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A cognitive effect of a moving object’s dynamic visual history : spatiotemporal integration of physical… Gibbs, Brian J. 1985

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A COGNITIVE EFFECT OF A MOVING OBJECT'S DYNAMIC VISUAL HISTORY: SPATIOTEMPORAL INTEGRATION OF PHYSICAL PROPERTIES By BRIAN J . GIBBS B . S c , The U n i v e r s i t y of B r i t i s h Columbia, 1982 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE STUDIES (Department of Psychology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September 1985 Q B r i a n J . Gibbs, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date sepr. /3 ns£ D E - 6 i i A b s t r a c t D e s p i t e enormous i n f o r m a t i o n a l complexity i n the o p t i c a l environment, the v i s u a l world i s e f f o r t l e s s l y seen as coherent. Indeed, an obj e c t may change i n v i r t u a l l y a l l of i t s p h y s i c a l p r o p e r t i e s and in i t s s p a t i a l l o c a t i o n and yet maintain a cons t a n t p e r c e p t u a l i d e n t i t y . Apparently p i e c e s of i n f o r m a t i o n r e g i s t e r e d in d i f f e r e n t segments of space-time, but r e f e r r i n g to the same o b j e c t , are p e r c e p t u a l l y i n t e g r a t e d . Kahneman, Treisman and Gibbs ( i n progress) explored the c o g n i t i v e o r g a n i z a t i o n corresponding to t h i s p e r c e p t u a l o r g a n i z a t i o n ; the present t h e s i s r e p r e s e n t s an exte n s i o n of t h e i r work. To study the spatiotemporal i n t e g r a t i o n of inf o r m a t i o n r e g a r d i n g moving o b j e c t s they developed the preview paradigm. The p r o t o t y p i c a l v i s u a l d i s p l a y of t h i s paradigm c o n s i s t s of three phases: (a) L e t t e r s are presented, each w i t h i n a l i n e - f i g u r e o b j e c t , and are then removed ( f i e l d - 1 ) , (b) the empty o b j e c t s move to new p o s i t i o n s , (c) l e t t e r s are again presented in the o b j e c t s and a marker appears, cueing one of them ( f i e l d - 2 ) . The task i s to name the l e t t e r i n the cued o b j e c t . The c r i t i c a l r e a c t i o n time (RT) comparison i s between c o n s i s t e n t c o n d i t i o n s (the t a r g e t l e t t e r i s previewed in the t a r g e t o b j e c t ) and i n c o n s i s t e n t c o n d i t i o n s (the t a r g e t l e t t e r i s previewed, but in another o b j e c t ) . An RT advantage f o r c o n s i s t e n t c o n d i t i o n s i s termed the object e f f e c t because i t represents o b j e c t - s p e c i f i c f a c i l i t a t i o n . Object e f f e c t s were generated in many experiments, i n c l u d i n g one u t i l i z i n g only apparent motion to c r e a t e o b j e c t s . C e r t a i n experiments suggested that the o b j e c t e f f e c t does not occur at a l e x i c a l or semantic l e v e l , but i n v o l v e s information concerning p h y s i c a l p r o p e r t i e s . The present t h e s i s f u r t h e r e x p l o r e s the p h y s i c a l nature of the i n f o r m a t i o n i n t e g r a t i o n u n d e r l y i n g the o b j e c t e f f e c t . Preview experiments were conducted, t y p i c a l l y not with a l e t t e r - n a m i n g task, but with tasks r e q u i r i n g s t i m u l u s i d e n t i f i c a t i o n on the b a s i s of a p a r t i c u l a r p h y s i c a l p r o p e r t y . In experiments u t i l i z i n g four moving l i n e f i g u r e s , o b j e c t e f f e c t s were obtained with presence and s i z e . These e f f e c t s were not a r t i f a c t s of a t t e n d i n g to f i e l d - 1 or of c o n f u s i n g f i e l d - 1 with f i e l d - 2 . In experiments u t i l i z i n g apparent motion, object e f f e c t s were obtained with c o l o r and with l e t t e r s . Duodimension experiments e l a b o r a t e d the paradigm by i n t r o d u c i n g v a r i a t i o n on a r e s p o n s e - i r r e l e v a n t dimension. The presence object e f f e c t was reduced by r e s p o n s e - i r r e l e v a n t shape i n c o n s i s t e n c y ; the s i z e o b j e c t e f f e c t was e l i m i n a t e d by r e s p o n s e - i r r e l e v a n t shape i n c o n s i s t e n c y ; the c o l o r o b j e c t e f f e c t was u n a f f e c t e d by r e s p o n s e - i r r e l e v a n t l e t t e r - s h a p e i n c o n s i s t e n c y ; the l e t t e r o b j e c t e f f e c t was s l i g h t l y reduced by r e s p o n s e - i r r e l e v a n t c o l o r i n c o n s i s t e n c y . The duodimension r e s u l t s suggest that the o b j e c t -s p e c i f i c r e p r e s e n t a t i o n u n d e r l y i n g the o b j e c t e f f e c t c o n s i s t s i v of somewhat co n j o i n e d p r o p e r t i e s . T h i s has i m p l i c a t i o n s f o r the r o l e of a t t e n t i o n i n the obj e c t e f f e c t , and i n s p i r e s the s p e c u l a t i o n that motion might be s p e c i a l with respect to a t t e n t i o n . Accounts of the o b j e c t e f f e c t r i v a l to Kahneman et a l . ' s can be proposed: that i t r e s u l t s from the i n t e g r a t i o n of response tendencies rather than stimulus i n f o r m a t i o n , that i t i s based on a decrease i n apparent d i s t a n c e between s t i m u l i r a t h e r than on t h e i r u n i t i z a t i o n , and that i t s seeming r e t r o a c t i v i t y i s an i l l u s i o n produced by the r e l a t i v e quickness with which low s p a t i a l frequencies are processed. The present r e s u l t s support arguments against each of these accounts. The general c o n c l u s i o n of t h i s t h e s i s i s that the spatiotemporal i n t e g r a t i o n u n d e r l y i n g the ob j e c t e f f e c t does i n v o l v e i n f o r m a t i o n about p h y s i c a l propert i e s . V Table of Contents A b s t r a c t i i L i s t of F i g u r e s v i i Acknowledgment v i i i INTRODUCTION 1 General Problem 2 Immediate Context: The Preview Paradigm 4 The Paradigm 4 A Review of the F i n d i n g s and I n t e r p r e t a t i o n s 9 Concl u s i o n s 26 Conceptual Issues 43 Spatiotemporal Information I n t e g r a t i o n 46 PRESENT INVESTIGATION 54 R e l a t i o n to the Previous Design 54 Purpose and R a t i o n a l e 55 G e n e r a l i z i n g the Object E f f e c t 57 Why a F e a t u r a l Object E f f e c t Cannot Be Assumed...59 An E l a b o r a t i o n of the Paradigm 61 The Monodimension Experiments 64 Subjects and Apparatus 64 Experiment 1: Presence (Late-Cue Version) 64 Experiment 2: Presence (Early-Cue Version) 75 Experiment 3: S i z e 78 Experiments 4 and 5: Presence and S i z e (Long-Duration-Preview V e r s i o n s ) 80 The Duodimension Experiments 85 v i S u bjects and Apparatus 86 Experiment 6: Presence (Shape as Response-Irrelevant Dimension) 87 Experiment 7: S i z e (Shape as Response-Irrelevant Dimension) 88 Experiment 8: C o l o r (Letter-Shape as Response-Irrelevant Dimension)..91 Experiment 9: L e t t e r (Color as Response-Irrelevant Dimension) 96 GENERAL DISCUSSION 99 The R e s u l t s 99 Q u a l i f i c a t i o n s on the S i z e F i n d i n g s 100 A n a l y s i s of the Duodimension Experiments 102 The " E l i m i n a t i o n " R e s u l t 104 The " N o - I n t e r a c t i o n " R e s u l t 104 Reduction of the Object E f f e c t by I r r e l e v a n t V a r i a t i o n 105 Color and Letter-shape 114 R i v a l Accounts of the Object E f f e c t 116 The Response-Integration Account 117 The Apparent-Distance Account 118 The S p a t i a l - F r e q u e n c y Account 120 I m p l i c a t i o n of the Study as a Whole 121 References 124 Appendix 1 34 v i i L i s t of F i g u r e s F i g u r e 1. The three c o n d i t i o n s of Kahneman, Treisman and Gibbs's ( i n progress) b a s i c t r i a n g l e - a n d - b o x d i s p l a y 6 F i g u r e 2. The three c o n d i t i o n s of the ba s i c Ternus d i s p l a y as used by Kahneman, Treisman and Gibbs ( i n progress) 17 F i g u r e 3. The four c o n d i t i o n s of the four-box d i s p l a y as used in the monodimension l a t e - c u e presence experiment 66 Ac knowledgment I thank Danny Kahneman and Anne Treisman--in whose l a b a l l of t h i s research was conducted--for p r o v i d i n g guidance on the t h e s i s p r o j e c t i n s p e c i f i c , and f o r being u n f a i l i n g l y s u p p o r t i v e i n g e n e r a l . I w i l l take much away from my a s s o c i a t i o n with them. A l s o a p p r e c i a t e d i s the encouragement o f f e r e d along the way by Jim S t e i g e r and by L a r r y Ward. F i n a l l y , I acknowledge the A t t e n t i o n Lab i t s e l f f o r t e a c h i n g me so much, and thank a l l the "Labbies" t h e r e i n f o r making even the toughest l e s s o n s so p l e a s a n t . While earning the Master's degree I was supported by a Postgraduate S c h o l a r s h i p from the N a t u r a l Sciences and E n g i n e e r i n g Research C o u n c i l of Canada and by a U n i v e r s i t y Graduate F e l l o w s h i p from the U n i v e r s i t y of B r i t i s h Columbia. 1 A C o g n i t i v e E f f e c t of a Moving O b j e c t ' s Dynamic V i s u a l H i s t o r y : Spatiotemporal I n t e g r a t i o n of P h y s i c a l P r o p e r t i e s A P l e i s t o c e n e hominid forages on a h i l l s i d e . Suddenly, some boulders become d i s l o d g e d and tumble down the h i l l s i d e toward her. From i n s t a n t to i n s t a n t the i n f o r m a t i o n i s s u i n g from any p a r t i c u l a r boulder changes d r a m a t i c a l l y . The l o c a t i o n of the i n f o r m a t i o n source undergoes v i o l e n t change. The boulder's s i z e and shape change as p i e c e s of i t break o f f , and i t s c o l o r changes as i t s v a r i o u s faces are r e v e a l e d by i t s s p i n . I t bounces i n and out of patches of l i g h t and i s sometimes completely obscured by i n t e r v e n i n g o b j e c t s . In s h o r t , there i s v i r t u a l l y nothing c o n s t a n t about i t s p h y s i c a l p r o p e r t i e s or l o c a t i o n . Yet i n f o r m a t i o n i s a p p r o p r i a t e l y c o l l a t e d a c r o s s space and time, and the c a r e e n i n g b o u l d e r s -complex sources of dynamic s t i m u l a t i o n - - a r e p e r c e i v e d as u n i t a r y o b j e c t s with constant i d e n t i t i e s and coherent h i s t o r i e s . The hominid's w e l l - o r g a n i z e d percept f a c i l i t a t e s a w e l l - o r g a n i z e d response, and she s u c c e s s f u l l y dodges the deluge, l i v i n g to pass her genes on to f u t u r e g e n e r a t i o n s . Obviously the o p t i c a l environment can be extremely r i c h . Because seeing i s normally e f f e c t i v e and e f f o r t l e s s , what may not be obvious i s that with the o p t i c a l r i c h n e s s comes great i n f o r m a t i o n a l complexity. D i r e c t - p e r c e p t i o n t h e o r i s t s ( f o l l o w i n g Gibson, 1959) c o n s i d e r the r i c h n e s s of o p t i c a l i n formation to i t s e l f account fo r the success of v i s i o n , but the more common view i s t h a t complexity i s a 'problem' to be 2 'solved' by the v i s u a l system through the c o g n i t i v e encoding and recoding of i n f o r m a t i o n (Broadbent, 1958; Ullman, 1980; Tversky, 1977; E p s t e i n , 1982). The d i f f e r e n c e between these two s c h o o l s of thought can be viewed no n p o l e m i c a l l y as one of emphasis (Demkiw & Michaels, 1976; Johansson, von Hofsten, & Jansson, 1980): emphasis on s t r u c t u r e i n the i n f o r m a t i o n a l environment versus emphasis on s t r u c t u r e i n c o g n i t i v e p r o c e s s i n g . The present t h e s i s takes the second approach. General Problem The r e s e a r c h h e r e i n seeks to i n v e s t i g a t e the c o g n i t i v e o r g a n i z a t i o n a s s o c i a t e d with the v i s u a l coherence of o b j e c t s and events i n the phenomenal world. How i s the p e r c e p t u a l i d e n t i t y of an object maintained d e s p i t e changes i n i t s l o c a t i o n and p r o p e r t i e s ? How are the p r o p e r t i e s of d i f f e r e n t o b j e c t s segregated? How i s i n f o r m a t i o n p e r t a i n i n g to a given moving o b j e c t i n t e g r a t e d a c r o s s space and time? T h i s s o r t of i n q u i r y , s t r e s s i n g o b j e c t s and the mutual interdependence of s t i m u l i , began with the G e s t a l t p s y c h o l o g i s t s and t h e i r search f o r the laws of v i s u a l o r g a n i z a t i o n . Koffka (1935, p. 97) noted that " s t i m u l i at two adjacent p o i n t s on the r e t i n a c o n t a i n nothing qua s t i m u l i that w i l l make the two c o r r e s p o n d i n g p o i n t s i n b e h a v i o r a l space belong to two d i f f e r e n t o b j e c t s or to one and the same o b j e c t . " He went on to e x p l a i n : "A t h i n g i s a p a r t i c u l a r l y w e l l i n t e g r a t e d part of the t o t a l f i e l d . The stronger i t s i n t e g r a t i o n , the stronger the f o r c e s which h o l d i t together, the more constant w i l l i t be i n changes of s t i m u l a t i o n . . . " 3 (p. 305). The f i e l d e x p l a n a t i o n s of v i s u a l p e r c e p t i o n o f f e r e d by G e s t a l t psychology were c r i t i c i z e d by Lashley (1942) f o r being ad hoc and o f t e n t a u t o l o g i c a l , but he too acknowledged the importance of the elementary o b s e r v a t i o n that " v i s u a l impressions c o n s i s t of organized o b j e c t s , seen a g a i n s t a l e s s coherent background." (p. 302) More contemporarily, i n a review of p e r c e p t i o n and r e p r e s e n t a t i o n , K o l e r s (1983) i d e n t i f i e s as a c e n t r a l i s s u e the q u e s t i o n of how the continuous f l u x of s t i m u l a t i o n f a l l i n g on sensory s u r f a c e s i s t r a n s l a t e d i n t o the p e r c e p t u a l experience of d i s c r e t e o b j e c t s moving in space. S i m i l a r l y , Attneave (1974) asks how the v i s u a l system keeps t r a c k of the p r o p e r t i e s of an o b j e c t and i s able to maintain the i n t e g r a l i t y of these p r o p e r t i e s even as the o b j e c t moves. Kahneman and Treisman (1984) propose the metaphor of a f i l i n g system: An "object f i l e " r e c e i v e s i n f o r m a t i o n about a s p e c i f i c o b j e c t i n the f i e l d , and does so even as the l o c a t i o n and p r o p e r t i e s of that o b j e c t change. The c o n t i n u i t y of the object f i l e accounts fo r the p r e s e r v a t i o n of o b j e c t i d e n t i t y ; i t s s p e c i f i c i t y accounts f o r the s e g r e g a t i o n of i n f o r m a t i o n about d i f f e r e n t o b j e c t s ; and i t s u n i t y accounts fo r the i n t e g r a t i o n of i n f o r m a t i o n about a s i n g l e o b j e c t . An experimental i n v e s t i g a t i o n of the c o g n i t i v e o r g a n i z a t i o n u n d e r l y i n g the p e r c e p t u a l coherence of o b j e c t s c o n s t i t u t e s the immediate r e s e a r c h context f o r the present t h e s i s . S p e c i f i c a l l y , Kahneman, Treisman and Gibbs ( i n 4 p r o g r e s s ) — h e n c e f o r t h c i t e d as KTG--have s t u d i e d the spatiotemporal i n t e g r a t i o n of i n f o r m a t i o n r e f e r r i n g to moving o b j e c t s . The present t h e s i s d e a l s with the same phenomenon. What d i s t i n g u i s h e s t h i s experimental s e r i e s i s t h a t , u n l i k e the mother p r o j e c t , i t i s not p r i m a r i l y concerned with l e t t e r s t i m u l i , but e x p l o r e s the spatiotemporal i n t e g r a t i o n of i n f o r m a t i o n r e g a r d i n g the p h y s i c a l p r o p e r t i e s of moving o b j e c t s . Immediate Context: The Preview Paradigm To i n v e s t i g a t e the spatiotemporal i n t e g r a t i o n of v i s u a l i n f o r m a t i o n , KTG developed the preview paradigm. The present p r o j e c t f o l l o w s , and concerns e m p i r i c a l q u e s t i o n s prompted by, the preview paradigm. The Paradigm As i t s name suggests, the preview paradigm i s c h a r a c t e r i z e d by the advance p r e s e n t a t i o n of a v i s u a l stimulus i d e n t i c a l to a subsequently presented t a r g e t s t i m u l u s . In t h i s sense i t i s l i k e a priming paradigm (Eichelman, 1970). However, what d i s t i n q u i s h e s the preview paradigm i s i t s manipulation of the f i g u r a l context w i t h i n which the t a r g e t and preview appear. In the t y p i c a l priming experiment there i s no compelling f i g u r a l r e l a t i o n between the t a r g e t and the preceding prime: The two s t i m u l i are simply presented c o n s e c u t i v e l y i n the same l o c a t i o n or perhaps simultaneously and s i d e - b y - s i d e . By c o n t r a s t , i n the preview experiment there i s a patent f i g u r a l r e l a t i o n between the t a r g e t and preview. The two s t i m u l i are d i s p l a y e d e i t h e r 5 as s e r i a l l y v i s i b l e p a r t s of a s i n g l e moving f i g u r e or as s e r i a l l y v i s i b l e p a r t s of two separate moving f i g u r e s . Experiments of the preview paradigm u t i l i z e three-phase v i s u a l d i s p l a y s . In the i n i t i a l phase a stimulus f i e l d i s pr e s e n t e d that may or may not i n c l u d e a preview of the f u t u r e t a r g e t . In the f i n a l phase another stimulus f i e l d i s pr e s e n t e d that i n c l u d e s the t a r g e t proper. In the i n t e r m e d i a t e phase these two stimulus f i e l d s are p e r c e p t u a l l y connected by r e a l and/or apparent motion o c c u r r i n g between them. The r e s u l t i s that o b j e c t s observed in the i n i t i a l d i s p l a y are seen to move and take up new p o s i t i o n s as o b j e c t s in the f i n a l d i s p l a y . The b a s i c i s s u e of i n t e r e s t i n such experiments i s whether response to the t a r g e t i s a f f e c t e d by the f i g u r a l r e l a t i o n between the t a r g e t and i t s preview. I t might be expected t h a t , r e g a r d l e s s of how the preview i s pr e s e n t e d with respect to the t a r g e t , the advance p r e s e n t a t i o n w i l l speed response; the e s s e n t i a l q u e s t i o n i s , w i l l t h i s f a c i l i t a t i o n be g r e a t e r f o r target-preview p a i r s seen as belonging to the same o b j e c t than f o r p a i r s seen as b e l o n g i n g to d i f f e r e n t o b j e c t s ? That i s , w i l l w i t h i n - o b j e c t i n f o r m a t i o n sources i n t e r a c t more f u l l y than between-object i n f o r m a t i o n sources? One of KTG's e a r l y experiments--a p r o g e n i t o r of the experiments that w i l l be repo r t e d i n t h i s t h e s i s — w a s aimed at answering t h i s b a s i c q u e s t i o n and can serve as an exemplar of the preview paradigm (see F i g u r e 1). The experiment employed a modified v e r s i o n of a d i s p l a y o r i g i n a t e d by von 6 C O N S I S T E N T A. 1 1 : B ; i J I N C O N S I S T E N T C O N T R O L F i g u r e 1. The three c o n d i t i o n s of Kahneman, Treisman and Gibbs's ( i n progress) b a s i c t r iangle-and-box d i s p l a y . (5/7 X a c t u a l s i z e ; dashed l i n e s r e f e r to the f i r s t f i e l d , dashed arrows to motion, and s o l i d l i n e s to the second f i e l d ) . 7 S c h i l l e r (1933, c i t e d i n Attneave, 1974). Each d i s p l a y sequence began with the p r e s e n t a t i o n of a p a i r of l i n e f i g u r e s arranged v e r t i c a l l y so as to b i s e c t the d i s p l a y s c r e e n — a t r i a n g l e above the c e n t r a l f i x a t i o n dot and a box below i t . A f t e r a delay, two l e t t e r s were presented, one w i t h i n each of the l i n e f i g u r e s . These f i r s t two l e t t e r s , r e f e r r e d to as the f i e l d - 1 s t i m u l i , remained on the screen fo r 1000 ms. As soon as the l i n e f i g u r e s were empty once again, they began moving d i a g o n a l l y a c r o s s the screen, the t r i a n g l e downward e i t h e r to the l e f t or r i g h t , and the box upward e i t h e r to the r i g h t or l e f t . In completing t h e i r 130 ms movement, the empty l i n e f i g u r e s became arranged h o r i z o n t a l l y so as to b i s e c t the s c r e e n — o n e f i g u r e to the l e f t of the c e n t r a l f i x a t i o n dot and the other to the r i g h t of i t . Immediately f o l l o w i n g t h i s movement, two events o c c u r r e d : A t a r g e t l e t t e r — t h e f i e l d - 2 s t i m u l u s — w a s presented in one of the l i n e f i g u r e s , and a v i s u a l cue was d i s p l a y e d to designate e i t h e r the t r i a n g l e or the box, whichever o b j e c t h e l d the t a r g e t . The s u b j e c t ' s task was to read aloud the l e t t e r appearing in the cued o b j e c t as q u i c k l y as p o s s i b l e . Reaction times (RTs) comprised the experimental data. In the p r o t o t y p i c a l preview experiment the preview of the t a r g e t l e t t e r can occupy e i t h e r of two l o c a t i o n s i n f i e l d - 1 . By o c c u r r i n g i n the o b j e c t that w i l l l a t e r c o n t a i n the t a r g e t , the preview occupies what w i l l be termed the target-yoked l o c a t i o n ; by o c c u r r i n g i n the other o b j e c t , the 8 preview occupies what w i l l be termed the target-nonyoked l o c a t i o n . The experimental c o n d i t i o n s r e f l e c t t h i s d i s t i n c t i o n . In the c o n s i s t e n t c o n d i t i o n , the preview l e t t e r i s presented i n the target-yoked l o c a t i o n , and a nonpreview l e t t e r i s presented in the target-nonyoked l o c a t i o n . In the i n c o n s i s t e n t c o n d i t i o n , the preview l e t t e r i s presented in the target-nonyoked l o c a t i o n , and a nonpreview l e t t e r i s presented i n the target-yoked l o c a t i o n . There i s a l s o a c o n t r o l c o n d i t i o n i n which nonpreview l e t t e r s are presented in both f i e l d - 1 p o s i t i o n s . The c r i t i c a l experimental c o n t r a s t i s between mean RTs f o r the c o n s i s t e n t and i n c o n s i s t e n t c o n d i t i o n s . The composition of the d i s p l a y does not d i f f e r between these c o n d i t i o n s : A preview l e t t e r and a nonpreview l e t t e r appear in f i e l d - 1 , followed by a t a r g e t l e t t e r in f i e l d - 2 that i s s p a t i a l l y and temporally e q u i d i s t a n t from both of the preceding l e t t e r s . Again, the only d i f f e r e n c e i s that in the c o n s i s t e n t c o n d i t i o n the t a r g e t and preview are presented w i t h i n the same moving o b j e c t , and i n the i n c o n s i s t e n t c o n d i t i o n the t a r g e t and preview are presented w i t h i n d i f f e r e n t moving o b j e c t s . A r e a c t i o n time advantage for the c o n s i s t e n t over the i n c o n s i s t e n t c o n d i t i o n t h e r e f o r e r e f l e c t s o b j e c t - s p e c i f i c f a c i l i t a t i o n , and so i s termed the object  e f f e c t . An RT advantage f o r the i n c o n s i s t e n t over the c o n t r o l c o n d i t i o n r e f l e c t s n o n - o b j e c t - s p e c i f i c f a c i l i t a t i o n , and so i s more akin to a standard priming e f f e c t . 9 A Review of the F i n d i n g s and I n t e r p r e t a t i o n s The d e s c r i b e d exemplar experiment d i d generate an o b j e c t e f f e c t . RTs i n the c o n s i s t e n t c o n d i t i o n were s i g n i f i c a n t l y s h o r t e r than RTs i n the i n c o n s i s t e n t c o n d i t i o n . C o n s i s t e n t 554 ms I n c o n s i s t e n t 567 C o n t r o l 572 In f a c t , the only s i g n i f i c a n t f a c i l i t a t i o n was o b j e c t -s p e c i f i c . The i n c o n s i s t e n t t r i a l s were not responded to s i g n i f i c a n t l y more r a p i d l y than the c o n t r o l t r i a l s , which lac k e d previews. A preview c o n f e r r e d a s i g n i f i c a n t RT advantage only when i t appeared i n the same obj e c t as the t a r g e t . So, the terms target-yoked and target-nonyoked, used in the f o r e g o i n g as nominal d e s c r i p t o r s , seem a l s o to apply to i n f o r m a t i o n p r o c e s s i n g . That i s , i f a t a r g e t and i t s preview appear w i t h i n the same o b j e c t , then i n f o r m a t i o n about them i s i n t e g r a t e d across space and time to improve performance. Another way to d e s c r i b e t h i s r e s u l t i s that a moving o b j e c t seems to c a r r y with i t information about i t s p e r c e p t u a l past, and t h i s dynamic v i s u a l h i s t o r y can i n f l u e n c e the c u r r e n t p r o c e s s i n g of the o b j e c t . Ramachandran (1981) d e s c r i b e s a " v i s u a l momentum" e f f e c t i n a s i m i l a r way. He used a d i s p l a y l i k e the m o d i f i e d von S c h i l l e r arrangement of KTG's triangle-and-box d i s p l a y (see F i g u r e 1), except that the s t i m u l i were dots r a t h e r than l e t t e r s and there were no l i n e f i g u r e s . The r e s u l t i n g apparent motion was ambiguous or at l e a s t b i s t a b l e , 10 proceeding c l o c k w i s e on some t r i a l s and counterclockwise on o t h e r s . However, by embedding the four s t i m u l i in two p a r a l l e l streams of s e q u e n t i a l l y - p r e s e n t e d dots that were angled a c r o s s the screen e i t h e r downward to the l e f t or downward to the r i g h t , Ramachandran was able to b i a s the d i r e c t i o n of the apparent motion. The von S c h i l l e r dots always moved with the flow of the apparent motion of the dots in which they were embedded, never a g a i n s t i t . Ramachandran i n f e r s that "the i n t e r a c t i o n s of a p a i r of dots seen i n sequence are i n f l u e n c e d by the h i s t o r y of t h e i r past i n t e r a c t i o n s with e a r l i e r d o t s . " (p. 18) Parametric V a r i a t i o n s KTG found o b j e c t - s p e c i f i c f a c i l i t a t i o n of the p r o c e s s i n g of one l e t t e r by another under a wide v a r i e t y of experimental circumstances. For example, they d i s c o v e r e d i t was not necessary f o r the c a r r i e r f i g u r e s to be d i f f e r e n t shapes, nor for there to be only two of them: Object e f f e c t s were observed i n d i s p l a y s i n v o l v i n g three and four moving boxes. O b j e c t - s p e c i f i c f a c i l i t a t i o n a l s o remained when d i s t r a c t o r s were presented i n the nontarget o b j e c t s of f i e l d - 2 . In some experiments the t a r g e t was precued by a marker appearing simultaneously with the disappearance of the f i e l d -1 l e t t e r s . Cueing the t a r g e t e a r l y l i k e t h i s tended to in c r e a s e the o b j e c t e f f e c t r e l a t i v e to that produced by cueing the t a r g e t s i m u l t a n e o u s l y with f i e l d - 2 . For e a r l y - c u e experiments, both a one second and a 30 ms d i s p l a y of the f i e l d - 1 s t i m u l i l e d to f a c i l i t a t i o n t h a t was completely 11 o b j e c t s p e c i f i c (as i t was f o r the d e s c r i b e d l a t e - c u e experiment with a one second f i e l d - 1 ) . However, i f the cue was l a t e and the f i e l d - 1 s t i m u l i were exposed for only 30 ms, f a c i l i t a t i o n was not completely o b j e c t - s p e c i f i c . That i s , although there was a s i g n i f i c a n t o b j e c t e f f e c t , there was a l s o a s i g n i f i c a n t RT advantage even when the preview appeared in the other o b j e c t . T h i s suggests that the o b j e c t -s p e c i f i c i t y of the f a c i l i t a t i o n takes some not-i n c o n s e q u e n t i a l time to develop. The e f f e c t s of manipulating movement parameters were s t u d i e d . There was no d i f f e r e n c e i n the magnitude of the o b j e c t e f f e c t between a s h o r t - d i s t a n c e c o n d i t i o n and a l o n g -d i s t a n c e c o n d i t i o n . Given that the s e p a r a t i o n between the t a r g e t and i t s preview had no i n f l u e n c e , the moving l i n e f i g u r e s are a p p a r e n t l y doing more than simply grouping the s t i m u l i or reducing the e f f e c t i v e d i s t a n c e between them (Ramachandran, 1981; Hoffman & Nelson, 1981). Rather, the moving l i n e f i g u r e s seem to e s t a b l i s h a deeper s p a t i a l c o n n e c t i o n between the s t i m u l i . With respect to the time v a r i a b l e , s h o r t e r - d u r a t i o n , higher-speed movement of the l i n e f i g u r e s produced s l i g h t l y l e s s o b j e c t - s p e c i f i c f a c i l i t a t i o n than d i d l o n g e r - d u r a t i o n , lower-speed movement. Although both movement d u r a t i o n s t e s t e d f a l l w i t h i n the quarter second o f t e n c o n s i d e r e d to be the l i f e t i m e of the icon ( C o l t h e a r t , 1980), the decided absence of a decay of o b j e c t advantage as the p r e v i e w - t a r g e t delay i n c r e a s e d from 120 ms to 220 ms i s i n c o n s i s t e n t with a simple i c o n - s e l e c t i o n account of the 1 2 object e f f e c t . Rather, the moving l i n e f i g u r e s seem to e s t a b l i s h a deeper temporal connection between the s t i m u l i . The q u e s t i o n of how much inf o r m a t i o n i s i n t e g r a t e d across space and time was addressed by s e r i a l l y d i s p l a y i n g two l e t t e r s i n each ob j e c t i n f i e l d - 1 . An RT advantage was obtained only i f the preview was the l a t t e r of the two f i e l d -1 s t i m u l i appearing i n the t a r g e t o b j e c t . Apparently the mechanism g i v i n g r i s e to the o b j e c t e f f e c t i n t e g r a t e s the tar g e t with only the most recent stimulus to appear i n the same c a r r i e r o b j e c t . A t t e n t i o n and the Object E f f e c t The r e s u l t s d i s c u s s e d so f a r demonstrate that p r o c e s s i n g of a t a r g e t stimulus b e n e f i t s when i t s preview i s presented in the same o b j e c t , and sometimes, a l b e i t to a l e s s e r degree, when i t s preview i s presented i n a d i f f e r e n t o b j e c t . But when only nonpreview l e t t e r s - - w h i c h could be thought of as " i n v a l i d previews"--are presented i n f i e l d - 1 , i s there any pr o c e s s i n g cost r e l a t i v e to when more n e u t r a l s t i m u l i are presented i n f i e l d - 1 ? T h i s i s an important q u e s t i o n because the absence of p r o c e s s i n g cost would perhaps suggest that the process i n t e g r a t i n g the preview and ta r g e t i n f o r m a t i o n i s an a t t e n t i o n a l l y p a s s i v e one (Posner & Snyder, 1975b; Neely, 1977), although even with regard to priming such i s s u e s are u n s e t t l e d . An absence of cost would not be d e c i s i v e because under the p r e v a i l i n g experimental circumstances " f a c i l i t a t i o n dominance" c o u l d be exp l a i n e d by a general expectancy mechanism (Becker, 1980); and c o s t may not be s t r i c t l y 13 . l i m i t e d to a t t e n t i o n a l p r o c e s s e s anyway (DeGroot, Thomassen & Hudson, 