{"Affiliation":[{"label":"Affiliation","value":"Arts, Faculty of","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","classmap":"vivo:EducationalProcess","property":"vivo:departmentOrSchool"},"iri":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","explain":"VIVO-ISF Ontology V1.6 Property; The department or school name within institution; Not intended to be an institution name."},{"label":"Affiliation","value":"Psychology, Department of","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","classmap":"vivo:EducationalProcess","property":"vivo:departmentOrSchool"},"iri":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","explain":"VIVO-ISF Ontology V1.6 Property; The department or school name within institution; Not intended to be an institution name."}],"AggregatedSourceRepository":[{"label":"Aggregated Source Repository","value":"DSpace","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","classmap":"ore:Aggregation","property":"edm:dataProvider"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","explain":"A Europeana Data Model Property; The name or identifier of the organization who contributes data indirectly to an aggregation service (e.g. Europeana)"}],"Campus":[{"label":"Campus","value":"UBCV","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","classmap":"oc:ThesisDescription","property":"oc:degreeCampus"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","explain":"UBC Open Collections Metadata Components; Local Field; Identifies the name of the campus from which the graduate completed their degree."}],"Creator":[{"label":"Creator","value":"Grabowecky, Marcia F.","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/creator","classmap":"dpla:SourceResource","property":"dcterms:creator"},"iri":"http:\/\/purl.org\/dc\/terms\/creator","explain":"A Dublin Core Terms Property; An entity primarily responsible for making the resource.; Examples of a Contributor include a person, an organization, or a service."}],"DateAvailable":[{"label":"Date Available","value":"2010-07-22T23:00:36Z","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"edm:WebResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"DateIssued":[{"label":"Date Issued","value":"1987","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"oc:SourceResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"Degree":[{"label":"Degree (Theses)","value":"Master of Arts - MA","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","classmap":"vivo:ThesisDegree","property":"vivo:relatedDegree"},"iri":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","explain":"VIVO-ISF Ontology V1.6 Property; The thesis degree; Extended Property specified by UBC, as per https:\/\/wiki.duraspace.org\/display\/VIVO\/Ontology+Editor%27s+Guide"}],"DegreeGrantor":[{"label":"Degree Grantor","value":"University of British Columbia","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","classmap":"oc:ThesisDescription","property":"oc:degreeGrantor"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","explain":"UBC Open Collections Metadata Components; Local Field; Indicates the institution where thesis was granted."}],"Description":[{"label":"Description","value":"The feature integration theory of object perception (Treisman & Gelade, 1980) suggests that the perception of multidimensional stimuli requires that attention be serially directed to the items in a visual display in order to correctly conjoin features into objects, while the perception of features does not require serial attention. Under conditions in which the serial focusing of attention is disrupted by reducing display duration, available information about conjunctions of two features should not exceed the independent information available about the constituent features. Three experiments using a partial report paradigm employing a location cue were conducted in order to test this prediction. Subjects viewed colored letter displays that varied in cue-display stimulus onset asynchrony. The dependent measure was accuracy of response. Results suggest that a small amount of information from a separate representation of conjunctions of features may be accessible.","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/description","classmap":"dpla:SourceResource","property":"dcterms:description"},"iri":"http:\/\/purl.org\/dc\/terms\/description","explain":"A Dublin Core Terms Property; An account of the resource.; Description may include but is not limited to: an abstract, a table of contents, a graphical representation, or a free-text account of the resource."}],"DigitalResourceOriginalRecord":[{"label":"Digital Resource Original Record","value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/26822?expand=metadata","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","classmap":"ore:Aggregation","property":"edm:aggregatedCHO"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","explain":"A Europeana Data Model Property; The identifier of the source object, e.g. the Mona Lisa itself. This could be a full linked open date URI or an internal identifier"}],"FullText":[{"label":"Full Text","value":"Feature and Conjunction Information from Brief V i s u a l Displays By Marcia F. Grabowecky B.A., The University of Calgary, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n THE FACULTY OF GRADUATE STUDIES (Department of Psychology) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July 1987 \u00a9 Marcia F. Grabowecky, 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of PsucUn loq^ The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3\/81) A b s t r a c t The f e a t u r e i n t e g r a t i o n theory of o b j e c t p e r c e p t i o n ( T r e i s m a n & G e l a d e , 1980) s u g g e s t s t h a t t h e p e r c e p t i o n of m u l t i d i m e n s i o n a l s t i m u l i r e q u i r e s t h a t a t t e n t i o n be s e r i a l l y d i r e c t e d t o the items i n a v i s u a l d i s p l a y i n order to c o r r e c t l y c o n j o i n f e a t u r e s i n t o o b j e c t s , while the p e r c e p t i o n of f e a t u r e s does not r e q u i r e s e r i a l a t t e n t i o n . Under c o n d i t i o n s i n which the s e r i a l f o c u s i n g of a t t e n t i o n i s d i s r u p t e d by r e d u c i n g d i s p l a y d u r a t i o n , a v a i l a b l e i n f o r m a t i o n about c o n j u n c t i o n s of two f e a t u r e s should not exceed the i n d e p e n d e n t i n f o r m a t i o n a v a i l a b l e about the c o n s t i t u e n t f e a t u r e s . T h r e e experiments u s i n g a p a r t i a l r e p o r t paradigm employing a l o c a t i o n cue were conducted i n order to t e s t t h i s p r e d i c t i o n . S u b j e c t s viewed c o l o r e d l e t t e r d i s p l a y s t h a t v a r i e d i n cue-d i s p l a y s t i m u l u s onset asynchrony. The dependent measure was accuracy of response. R e s u l t s suggest t h a t a s m a l l amount of i n f o r m a t i o n from a separate r e p r e s e n t a t i o n of c o n j u n c t i o n s of f e a t u r e s may be a c c e s s i b l e . i i i T a b l e o f C o n t e n t s A b s t r a c t i i L i s t o f F i g u r e s v L i s t o f T a b l e s . . v i A c k n o w l e d g m e n t v i i I n t r o d u c t i o n 1 S t a t e m e n t o f P r o g r a m 2 F e a t u r e I n t e g r a t i o n 3 B l o b P e r c e p t i o n 8 E a r l y a n d L a t e S e l e c t i o n 10 F e a t u r e I n t e g r a t i o n T h e o r y 13 The P a r t i a l R e p o r t P a r a d i g m 16 The P r e s e n t I n v e s t i g a t i o n 20 E x p e r i m e n t 1 24 E x p e r i m e n t 2 33 E x p e r i m e n t 3 37 i v General Discuss ion 48 Summary of Results 48 The Conjunction Advantage 54 E r r o r s 57 Extensions of the Research 61 Conclusion 63 References 65 V L i s t of F i g u r e s F i g u r e 1. Experiment 1: Feature and Conjunction Report Observed-Predicted D i f f e r e n c e s 32 F i g u r e 2. Experiment 2: Feature and C o n j u n c t i o n Report Observed-Predicted D i f f e r e n c e s 36 F i g u r e 3. Experiment 3: Feature and Conjunction Report Observed-Predicted D i f f e r e n c e s 43 F i g u r e 4. Experiment 3: E r r o r s by type 45 v i i Acknowledgement I w o u l d l i k e t o t h a n k Anne T r e i s m a n , i n whose l a b o r a t o r y a nd u n d e r whose s u p e r v i s i o n t h i s work was conducted, f o r her generous support, and to thank D a n i e l Kahneman f o r h i s s u p p o r t and u s e f u l comments. I a l s o a p p r e c i a t e the a s s i s t a n c e and encouragement of my committee, Lawrence Ward, Raymond Corteen and Janet Werker. I thank my c o l l e a g u e s i n the A t t e n t i o n Labs at both the U n i v e r s i t y of B r i t i s h C o l u m b i a and at t h e U n i v e r s i t y o f C a l i f o r n i a , B e r k e l e y f o r t h e i r i n v a l u a b l e comments and support. L a s t l y , I thank my pare n t s , my husband Jim MacDonald, and my son Devin f o r t h e i r p a t i e n c e and encouragement. The r e s e a r c h r e p o r t e d h e r e was s u p p o r t e d by a P o s t g r a d u a t e S c h o l a r s h i p f r o m t h e 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. v i L i s t o f T a b l e s T a b l e I . S u p e r i o r i t y o f p a r t i a l r e p o r t o v e r t o t a l r e p o r t f o r E x p e r i m e n t 1.. 