array must surround the point completely. It must be environing. The f i e l d must be closed i n the geometrical sense in which the surface of the sphere returns upon i t s e l f . More p r e c i s e l y , the f i e l d is unbounded.^ A p a r t i c u l a r visual f i e l d i s confined to t h a t which is in sight f o r a f i x e d p a i r of eyes in an unmoving organism. bounded.  This makes a visual  field  An a r r a y , c o n t r a r i l y , i s unbounded i n the sense that i t is not  confined t o t h a t which is in sight from a given, f i x e d p o s i t i o n , but consists of a l l the i l l u m i n a t e d surfaces which face a point of observation and are not obstructed by other surfaces from that p o i n t . The s t r u c t u r e of the visual array consists of "visual s o l i d angles", or "angles of i n t e r c e p t " , of surfaces.^  Gibson mentions Euclid and Ptolemy  in t h i s connection f o r p o s t u l a t i n g , r e s p e c t i v e l y , visual cones and visual pyramids.  These notions are v i r t u a l l y the same as the Gibsonian one, except  that Gibson shows recognition of the obvious f a c t that environmental surfaces are not neatly c l a s s i f i a b l e as e i t h e r e l l i p s e s or rectangles.  Thus,  considered as bases f o r three-dimensional f i g u r e s , these surfaces do not i n v a r i a b l y form e i t h e r cones or pyramids. A visual s o l i d angle i s a f i g u r e with some surface as i t s base and an eye ( b e t t e r s t i l l :  a point of observation) as i t s apex.  Every surface  which is unobstructed (or unoccluded) from a point of observation subtends some visual s o l i d angle.  Among other t h i n g s , t h i s implies that there i s  no "figure-ground" d i s t i n c t i o n i n the ecological approach.  Also, the angles  are "nested" w i t h i n o t h e r s , the smallest being surfaces of very small objects or textures of larger surfaces.  A very rough d i s t i n c t i o n is made by Gibson  between these r e l a t i v e l y small elements of the o p t i c a r r a y , which he c a l l s  " f a c e t s " and the larger surfaces t h a t he c a l l s "faces".  An o p t i c or visual  a r r a y , t h e n , is a set of visual s o l i d angles, t y p i c a l comprised of a nested set of facets and faces of the environmental layout.  Gibson's explanation  may be found in the f o l l o w i n g quote: There are several advantages i n conceiving the o p t i c array in t h i s way, as a nested hierarchy of s o l i d angles a l l having a common apex instead of as a set of rays i n t e r s e c t i n g at a p o i n t . Every s o l i d angle, no matter how s m a l l , has form i n the sense that i t s crossection has form, and a s o l i d angle is q u i t e unlike a ray in t h i s respect. Each s o l i d angle is unique, whereas a ray is not unique and can only be i d e n t i f i e d a r b i t r a r i l y , by a pair of coordinates. Solid angles can f i l l up a sphere in the way that sectors can f i l l up a c i r c l e , but i t must be remembered t h a t there are angles w i t h i n angles, so that t h e i r sum does not add_ up to a sphere.8 There is one f u r t h e r piece of terminology to add here. are separated from one another by edges and comers.  Solid angles  The s i g n i f i c a n c e of  t h i s point has to do with the importance i n Gibson's theory with the behav i o r of edges r e l a t i v e to a moving point of observation as part of the foundation of variant s t r u c t u r e , thereby playing a key r o l e in the detect i o n of i n v a r i a n t s .  This w i l l be explained presently.  The study of visual s o l i d angles is called the study of natural perspective by Gibson and he says i t is "a continuation of ancient and medieval o p t i c s " .  This kind of optics is mainly supposed to be the examin-  ation of trigonometric r e l a t i o n s elements of the environment and visual angles.  He distinguishes i t from the study of " a r t i f i c i a l  perspective". 9  This l a t t e r study is what Gibson refers to as "the a r t of picture-making" because i t pertains mainly to problems of representing three dimensions in two.  Gibson i s very careful to d i f f e r e n t i a t e between the two d i s c i p l i n e s  but he nevertheless concedes t h a t , as they are t r a d i t i o n a l l y conceived, they share the same l i m i t a t i o n of being concerned with "frozen" or arrested structure rather than the changing structure available at a moving point of  observation.  The ecological approach therefore extends the study of natural  perspective so that i t considers changing s t r u c t u r e . Gibson also modifies the t r a d i t i o n a l d i s c i p l i n e in two other respects. F i r s t , objects are replaced by i l l u m i n a t e d surfaces as the basic items of study.  Second, Gibson gives consideration to shading of the layout of envi-  ronmental surfaces.  This is a point apparently not accounted f o r by the  o p t i c a l t h e o r i s t s Gibson takes himself to be f o l l o w i n g .  Shading and changes  t h e r e i n are the r e s u l t of the f a c t t h a t the p r e v a i l i n g source of i l l u m i n a t i o n which is r e f l e c t e d by surfaces t y p i c a l l y comes from some d i r e c t i o n and the s p e c i f i c d i r e c t i o n v a r i e s . A f t e r elaborating his idea of the o p t i c ( o r v i s u a l ) a r r a y , Gibson goes on to note that the term " s t r u c t u r e " is vague as i t applies to his theory of information pickup because there are two d i f f e r e n t sorts of s t r u c t u r e i n an array.  The d i s t i n c t i o n is o r i g i n a l l y cast i n terms of perspective  s t r u c t u r e t h a t is disturbed with every movement of the point of observat i o n versus what is known in the ecological theory as "underlying i n v a r i ant s t r u c t u r e " . ^  Later in Gibson's discussion, however, i t comes to l i g h t  t h a t the proper contrast is a more general one between i n v a r i a n t and variant structure.*'''  Perspective s t r u c t u r e is a c t u a l l y merely one of four sources  of variant s t r u c t u r e .  The other sources are 2) movements in an organism's  eye-head system, 3) changes in i l l u m i n a t i o n , and 4) perceptible events that occur i n an organism's local environment.  These w i l l be explained s h o r t l y .  With regard t o 2 ) , movements of the eye-head system are distinguished by Gibson from the other bodily movements t h a t would c o n s t i t u t e a d i s t u r b ance o f the point o f observation. the eye-head system.  Looking around is the c h i e f function of  Scanning with the eyes might be included as well  although Gibson does not e x p l i c i t l y say so when he discusses scanning.  With  33 regard to 3 ) , both d i r e c t i o n and the frequency of sources of i l l u m i n a t i o n are considerations. In Gibson's exposition of i n v a r i a n t s , there is a d i v i s i o n made among the four sources of variance, the f i r s t three being discussed p r i o r to and independently of the f o u r t h .  The main r a t i o n a l e behind the order could be  that sources 1 ) , 2 ) , and 3) are a l l in some sense " e x t e r n a l " t o an organism's environment.  A source of radiant l i g h t , i l l u m i n a t i o n is never part of the  environment (although, Gibson would note, the object providing the source could be).  Also, from the point of view of a p a r t i c u l a r organism, i t  is  d i s t i n c t from i t s environment (although from a purely objective standpoint animals are of course part of the f u r n i t u r e of the environment):  all  of the organism's perceptions of i t s own body are proprioceptions and these are c l e a r l y distinguished on.the ecological approach from the pickup of information about i t s environment.  From a perceiving organism's own unique  perspective, then, i t s own body is as " e x t e r n a l " , as much a non-environmental phenomenon, as a source of i l l u m i n a t i o n .  Adjustments of an organism's body  and changes of i l l u m i n a t i o n , t h e r e f o r e , are in some sense not changes in the environment.  The f o u r t h source of variance, environmental events, quite  obviously c o n s t i t u t e s change in the environment. A l l of the sources of variance are such i n the sense that they produce disturbances of o p t i c a l s t r u c t u r e (changes in the o p t i c array —  Gibson  a c t u a l l y prefers to use "disturbance" and "non-disturbance" i n r e l a t i o n to the o p t i c a r r a y , confining "constancy" and "change" to features of the envi12 ronment).  Variances due to eye-head adjustment or change in e i t h e r point  of observation or i l l u m i n a t i o n can be, and by Gibson are, discussed with respect to an unchanging environment.  The discussion concerns the percep-  t i o n of constancy or persistence through disturbance of o p t i c a l s t r u c t u r e .  The addition of environmental events adds a new t w i s t to the theory because i t pertains t o the perception of environmental change through o p t i c a l disturbance. Now a theory in which the mere r e g i s t e r i n g of variances i n the o p t i c array brought about the pickup of information would s t i l l be a kind of Establishment theory in some respects. on some notion of variable i n p u t ;  Perception would s t i l l be based  i t could s t i l l require some means of  constructing information from variable s e r i e s .  On the ecological approach,  however, disturbance of o p t i c a l s t r u c t u r e is essential to the pickup of information but is not the basis of pickup.  Information is picked up only  when underlying invariants are detected by an organism's visual system. The r e l a t i o n between i n v a r i a n t and variant structure is complementary though.  While the former is the basis of perception, the l a t t e r allows  i t s detection because, as Gibson would put i t , the "flow" of the a r r a y , series of o p t i c a l disturbances produced by changing perspective and so on, "separates o f f " the underlying i n v a r i a n t s t r u c t u r e from the changing, ambient f l u x . The perceptual pickup of information thus involves the concurrent r e g i s t e r i n g of persistence and change.  More p r e c i s e l y , i t involves the  concurrent r e g i s t e r i n g of disturbance and non-disturbance of o p t i c a l s t r u c ture.  This is one of the previously l i s t e d f i v e respects i n which Gibson's  theory is alleged to be r e v o l u t i o n a r y .  From the ecological point of view,  the t r a d i t i o n a l approach t o our perception of constancy (of a stable e n v i ronment) would suggest that i t is perceived i n s p i t e of the r e g i s t e r i n g of variant structure.  The Gibsonian approach is t h a t , although variant s t r u c -  ture i s not i t s e l f a source of information about the environment, i t plays a c r u c i a l (causal) r o l e i n enabling perceptual system to e x t r a c t the abstract  r a t i o s and r e l a t i o n s , which are i n v a r i a n t properties and which remain i n t a c t through movements of the perceiving organism, the source of i l l u m i n a t i o n , or even environmental objects themselves.  When a visual system  detects an i n v a r i a n t specifying some p e r s i s t i n g feature of the environment, an organism perceives s t a b i l i t y through, not i n s p i t e o f , disturbance of the o p t i c array.  This d i f f e r e n t way of t h i n k i n g about the r o l e of variance in  perception e x p l a i n s , f o r example, why Gibson is opposed to studying percept i o n through experiments t h a t unduly constrain a perceiver's movements.  13  (iii) In the most general terms, i n v a r i a n t properties are r a t i o s and r e l a tions i n v o l v i n g substances and surfaces of the environment that remain constant through c e r t a i n kinds of o p t i c a l disturbance.  Gibson postulates four  types of i n v a r i a n t s , each associated with one of the four sources of variance in the visual array.  These are e n t i t l e d :  "Invariants underlying  change of point of observation", " I n v a r i a n t s of o p t i c a l s t r u c t u r e under changing i l l u m i n a t i o n " , Invariants across sampling of the ambient o p t i c a r r a y " , "and "Local invariants of the ambient array under local disturbances of i t s s t r u c t u r e " . A.  Invariants Under Changing Perspective  From a temporarily f i x e d point of observation, c e r t a i n surfaces facing i t w i l l be obstructed by others.  As the point of observation changes,  t h a t i s , the perceiving organism takes d i f f e r e n t perspectives on i t s e n v i ronment, previously covered surfaces become uncovered and vice versa.  The  covering of one s o l i d angle in the visual array by another i s r e f e r r e d to  14 by Gibson as occlusion.  In ecological terms, a moving point of observa-  t i o n produces deletion of o p t i c a l texture (what visual s o l i d angles consist of) along c e r t a i n edges and accretion of texture along others.  Where there  i s deletion of t e x t u r e , a surface is being occluded. t i o n of t e x t u r e , a surface is becoming unoccluded.  Where there is accreOne must of course  remember t h a t these disturbances occur i n comprehensive p a t t e r n s , not as i s o l a t e d instances. Among the kinds of things one may suppose would be s p e c i f i e d i n the deletion and accretion of texture along edges would be s p a t i a l  relations.  Patterns and rates of occlusion r e l a t i v e to p a r t i c u l a r changes i n the point of observation specify things in the environment as being behind or i n f r o n t of others, as being c e r t a i n distances apart, and as being at c e r t a i n d i s tances from the perceiver.  S i t t i n g down produces a compression of some  of the s o l i d angles in the visual array.  Perhaps the degree of compression  r e l a t i v e to the amount of displacement of point of observation specifies the angle of the surface r e l a t i v e to an organism's l i n e of s i g h t . Examples might also be constructed which do not r e a l l y involve an actual movement of the point of observation but which may s t i l l be thought of as the detection of invariants through changing perspective.  Perceivers  are sometimes in a p o s i t i o n to see d i f f e r e n t environmental phenomena which are of the same kind (exactly s i m i l a r in some respect) but which are p o s i t ioned rather d i f f e r e n t l y from them.  In his book, Gibson uses the example  of a series of telephone poles, a l l of the same height, extending i n t o the distance away from a perceiver.  In open country, the poles are seen as the  same h e i g h t , even though, because the perceiver i s taking a d i f f e r e n t perspective on each, each pole subtends a progressively smaller visual angle. The supposed explanation i s t h a t the r a t i o of the portion of o p t i c a l texture above the horizon to the p o r t i o n below is constant. poles as the same size is the r e s u l t of i t s detection of t h i s In general, more  Perceiving the invariant.  or less complex r a t i o s , r a t e s , and r e l a t i o n s emerge  through the patterns of disturbance, the " o p t i c a l f l o w " , as Gibson sometimes  has i t , produced by a perceiving organism moving through i t s environment. These are invariants under changing perspective.  Such constancies to be  extracted from the o p t i c a l flow perhaps would specify s i z e s , s p a t i a l positions, rigidity.  I f Gibson's approach to perception were c o r r e c t , they  would c e r t a i n l y specify objects as being s i z e d , shaped and s i t u a t e d so as to a f f o r d s h e l t e r , grasping, c l i m b i n g , w a l k i n g , and so on. i n v a r i a n t s would specify affordances of the environmental B.  That i s , the layout.  Invariants of Optical Structure Under Changing I l l u m i n a t i o n  The three sources of variance f a l l i n g under "changing i l l u m i n a t i o n " that Gibson mentions- are changes in d i r e c t i o n of the p r e v a i l i n g source, changes in i n t e n s i t y , and changes in colour or f r e q u e n c y - m i x t u r e . ^  The  d i s t r i b u t i o n of shaded and l i g h t e d surfaces in the environment, f o r example, is a function of the d i r e c t i o n of the p r e v a i l i n g source of i l l u m i n a t i o n . ^ As the d i r e c t i o n changes (the sun moving across the sky, a perceiver moving around a cave with a hand-held l a n t e r n , are a couple of examples), there are patterns of o p t i c a l disturbance in the shading.  Arrangement and patterns  o f disturbance would be thought to bring out invariants that help to specify size and distances of t h i n g s , and convexities and concavities i n surfaces. Change in spectral composition or i n t e n s i t y of p r e v a i l i n g i l l u m i n a t i o n means a difference i n the nature of l i g h t absorbed or r e f l e c t e d by a surface. The r e s u l t is d i f f e r i n g absolute colour of p a r t i c u l a r surfaces and of d e t a i l i n the o p t i c array.  With regard to i n t e n s i t y , the extremes simply make the  visual pickup of information impossible.  I f the i l l u m i n a t i o n is too s t r o n g ,  b l i n d i n g occurs.  I f i t is too weak, i t is said that conditions are too dim  i n which to see.  I mention t h i s to underscore the f a c t t h a t , on Gibson's  view, visual perception can f a i l to occur even when the receptors in the visual system are receiving some measure of s t i m u l a t i o n .  Each of these cases  can provide an example of how there can be visual sensation without visual perception. Among the features of the environment that are detected as constant through both changing i n t e n s i t y and spectral composition are texture and pigmentation.  Perception of a surface as being of a constant colour would  involve the detection of c h a r a c t e r i s t i c r a t i o s of reflectance f o r various pigmentations.  Pickup of information concerning environmental substances  may be r e l a t e d to c h a r a c t e r i s t i c s c a t t e r - p a t t e r n s that remain constant under 18 changes in the source of i l l u m i n a t i o n . C.  Invariants Across the Sampling of the Ambient Array  This kind of i n v a r i a n t is related to adjustments of the eye-head system.  In p a r t i c u l a r i t is r e l a t e d to the s p e c i f i c task of g e t t i n g informa-  t i o n by looking around.  As I have already noted, movements of the eye-  head system are distinguished in Gibson's c l a s s i f i c a t o r y system from other bodily movements ( e g . , s i t t i n g down, crouching, w a l k i n g ) .  Adjustments of  the eye-head system are t h e r e f o r e , not counted as a change in the point of observation. An explanation of invariants across sampling of the o p t i c array requires some account of the notion of the process, and of "sample".  A  sample of the o p t i c array is the portion of i t which is i n from a tempora r i l y f i x e d viewing p o s i t i o n . a new sample.  Any motion of the eye-head system produces  That which is in sight from a f i x e d eye-head position  constitutes the contents of an organism's f i e l d of view. " F i e l d of view", i n c i d e n t a l l y , i s a notion Gibson c l e a r l y wishes to 19 d i s t i n g u i s h from "visual f i e l d "  A f i e l d of view and a visual f i e l d are  both bounded in some sense, but Gibson takes the l a t t e r to r e f e r to some form of sensory mosaic accessible only through i n t r o s p e c t i o n , a "patchwork  of visual sensations".  A f i e l d of view is a bounded portion of the optic  array and therefore consists of i l l u m i n a t e d surfaces. To look around is t o sample the o p t i c array via movements of the eyehead system, to obtain successive, overlapping, and often r e v e r s i b l e series of samples.  There is somewhat of a complication in t h i s explanation in  t h a t the eye-head system must move whenever the point of observation does. However, t h i s can be remedied simply enough by specifying that the eyehead system i t s e l f must change state f o r invariants to be detected through sampling, rather than a change in perspective. There w i l l no doubt be some s i m i l a r i t i e s in the c o n t r i b u t i o n made to visual information pickup by looking around and by changing perspective. Use of the eye-head system w i l l produce series of samples of o p t i c a l  struc-  ture through which there w i l l occur systematic.and progressive deletion and accretion of o p t i c a l texture along edges of s o l i d angles.  As is the case  with occlusion (and i t s reverse) through changing perspective, the covering and uncovering of texture along edges through looking around should be important to perception of s p a t i a l positions of t h i n g s .  Gibson also regards  the r e v e r s i b i l i t y often associated with occlusion and w i t h things going out of and coming i n t o the f i e l d of view as important to the perception of persistence, and of the coexistence and connectedness of t h a t which is 20 temporarily in sight with that which is temporarily out of s i g h t . D.  Local Invariants of the Ambient Array under Local Disturbances of I t s Structure  The i n v a r i a n t - t y p e s considered so f a r have been explained i n r e l a t i o n to a "frozen" environmental layout (though they should not be thought of only as related to an unchanging environment).  A tenet in the ecological  approach, however, is that events and the perception of events must be part  of an account of perception.  Environmental events are themselves a source  of o p t i c a l disturbance, through which i n v a r i a n t properties are separated o f f and may be detected, as well as being perceptual objects.  Unlike the other  sorts of i n v a r i a n t s , the source of disturbance of o p t i c a l s t r u c t u r e (some environmental event) can be t h a t which is s p e c i f i e d by the i n v a r i a n t revealed by the associated o p t i c a l disturbance. Elaboration of invariants under local disturbance of environmental s t r u c t u r e requires some description of events.  Gibson's discussion p a r t i c -  u l a r l y concerns what he c a l l s " t e r r e s t r i a l events".  The only example given  of a n o n - t e r r e s t r i a l one is t h a t of the sun's progress across the sky.  The  point of the d i s t i n c t i o n Gibson makes seems only to confine the discourse, in accordance with his rough notion of the " t e r r e s t r i a l environment", to events at or near the surface of the e a r t h . 21 Three general event-types are c i t e d .  "Change of layout" includes  disruptions and deformations of surfaces, c o l l i s i o n s , turns and displacements of objects.  "Change in colour and texture due to change in compo-  s i t i o n " pertains to chemical metamorphosis, such as the bluing of heated steel.  Heating, o x i d a t i o n , reduction, the production of chemical substances  by l i v i n g things (one of Gibson's examples is of the fading colouration of a plant surface through a decrease in c h l o r o p h y l l .  F i n a l l y , there is  "waxing and waning of a surface due to change in the state of matter", such as the r o t t i n g of vegetable matter, evaporation or freezing of l i q u i d s , or the d i s s o l u t i o n of c r y s t a l s in l i q u i d .  Changes of these kinds c o n s t i t u t e  coming i n t o or going out of existence o f surfaces.  In general, the l i s t  Gibson provides takes i n t o account a l t e r a t i o n of a given surface, a l t e r a t i o n between surfaces, and t h e i r creation or d e s t r u c t i o n . The supposed revolutionary approach t o events i n perception taken by  Gibson and his followers is that events are perceived j u s t the same as per22 s i s t i n g features of the environment.  That i s , on the Gibsonian view there  are p e r s i s t i n g , abstract r a t i o s and r e l a t i o n s underlying disturbances of o p t i c a l s t r u c t u r e which specify events of c e r t a i n kinds, as well as specifying objects and t h e i r u n a l t e r i n g p r o p e r t i e s .  Also, a d i s t i n c t i o n needs to  be maintained between events as sources of o p t i c a l disturbance and events considered as perceptible features of the environment.  In s h o r t , the ecol-  ogical approach t r e a t s environmental events both as objects of perception and as sources of o p t i c a l disturbance.  Gibson could perhaps have made t h i s  point c l e a r e r . The reason f o r such a d i s t i n c t i o n is t h a t not every event that r e s u l t s i n some c h a r a c t e r i s t i c o p t i c a l disturbance is necessarily perceived as such. Optical disturbances produced by events should.be able to separate o f f invariants that specify things other than simply the source of the d i s t u r b ance.  A f t e r a l l , changes in perspective and i l l u m i n a t i o n reveal  invariants  t h a t specify features of the environment, rather than the sources of those disturbances (point of observation or l i g h t - s o u r c e ) . One of the f a v o u r i t e examples f o r ecological t h e o r i s t s of disturbance of o p t i c a l s t r u c t u r e by local events that allows the detection (or extract i o n of an i n v a r i a n t i s the previously mentioned case of the perception of imminent c o l l i s i o n : The magnification of the visual s o l i d angle of an object normally accelerates as i t approaches the l i m i t of a hemispheric angle, as the object comes up to the eye. The accelerated portion of t h i s sequence was called "looming" by S c h i f f , Caviness, and Gibson (1962). I t specifies impending c o l l i s i o n , and the rate of^ magnification is proportional to the imminence of the c o l l i s i o n . An explosive rate of surface magnification is part of the i n v a r i a n t s t r u c t u r e t h a t specifies a c e r t a i n event-type: or surface.  c o l l i s i o n with an object  This p a r t i c u l a r example is so frequently c i t e d by Gibsonians  because i t is taken as a source f o r one of the f i r s t concrete examples of 24 an i n v a r i a n t .  David Lee  has apparently worked out a mathematical variable  to explain human reaction to impending c o l l i s i o n s in ecological terms. Another somewhat s i m i l a r example ( t h i s one is mainly of my own design: i t is intended to i l l u s t r a t e the notion of invariants in environmental chang but the d e t a i l s may or may not be borne out in experiment) would be of a 25 b a l l thrown toward a perceiver.  The disturbance of the o p t i c array would  consist of the s o l i d angle subtended by the b a l l occluding progressively greater amounts of surrounding t e x t u r e .  The perceiver's visual system, on  Gibson's view, would r e g i s t e r the o p t i c a l disturbance created by the b a l l ' s changing p o s i t i o n r e l a t i v e to the surrounding environment. This event, f o r one t h i n g , i s quite d i f f e r e n t from a perceiver moving toward a s t a t i o n a r y o b j e c t , however q u i c k l y .  Part of the reason could be  that a p r o j e c t i l e has a c h a r a c t e r i s t i c arc that is not reproduced when one merely approaches a s t i l l o b j e c t .  Part of the reason would also no' doubt  be linked to proprioception ( v i a the visual system and otherwise).  An organ  ism's a b i l i t y t o perceive change and constancy i n the environment i s connected very c l e a r l y to i t s awareness of i t s own temporarily changing or fixed position in i t .  Also, the r e l a t i o n between the s o l i d angle subtended  by the b a l l and those subtended by surrounding surfaces is quite d i f f e r e n t when the perceiver is in motion r e l a t i v e to a s t a t i o n a r y b a l l , as opposed t o the reverse.  