1982; T a y l o r , 1977). With respect to f a c i l i t a t i o n , some authors contend that i t i s not dependent on a t t e n t i o n to the prime ( F i s c h l e r & Goodman, 1978), and others that a t t e n t i o n i s e s s e n t i a l or at l e a s t important ( C o l l i n s & L o f t u s , 1975; Henik, F r i e d i c h & K e l l o g g , 1983). To assess p r o c e s s i n g c o s t s , some preview experiments were run not only with the c o n t r o l c o n d i t i o n i n v o l v i n g the p r e s e n t a t i o n of nonpreview l e t t e r s i n f i e l d - 1 , but a l s o with one i n v o l v i n g the p r e s e n t a t i o n of d i g i t s in f i e l d - 1 . If d i g i t s can be c o n s i d e r e d n e u t r a l with respect to the l e t t e r t a r g e t s e t , the amount by which RT f o r the l e t t e r c o n t r o l c o n d i t i o n exceeds RT f o r the d i g i t c o n t r o l c o n d i t i o n should index any p r o c e s s i n g cost a s s o c i a t e d with an i n v a l i d "preview". In two-object experiments, there was no evidence of p r o c e s s i n g c o s t , but i n some f o u r - o b j e c t experiments there was. On the b a s i s of these experiments then, i t i s u n c e r t a i n whether the mechanism r e s p o n s i b l e f o r the o b j e c t e f f e c t i s a t t e n t i o n a l l y p a s s i v e or a c t i v e . More d i r e c t attempts were made to d i s c e r n the r o l e of a t t e n t i o n i n the o b j e c t - s p e c i f i c i n f o r m a t i o n i n t e g r a t i o n . A n a t u r a l m anipulation to employ i s that of making the cue an only p a r t i a l l y - v a l i d i n d i c a t o r of the t a r g e t l o c a t i o n (Posner & Snyder, 1975a). When a cue was used that m i s d i r e c t e d a t t e n t i o n on 27% of t r i a l s , the o b j e c t e f f e c t produced was greater f o r v a l i d l y - c u e d o b j e c t s than f o r i n v a l i d l y - c u e d ones, but i t was present i n both cases. T h i s r e s u l t suggests 1 4 that the moving ob j e c t does not have to be attended f o r i t to i n t e g r a t e i n f o r m a t i o n . Whether cue v a l i d i t y adequately c o n t r o l s a t t e n t i o n i s q u e s t i o n a b l e , and so an a l t e r n a t i v e manipulation was developed. In a t h r e e - o b j e c t d i s p l a y , one of the f i e l d - 1 l e t t e r s was f l a s h e d on i n i t s box twice. Presumably, the double f l a s h of t h i s s t i m u l u s a t t r a c t e d a t t e n t i o n to i t s e l f and away from the other f i e l d - 1 l e t t e r s . When the preview was the d o u b l e - f l a s h e d l e t t e r , i t generated strong o b j e c t -s p e c i f i c f a c i l i t a t i o n as w e l l as c o n s i d e r a b l e n o n s p e c i f i c priming; but when the preview was not the d o u b l e - f l a s h e d l e t t e r , i t generated only n o n s p e c i f i c priming. T h e r e f o r e , in t h i s experiment, the o b j e c t e f f e c t d i d seem to depend on a t t e n t i o n to the preview. To the extent that the o b j e c t e f f e c t r e q u i r e s the i n t e r r e l a t i o n of s t i m u l i as p a r t s of the same o b j e c t , t h i s r e s u l t i s c o n s i s t e n t with i n d i c a t i o n s that the apprehension of r e l a t i o n a l p r o p e r t i e s i s dependent upon a t t e n t i o n (Rock & Gutman, 1981; Becker, 1980). Furthermore, a t t e n t i o n not only i n the sense of s e l e c t i o n but a l s o i n the sense of c a p a c i t y (Kahneman, 1973), may be r e q u i r e d , because in a f o u r - o b j e c t , e a r l y - c u e experiment the o b j e c t e f f e c t was found to be s i g n i f i c a n t l y l a r g e r when there were two f i e l d - 1 s t i m u l i than when there were f o u r . Apparent Motion and the Object E f f e c t KTG found that when only one l e t t e r was presented i n f i e l d - 1 , so that some l i n e f i g u r e s were l e f t empty d u r i n g the i n i t i a l phase of the d i s p l a y , c o n s i d e r a b l e f a c i l i t a t i o n 1 5 occu r r e d but none of i t was o b j e c t - s p e c i f i c . A p o s s i b l e e x p l a n a t i o n f o r t h i s lack of an o b j e c t e f f e c t i n v o l v e s the f a c t that apparent motion i s witnessed between the preview and the t a r g e t . Normally t h i s apparent motion occurs only between s t i m u l i presented w i t h i n the same l i n e f i g u r e , and so i s redundant with the movement of the c a r r i e r o b j e c t s . C o n s i s t e n t with t h i s i s Shepard and Zare's (1983) demonstration of "path-guided" apparent motion. They were able to manipulate the p e r c e i v e d path of apparent motion by p l a c i n g between the two s e q u e n t i a l l y presented s t i m u l i a grey band f o r the motion to f o l l o w ; by u s i n g a c l o s e d c i r c u l a r band, they were even able to generate apparent motion of a stimulus i n t o i t s e l f . In the preview experiment with only a s i n g l e f i e l d - 1 l e t t e r , the moving frames are not completely e f f e c t i v e path guides, and sometimes apparent motion occurs between the preview and t a r g e t independently of the motion of the c a r r i e r o b j e c t s . On i n c o n s i s t e n t t r i a l s a short c i r c u i t sometimes o c c u r s : The preview i s seen to escape i t s l i n e f i g u r e and jump toward the t a r g e t l e t t e r . Consequently, i n t h i s experiment, the o b j e c t - o r g a n i z i n g f u n c t i o n of the moving frames i s v i t i a t e d by the a b i l i t y of the t a r g e t and s o l i t a r y preview to form an o b j e c t u n i t r e g a r d l e s s of whether or not they are presented w i t h i n the same l i n e f i g u r e . The o b j e c t - o r g a n i z i n g power of apparent motion was harnessed purposely in an experiment employing the Ternus d i s p l a y , which does not u t i l i z e moving l i n e f i g u r e s . In the Ternus d i s p l a y , the motion phase connecting f i e l d - 1 with 16 f i e l d - 2 i n v o l v e s only apparent movement—no r e a l displacement of the items on the screen occurs. S t i l l , the apparent motion of the Ternus d i s p l a y serves the same purpose as the combined r e a l and apparent motion of the four-box d i s p l a y : It l i n k s the t a r g e t with one, and only one, of the f i e l d - 1 s t i m u l i . The Ternus f i e l d - 1 c o n s i s t s of two l e t t e r s , one on e i t h e r s i d e of the c e n t r a l f i x a t i o n dot (see F i g u r e 2). A f t e r a c e r t a i n i n t e r v a l , these l e t t e r s are removed from the screen and a t h i r d l e t t e r , the t a r g e t , appears i n a cued l o c a t i o n e x a c t l y h a l f way between the two f i e l d - 1 s t i m u l i l o c a t i o n s . Were the d i s p l a y to c o n s i s t of j u s t these three l e t t e r s , the r e s u l t i n g sense of motion would be an ambiguous one: E i t h e r , both, or n e i t h e r of the f i e l d - 1 s t i m u l i might be p e r c e i v e d as moving i n t o the t a r g e t l o c a t i o n . Ternus (1926, c i t e d in Koffka, 1935) d i s c o v e r e d that i f one c r e a t e s the impression that the o v e r a l l g l o b a l form of a d i s p l a y i s moving i n a given d i r e c t i o n , then the apparent motions of the l o c a l c o n s t i t u e n t s of that d i s p l a y w i l l proceed i n the same d i r e c t i o n . T h i s e f f e c t i s engendered i n the Ternus preview d i s p l a y by p r e s e n t i n g another l e t t e r along with the t a r g e t in f i e l d - 2 . When t h i s f o u r t h l e t t e r i s presented to the l e f t of the three other stimulus l o c a t i o n s , the d i s p l a y appears to s h i f t to the l e f t and the right-hand f i e l d - 1 l e t t e r becomes l i n k e d with the t a r g e t by appa r e n t l y moving i n t o i t . When the f o u r t h l e t t e r i s presented to the r i g h t of the three other stimulus l o c a t i o n s , the d i s p l a y appears to s h i f t to the 17 I F i g u r e 2. The three c o n d i t i o n s of the b a s i c Ternus d i s p l a y as used by Kahneman, Treisman and Gibbs ( i n p r o g r e s s ) . (3 X a c t u a l s i z e ; hollow l e t t e r s r e f e r to the f i r s t f i e l d , dashed arrows to apparent motion, and s o l i d l e t t e r s to the second f i e l d ) . 18 r i g h t and the l e f t - h a n d f i e l d - 1 l e t t e r becomes l i n k e d with the t a r g e t by apparently moving i n t o i t . In the Ternus experiment, c o n s i s t e n t t r i a l s were responded to s i g n i f i c a n t l y more r a p i d l y than were i n c o n s i s t e n t t r i a l s . In t h i s experiment, apparent motion i s a l l that determines which l o c a t i o n i s d e f i n e d as target-yoked and which i s d e f i n e d as target-nonyoked; t h e r e f o r e , apparent motion must be r e s p o n s i b l e f o r the obtained o b j e c t e f f e c t . The i m p l i c i t assumption here i s that the o r g a n i z a t i o n of the d i s p l a y i n t o o b j e c t s i s achieved by the percept of motion. In support of t h i s , motion has been r e p o r t e d to be a f a c t o r potent i n determining the p e r c e p t u a l i n t e r p r e t a t i o n of scenes. I f l i g h t s are a t t a c h e d to the j o i n t s of a person standing i n the dark, a l l that w i l l be p e r c e i v e d i s an u n i n t e r p r e t a b l e group of dots. Within 100 ms of the i n d i v i d u a l beginning to move, however, the p a t t e r n of dots w i l l be r e c o g n i z e d as a person i n locomotion (Johansson, 1975; c f . Wallach & O'Connell's, 1953, k i n e t i c depth e f f e c t ) . Ramachandran (1981) produced a s i m i l a r r e s u l t i n v o l v i n g even more cue-impoverished d i s p l a y s i n which the apparent motion o c c u r r i n g between s e q u e n t i a l l y presented squares and t r i a n g l e s g i v e s r i s e to the impression that these geometric f i g u r e s c o n s t i t u t e a s i n g l e "walking" e n t i t y with q u a s i -independent p a r t s . He a t t r i b u t e s t o motion the p e r c e p t u a l f u n c t i o n s of a t t r a c t i n g a t t e n t i o n , of p r o v i d i n g cues to three dimensional shape, and, most important f o r the present p o i n t , of p r o v i d i n g cues to f i g u r e - g r o u n d s e g r e g a t i o n . Indeed, von 19 Fieandt and Moustgaard (1977) c o n s i d e r s t r o b o s c o p i c motion to be the p e r c e p t i o n of d i s c r e t e p r e s e n t a t i o n s as a uniform o b j e c t , and t h i s notion i s not n o v e l , f o r they c i t e Linke (1907) as an e a r l y proponent of i t . Beyond the f a c t that the Ternus d i s p l a y i s employed i n two of the t h e s i s experiments to be r e p o r t e d , the Ternus preview r e s u l t i s important i n i t s own r i g h t . The spatiotemporal i n t e g r a t i o n of i n f o r m a t i o n produced by moving l i n e f i g u r e s i s o b v i o u s l y not something p e c u l i a r to l i n e f i g u r e s themselves. I t can now more c o n f i d e n t l y be a t t r i b u t e d to c o g n i t i v e u n i t i z a t i o n o c c u r r i n g when two s t i m u l i are p e r c e p t u a l l y organized as a s i n g l e o b j e c t . Furthermore, t h i s i n t e g r a t i o n i s c l e a r l y not r e s t r i c t e d to s t i m u l i seen as s u b - s t r u c t u r e s of an obj e c t u n i t ( c f . Palmer, 1977) . The apparent motion i n the Ternus d i s p l a y takes p l a c e across a d i s t a n c e of about 45 minutes of a r c . Apparent motion ac r o s s d i s t a n c e s of 15 minutes of arc or more i s con s i d e r e d to occur r e l a t i v e l y l a t e i n p e r c e p t u a l p r o c e s s i n g , subsequent to the a n a l y s i s of form (Braddick, 1974; Ramachandran, 1981; A n s t i s , 1980). T h e r e f o r e , the o b j e c t -s p e c i f i c i n t e g r a t i o n of i n f o r m a t i o n i n the Ternus d i s p l a y i s probably not a very e a r l y event as f a r as p e r c e p t u a l p r o c e s s i n g of the t a r g e t goes. A time-course i s s u e of p a r t i c u l a r importance concerns the timing of the o b j e c t - s p e c i f i c i n t e g r a t i o n with r e s p e c t to the p r o c e s s i n g of the preview. O b t a i n i n g o b j e c t - s p e c i f i c 20 f a c i l i t a t i o n in the l a t e - c u e v e r s i o n of the triangle-and-box design suggests that the mechanism g i v i n g r i s e to such f a c i l i t a t i o n operates r e t r o a c t i v e l y from cue onset: The f i e l d - 1 s timulus i n the t a r g e t object has s p e c i a l s t a t u s , but not u n t i l the cue a p p e a r s - - i t i s only then that the t a r g e t o b j e c t i s d i s t i n g u i s h e d from the d i s t r a c t o r o b j e c t . The Ternus experiment makes the r e t r o a c t i v e nature of the object e f f e c t e s p e c i a l l y c l e a r because apparent motion i s i t s e l f a r e t r o a c t i v e phenomenon (Kahneman 1968; Kahneman & Wolman, 1970; but c f . Kahneman, 1967). Which of the two f i e l d - 1 l e t t e r s i s i n the target-yoked l o c a t i o n i s completely indeterminate u n t i l the i l l u s i o n of motion i s c r e a t e d ; and, of course, t h i s does not happen u n t i l f i e l d - 2 i s presented. A degenerate Ternus d i s p l a y was used to t e s t whether c o l o r c o n g r u i t y i s able to c o n t r o l the formation of p e r c e p t u a l o b j e c t s enough to support an o b j e c t e f f e c t . The i n d i c a t i o n s that f e a t u r e s i m i l a r i t y enhances apparent motion (Berbaum, Lenel & Rosenbaum, 1981; S q u i r e s , 1931)—though not uncontested (eg. Attneave, 1974; P e t e r s i k & P a n t l e , 1 9 7 9 ) — make t h i s a reasonable p o s s i b i l i t y . As i n the Ternus d i s p l a y , two l e t t e r s were presented i n f i e l d - 1 , and i n between them, but a f t e r t h e i r o f f s e t , a t a r g e t l e t t e r appeared in f i e l d - 2 . The f o u r t h , m o t i o n - b i a s i n g l e t t e r of the Ternus d i s p l a y was omitted. Consequently, there was no coherent apparent motion between e i t h e r one of the f i e l d - 1 s t i m u l i and the t a r g e t . C o n d i t i o n s were i n s t e a d d e f i n e d by the c o l o r r e l a t i o n s between the two stimulus f i e l d s . In the 21 c o n s i s t e n t c o n d i t i o n , the preview appeared i n the same c o l o r as the t a r g e t ; in the i n c o n s i s t e n t c o n d i t i o n i t appeared i n a d i f f e r e n t c o l o r than the t a r g e t ; i n the c o n t r o l c o n d i t i o n no preview was d i s p l a y e d . There was a l a r g e RT advantage to having a preview appear in f i e l d - 1 , but that advantage was no g r e a t e r on c o n s i s t e n t t r i a l s than on i n c o n s i s t e n t t r i a l s . C o l o r c o n g r u i t y i s not capable of supporting an o b j e c t ef f e c t . V i s u a l Search: A G e n e r a l i z a t i o n of the Object E f f e c t In a p r e v i e w - l i k e experiment i n v o l v i n g a f o u r - o b j e c t , moving-frame d i s p l a y , s u b j e c t s performed a v i s u a l search f o r the presence of a plus ("+"). Two of the f i e l d - 1 boxes co n t a i n e d a h o r i z o n t a l l i n e and two of them con t a i n e d a v e r t i c a l l i n e . T h i s was a l s o true of the f i e l d - 2 boxes except on p o s i t i v e t r i a l s , when one of them con t a i n e d a p l u s . On n e g a t i v e - p e r p e n d i c u l a r t r i a l s the l i n e s appearing w i t h i n each o b j e c t were of p e r p e n d i c u l a r o r i e n t a t i o n s , so t h a t , had they been superimposed, they would have formed a p l u s ; on n e g a t i v e - p a r a l l e l t r i a l s they were of p a r a l l e l o r i e n t a t i o n s . Although e r r o r r a t e s d i d not d i f f e r , i t took s i g n i f i c a n t l y longer f o r s u b j e c t s to respond "absent" on the n e g a t i v e -p e r p e n d i c u l a r t r i a l s than on the n e g a t i v e - p a r a l l e l t r i a l s . E v i d e n t l y , the l i n e components of a f i g u r e are s u b j e c t to o b j e c t - s p e c i f i c spatiotemporal i n t e g r a t i o n . T h i s search experiment represents an important g e n e r a l i z a t i o n of the f i n d i n g of o b j e c t - s p e c i f i c i n f o r m a t i o n i n t e g r a t i o n to a d i f f e r e n t task. In the l e t t e r reading task 22 deployment of a t t e n t i o n may be q u i t e d i f f e r e n t from that i n the search task. D e s p i t e the probable switch from focused to d i v i d e d a t t e n t i o n — w i t h the attendant changes i n i n f o r m a t i o n p r o c e s s i n g that are l i k e l y to occur--the o b j e c t - s p e c i f i c i n t e g r a t i o n r e s u l t holds up. N o t i c e , f o r example, that i n the l e t t e r reading task i t i s p o s s i b l e that s u b j e c t s focus a t t e n t i o n on one of the l i n e f i g u r e s at the time the f i e l d - 1 s t i m u l i are presented and then f o l l o w t h i s o b j e c t to i t s te r m i n a l l o c a t i o n . On i n c o n s i s t e n t t r i a l s s u b j e c t s w i l l make r e l a t i v e l y slow responses whether they s e l e c t the t a r g e t o b j e c t or the d i s t r a c t o r o b j e c t , because i n the former case t a r g e t i d e n t i t y w i l l be mis-cued, and i n the l a t t e r case t a r g e t l o c a t i o n w i l l be. On c o n s i s t e n t t r i a l s , however, su b j e c t s w i l l make r e l a t i v e l y quick responses because whenever they happen to s e l e c t the t a r g e t o b j e c t both t a r g e t i d e n t i t y and t a r g e t l o c a t i o n w i l l be v a l i d l y cued. In s h o r t , an "object e f f e c t " w i l l come about not as a consequence of spatiotemporal i n f o r m a t i o n i n t e g r a t i o n , but as a s i d e e f f e c t of the a t t e n t i o n a l s t r a t e g y used. T h i s reasoning does not allow f o r the p o s s i b i l i t y t h a t on c o n s i s t e n t t r i a l s when the subject s e l e c t s the d i s t r a c t o r box--and l o c a t i o n and i d e n t i t y are miscued--responses w i l l be slowed down d r a s t i c a l l y enough to compensate the speed of the c o n s i s t e n t t r i a l s on which the su b j e c t s e l e c t s the t a r g e t box. T h i s c o n s e r v a t i o n - o f - c o s t c o u n t e r - c r i t i c i s m n o t w i t h s t a n d i n g , the s e l e c t - a n d - f o l l o w hypothesis r i v a l to the spatiotemporal i n t e g r a t i o n view underscores the p o t e n t i a l 23 f o r confounding by s e l e c t i v e a t t e n t i o n s t r a t e g i e s . In any case, the s e l e c t - a n d - f o l l o w account simply cannot be a p p l i e d to the search experiment. The Form of Information Involved in the Object E f f e c t Of s p e c i a l s i g n i f i c a n c e to t h i s t h e s i s i s the i s s u e of what form of i n f o r m a t i o n i s being s p a t i o t e m p o r a l l y i n t e g r a t e d . The search experiment may i n v o l v e the i n t e g r a t i o n of v i s u a l i n f o r m a t i o n of a d i f f e r e n t l e v e l than t h a t i n t e g r a t e d i n the l e t t e r reading experiments. I t i s p o s s i b l e , f o r i n s t a n c e , that the i n f o r m a t i o n i n t e g r a t i o n measured with the l e t t e r reading task occurs at the l e v e l of response g e n e r a t i o n , although t h i s need not be the case. The o b j e c t - s p e c i f i c r e s u l t o b t a i n e d i n the search experiment suggests an i n t e g r a t i o n of q u i t e l i t e r a l information--perhaps even a spatiotemporal o v e r l a p p i n g of p e r c e p t s : There i s no " p l u s n e s s " i n a h o r i z o n t a l l i n e , nor i n a v e r t i c a l one, only i n the c o n j u n c t i o n of the two. I n t e r e s t i n g l y , no o b j e c t -s p e c i f i c e f f e c t was produced i n terms of e r r o r r a t e s . T h i s i m p l i e s that the moving o b j e c t s were not able to cause the s u b j e c t s to a c t u a l l y see p l u s e s . Given s i g n a l - d e t e c t i o n theory, however, perhaps the q u e s t i o n of whether s u b j e c t s ever r e a l l y saw p l u s e s i s fundamentally i n a p p r o p r i a t e . With a d i s p l a y l i k e the t r i a n g l e and box d i s p l a y , evidence f o r the o b j e c t - s p e c i f i c i n t e g r a t i o n of words was o b t a i n e d . A r e s u l t of g e n e r a l i n t e r e s t was that there was an uncommonly l a r g e amount of n o n - o b j e c t - s p e c i f i c p r i m i n g . KTG s p e c u l a t e that when a small set of s t i m u l i are used, as in 24 the l e t t e r experiments, a l l of the corresponding nodes in long-term memory are kept f a i r l y primed throughout the course of the experiment, and so there i s a c e i l i n g l i m i t i n g the r e p e t i t i o n priming that can be generated on any given t r i a l . Under these circumstances (and given an e a r l y cue or long-d u r a t i o n f i e l d - 1 s t i m u l i ) only the o b j e c t - s p e c i f i c f a c i l i t a t i o n r e v e a l s i t s e l f f u l l y and so dominates the n o n s p e c i f i c priming. When a l a r g e set of s t i m u l i are used, as i n the word experiments, b a s e l i n e priming i s i n s i g n i f i c a n t , and so r e p e t i t i o n priming i s manifest i n f u l l . Under these circumstances, an o b j e c t e f f e c t of the same abs o l u t e s i z e as before w i l l now be dominated by the n o n s p e c i f i c priming. I f v a l i d , t h i s account underscores the independence between o b j e c t - s p e c i f i c f a c i l i t a t i o n and node priming. The r e s u l t of more s p e c i f i c i n t e r e s t from the word experiment i s that an object e f f e c t o ccurred at a l l . I t took l e s s time to read a t a r g e t word that had been previewed in the same r e c t a n g l e than one that had been previewed in the other r e c t a n g l e . Although words are h i g h - l e v e l s t i m u l i in that they have semantic a t t r i b u t e s , the genera t i o n of an ob j e c t e f f e c t with words i s not i n c o n s i s t e n t with the f i n d i n g of l o w - l e v e l i n t e g r a t i o n i n the v i s u a l search experiment. The previewing of a t a r g e t word may confer an RT advantage s o l e l y through the i n t e g r a t i o n of l o w - l e v e l p e r c e p t u a l i n f o r m a t i o n , d e c r e a s i n g response l a t e n c y by i n c r e a s i n g the p e r c e p t i b i l i t y of the word. In keeping with t h i s view, when 25 a l e x i c a l d e c i s i o n task was used to t e s t f o r a t r u l y - s e m a n t i c object e f f e c t , the o n l y a s s o c i a t i v e f a c i l i t a t i o n produced was n o n - o b j e c t - s p e c i f i c . F i n a l l y , another experiment i n v e s t i g a t i n g the form of the i n f o r m a t i o n that i s s p a t i o t e m p o r a l l y i n t e g r a t e d by moving o b j e c t s a l s o supports the idea that t h i s i n f o r m a t i o n i s p e r c e p t u a l r a t h e r than c a t e g o r i c a l . The experimental d i s p l a y was very s i m i l a r to t h a t used i n the exemplary preview experiment d e s c r i b e d e a r l i e r , however the stimulus l e t t e r s c o u l d appear in e i t h e r upper or lower case ( f o r an a n a l y s i s of t h i s m a n i p u l a t i o n i n a priming paradigm, see B e l l e r , 1971). The t y p i c a l o b j e c t e f f e c t was observed when the l e t t e r s were presented i n the same case; but when they were presented i n d i f f e r e n t cases, when the t a r g e t and i t s preview--preview i n terms of name—were not p h y s i c a l l y i d e n t i c a l , the o b j e c t e f f e c t disappeared. These l a s t two experiments suggest that the i n t e g r a t i o n g i v i n g r i s e to the o b j e c t e f f e c t cannot be produced between l e x i c a l or semantic a t t r i b u t e s . The l e t t e r o b j e c t e f f e c t r e f l e c t s the s p a t i o t e m p o r a l i n t e g r a t i o n of i n f o r m a t i o n about the p h y s i c a l c h a r a c t e r i s t i c s of the l e t t e r s . Spatiotemporal i n t e g r a t i o n of p h y s i c a l i n f o r m a t i o n c e r t a i n l y seems to be o c c u r r i n g i n the v i s u a l search experiment. The experiments of the present t h e s i s f u r t h e r explore the p h y s i c a l nature of the s p a t i o t e m p o r a l i n f o r m a t i o n i n t e g r a t i o n u n d e r l y i n g the o b j e c t e f f e c t . 26 Conclusions The v a r i o u s preview experiments c o n s i s t e n t l y demonstrated spatiotemporal i n t e g r a t i o n of v i s u a l i n f o r m a t i o n . Two b a s i c q u e s t i o n s , corresponding l o o s e l y to Banks and P r i n z m e t a l ' s (1976) d i s t i n c t i o n between " p a r s i n g " and " a n a l y s i s " in p e r c e p t i o n , may be asked about KTG's spa t i o t e m p o r a l i n t e g r a t i o n . Which s t i m u l i become i n t e g r a t e d ? How i s the i n t e g r a t i o n achieved? Which S t i m u l i Become Integrated? Which s t i m u l i become i n t e g r a t e d i s determined by the f i g u r a l r e l a t i o n s between them. KTG propose that the o r g a n i z a t i o n of the scene i n t o o b j e c t s i s the c r i t i c a l f a c t o r . Those s t i m u l i comprising p a r t s of a s i n g l e object are i n t e g r a t e d , and those comprising parts of d i f f e r e n t o b j e c t s are not. Some of the d e s c r i b e d preview experiments, by o p e r a t i o n a l i z i n g o b j e c t s as moving l i n e f i g u r e s and then demonstrating o b j e c t - s p e c i f i c RT e f f e c t s , generated support f o r t h i s p r o p o s i t i o n . I t was shown that these moving l i n e f i g u r e s were not simply grouping the s t i m u l i or cueing the i c o n . Object e f f e c t s were a l s o obtained when a completely d i f f e r e n t o p e r a t i o n a l i z a t i o n i n v o l v i n g apparent motion was used to render o b j e c t s . A f u r t h e r reason f o r confidence i n the o b j e c t i n t e r p r e t a t i o n i s that an experiment fashioned a f t e r the KTG s t u d i e s compared moving with nonmoving l i n e f i g u r e s and found that o b j e c t - s p e c i f i c e f f e c t s disappeared when the t a r g e t and preview were not presented w i t h i n the same o b j e c t even though they were s t i l l s i n g l e d out by the 27 l i n e f i g u r e s that framed them. C o n s i s t e n t L i t e r a t u r e . The p l a u s i b i l i t y of the object i n t e r p r e t a t i o n i s enhanced by the e x i s t e n c e of work suppor t i n g the general c o n t e n t i o n that o r g a n i z a t i o n of the f i e l d i n t o p e r c e p t u a l u n i t s can have e f f e c t s on subsequent i n f o r m a t i o n p r o c e s s i n g . Although Treisman (1982) argues a g a i n s t the p r e a t t e n t i v e establishment of g l o b a l o r g a n i z a t i o n in v i s i o n , she allows f o r the p o s s i b i l i t y that the whole precedes i t s p a r t s in the sense that there i s an e a r l y , i n t r a - d i m e n s i o n p a r s i n g of the scene i n t o p o t e n t i a l o b j e c t s . E a r l y g l o b a l groups that are formed d e l i n e a t e the information to be i n t e r p r e t e d as belonging to a s i n g l e r e a l - w o r l d o b j e c t , and they " f u n c t i o n as p l a c e - h o l d e r s to which the r e s u l t s of f u r t h e r p r o c e s s i n g can be added" (Treisman, 1985). In Kahneman's (1973) model of p e r c e p t i o n , the f i e l d i s p a r t i t i o n e d i n t o p e r c e p t u a l u n i t s at an e a r l y " u n i t formation" stage coming immediately a f t e r sensory r e g i s t r a t i o n and storage, and immediately before an a t t e n t i o n a l l o c a t i o n stage termed " f i g u r a l emphasis". These p e r c e p t u a l u n i t s are formed ac c o r d i n g to the G e s t a l t laws of grouping, and are h i g h l y c o r r e l a t e d with the d i v i s i o n of p h y s i c a l space i n t o o b j e c t s . Subsequent i n f o r m a t i o n p r o c e s s i n g — n o t a b l y f i g u r a l emphasis--is i n f l u e n c e d by the outcome of the u n i t formation p r o c e s s . Kahneman's (1973) message i s echoed by E r i k s e n and Hoffman (1973). They suggest that " v i s u a l p e r c e p t i o n i s b a s i c a l l y o b j e c t o r i e n t e d and, when a new stimulus appears in the v i s u a l f i e l d , a c e r t a i n l e v e l of 28 gross p r o c e s s i n g and s t r u c t u r i n g of the s t i m u l a t i o n i s a p r e r e q u i s i t e to more c a r e f u l s e l e c t i v e p r o c e s s i n g of d e t a i l e d f e a t u r e s of the s t i m u l a t i o n . " (p. 159) An a n a l y s i s of v i s u a l masking provided by Kahneman (1968) makes apparent the importance of u n i t i z a t i o n in p e r c e p t i o n . He w r i t e s , " P e r c e p t i o n lags a f t e r s t i m u l a t i o n and. i n t e g r a t e s s u c c e s s i v e s t i m u l i i n t o composite chunks, or moments...in which some elements may be o b l i t e r a t e d and others a l t e r e d . " (p.421) In a treatment of masking that f o l l o w s Kahneman's in some important r e s p e c t s , Marcel (1983b, 1983a) d e s c r i b e s masking as a f a i l u r e of the t a r g e t to achieve " f i g u r a l s t a t u s " (see Fowler, Wolford, Slade & T a s s i n a r y , 1981). Although h i s emphasis i s c l e a r l y on the conscious recovery of p e r c e p t u a l i n f o r m a t i o n , Marcel c o u l d be commenting on the preview d i s p l a y s when he w r i t e s : Provided that element subsets are not too separated by f a c t o r s such as time or space, then i f elements from two o b j e c t i v e l y separate event s e t s can be fused to produce a f i g u r e which i t s e l f p r o v i d e s a more economical, expected, or h i g h - l e v e l s t r u c t u r a l d e s c r i p t i o n than e i t h e r of the two o b j e c t i v e element s e t s , then that may outweigh p h y s i c a l f a c t o r s to achieve f i g u r a l s t a t u s , l e a v i n g the other elements as ground, and thus unrecovered. (p. 265-266) • Banks and Pr i n z m e t a l (1976) measured p e r c e p t u a l grouping by g i v i n g s u b j e c t s p i c t u r e s of v i s u a l d i s p l a y s and asking 29 them to draw boundaries around the groups pres e n t . Using the number of boundaries between two s t i m u l i as an independent v a r i a b l e indexing the p e r c e p t u a l i s o l a t i o n , of the s t i m u l i , Banks and Prinzmetal found that i n a f o r c e d c h o i c e v i s u a l d e t e c t i o n task, the more the t a r g e t was grouped with noise s t i m u l i the g r e a t e r was the i n t e r f e r e n c e produced by these d i s t r a c t o r s . In r e l a t e d work, Kahneman and Henik (1981, 1977) t e s t e d the hypothesis that a t t e n t i o n a c t s on p e r c e p t u a l u n i t s — o r o b j e c t s — e s t a b l i s h e d by e a r l y p r o c e s s i n g . They found grouping e f f e c t s i n experiments i n v o l v i n g f i l t e r i n g , v i s u a l search, immediate r e c a l l , and the Stroop t a s k . A p a r t i c u l a r l y s t r i k i n g demonstration concerned the s u f f i x e f f e c t , the i n t e r f e r e n c e produced by p r e s e n t i n g an i r r e l e v a n t item at the end of a l i s t of a u d i t o r y or v i s u a l items to be r e c a l l e d . T h i s i n t e r f e r e n c e was reduced by having the s u f f i x grouped apart from t h e . r e l e v a n t items, in a separate p e r c e p t u a l u n i t . An i n f o r m a t i o n p r o c e s s i n g task that h i g h l i g h t s the importance of o b j e c t s i s v i s u a l f i l t e r i n g . Kahneman, Treisman and B u r k e l l (1983) demonstrate that c h o i c e response i n the presence of d i s t r a c t o r s i n v o l v e s i n t e r f e r e n c e , or " f i l t e r i n g c o s t " . I r r e l e v a n t o b j e c t s and events d i s r u p t the deployment of a t t e n t i o n even when the task i s the a l l e g e d l y -automatic, node-mediated one of reading a s i n g l e word. This f i n d i n g i s c o n s i s t e n t with a s p a t i a l conception of a t t e n t i o n emphasizing the s e l e c t i o n of o b j e c t s and events. Treisman, Kahneman and B u r k e l l (1983) found that when a word and a 30 d i s t r a c t o r frame were i n t e g r a t e d as one group, f i l t e r i n g c o s t was reduced. Both the word and the frame were processed more e f f e c t i v e l y when they were d i s p l a y e d as a s i n g l e p e r c e p t u a l u n i t . These authors s t a t e , "The o b j e c t s of a t t e n t i o n are d e f i n e d by p e r c e p t u a l grouping, not j u s t by s p a t i a l d i s t a n c e . The g r a d i e n t of i n t e r f e r e n c e i s d e f i n e d not i n r e t i n a l d i s t a n c e but i n 'belongingness'." (p. 530) C o n s i s t e n t with the success of the p a r t i c u l a r o b j e c t m anipulation used in the preview r e s e a r c h i s Pomerantz's (1981) o b s e r v a t i o n that grouping, or "the p e r c e p t u a l l i n k i n g of r e g i o n s i n t o u n i f i e d o b j e c t s and s u r f a c e s " (p. 143), can be achieved not only by l o c a l f a c t o r s such as p r o x i m i t y and s i m i l a r i t y , but a l s o by g l o b a l f a c t o r s concerning other elements in the f i e l d . I m p l i c a t i o n s . The f i n d i n g that i t i s the s t i m u l i comprising a s i n g l e object that become i n t e g r a t e d has two major i m p l i c a t i o n s . F i r s t , t h i s o b j e c t - s p e c i f i c i t y of f a c i l i t a t i o n i s i n c o n s i s t e n t with the usual accounts of priming e f f e c t s : I t cannot be accommodated by what has been c a l l e d the " d i s p l a y board model of mind" (Kahneman & Treisman, 1984), nor by r e l a t e d a l t e r n a t i v e s (eg. R a t c l i f f & McKoon, 1981). D i s p l a y board models can e a s i l y represent standard, n o n - o b j e c t - s p e c i f i c f a c i l i t a t i o n as p r e - a c t i v a t i o n in a more or l e s s permanent network of concept nodes or "logogens" ( C o l l i n s & L o f t u s , 1975; Morton, 1969). The logogen system, however, does not i n c l u d e temporary s t r u c t u r e s denoting f i g u r a l r e l a t i o n s between s t i m u l i d u r i n g p a r t i c u l a r p e r c e p t u a l episodes (nb. T u l v i n g , 1972, on 31 semantic memory). Morton (1969) e x p l i c i t l y s t a t e s that logogens simply count a t t r i b u t e s - - t h e o r i g i n s of those a t t r i b u t e s are considered i r r e l e v a n t . With respect to the f i e l d - 1 l e t t e r s of the preview paradigm, then, a d i s p l a y board should be completely e g a l i t a r i a n : A preview should be an e q u a l l y potent prime whichever l i n e f i g u r e happens to surround i t . Second, a more ba s i c c o n c l u s i o n to be drawn from the o b j e c t - s p e c i f i c i t y of f a c i l i t a t i o n generated in the preview paradigm i s that c o g n i t i v e o r g a n i z a t i o n can r e f l e c t p e r c e p t u a l o r g a n i z a t i o n . The p e r c e p t u a l h i s t o r y of an o b j e c t i n t e r a c t s with the c o g n i t i v e p r o c e s s i n g of that o b j e c t . The importance of o b j e c t s in p e r c e p t u a l o r g a n i z a t i o n has been recognized s i n c e the time of the G e s t a l t p s y c h o l o g i s t s (Koffka, 1935; Kohler, 1 9 6 9 ) . I t now seems prudent to co n s i d e r o b j e c t s , and t h e i r v i s u a l h i s t o r i e s , when c o n c e p t u a l i z i n g stimulus i n t e r a c t i o n s in c o g n i t i v e p r o c e s s i n g as w e l l . T h i s i m p l i c a t i o n of the preview rese a r c h f i t s w e l l i n t o a context of other research suggesting that there can be a c l o s e r e l a t i o n between p e r c e p t i o n and c o g n i t i o n . Ramachandran (1981) s p e c u l a t e s that p e r c e p t i o n i s i n t e l l i g e n t ( c f . Gregory, 1980) not because i n f e r e n t i a l c o g n i t i v e f u n c t i o n s guide p e r c e p t i o n , but r a t h e r because these so-c a l l e d higher c o g n i t i v e f u n c t i o n s , i n c l u d i n g reasoning, are r e a l l y j u s t e l a b o r a t i o n s of l o w - l e v e l o p e r a t i o n s l i k e p e r c e p t i o n . On a l e s s extreme note, Shepard and Podgorny 32 (1978) review a number of paradigms that r e v e a l p a r a l l e l s between pe r c e p t u a l and c o g n i t i v e p r o c e s s i n g . In a d i s c u s s i o n of Shepard's own mental r o t a t i o n paradigm (Shepard & Metz l e r , 1971; but see Y u i l l e & S t e i g e r , 1982) the i n t e r e s t i n g p o s s i b i l i t y i s r a i s e d that the r e p r e s e n t a t i o n s u n d e r l y i n g mental r o t a t i o n and apparent motion are one and the same. The two general c o n c l u s i o n s drawn by Shepard and Podgorny (1978) are that advances in our understanding of p e r c e p t i o n w i l l a l s o be advances i n our understanding of at l e a s t some aspects of c o g n i t i o n , and that we should be s u s p i c i o u s of any comprehensive theory of c o g n i t i v e p r o c e s s i n g t h a t i s not connected to a p l a u s i b l e theory of p e r c e p t i o n . A strong connection between p e r c e p t i o n and c o g n i t i o n , and one of relevance to the v i s u a l h i s t o r y e f f e c t of the preview paradigm, i s the concept of memory. T h e o r e t i c a l l y , i t would make sense f o r there to be c o n s i s t e n c y between the s t r u c t u r e of pe r c e p t i o n and the s t r u c t u r e of at l e a s t the component of memory that s t o r e s p e r c e p t u a l e p i s o d e s . In d i s t i n g u i s h i n g e p i s o d i c from semantic memory, T u l v i n g (1972; Neely, 1977) d e s c r i b e s the former as the storage of events in terms of p e r c e p t i b l e p r o p e r t i e s and a t t r i b u t e s . E p i s o d i c memory i s a "more or l e s s f a i t h f u l r e c o r d of tem p o r a l l y organized p e r c e p t u a l episodes" (p. 398), and i t s o r g a n i z a t i o n probably mimics the o r g a n i z a t i o n of the i n i t i a l percept ( T u l v i n g , 1972). McKoon and R a t c l i f f (1979), a r g u i n g against T u l v i n g ' s episodic-semantic d i s t i n c t i o n , go f a r t h e r and contend that spatiotemporal r e l a t i o n s are important even i n 33 tasks u s i n g semantic i n f o r m a t i o n . Treisman (1979) p o i n t s out that the s u f f i x e f f e c t i s an example of convergence between p e r c e p t i o n and memory because i t demonstrates that p h y s i c a l grouping i n the percept can a f f e c t the way items in s h o r t -term memory are "packaged" and r e t r i e v e d (Kahneman & Henik, 1981, 1977). Johansson (1979, 1983) recommends the study of events (eg. s t r o b o s c o p i c motion) as the a p p r o p r i a t e endeavor f o r p e r c e p t i o n r e s e a r c h e r s . Event p e r c e p t i o n i s the p e r c e p t i o n of any change in q u a n t i t y , q u a l i t y or p o s i t i o n , over a given time i n t e r v a l . Construed t h i s way, with change as a primary stimulus dimension, p e r c e p t i o n jjs a form of memory, and s p a t i a l i n f o r m a t i o n i s c o n s i d e r e d to have a temporal ex t e n s i o n . The p e r c e p t u a l act i s not c o n s i d e r e d to be punctuated on the time dimension ( a l s o E r i k s e n & S c h u l t z , 1978). Johansson (1979) o f f e r s as an i l l u s t r a t i o n the hallowed demonstration of an o b j e c t moving q u i c k l y enough in a c i r c u i t to give r i s e to the p e r c e p t i o n of i t s motion path. "Such demonstrations can show that w i t h i n a c e r t a i n span of angular v e l o c i t i e s , simple p h y s i c a l motions evoke a u n i t a r y e x p e r i e n c e . T h i s i s an argument for s a y i n g that we experience c o n s e r v a t i o n of s p a t i a l i nformation over time as a s i n g l e p e r c e p t u a l act and that p e r c e p t i o n i n f a c t i s 'remembering' as w e l l as ' r e c o r d i n g ' . " (p. 98) A p a r t i c u l a r l y i n t e r e s t i n g t h e o r e t i c a l consequence of studying the p e r c e p t i o n of change i s that a p r e v i o u s stimulus 34 and a subsequent stimulus might be thought of as a s i n g l e stimulus (Gibson, 1959), which i s c o n s i s t e n t with the n o t i o n that an o b j e c t ' s v i s u a l h i s t o r y may have c o g n i t i v e consequences. How Is the I n t e g r a t i o n Achieved? That the documented spatiotemporal i n t e g r a t i o n of i n f o r m a t i o n i n v o l v e s p e r c e p t u a l o b j e c t s i n a c e n t r a l r o l e , f o l l o w s e a s i l y from the data and i s c o n s i s t e n t with the l i t e r a t u r e . E x a c t l y how t h i s i n t e g r a t i o n i s achieved i s not as e v i d e n t , although some f a c t s about the mechanism r e s p o n s i b l e were uncovered. As d i s c u s s e d , the i n t e g r a t i o n appears to take a c e r t a i n f i n i t e time; the i n t e g r a t i o n occurs between a t a r g e t and i t s most recent predecessor in the same o b j e c t ; the i n t e g r a t i o n mechanism seems not to operate when s e l e c t i v e a t t e n t i o n has been focused on a d i f f e r e n t o b j e c t , though t h i s c o n c l u s i o n depends on the way a t t e n t i o n i s e x p e r i m e n t a l l y manipulated. F i n a l l y , the s e l e c t i o n of the stimulus to be i n t e g r a t e d with the t a r g e t i s r e t r o a c t i v e , o c c u r r i n g only once the t a r g e t has been presented. Object F i l e s . A p l a u s i b l e d e s c r i p t i v e account of o b j e c t - s p e c i f i c spatiotemporal i n f o r m a t i o n i n t e g r a t i o n i n v o l v e s the o b j e c t f i l e idea mentioned at the beginning of t h i s t h e s i s (Kahneman & Treisman, 1984; Kahneman & Henik, 1981). The o b j e c t f i l e , e s t a b l i s h e d a c c o r d i n g t o . s p a t i o t e m p o r a l c o n t i n u i t y i n the f i e l d ( c f . Treisman, 1985), i s the c o g n i t i v e c o u n t e r p a r t of a p e r c e p t u a l o b j e c t . I t i s a temporary e p i s o d i c r e p r e s e n t a t i o n i n t o which the i n f o r m a t i o n 35 accumulating about a p a r t i c u l a r o b j e c t i s entered, and i t i s what g i v e s o b j e c t s t h e i r p e r c e p t u a l u n i t y and coherence. Because an object f i l e i s a u n i t of information d e f i n e d p s y c h o l o g i c a l l y as opposed to c o n v e n t i o n a l l y , i t might be a l s o thought of as a p e r c e p t u a l "chunk" (Simon, 1974; Kahneman, 1968 and Marcel, 1983b). The i n f o r m a t i o n that i s entered i n an object f i l e i s i n i t i a l l y sensory, but may u l t i m a t e l y i nclude conceptual input from long-term memory, such as semantic l a b e l s f o r the o b j e c t , and responses that are a p p r o p r i a t e l y made to i t . F i l e d i n f o r m a t i o n i s c o n t i n u a l l y subject to updating, and although some rec o r d of the o b j e c t ' s h i s t o r y may be kept, none of the e n t r i e s need remain co n s t a n t . Rather, i t i s the c o n t i n u i t y of the f i l e i t s e l f that gives the corresponding object i t s p e r c e p t u a l i d e n t i t y . Given that the phenomenal world c o n s i s t s of coherent o b j e c t s and events, the o b j e c t f i l e metaphor makes good sense, q u i t e n a t u r a l l y accounting f o r the o r d e r l y c o l l a t i o n of i n f o r m a t i o n a s s o c i a t e d with d i f f e r e n t o b j e c t s . I t a l s o s u c c e s s f u l l y accommodates a number of experimental r e s u l t s (Kahneman & Treisman, 1984). The r e s u l t i n f i l t e r i n g paradigms that s e l e c t i o n by s t i m u l u s set i s more e f f i c i e n t than s e l e c t i o n by response s e t , might ob t a i n because of the r e l a t i v e l y l a t e entry of semantic inf o r m a t i o n i n t o the o b j e c t f i l e . In a d d i t i o n , the "heading" of the f i l e i s c o n s t r u e d to be the o b j e c t ' s s p a t i a l and temporal c o o r d i n a t e s , and so these and other such sensory a t t r i b u t e s would n a t u r a l l y be 36 the most e f f i c i e n t e n t r i e s by which to s e l e c t the f i l e . The s e v e r i t y of Stroop i n t e r f e r e n c e , and the f a c i l i t y with which a t t e n t i o n can be d i v i d e d between the p a r t s of a s i n g l e o b j e c t but not between d i f f e r e n t o b j e c t s (Treisman, Kahneman & B u r k e l l , 1983; Duncan, 1984), f o l l o w s from the simple assumption t h a t a t t e n t i o n operates on o b j e c t f i l e s as u n i t s ( c f . Kahneman & Chajczyk, 1983). I l l u s o r y c o n j u n c t i o n s (Treisman & Schmidt, 1982; Treisman & Gelade, 1980) are q u i t e e l e g a n t l y modelled as m i s f i l i n g s of f e a t u r e s due to time or resource l i m i t a t i o n s . The o b j e c t f i l e concept may even a f f o r d a middle ground where the e a r l y and l a t e s e l e c t i o n camps can meet: S e l e c t i o n c o u l d be e a r l y i n that i t i s c o n t r o l l e d only by p h y s i c a l f e a t u r e s ; s e l e c t i o n c o u l d be l a t e i n that i t a f f e c t s only the output from the f i l e , l e a v i n g the b u i l d u p of i n f o r m a t i o n to occur p r e a t t e n t i v e l y . For present purposes, the object f i l e c o n c e p t u a l i z a t i o n i s a p p o s i t e f o r the very reasons the d i s p l a y board c o n c e p t u a l i z a t i o n was not. Object f i l e s are separate from the s t r u c t u r e of semantic memory, and are not at a l l l i k e i n v a r i a n t pathways (Posner, 1978). They are f l e x i b l e and o b j e c t - o r i e n t e d whereas a network of nodes i s r i g i d and c o n c e p t - o r i e n t e d . O b j e c t - s p e c i f i c RT e f f e c t s are not s u r p r i s i n g w i t h i n the o b j e c t f i l e framework. I t seems reasonable ( a l b e i t not l o g i c a l l y necessary) that there would be g r e a t e r i n t e r a c t i o n between p i e c e s of i n f o r m a t i o n c o n t a i n e d w i t h i n the same o r g a n i z a t i o n a l r e p r e s e n t a t i o n than between those c o n t a i n e d i n d i f f e r e n t r e p r e s e n t a t i o n s . For 37 example, one of the many p o s s i b l e reasons f o r the e x i s t e n c e of a p r o c e s s i n g contingency might be that more resources are r e q u i r e d to change an entry to a new value (eg. A to B) than to r e g i s t e r a lack of change (eg. A to A), Re-Viewing. Although the object f i l e f o r m u l a t i o n p r o v i d e s a s a t i s f a c t o r y d e s c r i p t i o n of the o b j e c t e f f e c t at one l e v e l , an e l a b o r a t i o n can be added that accounts f o r the r e t r o a c t i v i t y of the e f f e c t . KTG d e s c r i b e the process of i n t e r a c t i o n between a t a r g e t and preview w i t h i n the same o b j e c t f i l e as re-viewing. The p r o c e s s i n g of a stimulus w i l l cause the p a r t i a l r e - p r o c e s s i n g of a p r e v i o u s , r e l e v a n t s t i m u l u s . One way--perhaps the most important way—a p r e v i o u s stimulus can be r e l e v a n t , i s by belonging to the same o b j e c t as the c u r r e n t s t i m u l u s . In other words, r e -viewing occurs p r e f e r e n t i a l l y w i t h i n as opposed to between o b j e c t f i l e s . When the t a r g e t l e t t e r and the p r e v i o u s l e t t e r evoked by the t a r g e t are the same, the i n f o r m a t i o n a l redundancy f a c i l i t a t e s p r o c e s s i n g of the c u r r e n t l e t t e r ( c f . Garner, 1974). T h i s process may resemble M c C l e l l a n d and Rumelhart's (1981) i n t e r a c t i v e a c t i v a t i o n p r o c e s s , but i n s t e a d of info r m a t i o n cascading between higher and lower co n c e p t u a l l e v e l s , i t may cascade between a c u r r e n t and p r e v i o u s stimulus i n the o b j e c t f i l e . In s h o r t , the o b j e c t e f f e c t may be a case of o b j e c t - s p e c i f i c r e - v i e w i n g . Re-viewing does not stand alone as an example of r e t r o a c t i v e i n f o r m a t i o n p r o c e s s i n g . S e v e r a l recent treatments of p e r c e p t u a l - c o g n i t i v e i n f o r m a t i o n r e f e r e n c e 38 mechanisms have emphasized the backward a c c e s s i n g of in f o r m a t i o n ( F e u s t e l , S h i f f r i n & Salasoo, 1983; K o r i a t , 1981; Jacoby & Brooks, in pr e s s ; Kahneman & M i l l e r , i n p r e s s ) . F e u s t e l , S h i f f r i n & Salasoo (1983) propose a model of stimulus r e p e t i t i o n e f f e c t s that i n v o l v e s the recruitment of images from e p i s o d i c memory. T h e i r model i s based on word i d e n t i f i c a t i o n experiments suggesting there i s no s t r u c t u r a l d i s t i n c t i o n between e p i s o d i c and semantic memory. The f a c i l i t a t i o n of word i d e n t i f i c a t i o n performance that r e s u l t s when a word i s repeated, i s u s u a l l y c o n s i d e r e d to be a semantic or l e x i c a l e f f e c t (eg. Morton, 1969). However, F e u s t e l et a l . (1983) obtained the r e p e t i t i o n e f f e c t even with nonwords. They i n t e r p r e t t h i s and other f i n d i n g s to be evidence that the r e p e t i t i o n e f f e c t i n word i d e n t i f i c a t i o n depends upon memory f o r i n d i v i d u a l episodes. Word i d e n t i f i c a t i o n i s modeled by these re s e a r c h e r s as a h i e r a r c h i c a l i n t e r a c t i v e process l i k e that proposed by M c C l e l l a n d and Rumelhart (1981). A c t i v a t i o n spreads i n both d i r e c t i o n s across p r o c e s s i n g l e v e l s . The c r i t i c a l a s s e r t i o n of F e u s t e l et a l . ' s (1983) model i s t h a t , as the word i d e n t i f i c a t i o n process progresses, i t r e c r u i t s from memory not only l e x i c a l / s e m a n t i c i n f o r m a t i o n but a l s o temporal-c o n t e x t u a l episodes, or " e p i s o d i c images". The s t o r e d m a t e r i a l i s r e c r u i t e d or a c t i v a t e d a c c o r d i n g to the extent to which i t i s a s s o c i a t e d with the t a r g e t stimulus and c o n t e x t . A c t i v a t i o n i n the e p i s o d i c images and semantic u n i t s spreads back to the p e r c e p t u a l l e v e l and i n c r e a s e s the e x c i t a t i o n of 39 c o n s i s t e n t f e a t u r e d e t e c t o r s , thereby speeding the p e r c e p t u a l a n a l y s i s of the t a r g e t word. Thus, the r e p e t i t i o n of a stimulus f a c i l i t a t e s p r o c e s s i n g because of the recruitment of e p i s o d i c images; i f the stimulus happens to be a word, then there w i l l be an a d d i t i o n a l advantage of semantic a s s o c i a t i o n . Combining F e u s t e l et a l . ' s (1983) framework with T u l v i n g ' s (1972) a s s e r t i o n that e p i s o d i c i n f o r m a t i o n i s organized along the l i n e s of p e r c e p t i o n leads to the i m p l i c a t i o n t h a t the r e p e t i t i o n e f f e c t may be su b j e c t to i n f l u e n c e by p e r c e p t u a l o r g a n i z a t i o n . Perhaps which e p i s o d i c images are r e c r u i t e d d u r i n g the p r o c e s s i n g of a t a r g e t p a r t l y depends on t h e i r r o l e s in the v i s u a l h i s t o r y of that t a r g e t . K o r i a t (1981) presents evidence of priming by backward a s s o c i a t e s (Rouse and V e r i n i s , 1962; c f . Kiger & G l a s s , 1983), which are words having a u n i d i r e c t i o n a l a s s o c i a t i v e r e l a t i o n that connects the t a r g e t word to the prime but not v i c e v e r s a . For example, a c c o r d i n g to word a s s o c i a t i o n norms, board i s a much stronger a s s o c i a t e of black than black i s of board, so f o r board to prime black would c o n s t i t u t e backward priming. Using a l e x i c a l d e c i s i o n task, K o r i a t (1981) found priming with backward a s s o c i a t e s to be j u s t as st r o n g as priming with forward a s s o c i a t e s . He p o i n t s out the i n c o n s i s t e n c y of t h i s r e s u l t with spreading a c t i v a t i o n theory ( C o l l i n s & L o f t u s , 1975) and d i s c u s s e s two a l t e r n a t i v e s c o n s i s t e n t with backward priming. One p o s s i b i l i t y i s that the priming r e l a t i o n between the t a r g e t and prime i s not indexed by i t s a s s o c i a t i v e r e l a t i o n , and i s 40 in f a c t symmetric. Meyer & Schvaneveldt's (1971) l o c a t i o n s h i f t h y p o thesis r e p r e s e n t s such symmetry because the d i s t a n c e between two attended l o c a t i o n s i n LTM i s the same going i n e i t h e r d i r e c t i o n . The other p o s s i b i l i t y i s that d i f f e r e n t processes give r i s e to the forward and backward a s s o c i a t i o n e f f e c t s . T h i s approach i s s i m i l a r to that taken by Rouse and V e r i n i s (1962); the important d i f f e r e n c e , however, i s that i n K o r i a t ' s (1981) "double-take h y p o t h e s i s " the process u n d e r l y i n g the backward e f f e c t i s genuinely r e t r o a c t i v e . In the double-take f o r m u l a t i o n there i s an a t t e n t i o n a l and an automatic mechanism u n d e r l y i n g context e f f e c t s in l e x i c a l d e c i s i o n (Posner & Snyder, 1975b). The a t t e n t i o n a l mechanism g i v e s r i s e to forward a s s o c i a t i v e p r i m i n g . It i n v o l v e s the a n t i c i p a t i o n of t a r g e t s r e l a t e d to the prime ( c f . Becker, 1980). The automatic mechanism giv e s r i s e to backward a s s o c i a t i v e p r i m i n g . I t i n v o l v e s the r e a c t i v a t i o n of primes r e l a t e d to the t a r g e t . With respect to t h i s r e t r o a c t i v e e f f e c t the two r e q u i s i t e assumptions are (a) that beyond the simple encoding of the t a r g e t i n l e x i c a l d e c i s i o n , there i s a f u r t h e r o p e r a t i o n s u s c e p t i b l e to context e f f e c t s , and (b) that the proposed r e a c t i v a t i o n begins before the t a r g e t i s f u l l y processed and that i t i s able to occur i n p a r a l l e l with t a r g e t p r o c e s s i n g . Although forward e x p e c t a t i o n a f f e c t s the e a r l y stages of t a r g e t encoding, backward r e a c t i v a t i o n can only take p l a c e a f t e r the d i s p l a y and p a r t i a l p r o c e s s i n g of the t a r g e t . 4 1 Along with the major c o n c l u s i o n of K o r i a t ' s (1981) study there are s e v e r a l other i n t e r e s t i n g i m p l i c a t i o n s . The double-take hypothesis suggests that there are two types of p r i m e - t a r g e t r e l a t i o n . P e r t i n e n t to e a r l y encoding i s the a p r i o r i r e l a t e d n e s s of words, or the degree to which an unseen t a r g e t can be p r e d i c t e d on the b a s i s of a prime. T h i s r e l a t i o n i s what i s captured by word a s s o c i a t i o n norms. P e r t i n e n t to l a t e r encoding and t e s t i n g o p e r a t i o n s i s the a p o s t e r i o r i r e l a t e d n e s s of words. T h i s r e l a t i o n i s what would be captured by asking s u b j e c t s to judge the i n t e n s i v e r e l a t i o n between a prime and t a r g e t word when both are p r e s e n t . Other a s s o c i a t e s i n f l u e n c e the degree of a p r i o r i r e l a t e d n e s s of the words but are completely i r r e l e v a n t to the degree of a p o s t e r i o r i r e l a t e d n e s s . That i s , the l i k e l i h o o d of one word being generated as an a s s o c i a t e of a second word w i l l depend on the a v a i l a b i l i t y of other a s s o c i a t e s , but once both words are present, the a s s o c i a t e s that might have been generated i n response to a given word—even b e t t e r associates--seem to be ignored. K o r i a t notes that t h i s may be analogous to the d i s r e g a r d of base-rate i n f o r m a t i o n i n p r o b a b i l i t y judgments; i t i s a l s o reminiscent of the h i n d s i g h t e f f e c t , i n which an outcome, once i t i s known, i s judged to be a more probable consequent of a given event than i t i s when only the i n i t i a l event i s known ( F i s c h h o f f , 1982). K o r i a t (1981) l i s t s f i v e hypotheses concerning the a s s o c i a t i o n e f f e c t i n l e x i c a l d e c i s i o n that f o l l o w from h i s f o r m u l a t i o n . (a) The c r i t i c a l word r e l a t i o n s w i l l be 42 d i f f e r e n t f o r the forward and the backward processes. (b) I n h i b i t i o n should be obtained only as a forward e f f e c t , and (c) forward e f f e c t s should be produced only by primes that p r e d i c t the t a r g e t with high v a l i d i t y . (d) Backward e f f e c t s should operate independently of a t t e n t i o n . (e) Because backward e f f e c t s are generated a f t e r the i n i t i a l r e c o g n i t i o n of the t a r g e t , v i s u a l q u a l i t y of the t a r g e t should have l e s s of an i n f l u e n c e on backward context e f f e c t s than on forward context e f f e c t s . R e t r o a c t i v e models have an economy that comes with backward a c c e s s i n g . The p o t e n t i a l f o r c o m b i n a t o r i a l e x p l o s i o n that faces a forward, expectancy-type process i s not a problem for a backward process, which only needs to access i n f o r m a t i o n that i n f a c t turns out to be r e l e v a n t . S p e c i f i c a l l y , re-viewing seems w e l l s u i t e d as a process e x p l a n a t i o n of the o b j e c t e f f e c t . In the preview paradigm, besides any n o n - o b j e c t - s p e c i f i c priming, there i s o b j e c t -s p e c i f i c f a c i l i t a t i o n , as i f the t a r g e t i s able to evoke i t s own prime. Only the most recent f i e l d - 1 stimulus presented i n the t a r g e t o b j e c t shows the o b j e c t e f f e c t , p o s s i b l y because the p e r c e p t u a l re-viewing mechanism only a c t s between a stimulus and a s i n g l e predecessor. T h i s recency e f f e c t i s perhaps l e s s n a t u r a l on the view that forward accumulation i n o b j e c t f i l e s alone i s important. Is i t p l a u s i b l e t h a t , w i t h i n a r e p r e s e n t a t i o n designed f o r the on-going accumulation of i n f o r m a t i o n , a l l e n t r i e s but the s i n g l e most recent one would be i n e r t ? No doubt f o r m a l l y a l l the r e s u l t s 43 that can be e x p l a i n e d by re-viewing can a l s o be d e a l t with by ob j e c t f i l e s a lone. But p a r t i c u l a r l y i n l i g h t of the r e s u l t s obtained with the Ternus apparent motion experiment, the r e -viewing idea a p t l y r e f l e c t s the r e t r o a c t i v e c h a r a c t e r of the ob j e c t e f f e c t . Conceptual Issues Now that the e m p i r i c a l o r i g i n of the work presented i n t h i s t h e s i s has been d i s c u s s e d , i t i s a p p r o p r i a t e before p r e s e n t i n g the t h e s i s experiments themselves to deal with a few c e n t r a l i s s u e s i n a more c o n c e p t u a l way. These i s s u e s are best viewed i n context by r e t r a c i n g the i n f e r e n t i a l s t r u c t u r e of the preview paradigm. The b a s i s f o r the i n f e r e n c e s of the preview paradigm i s a r a t h e r simple f i n d i n g . On average, time taken to name a t a r g e t l e t t e r which appears i n a moving l i n e f i g u r e i s l e s s i f the t a r g e t i s previewed i n that same l i n e f i g u r e than i f i t i s previewed i n another l i n e f i g u r e . That i s , f a c i l i t a t i o n of RT i s g r e a t e r f o r l e t t e r r e p e t i t i o n s w i t h i n a l i n e f i g u r e than i t i s f o r r e p e t i t i o n s between l i n e f i g u r e s . T h i s i s a f a c t , demonstrated i n a l a r g e number of preview experiments. T h i s f a c t takes on g r e a t e r importance as soon as i t i s coupled with the obj e c t assumption, that each moving l i n e f i g u r e and i t s contents re p r e s e n t s an o b j e c t i n a p s y c h o l o g i c a l l y r e a l way. Such an assumption has s t r o n g i n t u i t i v e appeal, but i t i s an assumption nonetheless. Although l i n e f i g u r e s have been c o n s i d e r e d v a l i d o b j e c t 44 d e l i m i t e r s i n other r e s e a r c h (Treisman, Kahneman & B u r k e l l , 1983), i t i s p o s s i b l e that such l i n e f i g u r e s and any items d i s p l a y e d w i t h i n them are not a l l p e r c e i v e d as a s i n g l e o b j e c t (Duncan, 1984). One reason the obj e c t assumption seems reasonable in the preview paradigm i s that another experimental i n s t a n t i a t i o n of 'object' not i n v o l v i n g moving l i n e f i g u r e s produced the same s o r t of RT e f f e c t s as those produced by the l i n e f i g u r e s . F o l l o w i n g immediately from the obj e c t assumption i s the o b j e c t - e f f e c t c h a r a c t e r i z a t i o n of the r e s u l t s : F a c i l i t a t i o n of l e t t e r naming RT by t a r g e t r e p e t i t i o n i s grea t e r f o r r e p e t i t i o n s w i t h i n an o b j e c t than i t i s f o r r e p e t i t i o n s between o b j e c t s . One account that can make sense of the preview paradigm r e s u l t s while r e j e c t i n g the object assumption w i l l be d i s c u s s e d i n the General D i s c u s s i o n . However, i t i s the o b j e c t - e f f e c t c h a r a c t e r i z a t i o n that seems to be the most n a t u r a l . R e c a l l that t h i s c h a r a c t e r i z a t i o n i s a l s o c o n s i s t e n t with other r e s e a r c h i n d i c a t i n g that p e r c e p t u a l u n i t i z a t i o n can i n f l u e n c e subsequent i n f o r m a t i o n p r o c e s s i n g . The o b j e c t e f f e c t can be viewed as an e f f e c t of a moving o b j e c t ' s dynamic v i s u a l h i s t o r y . The v i s u a l h i s t o r y metaphor i s simply t h a t , a metaphor--not r e q u i r e d by the re s e a r c h r e s u l t s but perhaps u s e f u l t o the humans t r y i n g to understand them. Using the term " h i s t o r y " communicates a s p e c i f i c i t y — even a p o s s e s s i v e n e s s — a p p r o p r i a t e to the obj e c t e f f e c t . What i s c r u c i a l to the o b j e c t e f f e c t i s not merely whether a 45 preview appeared w i t h i n a c e r t a i n s p a t i a l and temporal d i s t a n c e of a t a r g e t s t i m u l u s . What i s c r u c i a l i s whether the preview was s p a t i a l l y and temporally l o c a t e d so as to belong to the same o b j e c t as the t a r g e t . That i s , a preview had i t s f u l l e f f e c t only i f i t c o n s t i t u t e d an ev e n t - i n the h i s t o r y of the p a r t i c u l a r o b j e c t c o n t a i n i n g the t a r g e t . Preview events o c c u r r i n g at the same time and at the same d i s t a n c e from the t a r g e t , but concerning other o b j e c t s , were not as i n f l u e n t i a l . Thus, the idea that moving o b j e c t s somehow maintain v i s u a l h i s t o r i e s which can i n f l u e n c e the c o g n i t i v e p r o c e s s i n g of those o b j e c t s i s a d e s c r i p t i v e device that captures the essence of the obj e c t e f f e c t . Up to the point of c h a r a c t e r i z i n g the preview f i n d i n g as an o b j e c t e f f e c t , the i n f e r e n t i a l s t r u c t u r e of the paradigm i s q u i t e s t r a i g h t forward; f a r t h e r reaching i n t e r p r e t a t i o n becomes necessary i n d e a l i n g with the a c t u a l mechanics of the ob j e c t e f f e c t . I t i s proposed that (a) the mechanism u n d e r l y i n g the object e f f e c t f u n c t i o n s to i n t e g r a t e i n f o r m a t i o n a c r o s s space and time, and that (b) t h i s i n t e g r a t i o n occurs r e t r o a c t i v e l y . Reasons for viewing the ob j e c t e f f e c t as a r e t r o a c t i v e phenomenon were a l r e a d y d i s c u s s e d along with examples of other r e t r o a c t i v e i n f o r m a t i o n p r o c e s s i n g models. The r e t r o a c t i v e nature of the ob j e c t e f f e c t i s what prompted the re-viewing model, which i s at the peak of the i n f e r e n t i a l s t r u c t u r e of the preview paradigm. I f re-viewing i s the a p i c a l i n f e r e n c e , then i n f o r m a t i o n i n t e g r a t i o n i s the f o u n d a t i o n a l one. T h i s n o t i o n 46 was u b i q u i t o u s i n the d i s c u s s i o n of the KTG work and deserves deeper treatment. Spatiotemporal Information I n t e g r a t i o n As a r u l e , i n f o r m a t i o n p r o c e s s i n g i s h i g h l y i n t e r a c t i v e . The e x p l i c i t or i m p l i c i t response a p p r o p r i a t e to a stimulus i s o f t e n determined only through the r e l a t i n g of that stimulus to other i n f o r m a t i o n which occurs elsewhere in the f i e l d , which i s r e t r i e v e d from e p i s o d i c or semantic memory, or perhaps which i s produced by an act of mental c o n s t r u c t i o n . The human tendency to search f o r meaning i s not absent from p e r c e p t i o n , and i t i s almost never the case that the f u l l i n t e r p r e t a t i o n of a s t i m u l u s can be made without some referen c e to other i n f o r m a t i o n . Indeed, the concept of i n f o r m a t i o n i t s e l f i s based on the idea of a l t e r n a t i v e s , and so i m p l i c i t l y i n c l u d e s an i n t e r a c t i o n between what i s and what co u l d have been. Information i n t e g r a t i o n i m p l i e s a p a r t i c u l a r s o r t of information i n t e r a c t i o n . The term i n t e g r a t i o n suggests a b r i n g i n g together of p a r t s i n t o a whole, or a u n i t i z a t i o n . Thus, i f the c o g n i t i v e i n t e r a c t i o n between d i f f e r e n t i n f o r m a t i o n e n t i t i e s i s c o n s t r a i n e d by the o r g a n i z a t i o n of those e n t i t i e s i n t o a u n i t , or perhaps i f t h e i r i n t e r a c t i o n c r e a t e s a u n i t , then i t makes sense to c o n s i d e r the i n t e r a c t i o n to be an i n t e g r a t i o n . U n f o r t u n a t e l y , without a very c l e a r d e f i n i t i o n of u n i t , d i s t i n g u i s h i n g i n f o r m a t i o n i n t e g r a t i o n from other types of i n f o r m a t i o n i n t e r a c t i o n can become a r a t h e r empty e x e r c i s e . 