29 T a b l e I I . C o n f u s i o n M a t r i x f o r c o l o r s 46 T a b l e I I I . C o n f u s i o n M a t r i x f o r l e t t e r s 47 T a b l e I V . Summary T a b l e f o r O b s e r v e d P e r f o r m a n c e v s P r e d i c t e d P e r f o r m a n c e 49 T a b l e V. Summary T a b l e f o r C o l o r P e r f o r m a n c e a n d L e t t e r P e r f o r m a n c e 50 T a b l e V I . Summary T a b l e f o r P a r t i a l R e p o r t P e r f o r m a n c e o n C o n j u n c t i o n s A c r o s s E x p e r i m e n t s 52 1 Feature and Conjunction Information from B r i e f V i s u a l Displays There are at l east two d i s t i n c t l y d i f f e r e n t ways of looking at the perception of objects . I f we can r e l y on our i n t u i t i o n s , p e r c e p t i o n i s h o l i s t i c . We are aware of complete and r i c h l y d e t a i l e d objects and scenes i n the v i s i b l e environment. Objects have locat ions i n space, they have parts and features and as much d e t a i l as we care to see. In order to know th i s a l l we need do i s open our eyes. Seeing i s e f f o r t l e s s . An a l t e r n a t i v e to t h i s conception i s that what we do i s the ant i thes i s of th i s process. Rather than i n s t a n t l y and automatical ly representing the whole and then narrowing and focusing to extract i t s par t s , we f i r s t r eg i s t er the many components of the whole and only l a t e r recreate objects and scenes. This view of seeing implies a multitude of l o c a l processes r a p i d l y encoding and recoding the v i s i b l e scene many times over. B o t h of t h e s e a p p r o a c h e s a r e current ly taken by researchers , and both have long t r a d i t i o n s i n psychology. The f i r s t view found support among Gesta l t psychologists and now i s mainly found among d i r e c t perception theor i s t s (after Gibson, 1959). Proponents of d i r e c t perception argue that 2 t h e v e r y r i c h n e s s o f i n f o r m a t i o n i n t h e v i s i b l e environment i s enough t o a c c o u n t f o r t h e ease w i t h w h i c h we see, t h a t s t r u c t u r e i s i n h e r e n t i n t h e s t i m u l u s and a l l we need do i s use i t . The o t h e r v i e w of p e r c e p t i o n as s y n t h e s i s has r o o t s i n t h e a s s o c i a t i o n i s t t r a d i t i o n . From t h i s p e r s p e c t i v e t h e c o m p l e x i t y o f t h e i n f o r m a t i o n p r e s e n t i n a v i s u a l scene p o s e s p r o b l e m s w i t h w h i c h t h e p e r c e p t u a l system must s u c c e s s f u l l y d e a l i n o r d e r f o r t h e o r g a n i s m t o s u r v i v e . Because of t h e s e d i f f e r e n c e s i n approach th e two v i e w s have a l s o e m p h a s i z e d d i f f e r e n t a s p e c t s o f s e e i n g , t h e f i r s t d w e l l i n g on s t i m u l u s s t r u c t u r e and t h e second d w e l l i n g on s t r u c t u r e i n p r o c e s s i n g . Statement of Program The r e s e a r c h r e p o r t e d i n t h i s t h e s i s i s composed o f s e v e r a l f a c e t s . The h y p o t h e s i s t e s t e d o r i g i n a t e s from Treisman's f e a t u r e i n t e g r a t i o n t h e o r y (Treisman & Gelade, 1980). T h i s t h e o r y s u g g e s t s t h a t o b j e c t p e r c e p t i o n i s p a r t i a l l y d ependent upon t h e f o c u s i n g o f a t t e n t i o n f o r c o m b i n a t i o n s of f e a t u r e s t o be c o n s t r u c t e d c o r r e c t l y . The p r e s e n t h y p o t h e s i s i s t h a t no r e p r e s e n t a t i o n o f c o n j u n c t i o n s o f f e a t u r e s e x i s t s u n t i l a t t e n t i o n i s d i r e c t e d t o t h e i r l o c a t i o n i n space. I n o r d e r t o e s t a b l i s h the c o n t e x t f o r t h e r e s e a r c h , I w i l l d i s c u s s t h e problem of f e a t u r e i n t e g r a t i o n , f e a t u r e i n t e g r a t i o n t h e o r y and some of i t s 3 a l t e r n a t i v e s , and f i n a l l y , t h e n a t u r e o f t h e p a r a d i g m u s e d t o t e s t t h e p r e d i c t i o n . F e a t u r e I n t e g r a t i o n The a s s u m p t i o n t h a t f e a t u r e i n t e g r a t i o n i s an i m p o r t a n t p r o c e s s i s f u n d a m e n t a l t o many a p p r o a c h e s w i t h i n t h e i n f o r m a t i o n p r o c e s s i n g p a r a d i g m . F o r example, i n A n d e r s o n ' s ( 1 9 8 1 ) i n f o r m a t i o n i n t e g r a t i o n a p p r o a c h , i n f o r m a t i o n p r o c e s s i n g c o n s i s t s o f a s e q u e n c e o f o p e r a t i o n s t h a t c o n d e n s e m u l t i p l e s t i m u l i o r d i m e n s i o n s i n t o a s i n g l e r e s u l t w h i c h t h e n b e c o m e s t h e i n p u t t o t h e n e x t l e v e l o f p r o c e s s i n g . The i m p o r t a n c e o f f e a t u r e i n t e g r a t i o n may be a s s e s s e d b y s a m p l i n g t h e l i t e r a t u r e i n b o t h p h y s i o l o g y and p e r c e p t i o n . The l i t e r a t u r e p r o v i d e s s t r o n g ( t h o u g h n o t c o n c l u s i v e ) e v i d e n c e t h a t t h e d e c o m p o s i t i o n o f i n p u t i n t o i t s c o m p o n e n t f e a t u r e s i s t h e f u n c t i o n o f some b r a i n mechanisms. E a r l y e v i d e n c e f r o m H u b e l and W i e s e l (1959, 1968) i n d i c a t e d t h a t s i n g l e c e l l s i n t h e s t r i a t e c o r t e x r e s p o n d e d b e s t t o p a r t i c u l a r c o n f i g u r a t i o n s i n s t i m u l i , f o r example, t o l i n e s o f a p a r t i c u l a r o r i e n t a t i o n . A t l e a s t i n some c e l l s t h e s e r e s p o n s e s a r e i n v a r i a n t w i t h c h a n g e s i n o t h e r p r o p e r t i e s o f t h e s t i m u l u s , s u c h as i t s c o l o r . More r e c e n t l y t h e i d e a o f i n d i v i d u a l c e l l s s i n g l e - h a n d e d l y r e p r e s e n t i n g f e a t u r e s has b e e n r e p l a c e d w i t h t h e n o t i o n t h a t 4 groups of c e l l s a c t i n g i n concert are needed to code d i f f e r e n t values within the same dimension. Another p o s s i b i l i t y i s t h a t the v i s u a l system decomposes input, but not i n t o such n a t u r a l r e a l world features as Hubel's and Wiesel's l i n e s and edges. The v i s u a l system may instead perform something l i k e a rough Fourier analysis of the scene into i t s component s p a t i a l frequencies (De Valois & De Valoi s , 1980). In addition to s p a t i a l frequency the system needs to determine the phase of sti m u l i i n the f i e l d . For simple s t i m u l i , phase corresponds to or encompasses p o s i t i o n a l information. Information about r e l a t i v e phase, or the r e l a t i o n s h i p s of components of patterns to one another, must also be coded. A system which can capture t h i s type of information could then recognize a pattern i n spite of changes i n i t s orientation i n the v i s u a l f i e l d . If t h i s type of analysis i s the decomposition which takes place at the e a r l i e s t levels i n the v i s u a l system, then features which are more c l o s e l y related to r e a l world features are l a t e r constructs i n v i s u a l processing. Evidence f o r separate a n a l y s i s of features i s also a v a i l a b l e from performance i n such perceptual tasks as texture segregation and v i s u a l search. Treisman and Gelade (1980) found that texture segregation was easy when two areas d i f f e r e d along a single dimension, but d i f f i c u l t i f they d i f f e r e d only i n the conjunction of values from more 5 t h a n one d i m e n s i o n . As w e l l , T r e i s m a n ( 1 9 8 2 ) f o u n d t h a t a n e l e m e n t i n a d i s p l a y c o u l d be h i d d e n i f i t was l o c a t e d a t t h e b o r d e r o f two g r o u p s e a c h o f w h i c h s h a r e d one o f i t s f e a t u r e s . T h e s e d a t a s u g g e s t t h a t s e p a r a t e v a l u e s a n d n o t t h e i r c o m b i n a t i o n s a r e w h a t i s c o d e d a t t h e l e v e l o f t e x t u r e s e g r e g a t i o n . A s e c o n d t y p e o f e v i d e n c e comes f r o m a s y m m e t r i e s i n s e a r c h t a s k s ( T r e i s m a n , 1 9 8 5 ) . I n some s e a r c h t a s k s when t h e r o l e s o f t a r g e t a n d d i s t r a c t o r a r e r e v e r s e d , s e a r c h t i m e s c h a n g e . A t a s k w h i c h i s r a p i d a n d p a r a l l e l i n one c o n d i t i o n b e c o m e s s e r i a l a n d s l o w i n t h e o t h e r . T h i s a s y m m e t r y c a n be u s e d t o d e t e r m i n e w h i c h o f two p o t e n t i a l f e a t u r e s t h e v i s u a l s y s t e m i s u s i n g i n m a k i n g d i s c r i m i n a t i o n s . F o r e x a m p l e , i n d i s c r i m i n a t i n g c i r c l e s f r o m a r c s , c l o s u r e o r b o u n d e d n e s s i n t h e c a s e o f t h e c i r c l e c o u l d a l l o w i t t o \" p o p - o u t \" o f a f i e l d o f a r c s . A l t e r n a t i v e l y , t h e l i n e e n d s o r t e r m i n a t o r s o f t h e a r c s c o u l d p o p - o u t o f a f i e l d o f c o m p l e t e c i r c l e s . T h i s l a t e r c o n d i t i o n seems t o be t h e one w h i c h h o l d s , a t l e a s t w h e r e t h e d i s t i n c t i o n b e t w e e n c i r c l e a n d a r c i s n o t g r o s s l y a p p a r e n t . Some o f t h e s t r o n g e s t e v i d e n c e f o r t h e i n d e p e n d e n t r e p r e s e n t a t i o n o f f e a t u r e s i s t h e o c c u r r e n c e o f \" i l l u s o r y c o n j u n c t i o n s \" ( T r e i s m a n & S c h m i d t , 1 9 8 2 ) . I l l u s o r y c o n j u n c t i o n s a r e m i s c o m b i n a t i o n s o f f e a t u r e s i n t o o b j e c t s 6 t h a t d i d not appear i n a d i s p l a y . Treisman and Schmidt showed s u b j e c t s b r i e f d i s p l a y s of c o l o r e d l e t t e r s f l a n k e d by b l a c k d i g i t s . To ensure t h a t a t t e n t i o n was loade d and spread ac r o s s the d i s p l a y , the s u b j e c t ' s primary task was to r e p o r t the i d e n t i t i e s of the two d i g i t s , and o n l y then to r e p o r t the l e t t e r s and t h e i r c o l o r s . T r i a l s were i n c l u d e d i n the a n a l y s i s o n l y i f the d i g i t s were c o r r e c t l y r e p o r t e d . The t y p e s o f e r r o r s made by s u b j e c t s were a n a l y s e d t o compare c o n j u n c t i o n e r r o r s t o i n t r u s i o n e r r o r s . C o n j u n c t i o n e r r o r s were d e f i n e d as the r e p o r t i n g of f e a t u r e s t h a t had appeared i n the d i s p l a y , but t h a t d i d not appear i n t h a t combination. I n t r u s i o n e r r o r s were r e p o r t s of f e a t u r e s t h a t were n o t p r e s e n t i n t h e d i s p l a y . C o n j u n c t i o n e r r o r s o c c u r r e d s i g n i f i c a n t l y more o f t e n than d i d i n t r u s i o n e r r o r s . S i n c e t h e y o c c u r r e d more o f t e n t han e x p e c t e d , i t was u n l i k e l y t h a t a l l t h e c o n j u n c t i o n e r r o r s were simply guesses. The nature of c o n j u n c t i o n e r r o r s made by s u b j e c t s i s a l s o i l l u m i n a t i n g . They were as l i k e l y t o c o n j o i n the c o l o r from a s m a l l item w i t h the shape of a l a r g e one, or to f i l l an o u t l i n e o b j e c t as they were t o recombine f e a t u r e s from more s i m i l a r items. I t appeared t h a t s u b j e c t s were d e t e c t i n g the presence o f a f e a t u r e , and then p r o v i d i n g enough of i t to c r e a t e the p e r c e i v e d o b j e c t . The d i s t a n c e s e p a r a t i n g f e a t u r e s t h a t c o n t r i b u t e t o i l l u s o r y c o n j u n c t i o n s a l s o had no e f f e c t on c o n j u n c t i o n e r r o r s . S u b j e c t s were as 7 l i k e l y t o p u l l f e a t u r e s f r o m w i d e l y s e p a r a t e d s t i m u l i t o c o n j o i n a s t h e y w e r e o n e s t h a t w e r e c l o s e r t o g e t h e r . O t h e r e v i d e n c e f o r f e a t u r e a n a l y s i s comes f r o m s p e e d e d c l a s s i f i c a t i o n t a s k s . I n t h e s e t a s k s s u b j e c t s a r e a s k e d t o s e l e c t i v e l y a t t e n d t o a p a r t i c u l a r d i m e n s i o n o r d i m e n s i o n s i n a s e t o f s t i m u l i a n d q u i c k l y s o r t t h e s e t i n t