Surrounding texture is increasingly occluded by the b a l l ' s  s o l i d angle i n each case, but when the b a l l is s t i l l and the perceiver is moving toward i t , the "background" texture w i l l be magnified at the same rate.  When the b a l l is i n f l i g h t (assuming a stationary p e r c e i v e r ) , the  background texture w i l l not be magnified at a l l .  The clear r e s u l t is a  s t r i k i n g difference in the texture that is occluded in each instance.  The  d i f f e r e n t patterns of o p t i c a l disturbance which r e s u l t from the two d i f -  ferent occurrences would therefore make d i f f e r e n t i n v a r i a n t r a t i o s or rates available f o r detection by one's visual system. A perceiver's a b i l i t y to time his catch, or to avoid being h i t by the b a l l , is no doubt contingent upon his a b i l i t y t o perceive the speed of the b a l l accurately.  At least a p a r t i a l f a c t o r involves the detection of a  rate o f m a g n i f i c a t i o n .  Another f a c t o r could have to do w i t h the b a l l ' s arc.  A f a s t e r b a l l has a f l a t t e r arc.  A b a l l t r a v e l l i n g r e l a t i v e l y quickly  would therefore produce somewhat less decretion of surrounding o p t i c a l texture along i t s lower edge and somewhat less accretion of texture along i t s upper edge than would a s o l i d angle associated with a s l o w e r - t r a v e l l i n g b a l l that covered the same distance with greater arc. Perceiving a b a l l ' s speed and path of f l i g h t , in these terms, would thus be a matter of the detection of a c e r t a i n i n v a r i a n t , consisting of f a i r l y subtle mathematical r e l a t i o n s amongst a s e t of visual s o l i d angles which are not in motion, but are undergoing s t r u c t u r a l  disturbances.  I t i s important to remember t h a t even though the two examples given concern perception of changing s p a t i a l r e l a t i o n s , visual perception of events concerns f a r more. ones.  There are chemical events as well as mechanical  Chemical events bear some s i m i l a r i t i e s to changing i l l u m i n a t i o n  because a chemical ( i n c l u d i n g biochemical) event produces change in substance, usually r e s u l t i n g in some difference in pigmentation or surface texture.  The i n v a r i a n t s underlying such change w i l l , as with changing,  i l l u m i n a t i o n , pertain to how l i g h t from a source is r e f l e c t e d , absorbed, and scattered by surfaces. While the thought Gibson has put i n t o the categorization of environmental events i s impressive, i t involves a curious oversight.  Not every-  thing on Gibson's l i s t of t e r r e s t r i a l events would produce a disturbance  of o p t i c a l s t r u c t u r e because noticeable change occurs i n some of the cases over very long periods of time.  Some environmental events, l i k e  the ripening of a peach, w i l l not be registered as changing o p t i c a l s t r u c t u r e , unless one is extremely v i g i l a n t .  Others, l i k e the motion of t r e e -  branches i n the wind w i l l count as sources of disturbances of o p t i c a l s t r u c ture.  Gradual events may be considered as things perceived on the ecolo-  g i c a l approach:  i t is conceivable t h a t peaches are perceived as r i p e n i n g ,  s t a l a c t i t e s as lengthening, or whatever.  These sorts of gradual changes in  the environment, however, cannot be considered as sources of o p t i c a l urbances because no change is registered by the perceptual system.  distOne is  aware of a peach's ripening because of a state the f r u i t is i n , not because of a discernible change i t is undergoing. (iv) Some general points about invariants should be made in summary.  These  are, to emphasize, abstract r a t i o s and r e l a t i o n s (mathematical, but not necessarily geometric) t h a t hold among components of the ambient a r r a y , and are constant through c e r t a i n kinds of disturbance of ambient ( o p t i c a l ) s t r u cture.  These are said to be detected or extracted by perceptual systems  from the array.  I t is also said by Gibson that perceptual systems (or  "nervous systems") resonate to i n v a r i a n t p r o p e r t i e s .  Neither "detect" nor  " e x t r a c t " , nor "resonate" is explained. Invariants should by no means be thought of as some novel conception of sense-data, as one might be i n c l i n e d to do.  An i n v a r i a n t i s not, and  in many cases, Gibson b e l i e v e s , could not be an object of awareness.  In  f a c t , he claims they w i l l f o r the most part f a i l t o be "open to a n a l y t i c introspection".  This must mean more than t h a t one is not standardly  aware of i n v a r i a n t s .  Rather, i t must be that one could not attend to  45  one's own perceptual experience in such a way as t o discover the invariants upon which pickup of c e r t a i n information is based.  Invariant  properties are quite unlike sense-data or s i m i l a r notions in t h i s respect. Representational t h e o r i s t s as early as Locke are prepared to grant that perceivers are not t y p i c a l l y perceptually aware of the sensory q u a l i t i e s 27 upon which t h e i r awareness of the world is based. to maintain some conditional view instead:  I t is customary  a perceiver could be aware of  bare sense-data i f he were to attend to his perceptual experience in the r i g h t way.  For Gibson to claim t h a t invariants w i l l often not be  i n t r o s p e c t i b l e i s to deny they can be objects of awareness even i n t h i s weak, conditional sense. An immediate consequence of t h i s point is t h a t (assuming of course that i n v a r i a n t s are indeed discoverable), to the extent that they are not revealed by a n a l y t i c a l i n t r o s p e c t i o n , they must be so through independent, empirical t e s t i n g .  This explains Gibson's (otherwise puzzling) remark  regarding invariants under changing i l l u m i n a t i o n t h a t "they are not yet known but they almost c e r t a i n l y involve r a t i o s of i n t e n s i t y and color 28 among parts of the a r r a y " .  The study of invariants consists of d i s -  covering which p a r t i c u l a r ones there are ( t h a t the study is r e l a t i v e l y new perhaps stands as a temporary explanation f o r the decided lack of concrete examples).  This makes the f i n d i n g of i n v a r i a n t s , what they  s p e c i f y , and hence the question of what information can be picked up via t h e i r detection of a l l empirical issues.  This is an important point f o r  understanding how Gibson distinguishes perceptible and non-perceptible features of the environment, which w i l l be a central issue i n the next chapter. F i n a l l y , there is the matter of the r e l a t i o n between the notions  of " i n v a r i a n t properties" and " i n f o r m a t i o n " , or of the nature of i n f o r m a t i o n , on Gibson's conception.  In important respects, i t is an  issue that cannot be resolved u n t i l l a t e r in t h i s discussion since the major controversy between Gibsonians and Establishment t h e o r i s t s centers on the notion of information and whether i t manages to do a l l t h a t is required of i t .  The only c e r t a i n t y is that Gibson wants t o d i s t i n g u i s h c l e a r l y  between his conception and one that has come to philosophy and psychology via communication-theory: The information f o r perception is not t r a n s m i t t e d , does not consist of signals and does not e n t a i l a sender or a receiver. The environment does not communicate with the observers who inhabit i t . 2 5  Elsewhere, Gibson notes that information, when defined (as in communications-engineering) i n terms of the reduction of u n c e r t a i n t y , allows d i s c r i m i n a t i o n , not "perception of" (presumably meaning "meaningful perception" ) . ^ The basis of the controversy consists of whether or not i n v a r i a n t properties and information should be i d e n t i f i e d .  Some of Gibson's comments  and the locutions he uses suggests t h a t the two should be i d e n t i f i e d .  He  t a l k s , f o r example, about "information f o r perception" and information 31 specifying features of the environment".  The most natural reading of  these phrases r e s u l t s from assuming that "information" here refers t o invariants:  properties of s t r u c t u r e d , ambient energy that uniquely (and  l a w f u l l y ) correspond to environmental phenomena.  Also, information about  the environment is said to be "simply a v a i l a b l e " , i n the ambient array. On the other hand, invariants are supposed to be generally nonintrospectiblei  they could not be objects of awareness.  Surely i t would  be i n c r e d i b l e to hold such a view of the information organisms pick up about t h e i r environments.  The pickup of information is anyway defined by  Gibson sometimes as awareness of features of the environment and t h i s raises a precise l o g i c a l problem f o r the i d e n t i f i c a t i o n of information and invariants.  A d d i t i o n a l l y , examples of information pickup would be such as  "awareness of a surface as walk-on-able", "awareness of something as an enclosure".  The information picked up about the environment could be  reducible to or analyzed i n t o i n v a r i a n t properties of the o p t i c array.  If  there is such an analysis in Gibson's works, i t is not the least b i t explicit. Now Turvey, Shaw, Reed, and Mace have w r i t t e n t h a t " o p t i c a l  structure  specifies i t s environmental source and that therefore mobile organisms with active visual systems t h a t can pickup t h i s information w i l l see t h e i r environments and s u i t a b l y adjust t h e i r a c t i v i t y , i f and when they detect 32 t h a t information (and only t h e n ) " .  By s u b s t i t u t i n g " i n v a r i a n t "  for  " i n f o r m a t i o n " in t h i s quote ( s i n c e " i n v a r i a n t " is f a i r l y c l e a r l y what the authors have in mind), one can derive a workable proposal.  Since  there is some ( j u s t i f i a b l e ) controversy over whether Gibson has a single notion of information that can bear the t h e o r e t i c a l weight he places upon i t , l e t the basic ecological claim be that an organism perceptually picks up information about i t s environment when, and only when, the appropriate i n v a r i a n t i s detected by some of i t s perceptual systems.  One suspects  t h a t Gibsonians would l i k e to i d e n t i f y information about the environment with i n v a r i a n t , ambient, s t r u c t u r e .  Pending c l a r i f i c a t i o n of c e r t a i n  apparent c o n f l i c t s , however, t h i s r e l a t i o n should neither be assumed nor granted.  Instead, I w i l l regard the i n v a r i a n t - i n f o r m a t i o n r e l a t i o n only  as a b i c o n d i t i o n a l one.  Such a r e l a t i o n would hold i f "information" and  " i n v a r i a n t " were i d e n t i f i a b l e . however.  I t does not e n t a i l t h i s  identification,  Chapter Three The grand philosophical claims made by ecological t h e o r i s t s - - not merely that the Gibsonian approach is a d i r e c t theory of perception of the environment, but also that the view provides a new basis f o r r e a l i s m , a new theory of cognition generally, and even a new approach to epistemology* - - has drawn very l i t t l e reaction from mainstream figures working in the relevant areas of philosophy.  This is not s u r p r i s i n g f o r there is r a r e l y  a generous flow of discourse between d i f f e r e n t academic d i s c i p l i n e s .  The  w r i t i n g s of some of the Gibsonians, moreover, are quite inaccessible. 2  Fodor and Pylyshyn's commentary philosophical lack of i n t e r e s t .  is a rare exception to the evident  I t is even more rare because, since i t  is  r e l a t i v e l y recent, the a r t i c l e takes i n t o account The Ecological Approach To V i s i o n , which contains the most developed and d e t a i l e d version Gibson gives of his theory.  The Fodor/Pylyshyn a r t i c l e , a d d i t i o n a l l y , constitutes  one h a l f of a lengthy debate, having drawn a response from four prominent 3  Gibsonians.  However, the debate is incomplete:  f i r s t of a l l , subsequent  to the o r i g i n a l two (lengthy) a r t i c l e s , and probably owing to the i n t r a n sigence of the p a r t i c i p a n t s , there has been no comprehensive follow-up or rebuttal.  Second, Turvey, Shaw, Reed, and Mace ( h e r e i n a f t e r TSRM) do not  so much respond to Fodor and Pylyshyn's attack on Gibson as restate general ecologist qualms and redescribe Gibson's "theory of s p e c i f i c a t i o n " . As a r e s u l t , the ecological side f a i l s t o address the p o i n t s , good or bad, t h a t Fodor and Pylyshyn make.  The debate does, however, centre around the  key issue which, i n Fodor and Pylyshyn's terms, i s how the ecological  approach deals with i n t e n t i o n a l i t y i n perception.  The following chapters  w i l l focus on the c r i t i c i s m of the Gibsonian view by Fodor and Pylyshyn, and TSRM's r e p l y , with the underlying issue being t h i s one of i n t e n t i o n a l i t y (roughly put, whether or not Gibson's concept of information and theory of pickup could explain epistemic perception, how one perceives things as such).  I t is not at a l l clear how TSRM's response, although i t  is intended to handle the i n t e n t i o n a l i t y issue, even approaches the question.  The task of t h i s chapter, however, w i l l be to discuss the Fodor/  Pylyshyn side of the debate. The i n i t i a l argument against Gibson made by Fodor and Pylyshyn is t h a t Gibson has not provided appropriate constraints on his notions of " d i r e c t pickup" or " i n v a r i a n t " .  In other words, i t is not clear what  l i m i t s , i f any, there are on that which may be perceived. They w r i t e : The main l i n e of our argument w i l l go l i k e t h i s : Gibson's account of perception is empty unless the notions of ' d i r e c t pickup' and of ' i n v a r i a n t ' are s u i t a b l y constrained. For, p a t e n t l y , i f any property can count as an i n v a r i a n t , and i f any psychological process can count as the pickup of an i n v a r i a n t , then the i d e n t i f i c a t i o n of perception with the pickup of invariants excludes nothing.4 I w i l l show that t h i s p a r t i c u l a r c r i t i c a l l i n e is not a problem f o r Gibson.  He does have constraints of a k i n d , although they are not obvious,  and he is not caught in the dilemma Fodor and Pylyshyn fashion from t h e i r argument. The ecological approach can be understood as claiming that a l l "genuine" ( i n some sense) perception is d i r e c t perception, and therefore invariant-based.  The p e r c e p t i b l e , then, is constrained i n terms of what  i n v a r i a n t s there ( i n f a c t ) a r e , and what they ( i n f a c t ) specify. be elaborated upon l a t e r .  This w i l l  The f i r s t step the authors take is to pose what they c a l l a t r i v i a l i z a t i o n problem, the purpose of which is to show Gibson cannot do without constraints.  They then suggest four d i f f e r e n t constraining p r i n c i p l e s  (Fodor and Pylyshyn c a l l these "gambits") f o r which they claim Gibson shows some support in his w r i t i n g s .  These gambits are that only ecological  p r o p e r t i e s , only p r o j e c t i b l e p r o p e r t i e s , only phenomenological p r o p e r t i e s , or only that to which 'perceptual systems' respond are d i r e c t l y perceived. Each is rejected in turn as being e i t h e r inherently unworkable or anyway incompatible with the basic s t r u c t u r e of Gibson's approach.  To Fodor and  Pylyshyn, t h i s outcome is i n e v i t a b l e since they see Gibson as being caught in a dilemia:  he needs some constraining p r i n c i p l e but cannot introduce  one without allowing that some perception requires cognitive processing (inference).  In s h o r t , Fodor and Pylyshyn argue t h a t e i t h e r " d i r e c t pickup"  i s vacuous or else Gibson must forsake his claim that perception only i n volves the "pickup of i n v a r i a n t s " .  They base t h i s claim p a r t l y on what  they regard as a common assumption: Gibson and the Establishment agree that pickup and inference exhaust the psychological processes t h a t could produce perceptual knowledge; hence the more pickup is constrained the more there is l e f t f o r inference to d o . * Since one of Gibson's fundamental tenets is that perceiving does not require inference, then his agreement with t h i s assumption would seem to place him i n great d i f f i c u l t y .  The dilemma Fodor and Pylyshyn attempt to  set f o r Gibson, however, does not work because i t is based on some misunderstandings about the ecological approach.  One is t h a t the Fodor/  Pylyshyn dilemma requires an improper use of " i n v a r i a n t " .  Another is  t h a t the authors f a i l t o appreciate the extent to which the ecological approach to perception is an empirical theory. The f i r s t  mistake allows the t r i v i a l i z a t i o n problem, which Fodor  and Pylyshyn describe as f o l l o w s : Suppose that under c e r t a i n circumstances people can c o r r e c t l y perceive that some of the things in t h e i r environment are of type P. Since you cannot c o r r e c t l y perceive that something is P unless that t h i n g i s P, i t w i l l always be t r i v i a l l y true that things that can be perceived to be P share an i n v a r i a n t property: namely, being P. And since, according to Gibson, what people do i n perceiving i s d i r e c t l y pick up an appropriate i n v a r i a n t , the following pseudo-explanation of any perceptual achievement is always a v a i l a b l e : to perceive that something is P i s to pick up the ( i n v a r i a n t ) property P which things of that kind have. So, f o r example, we can give the f o l l o w i n g disarmingly simple answer to the question: how do people perceive that something is a shoe? There is a c e r t a i n ( i n v a r i a n t ) property that a l l and only shoes have - - namely the property of being a shoe. Perceiving that something is a shoe consists in the pickup o f t h i s property. >;  For good measure, they add a second example of such t r i v i a l explanations using the alleged a b i l i t y of Bernard Berenson to " t e l l by looking" whether a painting is a genuine DaVinci. The trouble f o r Fodor and Pylyshyn rests in the f a c t that the kind of thing they want to f i l l  in f o r "P" f a i l even t o be candidates f o r the  t i t l e of being an i n v a r i a n t property.  Optical invariants are the features  of and r e l a t i o n s between the faces and facets (explained in Ch.2) comprising a visual array that remain constant through various kinds of d i s t u r b ances of the s t r u c t u r e of t h e ' a r r a y .  "Being a shoe", "having been painted  by DaVinci", or the generic "being P", do not even remotely q u a l i f y as the s o r t o f t h i n g Gibson has in mind. The t r i v i a l i z a t i o n problem r e l i e s on a use of " i n v a r i a n t property" according to which one can postulate the existence of an i n v a r i a n t f o r v i r t u a l l y any d i s t i n g u i s h a b l e class of environmental phenomena.  Fodor and  Pylyshyn take the process of visual information pickup to be s i m i l a r to " t e l l i n g by l o o k i n g " .  On t h e i r i n t e r p r e t a t i o n o f Gibson, any feature of  the environment an organism can (learn to) be aware of by looking is called an " i n v a r i a n t " .  The r e s u l t is arm-chair science:  the p r o l i f e r a t i o n of  "explanations" of how c e r t a i n things are perceived that need no backing of empirical t e s t s .  However, o p t i c a l invariants are empirical  properties  of visual arrays so the matter of what constant r a t i o s and r e l a t i o n s of o p t i c a l s t r u c t u r e there are is only determinable by s c i e n t i f i c  investigation.  The empirical nature of invariants suggest one sense i n which Gibson's view of the perceptible might be thought of as unconstrained.  As an  empirical s c i e n t i s t , he ( r i g h t l y ) leaves questions of which invariants there are and what they specify r e l a t i v e l y open.  He cannot draw conclusions as  to the existence o f s p e c i f i c invariants p r i o r to the appropriate t e s t s . At the same time, one must of course grant t h a t Gibson has some c l e a r , general views, both on the nature of invariants and on the properties which w i l l prove to be s p e c i f i e d .  The views Gibson has can manage to' c o n s t i t u t e  constraints of a kind even though questions as to the existence of p a r t i c ular i n v a r i a n t s and s p e c i f i c a t i o n s are not known. Not even the question of types of invariants f o r d i f f e r e n t perceptual systems has been s e t t l e d , because Gibson comments t h a t : There are also surely invariants i n the flow of acoustic, mechanical, and perhaps even chemical s t i m u l a t i o n , and they may prove to be closely r e l a t e d to the o p t i c a l , but I leave them to the readers' speculation. The study of i n v a r i a n t s is j u s t beginning.' I f i n v a r i a n t s were simply a r b i t r a r y properties one could postulate at w i l l , i t would be d i f f i c u l t t o understand t h a t of which the study of i n v a r i a n t s might consist. Even given a corrected i n t e r p r e t a t i o n of the Gibsonian concept of an o p t i c a l i n v a r i a n t , i t may s t i l l be tempting to think the ecological approach is susceptible to some form of t r i v i a l i z a t i o n problem.  Consider-  ing Gibson's description of v i s u a l l y perceiving i n terms of "looking at" and "looking around",  o  there is a reasonably strong basis f o r the Fodor/  Pylyshyn claim t h a t visual perception is akin to t e l l i n g by looking. T e l l i n g by looking can be regarded as the pickup of information by looking. The revised issue is whether or not Gibsonians are committed to saying any instance of the pick up of information by looking is based on the detection of the appropriate i n v a r i a n t .  I f n o t , how does Gibson avoid supposing  t h a t some visual perception involves cognitive processing a f t e r a l l ?  I f so,  then is not Gibson committed to the assumption of i n v a r i a n t s i n f a i r l y u n r e a l i s t i c cases? ization:  The l a t t e r horn of t h i s dilemma y i e l d s a kind of t r i v i a l -  although one is not postulating the existence of a p a r t i c u l a r invar  i a n t (as Fodor and Pylyshyn do with t h e i r "pseudo-invariants", "being a shoe" e t c . . . . ) , one s t i l l assumes the existence of some i n v a r i a n t or other f o r any example of information pickup by looking. An enormous number of instances of epistemic, visual perception ( f o r t h i s e x p o s i t i o n , "seeing X as P", t h a t may involve the visual system e i t h e r as a mere p a r t i a l determinant or not at a l l .  Consider the statement  "Daniel Ortega sees the p o s s i b i l i t y of a l i b e r a l President as a chance to normalize r e l a t i o n s between the U.S. and Nicaragua".  This statement  refers to some non-perceptual judgement of Ortega's and does not make any use of the visual system at a l l .  There are other cases, such as (from  Fodor and Pylyshyn) Berenson seeing a painting as an authentic DaVinci or a meteorologist seeing black clouds over the ocean as an approaching hurricane, which requires some form of expert knowledge, not generally possessed and perhaps not even learnable by human perceivers, in addition to the normal f u n c t i o n i n g of the visual system, f o r the pickup of c e r t a i n information.  One should t h i n k that cases such as these, cases i n which  the visual system only p a r t i a l l y determines the information which is acquired, would not be considered to be instances of d i r e c t pickup.  Yet,  expert perceptions of meteorologists or a r t connisseurs, of which the perception of genuine DaVinci's or of approaching hurricanes are examples, are sometimes a mere matter of t e l l i n g by looking.  I f one assumes that  any information pickup by looking i s the mere product of i n v a r i a n t d e t e c t i o n , i t would seem that one must suppose that such perceptions are cases of d i r e c t pickup, t h a t there are invariants to specify genuine Da V i n c i ' s and the 1 i k e . Examples of seeing X as P which do not involve the visual system at a l l ( t h a t i s , where "sees" is being used i n the sense of "understands", or "thinks o f " , f o r example) of course pose no problem here.  I f seeing  X as P does not involve the visual system at a l l , i t could hardly be described as an instance of t e l l i n g by looking.  Cases in which the  visual system is a p a r t i a l determinant are the d i f f i c u l t ones. The environment is f u l l of customary signs in  v i r t u e of which  perceivers move from the contents of t h e i r f i e l d of view, from that which is manifestly before t h e i r eyes to information which goes well beyond t h i s . When t h i s occurs u n t h i n k i n g l y , as i t so often does, i t constitutes a case of t e l l i n g by looking - but i t is one i n which the pickup of information is not e x c l u s i v e l y determined by the visual system.  For example, W i l l  may see t h a t Abner is f i n a l l y planting his corn, when a l l there is f o r W i l l t o look at is Abner leaning on a fence post next to a f r e s h l y furrowed f i e l d , bag of seed in one hand, c i g a r e t t e i n the other.  Abner a c t u a l l y  p u t t i n g seed in the ground is not before W i l l ' s eyes but the contents of his f i e l d of view i s such t h a t , without any conscious computations, W i l l picks up the information t h a t Abner is i n the midst of doing his p l a n t i n g . Even though W i l l undergoes no conscious process to get t h i s i n f o r m a t i o n , i t would surely be correct t o assume there are_ some kinds of mental  processing involved.  This is why i t would be a t r i v i a l i z a t i o n of a notion  of " d i r e c t pickup" or " i n v a r i a n t " to suppose t h a t , because W i l l picks up the information he does, there must be some i n v a r i a n t specifying "man p l a n t i n g " t h a t W i l l ' s visual system detects t h i s when he looks at Abner r e s t i n g against a fence post. I t sometimes seems t h a t Gibson and his followers are content to accept the i n t e r p r e t a t i o n t h a t any instance of the pickup of information by looking is t o be explained simply in terms of i n v a r i a n t - d e t e c t i o n .  They  have occasion to express the expectation of the s p e c i f i c a t i o n by invariants of environmental phenomena which must appear to non-Gibsonians to be most unpromising candidates.  Michaels and C a r e l l o , f o r instance, speculate on 9  the p o s s i b i l i t y of "very h i g h - l e v e l " invariants f o r aesthetic q u a l i t i e s . I t is important to understand such i n d i s c r e t i o n s , however, as speculation, fueled p a r t l y by the enthusiasm that is often c h a r a c t e r i s t i c of a r e l a t i v e l y new t h e o r e t i c a l approach. A most i n t e r e s t i n g case can also be made f o r suggesting that Gibson is not committed t o the view that any case of information pickup by looking requires only the detection of the relevant i n v a r i a n t .  Although a l l  epistemic perception, according to the Gibsonian theory, is the pickup of i n f o r m a t i o n , the reverse need not o b t a i n .  Hence, not a l l cases of i n f o r -  mation pickup need be regarded as merely perception, and, i n p a r t i c u l a r , not every instance of information pickup by looking need be considered as merely the f u n c t i o n i n g of the visual system.  Some information picked up  by l o o k i n g , i n other words, may not be visual perception, even though the visual system is a p a r t i a l  determinant.  