47 T h i s i s not to say that i t i s wrong to c o n s i d e r i n f o r m a t i o n p r o c e s s i n g to be e s s e n t i a l l y i n t e g r a t i v e . Anderson (1981), f o r example, b e l i e v e s that rudimentary to human in f o r m a t i o n p r o c e s s i n g i s the c a p a c i t y to form c o g n i t i v e u n i t s , and that there e x i s t s a b a s i c b e h a v i o r a l tendency to i n t e g r a t e i n f o r m a t i o n . He views i n f o r m a t i o n p r o c e s s i n g as a sequence of i n t e g r a t i o n o p e r a t i o n s , each o p e r a t i o n s i m p l i f y i n g m u l t i p l e s t i m u l i i n t o a u n i t a r y r e s u l t a n t which serves as one of the inputs to the i n t e g r a t i o n at the next l e v e l , with the r e s u l t that each higher l e v e l i n the chain operates a c r o s s a broader st i m u l u s domain. However, i t should be recognized t h a t , because c o g n i t i v e u n i t s are i n f e r r e d r a t h e r than observed, i t i s p o s s i b l e to c l a s s i f y any case of i n f o r m a t i o n i n t e r a c t i o n as a case of i n f o r m a t i o n i n t e g r a t i o n , and so the two cases c o l l a p s e i n t o one. In the preview paradigm, d e s p i t e the l a c k of a s t r i c t and formal d e f i n i t i o n of what can count as a u n i t and what cannot, the use of the term i n t e g r a t i o n seems genuinely meaningful. T h i s i s because from the very beginning there was a strong a p r i o r i sense that o b j e c t s were the r e l e v a n t u n i t s , as i s apparent from the s o r t of r e a l - l i f e f e a t s of p e r c e p t i o n — l i k e the one d e s c r i b e d at the opening Of t h i s t h e s i s - - t h a t i n s p i r e d the preview r e s e a r c h . The dangers of h i n d s i g h t n otwithstanding, i t seems f a i r to a s s e r t that i f enhanced i n f o r m a t i o n i n t e r a c t i o n had been d i s c o v e r e d between s t i m u l i presented i n separate l i n e f i g u r e s i n s t e a d of between s t i m u l i presented i n a s i n g l e l i n e f i g u r e , such i n t e r a c t i o n 48 would not have been g l i b l y l a b e l l e d an obj e c t e f f e c t . Again, there i s nothing b a r r i n g one from t h i n k i n g of between-object in f o r m a t i o n i n t e r a c t i o n (or any other kind) as r e l a t e d to u n i t i z a t i o n and t h e r e f o r e as i n t e g r a t i o n ; the p o i n t here i s that the i n t e g r a t i o n l a b e l i s l e s s a r b i t r a r y when a p p l i e d t o inf o r m a t i o n i n t e r a c t i o n s such as those of the preview paradigm i n which the re l e v a n t u n i t s are not i n f e r r e d from the i n t e r a c t i o n s themselves. The i n f e r e n c e that the mechanism r e s p o n s i b l e f o r the obje c t e f f e c t i s one of inf o r m a t i o n i n t e g r a t i o n i s t h e r e f o r e not c i r c u l a r , but i t i s a l s o not very b o l d . I t f o l l o w s d i r e c t l y from (a) the f i n d i n g of i n f o r m a t i o n i n t e r a c t i o n , p l u s (b) the q u a l i f i c a t i o n that t h i s i n t e r a c t i o n i s obj e c t ( i e . u n i t ) c o n s t r a i n e d , and so i t i s not much d i f f e r e n t than a restatement of the o b j e c t - e f f e c t c h a r a c t e r i z a t i o n i t s e l f . However, because the idea of o b j e c t s as potent p e r c e p t u a l u n i t s i s so c e n t r a l to the preview paradigm, c o n s i d e r i n g the obje c t e f f e c t the r e s u l t of i n f o r m a t i o n i n t e g r a t i o n i s c o n c e p t u a l l y e f f i c i e n t and a f f o r d s an important b a s i s f o r f u r t h e r a n a l y s i s . Objects and the I n t e g r a t i o n The i n f o r m a t i o n i n t e g r a t i o n u n d e r l y i n g the obj e c t e f f e c t has been termed spatiotemporal, a d e s c r i p t i o n which, by c o n t r a s t i n g with simple s p a t i a l and simple temporal i n t e g r a t i o n , turns out to emphasize the o b j e c t - o r i e n t e d nature of the i n t e g r a t i o n . V i s u a l i n f o r m a t i o n can be i n t e g r a t e d over space i n the sense that under c e r t a i n 49 circumstances simultaneous s t i m u l i appearing at d i f f e r e n t l o c a t i o n s i n the f i e l d may be grouped enough to cause s p e c i a l p r o c e s s i n g i n t e r a c t i o n between them (eg.: Kahneman & Henik, 1981; Banks & P r i n z m e t a l , 1976). V i s u a l i n f o r m a t i o n can be i n t e g r a t e d over time i n the sense that under c e r t a i n circumstances s e q u e n t i a l l y presented s t i m u l i may be used as i f they were both present together (eg.: Di L o l l o , 1980; E r i k s e n & C o l l i n s , 1968). Although i t i s an i n t e r e s t i n g q u e s t i o n how much commonality there i s between these types of i n t e g r a t i o n and the i n t e g r a t i o n g i v i n g r i s e to the o b j e c t e f f e c t , the most s a l i e n t p o i n t i s that n e i t h e r s p a t i a l i n t e g r a t i o n nor temporal i n t e g r a t i o n i s s u f f i c i e n t to d e s c r i b e the object e f f e c t . The object e f f e c t r e p r e s e n t s the i n t e g r a t i o n of information a c r o s s both space and time, which i s why the object i n t e r p r e t a t i o n i s so n a t u r a l : A moving object i n v o l v e s the c o n s i s t e n t a s s i g n i n g of a s i n g l e p e r c e p t u a l i d e n t i t y to d i s p a r a t e segments of space-time. The reader may be bothered by an apparent c i r c u l a r i t y in the c a u s a l r e l a t i o n between o b j e c t s and i n f o r m a t i o n i n t e g r a t i o n . The admitted impetus for the preview experiments was the o b s e r v a t i o n that the o r d e r l y p e r c e p t i o n of moving o b j e c t s r e q u i r e s some so r t of sp a t i o t e m p o r a l i n f o r m a t i o n i n t e g r a t i o n ( c f . A n s t i s , 1978). I t may be d i s t u r b i n g t h e r e f o r e that i t i s the o r g a n i z a t i o n of the f i e l d i n t o o b j e c t s that i s put forward to account f o r the spatiotemporal i n f o r m a t i o n i n t e g r a t i o n . Is t h i s not a s s e r t i n g that the i n t e g r a t i o n i s r e s p o n s i b l e f o r the o b j e c t 50 and that the ob j e c t i s r e s p o n s i b l e f o r the i n t e g r a t i o n ? What must be recognized i s that the term o b j e c t can be used.in two d i f f e r e n t , a l b e i t not completely independent, ways. In the case of the n a t u r a l i s t i c o b s e r v a t i o n s that i n s p i r e d the rese a r c h , o b j e c t i s a p r i m a r i l y phenomenological concept. The f a c t that the v i s u a l world c o n s i s t s s u b j e c t i v e l y of coherent i n t e g r a t e d u n i t s i s p r i m a - f a c i e evidence of inf o r m a t i o n i n t e g r a t i o n o c c u r r i n g somewhere i n the system. In the case of the c h a r a c t e r i z a t i o n of the RT data, o b j e c t i s not a p r i m a r i l y phenomenological concept, but i s used more l i k e a shorthand to represent the c l u s t e r of as-y e t - u n s p e c i f i e d v a r i a b l e s a c c o r d i n g to which the o p t i c a l flow i s parsed i n t o s u b j e c t i v e o b j e c t s . True, i t i s the s u b j e c t i v e " o b j e c t n e s s " of the l i n e f i g u r e s that g i v e s the obje c t assumption concerning them i t s i n t u i t i v e f o r c e , but no assumption i s ever made that the l i n e f i g u r e s are e f f e c t i v e because they are s u b j e c t i v e l y good o b j e c t s . Even i n the Ternus d i s p l a y the c r i t i c a l c a u s a l f a c t o r may only be a s s o c i a t e d with the s u b j e c t i v e impression of movement, although, because such d i s p l a y s i n v o l v e only apparent motion, they do make the p o s s i b i l i t y t h a t phenomenal movement i s the important f a c t o r seem q u i t e reasonable. T h i s would not be at a l l i n c o n s i s t e n t with the re-viewing f o r m u l a t i o n e i t h e r , which models the i n t e g r a t i o n as a c t i n g backwards and o c c u r r i n g rather l a t e anyway; and r e c a l l that j u s t because a process i s r e t r o a c t i v e does not mean that i s cannot have e f f e c t s at a pe r c e p t u a l l e v e l ( F e u s t e l , S h i f f r i n 51 & Salasoo, 1983). N e v e r t h e l e s s , how important phenomenology a c t u a l l y i s to the p r o d u c t i o n of the ob j e c t e f f e c t i s an e m p i r i c a l q u e s t i o n r e q u i r i n g f u r t h e r a t t e n t i o n . What, then, i s the use of c a l l i n g the f i n d i n g of the preview paradigm an o b j e c t e f f e c t i f t h i s cannot be taken to mean that the s u b j e c t i v e percept of objecthood causes the spati o t e m p o r a l i n t e g r a t i o n ? To c a l l the f i n d i n g an o b j e c t e f f e c t i s simply to a s s e r t that those v a r i a b l e s of the o p t i c a l flow r e s p o n s i b l e f o r s u b j e c t i v e objecthood are a l s o important to the spatiotemporal i n t e g r a t i o n indexed by the ob j e c t e f f e c t . The s u b j e c t i v e goodness of an ob j e c t probably c o r r e l a t e s h i g h l y with the v a r i a b l e s of the o p t i c a l flow r e s p o n s i b l e f o r the spatiotemporal i n t e g r a t i o n , and so u n t i l these v a r i a b l e s are i d e n t i f i e d e m p i r i c a l l y , s u b j e c t i v e objecthood can be thought of as the most e f f i c i e n t p r e d i c t o r of the i n t e g r a t i o n u n d e r l y i n g the obj e c t e f f e c t . T h i s , of course, does not mean that the i n t e g r a t i o n depends d i r e c t l y or s o l e l y on the s u b j e c t i v e aspect of the o b j e c t s i n v o l v e d . I n f o r m a t i o n a l Domain of the I n t e g r a t i o n The f o r e g o i n g treatment of the concept of o b j e c t holds an important i m p l i c a t i o n f o r understanding the r o l e of the preview r e s e a r c h in the study of spatiotemporal i n f o r m a t i o n i n t e g r a t i o n . I t can reasonably be argued that i n f o r m a t i o n i n t e g r a t i o n a s s o c i a t e d with moving o b j e c t s should be co n s i d e r e d a s i n g l e s o r t of i n t e g r a t i o n because i t i s based on a s i n g l e s o r t of u n i t : o b j e c t s . However, i t should now be apparent t h a t , c o n c e p t u a l l y u n i t a r y or not, t h i s 52 i n t e g r a t i o n i s o c c u r r i n g at more than one i n f o r m a t i o n a l l e v e l . The s u b j e c t i v e v i s u a l coherence of moving o b j e c t s a t t e s t s to i n t e g r a t i o n of i n f o r m a t i o n at the l e v e l of phenomenal p e r c e p t s , and t h i s o b s e r v a t i o n prompted the s u c c e s s f u l search f o r concomitant o b j e c t i n t e g r a t i o n at another l e v e l , one concerning the i n f o r m a t i o n used i n making l e t t e r - n a m i n g responses. Thus, at i t s b a s i s , the preview paradigm can be viewed as an e x p l o r a t i o n of the extent to which o b j e c t - s p e c i f i c i n f o r m a t i o n i n t e g r a t i o n known to apply to one i n f o r m a t i o n a l domain can be g e n e r a l i z e d to another i n f o r m a t i o n a l domain. Of course, u l t i m a t e l y the goal i s to be a b l e to d e s c r i b e the p a r t i c u l a r c o g n i t i v e r e p r e s e n t a t i o n s or processes that cause the i n f o r m a t i o n i n t e r a c t i o n and that make i t o b j e c t -s p e c i f i c . The notions of o b j e c t f i l e and of re-viewing are e a r l y e f f o r t s in that d i r e c t i o n . Aside from being o b j e c t -s p e c i f i c , perhaps the s p a t i o t e m p o r a l i n t e g r a t i o n w i l l t urn out to be l i k e i n f o r m a t i o n i n t e g r a t i o n s t u d i e d by o t h e r s . A c c o r d i n g to Garner's (1974) work, f o r tasks i n which time i s the l i m i t i n g f a c t o r , simple element r e p e t i t i o n can cause an improvement in p e r f o r m a n c e — a r e s u l t c o n s i s t e n t with the preview r e s e a r c h . I n t e r e s t i n g l y , he suggests that s e q u e n t i a l l y presented redundant s t i m u l i might be more prone to i n f o r m a t i o n a l i n t e r a c t i o n than redundant s t i m u l i presented s i d e - b y - s i d e . Reasons Garner puts forward fo r why performance can be improved by i n f o r m a t i o n a l redundancy—and f o r him improved performance with redundant i n f o r m a t i o n 53 i m p l i e s i n t e g r a t i o n — i n c l u d e (a) that redundancy can produce a new and e a s i e r - t o - p r o c e s s stimulus dimension, and (b) that redundancy can improve the memory pr o c e s s . Another approach i s to seek t o d e s c r i b e i n f o r m a t i o n i n t e r a c t i o n i n terms of a " c o g n i t i v e a l g e b r a " of simple o p e r a t i o n s such as averaging, s u b t r a c t i n g and m u l t i p l y i n g (Anderson, 1981). In d e a l i n g with the case of two dimensions of p e r c e p t u a l i n f o r m a t i o n , each a s s o c i a t e d with i t s own response system, Garner (1974) makes apparent the f a c t that an important aspect of d e s c r i b i n g i n f o r m a t i o n i n t e r a c t i o n concerns the l e v e l i n the p r o c e s s i n g system at which that i n t e r a c t i o n i s o c c u r r i n g . He p o i n t s out that there are three ways the pr o c e s s i n g of these dimensions can be i n t e r a c t i v e . There may be an i n t e r a c t i o n between the i n f o r m a t i o n at the l e v e l of the stimulus dimensions themselves, so that they would be cons i d e r e d " i n t e g r a l " in h i s terminology and would i n e f f e c t be a s i n g l e dimension. At the other extreme, there may be no i n t e r a c t i o n u n t i l the l e v e l of the response processes. The t h i r d a l t e r n a t i v e i s that there may be an i n t e r a c t i o n as a consequence of each response system r e c e i v i n g some input from the other, i n a p p r o p r i a t e dimension. The preview experiments demonstrate that i n f o r m a t i o n i n v o l v e d i n the c o g n i t i v e p r o c e s s i n g of l e t t e r s t i m u l i can be i n t e g r a t e d by the o r g a n i z a t i o n of the f i e l d i n t o o b j e c t s . As po i n t e d out, t h i s i t s e l f r e presents an extension of the p r i n c i p l e of in f o r m a t i o n i n t e g r a t i o n from an i n f o r m a t i o n domain that i s phenomenological to one that i s not. Whatever 54 are the d e t a i l s of the mechanism un d e r l y i n g the o b j e c t e f f e c t , a l a r g e part of understanding that mechanism w i l l be understanding more p r e c i s e l y what kind of i n f o r m a t i o n i s i n v o l v e d i n the l e t t e r e f f e c t , and what other kinds of i n f o r m a t i o n are s u b j e c t to spatiotemporal i n t e g r a t i o n . PRESENT INVESTIGATION R e l a t i o n To the Previous P r o j e c t The present experiments f o l l o w KTG's preview paradigm. As was true i n the e a r l i e r p r o j e c t , the independent v a r i a b l e i s the f i g u r a l r e l a t i o n between a t a r g e t and a preview of that t a r g e t , and the dependent v a r i a b l e i s the l a t e n c y of response to the t a r g e t . The major m o d i f i c a t i o n here i s i n the type of s t i m u l i p r e s e n t e d . With the noted except i o n s , the KTG r e s e a r c h i n v o l v e d l e x i c a l s t i m u l i t h a t s u b j e c t s had to v o c a l l y name. Most of the experiments r e p o r t e d in t h i s t h e s i s i n v o l v e n o n l e x i c a l s t i m u l i that s u b j e c t s had to c l a s s i f y dichotomously on the b a s i s of a p h y s i c a l p r o p e r t y . In t h i s way, the present experiments probe the spatiotemporal i n t e g r a t i o n of i n f o r m a t i o n concerning the p h y s i c a l p r o p e r t i e s of o b j e c t s . The v i s u a l d i s p l a y s are much l i k e those developed by KTG. Both d i s p l a y s , the four-box d i s p l a y (see F i g u r e 3) and the Ternus d i s p l a y (see F i g u r e 2), c o n s i s t of a r e a l or apparent motion phase c o n n e c t i n g an i n i t i a l s t i m u l u s f i e l d with a subsequent one. The i n i t i a l f i e l d t y p i c a l l y i n c l u d e s a f e a t u r e preview (two i n the case of the four-box d i s p l a y ) , and the f i n a l f i e l d i n c l u d e s the t a r g e t . L i k e i n the mother 55 p r o j e c t , the c e n t r a l design f e a t u r e of both d i s p l a y s i s the p o t e n t i a l f o r a preview to appear as part of the same o b j e c t as the subsequent t a r g e t , or, a l t e r n a t i v e l y , as part of a d i f f e r e n t o b j e c t . Purpose and R a t i o n a l e The most b a s i c purpose of the present i n v e s t i g a t i o n i s to determine whether the spatiotemporal i n t e g r a t i o n observed between l e t t e r s i n KTG's preview experiments can be generated between p h y s i c a l f e a t u r e s as w e l l . Can an o b j e c t e f f e c t be produced i n preview experiments i n which responses are based on a p h y s i c a l p r o p e r t y of the t a r g e t stimulus r a t h e r than on i t s l e x i c a l i d e n t i t y ? A couple of f i n d i n g s i n the l i t e r a t u r e h i n t that i t might be p o s s i b l e that the o r g a n i z a t i o n of a scene i n t o moving o b j e c t s w i l l c o n s t r a i n the i n t e r a c t i o n of f e a t u r e s l i k e i t does the i n t e r a c t i o n of l e t t e r s . F i r s t , the c o g n i t i v e p r o c e s s i n g of f e a t u r e s can be context dependent. Treisman (1985) notes that whether a contour i s seen as the edge of an o b j e c t or the margin of a shadow i n f l u e n c e s the p e r c e i v e d b r i g h t n e s s of the s u r f a c e i t bounds. I l l u s o r y or s u b j e c t i v e contours are an extreme example: Such contours come i n t o e x i s t e n c e only as a consequence of the context i n which they are p e r c e i v e d . In her d e l i n e a t i o n of v i s u a l p r i m i t i v e s , Treisman ( i n press) found that d u r i n g v i s u a l search t i l t e d l i n e s pop out of v e r t i c a l l i n e s but not v i c e v e r s a , suggesting that v e r t i c a l i s coded as the n e u t r a l p o i n t on the o r i e n t a t i o n dimension. Of i n t e r e s t here i s the r e s u l t 56 that these same t i l t e d l i n e s , when surrounded by an e q u a l l y -t i l t e d frame so they appear r e l a t i v e l y v e r t i c a l , are d i f f i c u l t to search f o r ju s t as the v e r t i c a l l i n e s were in the context of the u n t i l t e d frame. Apparently t i l t can be coded r e l a t i v e to the f i g u r a l context i n which i t appears. Second, apparent motion, and the p r o c e s s i n g i m p l i c a t i o n s i t c a r r i e s , may apply to f e a t u r e s as w e l l as o b j e c t s . Studying apparent motion, Johansson (1978) n o t i c e d that i f two contiguous d i s c s get dimmer and b r i g h t e r in c y c l e s that are 180 degrees out of phase, something—but not an o b j e c t — w i l l appear to move between them. T h i s something may be thought of as a " t h i n g " such as a moving shadow. The i n t e r e s t i n g a l t e r n a t i v e i s that t h i s s h i f t i n g change in b r i g h t n e s s might represent the apparent motion of a disembodied a t t r i b u t e . One reason to conduct f e a t u r a l preview experiments i s that r e l a t i v e to the previous l e x i c a l preview experiments, they a c t u a l l y represent a more gen e r a l t r a n s l a t i o n of the t h e o r e t i c a l i s s u e s m o t i v a t i n g the preview r e s e a r c h . A f t e r a l l , l e t t e r s are a r a t h e r s p e c i a l type of s t i m u l u s : In v i s i o n the p e r c e p t u a l coherence of an o b j e c t must be maintained over changes in any of a number of p r o p e r t i e s , most of which are p h y s i c a l r a t h e r than c o n c e p t u a l . T e s t i n g for the o b j e c t e f f e c t across v a r i o u s p h y s i c a l p r o p e r t i e s may u l t i m a t e l y shed l i g h t on the fundamental issue of what tr a n s f o r m a t i o n s an o b j e c t can undergo and yet r e t a i n i t s p e r c e p t u a l i d e n t i t y (Kahneman & Henik, 1981). 57 A more s p e c i f i c reason to conduct f e a t u r a l preview experiments i s that they can h e l p determine the nature of the mechanism r e s p o n s i b l e f o r the spatiotemporal i n t e g r a t i o n of in f o r m a t i o n observed by KTG. If the ob j e c t e f f e c t t r u l y i s an e f f e c t of a moving o b j e c t ' s dynamic v i s u a l h i s t o r y , as some of KTG's experiments suggest, then the present experiments should produce p o s i t i v e r e s u l t s . Of course, t h i s v i s u a l h i s t o r y may not be exhaustive and so some p h y s i c a l p r o p e r t i e s may support the o b j e c t e f f e c t while others may not. The s t r a t e g y h e r e i n i s to t e s t f o r the spatiotemporal i n t e g r a t i o n of s e v e r a l d i f f e r e n t o b j e c t p r o p e r t i e s : presence, s i z e , and c o l o r . In t h i s way the present approach i s r e m i n i s c e n t of that taken by r e s e a r c h e r s who sought to d e s c r i b e the i n f o r m a t i o n a l composition of the icon by t e s t i n g f o r s u p e r i o r i t y of p a r t i a l r e p o r t with a v a r i e t y of p r o p e r t i e s (eg: Averbach & C o r i e l l , 1961; Von Wright, 1968; C l a r k , 1969; Turvey & Kravetz, 1970; Treisman, R u s s e l l & Green, 1975). G e n e r a l i z i n g the Object E f f e c t So f a r the major g e n e r a l i z a t i o n of the ob j e c t e f f e c t has been from the l e t t e r i d e n t i f i c a t i o n task to a v i s u a l search task (KTG). The present work attempts to g e n e r a l i z e the e f f e c t to another experimental s e t t i n g , but without l e a v i n g the realm of a stimulus i d e n t i f i c a t i o n task, i n which an item i n a p a r t i c u l a r cued l o c a t i o n must be i d e n t i f i e d . Because the v i s u a l search task d i d not r e q u i r e responses to be made to a p a r t i c u l a r l o c a t i o n , and t h e r e f o r e d i d not demand a 58 s p a t i a l f o c u s s i n g of a t t e n t i o n , r e s u l t s of the present s e r i e s of experiments c o u l d be q u i t e d i f f e r e n t from those of the search experiment (Treisman & Gelade, 1980). One minor way some of the experiments r e p o r t e d here g e n e r a l i z e the KTG work i s that they i n v o l v e the p r e s e n t a t i o n of two previews of the t a r g e t i n f i e l d - 1 . I f the mechanism r e s p o n s i b l e f o r the o b j e c t e f f e c t i s subject to " d i s t r a c t i o n " by m u l t i p l e previews, t h i s m o d i f i c a t i o n c o u l d p o s s i b l y e l i m i n a t e the e f f e c t . More importantly, the present r e s e a r c h seeks to f u r t h e r the g e n e r a l i z a t i o n of the o b j e c t e f f e c t from v e r b a l to nonverbal s t i m u l i . Alphanumeric s t i m u l i are d e t r i m e n t a l l y over-used i n c o g n i t i v e r e s e a r c h (Johansson, 1979). N e i s s e r (1983) goes so f a r as to suggest, fo r example, that p a r t i a l r e p o rt s u p e r i o r i t y , though r e s p o n s i b l e f o r the i n c l u s i o n of an i n i t i a l sensory storage stage i n i n f o r m a t i o n p r o c e s s i n g models, may be an e s s e n t i a l l y v e r b a l phenomenon (Haber, 1983; but see Treisman, R u s s e l l & Green, 1975). Depite some p a r a l l e l s between context e f f e c t s i n c o l o r naming and l e x i c a l d e c i s i o n tasks (Henik, F r i e d i c h & K e l l o g g , 1983; Logan, 1980), the u n i t i z e d responses a s s o c i a t e d with l e x i c a l s t i m u l i give them s p e c i a l s t a t u s when i t comes to stimulus r e p e t i t i o n e f f e c t s ( F e u s t e l , S h i f f r i n & Salasoo, 1983). A l s o p e c u l i a r to the i n f o r m a t i o n p r o c e s s i n g of v e r b a l s t i m u l i may be expectancies of semantic "coherence" (de Groot, Thomassen & Hudson, 1982). In o b t a i n i n g the o b j e c t e f f e c t with n o n l e x i c a l s t i m u l i , any account of i n f o r m a t i o n i n t e g r a t i o n 59 r e l y i n g on l e x i c a l r e p r e s e n t a t i o n s , as does C o l t h e a r t ' s (1980) l e x i c a l s t a b i l i z a t i o n idea, i s immediately r u l e d out ( C o l t h e a r t , 1983). A f e a t u r a l o b j e c t e f f e c t would a l s o be l e s s i n t e r p r e t a b l e as a response e f f e c t , because, r e l a t i v e to l e t t e r s , n o n l e x i c a l s t i m u l i should g i v e r i s e to weaker response tendencies (Kahneman & Chajczyk, 1983). Why a F e a t u r a l Object E f f e c t Cannot Be Assumed The reader may f e e l t h a t , given KTG's r e s u l t s , the o b j e c t e f f e c t can simply be assumed to o b t a i n with p h y s i c a l p r o p e r t i e s . The switch to n o n l e x i c a l s t i m u l i should not change the experimental r e s u l t s i f KTG are c o r r e c t that the spatiotemporal i n t e g r a t i o n of i n f o r m a t i o n witnessed in the preview experiments i s o c c u r r i n g at a v i s u a l l e v e l , because then the l e x i c a l o b j e c t e f f e c t i s r e a l l y based on the shape of the l e t t e r s r a ther than on t h e i r v e r b a l a t t r i b u t e s anyway. However, i t cannot be assumed that the experiments h e r e i n , which i n v o l v e responses based on d i f f e r e n t f e a t u r e s of an o b j e c t , w i l l produce p o s i t i v e r e s u l t s j u s t because experiments i n v o l v i n g responses based on l e t t e r shape d i d so. For one t h i n g , i n the v i s u a l p r o c e s s i n g h i e r a r c h y the d e t a i l s of l e t t e r shape may be a b s t r a c t e d at a higher, more d e c i s i o n -l i k e l e v e l than grosser f e a t u r e s would be, and i t i s probably g e n e r a l l y true that data are l o s t more r a p i d l y than d e c i s i o n s (Treisman, 1979). I f , as suspected by KTG, spatiotemporal i n t e g r a t i o n takes s i g n i f i c a n t time, low l e v e l f e a t u r a l data may become u n a v a i l a b l e too soon to support an o b j e c t e f f e c t . 