o c l a s s e s . The u s u a l p a r a d i g m h a s one o r more i r r e l e v a n t d i m e n s i o n s w h i c h v a r y e i t h e r r e d u n d a n t l y o r o r t h o g o n a l l y w i t h t h e d i m e n s i o n ( s ) o f i n t e r e s t . I f v a r i a t i o n o n t h e i r r e l e v a n t d i m e n s i o n d o e s n o t f a c i l i t a t e o r i n t e r f e r e w i t h s o r t i n g o r r e a c t i o n t i m e f o r t h e r e l e v a n t d i m e n s i o n i t i s assumed t o be s e p a r a b l e f r o m t h a t d i m e n s i o n . G a r n e r (19 74; G a r n e r & F e l f o l d y , 1 9 7 0 ) f o u n d s o m e d i m e n s i o n s t h a t f i t t h e d e f i n i t i o n o f s e p a r a b i l i t y a n d some t h a t d i d n o t . C o l o r a n d f o r m w e r e s e p a r a b l e e v e n w i t h i n t h e same o b j e c t , w h i l e d i m e n s i o n s s u c h a s s a t u r a t i o n a n d b r i g h t n e s s w e r e n o t . D i m e n s i o n s t h a t w e r e n o t s e p a r a b l e w e r e t e r m e d \" i n t e g r a l \" b y G a r n e r (who a d o p t e d L o c k h e a d ' s ( 1 9 6 6 ) t e r m ) . Y e t o t h e r d i m e n s i o n s a p p e a r t o c o m b i n e i n w a y s t h a t a r e n e i t h e r s e p a r a b l e n o r i n t e g r a l . A r e d u n d a n t c o m b i n a t i o n o f t h e h o r i z o n t a l a n d v e r t i c a l p o s i t i o n s o f d o t s c a u s e s f a c i l i t a t i o n o f r e s p o n s e t o a s i n g l e d i m e n s i o n ( e i t h e r h o r i z o n t a l o r v e r t i c a l p o s i t i o n r e p o r t e d s e p a r a t e l y ) , w h i c h s u p p o r t s a c o n c l u s i o n o f i n t e g r a l i t y , b u t when t h e s e a r e v a r i e d o r t h o g o n a l l y t h e y c a u s e much l e s s i n t e r f e r e n c e t h a n 8 do o r t h o g o n a l v a l u e s o f b r i g h t n e s s a n d s a t u r a t i o n ( G a r n e r & F e l f o l d y , 1 9 7 0 ) . D i m e n s i o n s o f t h i s s o r t h a v e b e e n c a l l e d c o n f i g u r a l , a n d t h e o r i g i n a l d i c h o t o m y , s e p a r a b l e v e r s u s i n t e g r a l d i m e n s i o n s , h a s b e e n r e p l a c e d b y a c o n t i n u u m on w h i c h t h e s e mark e n d p o i n t s . B l o b P e r c e p t i o n A t h e o r y i n t h e t r a d i t i o n o f h o l i s t i c p e r c e p t i o n i s L o c k h e a d ' s b l o b p e r c e p t i o n . L o c k h e a d ( 1 9 6 6 , 1972) s u g g e s t s t h a t a s t i m u l u s i s p e r c e i v e d h o l i s t i c a l l y i n t h e f i r s t s t a g e o f p e r c e p t i o n , a n d he c a l l s t h e r e s u l t i n g r e p r e s e n t a t i o n a b l o b . I f t h e t a s k s e t f o r t h e s u b j e c t i s d e s i g n e d s o t h a t a r e s p o n s e c a n be made b a s e d u p o n t h i s i n f o r m a t i o n a l o n e t h e n p r o c e s s i n g s t o p s h e r e . An e x a m p l e o f a t a s k L o c k h e a d t h i n k s c o u l d be a c c o m p l i s h e d d i r e c t l y f r o m a b l o b r e p r e s e n t a t i o n i s i d e n t i f y i n g o r p o s i t i o n i n g a n i t e m i n a m u l t i d i m e n s i o n a l f e a t u r e s p a c e . O n l y i f t h e t a s k r e q u i r e s d e c o m p o s i t i o n o f t h e s t i m u l u s i n t o i t s c o m p o n e n t s f o r r e s p o n s e s e l e c t i o n w i l l l a t e r s e r i a l s t a g e s o f p r o c e s s i n g o c c u r . L o c k h e a d p r o p o s e d h i s m o d e l t o d e a l w i t h d a t a i n d i c a t i n g t h a t a s a w - t o o t h p a i r i n g o f l e v e l s o f two o r more f e a t u r e s was e a s i e r t o d i s c r i m i n a t e t h a n w e r e l i n e a r l y a r r a n g e d p a i r i n g s o f t h e same f e a t u r e s ( L o c k h e a d , 1 9 6 6 ) . P a r a l l e l m o d e l s ( e . g . B i e d e r m a n & C h e c k o s k y , 1970) assume t h a t t h e a n a l y s i s o f t h e f e a t u r e s o f a n i t e m i s c o n c u r r e n t a n d t h a t t h e f i r s t f e a t u r e 9 to be i d e n t i f i e d w i l l p r o v i d e i n f o r m a t i o n f o r a response to be made i f r e s p o n s e s can be based upon e i t h e r f e a t u r e . Lockhead argued t h a t i f these models are c o r r e c t then l i n e a r and saw-tooth p a i r i n g s of d i m e n s i o n a l v a l u e s s h o u l d not d i f f e r i n speed or accuracy i n s o r t i n g t a s k s . Lockhead's blobs are i n t e g r a l s t i m u l i ; he does not have p a r a l l e l processes i n h i s model because h i s u n i t a r y s t i m u l i do not need to be processed f o r independent d e c i s i o n s s i n c e s u b j e c t s are responding to the s t i m u l u s as a whole. He proposes t h a t any k i n d of f i l t e r i n g task, a task where some component of a composite s t i m u l u s i s r e l e v a n t and another i s i r r e l e v a n t , w i l l r e q u i r e more time and e f f o r t than an i d e n t i f i c a t i o n t a s k . I t t a k e s l e s s p r o c e s s i n g time to respond to the item as a whole than to respond to a p a r t of i t . Presumably, responding to the t o t a l s t i m u l u s would be more ac c u r a t e as w e l l . Lockhead i s not c l e a r about which types of s t i m u l i w i l l produce s i n g l e b l o bs and which might produce more than one \" i n t e g r a l \" r e p r e s e n t a t i o n . He s u g g e s t s , i n an apparent c o n c e s s i o n t o f e a t u r e a n a l y s i s , (Lockhead, 1972) t h a t c l e a r l y s e p a r a b l e f e a t u r e s may produce more than one b l o b even from a s i n g l e s t i m u l u s . Lockhead contends t h a t h i s blobs are d i f f e r e n t from other t h e o r i s t ' s f e a t u r e s i n t h a t b l o bs may c o n s i s t of combinations o f s e v e r a l p h y s i c a l l y s p e c i f i a b l e d i m ensions. T h i s , however, i s a l s o t r u e of 1 0 f e a t u r e s s u c h a s c o l o r , w h i c h v a r y i n h u e , s a t u r a t i o n , a n d b r i g h t n e s s . W h a t i s n o t o b v i o u s i s how L o c k h e a d ' s m u l t i p l e \/ u n i t a r y b l o b s b e t t e r a c c o u n t f o r o b j e c t p e r c e p t i o n t h a n f e a t u r e i n t e g r a t i o n t h e o r i e s d o . E a r l y a n d L a t e S e l e c t i o n An e n d u r i n g q u e s t i o n i n a t t e n t i o n r e s e a r c h i s , w h e r e i n p r o c e s s i n g d o e s s e l e c t i v e a t t e n t i o n i n t e r v e n e ? T h e o r i s t s g e n e r a l l y d i v i d e i n t o t w o camps, t h o s e who p r o p o s e t h a t a t t e n t i o n i s u s e d t o s e l e c t t h e a p p r o p r i a t e r e s p o n s e a f t e r p e r c e p t u a l p r o c e s s i n g h a s s p e c i f i e d t h e s t i m u l i t h a t r e q u i r e d e c i s i o n s , a n d t h o s e who p r o p o s e t h a t a t t e n t i o n i s r e q u i r e d t o s e l e c t t h e s t i m u l i t h a t w i l l b e n e f i t f r o m p e r c e p t u a l p r o c e s s i n g . As w i t h m o s t o t h e r c o n t r o v e r s i e s , t h i s one i s r o o t e d i n d i f f e r e n c e s i n e m p h a s i s . E a r l y s e l e c t i o n t h e o r i s t s h a v e l a r g e l y b e e n c o n c e r n e d w i t h p e r c e p t u a l i s s u e s , a n d t h e f a c t t h a t p o t e n t i a l i n p u t s a r e s o numerous t h a t p e r c e p t u a l o v e r l o a d w o u l d c e r t a i n l y o c c u r i f some s o r t o f s t i m u l u s s e l e c t i o n d i d n o t o c c u r . L a t e s e l e c t i o n t h e o r i s t s , o n t h e o t h e r h a n d , h a v e b e e n m a i n l y c o n c e r n e d w i t h o u t p u t , a n d t h u s r e s p o n s e s e l e c t i o n . T h e m a j o r d i f f i c u l t y i s i n s u r i n g t h a t t h e s y s t e m e v e n t u a l l y c h o o s e s o n l y one o u t o f a number o f i n c o m p a t i b l e r e s p o n s e s . The r o l e o f a l i m i t e d c a p a c i t y m e c h a n i s m i s a l s o a c o n c e r n a n d m a r k s a n o t h e r d i f f e r e n c e i n e m p h a s i s . Some 11 m o d e l s assume a c e n t r a l c a p a c i t y l i m i t (Kahneman, 1973) a n d o t h e r s l i m i t s o n l y w i t h i n r e l a t i v e l y i n d e p e n d e n t s u b s y s t e m s ( A l l p o r t , A n t o n i s , & R e y n o l d s , 1972; T r e i s m a n , 1 9 6 9 ) . T h i s d i s t i n c t i o n i s o r t h o g o n a l t o t h e e a r l y - l a t e s e l e c t i o n i s s u e , s i n c e p r o p o n e n t s o f b o t h v i e w s c a n be f o u n d i n e a c h camp. Of c o u r s e , t h e two t y p e s o f l i m i t s a r e n o t e x c l u s i v e . I t i s p r o b a b l e t h a t b o t h c e n t r a l a n d l o c a l c a p a c i t y l i m i t s e x i s t . The e a r l y - l a t e d i c h o t o m y r e a l l y m a r k s t h e e n d s o f a c o n t i n u u m . The r e a l q u e s t i o n f o r u s i s , w h e r e i n e i t h e r p e r c e p t u a l o r r e s p o n s e p r o c e s s i n g d o e s a t t e n t i o n a c t ? Does a t t e n t i o n s e l e c t s t i m u l i f o r p e r c e p t u a l p r o c e s s i n g o r s e l e c t o n l y t h e r e s u l t o f t h a t p r o c e s s i n g ? I f a t t e n t i o n i s a p p l i e d p o s t - c a t e g o r i c a l l y , t h e n a number o f o p e r a t i o n s s u c h a s f i g u r e - g r o u n d s e g r e g a t i o n , f e a t u r e i n t e g r a t i o n and s t i m u l u s i d e n t i f i c a t i o n m u s t o c c u r p r e a t t e n t i v e l y . P o s t - c a t e g o r i c a l m o d e l s ( e . g . C o l t h e a r t ' s , ( 1 9 8 3) m o d e l o f i c o n i c memory) i m p l y t h a t a t t e n t i o n a l m a n i p u l a t i o n s s h o u l d h a v e no e f f e c t on a n y o f t h e s e p r o c e s s e s . A s e r i e s o f e x p e r i m e n t s t h a t d i r e c t l y t e s t e d t h e e f f e c t o f a t t e n t i o n o n f e a t u r e i n t e g r a t i o n s u g g e s t e d t h a t a t t e n t i o n i m p r o v e d b o t h t h e q u a l i t y o f i n f o r m a t i o n o b t a i n e d f r o m d i s p l a y s , a n d t h e i n t e g r a t i o n o f t h o s e f e a t u r e s ( P r i n z m e t a l , P r e s t i , & P o s n e r , 1 9 8 6 ) . S p a t i a l a t t e n t i o n was m a n i p u l a t e d b y e m p l o y i n g a p a r t i a l l y v a l i d s p a t i a l c u e . T h i s c u e c o r r e c t l y i n d i c a t e d t h e p o s i t i o n o f s t i m u l i i n t h e d i s p l a y 12 for 80 percent of the t r i a l s , but misdirected a t tent ion for the remaining 20 percent. Since subjects were required to determine whether or not a target stimulus was present at the l o c a t i o n of the stimulus array , s e l ec t ive a t tent ion was a l s o n e c e s s a r y once t h e i r s p a t i a l l oca t ion had been determined. The ir observation that a t tent ion improved the q u a l i t y of stimulus encoding, as