The basic claim here is t h a t only some information pickup by looking is the r e s u l t s o l e l y of the detection of some i n v a r i a n t by an organism's  perceptual system.  On a Fodor and Pylyshyn i n t e r p r e t a t i o n of the ecolo-  gical approach, t h i s claim would raise two problems f o r Gibson.  F i r s t , he  would need to supply the p r i n c i p l e ( s ) d i f f e r e n t i a t i n g between information t h a t i s d i r e c t l y picked up and information which is not d i r e c t l y picked up. Second, he would have to grant that such information as is not d i r e c t l y picked up involves cognitive processing.  The i m p l i c a t i o n of the f i r s t  point would be t h a t Gibson lacks a coherent p r i n c i p l e of d i f f e r e n t i a t i o n , the i m p l i c a t i o n of the second t h a t he would have to concede some instances of perceiving involve mental processing a f t e r a l l . The answer to the f i r s t problem begins with the assertion that that which is d i r e c t l y picked up i s that which i n v a r i a n t properties specify. This a s s e r t i o n , which Fodor and Pylyshyn would no doubt f i n d inadequate, avoids being c i r c u l a r or otherwise inherently defective because of a point mentioned previously.  The question of what i n v a r i a n t properties  there are is an empirical one.  I t is a question that is presumably to be  answered through the study of natural perspective (with Gibson's emendations). I f the existence of i n v a r i a n t s is only s c i e n t i f i c a l l y determinable, then so too must be t h a t which is s p e c i f i e d by invariants and hence t h a t which is d i r e c t l y picked up.  Thus there i_s a general constraining p r i n c i p l e :  t h a t which is d i r e c t l y picked i s t h a t which is s p e c i f i e d by i n v a r i a n t s . There i s also a suggested method f o r determining p a r t i c u l a r instances that explains why one cannot merely l i s t by r e f l e c t i n g or i n t r o s p e c t i n g the information about the environment that can be d i r e c t l y picked up:  the  determination of p a r t i c u l a r invariants and what they specify rests upon mutual t e s t i n g of perceptual and behavioral responses of various organisms and t e s t i n g f o r i n v a r i a n t properties i n structured energy. The a v a i l a b i l i t y of t h i s move can be missed f o r a couple of reasons.  The main one is t h a t Gibson does have, as part of his theory, very strong views on the terms in which the world is perceived.  Affordance-perception  w i l l prove to be basic according to Gibsonian d o c t r i n e . theory about what there is to be p e r c e i v e d " . ^  This is the "new  A key reason f o r the  i n c l u s i o n of a view about the terms of perception i s that Gibson believes perceptual theory should take account of e v o l u t i o n .  Hence, i t is a f a i r l y  natural move f o r him to claim that the main categories of perception f o r an organism are linked to i t s needs and a b i l i t i e s i n r e l a t i o n to i t s environment. Now the idea of perception being invariant-based makes some environmental properties b e t t e r candidates as possible objects of d i r e c t percept i o n than others.  In p a r t i c u l a r , properties t h a t can be linked to a more  or less r e s t r i c t e d range of physical parameters are the only ones which hold the promise of proving to be associated with given p e r s i s t i n g r a t i o s and r e l a t i o n s i n the o p t i c array.  Because affordances are d i s p o s i t i o n a l  properties objects possess r e l a t i v e to s p e c i f i c a b i l i t i e s and needs of organisms, they are j u s t such p r o p e r t i e s .  I t could have helped Gibson's  case i f he had mentioned t h i s point but he unfortunately does not. Some examples of these "best case" properties would be "enclosure", "supporting s u r f a c e " , "opening", and " c l i f f " .  In order f o r things in one's  environment to be a place one can pass through or a place one can f a l l from, they have to meet some physical requirements.  Where these require-  ments are s u f f i c i e n t l y s p e c i f i c (some a d d i t i o n a l l i m i t i n g p r i n c i p l e s w i l l be mentioned l a t e r ) , there is i n i t i a l p l a u s i b i l i t y i n the suggestion that a l l things having the affordance share some common i n v a r i a n t .  Sameness i n  some tangible respect, constancy of s i z e , pigmentation, or texture are also r e l a t i v e l y plausible candidates because i t is not too d i f f i c u l t to imagine  58 how o p t i c a l invariants might specify these.  The predominance of properties  characterizing the environment in terms of u t i l i t y ( i n functional terms) among the properties which are i n i t i a l l y plausible candidates f o r s p e c i f i c a t i o n may help to render the Gibsonian move to "affordance-perception" more understandable . To r e i t e r a t e , i n order f o r something to be an affordance f o r an organism w i t h a given physical c o n s t i t u t i o n depends on i t s meeting c e r t a i n physical s p e c i f i c a t i o n s .  Everything of the affordance's kind w i l l there-  fore share t h i s f e a t u r e .  Because there is some common, general feature  amongst things which a f f o r d a c e r t a i n kind of behavior f o r the organism in question, there is something which could explain why they are a l l r e l a t e d to the same o p t i c a l  structure.  Since there are best cases, there are also worse and worst ones - properties picking out sets of objects f o r which i t is v i r t u a l l y t o imagine there being some associated i n v a r i a n t . i n t o t h i s category.  impossible  Many object names f a l l  Hence one could imagine a Gibsonian saying that "being  a shoe" is not an e c o l o g i c a l l y coherent category, meaning only t h a t the extension of that property constitutes so loose and e c l e c t i c a c o l l e c t i o n of items i t is u n l i k e l y in the extreme that there should be an i n v a r i a n t s p e c i f i c to "being a shoe".  11  To adapt a point of W i t t g e n s t e i n ' s ,  12  there  need be no f u r t h e r s i g n i f i c a n c e to a t h i n g ' s having the property of being P than t h a t i t is c a l l e d a "P".  Where t h i s is most l i k e l y the case, i t  i s most u n l i k e l y t h a t the set of phenomena should be s p e c i f i e d by some invariant structure. To repeat, the supposition t h a t only some information pickup by looking is j u s t the r e s u l t of the detection of some i n v a r i a n t (and hence constitutes d i r e c t pickup) raises two ( r e l a t e d ) questions.  The f i r s t , as  >  discussed, is the issue of the p r i n c i p l e of d i f f e r e n t i a t i o n between i n f o r mation pickup by looking which is d i r e c t and that which is not.  Only  information that is i n f a c t s p e c i f i e d by an i n v a r i a n t property can be d i r e c t l y picked up.  The second issue is t h a t of how Gibson can avoid  admitting some perception must involve cognitive processing since some information pickup by looking is not merely the r e s u l t of i n v a r i a n t detection. Fodor and Pylyshyn c l e a r l y would t h i n k Gibson could not f i n d a way around t h i s problem.  In considering how d i r e c t pickup might be constrained,  the authors suggest stronger and weaker forms of the ecological approach's basic t h e s i s .  The stronger corresponds to the claim that a l l  pickup by looking i s d i r e c t pickup.  information  The weaker would correspond to the  claim that only some information pickup by looking is d i r e c t pickup. Fodor and Pylyshyn w r i t e : In s h o r t , the weak version of Gibson's claim is that there are some visual properties of the layout which a r e , to a f i r s t approximation, causally necessary and s u f f i c i e n t f o r properties of the l i g h t , which l a t t e r properties are themselves d i r e c t l y picked up. Our point has been that the Establishment theories say t h a t t o o ; i n p a r t i c u l a r , the Establishment theories provide precisely that account-in the case of the sensory properties of the layout . . . Translating out of Fodor/Pylyshyn terms, t h i s passage has Gibson's "weaker claim" as being that only some features of the environment (propert i e s of the l a y o u t ) , whose presence can be determined by looking, are s p e c i f i e d by i n v a r i a n t properties in the o p t i c array. onmental features are d i r e c t l y picked up.  Thus only some e n v i r -  Fodor's and Pylyshyn's conten-  t i o n i s t h a t t h i s weak, Gibsonian view amounts to a version of the Establishment approach, at least w i t h respect to the r o l e of cognitive processing in perception.  In s h o r t , the c r i t i c i s m would be that Gibson simply  claim that only some information pickup by looking is d i r e c t pickup  without caving in to the Establishment. Gibson does have a way of avoiding the envisaged problem, however, without saying that a l l information an organism picks up by looking i s d i r e c t l y picked up.  He can do t h i s by d i s t i n g u i s h i n g between information  pickup by looking and visual perception (or visual information pickup:  it  is convenient f o r my purposes to use t h i s expression as equivalent to visual perception, rather than as an equivalent of information pickup by looking).  The next move i s to say t h a t only cases i n which there can be  d i r e c t pickup of information by looking can there be visual perception. There can only be d i r e c t pickup of information by looking when there is some i n v a r i a n t s p e c i f i c to the environmental f e a t u r e .  Awareness of the  environmental phenomenon constitutes the instance of information pickup in question. Gibson is^ committed to the claim that a l l visual perception is d i r e c t pickup but t h i s can be shown not t o be the strong claim i t appears to be. Fodor and Pylyshyn, because they f a i l t o see how d i r e c t pickup can be constrained in terms of what ( i n f a c t ) invariants s p e c i f y , take i t that anything about the environment that can be found out by looking is perceptible.  Perhaps they side here with some notion of common usage:  that  which i s perceptible is t h a t which is commonly ( c o l l o q u i a l l y ) said to be perceptible.  I f t h i s were Gibson's c r i t e r i a f o r deciding what i s percep-  t i b l e , then " a l l perception i s d i r e c t perception" would be the strong claim Fodor and Pylyshyn imagine.  However, Gibson's c r i t e r i o n i s t h a t the  features of the environment which are perceptible are those, and only those f o r which there are i n f a c t i n v a r i a n t p r o p e r t i e s .  This may be regarded  as a recommendation f o r a ( s t r i c t ) usage o f "Perceives".  In spite of  ordinary usage, only that which i s d i r e c t l y picked up can be said to be  perceived and only t h a t which is specified by an i n v a r i a n t is perceptible (a matter to be s e t t l e d by empirical i n v e s t i g a t i o n ) .  Gibson's view is not,  as Fodor and Pylyshyn perhaps t h i n k , t h a t f o r everything one can o r d i n a r i l y be said to perceive, or f o r everything one can f i n d out by looking, there w i l l prove to be some associated i n v a r i a n t .  Hence the ecological approach  avoids an absurdly strong reading of the kind Fodor and Pylyshyn suggest, without caving in to the Establishment by saying that some visual perception is d i r e c t , some not. One can make use here of the e a r l i e r point that some cases of informat i o n pickup by l o o k i n g , including ones which would sometimes be referred to as "seeing X as P", are only p a r t i a l l y determined by the use of a perceptual system.  The d i s t i n c t i o n between the involvement of the visual  system as p a r t i a l and as exclusive determinant could be used as the basis of a d i s t i n c t i o n between those instances called "seeing X as P" which c o n s t i t u t e "genuine" perception, so to speak, and those instances which c o n s t i t u t e degenerate cases.  Perceiving X as P is a genuine perceptual  achievement i f and only i f an organism is perceptually aware of the very environmental f e a t u r e , X's being P.  This can obtain only when there is an  i n v a r i a n t which specifies phenomena of the kind to which X's being P belongs.  Degenerate cases are those i n which one i s perceptually aware  of something e l s e , such as X's being Q, from which awareness of X's being P i s derived by some cognitive process. Because the ecological approach is concerned with perception as such, a notion t h a t produces semantic o p a c i t y , t h a t an organism perceives X as P is no guarantee t h a t , even when "P" and "Q" are co-designative, i t perceives X as Q. Q may vary.  therefore  Moreover, the r e l a t i o n between X's being P and X's being  X's being P may be necessary and s u f f i c i e n t f o r i t to be Q i n  some cases.  In o t h e r s , X's being Q may be no more than some r e l i a b l e  or t y p i c a l i n d i c a t o r .  The epistemological distance in the association  between X's being P and i t s being Q can vary immensely.  Hence, some  cases of being aware of X as P by being perceptually aware of X as Q w i l l involve deliberate inference/computations, making use of f a i r l y extensive specialized knowledge and t r a i n i n g .  In other cases, the move w i l l be  natural and more or less automatic.  The degenerate instances are not to  be distinguished from the genuine on the basis of what information the t h e o r i s t feels he obtains automatically versus t h a t which requires cognitive effort.  I f appropriate empirical t e s t i n g shows subjects' awareness of  X as P can only be the r e s u l t of the detection of an i n v a r i a n t s p e c i f i c ( f o r instance) to phenomena of X's being Q's k i n d , then an organism can only be said to perceive X as P in some degenerate sense.  In the proper,  or s t r i c t sense of "perceives", the ecological t h e o r i s t should regard t h i s kind of "perception" of X as P as an i n t e l l e c t u a l , rather than a perceptual, achievement. TSRM contend, contrary  to Fodor and Pylyshyn, that the only "gambit" 14  Gibson requires is the gambit of d i r e c t perception.  They f u r t h e r claim  that i t is the Establishment who i n s u f f i c i e n t l y constrain t h e i r key notion 15 of perceiving.  The charges may i n i t i a l l y appear to be a mere case of  academic bravado but i n l i g h t of the discussion of how Gibson constrains the p e r c e p t i b l e , TSRM's counterclaims may be understood.  F i r s t , the  gambit of " d i r e c t perception" is j u s t the idea that only the information picked up by the mere detection of an i n v a r i a n t counts as a genuine case of perception.  Second, TSRM are suggesting that the Establishment, repres-  ented by Fodor and Pylyshyn, o f f e r no workable c r i t e r i a of t h e i r own f o r d i s t i n g u i s h i n g between the perceptible and the non-perceptible.  The basis  of t h i s c r i t i c i s m would be that Fodor and Pylyshyn consider what TSRM would regard as degenerate instances of perception to be genuine ones.  The  p a r t i c u l a r example which comes to mind i s t h a t of the perception of paintings as "authentic DaVincis".  The general complaint could be that  while t r a d i t i o n a l approaches acknowledge that some instances described as perceiving are not e x c l u s i v e l y determined by the operation of a perceptual system, they have no agreed-upon, s a t i s f a c t o r y account of the d i s t i n c t i o n between such instances and those which are exclusively determined by the f u n c t i o n i n g of a perceptual system. There is a possible irony in t h i s understanding of the ecological approach.  Fodor and Pylyshyn c a l l object recognition a "perceptual process  par excellence" , ^ with perception of shoes (as such) being a p e r f e c t l y good, t y p i c a l example of i t .  However, i f the c r i t e r i o n f o r determining  the l i m i t s and categories of the perceptible is that f o r which there are associated i n v a r i a n t s , Fodor and Pylyshyn's example of a perceptual process par excellence may well turn out to be an i n t e l l e c t u a l achievement, not a perceptual one. The prospect of discovering t h a t which is genuinely perceptible via experimentation raises an important problem as w e l l .  This  interpretation  of Gibson c l e a r l y carries a recommendation f o r a l t e r i n g the use of "perceives" not in ordinary language but at least in t h e o r e t i c a l communities.  I t is a  recommended change of usage in the sense of suggesting a c r i t e r i o n of  diff-  e r e n t i a t i o n t h a t stands an extremely good chance of doing violence to conventional views of which environmental phenomena are genuinely percept i b l e and which are not. Embedded in a recommendation of the envisaged kind are promises t o the e f f e c t t h a t acceptance of i t w i l l y i e l d some s i g n i f icant b e n e f i t , that i t w i l l do more good than harm.  One of Gibson's  s p e c i f i c promises is t h a t counting only invariant-based perception as genuine w i l l not too severely l i m i t the class of environmental phenomena which a c t u a l l y turn out to be p e r c e p t i b l e .  As U l r i c Neisser notes, the  " c r u c i a l i n v a r i a n t s have not yet been i s o l a t e d " , and that "the claim that they e x i s t is the largest outstanding promissory note i n ecological optics".  1 7  Another promise is t h a t the invariants that w i l l turn up w i l l be s u f f i c i e n t to explain the evolutionary success of organisms and t h e i r behavior.  Gibson's main complaints against the Establishment is that t h e i r 18  theories pay i n s u f f i c i e n t regard to ecology and evolutionary theory. This is supposed to r e s u l t in theories which cannot explain adequately how perception r e s u l t s in organisms having any knowledge about t h e i r environment at a l l .  There must therefore turn out to be invariants  sufficient  to explain the o r i g i n s of the knowledge various organisms evidently possess about t h e i r environments.  A l s o , given the concern f o r evolution and the  e c o l o g i c a l , there is a promise that invariants w i l l produce e c o l o g i c a l l y useful information f o r organisms.  There is a promise that they w i l l  specify the environment in terms of i t s needs, a b i l i t i e s and v u l n e r a b i l ities.  This point about ecological concern is another part of the explan-  ation f o r Gibson's i n t e r e s t in affordance-perception).  The ecological  approach w i l l u l t i m a t e l y stand or f a l l based on i t s a b i l i t y to show that there is an abundance of invariants that specify the environment i n useful terms to various organisms. (ii) To summarize, Gibson's notion of that which may count as the d i r e c t pickup of information i s constrained. of d i r e c t pickup of information.  Any instance of perception i s one  Direct pickup must be the mere r e s u l t of  the detection of the relevant i n v a r i a n t property by an organism's percept u a l system. I t is very much worth keeping i n mind, however, t h a t t h i s constraining p r i n c i p l e says nothing at a l l about what i s s p e c i f i c a l l y e n t a i l e d by the process of " d i r e c t pickup", o r , a l t e r n a t i v e l y , t h a t which constitutes the mere detection of an i n v a r i a n t .  As matters were l e f t at the end of chapter  two, the r e l a t i o n between information about the environment and i n v a r i a n t properties of the o p t i c array was vague.  As a r e s u l t , i t is not clear what  must obtain i n order f o r an organism t o get from the detection of i n v a r i a n t s t r u c t u r e in the array by i t s visual system to the pickup of some i n f o r mation (awareness of some feature of the environment as such). Fodor and Pylyshyn are among a number of c r i t i c s who have raised questions i n t h i s area.  The general suggestion is that Gibson's theory is 19  i n some sense incomplete, or that i t leaves a "gap".  On the Fodor/  Pylyshyn v e r s i o n , i t is claimed t h a t information about the environment is l i t e r a l l y in^ l i g h t only in the sense that informative properties (that i s , i n v a r i a n t s ) are i n l i g h t .  Informative p r o p e r t i e s , in other words, are  simply s t r u c t u r a l features of l i g h t . They w r i t e : So, f o r example, the frequency of the l i g h t can cause a state o f a detector, and the frequency of the l i g h t can be defacto informative about the color of r e f l e c t i n g surfaces in v i r t u e of a c o r r e l a t i o n t h a t holds between frequency and c o l o r . But the f a c t t h a t the frequency of the l i g h t i s correlated w i t h the color of r e f l e c t i n g surfaces cannot i t s e l f cause a state of a detector, and appeal to that f a c t exhausts Gibson's construal of the notion t h a t the l i g h t contains information about the color of surfaces. So we are back to the old problem: how (by what mental processes) does the organism get from the detection of an informative property of the medium to^the perception of a correlated property of the environment? *® Fodor and Pylyshyn's claim is t h a t no a l t e r n a t i v e to "perceptual i n f e r e n c e " , as they c a l l i t , has yet been suggested.  This apparent gap in Gibson's theory, as the authors go on to explain i t , consists in the absence of an account of the i n t e n t i o n a l i t y (epistemic) perception.  in  This issue quite r i g h t l y takes up the bulk of  TSRM's reply t o Fodor and Pylyshyn.  They argue that Gibson's "theory of  s p e c i f i c a t i o n " provides the basis f o r a new theory of i n t e n t i o n a l i t y .  In  remaining chapters, I w i l l consider TSRM's attempt to defend the ecological approach, arguing that t h i s defense is not successful.  Their discussion  nevertheless suggests a way of understanding the Gibsonian approach which shows i t can accomodate some account of i n t e n t i o n a l i t y .  This w i l l  involve  construing Gibson as what might be called a "perceptual b e h a v i o r i s t " .  I  use t h i s t i t l e to describe t h e o r i s t s who analyze the perceptual awareness of organisms in terms the a c q u i s i t i o n of behavior-states.  Two general  forms, the more sophisticated of which might more properly be considered a v a r i e t y of f u n c t i o n a l i s m , w i l l be described i n Chapter s i x .  Chapter Four As I noted at the end of l a s t chapter, Fodor and Pylyshyn are among a group of c r i t i c s who suggest that Gibson's account of perception does not explain something important.  D i f f e r e n t attempts have been made to make i t  clear what is supposed to be missing, but none of these have found much sympathy from Gibson's f o l l o w e r s .  Fodor and Pylyshyn i n i t i a l l y  explain  the gap they feel as the lack of an explanation of "how an organism gets from the detection of an informative property of the medium" to the perceptual pickup of information about the environment.  They l a t e r develop  t h e i r c r i t i c i s m of Gibson as the claim that he has no "theory of i n t e n t i o n a l i t y " , or no account of the i n t e n t i o n a l component i n epistemic perception:. Everybody has to face the issue about i n t e n t i o n a l i t y somewhere. For Gibson, push comes to shove with the question: What is i t f o r an event (a configuration of the l i g h t , e t c . ) to specify a property? To say that Gibson has no theory of i n t e n t i o n a l i t y is to say that he has no answer to t h a t question. Or, to put i t the other way around, the f a i l u r e of Gibson's theory of s p e c i f i c a t i o n is no minor flaw in his theory. I t marks the precise point at,which Gibson's treatment of i n t e n t i o n a l i t y proves to be bankrupt. D.W. Hamlyn expresses e s s e n t i a l l y the same concern by w r i t i n g : . . . when an object in a given context a f f e c t s a perceptual system in such a way that information is derived about i t because of the s t r u c t u r e of s t i m u l a t i o n , the perceiver is enabled to see the object in a c e r t a i n way, as a such and such. I t i s impossible f o r something to see something as X unless i t has some idea of what i t is f o r something to be an X. To say t h i s is to say that i t must have in some way, and to some e x t e n t , the concept of X. Thus to speak of i t as obtaining information i s not i ^ f a c t to r u l e out as unnecessary any reference to concept. The point which Fodor and Pylyshyn make and which Hamlyn makes is roughly the same.  There are only  two d i f f e r e n c e s .  F i r s t , Fodor and  Pylyshyn r e f e r to representations where Hamlyn refers to concepts. Second, Fodor and Pylyshyn are s l i g h t l y more c o n c i l i a t o r y than Hamlyn.  Hamlyn  appears to suggest that the ecological approach simply cannot do without concepts/representations.  Fodor and Pylyshyn argue only t h a t the Gibsonians  have i n f a c t given no a l t e r n a t i v e means of accounting f o r the i n t e n t i o n a l component.  They leave open the p o s s i b i l i t y that the ecological approach  could come up w i t h some a l t e r n a t i v e . To repeat, the underlying theme i n both Hamlyn's and Fodor and Pylyshyn's remarks is the same.  I f Gibson were merely taking account of  the extensional concept of simple perception, his view would be in no d i f f i c u l t y over the i n t e n t i o n a l i t y issue.  The ecological theory is in  p r i n c i p l e a p e r f e c t l y adequate explanation of the extensional notion of how perceptual systems detect s t r u c t u r e in the ambient a r r a y , f o r instance. The perceptual pickup of i n f o r m a t i o n , which is perceptual awareness of environmental features as such is c l e a r l y an i n t e n t i o n a l n o t i o n .  One way  t o put t h i s is that perception of X as P requires something to mean "P" to the'perceiver. explained:  The alleged gap in Gibson's theory may now be thus  the ecological approach explains the detection of an i n v a r i a n t  property by an organism's perceptual system, but not how a case of detect i o n manages t o mean anything to the perceiving organism. The substantial reply given by TSRM to Fodor and Pylyshyn's c r i t i q u e of the ecological approach consists predominantly of an attempt by the authors to c l a r i f y Gibson's view so as t o i l l u s t r a t e why i t i s not suscept i b l e t o the "gap" problem.  A considerable amount of philosophical  machinery is brought to bear on t h i s issue by the four Gibsonians, but there are e s s e n t i a l l y two notions upon which t h e i r re-explanation of Gibson's view r e s t s .  These are "natural kinds f o r animals" and "natural  law".  I w i l l argue that the philosophical terms and theories which are  meant to ground TSRM's explanation, however, do l i t t l e or no work because they are misapplied or the authors hold other points inconsistent with them.  The theories to which TSRM appeal are H i l a r y Putnam's theory of  natural kinds  3  and Fred I . Dretske s theory of natural laws.  4  Because the appeal to these two theories i s not the kind of thing TSRM need to explain how information can be picked up by mere i n v a r i a n t d e t e c t i o n , they f a i l to explain how the ecological approach avoids the "gap" problem. However, i t i s possible to i n t e r p r e t Gibson as avoiding t h i s problem by accounting f o r that which the detection of an i n v a r i a n t means to an organism in terms of behavior states of some s o r t .  