60 L e t t e r i d e n t i f i c a t i o n responses may r e q u i r e the p r o c e s s i n g of the l e t t e r as an o b j e c t , and t h i s would make them e s p e c i a l l y d i s t i n c t from f e a t u r e i d e n t i f i c a t i o n responses. Features d i f f e r from o b j e c t s in t h e i r encoding and p r o c e s s i n g . A prominent view i s that d i s t i n c t l e v e l s of p e r c e p t u a l p r o c e s s i n g are i n v o l v e d (Treisman, 1979). At the f i r s t l e v e l f e a t u r e s are de t e c t e d by independent a n a l y z e r s that operate i n p a r a l l e l . At the second l e v e l , through the a p p l i c a t i o n of f o c a l a t t e n t i o n , these f r e e - f l o a t i n g f e a t u r e s are c o n j o i n e d to form o b j e c t s . Thus, i n " f e a t u r e - i n t e g r a t i o n theory" (Treisman & Gelade, 1980), a t t e n t i o n a c t s as the glue that binds f e a t u r e s together to c r e a t e o b j e c t s . Kahneman and Treisman (1984; Treisman, 1969) note the importance of d i s t i n g u i s h i n g between the s e l e c t i o n of inputs ( o b j e c t s ) and the s e l e c t i o n of ana l y z e r s ( f e a t u r e s ) . A t t e n t i o n seems to s e l e c t o b j e c t s as opposed to p r o p e r t i e s of o b j e c t s (Treisman, Kahneman & B u r k e l l , 1983). The e a r l y stage p r i o r to the s y n t h e s i s of o b j e c t s , at which f e a t u r e s can be dete c t e d p r e a t t e n t i v e l y , i s probably l e s s i n f l u e n c e d by expectancy, and context (Treisman, 1979), and even though search f o r a c o n j u n c t i o n t a r g e t i s s u b s t a n t i a l l y i n f l u e n c e d by pre-cueing i t s l o c a t i o n , search f o r a f e a t u r e t a r g e t i s not (Treisman, in p r e s s ) . Furthermore, some unattended f e a t u r e s can be subsequently recognized, but t h i s i s not the case f o r unattended o b j e c t s and r e l a t i o n a l f e a t u r e s such as complex shape (Rock & Gutman, 1981). Of p a r t i c u l a r relevance i s the f i n d i n g that p e r c e p t u a l grouping i n f l u e n c e s v i s u a l search f o r 61 c o n j u n c t i o n s but not search f o r f e a t u r e s (Treisman, 1982). Even i f the i n f o r m a t i o n a l d i f f e r e n c e s between the fea t u r e and l e t t e r s t i m u l i do not demand p e r c e p t u a l p r o c e s s i n g d i f f e r e n c e s that i n t e r a c t with the o b j e c t e f f e c t , the d i f f e r e n c e s between the f e a t u r e and l e t t e r response tasks qua response tasks may be important. The nature of a task can i n f l u e n c e how a n a l y t i c a l l y incoming i n f o r m a t i o n i s processed (Treisman & Paterson, 1984; Garner, 1974) and how much of the processed i n f o r m a t i o n i s r e t r i e v e d (Marcel, 1983b). I t i s co n c e i v a b l e that a s k i n g s u b j e c t s to respond to a simple p h y s i c a l property of an o b j e c t w i l l encourage them to process the v i s u a l scene in a way that r e f l e c t s the i r r e l e v a n c e of i t s g l o b a l o r g a n i z a t i o n a l c h a r a c t e r i s t i c s , thus p r e c l u d i n g any o b j e c t - s p e c i f i c i n t e g r a t i o n of i n f o r m a t i o n . An E l a b o r a t i o n of the Paradigm The f e a t u r a l preview experiments a f f o r d an o p p o r t u n i t y to implement an i n t e r e s t i n g e l a b o r a t i o n of the paradigm. The f i e l d - 1 and f i e l d - 2 s t i m u l i appearing as p a r t s of the same ob j e c t can be made to vary not only on the f e a t u r e dimension c o n t r o l l i n g response but a l s o on a second dimension i r r e l e v a n t to response. For example, i n an experiment i n which s u b j e c t s respond to the s i z e of a t a r g e t , the two s t i m u l i may be c o n s i s t e n t or i n c o n s i s t e n t with r e s p e c t to . s i z e and at the same time c o n s i s t e n t or i n c o n s i s t e n t with respect to shape. In t h i s way the importance of complete i d e n t i t y between t a r g e t and preview can be ass e s s e d . KTG's 62 l e t t e r case and l e x i c a l d e c i s i o n experiments, which both i n v o l v e d " c o n s i s t e n t " s t i m u l i that were not p h y s i c a l l y i d e n t i c a l , f a i l e d to generate o b j e c t e f f e c t s . Perhaps t h i s f i n d i n g i s g e n e r a l l y t r u e and the p r o c e s s i n g of a t a r g e t i s only f a c i l i t a t e d by a f u l l y i d e n t i c a l preview. A l t e r n a t i v e l y , c o n s i s t e n c y on the f e a t u r a l dimension c o n t r o l l i n g response may be the only c r i t i c a l f a c t o r , and so the o b j e c t e f f e c t may be t o t a l l y u n a f f e c t e d by v a r i a t i o n on a r e s p o n s e - i r r e l e v a n t dimension. An i n t e r m e d i a t e p o s s i b i l i t y i s that c o n s i s t e n c y on each f e a t u r a l dimension c o n t r i b u t e s to the f a c i l i t a t i o n , so that the o b j e c t e f f e c t may simply get weaker as the p h y s i c a l s i m i l a r i t y of the s t i m u l i decreases. Such duodimension experiments w i l l p r o v i d e an i n d i c a t i o n of how comprehensive the i n t e g r a t i o n mechanism i s . KTG suggest that the re-viewing process a p p l i e s to only the same-ob j e c t f i e l d - 1 stimulus most recent with r e s p e c t to the t a r g e t ; but does i t apply to a l l the p r o p e r t i e s of that stimulus? A t t e n t i o n f a c i l i t a t e s the p r o c e s s i n g of a l l the p r o p e r t i e s of an o b j e c t to which i t i s a l l o c a t e d (Treisman, Kahneman & B u r k e l l , 1983) so perhaps a s e n s i b l e working assumption i s that a l l of the p r o p e r t i e s of an o b j e c t w i l l be re-viewed as a u n i t , and t h e r e f o r e that v a r i a t i o n on any dimension, r e s p o n s e - r e l e v a n t or not, w i l l be important. I t o should be recognized, however, that i n these experiments the only aspect of the d i s p l a y that must be attended i s the p a r t i c u l a r f e a t u r e of relevance i n the cued l o c a t i o n of f i e l d - 2 . Indeed, f o r f e a t u r e c o n s i s t e n c y on the i r r e l e v a n t 6 3 dimension to i n t e r a c t with the obj e c t e f f e c t on the r e l e v a n t dimension r e q u i r e s i n f l u e n c e by an i r r e l e v a n t f e a t u r e of an i r r e l e v a n t item i n an i r r e l e v a n t l o c a t i o n . Whether c o n s i s t e n c y on the response dimension i n t e r a c t s with c o n s i s t e n c y on the r e s p o n s e - i r r e l e v a n t dimension may depend on the p a r t i c u l a r f e a t u r e s i n q u e s t i o n . Some fe a t u r e s tend to be processed independently of one another and others tend not to be. Garner and F e l f o l d y (1970) ( a l s o see Biederman & Checkosky, 1970) had s u b j e c t s s o r t s t i m u l i v a r y i n g along a p a i r of dichotomous dimensions i n t o two c a t e g o r i e s d i s t i n q u i s h e d by the value along one of the dimensions. The dimension which was i r r e l e v a n t to the c l a s s i f i c a t i o n task was c o r r e l a t e d with the r e l e v a n t dimension i n one c o n d i t i o n , and i t was u n c o r r e l a t e d with the r e l e v a n t dimension i n another c o n d i t i o n . These authors found that f o r some p a i r s of dimensions, such as value and chroma of the same c o l o r patch, c o r r e l a t e d v a r i a t i o n on the i r r e l e v a n t dimension improved s o r t i n g performance and orthogonal v a r i a t i o n on the i r r e l e v a n t dimension i n t e r f e r e d with performance. For other p a i r s of dimensions, such as the s i z e of a c i r c l e and the angle of a diameter drawn across i t , v a r i a t i o n on the i r r e l e v a n t dimension had no i n f l u e n c e on s o r t i n g performance. These types of dimension p a i r s were dubbed " i n t e g r a l " and " n o n i n t e g r a l " r e s p e c t i v e l y , and t h i s c l a s s i f i c a t i o n task has been used to assess the encoding independence, or s e p a r a b i l i t y , of v a r i o u s f e a t u r e dimensions. E x t r a p o l a t i n g from F e l f o l d y ' s (1974) r e s u l t s with t h i s 64 paradigm, the re-viewing of width i n f o r m a t i o n , f o r example, might i n v o l v e the mandatory re-viewing of height i n f o r m a t i o n too. The Monodimension Experiments Subjects and Apparatus A l l experiments drew from the same subject p o p u l a t i o n . U n i v e r s i t y of B r i t i s h Columbia students, with normal or corre c t e d - t o - n o r m a l v i s i o n , served as p a i d volunteer s u b j e c t s . Some i n d i v i d u a l s performed in more than one experiment. Experiments 1, 2, 4, and 5 each employed e i g h t s u b j e c t s ; Experiment 3 employed 12 s u b j e c t s . The f i v e monodimension experiments a l l employed the same apparatus. A D i g i t a l Equipment C o r p o r a t i o n (DEC) PDP 11/34 d i g i t a l computer was used to run the experiments. I t presented the v i s u a l d i s p l a y s on a DEC VR 17-LC black and white g r a p h i c s t e r m i n a l , and recorded the s u b j e c t s ' responses, which were made on a set of three t e l e g r a p h keys. A blue viewing f i l t e r was anchored i n a bracket attached to the f r o n t of the graphics t e r m i n a l to f i l t e r out any screen p e r s i s t e n c e and a l s o to ensure a constant d i s t a n c e (60 cm) and angle (normal) of s c r u t i n y . Experiment 1: Presence (Late-Cue Version) A l o g i c a l experiment with which to begin the i n v e s t i g a t i o n of spatiotemporal i n t e g r a t i o n of p h y s i c a l p r o p e r t i e s i s one concerned with the l o w e s t - l e v e l p r o p e r t y imaginable: mere presence. Responding "present" or "absent" to an object r e q u i r e s only the g r o s s e s t — a n d presumably the 65 e a r l i e s t - - o f p e r c e p t u a l a n a l y s e s : Indeed, under some circumstances, d e t e c t i o n responses can be made without a t t e n d i n g to or l o c a t i n g the t a r g e t (Treisman & Gelade, 1980). By r e q u i r i n g a simple presence/absence judgment, Experiment 1 p r o v i d e s maximal c o n t r a s t to the KTG experiments r e q u i r i n g l e t t e r i d e n t i f i c a t i o n . I f any task can be performed on the b a s i s of in f o r m a t i o n made a v a i l a b l e p r i o r to the o b j e c t - o r g a n i z a t i o n r e s p o n s i b l e f o r the ob j e c t e f f e c t , a d e t e c t i o n task should be i t . Method S t i m u l i and D i s p l a y . The four-box d i s p l a y (see Fi g u r e 3) was used. The change from a two-object to a f o u r - o b j e c t d i s p l a y was i n i t i a t e d because, i n these p h y s i c a l p r o p e r t i e s experiments, there i s grea t e r scope f o r v i s u a l v a r i a b i l i t y between the items presented in a given stimulus f i e l d . L e t t e r s are a l l v i s u a l l y s i m i l a r g l o b a l l y . In the p h y s i c a l -property experiments s t i m u l i w i t h i n a s i n g l e f i e l d can d i f f e r in t h e i r gross p h y s i c a l c h a r a c t e r i s t i c s . I t was reasoned that r e l a t i v e to a two-object d i s p l a y a f o u r - o b j e c t arrangement would " d i f f u s e " the d i f f e r e n c e between l i n e f i g u r e s c o n t a i n i n g d i s p a r a t e s t i m u l i (eg. i n s t e a d of one box being empty and one being f u l l , two boxes would be empty and two would be f u l l ) , thereby e n s u r i n g that no s i n g l e l i n e f i g u r e would stand out p e r c e p t u a l l y . T h i s was necessary i n order to a v o i d untoward asymmetries i n the a l l o c a t i o n of a t t e n t i o n to s t i m u l u s f i e l d - 1 . 66 P R E S E N T - C O N S I S T E N T F i g u r e 3. The four c o n d i t i o n s of the four-box d i s p l a y as used in the monodimension l a t e - c u e presence experiment. ( A c t u a l s i z e ; dashed l i n e s r e f e r to the f i r s t f i e l d , dashed arrows to motion, and s o l i d l i n e s to the second f i e l d ) . 67 A l l t r i a l s followed the same sequence, although the a b s o l u t e p o s i t i o n of the o b j e c t s on the screen v a r i e d randomly from t r i a l to t r i a l . F i r s t , four empty boxes, each composed of four l i n e seqments 1.2 degrees of v i s u a l arc (deg) i n l e n g t h , appeared e q u a l l y spaced around a c e n t r a l f i x a t i o n dot (0.1 deg). They were s i t u a t e d at the c o r n e r s of an imaginary square, t h e i r c e n t e r s 2.0 deg away from the f i x a t i o n dot. A f t e r a p e r i o d of 500 ms, the f i e l d - 1 s t i m u l i were presented: Two of the four empty boxes were f i l l e d with an a s t e r i s k (two 0.9 deg l i n e s and two 0.6 deg l i n e s ) , and the other two boxes were " f i l l e d " with blanks. T h i r t y m i l l i s e c o n d s l a t e r , the a s t e r i s k s were turned o f f , l e a v i n g a l l four boxes empty once a g a i n . Immediately upon removal of the f i e l d - 1 s t i m u l i , the four boxes moved outwards away from the f i x a t i o n dot i n s i x equal s t e p s . Though the motion was a s e r i e s of d i s c r e t e d i splacements, i t was s u b j e c t i v e l y continuous because the boxes completed a l l s i x jumps i n j u s t 7 0 + 2 ms. The motion of the boxes r e l a t i v e to the cen t e r of the screen had a sideward, t r a n s v e r s e component (0.2 deg per step) as w e l l as an outward, r a d i a l component (0.1 deg per s t e p ) , so the d i s p l a y as a whole appeared to r o t a t e and expand. Because they a l l moved e i t h e r c l o c k w i s e or c o u n t e r - c l o c k w i s e to the same extent, when they stopped moving the boxes were s t i l l e q u a l l y spaced i n a square c o n f i g u r a t i o n around the f i x a t i o n dot. Now the cen t e r of each box r e s i d e d at a g r e a t e r e c c e n t r i c i t y than before, 2.8 deg from f i x a t i o n . Each box 68 occupied a p o s i t i o n that was an equal d i s t a n c e from an adjacent couple of the o r i g i n a l , f i e l d - 1 box l o c a t i o n s . As soon as the boxes stopped moving, the f i e l d - 2 s t i m u l i and a cue were presented and l e f t on the screen u n t i l the su b j e c t responded. L i k e the f i e l d - 1 s t i m u l i , the f i e l d - 2 s t i m u l i were two a s t e r i s k s and two blanks, so once again two of the boxes were f i l l e d and two remained empty, although not n e c e s s a r i l y the same boxes as be f o r e . A b i p a r t i t e cue, which served to designate the t a r g e t box, was presented at the same time as the f i e l d - 2 s t i m u l i . The cue c o n s i s t e d of two s o l i d squares (0.4 deg on a side) appearing one on e i t h e r s i d e of the t a r g e t box and separated by a gap of 1.4 deg. Prox i m i t y between the f i e l d - 1 s t i m u l i and the ta r g e t was c o n t r o l l e d . That i s , the t a r g e t l o c a t i o n was the same t o t a l d i s t a n c e from the two preview l o c a t i o n s as i t was from the two nonpreview l o c a t i o n s . Moreover, the two stimulus l o c a t i o n s of f i e l d - 1 that were nearest to the target p o s i t i o n - - t h e nearest-neighbor l o c a t i o n s (see Figure 3)--were e q u a l l y near the t a r g e t p o s i t i o n . Once the subject responded and the f i e l d - 2 s t i m u l i and cue were removed from the screen, a p e r i o d of 1000 ms was allowed to elapse i n which only the four empty boxes remained on the screen. When t h i s p e r i o d ended and the boxes were turned o f f , a 900 ms i n t e r t r i a l i n t e r v a l was begun. The one second a f t e r - d i s p l a y of j u s t the four s t a t i o n a r y boxes was i n c l u d e d on the b a s i s of p i l o t r e s u l t s . Why the a f t e r -d i s p l a y should make any d i f f e r e n c e to the s u b j e c t ' s response 69 i s unknown, but i t has been repo r t e d elsewhere that a l l o w i n g s u b j e c t s to view an o b j e c t at r e s t , f o r a p e r i o d e i t h e r before or a f t e r i t has moved, i n c r e a s e s the v e l o c i t y at which that o b j e c t can move without appearing b l u r r e d (Smith & G u l i c k , 1956). Perhaps the a f t e r - d i s p l a y reduces p e r c e p t u a l ambiguity about e x a c t l y what the moving boxes do on each t r i a l , and so i s able to a f f e c t responses in general even though i t occurs a f t e r the response i s made on any s p e c i f i c t r i a l . C o n d i t i o n s and Stimulus Placement. The i d e n t i t i e s of the s t i m u l i comprising each stimulus f i e l d were h e l d constant a c r o s s c o n d i t i o n s : Two of the f i e l d - 1 boxes contained a s t e r i s k s and two co n t a i n e d blanks. Rather than the i d e n t i t y of the s t i m u l i , what d i d d i f f e r e n t i a t e c o n d i t i o n s was the f i g u r a l r e l a t i o n between the f i e l d - 1 and f i e l d - 2 s t i m u l i . Of p a r t i c u l a r importance i n t h i s regard were the two s t i m u l i of f i e l d - 1 that bore nearest-neighbor r e l a t i o n s to the t a r g e t . One nearest-neighbor s t i m u l u s was i n the target-yoked l o c a t i o n , and the other nearest-neighbor stimulus was i n a target-nonyoked l o c a t i o n . That i s , one nearest-neighbor stimulus was framed by the box that would l a t e r c o n t a i n the t a r g e t , and the other was framed by one of the three boxes that would l a t e r c o n t a i n d i s t r a c t o r s . Four types of t r i a l o c c u r r e d with equal frequency (see Fi g u r e 3). These t r i a l types d e f i n e d the four experimental c o n d i t i o n s : p r e s e n t - c o n s i s t e n t , p r e s e n t - i n c o n s i s t e n t , a b s e n t - c o n s i s t e n t and a b s e n t - i n c o n s i s t e n t . The f i r s t p a r t of 70 these compound c o n d i t i o n names r e f e r s to the s t a t u s of the t a r g e t , and the second r e f e r s to the f i g u r a l r e l a t i o n between the t a r g e t and i t s previews. "Consistency" i s used here l i k e i n the d i s c u s s i o n of KTG's work: On c o n s i s t e n t t r i a l s a preview was shown i n the t a r g e t box i n f i e l d - 1 , and on i n c o n s i s t e n t t r i a l s a nonpreview was shown i n the t a r g e t box in f i e l d - 1 . Once the p o s i t i o n of the t a r g e t was determined randomly (but with a l l p o s i t i o n s being used an equal number of t i m e s ) , the other s t i m u l i of f i e l d s 1 and 2 were p o s i t i o n e d a c c o r d i n g to c e r t a i n c o n s t r a i n t s (see F i g u r e 3 ) . The two f i e l d - 1 a s t e r i s k s were always p o s i t i o n e d so that one occupied one of the nearest-neighbor p o s i t i o n s and the other d i d not. In other words, on every t r i a l , one of the two nearest-neighbor f i e l d - 1 boxes contained an a s t e r i s k and one c o n t a i n e d a blank. The two a s t e r i s k s in f i e l d - 1 were always l o c a t e d i n boxes on opp o s i t e s i d e s of the c e n t r a l f i x a t i o n dot, never i n adjacent boxes. For both the p r e s e n t - c o n s i s t e n t and the absent-c o n s i s t e n t c o n d i t i o n s the two boxes of f i e l d - 2 that c o n t a i n e d a s t e r i s k s were the ones that had c o n t a i n e d a s t e r i s k s in f i e l d - 1 . For the p r e s e n t - i n c o n s i s t e n t t r i a l s the nontarget a s t e r i s k of f i e l d - 2 appeared i n the box that had occupied the target-nonyoked nearest-neighbor l o c a t i o n i n f i e l d - 1 . For a b s e n t - i n c o n s i s t e n t t r i a l s one of the a s t e r i s k s of f i e l d - 2 appeared i n the only d i s t r a c t o r box that had contained an a s t e r i s k i n f i e l d - 1 . The other a s t e r i s k of f i e l d - 2 was 71 p o s i t i o n e d a c c o r d i n g to which d i r e c t i o n the boxes r o t a t e d . T h i s second a s t e r i s k appeared in the f i e l d - 2 box s i t u a t e d i n the d i r e c t i o n from which the t a r g e t box had t r a v e l l e d (see F i g u r e 3). I t was p o s i t i o n e d t h i s way, a g a i n s t the flow of the t a r g e t box movement, to discourage i t from f u n c t i o n i n g as a terminus f o r the apparent motion of the a s t e r i s k in the t a r g e t box i n f i e l d - 1 (Ramachandran, 1981). R e c a l l that KTG found that moving boxes may be able to "launch" ( c f . Michotte, 1963) t h e i r contents toward a v a i l a b l e terminus s t i m u l i . Procedure. To begin each s e s s i o n (which l a s t e d about one hour) the subject read i n s t r u c t i o n s which were then summarized by the experimenter. Once qu e s t i o n s had been answered, the subject was l e f t alone i n the darkened t e r m i n a l room to perform two p r a c t i c e b l o c k s , each c o n s i s t i n g of 48 t r i a l s . When these b l o c k s were completed, e i g h t blocks of 48 d a t a - c o l l e c t i o n t r i a l s were begun. At the beginning of a block, a message appeared on the screen r e q u e s t i n g the subject to press the c e n t e r of three t e l e g r a p h keys in order to s t a r t the b l o c k . A f t e r each block the computer o f f e r e d the subject an o p p o r t u n i t y to r e s t . U n l i k e the l e t t e r experiments of KTG, the four-box experiments i n v o l v e a dichotomous response. I f there was an a s t e r i s k i n the cued box, the s u b j e c t was to press the r i g h t -hand t e l e g r a p h key, and i f there was no a s t e r i s k i n the cued box, the s u b j e c t was to press the l e f t - h a n d t e l e g r a p h key. Because these responses were dichotomous, and because of the 72 nature of the s t i m u l i employed, i t was d i f f i c u l t to choose c o n t r o l s t i m u l i that were n e u t r a l with r e s p e c t to the p h y s i c a l f e a t u r e s under i n v e s t i g a t i o n ( c f . de Groot, Thomassen & Hudson, 1982). I t i s not c l e a r , for example, what would c o n s t i t u t e a stimulus that i s j u s t as present as i t i s absent. Th e r e f o r e , i n c o n t r a s t to the e a r l i e r l e t t e r experiments, the presence experiment (and the four-box experiments in general) d i d not i n c l u d e a c o n d i t i o n i n which there was no preview in f i e l d - 1 . R e s u l t s and D i s c u s s i o n The mean RTs were: p r e s e n t - c o n s i s t e n t 508 ms p r e s e n t - i n c o n s i s t e n t 552 a b s e n t - c o n s i s t e n t 583 a b s e n t - i n c o n s i s t e n t 560 Planned orthogonal comparisons were made between c o n s i s t e n t and i n c o n s i s t e n t c o n d i t i o n s . The d i f f e r e n c e of 44 ms between the p r e s e n t - c o n s i s t e n t and p r e s e n t - i n c o n s i s t e n t c o n d i t i o n s was s i g n i f i c a n t (t(7) = 8.20, p < 0.001) as was the -23 ms d i f f e r e n c e between the a b s e n t - c o n s i s t e n t and the absent-i n c o n s i s t e n t c o n d i t i o n s (t(7) = -3.75, p = 0.007). The 67 ms d i f f e r e n c e between these two d i f f e r e n c e s was a l s o s i g n i f i c a n t (t( 7 ) = 6.99, p < 0.001). The o b j e c t e f f e c t d e s c r i b e d by KTG was manifested by the 'present' t r i a l s of Experiment 1: The p r e s e n t - c o n s i s t e n t c o n d i t i o n generated f a s t e r responses than d i d the p r e s e n t -i n c o n s i s t e n t c o n d i t i o n . However, on 'absent' t r i a l s the 73 opposite was t r u e . The a b s e n t - c o n s i s t e n t c o n d i t i o n generated slower responses than d i d the a b s e n t - i n c o n s i s t e n t c o n d i t i o n . Thus, the r e s u l t s of experiment 1 are ambiguous with respect to the qu e s t i o n of whether presence i s a p r o p e r t y subject to KTG's spatiotemporal i n t e g r a t i o n . An i n t e r p r e t a t i o n of Experiment 1 may occur to the reader by c o n s i d e r i n g the v i s u a l d i s t i n c t i v e n e s s of the two types of f i e l d - 1 s t i m u l u s , a s t e r i s k and blank. S t i m u l i o u t s i d e of the s u b j e c t ' s v o l u n t a r y focus of a t t e n t i o n can "capture" a t t e n t i o n a l resources (Kahneman & Chajczyk, 1983). An onset of an item i n two of the f i e l d - 1 boxes, and nothing at a l l i n the other two, may w e l l induce a s h i f t of a t t e n t i o n toward one of the occupied boxes. Indeed, KTG's d o u b l e - f l a s h experiment demonstrated that stimulus onset may be one of the more powerful a t t r a c t o r s of a t t e n t i o n to a l o c a t i o n i n f i e l d -1 . The f o u r - o b j e c t d i s p l a y was developed f o r these f e a t u r a l preview experiments e x p r e s s l y f o r the purpose of decreasing the v i s u a l d i s t i n c t i v e n e s s of any given s t i m u l u s onset i n f i e l d - 1 . N e v e r t h e l e s s , i n c r e a s i n g the number of boxes does not solve the problem i n p r i n c i p l e , and given the r e s u l t s of Experiment 1, i t i s q u e s t i o n a b l e whether i t s o l v e s the problem i n p r a c t i c e e i t h e r . To see t h i s , c o n s i d e r the h y p o t h e s i s , r i v a l to the spatiotemporal i n t e g r a t i o n idea, that can be b u i l t on the assumption that a t t e n t i o n i s a t t r a c t e d t o one of the occupied boxes of f i e l d - 1 . Suppose t h a t , once a t t r a c t e d to a given box, the s u b j e c t ' s a t t e n t i o n can f o l l o w that box to i t s 74 t e r m i n a l p o s i t i o n i n f i e l d - 2 . If the fo l l o w e d box turns out to be the t a r g e t box, then response to the t a r g e t w i l l be r e l a t i v e l y f a s t because the s u b j e c t ' s a t t e n t i o n ends up in the cued l o c a t i o n . I f , however, the fo l l o w e d box turns out to be a d i s t r a c t o r box, then response w i l l be r e l a t i v e l y slow because the s u b j e c t ' s a t t e n t i o n ends up d i s p l a c e d from the cued l o c a t i o n and has to be s h i f t e d to f a l l upon the t a r g e t . T h i s s e l e c t - a n d - f o l l o w r i v a l h y p o t h e s i s i s l i k e that encountered i n the KTG work, but here there i s reason to suspect that s u b j e c t s would be b i a s e d to s e l e c t a p a r t i c u l a r box i n f i e l d - 1 ( i e . an occupied one). The s e l e c t - a n d - f o l l o w h y p o t h e s i s makes r e t r o d i c t i o n s about the p a t t e r n of RTs that should be obtained from Experiment 1. On a random h a l f of the p r e s e n t - c o n s i s t e n t t r i a l s , the subject should s e l e c t the t a r g e t box to f o l l o w and so should experience an RT advantage. On present-i n c o n s i s t e n t t r i a l s , however, the t a r g e t box never c o n t a i n s an a s t e r i s k i n f i e l d - 1 and so should never be s e l e c t e d . T h e r e f o r e , p r e s e n t - i n c o n s i s t e n t t r i a l s should never b e n e f i t from f o l l o w i n g and so should produce slower responses than the p r e s e n t - c o n s i s t e n t t r i a l s . T h i s r e s u l t mimics the obj e c t e f f e c t and i s , of course, e x a c t l y l i k e the r e s u l t obtained on the 'present' t r i a l s of Experiment 1. By the same reasoning, the s e l e c t - a n d - f o l l o w hypothesis r e t r o d i c t s the o b j e c t - e f f e c t - i n c o m p a t i b l e r e s u l t s obtained on the 'absent' t r i a l s of Experiment 1 . According to the s e l e c t - a n d - f o l l o w h y p o t h e s i s , on the 'absent' t r i a l s i t i s 75 the i n c o n s i s t e n t c o n d i t i o n which should b e n e f i t from f o l l o w i n g and not the c o n s i s t e n t c o n d i t i o n (see F i g u r e 3). Th e r e f o r e , the s e l e c t - a n d - f o l l o w hypothesis r e t r o d i c t s a negative o b j e c t e f f e c t on 'absent' t r i a l s . A b s e n t - c o n s i s t e n t t r i a l s should produce slower responses than absent-i n c o n s i s t e n t t r i a l s , which i s j u s t what happened i n Experiment 1. Experiment 2: Presence (Early-Cue V e r s i o n ) Experiment 2 t e s t s f o r a presence o b j e c t e f f e c t under c o n d i t i o n s that should not be conducive to the s e l e c t - a n d -f o l l o w s t r a t e g y . In Experiment 1 the cue was d i s p l a y e d l a t e , s i m u l t a n e o u s l y with the f i e l d - 2 s t i m u l i . As a consequence, there was nothing to occupy a t t e n t i o n while the f i e l d - 1 s t i m u l i were being presented, and so there was nothing to prevent one of the boxes framing these s t i m u l i from being s e l e c t e d and followed. In Experiment 2 the p r o b a b i l i t y of f o l l o w i n g i s reduced by having the cue appear e a r l y , 40 ms before even the f i e l d - 1 a s t e r i s k s are presented. T h i s e a r l y cue i s intended to a t t r a c t s e l e c t i v e a t t e n t i o n to the t a r g e t l o c a t i o n , away from the f i e l d - 1 l o c a t i o n s , before the onsets i n the f i e l d - 1 l o c a t i o n s have a chance to a t t r a c t a t t e n t i o n to themselves. I f the s e l e c t - a n d - f o l l o w s t r a t e g y i s r e s p o n s i b l e f o r the b i z a r r e r e s u l t s of Experiment 1, and i f the e a r l y cue i s e f f i c a c i o u s i n a t t r a c t i n g s e l e c t i v e a t t e n t i o n away from f i e l d - 1 , then Experiment 2 should produce the standard o b j e c t e f f e c t on both present and absent t r i a l s . 