evinced by a small though s i g n i f i c a n t reduct ion i n the number of feature errors on v a l i d cue t r i a l s , appears to c o n t r a d i c t the c l a i m that features are coded automat ica l ly . However, Prinzmetal et a l . d i d f i n d a large e f fec t of cue v a l i d i t y on the number of conjunction errors that subjects made as w e l l . Pashler (1984), tested a p r e d i c t i o n of la te s e l ec t ion theory that encoding of f a m i l i a r s t i m u l i to the l e v e l of i d e n t i f i c a t i o n occurs whether or not a t tent ion i s appl ied to them and whether or not the subject wishes i t ( e .g . i n Stroop in ter ference ) . I f t h i s process i s automatic, then i d e n t i f i c a t i o n of items i n a d i sp lay should be computed i n p a r a l l e l , and a probe or loca t ion cue would simply re t r i eve the i d e n t i t y of the item at the cued l o c a t i o n . Pashler manipulated factors such as stimulus d i s c r i m i n a b i l i t y and contras t , which he assumed would af fec t stimulus encoding but have no e f f e c t on the r e t r i e v a l o f a lready encoded i tems. He assumed that even with degraded s t i m u l i any encoding process would be complete by 300 ms, s ince choice 13 r e a c t i o n time f o r st i m u l u s c l a s s i f i c a t i o n may be l e s s than 300 ms. P a s h l e r found t h a t even w i t h 300 ms of previewing time i n which t o encode s t i m u l i , d i s c r i m i n a b i l i t y and c o n t r a s t had an e f f e c t on r e a c t i o n time t o respond t o a cued item i n the d i s p l a y . Previewing the e n t i r e - d i s p l a y d i d not produce a r e a c t i o n time advantage over p r e - c u e i n g a l o c a t i o n i n the d i s p l a y . Stimulus q u a l i t y a f f e c t e d r e a c t i o n time i n both cases. P a s h l e r concluded t h a t evidence supported e a r l y p r e - c a t e g o r i c a l s e l e c t i o n r a t h e r t han p o s t - c a t e g o r i c a l s e l e c t i o n . He l e f t o p e n t h e p o s s i b i l i t y t h a t some p r o c e s s e s , such as f e a t u r e e x t r a c t i o n , c o u l d proceed i n p a r a l l e l a c r o s s the d i s p l a y . Feature I n t e g r a t i o n Theory Feature i n t e g r a t i o n theory (Treisman & Gelade, 1980; Treisman, Sykes & Gelade, 1977) assumes as a s t a r t i n g p o i n t t h a t f e a t u r e i n t e g r a t i o n i s a problem f o r the p e r c e p t u a l system. Based p a r t l y upon the r e s u l t s d e s c r i b e d above, f e a t u r e i n t e g r a t i o n t h e o r y assumes t h a t f e a t u r e s are coded e a r l y , a u t o m a t i c a l l y and s p a t i a l l y i n p a r a l l e l a c r o s s the v i s u a l f i e l d . D i f f e r e n t dimensions are coded i n s p e c i a l i z e d modules w i t h d i f f e r e n t v a l u e s on the dimension r e p r e s e n t e d i n separate f e a t u r e maps w i t h i n a module. The f e a t u r e maps may o r may not be s p a t i a l l y c o n t i g u o u s a l t h o u g h h i g h l y d i s c r i m i n a b l e v a l u e s on a dimension would be e f f e c t i v e l y 14 s e p a r a b l e e v e n i f maps a r e c o n t i n u o u s . T h i s a l l o w s r a p i d a n d p a r a l l e l d e t e c t i o n o f d i s t i n c t i v e f e a t u r e s i n a d i s p l a y . T h e s e a u t o m a t i c a l l y c o d e d d i f f e r e n c e s m e d i a t e f i g u r e - g r o u n d s e g r e g a t i o n a n d a r e t h u s t h e f i r s t s t e p i n o b j e c t p e r c e p t i o n , p a r s i n g t h e f i e l d i n t o p o t e n t i a l o b j e c t s . When t h e d e t e c t i o n o f s p e c i f i c o b j e c t s d e f i n e d b y a c o n j u n c t i o n o f f e a t u r e s i s n e c e s s a r y , a t t e n t i o n i s r e q u i r e d t o e n s u r e t h e c o r r e c t c o m b i n a t i o n o f f e a t u r e s . A map o f l o c a t i o n s t h a t s h ows w h e r e f e a t u r e s a r e , b u t n o t w h i c h f e a t u r e s a r e p r e s e n t i n t h o s e l o c a t i o n s , i s t h e medium f r o m t h a t a t t e n t i o n s e l e c t s . When a t t e n t i o n i s f o c u s e d o n a p a r t i c u l a r l o c a t i o n , l i n k s t o t h e m o d u l a r f e a t u r e maps r e t r i e v e a l l f e a t u r e s w h i c h a r e c u r r e n t l y a c t i v e i n t h a t l o c a t i o n . T h e s e l i n k s a r e t h e o n l y way i n w h i c h l o c a t i o n s o f f e a t u r e s i n t h e f e a t u r e maps may be s p e c i f i e d . The s p a t i a l e x t e n t o f a t t e n t i o n i s v a r i a b l e , a n d a t r a d e - o f f b e t w e e n a c c u r a c y o f l o c a t i o n o f f e a t u r e s a n d c o n j u n c t i o n s a n d s p e e d o f p r o c e s s i n g i s a r e s u l t . The map o f l o c a t i o n s may be e i t h e r e a r l i e r o r l a t e r t h a n t h e f e a t u r e maps i n p r o c e s s i n g o r d e r ( o r p o s s i b l y , c o n c u r r e n t w i t h f e a t u r e m a p p i n g ) . I f i t i s b e f o r e o r c o n c u r r e n t w i t h f e a t u r e m a p p i n g , t h e n a n e a r l y r e p r e s e n t a t i o n o f c o n j o i n e d d i m e n s i o n s i s i m p l i e d , a n d i f a f t e r , no s u c h r e p r e s e n t a t i o n i s n e c e s s a r y . F e a t u r e a n a l y s i s o c c u r r i n g a f t e r l o c a t i o n m a p p i n g i s c o n s i s t e n t w i t h t h e d a t a t h a t a t l e a s t some 15 n e u r a l coding i s of combinations of f e a t u r e s on two or more dimensions. I t i s reasonable t h a t the f e a t u r e s c o n j o i n e d t o form o b j e c t r e p r e s e n t a t i o n s are f e a t u r e s t h a t encode r e a l world p r o p e r t i e s and more complex s t r u c t u r e s than those found i n e a r l y v i s u a l e n c o d i n g . T r e i s m a n and Paterson (1984) o b t a i n e d r e s u l t s s u g g e s t i n g t h a t f o r some s u b j e c t s the emergent f e a t u r e c l o s u r e c o u l d migrate from one stim u l u s t o a n o t h e r . In d i s p l a y s where s u b j e c t s searched f o r the p r e s e n c e of a t r i a n g l e , more f a l s e p o s i t i v e responses o c c u r r e d when a c i r c l e , p r o v i d i n g t h e emergent f e a t u r e c l o s u r e , was presen t ( i n a d d i t i o n t o l i n e s and angles) than when i t was not. The proposed f i n a l stage i n f e a t u r e i n t e g r a t i o n i s one i n w h i c h t h e d i f f e r e n t p r o p e r t i e s e x t r a c t e d from the environment are recombined to c r e a t e o b j e c t s and scenes. Conscious p e r c e p t i o n r e l i e s on the c r e a t i o n of temporary o b j e c t r e p r e s e n t a t i o n s which c o n t a i n c o l l e c t e d i n f o r m a t i o n about the f e a t u r e s p r e s e n t i n a p a r t i c u l a r l o c a t i o n i n space and any i n f o r m a t i o n about changes t h a t have o c c u r r e d to t h o s e p r o p e r t i e s (Kahneman & Treisman, 1984). These r e p r e s e n t a t i o n s a r e o b j e c t c e n t e r e d , and may c o n t a i n semantic or l e x i c a l i n f o r m a t i o n i f the o b j e c t i s f a m i l i a r ; however, the absence of such i n f o r m a t i o n poses no d i f f i c u l t y f o r the c o n s t r u c t i o n of t h i s type of r e p r e s e n t a t i o n . 16 The P a r t i a l Report Paradigm The p a r t i a l r e p o r t paradigm was developed by S p e r l i n g i n 1960, prompted by r e p o r t s from h i s s u b j e c t s t e l l i n g him t h a t they c o u l d see more i n s h o r t d u r a t i o n v i s u a l d i s p l a y s than they were capable of r e p o r t i n g . S p e r l i n g reasoned t h a t i f t h i s were the case, when s u b j e c t s were cued to r e p o r t a p a r t of the d i s p l a y t h e i r accuracy on t h i s subset c o u l d be used to estimate the amount of i n f o r m a t i o n they c o u l d \"see\" i n the whole d i s p l a y . F u r t h e r , i f some s o r t of complete, though b r i e f r e p r e s e n t a t i o n e x i s t e d , by v a r y i n g the i n t e r v a l between the o f f s e t of a d i s p l a y and the onset of a cue to r e p o r t a p a r t of i t the d u r a t i o n of the r e p r e s e n t a t i o n c o u l d be measured. S p e r l i n g (1960) demonstrated the expected 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 over t o t a l r e p o r t and a l s o t h a t t h i s s u p e r i o r i t y disappeared by 300 ms a f t e r the o f f s e t of the d i s p l a y . S p e r l i n g reasoned from h i s data t h a t the i c o n i c s t o r e c o n t a i n e d a h o l i s t i c and unanalyzed r e p r e s e n t a t i o n of the items i n the v i s u a l f i e l d . He concluded t h a t the i c o n was a h o l i s t i c r e p r e s e n t a t i o n s i n c e h i s s u b j e c t s c o u l d r e p o r t from any p o r t i o n of the d i s p l a y even wi t h a delayed cue. T h i s suggested t h a t they had a v a i l a b l e a complete \"copy\" of the d i s p l a y from which they c o u l d read o f f items i f a cue came bef o r e the r e p r e s e n t a t i o n decayed. He argued t h a t the i c o n 17 was a p r e - a n a l y t i c r e p r e s e n t a t i o n s i n c e h i s s u b j e c t s were u n s u c c e s s f u l i n r e p o r t i n g items from the d i s p l a y based upon c a t e g o r i c a l i n f o r m a t i o n , although they c o u l d r e p o r t based upon d i s t i n c t i o n s i n such f e a t u r e s as c o l o r and l o c a t i o n . Since S p e r l i n g ' s experiments were conducted, many other r e s e a r c h e r s have used the p a r t i a l r e p o r t paradigm t o examine the nature of i c o n i c storage and i t s r e l a t i o n s h i p to more en d u r i n g r e p r e s e n t a t i o n s and to d e c i s i o n a l and response p r o c e s s e s . The c l e a r p i c t u r e o f i c o n i c s t o r a g e as a complete u n a n a l y z e d v i s u a l s t o r e has been c o n s i d e r a b l y muddied, and the r e are now well-founded doubts t h a t data r e f e r r e d t o under the name \" i c o n i c memory\" r e f l e c t a u n i t a r y p r o c e s s . The major i s s u e i n i c o n i c memory r e s e a r c h became the nature of the i n f o r m a t i o n i t co n t a i n e d . E a r l y evidence i n the f i e l d i n d i c a t e d t h a t i t was a p r e - c a t e g o r i c a l s t o r e . S p e r l i n g found (1960) t h a t s u b j e c t s c o u l d use p h y s i c a l cues to s e l e c t i v e l y r e p o r t from d i s p l a y s , but not cues such as l e t t e r - d i g i t c a t e g o r y membership. Von Wright (1968) found t h a t s e l e c t i o n by c o l o r , l o c a t i o n , b r i g h t n e s s , and s i z e was easy, w h i l e s e l e c t i o n by the o r i e n t a t i o n of l e t t e r s was d i f f i