Such an understanding of the  ecological approach is suggested, perhaps only u n i n t e n t i o n a l l y , by parts of TSRM's discussion. Fodor and Pylyshyn suppose that perception of X as P has an i n t e n t i o n a l component t h a t needs explaining.  They give t h i s explanation in terms of a  perceiving organism's r e l a t i o n to a (mental) representation of X's being P ("concept o f " , " i n t e n s i o n " , or "meaning" could a l l be substituted f o r "representation of" as i t is used here), suggesting that any perceptual theory needs to subscribe to t h i s view of i n t e n t i o n a l i t y , or to another that does the same work.  So, f o r example, an organism's perception of X as  P would require the detection of the appropriate corresponding i n v a r i a n t which, though cognitive processes of c e r t a i n s o r t s , eventuates a representa t i o n of X's being P ( i n some sense, the apprehension by the organism of the intension t h a t X (something) is P).  The a l t e r n a t i v e which seems to be  open to the ecological t h e o r i s t s , which i s by no means novel, i s to make a r e d u c t i o n i s t move:  that the detection of some i n v a r i a n t means "X i s P"  to an organism i s to say only that i t s detection produces c e r t a i n sorts of  behavior, or behavior-producing states in the organism.  As I w i l l  later  suggest, the ecological approach to perception i s very l i k e D.M. Armstrong's so-called " B e l i e f - t h e o r y " (where " b e l i e f " is analyzed as "states apt f o r the production of c e r t a i n sorts of b e h a v i o r " ) .  Further d e t a i l of t h i s w i l l  be given a f t e r an evaluation of TSRM's own attempt t o avoid the gap. (ii) To begin, there are some t r o u b l i n g points about the l o g i c of portions of TSRM's commentary.  Part of t h i s i s a t t r i b u t a b l e to a less than  adequate grasp of terms as they would t y p i c a l l y appear i n philosophical discussion.  Their d i f f i c u l t i e s are also a t t r i b u t a b l e to TSRM's f a i l u r e to  appreciate the i m p l i c a t i o n of statements they make.  The l a t t e r is evident  i n a c r i t i c i s m directed at Fodor and Pylyshyn, for.example. TSRM spend a considerable length o f tiTfie. c r i t i c i z i n g what they r e f e r t o as Fodor and Pylyshyn's "argument from the philosophy of science". Since t h i s is a t i t l e of TSRM's choosing, and since there is no s p e c i f i c reference given f o r the Fodor and Pylyshyn a r t i c l e , i t is not clear what TSRM take the argument from the philosophy of science to be.  What the  argument may be, TSRM's c r i t i c i s m is that i t is based on notions which are too c o n t r o v e r s i a l : I t i s p a i n f u l l y obvious . . . that no substantive argument can be b u i l t from the notions of kinds, p r o j e c t i b l e s , laws, and counterfactuals given the current state of the a r t . In the p h i l osophy of science these notions are notoriously opaque and notori o u s l y uneven i n t h e i r usage and are commonly recognized as such without undue embarrassment . . . insofar as Fodor and Pylyshyn have chosen t o ground t h e i r argument i n the philosophy of science, we feel i t incumbent upon us to show t h a t t h a t foundation is porous - l e s t the philosophical wool.,J>e pulled; over the eyes of the non-philosopher.? This c r i t i c i s m i s a hopelessly general one of a kind t h a t TSRM cannot a f f o r d to make.  There is nothing wrong w i t h making use of notions,  when t h e o r i z i n g i n one area of philosophy, that are s t i l l subject to  debate in other areas:  TSRM ought to show s p e c i f i c a l l y how the  contentiousness of a given term a c t u a l l y bears on Fodor and Pylyshyn's c r i t i c i s m s of Gibson.  At best, they show only that some equivocation may  be occurring i n Fodor's and Pylyshyn's use of " l a w " , and of "natural kinds".  These points are unconvincing and are not developed.  The i n c r e d i b l e part about TSRM's argument is that t h e i r own defence of the ecological approach and t h e i r objections to the Establishment are based on some of the very notions which they claim provide too porous a foundation f o r "substantive argument".  A d d i t i o n a l l y , Shaw, Turvey and  Mace have elsewhere attacked t r a d i t i o n a l views and defended t h e i r own in terms of the notion of a proposition and of a possible w o r l d . ^ These two ideas are subject to no small amount of controversy i n t h e i r own r i g h t . I f Fodor and Pylyshyn must be discounted f o r t h e i r use of concepts whose meaning and the nature of whose referents is not at a l l decided, then so too should be TSRM.  In the i n t e r e s t of avoiding closure of t h i s , and most  other philosophical discussion, the kind of general complaint TSRM make ought to be dropped. (iii) Anyone whose background is predominantly i n philosophy (perhaps nonecological psychology as w e l l ) is bound to be somewhat confounded by the language found i n TSRM's a r t i c l e .  There are some words, " p r o p e r t y " ,  " i n t e n s i o n " , "extension", and "natural kind" being c h i e f instances, which often f i n d a place TSRM.  i n philosophical discussions and are also employed by  Their use of these words are of course the subject of some contro-  versy.  Nevertheless, there are accepted general usages f o r each, however  rough.  In places, i t is not clear at a l l t h a t TSRM are f o l l o w i n g any  general p r a c t i c e , but are instead usurping i t by employing reasonably f a m i l i a r terms in ways that merely s u i t the author's purposes.  Also, in  at least one instance TSRM are f l a t l y mistaken in t h e i r employment of one of these notions. Before proceeding, i t i s necessary, f o r purposes of subsequent discussion, to b r i e f l y describe a study mentioned i n TSRM's a r t i c l e .  The  study in question concerns the visual perception of plant stems by marsh periwinkles.  TSRM are fond of r e f e r r i n g to i t as an i l l u s t r a t i v e example  f o r various points they make. The marsh periwinkle i s a small snail found only in upper i n t e r t i d a l zones containing vegetation.  For the most p a r t , the p e r i w i n k l e ' s  a c t i v i t i e s consists of making i t s way, on the ground, amongst and around the plant stems i n h a b i t i n g i t s h a b i t a t .  When the t i d e advances, however,  the s n a i l climbs the plant stems to avoid water-bound predators.  In a  w e l l - c o n t r o l l e d study, Paul V. Hamilton finds convincing evidence to suggest t h a t the p e r i w i n k l e ' s a b i l i t y to locate plant-stems is v i s u a l l y controlled: Snails released on the substrate amid plant stems, j u s t p r i o r to the release area being inundated by the advancing t i d e , moved i n a r e l a t i v e l y s t r a i g h t path and usually (67%) ascended the closest plant stem. The propensity of these snails to ascend the closest stem was shown not to r e s u l t from c o l l i s i o n s r e s u l t i n g from snails t r a v e l l i n g a s t r a i g h t path in a random d i r e c t i o n . Field experiments involving transparent and black rods of equal size showed a s i g n i f i c a n t tendency f o r snails to move toward black rods. 7  The high percentage of instances i n which the periwinkle selects the nearest plant stem suggests a non-random process of o r i e n t a t i o n .  The  high p r o p o r t i o n , i n the subsequent f i e l d study, of selections of black rods ( f o r t y - f o u r black, s i x transparent, with ten snails reaching the perimeter of the plexiglass arena i n which the rods were placed, out of s i x t y t r i a l s ) suggest that i t is v i s i o n which guides the p e r i w i n k l e . TSRM r e f e r to t h i s study as suggesting t h a t when the periwinkle  selects and climbs a plant stem, i t is v i s u a l l y perceiving something as climb-upable.  When i t moves around  the stems (when the t i d e is not  advancing), i t v i s u a l l y perceives them as a b a r r i e r .  Hamilton himself  does not speculate on the s p e c i f i c content of the s n a i l ' s perception of i t s environment. barriers.  In p a r t i c u l a r , he makes no mention of perception of  This causes no special problems f o r TSRM but i t should be  made clear that Hamilton's study, which TSRM do not describe, receives a c e r t a i n amount of embellishment i n order to serve the ecological  theorists'  purposes. One use to which the authors put the marsh periwinkle example is in an objection to the Establishment approach to perception.  TSRM claim t h a t  the Establishment has no coherent explanation of why the periwinkles climb plant stems in one instance and avoid them i n others.  They claim  t h i s is because Establishment views take an "extensional" view of perceiving (such t h a t i f one perceives some property, one perceives anyt h i n g coextensive with i t ) .  Why t h i s is supposed to be a feature of  t r a d i t i o n a l approaches generally is not clear.  In the marsh periwinkle  s i t u a t i o n , the idea is t h a t , in the i n t e r t i d a l zone in which the snail is found, climb-upable things and impassable things ( b a r r i e r s ) happen to be co-extensive.  TSRM assume, because the Establishment view allows the  s u b s t i t u t i o n of co-extensive terms (apparently the authors mean i n g e n e r a l ) , a marsh periwinkle always perceives " c l i m b - u p a b i l i t y " and " i m p a s s i b i l i t y " together.  That i s , i t s perception of things i n i t s environment is  i n d i f f e r e n t between perception of things as climb-upable and perception of them as b a r r i e r s . The f i r s t mistake TSRM make i s in t h e i r understanding of coextensionality.  They w r i t e :  Let us say that f o r a thing to be a b a r r i e r i t must have the properties p , q , r . That i s , ( p , q , r ) is the intension b of " b a r r i e r " . And l e t us say that f o r a thing to be a climb-upable thing i t must have the properties s , t , u , v . That i s , ( s , t , u , v ) is the intension c of "climbable". The extension of b ( i n the i n t e r t i d a l zone) i s the plant stems and other s n a i l s . The extension of c ( i n the i n t e r t i d a l zone) i s the plant stems (other snails being u n w i l l i n g and too short to comply). Thus c i s coextensive with b . ° The same idea i s repeated a l i t t l e l a t e r in a table which purports to 9  make the "Establishment analysis" of the marsh periwinkle case e x p l i c i t . The i n t e n t is to show t h a t , on t r a d i t i o n a l views, the inputs to the s n a i l ' s visual system is not s p e c i f i c to "climb-upable" and " b a r r i e r " .  The ecol-  ogical t h e o r i s t s conclude t h a t the s n a i l ' s a b i l i t y to climb plant stems sometimes and avoid them at other times can only be explained by the Establishment by a t t r i b u t i n g inappropriately sophisticated cognitive processes to the p e r i w i n k l e . F i r s t , i t is f a i r l y obvious t h a t " c l i m b - u p a b i l i t y " and " b a r r i e r " are not coextensional:  TSRM's example contains a mistake.  The extension of  c i n the i n t e r t i d a l zone, since i t is comprised only of plant stems is included i n the extension of b, comprised as i t is of both plant stems and other s n a i l s , j u s t as the class of spouses includes but is not coextensive with the class of husbands.  I f TSRM have some v a l i d point to make against  the Establishment, the example could, of course, be a l t e r e d .  However,  t h a t TSRM should make such a mistake over the r e l a t i v e l y simple notion of c o e x t e n s i o n a l i t y , while using i t t o make a point they c l e a r l y regard as important, i s rather a blow to the authors' c r e d i b i l i t y .  One cannot help  but be a l i t t l e suspicious of TSRM's understanding of the o t h e r , more d i f f i c u l t philosophical concepts t h a t they employ. In a d d i t i o n , the c r i t i c i s m TSRM are attempting to make carries weight.  little  The universal p r i n c i p l e of s u b s t i t u t i v i t y of coextensive terms  75  that the authors a t t r i b u t e to the Establishment is f a r too strong. V i r t u a l l y any philosopher who has thought about questions of s u b s t i t u t i o n recognizes the existence of some opaque contexts i n which coextensive terms may not be s u b s t i t u t e d .  One of the more common of these contexts,  and i t i s one which Fodor and Pylyshyn e x p l i c i t l y recognize, is that of epistemic perception.  Therefore, i f a blanket p r i n c i p l e of s u b s t i t u t i v i t y  of co-extensive terms is taken by TSRM to be some essential tenet of the Establishment p o s i t i o n , they are objecting to a straw man, t o a theory to which few, i f any, would be committed. Another d i f f i c u l t y a r i s i n g in TSRM's a r t i c l e is the manner in which the authors jumble together the terms "property" (and "parameter") and "intension".  For example, they w r i t e that " . . . the i n t i m a t i o n is t h a t a  law relates intensions (properties and magnitudes) rather than extensions (domains of propertyless i n d i v i d u a l s )  and also that "the p r e d i l e c -  t i o n f o r extensionalism is sustained, one is t o l d , by the f a i l u r e to provide a c r i t e r i o n by which two p r o p e r t i e s , two i n t e n s i o n s , can be judged the same".  1 1  There are l e g i t i m a t e and i l l e g i t i m a t e ways of using " i n t e n s i o n " as an alternate for "property".  I t is l e g i t i m a t e to equate the two terms when  "property" is taken i n the abstract or universal sense, as t h a t which is i n s t a n t i a t e d by some set of i n d i v i d u a l s .  Another way of defining an abstract  property (to use an example of Fodor and Pylyshyn's) is as t h a t which is expressed by an open sentence, such as " i s a shoe".  An intension can be  very generally understood as that which is expressed by a given form of words.  I t could thus be considered a property i n the general sense when-  ever the form of words expressing i t is an open sentence. However, the term "property" is sometimes also used in a non-general  sense of property-instances o r , put another way, as p a r t i c u l a r s t h a t possess.  Properties as p a r t i c u l a r s cannot sensibly be i d e n t i f i e d with  intensions.  Yet, t h i s is what TSRM must do since, in s p i t e of using  "property" and " i n t e n s i o n " interchangeably, they deny the existence of a b s t r a c t , universal p r o p e r t i e s , saying there are only "propertied t h i n g s " . This denial of TSRM's w i l l come up again i n connection with t h e i r endorsement of Dretske. The absence of a proper d i s t i n c t i o n between d i f f e r e n t notions of "property" seems to lead TSRM t o a t t r i b u t e the view t h a t the world only contains bare, or "propertyless" i n d i v i d u a l s to Establishment t h e o r i s t s . According to TSRM, t r a d i t i o n a l views consider the intension ("c") " c l i m b - u p a b i l i t y " to be a mental representation or concept. least true of Fodor and Pylyshyn.  of  This is at  Since TSRM. also equate properties  any sense) with i n t e n s i o n s , they conclude that the t r a d i t i o n a l must consider properties to be mental representations.  (in  approach  TSRM would then  proceed to argue that these i n t e r n a l representations are a t t r i b u t e d to the environment and are not f e a t u r e s , hence not perceptible f e a t u r e s , of  it.  Therefore, the Establishment is committed to the notion that only bare, propertyless i n d i v i d u a l s are perceived.  This is a very strange claim  given t h a t there is an abundance of examples of t r a d i t i o n a l  perceptual  theories on which properties are not only p e r c e p t i b l e , but serve as the basis of perception. In defense of the Establishment, two points ought to be kept i n mind. F i r s t , there are two d i f f e r e n t notions of perception:  simple and epistemic.  Second, acceptance of universal properties does not automatically preclude the p o s t u l a t i o n of some p a r t i c u l a r i s t i c sense of "property" (as instances or as i n s t a n t i a t i o n s of the u n i v e r s a l , f o r example) as w e l l .  Now in the simple sense of "perceives", anyone, whether he is an ecological t h e o r i s t or not, who allows that there are properties as p a r t i c u l a r s may grant t h a t organisms (simple) perceive properties.  The  t h e o r i s t may do so independently of whether or not he a d d i t i o n a l l y believes there are properties in some general sense.  The simple sense  of "perceives", however, i s not the sense which should be of concern to TSRM.  On the other hand, in the epistemic sense of "perceives" (which is  i n t e n t i o n a l , unlike the simple sense), organisms are not related to p a r t i c u l a r instances of properties anyway.  To perceive something as  climb-upable i s to recognize a p a r t i c u l a r thing as being of a kind, so the r e l a t i o n is between a perceiving organism and the general property of "climb-upability".  E s s e n t i a l l y , TSRM need to be much more clear on t h e i r  conception of p r o p e r t i e s .  They need to develop a better understanding of  what can be sensibly claimed about properties as p a r t i c u l a r s (they are not intensions and they reside in the environment) and what can sensibly claimed about universal properties (they are intensions and they do not reside in the environment). (iv) Because TSRM confuse two d i f f e r e n t notions of "property" and take the misleading r e s u l t to be interchangeable with " i n t e n s i o n " , they tend to s h i f t between t a l k about simple perception of properties and t a l k about epistemic perception of things as having some property.  One reasonably  clear example of the d i f f i c u l t i e s that can a r i s e occurs when TSRM favourably r e f e r to an argument of Gibson's about affordances.  Gibson reasons:  . . . i f there i s information in l i g h t f o r the perception of surfaces, i s there information the perception of what they afford? Perhaps the composition and layout of surfaces cons t i t u t e s what they a f f o r d . I f so, to perceive them is to perceive what they afford.13  Gibson goes on to claim that t h i s i s a " r a d i c a l hypothesis" according to which values or meanings are d i r e c t l y perceived. There are a couple of separate issues raised by t h i s passage.  First,  Gibson's reasoning i n the conclusion of the foregoing passage, to perceive the composition and layout of surfaces of things is to perceive what they a f f o r d , requires a notion of "perceives" t h a t allows t r u t h - p r e s e r v i n g substitution.  Only the simple sense allows t h i s , and i t does so because i t i  an extensional sense of the term. sional.  Perceptual information pickup is i n t e n -  I t does not admit of the r e q u i s i t e kind of s u b s t i t u t i o n .  More-  over, TSRM e x p l i c i t l y assert that the ecological approach does not want s u b s t i t u t i o n of coextensive terms in perception contexts.  With regard to  Gibson's o v e r a l l theory, t h i s argument therefore r e l i e s on an equivocation of which TSRM are also g u i l t y because they endorse the Gibsonian argument. In addition to the slippage i n uses of "perceives", there is a second sort of equivocation in TSRM's a r t i c l e about which one must be c a r e f u l . I t sometimes appears as though TSRM are taking affordances themselves (which are d i s p o s i t i o n a l properties) to be objects of perception, instead of taking the (actual) things having the affordance to be the object. Taking affordances to be " p o s s i b i l i t i e s " f o r a c t i o n " , they w r i t e : . . . the ecological approach, with i t s commitment t o r e a l i s m . . . , focuses on real p o s s i b i l i t y ; f o r i t takes p o s s i b i l i t y to be an ontological category . . . P o s s i b i l i t i e s f o r action o r , more p r e c i s e l y , things w i t h p o s s i b i l i t i e s f o r a c t i o n , are among the kinds of things t h a t populate an animal's niche and a r e , t h e r e f o r e , things to be seen or heard or smelt e t c . W This move between " p o s s i b i l i t i e s f o r a c t i o n " and "things w i t h poss i b i l i t i e s " is no i n d i f f e r e n t matter.  The claim that some non-occurent  property, the p o s s i b i l i t y of being climbed, i s i t s e l f simply perceived i s rather d i f f e r e n t from the claim that things having the p o s s i b i l i t y are perceived (and i n such a way that the organism may thereby be said to  perceive the object as having the property in question).  The assertion  t h a t a marsh periwinkle perceives (the intension of) " c l i m b - u p a b i l i t y "  is  a quite misleading way of saying that i t perceives some environmental thing (a stem) having the affordance as a climb-upable t h i n g .  The s l i d e  between these two claims, which is no doubt encouraged by the confusion of " p r o p e r t y " , i n the sense of some kind of p a r t i c u l a r , and " i n t e n s i o n " , should be avoided.  One is owed some explanation of how the detection of  an o p t i c a l (or other) i n v a r i a n t associated with things which are climbupable f o r the snail in the i n t e r t i d a l zone manages to mean "climb-upable t h i n g " to a p e r i w i n k l e .  I t would be easy to lose sight of t h i s f a c t  if  the ecological t h e o r i s t s are permitted to t a l k too f r e e l y as though the meaning (intension) of " c l i m b - u p a b i l i t y " was i t s e l f simply perceived. This second issue raised by Gibson's argument is b a s i c a l l y the issue of what sense is to be made of the assertion that (actual) composition and layout c o n s t i t u t e ( d i s p o s i t i o n a l ) affordances. able concerns.  There are two d i s t i n g u i s h -  One is how t h i s claim may be turned i n t o a reasonable view  about affordances (qua d i s p o s i t i o n a l p r o p e r t i e s ) .  The second, which w i l l  mainly be dealt w i t h in the next chapter, is how t h i s view explains how things having p a r t i c u l a r affordances are perceptible as such. TSRM's view of how environmental substances and layout of surfaces could be understood as c o n s t i t u t i n g affordances amounts to a f a i r l y standard sort of modal realism.  Even though t h i s i n t e r p r e t a t i o n makes Gibson's  use of " c o n s t i t u t e s " a very queer one, TSRM's view f i t s very well with Gibson's discussion.  TSRM's view of affordances is t h a t the affordances  that things possess they possess i n v i r t u e of t h e i r actual manifest (occurrent) s t r u c t u r e .  In s h o r t , the non-occurrent properties a thing  holds are grounded in i t s occurrent p r o p e r t i e s .  I t has been pointed out  to me  t h a t t h i s p r i n c i p l e may not be u n i v e r s a l l y t r u e , that i t may not  hold f o r subatomic p a r t i c l e s .  I t does, however, work at the macroscopic  l e v e l , and since the ecological approach i s confined to considering the physical world at the environmental l e v e l , i t w i l l not matter that the p r i n c i p l e i s not generalizable to include basic, physical  particles.  A n e u t r a l , physical example t h a t TSRM use to indicate what they mean by saying t h a t d i s p o s i t i o n s (there is no relevant d i s t i n c t i o n to be made here between " d i s p o s i t i o n " , "affordance", and " p o s s i b i l i t y " ) are grounded in the occurrent i s t h a t of the s o l u b i l i t y of s a l t .  Salt has the property  of s o l u b i l i t y because i t i s comprised of l a t t i c e s of ions, bonded by e l e c t r i c a l a t t r a c t i o n s , the values of which are s u b s t a n t i a l l y reduced by the high d i e l e c t r i c constraints of c e r t a i n l i q u i d s .  TSRM's account of  affordances is along the very same l i n e s : A climb-upable thing must possess a c e r t a i n r i g i d i t y , a c e r t a i n surface area, a c e r t a i n height, a c e r t a i n textual q u a l i t y , e t c . , to support the climbing of the snail and the snail must be of a c e r t a i n mass, i t s mucous of a c e r t a i n v i s c o s i t y , i t s ventral . surface of a c e r t a i n f l e x i b i l i t y , e t c . , to e f f e c t the climbing. f i  A stem's being climb-upable f o r the s n a i l , in other words, consists in i t having the appropriate occurrent physical dimensions.  There i s only  one complication in the notion of affordances grounded in occurrent properties over the explanation TSRM giveof d i s p o s i t i o n a l properties in general.  This i s t h a t the common, physical structure among members of  the affordance must somehow also produce an i n v a r i a n t s p e c i f i c to i t  in  order f o r the affordance to'be perceived as such. (v) Affordances. c o n s t i t u t e what TSRM c a l l natural kinds f o r animals.  The  notion i t s e l f f a i r l y s t r a i g h t f o r w a r d l y serves to f u r t h e r r e s t r i c t the classes of environmental phenomena which must be considered as s p e c i f i c to  be a given, i n v a r i a n t , as I w i l l explain a l i t t l e l a t e r .  I t is l i k e l y to  produce a c e r t a i n amount of p e r p l e x i t y , however, because the use of "natural kind" by TSRM i s an atypical one.  Moreover, the authors claim  several times to be using the term in accordance w i t h the views of Hilary Putnam when i t is neither clear what they take to be Putnam's use of "natural kind" nor that what Putnam i n p a r t i c u l a r says is relevant to t h e i r case. As is f a r too common in the TSRM a r t i c l e , there is no proper reference t o i n d i c a t e what is said by Putnam with which the authors f i n d agreement. The only concrete a t t r i b u t i o n to Putnam occurs when TSRM w r i t e : Freeing the conception of a natural kind from the requirement of i n c l u s i o n in a natural law is the tack taken by Putnam (1970a, b ) : a natural kind term merely serves to draw commonalities among things that are s u p e r f i c i a l l y d i f f e r e n t ; i t is a s c i e n t i f i c convenience and an i n t e n t i o n a l l y temporary one at that.1? Three ideas are a t t r i b u t e d to Putnam in t h i s quote: 1. Natural kinds need not be included in natural laws 2. Natural kind terms only serve to draw a t t e n t i o n to commonalities amongst the s u p e r f i c i a l l y  dissimilar  3. Natural kind terms are " i n t e n t i o n a l l y temporary" In " I s Semantics Possible?" (TSRM's reference is "(Putnam, 1970a)"). Putnam introduces his discussion of natural kinds by w r i t i n g t h a t : An important c l a s s , p h i l o s o p h i c a l l y as well as l i n g u i s t i c a l l y , is the class of general nouns associated with natural kinds — t h a t i s , with classes of things t h a t we regard as of explanatory importance; classes whose normal d i s t i n g u i s h i n g c h a r a c t e r i s t i c s are "held together" or even explained by some deep-lying mechanisms. jgGold", "lemon", " t i g e r " , "acid" are examples of such nouns. Some examples of "deep-lying mechanisms" are "proton donor" f o r a c i d s , a p a r t i c u l a r DNA s t r u c t u r e f o r t i g e r s or lemons, atomic weight and number f o r chemical elements l i k e gold.  TSRM say that on Putnam's view natural kinds are not required to be included in natural laws. of t h i s claim.  There seems to be two possible i n t e r p r e t a t i o n s  The f i r s t is that what counts as a natural kind is not  determined by t h a t about which the current s c i e n t i f i c community have (discovered or postulated) natural laws.  Since natural kinds are taken by  Putnam to be classes held together by non-superficial s t r u c t u r e (mechanisms) which s c i e n t i s t s may or may not have discovered, t h i s i n t e r p r e t a t i o n of 1) is very l i k e l y t r u e .  