76 Method The method of Experiment 2 was the same as that of Experiment 1 except the cue was presented e a r l y , 40 ms before the f i e l d - 1 s t i m u l i were d i s p l a y e d . Note that t h i s e a r l y cue i s e a r l i e r than KTG's e a r l y cue, which d i d not appear u n t i l f i e l d - 1 was turned o f f . As in Experiment 1, the cue remained on the screen u n t i l the subject responded. R e s u l t s and D i s c u s s i o n The mean RTs were: p r e s e n t - c o n s i s t e n t 486 ms p r e s e n t - i n c o n s i s t e n t 526 a b s e n t - c o n s i s t e n t 555 a b s e n t - i n c o n s i s t e n t 576 Planned orthogonal comparisons were made between c o n s i s t e n t and i n c o n s i s t e n t c o n d i t i o n s . The d i f f e r e n c e of 40 ms between the p r e s e n t - c o n s i s t e n t and p r e s e n t - i n c o n s i s t e n t c o n d i t i o n s was s i g n i f i c a n t ( t(7) = 3.66, p = 0.008) as was the 21 ms d i f f e r e n c e between the a b s e n t - c o n s i s t e n t and absent-i n c o n s i s t e n t c o n d i t i o n s (t(7) = 4.77, p = 0.002). The 19 ms d i f f e r e n c e between these two d i f f e r e n c e s was not s i g n i f i c a n t (t(7) = 1.89, p = 0.100). The e r r o r rate was 1.6% f o r c o n s i s t e n t c o n d i t i o n s and 3.0% f o r i n c o n s i s t e n t c o n d i t i o n s , i n d i c a t i n g that the r e s u l t s are not the m a n i f e s t a t i o n of a speed-accuracy trade o f f . The r e s u l t s of Experiment 2 exemplify the p a t t e r n of RTs t y p i c a l of the l e t t e r preview experiments of KTG: C o n s i s t e n t t r i a l s were responded to more r a p i d l y than were i n c o n s i s t e n t 77 t r i a l s . In sharp c o n t r a s t to the r e s u l t s of Experiment 1, a presence o b j e c t e f f e c t was obtained both on the 'present' t r i a l s and on the 'absent' t r i a l s . Although the two experiments produced a s i m i l a r c o n s i s t e n c y e f f e c t on 'present' t r i a l s (44 ms f o r Experiment 1, 40 ms f o r Experiment 2) they produced opposite c o n s i s t e n c y e f f e c t s on 'absent' t r i a l s (-23 ms f o r Experiment 1, 21 ms f o r Experiment 2). The generation of a p o s i t i v e o b j e c t e f f e c t on 'absent' t r i a l s stands i n c o n t r a d i c t i o n to the s e l e c t - a n d - f o l l o w h y p o t h e s i s . I t seems t h a t under c o n d i t i o n s l i k e those of experiment 1 encouraging the s e l e c t - a n d - f o l l o w s t r a t e g y , r e s u l t s p e c u l i a r to such a s t r a t e g y can be obtained. But given that r e s u l t s c o n t r a r y to such a f o l l o w i n g s t r a t e g y were obt a i n e d i n Experiment 2, i t appears that the implementation of an e a r l y cue i s an adequate p r e c a u t i o n a g a i n s t f o l l o w i n g . The f a c t t h at the o b j e c t e f f e c t on the 'absent' t r i a l s of Experiment 2 was ( n o n s i g n i f i c a n t l y ) weaker than the o b j e c t e f f e c t on the 'present' t r i a l s , suggests there may s t i l l have been some tendency to s e l e c t and f o l l o w . However, t h i s tendency was dominated by another, opposing process, as evidenced by the p o s i t i v e s i g n of the 'absent' o b j e c t e f f e c t . The c o n t e n t i o n here would be that t h i s opposing process i s r e - v i e w i n g , although whether presence or b r i g h t n e s s i s the best way to c h a r a c t e r i z e the property being re-viewed i s not c e r t a i n . 78 Experiment 3: S i z e Experiment 3 i s analogous to Experiment 2 except that the f e a t u r e under i n v e s t i g a t i o n i s not presence but s i z e . T h e r e f o r e , c o n s i s t e n c y here r e f e r s to s i z e c o n s i s t e n c y r a t h e r than presence c o n s i s t e n c y . Method Except f o r the f o l l o w i n g d i f f e r e n c e s , the method of Experiment 3 was the same as that of Experiment 2. S t i m u l i . The important d i f f e r e n c e between Experiment 3 and Experiment 2 i s i n the f i e l d - 1 and f i e l d - 2 s t i m u l i . For each occurrence of an a s t e r i s k i n Experiment 2 there o c c u r r e d an i d e n t i c a l a s t e r i s k (two 0.9 deg l i n e s and two 0.6 deg l i n e s ) i n Experiment 3. But f o r each occurrence of a blank i n Experiment 2 there o c c u r r e d i n Experiment 3 a small a s t e r i s k (two 0.6 deg l i n e s and two 0.4 deg l i n e s ) . C o n d i t i o n s and Procedure. The experimental c o n d i t i o n s were l a r g e - c o n s i s t e n t , l a r g e - i n c o n s i s t e n t , s m a l l - c o n s i s t e n t and s m a l l - i n c o n s i s t e n t . "Large" responses were made on the rig h t - h a n d key and " s m a l l " responses were made on the l e f t -hand key. O r i g i n a l l y Experiment 3 i n c l u d e d two c o n t r o l c o n d i t i o n s . These c o n d i t i o n s i n v o l v e d a normal f i e l d - 2 with a l a r g e or small a s t e r i s k i n each box, but an unusual s o r t of f i e l d - 1 c o n s i s t i n g of four empty boxes. As mentioned e a r l i e r , s e l e c t i n g a p p r o p r i a t e n e u t r a l c o n t r o l s t i m u l i i s d i f f i c u l t . Indeed, even i n the e s t a b l i s h e d paradigm of l e x i c a l d e c i s i o n priming, the d i f f i c u l t i e s a s s o c i a t e d with d e v i s i n g a s u i t a b l e n e u t r a l prime stimulus that i t s e l f 79 produces n e i t h e r f a c i l i t a t i o n nor i n h i b i t i o n have not been overcome. De Groot, Thomassen and Hudson (1982) note that the popular, s t r i n g - o f - c r o s s e s " n e u t r a l " prime may have l e d to an o v e r e s t i m a t i o n of f a c i l i t a t i o n and an underestimation of i n h i b i t i o n i n the l e x i c a l d e c i s i o n l i t e r a t u r e . They use the word blank as a n e u t r a l prime, but then conclude that even t h i s may not provide a s u i t a b l e measure of b a s e l i n e pr iming. For two reasons the blank c o n t r o l c o n d i t i o n s used i n the c u r r e n t experiment were pr o b l e m a t i c . F i r s t , the c o n t r o l and experimental t r i a l s d i v e rged too r a d i c a l l y in p e r c e p t u a l q u a l i t y to be s t r i c t l y comparable. For example, on the preview t r i a l s f i e l d - 1 i n c l u d e d stimulus onsets and on the c o n t r o l t r i a l s i t d i d not. Second, as suggested above, a blank may simply not be n e u t r a l with respect to s i z e . Indeed, the r e s u l t s obtained with the c o n t r o l c o n d i t i o n s suggest that a f i e l d - 1 blank, at l e a s t in the context of these s i z e judgments, assumes the same pe r c e p t u a l r o l e as a small s t i m u l u s . T h e r e f o r e , although s i x c o n d i t i o n s were run — i n 12 blocks of 32 t r i a l s each--only the four t y p i c a l experimental c o n d i t i o n s w i l l be d i s c u s s e d h e n c e f o r t h . The i n t e r e s t e d reader w i l l f i n d the data f o r a l l s i x c o n d i t i o n s and a d i s c u s s i o n of them i n the Appendix. R e s u l t s and D i s c u s s i o n The mean RTs were: 80 l a r g e - c o n s i s t e n t 515 ms l a r g e - i n c o n s i s t e n t 540 s m a l l - c o n s i s t e n t 557 s m a l l - i n e o n s i stent 583 Planned orthogonal comparisons were made between c o n s i s t e n t and i n c o n s i s t e n t c o n d i t i o n s . The d i f f e r e n c e of 25 ms between the l a r g e - c o n s i s t e n t and l a r g e - i n c o n s i s t e n t c o n d i t i o n s was s i g n i f i c a n t (t_( 1 1 ) = 4.63, p < 0.001) as was the 26 ms d i f f e r e n c e between the s m a l l - c o n s i s t e n t and s m a l l -i n c o n s i s t e n t c o n d i t i o n s (t(11 ) = 4.41, p = 0.001). The e r r o r r a t e was 2.8% f o r c o n s i s t e n t c o n d i t i o n s and 5.3% f o r i n c o n s i s t e n t c o n d i t i o n s , i n d i c a t i n g that the r e s u l t s are not the m a n i f e s t a t i o n of a speed-accuracy trade o f f . C o n s i s t e n t t r i a l s were responded to more r a p i d l y than were i n c o n s i s t e n t t r i a l s . That i s , both when the response was " l a r g e " and when the response was " s m a l l " , an o b j e c t e f f e c t was obtained with the s i z e task. L i k e the r e s u l t s obtained with presence i n Experiment 2, the s i z e r e s u l t s f o l l o w the p a t t e r n c o n s i d e r e d to be demonstrative of spatiotemporal i n f o r m a t i o n i n t e g r a t i o n . Experiments 4 and 5: Presence and Si z e (Lonq-Duration-Preview The f i n d i n g that c o n s i s t e n t t r i a l s were responded to more r a p i d l y than were i n c o n s i s t e n t t r i a l s i n the e a r l y - c u e presence and s i z e experiments i m p l i e s the spatiotemporal i n t e g r a t i o n of presence and s i z e i n f o r m a t i o n . A r i v a l h y p o t h e s i s , t h a t the r e l a t i v e quickness of response on Ve r s i o n s ) 81 c o n s i s t e n t t r i a l s i s i n f a c t a r e s u l t of s e l e c t i n g the t a r g e t box i n f i e l d - 1 and f o l l o w i n g i t to the cued l o c a t i o n in f i e l d - 2 , was explo r e d and r e j e c t e d . Another, r e l a t e d r i v a l h y p o t h e s i s has not been r u l e d out. E n t e r t a i n two s u p p o s i t i o n s . F i r s t , suppose that the su b j e c t confuses f i e l d - 1 with f i e l d - 2 and mistakenly i n i t i a t e s a response to the f i r s t r a t her than to the second f i e l d . Second, suppose--and t h i s i s the dangerous p a r t - - t h a t the s u b j e c t i s somehow bia s e d toward responding to the t a r g e t box i n f i e l d - 1 . Under these circumstances, a c o n s i s t e n c y e f f e c t would r e s u l t f o r reasons other than i n f o r m a t i o n i n t e g r a t i o n . On c o n s i s t e n t t r i a l s the c o r r e c t response would be i n i t i a t e d and so cou l d be maintained when the t a r g e t a c t u a l l y appeared; on i n c o n s i s t e n t t r i a l s the i n c o r r e c t response would be i n i t i a t e d and so would need to be i n h i b i t e d and r e p l a c e d by the c o r r e c t response when the t a r g e t a c t u a l l y appeared. Both s u p p o s i t i o n s upon which t h i s c o n f u s i o n hypothesis i s based are weak on a p r i o r i grounds. Assuming f o r the moment that s u b j e c t s do respond to the f i r s t f i e l d , such behavior would not produce a sp u r i o u s object e f f e c t unless the stimulus i n the t a r g e t box were responded t o . I t i s ra t h e r u n l i k e l y that s u b j e c t s c o u l d s e l e c t the f i e l d - 1 s t i m u l u s i n the t a r g e t box. To respond to t h i s s t i m u l u s , s u b j e c t s would have to work backwards from the p o s i t i o n of the cue to the moving boxes, determine which of those boxes was heading i n the d i r e c t i o n of the cue, and i n i t i a t e a 82 response on the b a s i s of some s o r t of p e r s i s t i n g r e p r e s e n t a t i o n of the stimulus that had i n h a b i t e d the now-empty t a r g e t b o x - - a l l i n 70 ms. It i s u n l i k e l y that the s u b j e c t would respond to f i e l d - 1 anyway. C e r t a i n l y the subject has nothing to gain from responding to f i e l d - 1 on purpose because there are an equal number of c o n s i s t e n t and i n c o n s i s t e n t t r i a l s , so t h i s s t r a t e g y would turn out to be c o s t l y as o f t e n as not. Inadvertent response to f i e l d - 1 i s a l s o u n l i k e l y because, as the c o n t r a s t between the outcomes of Experiment 1 and Experiment 2 suggests, the e a r l y cue e f f e c t i v e l y d i r e c t s a t t e n t i o n to the t a r g e t l o c a t i o n , away from f i e l d - 1 . Furthermore, the two stimulus f i e l d s are s p a t i a l l y d i s t i n c t , and c o n f u s i o n i n s p a t i a l s e l e c t i o n tends only to be a problem when that s e l e c t i o n i s d i f f i c u l t (Duncan, 1980), which i t i s not in these experiments. Des p i t e the weakness of the c o n f u s i o n h y p o t h e s i s , the one t h i n g that makes i t p l a u s i b l e i s the f a c t that temporally the two s t i m u l u s f i e l d s are only separated by 70 ms. As a consequence, the subject may not d i s t i n g u i s h them w e l l temporally, and hence may i n i t i a l l y respond to f i e l d - 1 r a t h e r than to f i e l d - 2 . Experiments 4 and 5 are designed to t e s t f o r f e a t u r a l o b j e c t e f f e c t s under c o n d i t i o n s i n which the two stimulus f i e l d s are h i g h l y d i s t i n c t temporally and not c o n f u s a b l e i n terms of which one i s supposed to c o n t r o l response. 83 Method D i s p l a y . In most regards Experiments 4 and 5 were the same as Experiments 2 and 3 r e s p e c t i v e l y . The major d i f f e r e n c e was that i n Experiments 4 and 5 the f i e l d - 1 s t i m u l i remained on the screen f o r 800 ms r a t h e r than for the 30 ms of the e a r l i e r experiments. T h i s meant that i n s t e a d of the onsets of the two f i e l d s being separated by only 100 ms, they were now separated by 870 ms. The cue was presented 660 ms a f t e r the preview f i e l d had been turned on, so i t appeared 140 ms before the t a r g e t f i e l d , j u s t as i t d i d i n Experiments 2 and 3. Procedure. Experiments 4 and 5, i n v o l v i n g presence and s i z e tasks r e s p e c t i v e l y , were run together i n a s i n g l e one hour s e s s i o n . Subjects performed i n one experiment, took a r e s t , and then performed i n the other. Half of the subjects performed Experiment 4 f i r s t and the other h a l f performed Experiment 5 f i r s t . In each experiment two b l o c k s of 48 p r a c t i c e t r i a l s preceded s i x blocks of 48 d a t a - c o l l e c t i o n t r i a l s . R e s u l t s and D i s c u s s i o n The mean RTs f o r Experiment 4 were: p r e s e n t - c o n s i s t e n t 431 ms p r e s e n t - i n c o n s i s t e n t 477 a b s e n t - c o n s i s t e n t 460 a b s e n t - i n c o n s i s t e n t 499 Planned orthogonal comparisons were made between c o n s i s t e n t and i n c o n s i s t e n t c o n d i t i o n s . The d i f f e r e n c e of 46 ms between .84 the p r e s e n t - c o n s i s t e n t and p r e s e n t - i n c o n s i s t e n t c o n d i t i o n s was s i g n i f i c a n t (t(7) = 5.07, p = 0.001) as was the 39 ms d i f f e r e n c e between the a b s e n t - c o n s i s t e n t and the absent-i n c o n s i s t e n t c o n d i t i o n s ( t ( 7 ) = 5.39, p = 0.001). The e r r o r r a t e was 1.4% f o r c o n s i s t e n t c o n d i t i o n s and 2.8% f o r i n c o n s i s t e n t c o n d i t i o n s , i n d i c a t i n g that the r e s u l t s are not the m a n i f e s t a t i o n of a speed-accuracy trade o f f . The mean RTs for Experiment 5 were: l a r g e - c o n s i s t e n t 493 ms l a r g e - i n c o n s i s t e n t 518 s m a l l - c o n s i s t e n t 513 s m a l l - i n c o n s i s t e n t 544 Planned orthogonal comparisons were made between c o n s i s t e n t and i n c o n s i s t e n t c o n d i t i o n s . The d i f f e r e n c e of 25 ms between the l a r g e - c o n s i s t e n t and l a r g e - i n c o n s i s t e n t c o n d i t i o n s was s i g n i f i c a n t ( t ( 7 ) = 2.41, p = 0.047) as was the 31 ms d i f f e r e n c e between the s m a l l - c o n s i s t e n t and s m a l l -i n c o n s i s t e n t c o n d i t i o n s ( t ( 7 ) = 5.55, p < 0.001). The e r r o r r a t e was 2.5% f o r c o n s i s t e n t c o n d i t i o n s and 3.1% f o r i n c o n s i s t e n t c o n d i t i o n s , i n d i c a t i n g that the r e s u l t s here too are not the m a n i f e s t a t i o n of a speed-accuracy trade o f f . Both l o n g - d u r a t i o n preview experiments produced c l e a r o b j e c t e f f e c t s under c o n d i t i o n s i n which f i e l d s 1 and 2 were h i g h l y d i s t i n g u i s h a b l e . T h e r e f o r e , n e i t h e r the presence obj e c t e f f e c t nor the s i z e o b j e c t e f f e c t can be a t t r i b u t e d to a mere response c o n f u s i o n of the two stimulus f i e l d s . In a d d i t i o n , these r e s u l t s are i n c o n s i s t e n t with any suggestion 85 that the object e f f e c t may depend on v i s i b l e p e r s i s t e n c e , because the d u r a t i o n of such p e r s i s t e n c e i s i n v e r s e l y r e l a t e d to stimulus d u r a t i o n ( C o l t h e a r t , 1980); there would probably be no v i s i b l e p e r s i s t e n c e a f t e r the o f f s e t of a 1000 ms stimulus ( c f . Di L o l l o , 1980). The Duodimension Experiments I t has been shown i n the f o r e g o i n g that tasks i n v o l v i n g p h y s i c a l p r o p e r t i e s are able to generate o b j e c t e f f e c t s . I t has not been determined, in terms of spatiotemporal i n f o r m a t i o n i n t e g r a t i o n , how p h y s i c a l p r o p e r t i e s i n t e r a c t with one another. Are f e a t u r e s re-viewed independently or i s c o n s i s t e n c y on one f e a t u r e of a target-preview p a i r a f f e c t e d by c o n s i s t e n c y on other f e a t u r e s of that stimulus p a i r ? The duodimension experiments are designed to answer t h i s q u e s t i o n . As the name suggests, the duodimension experiments do not i n v o l v e the c o n s i s t e n c y of j u s t one f e a t u r e dimension. Of i n t e r e s t now i s another p h y s i c a l property i n a d d i t i o n to the one c o n t r o l l i n g response. A s l i g h t l y d i f f e r e n t p e r s p e c t i v e on the duodimension experiments r e v e a l s them to be important because they do not s u f f e r from what may be c o n s i d e r e d a confound in the monodimension experiments between the property supposedly being t e s t e d and stimulus i d e n t i t y . I t i s u n c e r t a i n whether the o b j e c t - s p e c i f i c advantage observed i n the f o r e g o i n g experiments o b t a i n s because the s t i m u l i i n the t a r g e t box are of the same value along the presence or s i z e dimension, or because they are wholly i d e n t i c a l s t i m u l i . I f the o b j e c t 86 e f f e c t depends e x c l u s i v e l y on stimulus i d e n t i t y , then the p o s i t i v e r e s u l t s i n the fo r e g o i n g experiments are not evidence of the spatiotemporal i n t e g r a t i o n of p h y s i c a l p r o p e r t i e s a f t e r a l l . S u b j e c t s and Apparatus A l l experiments drew from the same s u b j e c t p o p u l a t i o n . U n i v e r s i t y of B r i t i s h Columbia students, with normal or corrected-to-normal v i s i o n , served as p a i d v o l u n t e e r s u b j e c t s . Some i n d i v i d u a l s performed i n more than one experiment, although no o v e r l a p was allowed between the s u b j e c t s of experiments 8 and 9. Experiment 6 employed e i g h t s u b j e c t s ; Experiment 7 employed 12 s u b j e c t s ; and Experiments 8 and 9 each employed 24 s u b j e c t s . Experiments 6 and 7 i n v o l v e d the same apparatus used i n the f i v e monodimension experiments. For experiments 8 and 9 the same PDP 11/34 computer that c o n t r o l l e d the previous experiments was used, but u n l i k e the e a r l i e r experiments a c o l o r g r a p h i c s d i s p l a y t e r m i n a l — a n I n t e l l i g e n t Systems  C o r p o r a t i o n I n t e c o l o r t e r m i n a l model BS0C)1G--was employed. A head r e s t without a viewing f i l t e r was used with t h i s t e r m i n a l . A microphone and a Gerbrands G1341 v o i c e key accepted responses from the s u b j e c t . Otherwise the apparatus of Experiments 8 and 9 was the same as that employed i n Experiments 1 through 7. 87 Experiment 6: Presence (Shape as Response-Irrelevant Dimension) Method S t i m u l i and D i s p l a y . Experiment 6 u t i l i z e d the four-box d i s p l a y and was i n most resp e c t s the same as the b a s i c presence experiment, Experiment 2. The major d i f f e r e n c e was t h a t Experiment 6 i n v o l v e d not only a s t e r i s k s (two 0.9 deg l i n e s and two 0.6 deg l i n e s ) and blanks, but a l s o diamonds (four 0.6 deg l i n e s ) as s t i m u l i . The two f i g u r e s presented c o n c u r r e n t l y i n the same f i e l d were always the same, e i t h e r both a s t e r i s k s or both diamonds. C o n d i t i o n s and Procedure. There were f i v e c o n d i t i o n s : p r e s e n t - c o n s i s t e n t - 1 ( c o n s i s t e n t shape), p r e s e n t - c o n s i s t e n t - 2 ( i n c o n s i s t e n t shape), p r e s e n t - i n c o n s i s t e n t , a b s e n t - c o n s i s t e n t and a b s e n t - i n c o n s i s t e n t . Two 4 0 - t r i a l blocks of p r a c t i c e were performed before the 15, 4 0 - t r i a l blocks of data-c o l l e c t i o n t r i a l s . As in Experiment 2, the s u b j e c t s were to respond to the presence or absence of a stimulus; they were t o l d t h a t the shape of the s t i m u l u s d i d not matter and to respond "present" i f e i t h e r shape appeared in the cued box. R e s u l t s and D i s c u s s i o n The mean RTs were: p r e s e n t - c o n s i s t e n t - 1 ( c o n s i s t e n t shape) 398 ms p r e s e n t - c o n s i s t e n t - 2 ( i n c o n s i s t e n t shape) 41 1 p r e s e n t - i n c o n s i s t e n t 427 a b s e n t - c o n s i s t e n t 438 a b s e n t - i n c o n s i s t e n t 453 88 The t y p i c a l planned comparison between the a b s e n t - c o n s i s t e n t and a b s e n t - i n c o n s i s t e n t c o n d i t i o n s was made and the r e s u l t i n g 15 ms d i f f e r e n c e was s i g n i f i c a n t (t(7) = 4.46, p = 0.003). Three comparisons were made w i t h i n the 'present' c o n d i t i o n s . The 29 ms d i f f e r e n c e between the p r e s e n t - c o n s i s t e n t - 1 ( c o n s i s t e n t shape) and the p r e s e n t - i n c o n s i s t e n t c o n d i t i o n s was s i g n i f i c a n t (t(7) = 4.77, p = 0.002). Likewise the 16 ms d i f f e r e n c e between the p r e s e n t - c o n s i s t e n t - 2 ( i n c o n s i s t e n t shape) and the p r e s e n t - i n c o n s i s t e n t c o n d i t i o n s was s i g n i f i c a n t (t(7) = 4.83, p = 0.002). The d i f f e r e n c e of 13 ms between these two e f f e c t s was i t s e l f s i g n i f i c a n t (t_(7) = 2.69, p = 0.031). The e r r o r r a t e was 3.0% f o r c o n s i s t e n t c o n d i t i o n s and 5.1% f o r i n c o n s i s t e n t c o n d i t i o n s , i n d i c a t i n g that the r e s u l t s are not the m a n i f e s t a t i o n of a speed-accuracy trade o f f . As i n the previous experiments, in Experiment 6 c o n s i s t e n t c o n d i t i o n s were responded to more r a p i d l y than were i n c o n s i s t e n t c o n d i t i o n s . The new f i n d i n g here i s that t h i s object e f f e c t o b t a i n s , a l b e i t to a l e s s e r extent, when the t a r g e t and i t s preview are i n c o n s i s t e n t with r e s p e c t to a f e a t u r e dimension other than the one c o n t r o l l i n g response. That i s , shape d i s p a r i t y reduced the presence o b j e c t e f f e c t but d i d not e l i m i n a t e i t . Experiment 7: S i z e (Shape as Response-Irrelevant Dimension)  Method S t i m u l i and D i s p l a y . Experiment 7 u t i l i z e d the four-box d i s p l a y and was s i m i l a r to Experiment 3, except t h a t , as i n 89 experiment 6, s t i m u l i of two shapes were used. Experiment 7 employed two s i z e s of a s t e r i s k and two s i z e s of diamond. Large a s t e r i s k s were composed of two 0.9 deg l i n e s and two 0.6 deg l i n e s and small a s t e r i s k s were composed of two 0.6 deg l i n e s and two 0.4 deg l i n e s . Large diamonds were composed of four 0.6 deg l i n e s and small diamonds were composed of four 0.4 deg l i n e s . Due to programmer l i m i t a t i o n s only diamond shapes appeared i n f i e l d - 2 and only a s t e r i s k shapes appeared i n f i e l d - 1 . C o n d i t i o n s and Procedure. Because the t a r g e t box always contained a diamond i n f i e l d - 2 and an a s t e r i s k i n f i e l d - 1 , a l l t r i a l s were shape i n c o n s i s t e n t . With resp e c t to the response dimension however, the four t y p i c a l c o n d i t i o n s e x i s t e d : l a r g e - c o n s i s t e n t , l a r g e - i n c o n s i s t e n t , s m a l l -c o n s i s t e n t , s m a l l - i n c o n s i s t e n t . I f the diamond i n the cued box was l a r g e the right-hand response key was to be pressed, and i f the diamond i n the cued box was sm a l l , the l e f t - h a n d response key was to be pressed. E i g h t 4 8 - t r i a l blocks were run a f t e r two 4 8 - t r i a l b l o c ks of p r a c t i c e t r i a l s had been s a t i s f a c t o r i l y completed. R e s u l t s and D i s c u s s i o n The mean RTs were: l a r g e - c o n s i s t e n t 500 ms l a r g e - i n c o n s i s t e n t 498 s m a l l - c o n s i s t e n t 510 s m a l l - i n c o n s i s t e n t 519 The usual planned orthogonal comparisons were made between 90 c o n s i s t e n t and i n c o n s i s t e n t c o n d i t i o n s . The d i f f e r e n c e of 2 ms between the l a r g e - c o n s i s t e n t and l a r g e - i n c o n s i s t e n t c o n d i t i o n s was not s i g n i f i c a n t (t(11 ) = -0.39, p = 0.704). The d i f f e r e n c e of 9 ms between the s m a l l - c o n s i s t e n t and s m a l l - i n c o n s i s t e n t c o n d i t i o n s was a l s o not s i g n i f i c a n t (t(11 ) = 2.05, p = 0.065). The d i f f e r e n c e between these two d i f f e r e n c e s was not s i g n i f i c a n t e i t h e r (t(11) = 2.05, p = 0.065). The e r r o r r a t e was 2.3% f o r c o n s i s t e n t c o n d i t i o n s and 3.0% f o r i n c o n s i s t e n t c o n d i t i o n s . Experiment 7 f a i l e d to produce any s i g n i f i c a n t object e f f e c t s . I t appears that shape i n c o n s i s t e n c y i n the t a r g e t -preview p a i r does not merely reduce the s i z e o b j e c t e f f e c t as i t d i d the presence o b j e c t e f f e c t ; shape i n c o n s i s t e n c y e l i m i n a t e s the s i z e o b j e c t e f f e c t . T h i s c o n c l u s i o n may seem brash given that the object e f f e c t witnessed on the 'small' c o n d i t i o n s was n e a r l y s i g n i f i c a n t . However, when d e a l i n g with small s t i m u l i i t i s not s u r p r i s i n g to f i n d t h a t shape i n c o n s i s t e n c y does not have the f u l l damping i n f l u e n c e on the s i z e object e f f e c t i t might otherwise have. This i s because, as s t i m u l i get s m a l l e r , shape d i f f e r e n c e s between them are l i k e l y to become l e s s p e r c e p t i b l e . In short, very small s h a p e - i n c o n s i s t e n t s t i m u l i v i s u a l l y approximate shape-consistent s t i m u l i . Thus, for now at l e a s t , i t i s probably best to focus on the f a c t t h at the s m a l l - t a r g e t r e s u l t s are n o n s i g n i f i c a n t rather than on the f a c t that they are almost s i g n i f i c a n t . 91 Experiment 8: Color (Letter-Shape as Resp o n s e - I r r e l e v a n t Dimension) The f i n a l two experiments employed the Ternus d i s p l a y . The four-box experiments generated o b j e c t e f f e c t s with p h y s i c a l p r o p e r t i e s , so i f - - a s KTG b e l i e v e — t h e Ternus manipulation and the moving l i n e - f i g u r e manipulation are i n s t a n t i a t i o n s of the same o b j e c t - o r g a n i z a t i o n p r i n c i p l e , then the Ternus experiments should generate f e a t u r a l o b j e c t e f f e c t s too. Beyond simply a f f o r d i n g a g e n e r a l i z a t i o n of the f e a t u r a l o b j e c t e f f e c t , the Ternus design ensures that a p e c u l i a r i t y of stimulus placement in the four-box experiments i s not r e s p o n s i b l e f o r t h e i r success. The reader may have n o t i c e d that i n the four-box experiments the t a r g e t and the t a r g e t -congruent d i s t r a c t o r of f i e l d - 2 occupy adjacent boxes on i n c o n s i s t e n t t r i a l s but not on c o n s i s t e n t t r i a l s . Perhaps t h i s adjacency on i n c o n s i s t e n t t r i a l s i s somehow r e s p o n s i b l e f o r the r e l a t i v e slowness of response on such t r i a l s . The adjacency e x p l a n a t i o n i s not c o n v i n c i n g however. The d i s t a n c e between the t a r g e t and the target-congruent d i s t r a c t o r only v a r i e s between 4.0 deg when adjacent and 5.6 deg when nonadjacent. Because the t a r g e t l o c a t i o n i s c l e a r l y pre-cued, adjacency would probably not cause c o n f u s i o n i n s e l e c t i n g the c o r r e c t stimulus to respond t o . Indeed, g i v e n t h a t t a r g e t s e l e c t i o n i s easy, an adjacent target-congruent s t i m u l u s might be j u s t as l i k e l y to decrease RT as i n c r e a s e i t . Furthermore, at 4.0 deg s e p a r a t i o n , the s t i m u l i are not 92 very "adjacent" anyway, n e i t h e r i n terms of p o t e n t i a l f o r sensory i n t e r a c t i o n (Bouma, 1978) nor in terms of p o t e n t i a l f o r " a t t e n t i o n a l s p i l l o v e r " ( c f . Hoffman & Nelson, 1981). De s p i t e these arguments, the adjacency i s s u e cannot be d i s m i s s e d . F o r t u n a t e l y , f e a t u r a l object e f f e c t s i n the Ternus experiments are not a t t r i b u t a b l e to such adjacency. I t should be mentioned that the best way to d e s c r i b e the l e t t e r "dimension" in Experiment 8 i s u n c e r t a i n . S p e c i a l mechanisms might e x i s t f o r p r o c e s s i n g l e t t e r s , so the shape of a l e t t e r may not f u n c t i o n i n c o g n i t i o n the same way l e s s -w e l l - l e a r n e d shapes do. Because of the evidence that the o b j e c t e f f e c t occurs at a p e r c e p t u a l l e v e l even with l e x i c a l s t i m u l i , the l a b e l " l e t t e r - s h a p e " has been opted f o r h e r e i n . T h i s term should remind the reader that although the shape of the l e t t e r i s probably the important f a c t o r with r e s p e c t to r e s p o n s e - i r r e l e v a n t v a r i a t i o n , i t may not be the only one. Method S t i m u l i and D i s p l a y . Experiment 8 u t i l i z e d a Ternus d i s p l a y v i r t u a l l y i d e n t i c a l to the one used by KTG except that here the s t i m u l i appeared i n f i v e d i f f e r e n t c o l o r s r a t h e r than in only white (see F i g u r e 2). Each t r i a l began with a c e n t r a l f i x a t i o n dot (0.1 deg). The d i s p l a y c o u l d take p l a c e d e i t h e r above or below the h o r i z o n t a l m i d l i n e of the screen so that the c e n t e r s of the l e t t e r s were e i t h e r 1.5 deg above or 1.5 deg below that imaginary l i n e . A f t e r 1000 ms the f i x a t i o n dot disappeared and immediately two l e t t e r s of d i f f e r e n t c o l o r and d i f f e r e n t l e t t e r - s h a p e were presented 93 ( c o l o r s : red, yellow, green, blue, white; shapes: A, E, I, 0, U). The gap of 3.7 deg that separated these l e t t e r s (center to c e n t e r ) was b i s e c t e d by the v e r t i c a l m i d - l i n e of the scre e n . A f t e r 300 ms the f i e l d - 1 l e t t e r s were removed from the screen and a f t e r a f u r t h e r delay of 49 ms two f i e l d - 2 l e t t e r s appeared that were d i f f e r e n t from one another i n terms of c o l o r and l e t t e r - s h a p e . Again, there were f i v e p o s s i b l e c o l o r s and f i v e p o s s i b l e l e t t e r shapes, j u s t as i n f i e l d - 1 . The t a r g e t l e t t e r of f i e l d - 2 appeared p e r f e c t l y centered between the two l o c a t i o n s that had hel d the f i e l d - 1 l e t t e r s . At the same time the other l e t t e r of f i e l d - 2 appeared to the l e f t or r i g h t of the other three stimulus l o c a t i o n s . T h i s f o u r t h l e t t e r was not the same c o l o r or l e t t e r - s h a p e as any of the other three l e t t e r s i n the d i s p l a y . L i k e the two f i e l d - 1 l e t t e r s , the c e n t r a l t a r g e t l e t t e r and the e c c e n t r i c f o u r t h l e t t e r were d i s p l a y e d 3.7 deg apart center to c e n t e r . A l l the l e t t e r s that appeared were drawn in r e c t a n g u l a r g r a p h i c s c e l l s 1.0 deg high and 0.4 deg wide. Because the t a r g e t l e t t e r was d i s p l a y e d soon a f t e r the o f f s e t of f i e l d - 1 , i t seemed to move i n t o i t s c e n t r a l p o s i t i o n from one of the f i e l d - 1 l e t t e r l o c a t i o n s ; and because the f o u r t h , outer l e t t e r a l s o appeared to a r r i v e from the d i r e c t i o n of the f i e l d - 1 l o c a t i o n s , the t a r g e t l e t t e