c u l t . Other evidence suggests t h a t some d i s c r i m i n a t i o n s based upon ca t e g o r y membership are p o s s i b l e even when c a t e g o r i e s are not d e f i n e d by p h y s i c a l f e a t u r e s . Some r e s e a r c h e r s have 18 f o u n d p a r t i a l r e p o r t s u p e r i o r i t y w i t h l e t t e r - d i g i t categories (Merikle , 1980). Var ia t ions i n methodology make a s s e s s i n g the c o n t r a d i c t o r y f i n d i n g s on t h i s issue d i f f i c u l t . In an a t t e m p t to c l a r i f y some o f these i ssues , Col theart (1980) analysed the i con ic memory l i t e r a t u r e to see whether the c o n c e p t of an i c o n i c memory as an informational representat ion d i s t i n c t from after-images and v i s i b l e pers is tence could be supported. He c l a s s i f i e d the studies he found in to those that recorded neurophys io logica l d a t a , those that r e l i e d upon phenomenological r e p o r t s ( ca l l ed v i s i b l e pers i s tence ) , and i con ic memory. Only the l a t t e r category i s p r i m a r i l y concerned with how subjects extract and use information from v i s u a l d i s p l a y s . Co l thear t suggested that i con i c memory i s d i f f e r e n t from v i s i b l e persistence or after-images. A p a r t i a l report advantage occurs i n report condit ions that do not create after- images , and while v i s i b l e pers i s tence i s i n v e r s e l y re la ted to stimulus durat ion and luminance, i c o n i c memory i s not (but see E r i k s e n & Schultz , 1978 , for a d i s s en t ing view). C o l t h e a r t concludes that while a f t e r images and v i s i b l e p e r s i s t e n c e are p r e - c a t e g o r i c a l , i c o n i c memory r e f l e c t s a pos t - ca tegor i ca l s tore . Haber (1983) published a c o n t r o v e r s i a l attack on the idea of the icon i n information processing psychology. He 19 r e j e c t e d t h e t r a d i t i o n a l image of t h e i c o n as a s t a t i c r e t i n o t o p i c s t o r e , c l a i m i n g t h a t such a system would not o n l y be u s e l e s s , i t would be d e t r i m e n t a l to v i s i o n . An i d e a o f t h e i c o n as a s t a t i c r e t i n a l r e p r e s e n t a t i o n i s p r o b l e m a t i c . S u c c e s s i v e images should mask one another, and saccades should cause smearing of t h e image. Since our v i s i o n i s not o c c a s i o n a l l y m i s s i n g chunks, and b l u r r y the r e s t of t h e time, Haber i s c o r r e c t i n r e j e c t i n g such a s t o r e . I c o n i c memory need not be e i t h e r r e t i n o t o p i c or s t a t i c . D a v i dson, Fox and D i c k (1973) showed t h a t m e t a c o n t r a s t masking a c t e d upon a r e t i n a l l o c a t i o n but allowed a sti m u l u s presented i n the same s p a t i a l l o c a t i o n but at a d i f f e r e n t r e t i n a l l o c a t i o n (by a l l o w i n g an i n t e r v e n i n g saccade) t o be p r o c e s s e d u n h i n d e r e d . T h i s c o n t r a s t s w i t h an e a r l i e r c o n c l u s i o n (Averbach & C o r i e l l , 1961) t h a t s t a t i c viewing ( i n the same f i x a t i o n ) of a d i s p l a y and metacontrast mask a c t s upon r e t i n a l l o c a t i o n , but i n t h a t experiment r e t i n a l and s p a t i a l l o c a t i o n s were confounded. Icons need not be s t a t i c e i t h e r . Treisman, R u s s e l l and Green (1975) p r e s e n t e d s u b j e c t s w i t h moving dot s t i m u l i . The s u b j e c t ' s t a s k was to r e p o r t the d i r e c t i o n of movement of the dots (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 ) . Data showed a p a r t i a l r e p o r t s u p e r i o r i t y i n t h i s t a s k , i n d i c a t i n g t h a t i c o n i c storage of dynamic s t i m u l i was p o s s i b l e . 20 A l i k e l y source of the confusion over the nature of i con i c memory i s the metaphor of the icon i t s e l f . An icon i m p l i e s a s t a t i c , p h o t o g r a p h - l i k e image , and t h i s i m p l i c a t i o n was imported into the theory . However, the impl icat ions may be rejected without d i scard ing e i ther the research or the concept. I w i l l continue to use \"icon\" and \"iconic\" i n t h i s paper, while r e f e r r i n g to a process that i s dynamic and spat io topic rather than r e t i n o t o p i c . The Present Invest igat ion P a r t i a l report studies have not d i r e c t l y addressed the q u e s t i o n of whether or not i c o n i c r e p r e s e n t a t i o n s are u n i t a r y . Although p a r t i a l report has been discussed as i f i t were from some kind of h o l i s t i c s tore , be i t pre- or p o s t - c a t e g o r i c a l , no evidence i n the l i t e r a t u r e requires that i t be. Report may just as wel l be based on a c t i v a t i o n o f i n d e p e n d e n t f e a t u r e maps as on a s i n g l e object r e p r e s e n t a t i o n . C e r t a i n l y evidence that subjec t s are capable of s e l ec t ing by features does not contradic t th i s a s ser t ion . Unfortunately , evidence suggesting that i con ic storage i s pos t - ca tegor i ca l has i n general used l e t t e r s and d i g i t s to def ine c a t e g o r i e s , and these s t i m u l i seem to behave d i f f e r e n t l y than other shapes (But ler , 1980; B u t l e r , 21 Browse, & Mewhort, 1986; Ceraso, 1985). I t i s p o s s i b l e t h a t l e t t e r s may be t r e a t e d as f e a t u r e s by a l i t e r a t e v i s u a l system. For the purposes of the present study I w i l l not d i s c r i m i n a t e between l e t t e r s and t h e i r component f e a t u r e s when d i s c u s s i n g f e a t u r e r e p o r t , because I chose l e t t e r s t h a t c o u l d be d i s t i n g u i s h e d from each other by a s i n g l e f e a t u r e . Feature i n t e g r a t i o n t h e o r y suggests t h a t i n f o r m a t i o n about c o n j u n c t i o n s of f e a t u r e s w i l l n o t become a v a i l a b l e u n l e s s the observer attends t o the l o c a t i o n of a c o n j u n c t i o n of f e a t u r e s . An e a r l y h o l i s t i c r e p r e s e n t a t i o n or map of l o c a t i o n s and f e a t u r e s may or may not e x i s t , but even i f i t does i t may n o t be a c c e s s i b l e f o r r e p o r t . When t h e s e l e c t i o n of a p a r t i c u l a r l o c a t i o n i s delayed, as w i t h a d e l a y e d cue to r e p o r t , c o n j u n c t i o n s o f f e a t u r e s may be c o n s t r u c t e d i f the a c t i v a t i o n of the f e a t u r e s i n t h e i r r e s p e c t i v e f e a t u r e maps i s c o n t i n u i n g and i f i n f o r m a t i o n about the l o c a t i o n of these f e a t u r e s i s pr e s e r v e d u n t i l they can be attended. I f a t t e n t i o n i s prevented from s e l e c t i n g or r e t r i e v i n g t h e c o r r e c t f e a t u r e s , f e a t u r e s from the d i s p l a y may be miscombined and i l l u s o r y c o n j u n c t i o n s may o c c u r . I f , on the o t h e r hand, l o c a t i o n i n f o r m a t i o n i s u n a v a i l a b l e but i n f o r m a t i o n about f e a t u r e combinations i s a v a i l a b l e , s u b j e c t s may r e p o r t items t h a t were p r e s e n t elsewhere i n the d i s p l a y i f these are a l r e a d y c o n j o i n e d i n some r e p r e s e n t a t i o n . F i n a l l y , i f s u b j e c t s are working from 22 a d e c a y i n g t r a c e t h a t m a k e s f e a t u r e s i n c r e a s i n g l y c o n f u s a b l e , t h e y may p r o d u c e a l a r g e number o f i n t r u s i o n e r r o r s . I f s u b j e c t s h a v e o n l y a n i n i t i a l h o l i s t i c r e p r e s e n t a t i o n o f t h e o b j e c t s i n a d i s p l a y , as L o c k h e a d ( 1 972) s u g g e s t s , t h e n r e p o r t s o f c o n j u n c t i o n s o f f e a t u r e s s h o u l d b e e a s i e r t h a n r e p o r t s o f t h e i r c o m p o n e n t p a r t s . W i t h a d e l a y e d c u e , L o c k h e a d m i g h t p r e d i c t t h a t m i s l o c a t i o n s w o u l d o c c u r more f r e q u e n t l y , b u t he w o u l d n o t p r e d i c t t h a t i l l u s o r y c o n j u n c t i o n s w o u l d o c c u r . A t h i r d p o s s i b i l i t y i s a c o m p r o m i s e b e t w e e n an e a r l y h o l i s t i c r e p r e s e n t a t i o n o r o n l y i n d e p e n d e n t f e a t u r e r e p r e s e n t a t i o n s . P e r h a p s b o t h r e p r e s e n t a t i o n s e x i s t , a n d we h a v e s e p a r a t e f e a t u r e r e p r e s e n t a t i o n s a n d h o l i s t i c r e p r e s e n t a t i o n s . I f t h i s i s t h e c a s e , i n f o r m a t i o n a b o u t b o t h c o n j u n c t i o n s and f e a t u r e s c o u l d be r e t r i e v e d u s i n g e i t h e r r e p r e s e n t a t i o n , a l t h o u g h f e a t u r e s w o u l d t a k e l o n g e r t o e x t r a c t f r o m a c o n j u n c t i o n r e p r e s e n t a t i o n , a n d c o n j u n c t i o n s w o u l d r e q u i r e t i m e t o be c o n s t r u c t e d f r o m f e a t u r e r e p r e s e n t a t i o n s . H o w e v e r , a c c u r a c y c o u l d be i m p r o v e d a t t h e e x p e n s e o f s p e e d b e c a u s e i f o n e r e p r e s e n t a t i o n was d e g r a d e d t h e o t h e r m i g h t s t i l l . c o n t a i n e n o u g h i n f o r m a t i o n t o r e p o r t i t e m s f r o m t h e d i s p l a y , a l t h o u g h t h i s w o u l d i n v o l v e a d d i t i o n a l p r o c e s s i n g . I f s t i m u l u s c o n d i t i o n s w e r e s u c h t h a t one t y p e o f r e p o r t was 23 e a s i e r t o u s e t h a n t h e o t h e r , s u b j e c t s m i g h t be a b l e t o s t r a t e g i c a l l y r e p o r t f r o m one o r t h e o t h e r r e p r e s e n t a t i o n . I f c o n j u n c t i o n s w e r e f a r a p a r t i n a h o l i s t i c r e p r e s e n t a t i o n , b u t t h e i r c o m p o n e n t f e a t u r e s w e r e n o t , a c o n j o i n e d r e p r e s e n t a t i o n w o u l d be e a s i e r t o u s e . I f t h e f e a t u r e s w e r e m o r e d i s c r i m i n a b l e o n t h e i r o w n i n d e p e n d e n t f e a t u r e r e p r e s e n t a t i o n s may be e a s i e r t o u s e . The p r e s e n t i n v e s t i g a t i o n t e s t e d t h e p r e d i c t i o n f r o m f e a t u r e i n t e g r a t i o n t h e o r y t h a t no h o l i s t i c r e p r e s e n t a t i o n o f c o n j u n c t i o n s o f f e a t u r e s e x i s t s u n t i l a t t e n t i o n i s f o c u s e d o n t h e i r l o c a t i o n . When a t t e n t i o n i s c o n s t r a i n e d b y u s i n g b r i e f e x p o s u r e d u r a t i o n s , t h e r e w i l l be no i n f o r m a t i o n a b o u t t h e c o n j u n c t i o n s i n a d i s p l a y i n e x c e s s o f w h a t i s a v