TSRM want to postulate natural kinds ( i n some  sense) about which there are presently no expressed natural laws, so there is some basis f o r t h i n k i n g the authors do_ mean that a kind is not a natural one in v i r t u e of having laws postulated about i t .  The a l t e r n a t i v e  inter-  p r e t a t i o n i s t h a t there need not e x i s t any natural laws (discovered or not) concerning a given natural kind.  The kinds of deep-lying mechanisms which  would make natural kinds s u i t a b l e subjects f o r laws.  Thus t h i s second  i n t e r p r e t a t i o n , that natural kinds need not be i n f a c t included in natural laws, is surely not Putnam's view. Regarding 2 ) , TSRM seem to be mistakenly taking the existence of " s u p e r f i c i a l differences" among members of a natural kind to be some key feature of natural kinds.  Perhaps the authors have not quite grasped the 19  points which Putnam attempts to make?  Putnam uses d i f f e r e n t examples  (green lemons, three-legged or non-striped t i g e r s ) in an attempt to stress the point that since members of natural kinds could be, and sometimes are observably d i f f e r e n t , i t is implausible to hold that membership in natural kinds is determined by s u p e r f i c i a l , observable p r o p e r t i e s .  This point 20  is made i n support of a view about the meaning of natural kind terms. Whether or not members of the extension of a general noun do happen to be s u p e r f i c i a l l y d i s s i m i l a r is quite i r r e l e v a n t to the question of whether  t h a t noun picks out a natural kind.  The meaning of a natural kind term  (and the class i t picks out) therefore cannot be f i x e d i n terms of s u p e r f i c i a l , observable s i m i l a r i t i e s between t h i n g s . The a t t r i b u t i o n of 3) to Putnam may embody the very same kind of confusion.  To say t h a t the use of some term is " i n t e n t i o n a l l y temporary",  one must assume, means only that i t s meaning is subject to change.  It  i s part of Putnam's view about natural kind terms that t h e i r meanings can_ change but i t i s not Putnam's view that changes i n meaning are e i t h e r a common or d i s t i n g u i s h i n g c h a r a c t e r i s t i c of natural kind terms.  Putnam  says that which is conveyed by a natural kind term is i t s extension and 21 an associated stereotype.  The meaning of such a word can change because  f o r example, s c i e n t i f i c developments can bring about a change i n the assoc iated stereotype (and hence that which is thought to be a member of the extension).  Putnam is w r i t i n g in contrast to those who would hold that th  meaning of a natural kind term, unlike the meanings of other general nouns is permanently f i x e d . The large puzzle, however, is why TSRM bother to r e f e r to Putnam's p a r t i c u l a r theory at a l l .  The p o s i t i v e use that is made by the ecolog-  i c a l t h e o r i s t s of "natural kind" does not obviously require acceptance of the Putnam account.  In f a c t , TSRM's use of "natural kind" may not even  be the notion over which philosophers debate.  Their use is of "natural  kinds f o r animals", explained as f o l l o w s : Construed as natural kinds f o r animals, affordances do not require grounding i n occurrent properties t h a t s a t i s f y the explanatory s t r i c t u r e s of science but in occurrent properties that s a t i s f y the pragmatic c r i t e r i a of successful a c t i v i t y i n a r e s t r i c t e d universe of p o s s i b i l i t i e s , v i z . , an ecological world.22 "Occurrent p r o p e r t i e s " , as TSRM mean t h i s could be taken as the same as what Putnam means by "underlying mechanism" and therefore one can  speculate that the authors have simply h i t on t h i s p a r t i c u l a r feature of Putnam's view. criteria"?  But what i s to be made of the reference to "pragmatic  The point TSRM are attempting to make turns out to be consid-  erably simpler than the obscure phrase would suggest. In the phrase "natural kind f o r an animal", the word " n a t u r a l " is given a rather d i f f e r e n t emphasis than is customary i n t a l k about natural kinds.  The affordances environments hold f o r perceiving organisms are  grounded in the manifest structures of the f u r n i t u r e of the environment, as noted previously.  Anything at a l l meeting c e r t a i n physical  ations could a f f o r d c e r t a i n kinds of behavior.  specific-  The general class of  things which could a f f o r d some p a r t i c u l a r a c t i v i t y , though, w i l l almost i n v a r i a b l y be larger than the subclass of those things that n a t u r a l l y or t y p i c a l l y occur i n an organism's local environment ( " h a b i t a t "  i s a word  t h a t corresponds most nearly to TSRM's use of "environment"). So, f o r example, anything at a l l of a c e r t a i n minimum height, r i g i d i t y , of a c e r t a i n textual q u a l i t y , and so could be climbed by a marsh periwinkle as long as i t s a t i s f i e s some general, mostly minimum requirements.  This general class of things the snail could climb may well  include objects such as p e n c i l s , p l a s t i c plant stems or swizzel s t i c k s . As TSRM use the phrase, none of these are natural kinds f o r the p e r i w i n k l e . Swizzel s t i c k s and the l i k e are not members of "climb-upable t h i n g " because they are non-typical features of the habitat (the upper i n t e r t i d a l zone) in which the species resides and in which ( t h i s is an important point to the ocological t h e o r i s t s ) i t evolved.  The idea TSRM therefore want is  not so much t h a t of a natural kind as t h a t of a r e s t r i c t e d kind:  "climb-  upable t h i n g " , as a perceptible category f o r the p e r i w i n k l e , consists only of the usual constituents of i t s environment (a subclass of plant stems) t h a t a f f o r d climbing f o r members of that species.  To c l a r i f y TSRM's conception, the p e r i w i n k l e ' s environment i s upper i n t e r t i d a l zones containing c e r t a i n kinds of vegetation.  This local  environment and i t s natural contents constitutes the " r e s t r i c t e d universe of p o s s i b i l i t i e s " i n which the species and i t s perceptual systems evolved. The so-called natural kinds f o r the marsh p e r i w i n k l e , or f o r any other organism, are defined by TSRM in terms of the things in i t s environment t h a t a f f o r d a c e r t a i n kind of behavior.  In the present case, "climb-up-  able t h i n g " has as i t s extension plant-stems f a l l i n g w i t h i n some set of physical dimensions represented in TSRM's discussion by the set  s,t,u,v.  These c o n s t i t u t e the occurrent p r o p e r t i e s , TSRM's c o r r e l a t e of Putnam's "underlying mechanisms", which ground or explain the a b i l i t y of things with the physical c h a r a c t e r i s t i c s of the periwinkle t o climb a subclass of plant-stems. I f an affordance, which is a natural kind f o r an animal, is  restric-  ted t o items i n an organism's environment that allows a p a r t i c u l a r kind of a c t i v i t y , then i t is w i t h i n t h i s context that some i n v a r i a n t property must be s p e c i f i c t o environmental features that a f f o r d an a c t i v i t y .  The  idea would then be that i f periwinkles do perceive climb-upable t h i n g s , there i s some o p t i c a l i n v a r i a n t in the p e r i w i n k l e ' s habitat associated w i t h a l l and only things having s , t , u , v (plant stems of c e r t a i n minimum dimensions).  These dimensions are the ones i n v i r t u e of which plant  stems are climb-upable.  The p e r i w i n k l e ' s responding c l i m b i n g l y , as i t  were, only t o the detection t>f a p a r t i c u l a r o p t i c a l i n v a r i a n t works in i t s local environment in the sense ttvat a successful bout of climbing i s , other things being equal, the i n e v i t a b l e r e s u l t . Outside the r e s t r i c t e d universe, matters may be quite  different.  This includes the removal o f the organism from i t s h a b i t a t and also the  i n t r o d u c t i o n of some non-typical element i n i t s h a b i t a t .  In e i t h e r case,  the periwinkle could be expected t o pass up things i t could in f a c t climb and t r y out many "non-climbables".  The l a t t e r would occur i f there were  phenomena outside the habitat which happens t o produce the same o p t i c a l i n v a r i a n t associated with climb-upable plant-stems.  The former holds  because the o p t i c a l i n v a r i a n t to which periwinkles respond is not necessa r i l y produced by anything the organism could climb.  In p a r t i c u l a r ,  it  would not be produced by things which the periwinkle could as a matter of f a c t climb, but does not possess the s t r u c t u r e s , t , u , v .  Hamilton's  study would seem to i n d i c a t e , f o r example, that (if_ the p e r i w i n k l e ' s perception is i n f a c t invariant-based) the relevant o p t i c a l s t r u c t u r e is not produced by clear plexiglass rods. To summarize, the extension of a natural kind f o r an animal consists of the n a t u r a l l y occurring features of the environment i n which i t s species evolved and l i v e s which a f f o r d some kind of a c t i v i t y . points need to be made about t h i s .  Two general  F i r s t , TSRM's account of affordances  has the advantage of reducing the size of the classes of things to which i n v a r i a n t s must be s p e c i f i c from anything t h a t would a f f o r d a c e r t a i n a c t i v i t y f o r an animal to the usual constituents of i t s environment which do so.  Thus narrowing the f i e l d , so to speak, makes i t a l l the more easy  to envisage a p a r t i c u l a r o p t i c a l i n v a r i a n t being uniquely associated with the class of phenomena an organism perceives as affording some kind of behavior.  At the same t i m e , i t is worth observing that the marsh p e r i -  w i n k l e , because i t s habitat i s quite r e s t r i c t e d , provides a misleadingly simple case.  As one moves on to consider more adaptable and mobile organ-  isms (humans, f o r i n s t a n c e ) , i t w i l l become increasingly d i f f i c u l t to c l e a r l y i d e n t i f y t h e i r p a r t i c u l a r " r e s t r i c t e d universe".  I t w i l l conseq-  uently become ever more d i f f i c u l t to i d e n t i f y perceptual categories and  t h e i r extensions f o r those organisms. The second general point is to emphasize the f a c t that TSRM's sole c r i t e r i a f o r determining the content of the p e r i w i n k l e ' s , and other organisms', perception is i t s behavior.  The basis f o r the claim that  periwinkles perceive c e r t a i n plant stems as climb-upable things is that the snails in f a c t respond climbingly in c e r t a i n circumstances to those stems.  The step from using behavior as the c r i t e r i a f o r determining  what organisms perceive things as to analyzing what they perceive things as in terms of behavior (or behavior-states) i s a f a i r l y short one. In t h i s chapter, I have indicated that TSRM's discussion is bedevilled by some confusions about c e r t a i n p h i l o s o p h i c a l l y common notions.  They  allow themselves to make mistakes about e x t e n s i o n a l i t y and i n t e n s i o n a l i t y and about the r e l a t i o n between properties and intensions.  These lead to  confusions about commitments the Establishment must make,  TSRM also have  a very queer understanding of "natural kind" which leaves i t unclear as to why they are so favourably disposed toward the views of Putnam.  Their  concept of natural kind turns out t o be a concept of a " r e s t r i c t e d k i n d " . The kinship with Putnam seems to consist only i n the idea of underlying mechanisms that "ground" c e r t a i n p r o p e r t i e s . the c r i t i c a l discussion of TSRM's a r t i c l e .  The next chapter w i l l This continuation w i l l  continue finally  focus on TSRM's attempt to show how Gibson's theory can account f o r i n t e n t i o n a l i t y , which w i l l l a r g e l y involve TSRM's adoption of Dretske's theory of natural laws.  Chapter Five The idea of natural kinds f o r animals and a p a r t i c u l a r view about natural laws is the basis of TSRM's description of the Gibsonian theory of specification.  TSRM attempt to use these notions answer the charge that  the ecological approach has no account of i n t e n t i o n a l i t y i n perceiving. The basic idea i s t h a t the ecological approach somehow manages to account f o r i n t e n t i o n a l i t y in perceiving because there are lawful connections between ecological properties (natural kinds f o r animals or any other environmental features the ecological t h e o r i s t s take to be perceptible) and occurrent physical properties of the environment, and between invariants and the manifest environmental ones. According to TSRM, f a i l i n g to recognize the point that there e x i s t lawful connections of c e r t a i n kinds is the c r u c i a l mistake Fodor and Pylyshyn make in t h e i r c r i t i c i s m s .  They claim that Fodor and Pylyshyn repea-  t e d l y a t t r i b u t e a "weak c o r r e l a t i o n a l view" to Gibson, meaning, one would suppose, a view on which r e l a t i o n s between ecological properties and invariants are correlated merely in some s t a t i s t i c a l sense.*  However, i t  is not clear t h a t Fodor and Pylyshyn do_ a t t r i b u t e t h i s weak view to Gibson or that i t would a f f e c t t h e i r central objections in any case.  That is to  say, i t w i l l prove unclear as to how, through the postulation of lawful r e l a t i o n s between occurrent "underlying mechanisms", ecological p r o p e r t i e s , and i n v a r i a n t s , TSRM can show how the theory of s p e c i f i c a t i o n has an account of  intentionality.  Now a central feature of TSRM's supposed a l t e r n a t i v e account of i n t e n -  t i o n a l i t y i n perception is t h e i r adoption of Dretske's intensional theory 2 of natural laws.  The most reasonable way to proceed with t h i s discussion  t h e r e f o r e , i s as f o l l o w s .  F i r s t , TSRM's version of the theory of specif-  i c a t i o n should be explained.  They c l e a r l y indicate that the notion of a  natural law on. a more conventional understanding of laws, is of no help. I w i l l then examine TSRM's claims in l i g h t of the Dretskean theory to see why TSRM might t h i n k they derive some advantage from embracing t h i s theory in particular. (i) TSRM's version of the theory of s p e c i f i c a t i o n consists of four large claims.  The f i r s t two of these were elaborated i n the previous chapter  but i t is u s e f u l , f o r c l a r i t y , to l i s t a l l four of them here.  Given some  occurrent, physical s t r u c t u r e , P, and o p t i c a l i n v a r i a n t , 0, both of which are associated with the ecological property, A: 1. In the context of an organism's environment, P is a necessary condition f o r A 2. A must be grounded in P, in the sense t h a t , i n the organism s J  environment, A's presence is explained by the presence of P 3. Among the t y p i c a l constituents of an organism's environment, things having 0 are uniquely correlated with things that have A 4. The environmental constituents having A and those having 0 are uniquely correlated in an organism's environment because the same physical structure which explains the presence of A also explains the presence of 0 1) and 2) j u s t serve to indicate that A constitutes a natural kind f o r some organism, and that the r e l a t i o n between P and A is non-accidental 3) states t h a t , under c e r t a i n r e s t r i c t i n g c o n d i t i o n s , 0 i s s p e c i f i c  to things having A.  The main r e s t r i c t i n g c o n d i t i o n , mentioned i n chapter  f o u r , is t h a t the r e l a t i o n only needs t o hold between occurrences of 0 and the presence of A i n the organism's natural h a b i t a t .  Outside t h i s envir-  onment, things may have A but f a i l to e x h i b i t 0 because the property A can be produced by occurrent properties other than P (other than the only occurrent s t r u c t u r e in the organism's environment which in f a c t produces it).  S i m i l a r l y , things may produce 0 but f a i l to have A because, outside  the organism's environment, 0 may be produced by occurrent physical structures other than P. Another l i m i t a t i o n TSRM mention is that 0 only needs to be s p e c i f i c to A from the "perspectives" which an organism normally takes on i t s environment.  By "perspectives" the authors mean the positions from which,  and the conditions under which members of a given species n a t u r a l l y observe features of t h e i r environments.  Hawks and f i e l d mice may be found  l a r g e l y i n the same kinds of regions, but the perspectives they would have on t h e i r t e r r e s t r i a l environment would be quite d i f f e r e n t .  The claim  must be t h a t the invariants available to each species would s i m i l a r l y differ. 4) states t h a t the manifest property that grounds A is the very one that produces 0.  Since the manifest property, P, produces 0, the connec-  t i o n between the two is non-accidental.  S i m i l a r l y , since P produces A,  the connection between these two properties is non-accidental.  TSRM use  these points that they make i n order to claim that the r e l a t i o n between A and 0 i s also non-accidental.  The argument used f o r t h i s purpose w i l l  be examined s h o r t l y . Assertion 4) places an obvious r e s t r i c t i o n on the ecological approach' conception of which p a r t i c u l a r invariants could specify which features of  91  the environment.  The r e s t r i c t i o n is t h a t the very same manifest physical  property responsible f o r the presence of some ecological property must also be the very one which produces the i n v a r i a n t which specifies the ecological property in question.  V i s u a l , s p a t i a l l y - o r i e n t e d examples seem  to lend themselves r e a d i l y t o t h i s idea:  A s i t - o n a b l e , climb-upable, or  cut-withable thing f o r a human is so because of the size and angles between the surfaces (as well as the r i g i d i t y and perhaps other t h i n g s ) , f o r instance.  I f there is an i n v a r i a n t s p e c i f i c to any df these a f f o r d -  ances, i t is l i k e l y t o be s i m i l a r l y due to such physical parameters as size and angular arrangements.  The ecological approach is supposed to  be generalizable to other sorts of ecological properties and other percept u a l modalities ( i n c l u d i n g those which are not analyzable in terms of surfaces), though.  These other instances may not prove to be so promising.  There is no p a r t i c u l a r reason, f o r example, to expect that the very same underlying properties which make c e r t a i n things edible are the very ones which could produce the i n v a r i a n t that would specify i t as such. To continue with the main t o p i c , TSRM are very clear i n i n s i s t i n g that only an intensional view of laws w i l l help t h e i r case.  They are quite  committed to the view t h a t the ecological approach gains no advantage by asserting that s p e c i f i c a t i o n of ecological properties is l a w f u l , given some extensional conception of laws.  One can make a reasonable guess as to why  the authors believe t h i s based on what they have to say about Establishment views.  They claim that such t r a d i t i o n a l views as Fodor and Pylyshyn  defend can only explain an organism's a b i l i t y to d i f f e r e n t i a t e between two perceptible p r o p e r t i e s , A and B, t h a t happen to be coextensive by appealing  4 to concept a c q u i s i t i o n and possession and the cognitive processing.  Where  such appeals can not work, TSRM claim, the Establishment must simply concede t h a t the perceiver in question does not d i f f e r e n t i a t e between A and  B, even when the organism's behavior indicates that i t can.  The problem  i s alleged t o arise because of a committment to an extensional or empiri c i s t , theory of natural laws on the part of the Establishment.  TSRM  (mistakenly) suppose that an e x t e n s i o n a l i s t view takes statements' status as laws survive s u b s t i t u t i o n of coextensive terms.  On such a view, any  laws in which A p a r t i c i p a t e s are ones in which B equally p a r t i c i p a t e s . The authors would then go on to reason t h a t i f some law explains an organism's perception of A, i t also explains i t s perception of B. The lesson which TSRM wish to draw from t h i s problem they envisage f o r the Establishment is t h a t a b e t t e r explanation of how organisms d i f f e r e n t i a t e between coextensive properties must be devised.  The prominence of  the notion of natural laws in t h e i r discussion suggests very c l e a r l y t h a t TSRM t h i n k the postulation of c e r t a i n kinds of lawful connections w i l l y i e l d the explanation they want. to the f o l l o w i n g :  In general, t h e i r account seems to come  even though properties A and B are coextensive, A is  l a w f u l l y r e l a t e d to a d i f f e r e n t i n v a r i a n t than is B.  The organism some-  times behaves i n ways appropriate to the perception of something as A because i t detects the i n v a r i a n t which is l a w f u l l y related t o A.  Because  A and B are coextensive, B i s always and only present when A's i n v a r i a n t is present, but B's r e l a t i o n t o t h a t i n v a r i a n t is "merely c o r r e l a t i o n a l " . The organism responding as though i t perceives something as A when i t s perceptual systems detect a p a r t i c u l a r i n v a r i a n t is supposed to be explained in terms of the f a c t that the r e l a t i o n between invariants of t h a t s o r t and the ecological property A is non-accidental, while i t s r e l a t i o n t o B is a c c i d e n t a l . As an example, one might consider again TSRM's case of the marsh p e r i w i n k l e , amending t h e i r description so that "climb-upable t h i n g " and  " b a r r i e r " are genuinely coextensive in the s n a i l ' s habitat (that i s , other snails and plant-stems are b a r r i e r s i f and only i f they are climb-upable). TSRM imagine that c e r t a i n manifest p r o p e r t i e s , s , t , u , v , are the ones which make something climb-upable.  I f t h i s is a perceptible property,  s,t,u,v  (or perhaps some subset of them) must be the properties which produce the i n v a r i a n t the periwinkle detects whenever i t perceives something as climbupable.  TSRM are assuming that some other manifest p r o p e r t i e s , p , q , r , are  the ones which make something a b a r r i e r f o r the p e r i w i n k l e . Assuming t h a t i t i s not plausible to a t t r i b u t e concepts, cognitive processes, or the l i k e to s n a i l s , TSRM claim that the Establishment has no explanation of how periwinkles d i f f e r e n t i a t e between "climb-upable" and "collide-withable".  I t is also assumed, of course, that the creature's  behavior i s s u f f i c i e n t evidence that they do so d i f f e r e n t i a t e .  The  Establishment, so the argument goes, does not have cognitive processing available to explain the d i f f e r e n t i a t i o n s made by the p e r i w i n k l e .  Since  "climb-upable t h i n g " and " b a r r i e r " are coextensive, they are equally correlated with the i n v a r i a n t which s , t , u , v produces.  Therefore, neither  can the Establishment claim that the p e r i w i n k l e ' s perceptual systems have picked up on some association between a property of the o p t i c array and "climb-upable" t h a t does not e x i s t as well between that optical and b a r r i e r s .  property  TSRM want t o conclude that t r a d i t i o n a l t h e o r i s t s such as  Fodor and Pylyshyn must therefore disregard the p e r i w i n k l e ' s evident a b i l i t y t o d i f f e r e n t i a t e between b a r r i e r s and climb-upables. TSRM claim to solve such puzzles in terms of the lawful connections they p o s t u l a t e :  c l i m b - u p a b i l i t y , grounded as i t is i n the properties  s , t , u , v i s l a w f u l l y related to the i n v a r i a n t produced by s , t , u , v this invariant 0 ( c ) ) .  (call  C o l l i d e - w i t h a b i l i t y , on the other hand, is only  a c c i d e n t a l l y related to s , t , u , v since i t is grounded in other manifest properties (namely p , q , r ) .  Thus the i n v a r i a n t s , t , u , v produces l a w f u l l y  specifies "climb-upable t h i n g " , and does not l a w f u l l y specify withable t h i n g " ( b a r r i e r ) .  "collide-  Therefore, TSRM would conclude, the periwinkle  perceives something as climb-upable, and not as a b a r r i e r , whenever i t detects 0 ( c ) . Two points should be made about t h i s suggested explanation of how organisms d i f f e r e n t i a t e between instances of ecological p r o p e r t i e s .  First,  in defence of the Establishment, i t is not at a l l clear why they should be caught in the d i f f i c u l t i e s t h a t TSRM seem to be suggesting.  One should  t h i n k the problem of explaining differences in the p e r i w i n k l e ' s behavior toward the very same class of physical things (plant stems) could be handled in terms of a notion such as readiness or expectancy sets:  given  one set of background conditions (receding t i d e , f o r example) which the periwinkle can sense, the detection of a given i n v a r i a n t constitutes the perception of something as a b a r r i e r . the objects perceived.  That i s , the periwinkle moves around  Given a d i f f e r e n t set of background conditions t h a t  the periwinkle can sense (advancing t i d e ) , detection of the very same i n v a r i a n t constitutes the perception of something as climb-upable. ceived background conditions prime the p e r i w i n k l e , as i t were;  Per-  they  cause i t to be in an expectancy set such that the snail responds " c l i m b i n g l y " t o the detection of the i n v a r i a n t . Second, i t i s not at a l l clear how, on any conventional understanding of natural laws, they w i l l do what TSRM require of them.  That 0 (c) law-  f u l l y specifies climb-upable things but is merely i n v a r i a b l y correlated w i t h perceived b a r r i e r s does represent a difference between the two ecol o g i c a l p r o p e r t i e s , but the key question is whether or not t h i s is a d i f -  ference of which perceptual systems of organisms could take advantage. The two ecological properties are correlated t o precisely the same degree in the p e r i w i n k l e ' s environment.  In order f o r the difference to be usable,  the visual system of the organism must somehow be s e n s i t i v e to the r e l a t i o n between 0 (c) and c l i m b - u p a b i l i t y . does not detect the r e l a t i o n in question: 0 (c), itself.  However, the visual system i t detects the o p t i c a l  invariant,  Given t h i s , and the f a c t that the presence of 0 (c) is  equally and i n v a r i a b l y correlated with the two ecological p r o p e r t i e s ,  it  should be a mystery as to why a species t h a t has evolved i n t h i s environment should have evolved so as to perceive things as climb-upable (but not as c o l l i d e - w i t h a b l e ) whenever i t detects the i n v a r i a n t o p t i c a l 0 (c).  structure,  In other words, a general appeal to natural laws does not explain  how organisms manage to perceptually d i f f e r e n t i a t e between coextensive ecological p r o p e r t i e s . For t h i s reason, and also because TSRM take the acceptance of a part i c u l a r theory about natural laws t o be of fundamental importance, i t  is  reasonable to assume t h a t TSRM's account of i n t e n t i o n a l i t y in terms of the ecological theory of s p e c i f i c a t i o n could not possibly work without Dretske's intensional view of natural laws.  