r appeared to a r r i v e e i t h e r from the d i r e c t i o n of the l e f t f i e l d - 1 l e t t e r or from the d i r e c t i o n of the r i g h t f i e l d - 1 l e t t e r . T h e r e f o r e , only one of the f i e l d - 1 l e t t e r s was 94 p e r c e p t u a l l y l i n k e d with the t a r g e t l e t t e r . To make l o c a l i z a t i o n of the t a r g e t e a s i e r , two re c t a n g u l a r paper cues (1.0 deg x 2.9 deg) were attached to the s u r f a c e of the screen. Both were p l a c e d along the imaginary v e r t i c a l m i d - l i n e of the screen, one p r o j e c t i n g down from the top of the screen and the other p r o j e c t i n g up from the bottom of the screen. Each cue extended to a point 1.0 deg from the t a r g e t l o c a t i o n i t designated. Once the sub j e c t responded, the two l e t t e r s of f i e l d - 2 were removed and the screen remained blank f o r an i n t e r t r i a l i n t e r v a l of 900 ms. C o n d i t i o n s . The b a s i s of the experimental c o n d i t i o n s were f e a t u r e r e l a t i o n s i n the target-preview p a i r . In c o l o r -c o n s i s t e n t c o n d i t i o n s a preview of the t a r g e t c o l o r appeared in f i e l d - 1 i n the target-yoked l o c a t i o n . In c o l o r -i n c o n s i s t e n t c o n d i t i o n s a preview of the t a r g e t c o l o r appeared i n f i e l d - 1 but in the target-nonyoked l o c a t i o n . In c o l o r - c o n t r o l c o n d i t i o n s a preview of the t a r g e t c o l o r d i d not appear anywhere i n f i e l d - 1 . These three c o l o r c o n d i t i o n s e x i s t e d f o r each of three l e t t e r c o n d i t i o n s ( l e t t e r -c o n s i s t e n t , l e t t e r - i n c o n s i s t e n t and l e t t e r - c o n t r o l ) , and so there were nine experimental c o n d i t i o n s i n t o t a l . Procedure. The experiment was run i n bl o c k s of 36 t r i a l s , f i r s t two blocks of p r a c t i c e t r i a l s then 15 blocks of d a t a - c o l l e c t i o n t r i a l s . A message appeared on the screen r e q u e s t i n g the s u b j e c t to begin the experiment by p r e s s i n g the c e n t e r t e l e g r a p h key. The s u b j e c t ' s task i n Experiment 8 95 was to v o c a l l y r e p o r t the c o l o r of the l e t t e r that appeared "to move i n t o the c e n t e r of the screen". R e s u l t s and D i s c u s s i o n The mean RTs f o r the l e t t e r - c o n s i s t e n t c o n d i t i o n s were: c o l o r - c o n s i s t e n t 556 ms c o l o r - i n c o n s i s t e n t 573 c o l o r - c o n t r o l 611 The mean RTs f o r the l e t t e r - i n c o n s i s t e n t c o n d i t i o n s were: c o l o r - c o n s i s t e n t 572 ms c o l o r - i n c o n s i s t e n t 580 c o l o r - c o n t r o l 619 The mean RTs f o r the l e t t e r - c o n t r o l c o n d i t i o n s were: c o l o r - c o n s i s t e n t 570 ms c o l o r - i n c o n s i s t e n t 586 c o l o r - c o n t r o l 616 An a n a l y s i s of v a r i a n c e of the data was performed. Color c o n s i s t e n c y had a s i g n i f i c a n t main e f f e c t on c o l o r response (F(2, 46) = 94.6, p < 0.001). L e t t e r c o n s i s t e n c y a l s o had a s i g n i f i c a n t main e f f e c t on c o l o r response (F(2, 46) = 8.91, p < 0.001). The i n t e r a c t i o n e f f e c t was not s i g n i f i c a n t (F(4, 92) = 1.22, p = 0.308). Thus, a c o l o r o b j e c t e f f e c t was produced when l e t t e r - s h a p e c o n d i t i o n was c o n s i s t e n t (16 ms, t(23) = 3.32, p = 0.003), i n c o n s i s t e n t (9 ms, t(23) = 2.15, p = 0.042) or c o n t r o l (17 ms, t(23) = 3.58; p = 0.002). The magnitude of the c o l o r o b j e c t e f f e c t was not s i g n i f i c a n t l y i n f l u e n c e d by c o n s i s t e n c y on the r e s p o n s e - i r r e l e v a n t , l e t t e r -shape dimension. Shape i n c o n s i s t e n c y n e i t h e r reduced the 96 o b j e c t e f f e c t as i t d i d with the presence task, nor e l i m i n a t e d the o b j e c t e f f e c t as i t d i d with the s i z e task; r a t h e r , i t l e f t the c o l o r o b j e c t e f f e c t u n a l t e r e d . An i n f o r m a t i v e p a t t e r n of r e s u l t s was generated w i t h i n the main e f f e c t of c o l o r c o n s i s t e n c y . Averaged ac r o s s l e t t e r - s h a p e c o n d i t i o n , the RTs were: c o l o r - c o n s i s t e n t 566 ms c o l o r - i n c o n s i s t e n t 580 c o l o r - c o n t r o l 615 When the t a r g e t c o l o r was previewed i n the target-nonyoked l o c a t i o n , c o l o r naming responses were 35 ms q u i c k e r than when the t a r g e t c o l o r was not previewed at a l l (j:(23) = 9.04, p < 0.001). When the t a r g e t c o l o r was previewed i n the t a r g e t -yoked l o c a t i o n , there was an a d d i t i o n a l 14 ms of RT advantage (t(23) = 3.94, p < 0.001). Note that i n Experiment 8 the n o n s p e c i f i c e f f e c t i s l a r g e r e l a t i v e to the a s s o c i a t e d l o c a t i o n - s p e c i f i c advantage or ob j e c t e f f e c t (21 ms l a r g e r , t(23) = 3.35, p = 0.003). Experiment 9: L e t t e r (Color as Response-Irrelevant Dimension) The preceding duodimension experiments used shape as the r e s p o n s e - i r r e l e v a n t dimension. Experiment 9 uses c o l o r as the r e s p o n s e - i r r e l e v a n t dimension and l e t t e r as the dimension c o n t r o l l i n g response. In t h i s way Experiment 9 c o n s t i t u t e s a p e r f e c t r e v e r s a l of Experiment 8 and so w i l l p r o v i d e a u s e f u l comparison to i t . By r e q u i r i n g l e t t e r i d e n t i f i c a t i o n responses, Experiment 9 a l s o serves to r e u n i t e the present 97 p r o j e c t with the KTG experiments. Method C o n d i t i o n s and Procedure. Except f o r the response r e q u i r e d of the subject, Experiment 9 was i d e n t i c a l to experiment 8. In f a c t , the same computer program ran both experiments. In Experiment 9, ra t h e r that v o c a l l y r e p o r t i n g the c o l o r of the target l e t t e r and i g n o r i n g i t s shape, the subject v o c a l l y reported the l e t t e r name of the t a r g e t and ignored i t s c o l o r . The nine experimental c o n d i t i o n s comprising Experiment 9 were analogous to those t h a t comprised Experiment 8. Res u l t s and D i s c u s s i o n The mean RTs f o r the c o l o r - c o n s i s t e n t c o n d i t i o n s were: l e t t e r - c o n s i s t e n t 450 ms l e t t e r - i n c o n s i s t e n t 473 l e t t e r - c o n t r o l 479 The mean RTs f o r the c o l o r - i n c o n s i s t e n t c o n d i t i o n s were: l e t t e r - c o n s i s t e n t 454 ms l e t t e r - i n c o n s i s t e n t 469 l e t t e r - c o n t r o l 478 The mean RTs f o r the c o l o r - c o n t r o l c o n d i t i o n s were: l e t t e r - c o n s i s t e n t 452 ms l e t t e r - i n c o n s i s t e n t 471 l e t t e r - c o n t r o l 475 An a n a l y s i s of va r i a n c e of the data was performed. L e t t e r c o n s i s t e n c y had a s i g n i f i c a n t main e f f e c t on l e t t e r response (F(2, 46) = 54.3, p < 0.001). Color c o n s i s t e n c y d i d not have 98 a s i g n i f i c a n t main e f f e c t on l e t t e r response (F(2, 46) = 0.507, p = 0.606) but there was a s i g n i f i c a n t i n t e r a c t i o n between these two f a c t o r s (F(4, 92) = 2.74, p = 0.033). Thus, a l e t t e r object e f f e c t was produced when c o l o r c o n d i t i o n was c o n s i s t e n t (23 ms, t(23) = 8.43, p < 0.001), i n c o n s i s t e n t (15 ms, t(23) = 5.75, p < 0.001) and c o n t r o l (19 ms, M23) = 5.62, p < 0.001). The magnitude of the l e t t e r o b j e c t e f f e c t was s i g n i f i c a n t l y i n f l u e n c e d by c o l o r c o n s i s t e n c y . The d i f f e r e n c e between the l e t t e r o b j e c t e f f e c t when c o l o r was c o n s i s t e n t and when c o l o r was i n c o n s i s t e n t was s i g n i f i c a n t (t(23) = 3.28, p = 0.003), so c o l o r i n c o n s i s t e n c y d i d reduce the l e t t e r o b j e c t e f f e c t . The most s t r i k i n g aspect of t h i s r e d u c t i o n , however, i s that i t i s so s l i g h t , only 8 ms. In view of the f a c t that the 8 ms r e d u c t i o n here i s no d i f f e r e n t than the n o n s i g n i f i c a n t 8 ms r e d u c t i o n observed i n Experiment 8, a sharp d i s t i n c t i o n cannot j u s t i f i a b l y be made between the i n f l u e n c e of l e t t e r - s h a p e on the c o l o r object e f f e c t and the i n f l u e n c e of c o l o r on the l e t t e r o b j e c t e f f e c t . Perhaps the best f i r s t approximation to make, then, i s that c o l o r c o n s i s t e n c y a f f e c t s the l e t t e r o b j e c t e f f e c t l i k e l e t t e r c o n s i s t e n c y a f f e c t s the c o l o r o b j e c t e f f e c t : They have l i t t l e or no impact on one another. Within the main e f f e c t of l e t t e r c o n s i s t e n c y , the r e s u l t s of Experiment 9 are q u i t e d i s t i n c t from the analogous r e s u l t s of Experiment 8. Averaged across c o l o r c o n d i t i o n , the RTs were: 99 l e t t e r - c o n s i s t e n t 452 ms l e t t e r - i n c o n s i s t e n t 471 l e t t e r - c o n t r o l 477 L e t t e r naming responses were only 6 ms q u i c k e r when the t a r g e t l e t t e r was previewed in the target-nonyoked l o c a t i o n than when the t a r g e t l e t t e r was not previewed at a l l (t(23) = 3.12, p = 0.005). When the t a r g e t l e t t e r was previewed i n the target-yoked l o c a t i o n , there was an a d d i t i o n a l 19 ms of RT advantage (t(23) = 7.72, p < 0.001). Note that in Experiment 9 the n o n s p e c i f i c e f f e c t i s small r e l a t i v e to the a s s o c i a t e d l o c a t i o n - s p e c i f i c advantage or o b j e c t e f f e c t (13 ms s m a l l e r , t(23) = -3.95, p < 0.001). GENERAL DISCUSSION The R e s u l t s There were twelve major f i n d i n g s of the present s e r i e s of experiments. (a) Kahneman et a l . ' s ( i n progress) o b j e c t e f f e c t on l e t t e r naming was c o r r o b o r a t e d (Experiment 9). (b) The o b j e c t e f f e c t was produced on a response task i n v o l v i n g stimulus c l a s s i f i c a t i o n a c c o r d i n g to the p h y s i c a l property presence (Experiment 2 ) . (c) The o b j e c t e f f e c t was produced on a response task i n v o l v i n g s t i m u l u s c l a s s i f i c a t i o n a c c o r d i n g to the p h y s i c a l p r o p e r t y s i z e (Experiment 3). (d) The o b j e c t e f f e c t was produced on a response task i n v o l v i n g stimulus c l a s s i f i c a t i o n a c c o r d i n g to the p h y s i c a l property c o l o r (Experiment 8 ) . (e) I t was e x p e r i m e n t a l l y demonstrated that the o b j e c t e f f e c t s produced i n the four-box experiments were not simply the r e s u l t of s u b j e c t s s e l e c t i n g and 1 00 f o l l o w i n g a f i e l d - 1 box to i t s t e r m i n a l l o c a t i o n in f i e l d - 2 (Experiments 1 and 2); ( f ) nor were these o b j e c t e f f e c t s the r e s u l t of s u b j e c t s c o n f u s i n g the two f i e l d s and i n a p p r o p r i a t e l y responding to f i e l d - 1 (Experiments 4 and 5). (g) The presence o b j e c t e f f e c t was reduced by i n c o n s i s t e n c y on the r e s p o n s e - i r r e l e v a n t dimension of shape (Experiment 6 ) . (h) The s i z e o b j e c t e f f e c t was e l i m i n a t e d by i n c o n s i s t e n c y on the r e s p o n s e - i r r e l e v a n t dimension of shape (Experiment 7). ( i ) The c o l o r o b j e c t e f f e c t was u n a f f e c t e d by i n c o n s i s t e n c y on the r e s p o n s e - i r r e l e v a n t dimension of l e t t e r - s h a p e (Experiment 8). ( j ) The l e t t e r o b j e c t e f f e c t was only very s l i g h t l y reduced by i n c o n s i s t e n c y on the r e s p o n s e - i r r e l e v a n t dimension of c o l o r (Experiment 9 ) . (k) C o l o r supported a l a r g e n o n - o b j e c t - s p e c i f i c f a c i l i t a t i o n r e l a t i v e to the o b j e c t e f f e c t i t supported (Experiment 8 ) . (1) L e t t e r supported a small n o n - o b j e c t - s p e c i f i c f a c i l i t a t i o n r e l a t i v e to the o b j e c t e f f e c t i t supported (Experiment 9 ) . Q u a l i f i c a t i o n s on the S i z e F i n d i n g s For s e v e r a l reasons the s i z e r e s u l t s are q u e s t i o n a b l e , and any c o n c l u s i o n s drawn from them must be c o n s i d e r e d s p e c u l a t i v e . As d i s c u s s e d p r e v i o u s l y , the monodimension experiments are i n c o n c l u s i v e on t h e i r own because they confound o v e r a l l s t i m u l u s i d e n t i t y with i d e n t i t y on the f e a t u r e dimension being i n v e s t i g a t e d . In duodimension experiments, presence, c o l o r and l e t t e r - s h a p e o b j e c t e f f e c t s were obtained even when the s t i m u l i g i v i n g r i s e to them were not completely i d e n t i c a l . The same cannot be s a i d f o r the 101 s i z e o b j e c t e f f e c t . I t , t h e r e f o r e , may be nothing more than an i d e n t i t y e f f e c t . S i z e i n f o r m a t i o n in and of i t s e l f may simply not be subject to spatiotemporal i n t e g r a t i o n of the so r t under study. Arguing a g a i n s t t h i s p o s s i b i l i t y i s the f i n d i n g that stimulus i d e n t i t y made l i t t l e or no d i f f e r e n c e in the l e t t e r -shape and c o l o r experiments, and made only a modest d i f f e r e n c e i n the presence experiment. Consequently, i t seems u n l i k e l y that the e n t i r e s i z e object e f f e c t can be a t t r i b u t e d to stimulus i d e n t i t y independent of s i z e . I t i s not unreasonable, t h e r e f o r e , to t e n t a t i v e l y i n t e r p r e t the monodimension s i z e experiment as i n f a c t having generated a genuine s i z e object e f f e c t , and the duodimension experiment as having e l i m i n a t e d t h i s e f f e c t by i n t r o d u c i n g i n c o n s i s t e n c y on the r e s p o n s e - i r r e l e v a n t dimension of shape. Such an e l i m i n a t i o n of a r e p e t i t i o n e f f e c t by change on a r e s p o n s e - i r r e l e v a n t dimension i s not unprecedented in tasks i n v o l v i n g the c l a s s i f i c a t i o n of s t i m u l i a c c o r d i n g to a p a r t i c u l a r p h y s i c a l dimension ( c f . F e l f o l d y , 1974). However, even i f the s i z e object e f f e c t can be co n s i d e r e d genuine per se, the c o n c l u s i o n that shape i n c o n s i s t e n c y e l i m i n a t e s the s i z e o b j e c t e f f e c t i s i t s e l f suspect. For one t h i n g , t h i s c o n c l u s i o n r e s t s on the ch o i c e to t r e a t as negative r e s u l t s that narrowly miss s t a t i s t i c a l s i g n i f i c a n c e . For another t h i n g , u n l i k e the other duodimension experiments, the s i z e experiment i n v o l v e d s i z e c l a s s i f i c a t i o n of s t i m u l i of onl y one shape. Tar g e t s were 1 02 always diamonds and previews were always a s t e r i s k s . The f a i l u r e to produce an ob j e c t e f f e c t may have had something to do with the f a c t that s u b j e c t s never had to make a s i z e response to a s t e r i s k - s h a p e d s t i m u l i ( c f . A l l p o r t , Tipper & Chmiel, in p r e s s ) . These two c r i t i c i s m s are not u n c o n t e s t a b l e . F i r s t , the cho i c e to t r e a t the n e a r - s i g n i f i c a n t r e s u l t s as negative, a l b e i t never a comfortable one to make, has been argued to be j u s t i f i e d i n the present context (see R e s u l t s and D i s c u s s i o n of Experiment 7 ) . Second, given that i n the preview paradigm the f i e l d - 1 s t i m u l i cannot even be excluded from p r o c e s s i n g on the b a s i s of appearing in r e s p o n s e - i r r e l e v a n t l o c a t i o n s , i t seems u n l i k e l y that they would be so e f f e c t i v e l y excluded on the b a s i s of whether or not they had been a s s o c i a t e d with a response before. N e v e r t h e l e s s , i t i s c l e a r t h a t what i s r e q u i r e d before any f i r m c o n c l u s i o n s can be drawn i s a r e p l i c a t i o n of the duodimension s i z e experiment but with s t i m u l i l a r g e r i n absolute s i z e and with both a s t e r i s k s and diamonds appearing as t a r g e t s . A n a l y s i s of the Duodimension Experiments Although the monodimension design i s the most s t r a i g h t forward approach to the i s s u e of f e a t u r a l o b j e c t e f f e c t s and forms the foundation of the present i n v e s t i g a t i o n , i t i s the duodimension design that has y i e l d e d the r i c h e s t d a ta. In c o n t r a s t to the u n i f o r m i t y of the monodimension r e s u l t s (every property t e s t e d i n such experiments supported an ob j e c t e f f e c t ) , the duodimension r e s u l t s were d i f f e r e n t f o r 103 each p r o p e r t y . The duodimension experiments 8 and 9 a l s o allowed a s p e c i a l comparison of the p r o p e r t i e s c o l o r and l e t t e r - s h a p e . The d i f f e r e n c e s between p h y s i c a l p r o p e r t i e s with respect to the obj e c t e f f e c t are almost c e r t a i n l y r e l a t e d to basic d i f f e r e n c e s between the p r o p e r t i e s themselves. For example, presence i s a property that p e r t a i n s to a stim u l u s as a whole, and that i s necessary i n order f o r a stim u l u s to have any other p r o p e r t i e s . S i z e i s an e s p e c i a l l y q u a n t i t a t i v e p r o p e r t y , easy to c o n c e p t u a l i z e as a dimension. An i n t e r e s t i n g o b s e r v a t i o n i s that s i z e i s one pr o p e r t y of a proximal o b j e c t that normally changes when the unchanging d i s t a l o b j e c t moves i n depth. Color a p p l i e s to each point of a s t i m u l u s . L e t t e r - s h a p e , as w e l l as p o s s i b l y having unique h i g h e r - o r d e r l e x i c a l q u a l i t i e s , i s dependent upon s p a t i a l r e l a t i o n s between p a r t s of a s t i m u l u s . Future r e s e a r c h may be a b l e to c l a r i f y what i t i s about p a r t i c u l a r p h y s i c a l p r o p e r t i e s that g i v e s them t h e i r d i s t i n c t i v e r o l e s i n the o b j e c t - s p e c i f i c spatiotemporal i n t e g r a t i o n of i n f o r m a t i o n . The present treatment does not attempt such an undertaking. Instead, a u s e f u l a n a l y s i s can be based simply on the types of i n t e r a c t i o n observed between p h y s i c a l p r o p e r t i e s i n the duodimension experiments. A l l three of the p o s s i b l e major outcomes of the duodimension experiments were obta i n e d : In one experiment i n c o n s i s t e n c y on the response-i r r e l e v a n t dimension e l i m i n a t e d the o b j e c t e f f e c t , i n another experiment i t d i d not i n t e r a c t at a l l with the o b j e c t e f f e c t , 1 04 and i n yet another i t reduced the o b j e c t e f f e c t . I t i s the l a t t e r of these three outcomes that has the most i n t e r p r e t i v e s i g n i f i c a n c e . The " E l i m i n a t i o n " Result C l e a r l y , i t i s best to c o n s i d e r the Experiment 7 r e s u l t s showing an e l i m i n a t i o n of the s i z e o b j e c t e f f e c t by response-i r r e l e v a n t shape i n c o n s i s t e n c y to be p i l o t data. If they are confirmed i n a b e t t e r experiment, they w i l l i n d i c a t e that s i z e and shape are p a r t i c u l a r l y i n t i m a t e l y r e l a t e d i n an o b j e c t ' s dynamic v i s u a l h i s t o r y . P i l o t work by Kahneman, Treisman and Gibbs has suggested that spatiotemporal c o n t i n u i t y may be a necessary c o n d i t i o n f o r p r o d u c t i o n of the o b j e c t e f f e c t . I f v a l i d , the l a c k of an o b j e c t e f f e c t i n the duodimension s i z e experiment w i l l i n d i c a t e that spatiotemporal c o n t i n u i t y i s not a s u f f i c i e n t c o n d i t i o n f o r the o b j e c t e f f e c t . The " N o - I n t e r a c t i o n " Result In Experiment 8 there was no i n t e r a c t i o n between the c o l o r o b j e c t e f f e c t and r e s p o n s e - i r r e l e v a n t l e t t e r - s h a p e i n c o n s i s t e n c y . T h i s r e s u l t i s not unexpected under any of a number of i n f o r m a t i o n p r o c e s s i n g circumstances, i n c l u d i n g those having nothing to do with f i g u r a l r e l a t i o n s between s t i m u l i , and so i s not very f r u i t f u l i n terms of i m p l i c a t i o n s s p e c i f i c t o the o b j e c t e f f e c t or re-viewing process. T h i s i s because c o l o r and shape are thought to be separable f e a t u r e s (Treisman, 1985). For example, i t might be tempting to conclude from Experiment 7 alone that r e s p o n s e - i r r e l e v a n t 1 05 p r o p e r t i e s are not i n c l u d e d i n the o b j e c t - s p e c i f i c r e p r e s e n t a t i o n u n d e r l y i n g the o b j e c t e f f e c t . A l t e r n a t i v e l y , the a s s e r t i o n might be t h a t , although a l l the i n f o r m a t i o n i s present i n the o b j e c t - s p e c i f i c r e p r e s e n t a t i o n , f e a t u r e s w i t h i n t h i s r e p r e s e n t a t i o n are l e f t unconjoined and are coded as independent dimensions that can be re-viewed s e p a r a t e l y . However, n e i t h e r of these c o n c l u s i o n s i s warranted: Any l a c k of i n t e r a c t i o n between c o l o r and shape can be more parsimoniously a t t r i b u t e d to t h e i r s e p a r a b i l i t y . Reduction of the Object E f f e c t by I r r e l e v a n t V a r i a t i o n Of g r e a t e s t i n t e r p r e t i v e impact i s the f i n d i n g that r e s p o n s e - i r r e l e v a n t shape i n c o n s i s t e n c y can i n f l u e n c e the object e f f e c t . T h i s was the r e s u l t obtained i n Experiment 6, the duodimension presence experiment. In Experiment 9, the l e t t e r o b j e c t e f f e c t was a l s o s i g n i f i c a n t l y reduced by c o l o r i n c o n s i s t e n c y , but the r e d u c t i o n was very s l i g h t and, as d i s c u s s e d , l i t t l e i n t e r p r e t i v e weight should be p l a c e d on i t because i t i s not d i s t i n g u i s h a b l y d i f f e r e n t from the n o n s i g n i f i c a n t r e d u c t i o n produced i n Experiment 8. T h e r e f o r e Experiment 6 provides the c l e a r e s t i n s t a n t i a t i o n of response-i r r e l e v a n t i n c o n s i s t e n c y reducing the o b j e c t e f f e c t . How can the outcome of Experiment 6 be explained? The o b j e c t e f f e c t per se demonstrates that the p r o c e s s i n g of a t a r g e t stimulus can be a f f e c t e d by another stimulus that i s , with respect to the task the s u b j e c t must perform, i r r e l e v a n t in form and l o c a t i o n . The duodimension presence experiment demonstrates that the value on an i r r e l e v a n t f e a t u r e 1 06 dimension of t h i s i r r e l e v a n t s t i m u l u s in an i r r e l e v a n t l o c a t i o n can a l s o be i n f l u e n t i a l . Obviously i n f o r m a t i o n c o n c e r n i n g both the r e l e v a n t and the i r r e l e v a n t property i s i n c l u d e d i n the o b j e c t - s p e c i f i c r e p r e s e n t a t i o n u n d e r l y i n g the o b j e c t e f f e c t . The q u e s t i o n that remains i s , why i s the i n f o r m a t i o n p e r t a i n i n g to the d i f f e r e n t p r o p e r t i e s not processed independently? It seems rather u n l i k e l y that presence and shape are i n t e g r a l dimensions, that i s , that they are p s y c h o l o g i c a l l y not two dimensions but one. In f a c t , a c c o r d i n g to Garner's (1974) f o r m u l a t i o n of i n t e g r a l i t y , such nominal dimensions cannot be i n t e g r a l because the concept of a E u c l i d e a n metric does not apply to them. A u s e f u l p i e c e of i n f o r m a t i o n to have would be whether r e p e t i t i o n e f f e c t s i n the s o r t i n g of cards i n t o s t i m u l u s - p r e s e n t and stimulus-absent p i l e s ( c f . F e l f o l d y , 1974) are a f f e c t e d by i r r e l e v a n t v a r i a t i o n i n the shape of the s t i m u l i . One would think that i n the preview paradigm to judge simply whether a stimulus i s present i n or absent from a pre-cued l o c a t i o n would i n v o l v e only i n f o r m a t i o n made a v a i l a b l e e a r l y and independently of i n f o r m a t i o n concerning s t i m u l u s shape. Of course s u b j e c t s might v o l i t i o n a l l y i n v o l v e shape, in t h e i r d e t e c t i o n judgments, but there i s no i n c e n t i v e to do so i n Experiment 6 and, i n g e n e r a l , c l a s s i f i c a t i o n t a s k s with one dimension r e l e v a n t a r e performed a n a l y t i c a l l y (Treisman, 1985). If presence and shape are not i n t e g r a l f e a t u r e s , then Experiment 6 suggests that the i n t e r a c t i o n between them i s 1 07 p e c u l i a r to o b j e c t - s p e c i f i c spatiotemporal i n t e g r a t i o n such as that observed i n the preview paradigm. Garner (1974) r e p o r t s a f a s c i n a t i n g r e s u l t a l s o suggesting that the p r e s e n t a t i o n of in f o r m a t i o n sources as dimensions of the same ob j e c t can r e s u l t in t h e i r i n t e r a c t i o n when they might otherwise be expected to be processed independently. The two dimensions s t u d i e d (hue and t a c t i l e roughness) were not even of the same sensory modality, and yet t a c t i l e roughness judgments were a f f e c t e d by v a r i a t i o n i n hue. So although the i n f o r m a t i o n sources entered the organism along d i f f e r e n t m o d a l i t i e s , the more i n f l u e n t i a l f a c t o r seemed to be that the i n f o r m a t i o n a p p l i e d to the same d i s t a l o b j e c t . Apparently what i s c r i t i c a l to the o b j e c t e f f e c t i s not p r o p e r t i e s as separate i n f o r m a t i o n a l e n t i t i e s . What i s important i n the presence task i s not only whether the stim u l u s re-viewed during the p r o c e s s i n g of the t a r g e t i s present or absent, but a l s o whether t h i s re-viewed st i m u l u s shares other p h y s i c a l q u a l i t i e s such as shape with the t a r g e t . The c o n s i s t e n c y that seems to be c r u c i a l to the o b j e c t e f f e c t , then, i s n e i t h e r c o n s i s t e n c y i n a semantic sense ( i e . the s t i m u l i can or cannot be l a b e l l e d " i d e n t i c a l " ) , nor c o n s i s t e n c y i n an a n a l y t i c sense ( i e . the s t i m u l i are or are not i d e n t i c a l with respect to a p a r t i c u l a r p r o p e r t y ) ; r a t h e r , what i s c r u c i a l i s c o n s i s t e n c y i n a comprehensive sense ( i e . the s t i m u l i are i d e n t i c a l with res p e c t to v a r i o u s p r o p e r t i e s but not with res p e c t to v a r i o u s o t h e r s ) . 