a i l a b l e a b o u t t h e i r c omponent f e a t u r e s . I n o t h e r w o r d s , t h e r e may be no a d d i t i o n a l h o l i s t i c i n f o r m a t i o n a r i s i n g f r o m t h e p a i r i n g o f i n d i v i d u a l f e a t u r e s -- a t l e a s t i n t h e c a s e w h e r e t h o s e f e a t u r e s a r e s e p a r a t e v i s u a l e l e m e n t s i n t h e c o d i n g u s e d b y e a r l y v i s i o n a n d w h e r e no e m e r g e n t f e a t u r e s ( s u c h a s c l o s u r e ) a r e f o r m e d . A p a r t i a l r e p o r t p a r a d i g m e m p l o y i n g s h o r t s t i m u l u s d u r a t i o n s a n d v a r i a b l e s t i m u l u s o n s e t a s y n c h r o n i e s (SOA) was u s e d i n t h e s e e x p e r i m e n t s . S u b j e c t s s e p a r a t e l y r e p o r t e d t h e c o l o r o f d i s p l a y e d l e t t e r s , t h e l e t t e r i d e n t i t y , o r t h e c o n j u n c t i o n o f b o t h c o l o r a n d i d e n t i t y . C o l o r a nd s h a p e g e n e r a l l y b e h a v e a s s e p a r a b l e f e a t u r e s ( G a r n e r , 1974) and 24 t h e r e f o r e t h e s e w e r e c h o s e n a s f e a t u r e s f o r t h e e x p e r i m e n t s . B o t h c o l o r s a n d l e t t e r s w e r e c h o s e n f o r t h e i r d i s c r i m i n a b i 1 i t y . I f f e a t u r e s a r e r e p r e s e n t e d i n d e p e n d e n t l y , t h e p r o b a b i l i t y o f c o r r e c t l y r e p o r t i n g t h e c o n j u n c t i o n o f f e a t u r e s s h o u l d b e t h e p r o d u c t o f t h e i r i n d e p e n d e n t p r o b a b i l i t i e s o f b e i n g c o r r e c t l y r e p o r t e d . I n t h i s c a s e : P ( c o n j u n c t i o n ) = P ( c o l o r ) x P ( l e t t e r ) I c o m p a r e d t h e o b s e r v e d v a l u e s [ p ( c o n j u n c t i o n ) ] w i t h t h e p r e d i c t e d v a l u e s ( c a l c u l a t e d f r o m o b s e r v e d p e r f o r m a n c e i n t h e f e a t u r e c o n d i t i o n s , [ p ( c o l o r ) x p ( l e t t e r ) ] ) , t o s e e w h e t h e r a n y a d d i t i o n a l i n f o r m a t i o n s p e c i f i c a l l y a b o u t t h e c o n j u n c t i o n o r p a i r i n g o f f e a t u r e s was a v a i l a b l e . I f a n y a d d i t i o n a l i n f o r m a t i o n was a v a i l a b l e , i t w o u l d s u g g e s t t h a t some t y p e o f h o l i s t i c r e p r e s e n t a t i o n may be a v a i l a b l e . E x p e r i m e n t 1 T h e f i r s t e x p e r i m e n t w a s d e s i g n e d t o t e s t t h e p r e d i c t i o n f r o m f e a t u r e i n t e g r a t i o n t h e o r y t h a t c o n j u n c t i o n 25 p e r f o r m a n c e c o u l d be a c c o u n t e d f o r b y p e r f o r m a n c e on t h e f e a t u r e s f o r m i n g t h e c o n j u n c t i o n . T h i s e x p e r i m e n t a l s o m e a s u r e d t o t a l r e p o r t p e r f o r m a n c e o n c o l o r , l e t t e r a n d t h e c o n j u n c t i o n o f t h e two f e a t u r e s . M e t h o d S u b j e c t s : S i x v o l u n t e e r s f r o m t h e A t t e n t i o n L a b s u b j e c t p o o l w e r e e m p l o y e d f o r f i v e o n e - h o u r s e s s i o n s f o r w h i c h t h e y w e r e p a i d f o u r d o l l a r s p e r s e s s i o n . A l l s u b j e c t s h a d n o r m a l o r c o r r e c t e d - t o - n o r m a l v i s i o n a n d none s u f f e r e d f r o m a n y known d e f i c i t s i n c o l o r v i s i o n . D i s p l a y s : The d i s p l a y s w e r e shown on a n I n t e l l i g e n t  S y s t e m s C o r p o r a t i o n I n t e c o l o r 8001 t e r m i n a l ( m o d e l BS001G) c o n t r o l l e d b y a D i g i t a l E q u i p m e n t C o r p o r a t i o n PDP 11\/34 d i g i t a l c o m p u t e r . T h e y w e r e made up o f e i g h t c h a r a c t e r s i n a c i r c u l a r a r r a y t h a t s u b t e n d e d a v i s u a l a n g l e o f 2.7 d e g r e e s h o r i z o n t a l l y a n d 2.3 d e g r e e s v e r t i c a l l y . The e i g h t c h a r a c t e r s a p p e a r e d o n a d a r k b a c k g r o u n d a n d w e r e composed o f f o u r c o l o r s : r e d , g r e e n , b l u e , a n d w h i t e , a n d f o u r l e t t e r s : T, O, S, a n d V. The l e t t e r s a n d c o l o r s w e r e c h o s e n f o r t h e i r d i s c r i m i n a b i l i t y . The c h a r a c t e r s s u b t e n d e d a n a v e r a g e v i s u a l a n g l e o f .6 d e g r e e s h o r i z o n t a l l y a n d v e r t i c a l l y . The g e n e r a t i o n a n d p r e s e n t a t i o n o f t h e d i s p l a y was r a n d o m i z e d w i t h t h e f o l l o w i n g c o n s t r a i n t s : e a c h c o l o r a n d l e t t e r a p p e a r e d t w i c e a n d no c o l o r - l e t t e r c o m b i n a t i o n 26 was r e p e a t e d w i t h i n a t r i a l . At t h e b e g i n n i n g of a l l t r i a l s , a f i x a t i o n dot appeared i n the c e n t e r of the scree n f o r 100 ms f o l l o w e d by a 700 ms blank i n t e r v a l , and then the d i s p l a y was presented f o r 100 ms. The cue to r e p o r t an item was a p u r p l e dot which appeared adjacent to and o u t s i d e of the p o s i t i o n of the r e l e v a n t item. The cued item was chosen randomly. The cue c o u l d appear at the f o l l o w i n g SOAs: -200 (a p r e - c u e ) , 0 (a simultaneous cue), 200, 300, 400, 600, and 1100 ms. These SOAs were mixed randomly w i t h i n b l o c k s . The cue was p r e s e n t e d f o r 10 0 ms. A f t e r t h e a p p r o p r i a t e i n t e r v a l the d i s p l a y , the cue and the d i s p l a y , or the cue alone was presented. Procedure: Each s u b j e c t p a r t i c i p a t e d i n f i v e f i f t y -minute s e s s i o n s o f the experiment. The f i r s t and l a s t s e s s i o n s were t o t a l r e p o r t s e s s i o n s , measuring t o t a l r e p o r t f o r c o n j u n c t i o n , c o l o r and l e t t e r , w i t h t r i a l s i n each c o n d i t i o n b l o c k e d and separated by a r e s t p e r i o d . The order of p r e s e n t a t i o n o f t h e s e r e p o r t c o n d i t i o n s was counter-b a l a n c e d a c r o s s s u b j e c t s i n a L a t i n s q u a r e d e s i g n . S u b j e c t s ' heads were h e l d a t a f i x e d d i s t a n c e from the monitor by i n s u r i n g t h a t they used a c h i n r e s t . In the t o t a l r e p o r t s e s s i o n s , s u b j e c t s r e c e i v e d 24 p r a c t i c e t r i a l s b e f o r e each c o n d i t i o n and then 32 t r i a l s of data c o l l e c t i o n i n each of the three c o n d i t i o n s . T h i s r e s u l t e d i n the same number of \" t r i a l s p e r i n t e r v a l \" as the p a r t i a l r e p o r t 27 c o n d i t i o n s . In t o t a l r e p o r t s e s s i o n s , the cue appeared at one of t h e e i g h t p o s i t i o n s 20 0 ms b e f o r e the d i s p l a y . S u b j e c t s r e p o r t e d a l l the i n f o r m a t i o n they c o u l d s t a r t i n g a t one p o s i t i o n c o u n t e r - c l o c k w i s e from the cued l o c a t i o n . T h i s i n s t r u c t i o n was g i v e n to induce s u b j e c t s to spread t h e i r a t t e n t i o n to e i t h e r s i d e of the cued l o c a t i o n and was based on the assumption t h a t i n f o r m a t i o n c o u n t e r - c l o c k w i s e from the cued l o c a t i o n might be o b t a i n e d and then f o r g o t t e n by the time s u b j e c t s worked around the perimeter of the c i r c l e . S u b j e c t s responded v e r b a l l y and t h e i r responses were ent e r e d by the experimenter on the PDP 11\/34 keyboard. E n t e r i n g a response i n i t i a t e d the s t a r t of a new t r i a l . T h i s procedure c r e a t e d a v a r i a b l e i n t e r - t r i a l i n t e r v a l . In a d d i t i o n , at the end of the f i n a l s e s s i o n , s u b j e c t s d i d a w r i t t e n v e r s i o n of t h e f u l l r e p o r t t a s k , i n which t h e y wrote down the i n i t i a l l e t t e r of the c o l o r s and the l e t t e r s i n t h e i r observed p o s i t i o n s on a \" c l o c k f a c e \" diagram s u p p l i e d by the experimenter. T h i s c o n d i t i o n was arranged as was the v e r b a l t o t a l r e p o r t , but s u b j e c t s were f r e e to r e p o r t items i n any order and no cue was presented. They (received 16 p r a c t i c e t r i a l s and 24 t e s t t r i a l s i n t h i s l a s t s u b - s e s s i o n . The w r i t t e n t o t a l r e p o r t was hand scored by the experimenter, a g a i n f o r c o r r e c t c o n j u n c t i o n , c o l o r c o r r e c t , l e t t e r c o r r e c t or i n c o r r e c t . 28 T h e t h r e e p a r t i a l r e p o r t s e s s i o n s w e r e r u n on c o n s e c u t i v e d a y s a n d c o n s i s t e d o f 48 p r a c t i c e t r i a l s a n d 224 d a t a c o l l e c t i o n t r i a l s . The p r o c e d u r e was a s d e s c r i b e d a b o v e , e x c e p t t h a t s u b j e c t s v e r b a l l y r e p o r t e d o n l y t h e i t e m a t t h e c u e d l o c a t i o n , a n d SOAs v a r i e d a s d e s c r i b e d a b o v e . The o r d e r o f p r e s e n t a t i o n o f c o n j u n c t i o n , c o l o r , a n d l e t t e r c o n d i t i o n s was c o u n t e r - b a l a n c e d a c r o s s s u b j e c t s i n a L a t i n s q u a r e d e s i g n . R e s p o n s e s w e r e s c o r e d w i t h a s c o r i n g p r o g r a m o n t h e PDP 1 1 \/ 3 4 , a n d c o u n t e d a s e i t h e r c o r r e c t c o n j u n c t i o n , c o l o r c o r r e c t , l e t t e r c o r r e c t , o r i n c o r r e c t , d e p e n d i n g u p on w h a t p o r t i o n o f t h e i r r e s p o n s e s m a t c h e d t h e i t e m s d i s p l a y e d . R e s u l t s a n d D i s c u s s i o n T h e r e was a p a r t i a l r e p o r t s u p e r i o r i t y f o r c o n j u n c t i o n r e p o r t s o v e r t o t a l r e p o r t a t a l l SOAs e x c e p t 1100 a n d a p a r t i a l r e p o r t s u p e r i o r i t y f o r t h e f e a t u r e r e p o r t a t a l l SOAs f o r c o l o r , a n d a t a l l e x c e p t 1100 f o r l e t t e r ( s e e T a b l e I ) . P e r f o r m a n c e s i n f i r s t a n d l a s t t o t a l r e p o r t s e s s i o n s w e r e n o t s i g n i f i c a n t l y d i f f e r e n t ( t [ 1 0 ] = 1 . 7 4 ) , a nd a s a r e s u l t we may c o n c l u d e t h a t p r a c t i c e w i t h t h e s e d i s p l a y s h a d l i t t l e e f f e c t u p o n t o t a l r e p o r t p e r f o r m a n c e . S u p e r i o r i t y o f p a r t i a l r e p o r t f o r c o n j u n c t i o n s i s much h i g h e r t h a n t h a t o f 29 t h e f e a t u r e s w i t h a p r e - c u e (-200 SOA), b u t a f t e r t h a t SOA, f a l l s t o t h e same l e v e l a s t h e f e a t u r e s . T a b l e I S u p e r i o r i t y o f p a r t i a l r e p o r t o v e r t o t a l r e p o r t f o r E x p e r i m e n t 1. SOA R e p o r t t d f E A d v a n t a c (# o f i i -200 C o n j u n c t i o n 31.77 16 < 0. 