Since acceptance of Dretske's  p a r t i c u l a r theory is to be regarded as essential to TSRM's case, therefore any one of the f o l l o w i n g three points would show t h a t t h e i r account of i n t e n t i o n a l i t y does not work: 1. Dretske's theory is mistaken 2. The intensional view of laws affords TSRM no advantage which would not have been available to them on a conventional, e m p i r i c i s t conception of laws 3. TSRM cannot c o n s i s t e n t l y accept the Dretskean theory because of other views the authors hold.  My discussion of the Dretskean theory in r e l a t i o n to what TSRM say about i t w i l l reveal reasons f o r both 2) and 3 ) . (ii) There are a number of confusions which TSRM appear to make about Dretske's view t h a t a natural law is a r e l a t i o n between intensions.  The  largest one might be the idea that embracing t h i s intensional theory of laws w i l l somehow grant t h e i r theory of s p e c i f i c a t i o n the a b i l i t y to r e l a t e perceivers to (some conception of) intensions.  In any case, a  thorough discussion of the mistakes about Dretske's account should show that i t is doubtful TSRM have any proper understanding of Dretske's theory at a l 1 . Dretske's account is w r i t t e n against what he c a l l s " e m p i r i c i s t " conceptions of natural laws.  The e m p i r i c i s t view is taken to be b a s i c a l l y  the view that what is expressed by a law-statement is the very same kind of thing which is expressed by any ( t r u e ) u n i v e r s a l l y general statement of f a c t , plus an a d d i t i o n a l , special  ingredient:  This response to the alleged uniqueness of natural laws is more or less standard fare among e m p i r i c i s t s i n the Humean t r a d i t i o n . Longstanding (= venerable) epistemological and ontological commitments motivate the equation: law= universal t r u t h + X. There is disagreement among authors about the d i f f e r e n t i a X, but there is near unanimity about the f a c t that laws are a species of universal t r u t h . 5 Dretske says that that which is expressed by some universal c o n d i t i o n a l , " A l l F's are G", is a r e l a t i o n between extensions:  every member of the  extension of F i s also a member of the extension of G.  He takes the empir-  i c i s t models of laws t o s i m i l a r l y consist of t h i s extensional sort of relation.  The puzzle, then, is to f i n d the special ingredient X which  explains the necessity of the r e l a t i o n .  One must f i n d whatever i t is that  confers on laws the peculiar functions and feature that are not possessed by  j u s t any universal g e n e r a l i z a t i o n .  Dretske's a l t e r n a t i v e , which he neatly  encapsulates by saying a law is a singular r e l a t i o n between i n t e n s i o n s , is introduced thus: To say that i t is a law t h a t F's are G is to say that " A l l F's are G" is to be understood ( i n so f a r as i t expresses a l a w ) , not as a statement about the extension of the predicates "F" and "G" but as a singular statement describing a r e l a t i o n s h i p between the universal properties F-ness and G-ness. In other words, ( C ) i s to be understood as having the form: ( 6 ) F-ness—> G-ness.6 ( " ( C ) " , i n t h i s passage, denotes " I t i s a law t h a t F's are G".) There are two points which need to be made about t h i s quote.  First,  a footnote is attached to i t in which Dretske indicates that the arrow used i n ( 6 ) is to be taken as a "dummy connective", meaning that he does not intend i t to indicate a given r e l a t i o n (material or causal i m p l i c a t i o n , f o r example). one.  Second, the theory Dretske i s proposing is a conditional  If_ there are any natural laws, then they are singular r e l a t i o n s  between universal p r o p e r t i e s .  The idea is t h a t the acceptance o f the  existence of natural laws e n t a i l s a form of Platonism.^ The f i r s t point relates to the argument by which TSRM attempt to show t h a t the r e l a t i o n between an ecological property and i t s associated i n v a r i a n t is non-accidental ( l a w f u l ) .  Using Dretske's n o t a t i o n , TSRM t r y  to argue by an appeal to t r a n s i t i v i t y : Thus we have two laws r e l a t i n g p r o p e r t i e s : " o - n e s s — > c-ness" (between occurrent property and affordance) and " e - n e s s - > o-ness" (between o p t i c a l property and occurrent environmental p r o p e r t y ) . By t r a n s i t i v i t y we have: " e - n e s s - > c-ness". That i s , theregis lawful s p e c i f i c a t i o n o f an affordance by an o p t i c a l property. q Since Dretske "attaches no s i g n i f i c a n c e "  to the arrow, i t is a l i t t l e  premature f o r TSRM to endow i t w i t h s p e c i f i c l o g i c a l properties without saying what r e l a t i o n they s p e c i f i c a l l y have in mind.  They need to defend  a p a r t i c u l a r view o f the r e l a t i o n involved i n laws on which i t is t r a n s i t i v e . TSRM also need to give some explanation o f why the o ' s , c ' s , and e's in  t h e i r argument occur in j u s t the order they do.  I f the order matters ( t h a t  i s , the r e l a t i o n is not symmetrical), then TSRM need to give an account of lawful r e l a t i o n s which make sense, f o r example, of why " o - n e s s — > c-ness" and " e - n e s s o - n e s s " , rather than "c-ness - > o-ness", or " o - n e s s — > e-ness" That i s , i t seems a l i t t l e odd t h a t the occurrent physical s t r u c t u r e (which produces both the ecological property and the i n v a r i a n t by which i t is perceived) should be the f i r s t term i n the one r e l a t i o n and the second term in the other.  I f the order i n which the o ' s , c's and e's occur does not  matter then TSRM need to provide some conception of lawful r e l a t i o n s on which they are symmetrical.*^  Until these conditions have been met TSRM's  attempt e i t h e r to derive or to explain lawful r e l a t i o n s between ecological properties and i n v a r i a n t s i n terms of t h e i r " t r a n s i t i v i t y argument" i s quite without substance. The point that the b e l i e f in natural laws, given Dretske's view, requires one to postulate a b s t r a c t , universal p r o p e r t i e s , is a feature of the intensional theory o f laws t h a t TSRM miss e n t i r e l y .  They w r i t e :  Let us ecological r e a l i s t s put our major ontological cards on the t a b l e : ( i ) there are no bare p a r t i c u l a r s ( i n d i v i d u a l s ) and there are no pure forms. The nominalist claim that universals are c o l l e c t i o n s of i n d i v i d u a l s is denied as i s the P l a t o n i s t claim that i n d i v i d u a l s in themselves are clusters of universals (Bunge, 1977). There are no universals i n themselves but there are properties that are i n v a r i a n t across a given c o l l e c t i o n of evolving i n d i v i d u a l s . . . ( v i i ) Properties are not a separate category of i n d i v i d u a l , f o r there are only propertied things (Bunge, 1977). ^ I w i l l not speculate on whether or not there is a viable p o s i t i o n i n what TSRM say.  The important point here is t h e i r r e j e c t i o n of the idea of  Platonism about p r o p e r t i e s .  They are f i r m l y and c l e a r l y committed to the  existence o f natural laws, and also to Dretske's view of them.  But  according to Dretske, his intensional model r e q u i r e s , i f there are any natural laws, the sort of Platonism t h a t TSRM r e j e c t .  A law cannot be a  singular r e l a t i o n between certain kinds of existents i f there are no existents of that kind. Something has to be s a c r i f i c e d here.  Since TSRM's e n t i r e defence of  the Gibsonian approach is grounded in the notion t h a t there are laws connecting organisms' perceptions and t h e i r environment, TSRM can hardly be expected to abandon t h e i r commitment to ecological laws.  The authors  must therefore e i t h e r give up the advantage, whatever i t i s , they are supposed to derive from the Dretskean model, or they must take up a metaphysical view about properties on which there w i l l be r e l a t a f o r t h e i r relation.  As i t s p e c i f i c a l l y a f f e c t s the ecological approach, i t does  not seem to matter p a r t i c u l a r l y which a l t e r n a t i v e one adopts.  On the  one hand, the issue o f whether there are universals is quite i r r e l e v a n t to the acceptance of Gibson's, as opposed to any o t h e r , approach to perception.  On the other hand, there are only three imaginable reasons sug-  gested by TSRM's a r t i c l e as to why they should think they require the intensional theory of laws.  None of these prove to be genuine grounds  f o r adoption o f the theory by the ecological t h e o r i s t s .  These p o s s i b i l -  i t i e s are as f o l l o w s : A) TSRM mistakenly believe a l t e r n a t i v e s to the Dretskean view allow s u b s t i t u t i o n o f coextensive predicates in law-statements.  In r e l a t i o n  to the periwinkle discussion, TSRM claim: The Establishment/extensional analysis goes through on the following assumptions: ( i ) t h a t the generalization of law or o f f a c t i s in the form of a syntactic universal . . . ; ( i i ) the s u b s t i t u t i v i t y of coextensive predicates . . . Assumptions ( i ) and ( i i ) f o l l o w from the t r a d i t i o n a l conception o f law. They are both rejected i n the view of law advanced by Dretske (1977), a view which sustains the e c o l o g i c a l / i n t e n s i o n a l analysis.12 The " e c o l o g i c a l / i n t e n s i o n a l " analysis r e f e r r e d to here is the assert i o n that the p e r i w i n k l e ' s d i f f e r e n t i a l behavior toward plant stems is  to be explained in terms of the detection of d i f f e r e n t invariants which l a w f u l l y s p e c i f y , r e s p e c t i v e l y , "climb-upable t h i n g " and " b a r r i e r " . The i m p l i c a t i o n , in the foregoing passage is t h a t the e m p i r i c i s t theories of laws (upon which, TSRM would claim, Establishment accounts of perception must r e l y ) hold that s u b s t i t u t i o n of coextensive predicates in law-statements w i l l y i e l d another statement which expresses a law.  This  " p r i n c i p l e of s u b s t i t u t i v i t y " is not part of t r a d i t i o n a l theories of laws and Dretske in no way suggests (as the TSRM quote implies) that i t  is.  The authors appear to have mistaken something which Dretske regards as a puzzle f o r something he is claiming to be a tenet of other t h e o r i e s . Dretske introduces his description of e m p i r i c i s t accounts and his own view of natural laws by making the point that s u b s t i t u t i o n of a coextensive predicate i n t o a statement of law does not always produce another law-statement.  He puts t h i s more simply by noting that s u b s t i t u t i o n of  coextensive terms w i t h i n the scope of the functor " i t is a law that  ..."  13 is n o n - t r u t h - p r e s e r v i n g .  This kind o f opacity is one important way of  showing the difference between statements which express laws and those which merely express universal generalizations.  The purpose i s not to  suggest t h a t the e m p i r i c i s t s are incognizant of differences between laws and simple universal g e n e r a l i z a t i o n s , but that t h e i r approach to expl a i n i n g the differences is wrong from Dretske's point of view.  No-one,  however, whether they are e m p i r i c i s t or not, imagines t h a t the s u b s t i t u t i o n of any coextensive predicate into a statement of law w i l l always r e s u l t in another statement o f Taw. TSRM's adoption of the intensional model of laws might be explained by t h i s mistake o f a t t r i b u t i n g a blanket p r i n c i p l e of s u b s t i t u t i v i t y to Dretske's r i v a l s .  TSRM want c e r t a i n l i n g u i s t i c contexts that are relevant  to perceptual theory to be opaque.  Any theory which interpreted " i t is a  law t h a t . . . " as r e f e r e n t i a l l y transparent would allow s u b s t i t u t i o n in the contexts TSRM take to be opaque.  Since they think e m p i r i c i s t theories  about natural laws are offenders i n t h i s respect, TSRM perhaps think they must adopt Dretske's theory i n p a r t i c u l a r .  However, an e m p i r i c i s t theory  of laws does not contain the p r i n c i p l e of s u b s t i t u t i v i t y TSRM have in mind, but would regard f a i l u r e of s u b s t i t u t i o n as a puzzle, as Dretske does. TSRM thus gain no advantage here by taking up the intensional model. B) Another possible source of TSRM's conclusion about laws i s not based on anything they d i r e c t l y say, but i s instead the product of a body of circumstantial evidence. F i r s t , Dretske l i k e s to describe laws as singular r e l a t i o n s between intensions, where an intension is some kind o f a b s t r a c t , universal property.  Hence, Dretske sometimes uses "property" ( i n the abstract sense) in  place of " i n t e n s i o n " .  Second, TSRM both endorse Dretske's notion of a law,  and s i m i l a r l y take up the practice o f using "property" and " i n t e n s i o n " interchangeably.  TSRM e x p l i c i t l y r e j e c t the idea of a b s t r a c t , universal  14 p r o p e r t i e s , however.  T h i r d , the important c r i t i c i s m Fodor and Pylyshyn  make against Gibson may be thought of as the claim that perception as mere i n v a r i a n t - d e t e c t i o n lacks an a l t e r n a t i v e the Establishment's r e l a t i o n between a perceiver and an intension ( i n the sense of some sort of i n t e r im nal representation).  F i n a l l y , as noted e a r l i e r , TSRM, w i t h e x p l i c i t  support from Gibson, tend to think of meanings or values as being (simply) perceived.  Gibson asserts that affordances are d i r e c t l y perceived, and  t h a t to perceive what things a f f o r d i s to perceive what they m e a n .  16  Given these points as background, i t is possible that TSRM t h i n k that by accepting Dretske's view about laws, they can r e l a t e perceivers  102  and intensions (of some kind) without recourse to the a t t r i b u t i o n of mental representations to perceivers.  The lawful s p e c i f i c a t i o n of some  ecological property, A, by some i n v a r i a n t , 0 , is (qua lawful r e l a t i o n ) a r e l a t i o n between the intensions "A" and " 0 " .  So TSRM might then be t r y i n g  to argue that when an organism's perceptual system detects 0 , i t perceives the " i n t e n s i o n " A.  In other words, the idea would be to conceive  intensions so that they would somehow be in the world as p a r t i c u l a r  feat-  ures of objects. I f t h i s happens to be what TSRM have i n mind, they gain nothing at a l l from Dretske's view.  The foregoing l i n e of reasoning rests on the  r e l a t i v e l y obvious f a l l a c y of confusing "property" i n the abstract.sense w i t h "property" in the sense of an instance. between abstract e n t i t i e s ( u n i v e r s a l s ) .  Dretske's r e l a t i o n is  When.an organism's perceptual  system f u n c t i o n s , i t detects p a r t i c u l a r instances of i n v a r i a n t s .  This does  not r e l a t e a perceiver to an intension on any theory of natural laws. Adoption of the intensional theory of laws, to put i t b r i e f l y , does not in any way change the conception of what organisms are related to when they perceive. I t should be emphasized, once again, that TSRM may not be committing the suggested f a l l a c y .  Working out the motivations behind a view is not  exactly l i k e showing what i t e n t a i l s :  l o g i c is often not on one's s i d e ,  and t h i s i s especially so when the author(s) being studied appears to have been led astray.  Therefore, in spite of the uncanny coherence in a c e r t a i n  body o f evidence, i t would indeed be u n f a i r to simply conclude that TSRM are g u i l t y o f the suggested confusion.  One can only hope that they are  not and note t h a t i f t h e i r reason f o r adopting Dretske's model of laws is an attempt to r e l a t e perceiving organisms w i t h "intensions" TSRM are quite  misguided.  Any advantage the ecological approach might therefore hope to  gain from the intensional construal of natural laws does not l i e here. C) F i n a l l y , TSRM might be adopting the Dretskean view because they think i t allows them a notion of laws which are r e s t r i c t e d in scope.  They  evidently want such a notion in order to have natural laws that hold only in c e r t a i n environments.  Once again, they take Dretske to be expounding  the point they wish to make: The universal scope of laws of nature should not be taken to mean t h a t the same laws apply everywhere and everywhen, f o r laws can apply only where they are i n s t a n t i a t e d . The laws governing electron o r b i t s are u n i v e r s a l , but no one expects them to operate in the solar nacleus, where atoms are deprived of t h e i r electron shells by the intense play of other forces. Following Dretske, we take laws to be p a r t i c u l a r statements about properties t h a t are more or less widely d i s t r i b u t e d in s p a c e - t i m e . ^ There is a great deal to puzzle about in t h i s q u o t a t i o n , which makes i t a f a i r sample of TSRM's very b r i e f and very d i f f i c u l t discussion on the scope of natural laws.  The authors want a r e l a t i o n between invariants  and ecological properties such t h a t , in a r e s t r i c t e d natural environment, an i n v a r i a n t and an ecological property are the r e s u l t of the same underl y i n g , occurrent property, and the i n v a r i a n t i s found in the available optical  (or other) s t r u c t u r e always and only when the ecological  is present.  property  Why TSRM should think they need Dretske's theory of laws to  postulate t h i s r e l a t i o n is mysterious. A couple of points about the foregoing quote should be made.  First,  the statement "laws can only apply where they are i n s t a n t i a t e d " could only have one o f two i n t e r p r e t a t i o n s here. only apply where they apply".  I t could be meant as "laws can  A l t e r n a t i v e l y , i t could mean that a law  can apply only where the properties which are the subjects of i t are instantiated.  The former i n t e r p r e t a t i o n is t r i v i a l while the l a t t e r is  p l a i n l y false and does not f o l l o w from anything Dretske says.  104 The example of the electron o r b i t s , as well as the comment that laws are about properties " t h a t are more or less widely d i s t r i b u t e d in spacetime" suggest t h a t TSRM are taking the f a l s e i n t e r p r e t a t i o n .  They seem to  claim t h a t laws whose subjects are atoms with electron shells do not hold where there are no atoms with electron s h e l l s .  However, one of the main  problems in analyzing laws, and one of the reasons Dretske gives the f o r mulation he does i s precisely t h a t i f "F-ness — ^  G-ness" is law,  it  18 obtains even  when and where there are no F's.  A closely related point pertains to a l o g i c a l mistake that TSRM make in the foregoing passage.  I t cannot be the case both t h a t laws about  electron o r b i t s are universal and that they f a i l to obtain at the solar nucleus.  I f the l a t t e r were t r u e , the laws would f a i l to hold u n i v e r s a l l y .  On the other hand, i f the laws apply u n i v e r s a l l y , then the laws apply to the solar nucleus as well as anywhere else. laws apply c o u n t e r f a c t u a l l y :  I f they are u n i v e r s a l , the  i f atoms could have electron shells at the  solar nucleus, the electrons would conform to the relevant laws concerning their orbits.  I t j u s t happens that there can be no atoms in the nucleus  that possess t h e i r electron s h e l l s , which is only to say that in c e r t a i n regions, there are no subjects of laws about electron o r b i t s .  This f i t s  with Dretske's conception of laws j u s t as much as e m p i r i c i s t ones. There are also two mistakes evident in TSRM's discussion with r e spect to t h e i r view of Dretske's theory.  F i r s t , they claim t h a t , on the  intensional theory, laws are " p a r t i c u l a r statements", which i s f a l s e because they are not conceived of as any kind of statement at a l l .  This  is an instance of a confusion against which Dretske s p e c i f i c a l l y warns, between statements of law and the laws expressed by them.  Unfortunately,  Dretske cautions at the same time t h a t he sometimes speaks " i n d i f f e r e n t l y " 19 between the two.  The other mistake TSRM make here again has to do with the conception of a property.  " P r o p e r t i e s " , in the sense i n which these are the subjects  of singular r e l a t i o n s Dretske conceives, are not "more or less widely d i s t r i b u t e d in space-time". time at a l l .  In f a c t , they are not d i s t r i b u t e d in space-  To r e i t e r a t e , Dretske i s using "property" i n the sense of  universal p r o p e r t i e s .  The only sense TSRM have available is that of prop-  e r t i e s as p a r t i c u l a r s . Part of the d i f f i c u l t y i n TSRM's discussion of the scope of laws is t h a t they do not appear, once again, to understand the p o s i t i o n against which they are (through Dretske) arguing.  They suppose that  traditional  accounts of laws are based on the assumption " t h a t laws must be expressed as u n i v e r s a l l y q u a n t i f i e d statements about extensions" and that t h i s 20 "implies to many that the scope of any law is u n i v e r s a l " .  Of course  no-one thinks t h a t laws must be expressed as universal conditionals ( u n i v e r s a l l y q u a n t i f i e d sentences) although there are undoubtedly those who believe they must be expressible by some universal  conditional.  Dretske's own p o s i t i o n is t h a t " l a w - l i k e statements are singular statements of f a c t describing a r e l a t i o n s h i p between properties or magnit21 udes",  hastening to add i n a footnote: I am not denying that we can, and do, express laws as simply " A l l F's are G" (sometimes t h i s is the only convenient way to express them). A l l I am suggesting is that when l a w - l i k e s t a t e ments are presented i n t h i s form i t may not be clear what is being asserted: a law or a universal g e n e r a l i z a t i o n . " TSRM c l e a r l y cannot be g e t t i n g at the heart of the matter by complain-  ing about views which allow law-statements to be " u n i v e r s a l l y q u a n t i f i e d statements".  TSRM c i t e "A r i g i d object with a sharp dihedral angle, an  edge, affords c u t t i n g , i t i s a k n i f e " as a t y p i c a l example of an ecologi c a l law.  They go on to note that i t is not the kind of example of a law  t h a t philosophers would give because " i t does not f i t the schema (x)(Fx — > Gx)".  There i s absolutely nothing f o r TSRM to gain by making t h i s  claim.  According to Dretske, the form a statement has or lacks does not  determine whether or not i t can be a law-statement.  This is j u s t as well  f o r TSRM because, unless t h e i r example of an ecological law is meant to r e f e r to a p a r t i c u l a r r i g i d o b j e c t , i t i_s_ a universal generalization and does f i t the schema ( x ) ( F x — ^ G x ) . Again TSRM appear to be confused over the difference between making claims about c e r t a i n kinds of statements and claims about what these express. Dretske's denial of " u n i v e r s a l i t y " of laws comes to the denial that f o r a statement to express a law is f o r i t to express a universal t r u t h  (In this  context, "universal, t r u t h " should be taken to mean simply a true universal generalization).  This is not to deny that the same form of statement by  which universal generalizations are expressed might also express laws.  In  f a c t , Dretske even holds that a given statement that expresses some law can also express a universal g e n e r a l i z a t i o n .  He claims only t h a t , when a  statement does express a Taw, t h i s is not a matter of i t s expressing a special kind of universal g e n e r a l i z a t i o n .  This point exhausts Dretske's  denial of " u n i v e r s a l i t y " of laws. The point that TSRM want is that lawful s p e c i f i c a t i o n may be r e s t r i c ted in scope.  That i s c e r t a i n i n v a r i a n t properties are present only when  a p a r t i c u l a r ecological property is present i n s p e c i f i c natural environments.  This is because, i n these l i m i t e d c o n d i t i o n s , only the underlying  manifest property which grounds the ecological one produces the p a r t i c u l a r invariant.  TSRM's denial o f " u n i v e r s a l i t y " , i n other words, comes to the  claim that c e r t a i n unique, non-accidental correspondences hold between i n v a r i a n t , e c o l o g i c a l , and occurrent properties when the frame of reference i s confined to p a r t i c u l a r local environments. TSRM's point i s thus t h a t some lawful r e l a t i o n s hold only in c e r t a i n  places ( i e . , some non-accidental c o r r e l a t i o n s hold only in c e r t a i n places) Dretske's claim is that a statement does not express a law i n v i r t u e of expressing a true universal g e n e r a l i z a t i o n . that there i s no connection between the two.  I t should be r e a d i l y apparent As such, there is no p a r t i c -  ular reason to think t h a t TSRM must adopt Dretske's, as opposed to the more conventional e m p i r i c i s t  view of laws in order to make t h e i r point  about r e s t r i c t e d scopes. F i n a l l y , there i s a b i t of irony i n TSRM's use of the Dretskean view to develop some concept of non-universal, lawful r e l a t i o n s .  One of the  c h i e f problems Dretske claims against the e m p i r i c i s t formula is that the r e s u l t cannot be universal enough.  Using the analogy of legal imperatives  he w r i t e s : I f a law was to be i n t e r p r e t e d as of the form: "For a l l x, i f x is (was or w i l l be) President of the United States, then x must ( l e g a l l y ) consult Congress on matter M", i t would be incomprehensible why Sally B i c k l e , were she to be President, would have to consult Congress on matter M. For since Sally Bickle never was and never w i l l be President, the law, understood as an imperative applying to actual Presidents (past, present, and f u t u r e ) , does not applyT^** Dretske's claim here, i n r e l a t i o n to the e m p i r i c i s t model, is t h a t his view allows laws to apply to additional things (to which they should apply):  not merely actual F's, but things that would be F i n d i f f e r e n t  counterfactual s i t u a t i o n s , or things that are F i n d i f f e r e n t possible worlds.  Hence, i f Dretske's assessment is c o r r e c t , the intensional view  o f laws makes them, in one respect, more universal than other accounts of natural laws. To summarize, TSRM cannot accept Dretske's theory because they hold t h a t there are natural laws while denying the existence of universals. Their f a i l u r e to appreciate the role of universal properties in the intensional view, as well as some of the other very odd mistakes TSRM make  regarding Dretske's theory, suggest very strongly that t h e i r grasp of the theory i s tenuous at best. Three possible reasons have been proposed as to why TSRM imagine they need the intensional theory o f laws in p a r t i c u l a r , and none of these do in f a c t give the ecological t h e o r i s t s any advantage over an i n t e r p r e t a t i o n of t h e i r theory of s p e c i f i c a t i o n on a conventional view of laws.  Dretske  does not need to have any d i f f e r e n t view regarding the s u b s t i t u t i v i t y of coextensive predicates i n law-statements.  