108 The f i n d i n g that comprehensive c o n s i s t e n c y i s c r i t i c a l to the o b j e c t e f f e c t suggests that in determining whether one stimulus i s a preview of another i t i s not a p p r o p r i a t e to examine merely the f e a t u r e dimension p e r t i n e n t to response. It may be best to c h a r a c t e r i z e the extent to which one stimulus i s a preview of another l i k e Tversky (1977) does stimulus s i m i l a r i t y , as a c o n t r a s t , or l i n e a r combination of a number of fe a t u r e v a l u e s . Presumably the weights a p p l i e d to each dimension would vary depending on such f a c t o r s as the response-relevance of the dimension, i t s i n t e g r a l i t y with the other dimensions i n v o l v e d , and i t s i d e n t i t y (eg. a n u l l weight might be a p p l i e d to the l e t t e r - s h a p e dimension i n the context of a c o l o r t a s k ) . In essence, the o b j e c t - s p e c i f i c r e p r e s e n t a t i o n upon which the obj e c t e f f e c t depends cannot be something l i k e a l i s t of p r o p e r t i e s , a l l of which are a c c e s s i b l e independently, although some p r o p e r t i e s may be. The o b j e c t - s p e c i f i c r e p r e s e n t a t i o n must be a r e p r e s e n t a t i o n of p r o p e r t i e s that are i n some sense c o n j o i n e d . A t t e n t i o n and the O b j e c t - S p e c i f i c Representation If a t t e n t i o n c o n j o i n s f e a t u r e s i n t o o b j e c t s , the suggestion that the obj e c t e f f e c t depends on conjoined i n f o r m a t i o n about ob j e c t p r o p e r t i e s i s c o n s i s t e n t with those r e s u l t s of the KTG p r o j e c t i n d i c a t i n g that the object e f f e c t i s not produced i n the absence of a t t e n t i o n to f i e l d - 1 . R e c a l l , however, that some preview experiments l e d to the opposite c o n c l u s i o n , that the o b j e c t - s p e c i f i c spatiotemporal i n t e g r a t i o n of in f o r m a t i o n c o u l d occur e x t r a - a t t e n t i v e l y . At 109 t h i s p o i n t , i t i s i n t e r e s t i n g to note that, t h e o r e t i c a l l y , some of the economy of a r e t r o a c t i v e information r e f e r e n c e process (namely, the a b i l i t y to spend resources on only those past s t i m u l i that turn out to be r e l e v a n t to the present stimulus) i s l o s t i f that process can only apply to s t i m u l i that have a l r e a d y been s e l e c t i v e l y attended. The same t e n s i o n e x i s t s i n the present work too, because d e s p i t e the suggestion that the o b j e c t - s p e c i f i c r e p r e s e n t a t i o n c o n s i s t s of c o n j o i n e d p r o p e r t i e s there are h i n t s that a t t e n t i o n i s not d i r e c t e d to f i e l d - 1 . Responding to the presence of a fe a t u r e t a r g e t i n a c l e a r l y pre-cued l o c a t i o n — p r e c u e d even before the f i e l d - 1 s t i m u l i are p r e s e n t e d — s h o u l d not i n v o l v e a l l o c a t i o n of a t t e n t i o n to those i r r e l e v a n t f i e l d - 1 l o c a t i o n s . As always, i t can be argued that whether or not s u b j e c t s should have attended to f i e l d - 1 , they may have i n f a c t done so i n v o l u n t a r i l y or even i n t e n t i o n a l l y . However, the emphasis on r a p i d and accurate responding made s u b j e c t s v i g i l a n t f o r the cue and discouraged them from wasting a t t e n t i o n elsewhere. In c a s u a l s e l f -r e p o r t s some s u b j e c t s s a i d they were never even aware of the f i e l d - 1 d i s p l a y (though they knew about i t from the i n s t r u c t i o n s ) . B e t t e r evidence that f i e l d - 1 was not attended, at l e a s t in the e a r l y - c u e experiments, i s provided by comparing such experiments to the l a t e - c u e experiment. The l a t e - c u e experiment generated unexpected data that were s u c c e s s f u l l y e x p l a i n e d (ad hoc) as r e s u l t i n g from su b j e c t s s e l e c t i n g a 110 f i e l d - 1 s t i m u l u s . Once the e a r l y - c u e manipulation was implemented to a t t r a c t a t t e n t i o n away from f i e l d - 1 , the p e c u l i a r r e s u l t s c h a r a c t e r i s t i c of the l a t e - c u e experiment, and presumably i n d i c a t i v e of a t t e n d i n g to f i e l d - 1 , disappeared and were r e p l a c e d by r e s u l t s t y p i c a l of the e a r l i e r preview research. The i m p l i c a t i o n i s that the s a l i e n t e a r l y cue, o c c u r r i n g 40 ms before the f i e l d - 1 s t i m u l i were even presented, d i d i n f a c t prevent s u b j e c t s from a t t e n d i n g to f i e l d - 1 . Despite the r e s u l t s of Experiment 1 and 2, an argument can be made t h a t , even with an e a r l y cue, s e l e c t i v e a t t e n t i o n i s not r e s t r i c t e d to f i e l d - 2 . I t i s probably safe to c l a i m that i n i t i a l l y a t t e n t i o n i s s u c c e s s f u l l y a t t r a c t e d by the e a r l y cue: Even i f s u b j e c t s were not making an e f f o r t to atten d to i t - - w h i c h they c l e a r l y were--such a p e r i p h e r a l cue would l i k e l y a t t r a c t a t t e n t i o n i n v o l u n t a r i l y (Jonides, 1976). The problem i s that once a t t r a c t e d t h e r e , a t t e n t i o n may not stay. A t t e n t i o n may leave the cue, move back toward f i e l d - 1 , and go to the box that i s headed i n the d i r e c t i o n of the cue ( i e . the t a r g e t box). On t h i s view, the b i z a r r e negative o b j e c t e f f e c t would disappear with an e a r l y cue because, r e g a r d l e s s of c o n d i t i o n or t a r g e t type, a t t e n t i o n would never be m i s d i r e c t e d to a d i s t r a c t o r l o c a t i o n i n f i e l d - 2 , as i t was sometimes i n Experiment 1. It i s improbable that the su b j e c t would s h i f t a t t e n t i o n to the cue and then immediately go back to the f i e l d - 1 s t i m u l i , because, once attended, the cue would r e q u i r e 111 something on the order of 200-300 ms to process ( E r i k s e n & Hoffman, 1973; E r i k s e n & C o l l i n s , 1969). Of course, there i s nothing f o r c i n g s u b j e c t s to remain a t t e n t i v e of a l o c a t i o n u n t i l the stimulus that a t t r a c t e d a t t e n t i o n there i s f u l l y p e r c e i v e d , but they may w e l l do so (Townsend, 1973). More c r u c i a l i s the f a c t t h a t , although the timing of the d i s p l a y sequence may allow a t t e n t i o n to s e l e c t the empty moving t a r g e t box, i t probably would not allow a t t e n t i o n to s e l e c t any of the f i e l d - 1 s t i m u l i . Subjects need 50 ms to make even the most r a p i d s h i f t s of f o c a l a t t e n t i o n ( J u l e s z , 1983), and so would not have time to leave the cue and att e n d to a f i e l d - 1 s timulus before f i e l d - 1 i s removed. To ca t c h j u s t the o f f s e t of the f i e l d - 1 s t i m u l i , s u b j e c t s would have to switch a t t e n t i o n to the e a r l y cue and back to f i e l d - 1 i n 70 ms. T h i s means that the a t t e n t i o n - v o l l e y n o t i o n can support only the c l a i m that the empty moving t a r g e t box was s e l e c t i v e l y a t t e n d e d — n o t that the f i e l d - 1 s t i m u l i themselves were s e l e c t e d . A r e p l y to t h i s p o i n t might be that s u b j e c t s do not need to s e l e c t i v e l y a t t e n d to the a c t u a l f i e l d - 1 s t i m u l i to i n  e f f e c t a t t e n d to them. Su b j e c t s may att e n d to the cue, leave i t , s e l e c t the (empty) moving t a r g e t box, use the d i r e c t i o n from which t h i s box is. moving to i n d i c a t e the l o c a t i o n that once h e l d the target-box s t i m u l u s of f i e l d - 1 , and then s e l e c t i v e l y a t t e n d to an i c o n i c r e p r e s e n t a t i o n of the stimulus i n that l o c a t i o n . Beside demanding that the su b j e c t perform a p l e t h o r a of tas k - i n c o n g r u e n t a c t i v i t y i n a short 1 1 2 p e r i o d of time, t h i s r e p l y i s weakened by two f i n d i n g s . F i r s t , KTG's f i n d i n g t h a t movement speed had no i n f l u e n c e on the o b j e c t e f f e c t i s not what would be expected i f the object e f f e c t were dependent on a fading i c o n . Second, Experiments 4 and 5 of the present t h e s i s demonstrate that s t r o n g o b j e c t e f f e c t s can be produced when the f i e l d - 1 s t i m u l i are exposed f o r 1000 ms. As a l r e a d y mentioned, t h i s c o n t r a s t s with the f i n d i n g that the a b i l i t y to use p e r s i s t i n g v i s i b l e i n f o r m a t i o n drops o f f sharply once stimulus d u r a t i o n s exceed about 100-150 ms (Di L o l l o , 1980). A t t e n t i o n : S e l e c t i o n Versus C a p a c i t y . How can the apparent c o n f l i c t concerning the r o l e of a t t e n t i o n be resolved? Perhaps the key i s to make a d i s t i n c t i o n between a t t e n t i o n as s e l e c t i o n and a t t e n t i o n as c a p a c i t y (Treisman, 1982). The object e f f e c t may depend on the s p a t i a l l y d i s t r i b u t e d a l l o c a t i o n of s u f f i c i e n t resources to f i e l d - 1 , but not on the a l l o c a t i o n of a t t e n t i o n in a more focused, s e l e c t i v e way. T h i s might e x p l a i n how d i f f e r e n t manipulations of a t t e n t i o n can l e a d to opposite r e s u l t s , and how the p r o p e r t i e s of s t i m u l i i n f i e l d - 1 can be at l e a s t somewhat conjoined without any of the s t i m u l i a c t u a l l y being s e l e c t e d by a t t e n t i o n . Normally the c o n j u n c t i o n of f e a t u r e i n f o r m a t i o n does r e q u i r e s e l e c t i v e a t t e n t i o n (Treisman & Gelade, 1980), so why would only d i s t r i b u t e d a t t e n t i o n a l resources be r e q u i r e d i n the preview d i s p l a y s ? An i n t e r e s t i n g — a d m i t t e d l y h i g h l y s p e c u l a t i v e — p o s s i b i l i t y i s that the obj e c t e f f e c t r e q u i r e s 1 1 3 only the resource aspect of a t t e n t i o n because the s e l e c t i o n aspect of a t t e n t i o n i s a l r e a d y p r o v i d e d by the motion. That i s , given the r e q u i s i t e p r o c e s s i n g r e s o u r c e s , motion i t s e l f may cause f e a t u r e s to be bundled t o g e t h e r i n a re-viewable u n i t . If t h i s s p e c u l a t i o n i s c o r r e c t , i t should not be p o s s i b l e to form i l l u s o r y c o n j u n c t i o n s of f e a t u r e s that belong to moving o b j e c t s . Motion does seem to have s p e c i a l s t a t u s i n p e r c e p t i o n (Johansson, 1979). Indeed, there i s evidence that motion i s sensed by s p e c i a l d i r e c t i o n - s p e c i f i c p h y s i o l o g i c a l mechanisms (Sekuler, Pantle & Levinson, 1978; Beverley & Regan, 1973), and at l e a s t r e l a t i v e to shape i n f o r m a t i o n , movement information e x h i b i t s p e c u l i a r r e s i s t a n c e to v i s u a l masking (Treisman, R u s s e l l & Green, 1975). As a l r e a d y mentioned, the k i n e t i c depth e f f e c t and Johansson's (1975) s t u d i e s of b i o l o g i c a l motion demonstrate that r e c o g n i t i o n of a s t i m u l u s p a t t e r n as that a r i s i n g from a s p e c i f i c o b j e c t becomes easy once the p a t t e r n i s put i n t o motion. Most r e l e v a n t l y , motion appears to be s p e c i a l with r e s p e c t t o a t t e n t i o n . N e i s s e r and Becklen (1975) found that s u b j e c t s had d i f f i c u l t y f o c u s i n g a t t e n t i o n on one of two superimposed videotaped scenes when those scenes.were motio n l e s s , but t h i s d i f f i c u l t y disappeared when the video tapes were set i n motion and each scene became a dynamic v i s u a l episode. The c o n c l u s i o n to be drawn here i s c e r t a i n l y not a f i r m one. There i s much converging evidence that s e l e c t i v e a t t e n t i o n i s needed to c r e a t e a c o n j o i n e d r e p r e s e n t a t i o n of 1 1 4 f e a t u r e s (eg. Treisman & Gelade, 1980). However, the present r e s e a r c h at l e a s t r a i s e s the p o s s i b i l i t y that t h i s general r u l e may r e q u i r e some q u a l i f i c a t i o n i n s i t u a t i o n s i n v o l v i n g p e r c e p t u a l o r g a n i z a t i o n by motion. Color and Letter-Shape Considered together, the s i s t e r experiments 8 and 9 l e a d to the c o n c l u s i o n that the e f f e c t of l e t t e r - s h a p e c o n s i s t e n c y on the re-viewing of c o l o r i n f o r m a t i o n , and the e f f e c t of c o l o r c o n s i s t e n c y on the re-viewing of l e t t e r i n f o r m a t i o n , are both minimal (although the l a t t e r e f f e c t i s s i g n i f i c a n t s t a t i s t i c a l l y ) . Symmetry between c o l o r and shape has been re p o r t e d i n work on s e l e c t i v e a t t e n t i o n : In an i d e n t i f i c a t i o n task, not only are s u b j e c t s able to s e l e c t a subset of shapes d e f i n e d by c o l o r , but they are a l s o able to s e l e c t a subset of c o l o r s d e f i n e d by shape (Treisman, 1969). There are, however, a couple of n o t i c e a b l e asymmetries between the r e s u l t s of Experiments 8 and 9 as w e l l . The f i r s t asymmetry i s that c o l o r engenders strong non-o b j e c t - s p e c i f i c priming r e l a t i v e to the object e f f e c t i t supports and l e t t e r engenders weak n o n - o b j e c t - s p e c i f i c priming r e l a t i v e to the o b j e c t e f f e c t i t supports. I m p l i c i t in the preceding statement i s the view that t h i s asymmetry i s a d i s p a r i t y i n the amount of n o n - o b j e c t - s p e c i f i c f a c i l i t a t i o n supported by c o l o r and l e t t e r . T h i s view i s s e n s i b l e because the o b j e c t e f f e c t s supported by c o l o r and l e t t e r are, a f t e r a l l , about the same a b s o l u t e s i z e i n m i l l i s e c o n d s . However, some of KTG's experiments suggest that there i s a f i x e d 1 1 5 amount of f a c i l i t a t i o n to be shared between the o b j e c t -s p e c i f i c and the n o n s p e c i f i c mechanisms, and so the observed asymmetry might a l t e r n a t i v e l y be c h a r a c t e r i z e d as a d i f f e r e n c e i n the p r o p o r t i o n of f a c i l i t a t i o n that i s o b j e c t -s p e c i f i c : The f a c i l i t a t i o n i n the c o l o r experiment i s predominantly n o n - o b j e c t - s p e c i f i c , and the f a c i l i t a t i o n i n the l e t t e r - s h a p e experiment i s predominantly o b j e c t - s p e c i f i c . T h i s c h a r a c t e r i z a t i o n r e v e a l s the p o s s i b i l i t y that the asymmetry i n question may be r e l a t e d to another asymmetry between c o l o r and shape r e p o r t e d by Kahneman, Treisman and B u r k e l l (1983). I t seems that shape naming i s more s u s c e p t i b l e to f i l t e r i n g c o s t than i s c o l o r naming. Given that both experimental s e t t i n g s i n v o l v e manipulations of the obj e c t o r g a n i z a t i o n of the f i e l d , i t i s p o s s i b l e that t h i s asymmetry represents a fundamental d i f f e r e n c e in the way shape and c o l o r r e l a t e to p e r c e p t u a l u n i t i z a t i o n : The p r o c e s s i n g of c o l o r may be simply more independent of the o r g a n i z a t i o n of the f i e l d i n t o o b j e c t s . The second asymmetry between c o l o r and l e t t e r - s h a p e i n v o l v e s t h e i r r e s p e c t i v e r e l a t i o n s to the ob j e c t e f f e c t . Both dimensions support o b j e c t e f f e c t s : c o l o r c o n s i s t e n c y has a main e f f e c t on c o l o r response, and l e t t e r c o n s i s t e n c y has a main e f f e c t on l e t t e r response. However, although l e t t e r c o n s i s t e n c y has a main e f f e c t on c o l o r response, c o l o r c o n s i s t e n c y does not have a main e f f e c t on l e t t e r response (Anne Treisman f i r s t r e c o g n i z e d the s i g n i f i c a n c e of t h i s r e s u l t ) . That i s , r e p e t i t i o n s of l e t t e r - s h a p e generate 116 o b j e c t - s p e c i f i c f a c i l i t a t i o n of c o l o r responses, but r e p e t i t i o n s of c o l o r do not generate o b j e c t - s p e c i f i c f a c i l i t a t i o n of l e t t e r responses. T h i s suggests that the information i n t e r a c t i o n goes i n one d i r e c t i o n between c o l o r and l e t t e r - s h a p e but not i n the other. In a d i s c u s s i o n of asymmetric i n t e g r a l i t y , Garner (1974) s p e c u l a t e s that c o l o r should a f f e c t form d i s c r i m i n a t i o n but form should not a f f e c t c o l o r d i s c r i m i n a t i o n , which i s not c o n s i s t e n t with the p a t t e r n of main e f f e c t s obtained i n Experiments 8 and 9. When i t comes to i n f l u e n c i n g simple d i s c r i m i n a t i o n , form seems to a f f e c t c o l o r more than c o l o r does form. However, Garner's (1974) ranking of the potency of c o l o r and form on each other's p r o c e s s i n g i s borne out when i t comes to i n f l u e n c i n g o b j e c t - s p e c i f i c i t y . C o l o r c o n s i s t e n c y a f f e c t s l e t t e r c o n s i s t e n c y , but l e t t e r c o n s i s t e n c y does not a f f e c t c o l o r c o n s i s t e n c y . These f i n d i n g s taken a l l together are i n t e r e s t i n g because they imply t h a t , r e l a t i v e to form, c o l o r i s l e s s c o n s t r a i n e d by o b j e c t s ( i e . i t s c o n s i s t e n c y does not generate a l e t t e r o b j e c t e f f e c t ) but i s more c o n s t r a i n i n g of o b j e c t s ( i e . i t s c o n s i s t e n c y does determine the s t r e n g t h of the l e t t e r o b j e c t e f f e c t ) . Given t h i s p r o p o s i t i o n i t i s s u r p r i s i n g that KTG found that c o l o r c o n s i s t e n c y c o u l d not support a l e t t e r o b j e c t e f f e c t i n the degenerate Ternus d i s p l a y s . R i v a l Accounts of the Object E f f e c t C e r t a i n accounts of the obj e c t e f f e c t can be put forward to r i v a l KTG's ( i n p r o g r e s s ) , which i n v o l v e s spatiotemporal 1 1 7 i n t e g r a t i o n of stimulus i n f o r m a t i o n . Some of the f i n d i n g s of t h i s t h e s i s provide evidence a g a i n s t these r i v a l accounts. The Response-Integration Account The r e s p o n s e - i n t e g r a t i o n account a s s e r t s that a moving o b j e c t does not cause an i n t e g r a t i o n of i n f o r m a t i o n about the s t i m u l i that appear w i t h i n that o b j e c t ; r a t h e r , i t causes an i n t e g r a t i o n of response tendencies a s s o c i a t e d with those s t i m u l i . C o n s i s t e n t c o n d i t i o n s have f a s t e r RTs than i n c o n s i s t e n t c o n d i t i o n s not because the t a r g e t and preview are c o n s i s t e n t as s t i m u l i , but because they are response-c o n s i s t e n t . Two of KTG's f i n d i n g s are good evidence a g a i n s t t h i s . (a) When the t a r g e t and preview were the same l e t t e r and were t h e r e f o r e a s s o c i a t e d with the same response, but one was i n upper case and the other was i n lower case, there was no o b j e c t e f f e c t . (b) An o b j e c t - s p e c i f i c e f f e c t was y i e l d e d by the v i s u a l search experiment even though there was no response a s s o c i a t e d with any f i e l d - 1 s t i m u l u s . Further support f o r the co n t e n t i o n that the ob j e c t e f f e c t i s not p u r e l y a case of response f a c i l i t a t i o n i s a f f o r d e d by Experiment 6 of the present s e r i e s . If the spat i o t e m p o r a l i n t e g r a t i o n i n the preview paradigm were o c c u r r i n g s o l e l y between response tendencies, then v a r i a t i o n on a dimension that i s i r r e l e v a n t with respect to response should have been i n c o n s e q u e n t i a l . In the two pre s e n t -c o n s i s t e n t c o n d i t i o n s of Experiment 6 the response "present" should have been a s s o c i a t e d with both the t a r g e t and the preview r e g a r d l e s s of t h e i r shapes, which had no response 1 18 relevance whatsoever. The only way to salvage the response-i n t e g r a t i o n account given the r e s u l t s of Experiment 6, i s to propose that responses a s s o c i a t e d with s t i m u l i that d i f f e r on some p h y s i c a l property are not i n t e g r a t e d as f u l l y as those a s s o c i a t e d with s t i m u l i that are completely i d e n t i c a l - - a n d t h i s would imply that the o b j e c t - s p e c i f i c i n t e g r a t i o n depends on i n f o r m a t i o n i n a d d i t i o n to that at the l e v e l of response. The Apparent-Distance Account The r e s u l t s of Experiment 6 are a l s o of i n t e r e s t with respect to another e x p l a n a t i o n of the o b j e c t e f f e c t r i v a l to KTG's account. R e c a l l that KTG contend that the o b j e c t e f f e c t i s the r e s u l t of two s t i m u l i being i n t e g r a t e d as a s i n g l e u n i t . These s t i m u l i i n t e r a c t so thoroughly because, in some senses, they are made more l i k e a s i n g l e s t i m u l u s . A c o n t r a s t i n g e x p l a n a t i o n can be founded on the o b s e r v a t i o n that the average apparent d i s t a n c e between two s t i m u l i i n s t r o b o s c o p i c motion i s l e s s than the o b j e c t i v e d i s t a n c e between them. Just because the c o n t r a c t i o n of d i s t a n c e i s only phenomenal, i t does not f o l l o w that i t can have no p e r c e p t u a l consequences (eg. Rock and Ebenholtz, 1962, found that s t r o b o s c o p i c motion i s dependent on change i n phenomenal l o c a t i o n ) . Apparent motion may e f f e c t i v e l y warp v i s u a l space, b r i n g i n g s t i m u l i c l o s e r together p s y c h o l o g i c a l l y . The crux of the p r o p o s i t i o n i s that the " o b j e c t - s p e c i f i c " i n t e r a c t i o n o c c u r r i n g between s t i m u l i l i n k e d by pure apparent motion or by apparent motion guided by the r e a l motion of l i n e f i g u r e s has nothing to do with u n i t i z a t i o n : The 1 19 enhanced i n t e r a c t i o n i s the r e s u l t of q u i t e d i s t i n c t o b j e c t s being brought p e r c e p t u a l l y c l o s e r together (nb. Hoffman & Nelson, 1981). T h i s n o t i o n i s c o n s i s t e n t with Shaw and P i t t e n g e r ' s (1977) " r e l a t i v i s t i c " conception of p e r c e p t u a l space, and with Ramachandran's (1981) o b s e r v a t i o n that apparent motion causes misjudgment of stimulus l o c a t i o n i n the d i r e c t i o n of the motion. I t i s not very c o n s i s t e n t with Attneave and Block's (1973) a s s e r t i o n that the p e r c e p t u a l r e p r e s e n t a t i o n of space precedes the genesis of apparent motion. As p r e v i o u s l y d i s c u s s e d , i t i s a l s o i n c o n s i s t e n t with KTG's experiment showing no d i f f e r e n c e i n the o b j e c t e f f e c t between a n e a r - d i s t a n c e and a f a r - d i s t a n c e c o n d i t i o n . Because i t maintains that the t a r g e t and preview are separate o b j e c t s , the apparent d i s t a n c e account of the preview r e s u l t s would be o b l i g e d to p r e d i c t no e f f e c t of r e s p o n s e - i r r e l e v a n t shape i n c o n s i s t e n c y on the presence o b j e c t e f f e c t . Even the dimension p a i r value and chroma--a paragon of i n t e g r a l i t y - - b e h a v e s l i k e a n o n i n t e g r a l p a i r when the value and chroma p e r t a i n to separate o b j e c t s (Garner & F e l f o l d y , 1974). S u r e l y , then, on the apparent-distance view, the d e t e c t i o n of one o b j e c t should not be a f f e c t e d by the shape of a nearby but d i s t i n c t o b j e c t ; and so the a p p a r e n t - d i s t a n c e account of the o b j e c t e f f e c t i s c o n t r a d i c t e d by the r e s u l t s of the duodimension presence experiment. 1 20 The S p a t i a l - F r e q u e n c y Account There seems to be a n o n r e t r o a c t i v e a l t e r n a t i v e to the re-viewing f o r m u l a t i o n . According to the re-viewing idea, once the t a r g e t ( i n the Ternus experiment for example) i s presented and the apparent motion i s crea t e d , the a l r e a d y -removed f i e l d - 1 stimulus that has turned out to be the o r i g i n of the t a r g e t ' s apparent movement i s i n t e g r a t e d with the t a r g e t . Another e x p l a n a t i o n based on the d i f f e r e n t i a l p r o c e s s i n g of high and low s p a t i a l f r e q u e n c i e s might be e n t e r t a i n e d . The v i s u a l system seems to analyze a scene a c c o r d i n g to s p a t i a l frequency ( P o l l e n , Lee & T a y l o r , 1971), and d i f f e r e n t high and low s p a t i a l f r e q u e n c i e s may be processed by d i f f e r e n t channels that have d i f f e r e n t response l a t e n c i e s (Breitmeyer & Ganz, 1976). Low s p a t i a l f r e q u e n c i e s are processed f a s t e r than high s p a t i a l f r e q u e n c i e s . The apparent motion i n the Ternus d i s p l a y r e f l e c t s the p r o c e s s i n g of in f o r m a t i o n of low s p a t i a l frequency (Attneave, 1974) r e l a t i v e t o the more d e t a i l e d i n f o r m a t i o n concerning l e t t e r shape. Thus, the p r o c e s s i n g of l e t t e r shape may be slow enough t h a t , d e s p i t e the o b j e c t i v e t i m i n g in the p h y s i c a l d i s p l a y ( c f . Kahneman, 1967), the t a r g e t i s l i n k e d to a f i e l d - 1 l e t t e r before that l e t t e r i s f u l l y processed. The r e s u l t i s that t h i s f i e l d - 1 l e t t e r c o u l d produce g r e a t e r f a c i l i t a t i o n because i t r e c e i v e s favored treatment at the time of i t s i n i t i a l p r o c e s s i n g , not because i t r e c e i v e s s p e c i a l r e - p r o c e s s i n g . 121 One problem with t h i s framework i s i t s i n a b i l i t y to account for the object e f f e c t in the experiments with l o n g -d u r a t i o n i n i t i a l f i e l d s (Experiments 4 and 5; KTG). With f i e l d - 1 s t i m u l i of 1000 ms, there would be time to process a l l of them f u l l y and so any advantage f o r the stimulus i n the target-yoked l o c a t i o n would have to be bestowed a f t e r the t a r g e t had been p r e s e n t e d — i e . r e t r o a c t i v e l y . In a d d i t i o n , the presence o b j e c t e f f e c t per se counts as evidence a g a i n s t the s p a t i a l - f r e q u e n c y account. The presence or absence of a t a r g e t s timulus—when i t i s as l a r g e as the ones used i n Experiment 2 - - i s i t s e l f i n f o r m a t i o n of r e l a t i v e l y low s p a t i a l frequency. The s p a t i a l - f r e q u e n c y account would t h e r e f o r e p r e d i c t that implementing a presence/absence judgment with such s t i m u l i i n the preview paradigm would s e v e r e l y reduce or e r a d i c a t e the object e f f e c t . I m p l i c a t i o n of the Study as a Whole The experiments rep o r t e d in t h i s t h e s i s , as w e l l as p r o v i d i n g a g e n e r a l i z a t i o n of KTG's o b j e c t e f f e c t to a new experimental s e t t i n g , support two fundamental c o n c l u s i o n s , (a) The mechanism u n d e r l y i n g the o b j e c t e f f e c t can operate on i n f o r m a t i o n r e f e r r i n g to the p h y s i c a l p r o p e r t i e s of an o b j e c t . (b) The object e f f e c t can be produced without complete c o n g r u i t y between the t a r g e t and preview s t i m u l i : I t i s not simply an e f f e c t of s t r i c t s timulus r e p e t i t i o n . These g e n e r a l c o n c l u s i o n s support KTG's c o n t e n t i o n that the spatiotemporal i n t e g r a t i o n witnessed in the preview paradigm concerns p h y s i c a l or p e r c e p t u a l i n f o r m a t i o n as opposed to 1 22 a b s t r a c t or conceptual i n f o r m a t i o n . Whether one p r e f e r s to model the obj e c t e f f e c t as based on an o b j e c t - s p e c i f i c r e p r e s e n t a t i o n or on an o b j e c t - s p e c i f i c p r o c e s s — f o r m a l l y they are probably not e s s e n t i a l l y d i f f e r e n t anyway--this r e p r e s e n t a t i o n / p r o c e s s must i n c l u d e p e r c e p t u a l i n f o r m a t i o n . Indeed, given KTG's l e t t e r - c a s e and l e x i c a l -d e c i s i o n experiments, i t looks as though the r e p r e s e n t a t i o n / p r o c e s s i n c l u d e s only p e r c e p t u a l i n f o r m a t i o n . Of course, i t c o u l d be a s s e r t e d that i n f o r m a t i o n at a l l l e v e l s i s present but not a l l of i t i s subject to spati o t e m p o r a l i n t e g r a t i o n ; however, t h i s would not be a very u s e f u l d i s t i n c t i o n to make because the purpose of invoking the r e p r e s e n t a t i o n / p r o c e s s in the f i r s t p l a c e was to account f o r the i n t e g r a t i o n . U n t i l there i s some s p e c i f i c reason to do otherwise, then, i t would probably be b e t t e r simply to c o n s i d e r n o n i n t e g r a t a b l e i n f o r m a t i o n to be absent from the r e p r e s e n t a t i o n / p r o c e s s . The b a s i c f i n d i n g of t h i s t h e s i s , that the spati o t e m p o r a l i n t e g r a t i o n g i v i n g r i s e to the obj e c t e f f e c t can apply to p h y s i c a l p r o p e r t i e s , makes more p l a u s i b l e the c o n t e n t i o n that KTG's l e t t e r e f f e c t i s not based on nonperceptual l e x i c a l i n f o r m a t i o n . F u r t h e r , i t a l s o encourages the thought that such i n t e g r a t i o n , manifested as a c o g n i t i v e e f f e c t , i s c l o s e l y r e l a t e d to the p e r c e p t u a l i n t e g r i t y of o b j e c t s . As argued e a r l i e r , the c a u s a l r e l a t i o n between i n t e g r a t i o n o p e r a t i o n s at d i f f e r e n t i n f o r m a t i o n a l l e v e l s i s d i f f i c u l t to d i s c e r n . 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P e r c e p t i o n &  Psychophysics, 3J_, 201-209. 133 Appendix A l l Six C o n d i t i o n s of Experiment 3 The mean RTs of Experiment 3 were: l a r g e - c o n s i s t e n t 515 ms l a r g e - i n c o n s i s t e n t 540 LARGE-CONTROL 536 s m a l l - c o n s i s t e n t 557 s m a l l - i n e o n s i s t e n t 583 SMALL-CONTROL 556 The s e g r e g a t i o n of preview c o n d i t i o n s from the c o n t r o l c o n d i t i o n s f o r i n t e r p r e t i v e purposes i s not m e t h o d o l o g i c a l l y i d e a l . Poulton (1982) has issued a str o n g warning against i g n o r i n g the p o t e n t i a l f o r the s t r a t e g y employed i n one c o n d i t i o n to i n f l u e n c e performance on a companion c o n d i t i o n in w i t h i n - s u b j e c t s d e s i g n s , and such problems have been encountered i n f o r e p e r i o d p r e p a r a t i o n experiments at l e a s t l o o s e l y resembling the present s t u d i e s (Sudevan, 1980). However, the se g r e g a t i o n p r a c t i c e d h e r e i n i s p a r t i a l l y v i n d i c a t e d by the f a c t t h at the segregated c o n d i t i o n s d i f f e r only with re s p e c t to f i e l d - 1 - - a n d f i e l d - 1 i s i r r e l e v a n t to the s u b j e c t ' s task. According to Poulton (1982), c o n d i t i o n s that normally r e q u i r e d i f f e r e n t s t r a t e g i e s are the ones most l i k e l y to generate asymmetric s t r a t e g y t r a n s f e r s . C o n d i t i o n s with only t a s k - i r r e l e v a n t d i f f e r e n c e s , then, are not at great r i s k . Moreover, not only are the d i f f e r e n c e s here task-i r r e l e v a n t , they are a l s o d i f f i c u l t to n o t i c e even when 1 34 looked f o r . A p a t t e r n r e v e a l s i t s e l f i n the complete r e s u l t s of Experiment 3. For the ' l a r g e ' c o n d i t i o n s , c o n t r o l RTs are i n d i s t i n g u i s h a b l e from the r e l a t i v e l y slow i n c o n s i s t e n t RTs, and f o r the 'small' c o n d i t i o n s , c o n t r o l RTs are i n d i s t i n g u i s h a b l e from the r e l a t i v e l y f a s t c o n s i s t e n t RTs. As i n d i c a t e d i n the main body of the paper, t h i s p a t t e r n of r e s u l t s i s i n t e r p r e t i v e l y p r o b l e m a t i c because a f i e l d - 1 c o n s i s t i n g of empty boxes i s probably not an a p p r o p r i a t e c o n t r o l f i e l d . A number of e x p l a n a t i o n s f i t the data. One e x p l a n a t i o n i s t h a t , as o r i g i n a l l y intended, the c o n t r o l c o n d i t i o n s r e a l l y do serve as i n s t a n c e s of spatiotemporal i n t e g r a t i o n i n v o l v i n g n e u t r a l s t i m u l i . T h i s leads to the rather unparsimonious i n f e r e n c e that the s i z e o b j e c t e f f e c t takes the form of f a c i l i t a t i o n on ' l a r g e ' t r i a l s and i n h i b i t i o n on 'small' t r i a l s . An a l t e r n a t i v e e x p l a n a t i o n a s s e r t s that s u b j e c t s look i n the t a r g e t box only for the l a r g e stimulus and use a process of e l i m i n a t i o n to respond to the small stimulus ( i e . as a n o t - l a r g e s t i m u l u s ) . Notice that the r e s u l t s are compatible with the idea that only the l a r g e a s t e r i s k i s at a l l i n f l u e n t i a l when presented i n f i e l d - 1 . For l a r g e t a r g e t s , on l a r g e - i n c o n s i s t e n t t r i a l s , the RTs would match those produced by d i s p l a y i n g a blank in f i e l d - 1 because a small stimulus was presented i n f i e l d - 1 ; f o r small t a r g e t s , on s m a l l - c o n s i s t e n t t r i a l s the RTs would match those produced by d i s p l a y i n g a blank i n f i e l d - 1 again because a small stimulus was presented 1 35 i n f i e l d - 1 . Perhaps the most parsimonious hypothesis i s that the empty-field-1 c o n t r o l i s not i n f a c t n e u t r a l with respect to s i z e . The c o n t r o l c o n d i t i o n s mimic those c o n d i t i o n s having a small s t i m u l u s i n the f i e l d - 1 t a r g e t box. These r e s u l t s conform to the p a t t e r n expected i f the blanks were p e r c e p t u a l l y e q u i v a l e n t (at l e a s t with respect to the s i z e o b j e c t e f f e c t ) to the small s t i m u l i . C o n s i d e r a t i o n of the c o n t r o l c o n d i t i o n s of Experiment 3 makes apparent the d i f f i c u l t y of implementing an adequate c o n t r o l c o n d i t i o n i n the f e a t u r a l preview experiments. U n f o r t u n a t e l y , the p a t t e r n of r e s u l t s obtained with the c o n t r o l c o n d i t i o n s i s so ambiguous i t sheds no l i g h t on the spatiotemporal i n t e g r a t i o n of p h y s i c a l p r o p e r t i e s o c c u r r i n g in these experiments. 

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