01 5.91 C o l o r 12.39 16 < 0. 01 4.76 L e t t e r 15.87 16 < 0. 01 4.98 0 C o n j u n c t i o n 9.65 16 < 0. 01 4.19 C o l o r 6.27 16 < 0. 01 3.81 L e t t e r 9.11 16 < 0. 01 3.77 200 C o n j u n c t i o n 2.86 16 < 0. 01 1.06 C o l o r 2.01 16 < 0. 05 1.56 L e t t e r 2.63 16 < 0. 01 1.37 300 C o n j u n c t i o n 2.52 16 < 0. 05 0.95 C o l o r 2.92 16 < 0. 01 2.11 L e t t e r 3.08 16 < 0. 01 1.61 400 C o n j u n c t i o n 2.04 16 < 0. 05 0.78 C o l o r 1.86 16 < 0. 05 1.51 L e t t e r 2.51 16 < 0. 05 1.31 600 C o n j u n c t i o n 1.90 16 < 0. 05 0.83 C o l o r 1.87 16 < 0. 05 1.28 L e t t e r 2.19 16 < 0. 05 1.34 1100 C o l o r 2.16 16 < 0. 05 1.47 The e x p e r i m e n t a l a p p a r a t u s i n t h i s e x p e r i m e n t i n c l u d e d a c o l o r m o n i t o r ( t h e I n t e c o l o r 8001 m o n i t o r ) w i t h p h o s p h o r s t h a t p e r s i s t e d f o r v a r y i n g amounts o f t i m e a f t e r d i s p l a y o f f s e t . I n o r d e r t o e s t i m a t e t h e c o n t r i b u t i o n o f 30 p e r s i s t e n c e o f t h e p h o s p h o r s t o t a s k p e r f o r m a n c e , I r a n a v e r s i o n o f t h e t a s k u s i n g a s h u t t e r w h i c h b l o c k e d o u t t h e d i s p l a y a n d o p e n e d a t t h e same o n s e t t i m e s a s d i d t h e c u e . T h r e e new s u b j e c t s r a n i n t h i s t e s t . On a v e r a g e , s u b j e c t s w e r e a b l e t o r e p o r t i t e m s a t l e v e l s a b o v e c h a n c e up t o 120 ms a f t e r t h e d i s p l a y o f f s e t w i t h o u t a c t u a l l y s e e i n g t h e o r i g i n a l d i s p l a y . When t h e r e p o r t s f r o m t h e p e r s i s t e n c e a l o n e w e r e s u b t r a c t e d f r o m t h e o b t a i n e d r e p o r t s a n d t h e y w e r e a g a i n t e s t e d f o r p a r t i a l r e p o r t s u p e r i o r i t y t h e s i g n i f i c a n c e o f t h e p a r t i a l r e p o r t s u p e r i o r i t y o v e r t o t a l r e p o r t r e m a i n e d u n c h a n g e d . A somewhat s u r p r i s i n g f i n d i n g was t h a t p e r f o r m a n c e o n t h e v e r b a l t o t a l r e p o r t t a s k was b e t t e r t h a n p e r f o r m a n c e o n t h e w r i t t e n t o t a l r e p o r t t a s k ( t [ 1 6 ] = 3.106, p < . 0 1 ) . The w r i t t e n t o t a l r e p o r t t a s k was a d d e d t o t h e f i r s t e x p e r i m e n t b e c a u s e I was n o t c e r t a i n t h a t f o r c i n g s u b j e c t s t o s t a r t r e p o r t i n g f r o m a p a r t i c u l a r l o c a t i o n i n t h e d i s p l a y w o u l d p r o v i d e a n a d e q u a t e m e a s u r e o f a l l t h e y c o u l d r e p o r t f r o m t h e d i s p l a y . S u b j e c t s v o l u n t e e r e d a p r e f e r e n c e f o r t h e v e r b a l t o t a l r e p o r t t a s k . I t seemed t h a t t h e p r e s e n c e o f t h e c u e h e l p e d s u b j e c t s t o d i r e c t t h e i r a t t e n t i o n t o a s e c t i o n o f t h e d i s p l a y a n d g a v e them a s t a r t i n g p o i n t f o r r e p o r t i n g t h e i t e m s p r e s e n t . When t h i s c u e was a b s e n t t h e y f l o u n d e r e d . 31 The f i n d i n g o f m o s t i m p o r t a n c e f o r t h i s s t u d y was t h e l a c k o f a s i g n i f i c a n t l y b e t t e r p e r f o r m a n c e o n t h e c o n j u n c t i o n r e p o r t t h a n w o u l d b e e x p e c t e d f r o m t h e i n d e p e n d e n t r e p o r t o f f e a t u r e s . The p e r f o r m a n c e o n . t h e c o n j u n c t i o n a n d f e a t u r e r e p o r t s a n d t h e d i f f e r e n c e b e t w e e n o b t a i n e d a n d p r e d i c t e d c o n j u n c t i o n p e r f o r m a n c e a r e p r e s e n t e d b e l o w ( F i g u r e 1 ) . A r e p e a t e d m e a s u r e s a n a l y s i s o f v a r i a n c e was p e r f o r m e d t o e s t a b l i s h w h e t h e r t h e r e was a s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e c o n j u n c t i o n p e r f o r m a n c e a s p r e d i c t e d f r o m f e a t u r e p e r f o r m a n c e ( h e n c e f o r t h c a l l e d \" b e t w e e n s e s s i o n \" ) , a n d o b s e r v e d p e r f o r m a n c e . The d i f f e r e n c e b e t w e e n o b s e r v e d a n d p r e d i c t e d p e r f o r m a n c e d i d n o t r e a c h s i g n i f i c a n c e ( F [ l , 5 ] = 1.04 p > 0 . 3 ) . We c a n a l s o l o o k a t t h e i n d e p e n d e n c e p r e d i c t i o n w i t h i n t h e c o n j u n c t i o n r e p o r t c o n d i t i o n . C o l o r a nd l e t t e r p e r f o r m a n c e may be m e a s u r e d b y a d d i n g c o r r e c t r e p o r t s o f c o l o r o n l y ( i . e . t r i a l s w h e r e l e t t e r i s r e p o r t e d i n c o r r e c t l y ) t o c o r r e c t c o n j u n c t i o n r e p o r t s t o o b t a i n a m e a s u r e o f t h e t o t a l number o f c o r r e c t c o l o r r e p o r t s . The same may be d o n e w i t h l e t t e r r e p o r t s . The p e r f o r m a n c e v a l u e s f o r t h e f e a t u r e s o b t a i n e d i n t h i s way w e r e m u l t i p l i e d t o p r o d u c e p r e d i c t e d v a l u e s f o r c o n j u n c t i o n p e r f o r m a n c e f o r e a c h s u b j e c t ( T h i s w i l l be r e f e r r e d t o a s \" w i t h i n s e s s i o n p r e d i c t i o n \" ) . H e r e I f o u n d a s m a l l a d v a n t a g e f o r o b s e r v e d c o n j u n c t i o n s o v e r p r e d i c t e d c o n j u n c t i o n r e p o r t s , a v e r a g i n g E x p e r i m e n t 1: F e a t u r e and C o n j u n c t i o n R e p o r t O b s e r v e d - P r e d i c t e d D i f f e r e n c e s o _ 0.200-o.100 -o.ooo --o. loo i 1 1 1 1 1 r 1 1 1 1 1 1 1 - 2 5 0 - 1 5 0 - 5 0 5 0 1 5 0 2 5 0 3 5 0 4 5 0 5 5 0 6 5 0 7 5 0 8 5 0 9 5 0 1 0 5 0 1 1 5 0 S t i m u l u s O n s e t A s y n c h r o n y (ms) F i g u r e 1 33 5.6 % a n d p r e s e n t a t a l l i n t e r v a l s b e t w e e n c u e a n d d i s p l a y ( F [ l , 5 ] = 6 3 . 6 , p < .01) . T h e r e w a s a s i g n i f i c a n t i n t e r a c t i o n b e t w e e n t h e o b s e r v a t i o n - w i t h i n s e s s i o n p r e d i c t i o n d i f f e r e n c e a n d SOA ( F [ 6 , 3 0 ] = 2.95, p < 0 . 0 5 ) . The i n t e r a c t i o n i s a c c o u n t e d f o r b y t h e n e a r p e r f e c t p e r f o r m a n c e w i t h t h e a d v a n c e c u e a n d s m a l l e r s t a n d a r d d e v i a t i o n s i n t h e w i t h i n s e s s i o n m e a s u r e . T h i s w i t h i n s e s s i o n m e a s u r e p r o v i d e s a n u p w a r d b o u n d f o r t h e a v a i l a b i l i t y o f c o n j u n c t i o n i n f o r m a t i o n . W i t h i n a s e s s i o n , s t a t e v a r i a b l e s s u c h a s a l e r t n e s s w i l l p r o d u c e c o r r e l a t i o n s b e t w e e n f e a t u r e a n d c o n j u n c t i o n r e p o r t e v e n i f t h e r e p r e s e n t a t i o n s a r e i n d e p e n d e n t ; f o r e x a m p l e , i f s u b j e c t s l o o k e d away f r o m t h e d i s p l a y t h e y w o u l d g e t n e i t h e r f e a t u r e n o r c o n j u n c t i o n c o r r e c t . T h e same s e s s i o n r e p o r t a l s o c o n t r o l s f o r memory a n d r e s p o n s e l o a d , f a c t o r s w h i c h c o u l d i n f l a t e s c o r e s when o n l y c o l o r o r l e t t e r a r e r e p o r t e d . E x p e r i m e n t 2 S i n c e t h e assumed d u r a t i o n o f t h e i c o n may be a s s h o r t a s 150 ms w i t h SOA r a t h e r t h a n I S I t h e i m p o r t a n t v a r i a b l e ( D i L o l l o , 1 9 7 7 ) , t h e d u r a t i o n o f t h e d i s p l a y s i n E x p e r i m e n t 1 a n d t h e l e n g t h o f SOAs may h a v e p r e v e n t e d a c o n j u n c t i o n 34 a d v a n t a g e f r o m b e i n g o b s e r v e d t h e r e . I t i s p o s s i b l e t h a t t h e i n t e r v a l s e x a m i n e d p a s s e d o v e r t h e t i m e p e r i o d w h e r e a n i c o n i c r e p r e s e n t a t i o n o f c o n j u n c t i o n s i s p r e s e n t a n d a c c e s s i b l e . W i t h o u t l o o k i n g a t t h e i n t e r v e n i n g p e r i o d i t i s n o t p o s s i b l e t o c o n c l u d e t h a t c o n j u n c t i o n s do n o t h a v e an a d v a n t a g e o v e r f e a t u r e s . E x p e r i m e n t 2 was r u n t o l o o k a t s h o r t e r SOAs. The d u r a t i o n o f t h e d i s p l a y was r e d u c e d t o 20 ms, a n d t h e f i r s t p o s t - d i s p l a y SOA was s h o r t e n e d t o 70 ms. M e t h o d S u b j e c t s : F o u r v o l u n t e e r s f r o m t h e A t t e n t i o n L a b s u b j e c t p o o l w e r e e m p l o y e d f o r t h r e e one h o u r s e s s i o n s f o r w h i c h t h e y w e r e p a i d f o u r d o l l a r s p e r s e s s i o n . A l l s u b j e c t s h a d n o r m a l o r c o r r e c t e d t o n o r m a l v i s i o n a n d none s u f f e r e d f r o m a n y known d e f i c i t s i n c o l o r v i s i o n . D i s p l a y s : The d i s p l a y s , c u e s a n d a p p a r a t u s f o r t h i s e x p e r i m e n t w e r e t h e same as f o r e x p e r i m e n t 1. The c u e c o u l d a p p e a r a t t h e f o l l o w i n g SOAs: 0, 70, 100, 140, 320, a n d 1020 ms. The d i s p l a y s w e r e p r e s e n t e d f o r 20 ms, a s w e r e t h e c u e s . P r o c e d u r e : S u b j e c t s r e c e i v e d 48 p r a c t i c e t r i a l s a n d 288 t e s t t r i a l s i n e a c h s e s s i o n , r e s u l t i n g i n 48 t r i a l s p e r c o n d i t i o n . The o r d e r o f p r e s e n t a t i o n o f c o n j u n c t i o n , c o l o r a n d l e t t e r c o n d i t i o n s was c o u n t e r - b a l a n c e d a c r o s s s u b j e c t s i n a L a t i n s q u a r e d e s i g n . R e s p o n s e s w e r e e n t e r e d a n d s c o r e d 35 a s i n E x p e r i m e n t 1. The t o t a l r e p o r t c o n d i t i o n s w e r e n o t r u n i n t h i s e x p e r i m e n t . R e s u l t s a n d D i s c u s s i o n The p e r f o r m a n c e on t h e c o n j u n c t i o n a n d f e a t u r e r e p o r t s a n d t h e d i f f e r e n c e b e t w e e n o b t a i n e d a n d p r e d i c t e d c o n j u n c t i o n p e r f o r m a n c e a r e p r e s e n t e d b e l o w ( F i g u r e 2 ) . A r e p e a t e d m e a s u r e s a n a l y s i s o f v a r i a n c e was p e r f o r m e d t o e s t a b l i s h w h e t h e r t h e d i f f e r e n c e s b e t w e e n p r e d i c t e d a n d o b s e r v e d v a l u e s w e r e s i g n i f i c a n t f o r t h e b e t w e e n s e s s i o n p r e d i c t i o n a n d f o r t h e w i t h i n s e s s i o n p r e d i c t i o n . T h e b e t w e e n s e s s i o n p r e d i c t i o n d i f f e r e n c e was n o t s i g n i f i c a n t ( F [ l , 3 ] = 0 . 1 6 , p > 0 . 7 1 ) w h i l e t h e w i t h i n s e s s i o n p r e d i c t i o n d i f f e r e n c e was s i g n i f i c a n t ( F [ l , 3 ] = 1 6 .58, p < 0 . 