No-one with a theory in t h i s  area would claim that the s u b s t i t u t i o n of any coexistensive predicate i n t o a statement governed by " I t is a law that . . . " would preserve the t r u t h value of the statement.  Second, adoption of the Dretskean view of laws  does not allow organisms to simply perceive intensions nor does i t allow t h e i r perceptual systems to detect them. abstract properties with t h e i r instances.  This would be to confuse T h i r d , the intensional theory  of laws i s not required in order to postulate unique, non-accidental correspondences t h a t obtain only in c e r t a i n animal-environments.  109  Chapter Six The important point which TSRM wish to make to explain how the ecological approach accounts f o r i n t e n t i o n a l i t y i n perceptual awareness is t h a t the theory of s p e c i f i c a t i o n postulates lawful r e l a t i o n s between i n v a r i a n t s and ecological properties (especially natural kinds f o r organisms). TSRM take i t as central to t h e i r case that one understands the natural laws holding between invariants and ecological properties on the Dretskean, intensional view of laws.  The authors regard t h i s point as key,  and i t is anyway q u i t e unclear how tine postulation of natural laws on a more conventional conception of these could help t h e i r case.  Therefore,  l e t i t be assumed that i f TSRM's e f f o r t s to adopt the Dretskean theory f a i l s , so too does t h e i r explanation o f how the so-called theory of s p e c i f i c a t i o n manages to account f o r i n t e n t i o n a l i t y in perception. There are three grounds upon which TSRM's defence in terms of the intensional conception of natural laws could f a i l : 1. Dretske's view is mistaken 2. The intensional view affords TSRM no advantage which would not have been available to them on a conventional, e m p i r i c i s t conception of 1 aws 3. TSRM cannot c o n s i s t e n t l y accept the Dretskean theory because of other views the authors hold I have endeavoured to show both 2) and 3 ) .  That I do not attempt to  show 1) as well is no i n d i c a t i o n of acceptance o f Dretske's theory o f laws, however.  There may well be good reasons f o r r e j e c t i n g i t .  However, since  the advantage TSRM imagine themselves as gaining by endorsing Dretske's theory in p a r t i c u l a r i s so mysterious, i t seems u n f r u i t f u l to go on to c r i t i c i z e the theory as w e l l . One should note that there are d i f f e r e n t , more or less sophisticated versions of perceptual behaviorism as I intend to use t h i s n o t i o n .  The  least sophisticated would be c l a s s i c a l , stimulus-response behaviorism: an organism is pkrceptually aware of some phenomenon when, and only when, p a r t i c u l a r behavior is e l i c i t e d as a r e s u l t of the detection of a c e r t a i n kind of stimulus. behavior:  More sophisticated variants would not require actual  an organism is perceptually aware of some phenomenon when, and  only when, i t comes to be disposed to behave in some way as a r e s u l t of the detection of some stimulus.  The forms of perceptual behaviorism become  increasingly sophisticated as one attempts to account adequately f o r d i s p o s i t i o n s , relevant behavior, and the i n t e r a c t i o n between states of perceptual systems and other states of the organism. The r e s u l t of a l l such considerations is a f a m i l y of views. of these may more properly be c a l l e d versions of functional ism.  Some It  is  convenient f o r me to r e f e r to the e n t i r e family as forms of perceptual behaviorism.  What makes these theories a family is t h a t each is an attempt  to explain perceptual awareness of organisms with reference to the output behavior produced by the functioning of t h e i r perceptual systems.  There  i s a great deal of controversy in the philosophy of mind and perception about whether analyses of cognitive or perceptual awareness in terms of output behavior (manifest or d i s p o s i t i o n a l ) are p l a u s i b l e .  On the side  of those who do not t h i n k any such theory is plausible is D r e t s k e ,  1  a phil-  osopher with whom TSRM are f a m i l i a r . Treating the Gibsonian theory as a form of perceptual  behaviorism  Ill  allows the approach to avoid a serious i n i t i a l d i f f i c u l t y :  the charge .  that i t has no account of how the detection of some i n v a r i a n t manages to mean anything to a perceiving organism.  This is managed by giving an  answer to the question of what i t is f o r the detection of an i n v a r i a n t to mean something to an organism ( o r , a l t e r n a t i v e l y , what i t is f o r an organism to be perceptually aware of some feature of i t s environment as such).  Indeed, one might speculate that the reason c e r t a i n philosophical  c r i t i c s do not see how Gibson could account f o r i n t e n t i o n a l i t y i n knowing perception is t h a t they have a d i f f e r e n t answer to the "what"-question, a d i f f e r e n t view on what i t i s f o r the deliverances of a perceptual system to mean something to an organism, i n mind. Now there is a c e r t a i n amount of evidence f o r t h i n k i n g that Gibson and his followers might a c t u a l l y subscribe to perceptual behaviorism (as opposed, that i s , to holding a theory which happens to be compatible with it).  Ecological t h e o r i s t s in general are at pains to stress a t i g h t con-  nection between perception and a c t i v i t i e s of organisms.  Both perceiving  and knowing are conceived of more as acts than as r e l a t i o n s o f an organism 2 to e i t h e r descriptions or propositions.  While commenting on affordances  on the c l a s s i f i c a t i o n of objects Gibson w r i t e s t h a t " I f you know what can be done with a graspable detached o b j e c t , what i t can be used f o r , you can 3  c a l l i t whatever you please".  Evidently, the possession of some p a r t i c -  u l a r description by a perceiver is not nearly so important as i t s being in a p o s i t i o n to make some use of some environmental t h i n g . In TSRM's commentary, the main clues t h a t the authors may have some form of perceptual behaviorism in mind occur i n connection with t h e i r 4  view o f perceptual e r r o r and w i t h what they c a l l t h e i r "semantic theory". They claim to adopt a semantic theory consisting of three terms: referent (or extension), the designation and the meaning.  the  For example, i f  a marsh periwinkle perceives a climb-upable t h i n g , the referent is the plant-stem, the designation is the i n v a r i a n t which specifies the climbupable things i n i t s environment ( I suppose the idea is t h a t the i n v a r i a n t "designates" the plant-stems which can be climbed), and the meaning is the d e s c r i p t i o n "climb-upable t h i n g " .  The l a s t component is not available to  the s n a i l , but is ascribed to the perceptual s i t u a t i o n by some observer. From the s n a i l ' s perspective, then, a l l that is involved i n the s i t u a t i o n is the detection of some i n v a r i a n t and subsequent performance of the appropriate behavior. This same idea is found in TSRM's very strange attempt to deal with 5  so-called errors i n perception i n normative terms.  A number of examples  are given, a l l of which have the same basic structure and moral:  Suppose  t h a t one reproduces an i n v a r i a n t by non-natural means so that i t does not have i t s usual physical accompaniment r e l a t i v e to some species' environment. A member o f t h a t species whose perceptual system detects the i n v a r i a n t w i l l take i t t h a t an instance of the usual environmental accompaniment is present.  TSRM want to say the organism is not wrong because the detection  of the i n v a r i a n t ought to have yielded an environmental phenomenon of a certain kind. One of the examples used is t h a t of a shark which is aware of something as edible whenever i t detects a c e r t a i n kind of b i o e l e c t r i c  field  (TSRM r e f e r to i t as a "type F" e l e c t r i c a l f i e l d ) because t h i s f i e l d , i n the shark's h a b i t a t , i s produced only by the species of f i s h which serve as i t s food.  TSRM describe a case i n which a type F f i e l d is reproduced  by placing electrodes in the sand at the ocean bottom.  The r e s u l t is  that the sharks e x h i b i t the same predatory behavior toward the electrodes as they would toward the f l a t f i s h they normally eat:  113 The shark digs tenaciously at the source of the f i e l d departing from the s i t e only when the act f a i l s to reveal an edible thing (Kalmijn, 1971). Now there is no i n t e l l i g i b l e sense in which i t can be claimed that the source ought to have appeared inedible i f the shark's perception were free from e r r o r and i f the shark's perceptions of affordances were d i r e c t . ° The c r u c i a l issue to raise here i s that of what TSRM could conceivably mean by something appearing inedible or e d i b l e , or what they could mean in predicating (as they do) "takes to be an edible t h i n g " to the shark. Quite obviously, TSRM's attempt to handle errors in perception does not contact at a l l the epistemological  issue of how one can wrongly take one-  s e l f to perceive some phenomena of one i s supposed to d i r e c t l y perceive it.  TSRM's claim t h a t the shark i s somehow "not wrong" in taking the  electrodes to be edible f l a t l y contradicts the simple epistemological  fact  t h a t i f one takes something to be edible that is in f a c t i n e d i b l e , one is mistaken.  The shark can only be said to be correct in some normative  sense when i t takes buried electrodes to be edible.  That i s , given the  c o n s t i t u t i o n of i t s natural environment, the shark behaved as i t ought to have. TSRM are i n s i s t i n g that the shark c o r r e c t l y perceives something as edible even though nothing in the given example is in f a c t edible f o r sharks. The only way to combine these two points i s i f one assumes that the shark's perception of something as edible i s j u s t a matter of i t e x h i b i t i n g predatory behavior.  This is to analyze what i t i s f o r the detection of a type  F e l e c t r i c a l f i e l d to mean "edible" f o r a shark in behavioral terms.  The  shark e x h i b i t s predatory behavior as a r e s u l t of the detection of an i n v a r i ant which i s s p e c i f i c to edible things w i t h i n i t s environment. There are two general comments I wish to go on to make in concluding this thesis.  The f i r s t w i l l be that there are very close s i m i l a r i t i e s  between D.M. Armstrong's so-called " b e l i e f - t h e o r y " of perception and the ecological approach, e s p e c i a l l y understood as a form of perceptual behaviorism.  The kinship may be mutually b e n e f i c i a l .  The second, and f i n a l  point w i l l be that Ecological t h e o r i s t s do not establish the strong hypothesis that a l l perception i s the mere r e s u l t of the detection of invariant properties. (ii) There are s u f f i c i e n t s u p e r f i c i a l s i m i l a r i t i e s between Armstrong's b e l i e f - t h e o r y and the ecological approach to i n v i t e prima facie comparison. Further i n v e s t i g a t i o n reveals s t i l l deeper resemblances.  To develop the  comparison, I w i l l b r i e f l y describe Armstrong's theory, which he introduces by w r i t i n g : I t is clear t h a t the b i o l o g i c a l function of perception is to give the organism information about the current state of i t s own body and i t s physical environment, information t h a t w i l l a s s i s t the organism i n the conduct of l i f e . This is the most important clue to the nature of perception. I t leads to the view t h a t perception is nothing but the acquiring of true and false b e l i e f s concerning the current state of the organism's body and environment . . . Veridical perception is the acquiring of true b e l i e f s , sensory i l l u s i o n the acquiring of false b e l i e f s . 7  In w e l l - f o u n d e d ' a n t i c i p a t i o n of resistence to the a t t r i b u t i o n of b e l i e f s to many evident perceivers (including p r e - l i n g u i s t i c humans), Armstrong is quick to subject his claim to q u a l i f i c a t i o n .  His notion of  b e l i e f is said to be a "sub-verbal" conception, so that l i n g u i s t i c i s not a p r e r e q u i s i t e to the possession of b e l i e f s .  ability  S t i l l no doubt  concerned t h a t some w i l l regard a b e l i e f as too sophisticated a state to a t t r i b u t e to some perceiving organisms,  Armstrong goes on to suggest the  o  word " i n f o r m a t i o n " as an a l t e r n a t i v e .  Part of the motivation f o r using  " i n f o r m a t i o n " i n p a r t i c u l a r is that i t makes good grammatical sense to t a l k about " f a l s e " i n f o r m a t i o n , whereas Armstrong notices there is no  c o r r e l a t e to describe what he c a l l s sensory i l l u s i o n with other a l t e r n a t i v e s t h a t he e n t e r t a i n s .  Subsequent to an elaboration of his basic theory, he  then proceeds to analyze b e l i e f s as "states apt f o r bringing about c e r t a i n 9  behavior".  Armstrong thus has a view on which perceptual awareness w i l l  receive some form of behavioral analysis.  The b e l i e f - t h e o r y can be  considered as a form o f perceptual behaviorism even though Armstrong (as, f o r that matter, does Gibson) disavows orthodox behaviorism. A number of s u p e r f i c i a l s i m i l a r i t i e s thus e x i s t between the two theories: 1. Perception is fundamentally conceived as the acquiring of information 2. The main function of perception is to allow organisms to serve t h e i r ecological needs (conduct t h e i r  life)  3. That the service of ecological needs is the chief function of perception is taken to be the key to understanding the nature of i t 4. Organisms are said to be related t o , and to conduct t h e i r l i v e s i n an environment 5. The information organisms acquire is categorized as e i t h e r being about i t s e l f ( p r o p r i o s p e c i f i c ) , or being about i t s environment (exterospecific) 6 . Perception is treated as an epistemic notion These s i m i l a r a t i e s , of course, hardly s u f f i c e to show the two t h e o r i s t s are committed to the same view.  The idea expressed i n 2), as well as the  concept of an "environment" are given f a i r l y extensive treatment on the ecological approach, but are undeveloped by Armstrong.  He mentions 2) in  r a t i o n a l i z i n g the approach he takes, but i t does not pervade Armstrong's thought on such advanced issues as the terms o f perception as i t does with Gibson.  Gibson's use of "environment" is a technical one, whereas Arm-  strong's need not be regarded as anything more than a c c i d e n t a l .  The s i g -  n i f i c a n c e of 4) ia also affected by t h i s p o i n t . 6 ) at least indicates that Armstrong and Gibson are endeavouring to give theories on the same topic (as opposed to authors who are w r i t i n g about simple perception, or about the j u s t i f i c a t i o n , rather than the causation, of perceptually acquired knowledge).  I have indicated two gen-  eral forms of epistemic perception: "perceiving t h a t " and "perceiving as". The main difference i s that i t i s always f a l s e t h a t one perceives that a p a r t i c u l a r thing i s P unless i t i s true that the thing perceived i_s P.  On  the other hand, one may perceive something as P when the thing perceived i s not in f a c t P.  Since Armstrong allows t h a t perceiving may be the  acquiring of f a l s e information, his theory must be ( i n spite of what he e v i d e n t l y t h i n k s ) based upon "perceiving as".  Gibson occasionally makes'  use of t h i s l o c u t i o n , but he is unsettled on how to handle non-veridical perception.  One's approach to non-veridical perception i s the best  i n d i c a t o r of a commitment to one locution or the other in the absence of an e x p l i c i t  statement.  On the handling of errors in perception there e x i s t s a clear possib i l i t y of difference between Gibson and Armstrong, though.  Many of the  ecologists are i n c l i n e d to t r y to explain away apparent e r r o r s .  It  is  sometimes suggested that when organisms appear to have made a perceptual e r r o r , they have simply f a i l e d to explore t h e i r immediate environments long or hard enough, and so have not picked up a l l the available information.  TSRM's curious normative view is another example of an attempt to  explain away evident perceptual e r r o r .  Gibson himself, a f t e r suggesting  a v a r i e t y of examples he considers to be perceptual e r r o r , w r i t e s :  Optical misinformation enters i n t o each of these cases in a d i f f e r e n t way, but in the l a s t a n a l y s i s , are they explained by misinformation? Or,is it..simply a matter of f a i l u r e to pickup a l l the information . . . ? Gibson would l i k e to explain away evident mistakes somehow but he is more c o n c i l i a t o r y than some of his f o l l o w e r s .  That non-veridical percep-  t i o n is to be accounted f o r as the acquiring of false information remains a p o s s i b i l i t y , and acceptance of such an approach would be tantamount to taking the "perceiving as" approach to epistemic perception. S i m i l a r l y 1) i s c r u c i a l since i t turns out to be a deeper resemblance than one might be i n i t i a l l y i n c l i n e d to suppose.  Armstrong equates " b e l i e f "  and"information", whereas the Gibsonians sometimes seem to be t r y i n g to equate " i n f o r m a t i o n " and " i n v a r i a n t property".  Armstrong is c e r t a i n l y not  l i k e l y to suggest t h a t i n f o r m a t i o n , i n his sense, i s "simply a v a i l a b l e " . On the other hand, some of the Gibsonians, Shaw, Turvey and Mace, expressly 12 deny a connection between perception and b e l i e f .  Their reasoning,  however, i t both t e r r i b l y obscure and i r r e l e v a n t to t h i s context.  Once  one has seen that Armstrong i n t e r p r e t s b e l i e f s i n terms of behavior-states, and that the ecological approach would lack some account o f i n t e n t i o n a l i t y in perception i f i t were not i n t e r p r e t e d as analyzing perceptual awareness i n terms of behavior, one can see that the two approaches to perceptual information pickup bear a s t r i k i n g  similarity.  In a d d i t i o n to the s i m i l a r i t i e s i n the two t h e o r i e s , there are two important differences that should be mentioned: 7. I t i s not clear that the b e l i e f - t h e o r y and the ecological approach should be seen as giving the same kind o f behavioral analysis 8. The two theories d i f f e r on the terms in which organisms perceive t h e i r environments  With respect to 8):  on the issue of the categories of perception,  Armstrong must be regarded as an Establishment t h e o r i s t .  In the examples  he chooses, and through his discussion of the problem of secondary q u a l i t i e s , i t is apparent t h a t Armstrong accepts the basic categories of perception which have remained s u b s t a n t i a l l y unchanged since Locke's time.  Armstrong  shows no sign of deviating from the t r a d i t i o n a l formula t h a t the environment is perceived in terms of colours, shapes, t e x t u r e s , weights, and the l i k e (sensible q u a l i t i e s ) , and useful information is constructed out of these.  Gibson, who takes affordance-perception as basic, would regard  such properties as f e l t weight, sensed colour and perspectival shape as q u a l i t i e s of sensation.  As such, they would neither be perceived nor the  basis of perception of the environment.  On a physical construal of  sensible q u a l i t i e s , awareness of a thing as having a p a r t i c u l a r colour, shape, or the l i k e , the Gibsonian l i n e would presumably be t h a t these are d e r i v a t i v e , a product of the perception of e c o l o g i c a l l y  significant  parameters of the environment. There is nothing in Armstrong's central view t h a t i s incompatible with the Gibsonian conception of the categories of perception, though.  More-  over, the b e l i e f - t h e o r y could derive a couple of advantages from the idea t h a t ecological properties are perceived.  In the f i r s t place, although  Armstrong takes the f a c t t h a t the c h i e f purpose of perception i s to provide an organism with information important to the "conduct of l i f e " to be a key determinant of the nature of perception, he does not make use of t h i s basic point i n subsequent discussion.  This claim as to the purpose  of perception i s j u s t the kind of point which motivates Gibson to adopt his theory about affordances. could develop his claim.  Gibson's approach thus shows how Armstrong  In a d d i t i o n , Armstrong's theory has very  little  to say about the behavior a given state is apt to bring about.  What  behavior, f o r example, i s apt to be produced by the perception of something as r e d , c u b i c a l , or soft?  Beyond c e r t a i n obvious suggestions, such  as verbal behavior or d i s c r i m i n a t i v e behavior produced i n a r t i f i c i a l  test  c o n d i t i o n s , which have l i m i t e d applications nothing comes r e a d i l y to mind. On the supposition that the environment is perceived in terms of what i t a f f o r d s , i t is rather easier to give substantive descriptions of the behavior-states which c o n s t i t u t e perceptually acquired information. With regard to 7): there are both d i s p o s i t i o n a l and non-dispositional ways of t r y i n g to analyze perception. to a d i s p o s i t i o n a l view.  Armstrong is e x p l i c i t l y committed  In p a r t i c u l a r , he maintains that to perceive is  to acquire a b e l i e f , where a b e l i e f is analyzed as a d i s p o s i t i o n a l apt f o r bringing about c e r t a i n behavior.  states  A non-dispositional account of  perceptual information pickup in behavioral terms would be to claim that an organism perceives some phenomena when, and only when i t a c t u a l l y exh i b i t s c e r t a i n behavior. TSRM might be held to a non-dispositional view since i n such examples as that of the shark or of the p e r i w i n k l e , they make no mention of invariants producing dispositions to behave.  I f the authors have any tendency  to embrace such a view, they should abandon i t .  The non-dispositional  form of perceptual behaviorism i s very strong and not very p l a u s i b l e . The main problem the non-dispositional view raises is t h a t every instance of a perceiver f a i l i n g to e x h i b i t some sort of behavior must be counted as a f a i l u r e to perceive, even when circumstances make i t implausi b l e to believe that the perceiver has f a i l e d to notice some environmental item.  I f I look at a pen but do not pick i t up and w r i t e with i t , must I  have f a i l e d to perceive i t as write-withable?  Does a shark, because i t  only e x h i b i t s predatory behavior when i t i s hungry, f a i l to perceive edible  things unless i t is in t h i s state?  Unquestionably, an animal's a t t e n t i o n  is s e l e c t i v e , and t h i s s e l e c t i v i t y i s directed by present wants and needs. However, i t would be rash to suppose that an organism always f a i l s to notice features of i t s environment whenever they would not a c t u a l l y e l i c i t behavior of a c e r t a i n kind because the organism i s in some s t a t e . Various t a c t i c s f o r avoiding such p o t e n t i a l l y embarrassing cases might be suggested.  One is to expand the range of o v e r t , physical behav-  i o r which constitutes perception of the environment i n p a r t i c u l a r terms. For example, an opossum's running away, climbing a t r e e , remaining motionl e s s , or defending i t s e l f may each c o n s t i t u t e perceptual awareness of a fox as a predator.  There are l i m i t s to t h i s t a c t i c , however, because the  more one expands the range of relevant behavior f o r perception of something as a such-and such, the more unclear i t becomes as to why t h i s should c o n s t i t u t e perception as a such-and-such in p a r t i c u l a r .  As one expands  the range of opossum-behavior that counts as perceiving something as a predator, i t becomes increasingly d i f f i c u l t to explain how t h i s  differs  from perception of non-predators in c e r t a i n terms (other opossums as mates, competitors, and so f o r t h ) , or perception of foxes as things other than predators.  I t becomes correspondingly d i f f i c u l t to explain why a c e r t a i n  a c t i v i t y by the opossum is appropriately described as perception of a fox as a predator. Other possible t a c t i c s would be to count verbal and/or i n t e l l e c t u a l behavior among that which constitutes perceptual awareness.  Both would  obviously be l i m i t e d i n terms of the organisms to which they could be a p p l i e d , though.  Moreover, i t would be d i f f i c u l t to argue that c a l l i n g  phenomena such as " t h i n k i n g of X as P" behavior is not merely as semantic t r i c k by which the perceptual behaviorist is allowed to smuggle in the  121 very representational component of perception that he purports to analyze away. However, philosophers attempting behavioral accounts of intentional states abandon the non-dispositional analysis rather than t r y to use my sugested compromises.  I t i s f a r more preferable to take up a d i s p o s i t i o n a l  account such as Armstrong suggests. Now i t is possible to sketch roughly a possible ecological of perception.  analysis  The f i r s t step i s to characterize the detection of (or r e s -  onation t o ) an i n v a r i a n t by an organism's perceptual system as the acquired state that tends to produce a c e r t a i n kind of behavior. organism perceives X as P i f and only  Given t h i s , an  if:  1. P i s specified by some i n v a r i a n t , 0, according to the p r i n c i p l e s of the theory of s p e c i f i c a t i o n 2. An instance of 0 i s detected by a perceptual system of the organism 3. The instance of 0 in question is produced by some underlying mechanism of X To repeat an e a r l i e r p o i n t , Gibson does not elaborate on such funct i o n s as detection or resonation.  I t i s therefore open to question whether  these functions should be said to produce a behavior-state or to c o n s t i t u t e the s t a t e .  The stronger i n t e r p r e t a t i o n that I use seems to be called f o r by  TSRM's previously noted assertion t h a t organisms pick up information when, and only when, t h e i r perceptual systems detect/resonate to i n v a r i a n t s . With respect to the enumerated c o n d i t i o n s , 1) s t i p u l a t e s that P is a genuinely perceptible property.  I f 2) f a i l s to o b t a i n , the state of the  organism i s not the product of the normal functioning of i t s perceptual system. X.  3) is a simple causal condition t h a t t i e s perception of X as P to  The detection of 0 means "P" to the organism in that the r e s u l t is  i n v a r i a b l y a d i s p o s i t i o n f o r behavior appropriate f o r i t toward things having  122 P.  This i s p a r t l y a theory of what i t i s f o r perception of things to mean  something to the perceiving organism. On t h i s d i s p o s i t i o n a l view, some f a i l u r e s to behave, in circumstances in which perception should be expected to occur, can be explained in terms of modifications of the state which i s produced by a given i n v a r i a n t .  The  invariant-caused perceptual state may be modified, that i s , by other condit i o n s or states both of the perceiving organism and i t s environment.  For  example, the shark may detect a type F b i o e l e c t r i c f i e l d , but f a i l to exh i b i t predatory behavior because i t i s sick or not hungry, or because i t senses danger or some i n t r u s i o n into i t s surroundings.  On the a l t e r n a t i v e  non-dispositional a n a l y s i s , such modifying states and conditions must a l ways be explained as causing f a i l u r e s to perceive rather than as mere f a i l ures of the perceptual state to produce the usual behavior. However, there i s a disadvantage to explaining the i n t e n t i o n a l component in perception in terms of being in states apt f o r the production of c e r t a i n sorts of behavior.  On the non-dispositional view, i t i s quite clear  t h a t nothing in the perceptual process could be regarded as representations of the environment in another guise.  Given Armstrong's account of informa-  t i o n pickup in terms of the production of c e r t a i n behavioral s t a t e s , i t would be incumbent upon an ecological t h e o r i s t to explain his notion of a state in a way which would show that i t should not be regarded as yet another form of internal representation.  In p a r t i c u l a r , he would have to con-  strue these in some physical terms, as physiological states apt f o r b r i n g ing about behavior, f o r example.  Armstrong's own view i s designed to leave  open t h i s question of whether or not such states are mental or physical (Remember t h a t Armstrong claims his notion of a state is compatible w i t h , but does not e n t a i l m a t e r i a l i s m ) .  The ecological t h e o r i s t would thus need  123  to give a convincing account of the reduction of cognition to physical phenomena, a task which has proven i n t r a c t a b l e . One of the problems that would have to be faced is the product of a d i s t i n c t i o n which i s ignored on the ecological approach.  I t is generally  held that there i s a d i s t i n c t i o n between the mere d i s c r i m i n a t i v e behavior of organisms t h a t i s produced by the functioning of t h e i r perceptual systems, and genuine epistemic states so produced.  A marsh periwinkle  successfully climbing a plant stem as a r e s u l t of the functioning of i t s visual system would no doubt be regarded by many t h e o r i s t s as an example of mere d i s c r i m i n a t i v e behavior and not as the product of perception in some i n t e n t i o n a l sense at a l l .  In f a c t , i t i s a weakness of TSRM's de-  fence of the ecological approach that the examples which they t r e a t in any d e t a i l involve most unsophisticated perceivers (low-grade i n t e n t i o n a l systems in Daniel Dennett's terms  13  ) , ranging from household scales to 14  gannets.  Some philosophers, such as Karl P f e i f e r and C.B. M a r t i n ,  would undoubtedly even consider the use of such subjects as scales and bean plants in giving an account of the i n t e n t i o n a l component in percept i o n as showing that TSRM simply have the wrong c r i t e r i a f o r  identifying  intentionality. I f one were to account convincingly f o r epistemic perception in terms of manifest states apt f o r the production of behavior, one would need to give examples involving creatures which are capable of some reasonably high degree of novel and/or adaptive behavior as subjects.  The tendency  to suppose that something more i s involved in perceptual information pickup by human beings than by marsh periwinkles might u l t i m a t e l y prove to be unfounded.  Until such time as i t does, the d i s t i n c t i o n between states  apt to produce some behavior and genuine epistemic s t a t e s , the d i s t i n c -  t i o n which underlies the tendency to d i f f e r e n t i a t e between human and p e r i winkle perceptions, has to be acknowledged.  This i s done by defending the  view t h a t the i n t e n t i o n a l component in perception is accounted f o r in terms of d i s p o s i t i o n a l states of perceiving organisms using examples which are clear cases of epistemic perception (hence, cases which involve percept i o n in some i n t e n t i o n a l sense).  The d i f f i c u l t y l i e s in the f a c t that the  ease with which one may achieve concensus on whether a given case of perceiving i s an instance of epistemic perception i s inversely proportional to the ease of giving convincing reasons f o r saying that case i s analyzable in terms of the causation of some physiological state l i k e l y to produce c e r t a i n sorts of behavior. To summarize, i t appears that in t h e i r general s t r u c t u r e the e c o l ogical approach and Armstrong's b e l i e f - t h e o r y are quite s i m i l a r .  Moreover,  the apparent d i f f e r e n c e s , as well as the s u p e r f i c i a l i t y of some of the s i m i l a r i t i e s , are not insurmountable.  They are no doubt p a r t l y a mere  r e f l e c t i o n of the f a c t t h a t , because Armstrong and Gibson come from d i f f e r e n t academic f i e l d s , they have somewhat d i f f e r e n t p r i o r i t i e s and also ways of looking at problems.  Thus there are points which both  authors make that are subsequently developed in d e t a i l by one and not developed at a l l by the other. The main c o n t r i b u t i o n Armstrong can make to the ecological approach i s his idea that the operations of organisms' perceptual systems produces d i s p o s i t i o n a l states of the perceiver apt f o r bringing about behavior.  It  provides the ecological t h e o r i s t s with something they need: a way of showing t h a t they avoid the i n i t i a l  problem of lacking  t i o n a l component in perception.  some account of the i n t e n -  Also, i f i t is correct to i n t e r p r e t the  ecological approach in t h i s l i g h t , Gibson's view turns out to be somewhat  less s i n g u l a r l y revolutionary than some of his d i s c i p l e s would wish.  The  good news i s t h a t there is a precedent f o r the theory which could make i t more accessible and understandable from a philosophical point of view. (iii) To repeat, i t i s s t i l l a matter of great controversy as to whether or not perception or cognition can be accounted f o r in terms of some kind of behavior-state.  The p o s s i b i l i t y of such an a n a l y s i s , however, shows  t h a t , contrary to Fodor and Pylyshyn's c r i t i c i s m , the Gibsonian theory i s not completely lacking in providing some view about the i n t e n t i o n a l component in perceiving.  One job of the ecological t h e o r i s t is to pursue  the i n t e n t i o n a l i t y issue along behavioral l i n e s by developing a v i a b l e account in d e t a i l . However, there would s t i l l  be at least two important reasons f o r  reserving judgement on the general hypothesis of the ecological approach. This general hypothesis i s that a l l perceptual information pickup i s d i r e c t , in the sense, of being the mere r e s u l t of the detection of some i n v a r i a n t by an organism's perceptual systems.  The two reasons f o r  remaining doubtful are as f o l l o w s : 1. As I have noted (along with U l r i c Neisser), i t remains to be seen whether or not enough i n v a r i a n t properties (specifying environmental phenomena of the r i g h t s o r t ) can be discovered. The view contains a c r i t e r i o n f o r d i f f e r e n t i a t i n g between genuine and degenerate cases which are commonly described as instances of perception.  The c r i t e r i o n i s that only the cases in which the information an  organism acquires i s exclusively determined by the detection of an invariant by some of i t s perceptual systems should be considered as a genuine case.  The a c c e p t a b i l i t y of t h i s c r i t e r i o n is contingent upon i t s  ability  to f u l f i l l  some very large promises.  There is a general promise that  common usage of "perceives" and/or commonsense conceptions of what is perceptible w i l l not be disrupted to too great an extent.  There is the  more s p e c i f i c promise that s u f f i c i e n t invariants w i l l be discovered to s a t i s f y general conceptions of how much of one's environment is perceptible. Also, Gibson and his followers object to t r a d i t i o n a l approaches l a r g e l y by claiming t h a t they cannot explain the o r i g i n s of knowledge of the environment, and t h a t the basic terms i n which such theories assume animals perceive t h e i r environments are not e c o l o g i c a l l y u s e f u l .  There  are therefore promises to the e f f e c t that such invariants as w i l l be found in future research w i l l specify the environment in useful terms, and w i l l be of a sort to explain the knowledge various animals have of t h e i r environment. As long as i t remains f o r the ecological t h e o r i s t s to a c t u a l l y f i n d considerable numbers of the underlying i n v a r i a n t structures which are supposed to serve as the basis of perceptual information pickup, these promises go u n f u l f i l l e d . 2. The c h i e f general objection to Establishment views, as Shaw, Turvey, and Mace put i t , i s t h a t they subscribe to "the doctrine of i n t r a c 15  table n o n - s p e c i f i c i t y " .  This i s j u s t to say that Establishment versions  of the input to perceptual systems i s not s p e c i f i c to features of an organ ism's environment. processing.  I t must therefore get the information via cognitive  The ecological t h e o r i s t s claim t h i s requires p r i o r knowledge  or concepts, the; means f o r representing the world i n p a r t i c u l a r terms. They argue t h a t i f a l l perception is o f t h i s k i n d , one cannot explain how an organism acquires information about i t s environment in the f i r s t place.  The pickup of some information requires possession of p r i o r information, which requires s t i l l p r i o r possession of i n f o r m a t i o n , ad i n f i n i t u m . The conclusion the ecological t h e o r i s t s draw is t h a t perception should be conceived so that al1 perception is the d i r e c t pickup of i n f o r mation.  In other words, no genuine perceptual information pickup involves  the a p p l i c a t i o n of p r i o r knowledge (cognitive processing) to the present deliverances of the perceptual systems.  This conclusion, however, is too  strong and does not f o l l o w from the premisses from which i t i s derived. Given the i n i t i a l premisses, one can at best conclude t h a t at least some of the genuine cases of perception cannot involve cognitive processing. Hence, the ecological theory's most important argument agsinst E s t a b l i s h ment views y i e l d s only the conclusion which is a form of Fodor and Pylyshyn 's Establishment p o s i t i o n :  perceptual awareness of some features  of the environment i s d i r e c t .  Acceptance of the stronger, intended con-  clusion is at least contingent at least upon the s a t i s f a c t i o n of the promises indicated i n point  1). (iv)  O v e r a l l , Gibson's ecological approach does not contain the fundament a l conceptual flaw suggested by c e r t a i n c r i t i c s since i t can be i n t e r p r eted as analyzing the i n t e n t i o n a l component in perception i n behavioral terms.  This is a d i f f i c u l t p o s i t i o n to argue, but i t is one with which  I f i n d a great deal of sympathy.  On the other hand, ecological  theorists  do not manage, by any means, to e s t a b l i s h t h e i r hypothesis, p a r t l y because i t embodies a recommendation to adopt a c r i t e r i o n f o r determining genuine cases o f perception which has not yet proven acceptable.  Moreover, the  " o r i g i n s o f knowledge" argument does not y i e l d the strong conclusion desired of  it.  In spite of t h i s , the ecological approach contains many challenging ideas f o r perceptual theory, not a l l of which have been given the discussion they deserve in t h i s t h e s i s .  Nor do a l l of these ideas require  acceptance of Gibson's general view. in mind.  There are two such ideas that I have  One is the novel conception of perceptual systems and t h e i r  functioning.  One can only wish t h a t Gibson had spent some time in expand-  ing on such notions as the e x t r a c t i o n , resonating t o , and detection of invariant structure.  The second idea is t h a t an organism perceives i t s  environment predominantly in terms of affordances.  The theory of a f f o r d -  ances constitutes an i n t e r e s t i n g and rare challenge to mainstream views on what is perceived.  Assumptions i n t h i s area of the categories of  perception, especially in the philosophy of perception have too often gone unexamined.  Footnotes Chapter One *The theory I w i l l o u t l i n e i s developed by Gibson mainly in The Senses Considered as Perceptual Systems (Boston: Houghton M i f f l i n Co., 1966) and The "Ecological Approach to Visual Perception (Boston: Houghton M i f f l i n Co., 1979). Also helpful is James Gibson, Reasons f o r Realism, ed. Edward S. Reed arid Rebecca Jones ( H i l l s d a l e , N.J.: Lawrence Erlbaum Assoc., 1982). 2  Claire F. Michaels and Claudia C a r e l l o , Direct Perception (Englewood C l i f f s , N.J.: Prentice-Hall I n c . , 1981), 115, 3  Jerry A. Fodor and Zenon W. Pylyshyn, "How Direct i s Visual Perception?" Cognition, 9, no. 2 (1981): 141. 4 Gibson, Ecological Approach, 239. 5 Gibson, Ecological Approach, 75, 116; Gibson, Senses, 33-34, 200-201. Related terms include "proprioceptor," "exteroceptor," and " p r o p r i o s p e c i f i c , " and " e x t e r o s p e c i f i c i n f o r m a t i o n . " ^Frank Jackson, Perception, (Cambridge: Cambridge U n i v e r s i t y Press,, 1977). ^Jackson, Perception, 154-172. A classic discussion given in terms of propositional versus non-propositional perceiving may be found in Roderick Chisholm, Perceiving, Ithaca, N.Y.: Cornell U n i v e r s i t y Press, 1957. Q  G.N.A. Vesey, "Seeing and Seeing As," Perceiving, Sensing and Knowing, 68-83, ed. Robert J . Swartz (Berkeley and Los Angeles: U n i v e r s i t y of C a l i f o r r i i a Press, 1965), i s an example of an analysis of "perceiving a s " . D.M. Armstrong, A M a t e r i a l i s t Theory of Mind, (London: Rout!edge and Kegan Paul, 1968), 208-244. Armstrong holds that perception i s the acquiring both of true and f a l s e b e l i e f s . 10  Fodor and Pylyshyn, "How D i r e c t ? " , passim.  **S. Ullman, "Against Direct Perception," The Behavioural and Brain Sciences, 3 (1980): 375. 12 Gibson, Senses, 266.  13  Herman von Helmholtz, E p i s t e m o l o g i c a l W r i t i n g s , Centenary of 1921 ed. Paul Hertz and Moritz Schlick, new t r a n s , by F. Lowe, ed. Robert S. Cohen and Marx W. Wartofsky, Boston in the Philosophy of Science, 37 (Dordrecht, Holland and D. Reidel Publishing Co., 1977), 117 f f .  edition Malcolm Studies Boston:  *^John Locke, An Essay Concerning Human Understanding, 2 v o l s , c o l l a t e d and annotated by A.C. Fraser (New York: Dover Publications, 1959), Book I I , chapter 9, sections 9-10. 15 Gibson, Ecological Approach, 238. 1 6  I b i d . , 251.  1 7  Ibid..  1 8  I b i d . , 251-252.  1 9  I b i d . , 251-; Gibson, Senses, 275.  "Gibson, Senses, 306 f f . Gibson, Ecological Approach, chapter one ( e s p e c i a l l y 9-10, 12). The existence of l e v e l s of explanation and/or description in science of some kind is widely accepted in the philosophy of science, although there i s considerable dispute as to the exact nature of these l e v e l s and as to the extent to which the hierarchy is collapsable. I t is an i n t e r e s t i n g part of Gibson's view that he believes t r a d i t i o n a l perceptual t h e o r i s t s have d i f f i c u l t y because they have not established the proper level of explanation of psychological theories of perception and c o g n i t i o n . One of Gibson's goals is to e s t a b l i s h the proper l e v e l , mainly through his notion of perceptual systems and the parameters of physical energy to which these are s e n s i t i v e . I w i l l not discuss the ecological approach in terms of levels of explanation and d e s c r i p t i o n . This i n t e r e s t i n g issue i s discussed by Lawrence Carleton in "Levels of Description and Explanation," Philosophy Research Archives, 1 1 , 89-109 ( H i l l s d a l e , New Jersey: Lawrence Erlbaum Assoc., 1986). 2 2  1 b i d . , 148.  2 3  1 b i d . , 148-149.  I b i d . , 220. 25 David Hume, Enquiries Concerning Human Understanding and Concerning the P r i n c i p l e s of Morals, 3rd e d i t i o n , ed. P.H. Nidi i t c h (Oxford: Clarendon Press, 1975, a r e p r i n t from the 1777 e d i t i o n , ed. e i t h i n t r o d u c t i o n by, L.A. Selby-Bigge) 151-153. Hume's problem here i s epistemological rather than psychological, though. 2 4  Of.  Gibson, Ecological Approach, 221. Gibson, Senses, 276.  po  W. S c h i f f , J.A. Caviness, and J . J . Gibson, "Persistent Fear Responses in Rhesus Mondeys to the Optical Stimulus of 'Looming'," Science, 136 (1962): 982-983. pq  W. S c h i f f , "Perception o f Impending C o l l i s i o n , " Psychological Monograph, 79, no. 604. 30  Gibson, Ecological Approach, 175-176. 31  Michael T. Turvey et a l . , "Ecological Laws in Perceiving and A c t i n g : In Reply to Fodor and Pylyshyn (1981)," Cognition, 9, no. 3 (1981): 294 32  G i b s o n , Senses, 280.  R . E . Shaw, M7T. Turvey, and W.M. Mace, "Ecological Psychology: the Consequences of a Commitment to Realism," Cognition and the Symbolic Processes, 2, ed. Walter B. Weimer and David S. Palermo ( H i l l s d a l e N.J.: Lawrence Erlbaum Assoc., 1982), 164-167. 3 3  34  Gibson, Ecological Approach, 253. I b i d . , 3.  3 5  O C  Turvey et a l . , "Ecological Laws," 243. Similar d e s c r i p t i o n of the Ecological Approach in E.S. Reed, "Two Theories of the I n t e n t i o n a l i t y of Perceiving". G i b s o n , Ecological Approach, 243, 262-263, 307. 37  I b i d . , 127, 238.  3 8  Gibson, Senses, 267.  39  G.E. Moore, "Proof of an External World," Philosophical Papers (London: George Allen and Unwin L t d . , 1959; r e p r i n t ed. New York: Humanities Press I n c . , 1977), 127-130. 40  Gibson, Ecological Approach, 8-9. 4 1  I b i d . , chapter 2, 307.  4 2  1 b i d . , 307.  43  T u r v e y et a l . , "Ecological Laws," 237-304.  G i b s o n , Ecological Approach, 127. N e l s o n Goodman, Fact, F i c t i o n , and Forecast, 4th e d . , with forward by H i l l a r y Putnam (Cambridge, Mass.: Harvard U n i v e r s i t y Press, 1983), 40. G i b s o n , Ecological Approach, 127, 137-141. 44  45  46  Chapter Two •^Gibson, Senses, 50. 2 Gibson, Ecological Approach, 245. 3  Ibid.  4 Gibson, Senses, 50. 5 Gibson, Ecological Approach, 65-66. 6  I b i d . , 65.  7  I b i d . , 68-69.  8  I b i d . , 68.  9  I b i d . , 283-286.  10  Gibson, Senses, 235-237.  G i b s o n , Ecological Approach, 73. I b i d . , 87.  1 1  I b i d . , 247. 1 b i d . , 166-168, 169, 244. f a v o u r i t e point of Gibson's. 1 2  1 3  1 4  I b i d . , 78-86.  There may be others: t h i s i s a  Gibson, Senses, 203-206..  15 Gibson, Ecological Approach, 165. 1 6  I b i d . , 310.  1 7  I b i d . , 87-91.  18  M i c h a e l s and Carello, Direct Perception, 21-22.  19 Gibson, Ecological Approach, 114. Gibson, Senses, 237. "Gibson, Ecological Approach, 208-209. Gibson, Senses, 284-285. pi Gibson, Ecological Approach, 95-100. 2 2  I b i d . , 10-12, 100-102.  I b i d . , 175. 24 David Lee, A Theory of Visual Control of Braking Based on Gibson, Information aboutSenses, Time-to280 C o(lilni s ipassing). o n , " Perception, 5 (1976): 431-459. 2 3  or  I b i d . , 237.  2 6  27 28  Locke, Essay, Book I I , chapter 9, sections 8-10. Gibson, Ecological Approach, 310.  I b i d . , 63.  2 9  30  G i b s o n , Senses, 245. 31 Turvey et a l . , "Ecological Laws," 243. JU  Chapter Three  Michaels  and C a r e l l o , Direct Perception, ch. 5; Shaw, Turvey, and Mace, "Ecological Psychology," passim; E.S. Reed and Rebecca Jones, "Gibson's Theory of Perception: A Case of Hasty Epistemologizing?" Philosophy of Science, 45, no. 4 (Dec. 1978): 526-529 are three examples, Fodor and Pylyshyn, "How Direct?" 139-196. 3  2  Turvey et a l . , "Ecological Laws," 240. 4  Fodor and Pylyshyn, "How Direct?" 141.  5  Ibid.  6  I b i d . , 142.  7  Gibson, Ecological Approach, 311.  I b i d . , 203-205. g Michaels and C a r e l l o , Direct Perception, 178. G i b s o n , Ecological Approach, 134-135, 240.  8  10  **Turvey et a l . , "Ecological Laws," 261. 12 Ludwig Wittgenstein, The Blue and Brown Books, (New York: Harper and Row, Pub., 1958; Harper Torchbooks, 1965). 13  F o d o r and Pylyshyn, "How Direct?" 169.  14  T u r v e y et a l . , "Ecological Laws," 282-284.  1 5  I b i d . , 244-245. Fodor and Pylyshyn, "Ecological Laws," 188.  U l r i c Neisser, "Gibson's Ecological Optics: Consequences of D i f f e r e n t Stimulus D e s c r i p t i o n , " Journal f o r Theory of Social Behaviour, 7, no. 1 (Apr. 1977): 24. 1 7  18  Robert E. Shaw and John Bransford, " I n t r o d u c t i o n : Psychological Approaches to the Problem of Knowldge," Perceiving, A c t i n g , and Knowing, ed. R.E. Shaw and J . Bransford ("Hillsdale, N.J.: Lawrence Erlbaum Assoc., 1977), 1-10. 19  John Heil uses t h i s term to describe the problem in Gibson's approach t h a t (he suggests) both D.W. Garniyn and U l r i c Neisser attempt to point out in "What Gibson's Missing," Journal f o r the Theory of Social Behaviour, 9, no. 3 (Oct. 1979): 265-269. ?o Fodor and Pylyshyn, "How Direct?" 167. Chapter Four ^ o d o r and Pylyshyn, "How Direct?" 192. 2 D.W. Hamlyn, Perception, Learning, and the Self (London: Rout!edge arid Kegan Paul, 1983), 30-42. 3  TSRM's references to Putnam are H i l l a r y Putnam, " I s Semantics Possible?" Language, BeTief, and Metaphysics, ed. H.E. Kiefer and M.K. Munitz (New York: SUNY Press, 1970), 50-63 and "On P r o p e r t i e s , " Essays in Honour of Carl Hempel, ed. Nichol Rescher et a l . (Dordrecht, Holland D. Reidel Publishing Co., 1969), 234-254. 4 Fred I . Dretske, "Laws of Nature," Philosophy of Science, 44, no. 2 (June 1977): 248-268. 5 Turvey et a l . , "Ecological Laws," 255. Shaw, Turvey, and Mace, "Ecological Psychology," 182-185, 194-203. ^Paul V. Hamilton, "Daily Movements and Visual Location of Plant Stems by L i t t o r i n a I r r o r a t a (Mollusca: Gastropoda)," Marine Behaviour and Physiology, 4, (1977): 293-304. o  Turvey et a l . , "Ecological Laws," 249. 9  I b i d . , 268.  1 0  n  I b i d . , 256.  ibid.,  265.  I b i d . , 251. 13 Gibson, Ecological Approach, 127. Turvey et a l . , "Ecological Laws," 267. T u r v e y et a l . , "Ecological Laws," 262. 1 2  14  15  B y G. Wedeking.  Turvey et a l . , "Ecological Laws," 264. I b i d . , 255. 'Putnam, "Semantics?" 50. ' i b i d . , 5 1 , 53-54. ' i b i d . , 50. I b i d . , 58-59. Turvey et a l . , "Ecological Laws," 264. Chapter Five ^Turvey et a l . , "Ecological Laws," 273. 2  I b i d . , 265, 267-275.  3  I b i d . , 266.  4  I b i d . , 249-250, 284-295.  5  D r e t s k e , "Laws," 252.  6  I b i d . , 252-253.  7  I b i d . , 267.  Q  Turvey et a l . , "Ecological Laws," 266. D r e t s k e , "Laws," 253 n. •^Turvey et a l . , in "Ecological Laws," 237, favourably note a comment of Gibson's that would indicate the lawful r e l a t i o n s they have in mind are causal ones. In the f i r s t place, causal r e l a t i o n s are not symmetrical, so some story needs to be t o l d as to how TSRM a r r i v e at the arrangement of the predicates in t h e i r " t r a n s i t i v i t y argument" since i t does make a difference to the t r u t h of the premisses (because causal r e l a t i o n s are not symmetrical) as to how the predicates are ordered. In a d d i t i o n , there i s no causal r e l a t i o n that f i t s the order TSRM use. Suppose the r e l a t i o n is"causes": While i t makes sense to suggest t h a t an occurrent, physical property i s the cause of affordance (o-ness — > e-ness), i t i s c l e a r l y f a l s e t h a t an o p t i c a l property causes the occurrent property (e-ness — > o-ness). Suppose, then, t h a t the r e l a t i o n i s " i s caused by": the r e s u l t i s the reverse of the foregoing. I t could be true that an o p t i c a l i n v a r i a n t i s caused by an occurrent property (e-ness — ^ o-ness) but i t could not be t r u e t h a t an occurrent property i s caused by an affordance (o-ness — c - n e s s ) . Moreover, the affordance neither causes nor are caused by an o p t i c a l i n v a r i a n t . I f the r e l a t i o n is causal, theref o r e , the order of the predicates o, c, and e, matter in TSRM's argument, and as they are presently arranged, at least one 9  135  of the premisses  bound  is to be f a l s e no matter which way one t r i e s to express the causal r e l a t i o n . ^ T u r v e y et a l . , "Ecological Laws," 260. I b i d . , 268-269.  1 2  13  D r e t s k e , "Laws," 250.  14  T u r v e y et a l . , "Ecological Laws," 260.  15  Fodor and Pylyshyn, "How Direct?" 168, 188-193. '  * Gibson, Ecological Approach, 127. 6  17  T u r v e y et a l . , "Ecological Laws," 274.  18  D r e t s k e , "Laws," 266. I b i d . , 249 n.  1 9  u  21  2 2  Turvey et a l . , "Ecological Laws," 274.  D r e t s k e , "Laws," 253. I b i d . , 253 n.  23  T u r v e y et a l . , "Ecological Laws," 274.  24  D r e t s k e , "Laws," 265. Chapter Six  ^Gibson, Ecological Approach, 239; Shaw, Turvey, and Mace, "Ecological Psychology," 191-194. 2 Gibson, Ecological Approach, 134. Dretske, Knowledge and the Flow of Information (Cambridge, Massachusetts: MIT Press, 1981), 202-206. Dretske's main complaint i s t h a t he thinks one puts the matter backwards by analyzing (or giving "content" t o ) i n t e n t i o n a l states in terms of the behaviour or d i s positions to behave that are produced by them. He believes on the c o n t r a r y , t h a t i t i s the content an i n t e n t i o n a l state already has which explains the output. This is by no means an o r i g i n a l c r i t i c i s m of behavioural analysis of i n t e n t i o n a l states. 4  Turvey et a l . , "Ecological Laws," 290.  5  I b i d . , 275-282.  6  I b i d . , 277.  Armstrong, Material i s t ,  209.  I b i d . , 210. 9  I b i d . , 245-248.  1 0  I b i d . , 227-229.  ^ G i b s o n , Ecological Approach, 243. 12 Shaw, Turvey, and Mace, "Ecological Psychology," 177-178, 182-183. 13  Daniel Dennett, "Conditions of Personhood," The_ I d e n t i t i e s of Persons, ed. Amelie 0. Rorty (Berkeley and Los Angeles: University of C a l i f o r n i a Press, 1976), 179-180. * \ a r l P f e i f e r and C.B. M a r t i n , " I n t e n t i o n a l i t y and the Nonpsychological," Philosophy and Phenomenological Research, 46, no. 4 (June 1986): 531-554. P f e i f e r and Martin argue that many t y p i c a l accounts of I n t e n t i o n a l i t y apply to d i s p o s i t i o n a l properties of purely physical systems. They would take t h i s to show that the c r i t e r i a f o r i d e n t i f y i n g i n t e n t i o n a l i t y in question is wrong. Hence, TSRM's view about i n t e n t i o n a l i t y , which considers " s e n s i t i v i t y to four ounces or more" to be an i n t e n t i o n a l state of a balance would be taken by P f e i f e r and Martin as showing that the ecological t h e o r i s t s have the wrong c r i t e r i a f o r i d e n t i f y i n g i n t e n t i o n a l s t a t e s . Shaw, Turvey, and Mace, "Ecological Psychology," 164-167.  Sources Cited Armstrong, David M. A M a t e r i a l i s t Theory of Mind. and Kegan Paul, 1968.  London: Rout!edge  Carleton, Lawrence R. "Levels in Description and Explanation." Philosophy Research Archives, 11 (March, 1986): 89-109. Chisholm, Roderick. Perceiving: A Philosophical Study. York: Cornell U n i v e r s i t y Press, 1957.  Ithaca, New  Dennett, Daniel. "Conditions of Personhood." In The I d e n t i t i e s of Persons, 175-196. Edited by Amelie Oksenberg Rorty. Berkeley and Los Angeles: U n i v e r s i t y of C a l i f o r n i a Press, 1976. Dretske, Fred I . Knowledge and the Flow of Information. Massachusetts?' MIT Press, 1981. .  "Laws of Nature."  Cambridge,  Philosophy of Science, 44 (1977): 248-268.  Fodor, Jerry A. and Pylyshyn, Zenon W. "How Direct i s Visual Percept i o n ? : Some Reflections on Gibson's 'Ecological Approach'." Cognition, 9, no. 2 (1981): 139-196. Gibson, James J . 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