0 3 ) . T h i s s u g g e s t s t h a t c o n j u n c t i o n s h a v e o n l y a s m a l l a d v a n t a g e , a v e r a g i n g 3.9 p e r c e n t o v e r a l l SOAs, o v e r w h a t w o u l d be e x p e c t e d f r o m t h e p e r f o r m a n c e on f e a t u r e s . 4-> U CD f_ C_ o C J E x p e r i m e n t 2 : F e a t u r e and C o n j u n c t i o n R e p o r t O b s e r v e d - P r e d i c t e d D i f f e r e n c e s 1.000 0.900 0.800 -0.700 0.600 0.500 0.400 c o \u2022r-l 4-> c_ o a. o c_ Q- o.ioo 0.300 -0.200 -0.000 --0.100 Q Conjunction Report ^ Color Report ^ Letter Report Observed - Predicted Differences -50 50 150 250 350 450 550 650 750 850 950 1050 S t i m u l u s O n s e t A s y n c h r o n y (ms) F i g u r e 2. 37 E x p e r i m e n t 3 T h i s e x p e r i m e n t was c o n d u c t e d t o c o n f i r m t h e r e s u l t s o f t h e f i r s t two e x p e r i m e n t s . An i n i t i a l p i l o t s t u d y was r u n t o a t t e m p t t o r e p l i c a t e t h e e a r l i e r r e s u l t s o n a d i f f e r e n t c o l o r m o n i t o r s y s t e m . T h i s s y s t e m h a d t h e a d v a n t a g e o f p o s s e s s i n g s h o r t p e r s i s t e n c e p h o s p h o r s f o r a l l t h r e e c o l o r g u n s , a l l o w i n g me t o a s s e s s t h e c o n t r i b u t i o n o f t h e l o n g p e r s i s t e n c e t o p e r f o r m a n c e . T h i s p i l o t a l s o s w i t c h e d s u b j e c t s ' r e s p o n s e s f r o m v e r b a l t o t y p e d . The SOAs u s e d w e r e t h e o n e s w h i c h e x p e r i m e n t s 1 a n d 2 h a d i n common, 0, 100, 300, a n d 1000 ms. F i n a l l y , t h e p i l o t e m p l o y e d a s m a l l e r d i s p l a y s i z e , r e d u c i n g t h e number o f e l e m e n t s t o f o u r f r o m e i g h t . The r e d u c t i o n r e m o v e d t h e r e d u n d a n c i e s i n c o l o r a n d l e t t e r t h a t w e r e p r e s e n t i n t h e e a r l i e r e x p e r i m e n t s , a n d t h u s s h o u l d r e d u c e w i t h i n d i s p l a y c o n f u s i o n s . R e s u l t s o f t h e p i l o t r e p l i c a t e d t h e f i r s t two e x p e r i m e n t s , a n d s u g g e s t e d t h a t t h e l o n g p h o s p h o r p e r s i s t e n c e was n o t r e s p o n s i b l e f o r t h e o b s e r v e d p a r t i a l r e p o r t s u p e r i o r i t y , a n d a t h i r d e x p e r i m e n t was t h e n c o n d u c t e d t o e x t e n d t h e o t h e r r e s u l t s . The t h i r d e x p e r i m e n t was d e s i g n e d t o l o o k a g a i n a t s h o r t e r SOAs a n d t o a l l o w a more d e t a i l e d a n a l y s i s o f e r r o r s t h a n was p o s s i b l e i n t h e e a r l i e r v e r s i o n s . One o f t h e f i v e 38 l e v e l s o f e a c h f e a t u r e was a b s e n t f r o m e a c h d i s p l a y i n t h i s v e r s i o n t o a l l o w l o c a t i o n a n d i n t r u s i o n e r r o r s t o be c o m p a r e d . As w e l l , two g r o u p s o f i s o l u m i n o u s c o l o r s w e r e c o n s t r u c t e d i n o r d e r t o d e t e r m i n e w h e t h e r s u b j e c t s w e r e r e s p o n d i n g t o t h e c o l o r o r t o t h e l u m i n a n c e o f p r e s e n t e d i t e m s . Two c u e d u r a t i o n s , 50 a n d 500 ms w e r e u s e d i n t h i s e x p e r i m e n t t o d e t e r m i n e w h e t h e r o r n o t s h o r t c u e d u r a t i o n s w e r e i n t e r f e r i n g w i t h s u b j e c t s ' a b i l i t y t o l o c a t e t h e c o r r e c t d i s p l a y p o s i t i o n f o r r e p o r t . The l o n g (500 ms) c u e d u r a t i o n s h o u l d a l l o w a m ple t i m e f o r t h e p o s i t i o n o f t h e c u e i n t h e d i s p l a y t o be d e t e r m i n e d , a n d i f t h e r e i s n o d i f f e r e n c e b e t w e e n t h e l o n g a n d s h o r t c u e d u r a t i o n s , f a i l u r e t o l o c a t e d t h e c u e may be d i s c a r d e d a s a p o t e n t i a l s o u r c e o f e r r o r . M e t h o d S u b j e c t s : S u b j e c t s w e r e s i x t e e n p a i d v o l u n t e e r s f r o m t h e U n i v e r s i t y o f C a l i f o r n i a ( B e r k e l e y ) A t t e n t i o n L a b o r a t o r y s u b j e c t p o o l who w e r e e m p l o y e d f o r two o n e - h o u r s e s s i o n s . T h e y w e r e p a i d e i t h e r f i v e d o l l a r s ( e i g h t s u b j e c t s ) o r s e v e n d o l l a r s ( e i g h t s u b j e c t s ) p e r s e s s i o n f o r t h e i r p a r t i c i p a t i o n . T h r e e s u b j e c t s w e r e d i s c a r d e d f o r f a i l i n g t o a c h i e v e a n a c c u r a c y o f 75 p e r c e n t w i t h 0 c u e d e l a y , a n d one s u b j e c t was d i s c a r d e d b e c a u s e o f a c o m p u t e r m a l f u n c t i o n d u r i n g d a t a c o l l e c t i o n t h a t r e s u l t e d i n t h e l o s s o f d a t a . A l l h a d n o r m a l o r c o r r e c t e d - t o - n o r m a l v i s i o n , a n d none s u f f e r e d f r o m a n y known d e f i c i t s i n c o l o r v i s i o n . D i s p l a y s : The d i s p l a y s w e r e shown o n a M i t s u b i s h i H i g h R e s o l u t i o n RGB c o l o r m o n i t o r c o n t r o l l e d b y an A r t i s t P l u s c o l o r g r a p h i c s b o a r d i n s t a l l e d i n a n I B M AT c o m p u t e r . D i s p l a y s w e r e composed o f e i g h t c h a r a c t e r s a r r a n g e d i n a c i r c u l a r a r r a y t h a t s u b t e n d e d a v i s u a l a n g l e o f 5.84 d e g r e e s h o r i z o n t a l l y a n d 7.3 2 d e g r e e s v e r t i c a l l y . T h e s e i t e m s a v e r a g e d 0 . 6 9 d e g r e e s h o r i z o n t a l l y a n d 0.97 d e g r e e s v e r t i c a l l y . The i t e m s i n t h e d i s p l a y w e r e s e l e c t e d f r o m t h e c o l o r s e t r e d , g r e e n , b l u e , y e l l o w , a n d p u r p l e , a n d f r o m t h e l e t t e r s e t N, O, S, T, a n d X. S t i m u l i w e r e shown o n a d a r k b a c k g r o u n d . I t e m s w e r e s e l e c t e d r a n d o m l y w i t h t h e f o l l o w i n g c o n s t r a i n t s : e a c h c o l o r o r l e t t e r s e l e c t e d a p p e a r e d t w i c e i n t h e d i s p l a y w i t h no c o l o r - l e t t e r c o m b i n a t i o n r e p e a t e d . T h i s r e s u l t e d i n f o u r c o l o r s a n d l e t t e r s b e i n g p r e s e n t i n a d i s p l a y a n d one c o l o r a n d one l e t t e r b e i n g a b s e n t . A t t h e b e g i n n i n g o f a t r i a l a f i x a t i o n d o t a p p e a r e d i n t h e c e n t e r o f t h e m o n i t o r s c r e e n f o r 500 ms. T h i s was f o l l o w e d b y a 200 ms b l a n k i n t e r v a l a n d t h e n t h e d i s p l a y was p r e s e n t e d f o r 50 ms. The c u e t o r e p o r t a n i t e m was a w h i t e d o t w h i c h a p p e a r e d a d j a c e n t t o a n d o u t s i d e o f t h e p o s i t i o n o f t h e r e l e v a n t i t e m i n t h e d i s p l a y . The i t e m c u e d was c h o s e n r a n d o m l y . The c u e was 50 ms i n d u r a t i o n f o r s i x o f t h e s u b j e c t s a n d 500 ms f o r t h e r e m a i n i n g s i x . Cues a p p e a r e d a t 40 t h e f o l l o w i n g SOAs: 0 ms ( a s i m u l t a n e o u s c u e ) , 125 ms, 200 ms, 300 ms, a n d 1050 ms. The e x p e r i m e n t a l room was l i t w i t h a 75 w a t t l i g h t b u l b i n a lamp d i r e c t e d u p w a r d t o p r o v i d e l o w l e v e l d i f f u s e l i g h t . P r o c e d u r e : E a c h s u b j e c t p a r t i c i p a t e d i n two 50 m i n u t e s e s s i o n s o f t h e e x p e r i m e n t . A s i n g l e s e s s i o n was d i v i d e d i n t o t h r e e s e c t i o n s f o r e a c h r e p o r t i n g c o n d i t i o n , c o n j u n c t i o n r e p o r t , c o l o r r e p o r t , a n d l e t t e r r e p o r t , w i t h t h e o r d e r o f t h e s e c o u n t e r - b a l a n c e d a c r o s s s e s s i o n s i n a L a t i n s q u a r e d e s i g n . The f i r s t s e s s i o n o f t h e e x p e r i m e n t was t r e a t e d a s a p r a c t i c e s e s s i o n a n d d a t a w e r e n o t a n a l y s e d f r o m t h i s p o r t i o n o f t h e e x p e r i m e n t . I n t h e s e c o n d s e s s i o n , s u b j e c t s r e c e i v e d 40 p r a c t i c e t r i a l s i n e a c h c o n d i t i o n , a n d 200 d a t a c o l l e c t i o n t r i a l s i n e a c h c o n d i t i o n (40 t r i a l s p e r c u e d e l a y ) . T h i s r e s u l t e d i n a t o t a l o f 40 t r i a l s a t e a c h c u e d e l a y p e r c o n d i t i o n . S u b j e c t s r e s p o n d e d b y e n t e r i n g t h e f i r s t l e t t e r o f t h e c o l o r name, t h e l e t t e r , o r t h e c o l o r -l e t t e r c o m b i n a t i o n o f t h e i t e m a t t h e c u e d l o c a t i o n o n t h e IBM AT k e y b o a r d . I f s u b j e c t s made a r e s p o n s e w h i c h was n o t one o f t h e p o s s i b l e r e s p o n s e s , t h e y h e a r d a b e e p a n d saw a n e r r o r m essage a s k i n g them t o c o r r e c t t h e t y p i n g e r r o r . T h e y r e c e i v e d no o t h e r e r r o r f e e d b a c k . S i x s u b j e c t s v i e w e d d i s p l a y s w i t h t h e i r h e a d s h e l d a g a i n s t a f o r e h e a d r e s t a n d h o o d w h i c h a l s o s h i e l d e d t h e m o n i t o r s c r e e n f r o m g l a r e . The r e m a i n i n g s i x s u b j e c t s d i d n o t u s e t h i s h e a d r e s t . 41 R e s u l t s a n d D i s c u s s i o n The two g r o u p s o f s i x s u b j e c t s w e r e c o m p a r e d t o t e s t f o r a n y s i g n i f i c a n t d i f f e r e n c e s i n p e r f o r m a n c e a s a r e s u l t o f t h e d i f f e r e n t t e s t i n g c o n d i t i o n s ( t h e d i f f e r e n t c u e d u r a t i o n s a n d t h e p r e s e n c e o r a b s e n c e o f t h e hood) . T h e r e was no s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e g r o u p s ( F [ l , 1 0 ] = 0.05, p > 0.80) s o t h e two g r o u p s w e r e c o l l a p s e d i n t o one f o r s u b s e q u e n t a n a l y s e s . The l e v e l s o f f e a t u r e a n d c o n j u n c t i o n r e p o r t s , a n d d i f f e r e n c e s b e t w e e n o b t a i n e d a n d p r e d i c t e d p e r f o r m a n c e o n t h e c o n j u n c t i o n r e p o r t s a r e p r e s e n t e d b e l o w ( F i g u r e 3 ) . A r e p e a t e d m e a s u r e s a n a l y s i s o f v a r i a n c e was p e r f o r m e d t o e s t a b l i s h w h e t h e r t h e d i f f e r e n c e s b e t w e e n p r e d i c t e d a nd o b s e r v e d v a l u e s w e r e s i g n i f i c a n t f o r e a c h t y p e o f p r e d i c t i o n . T h e d i f f e r e n c e f o r t h e b e t w e e n s e s s i o n p r e d i c t i o n was n o t s i g n i f i c a n t ( F [ l , l l ] = 2.92, p > 0.11) w h i l e t h e d i f f e r e n c e f o r t h e w i t h i n s e s s i o n p r e d i c t i o n was s i g n i f i c a n t ( F [ l , l l ] = 4 8 . 8 1 , p < 0 . 0 0 1 ) . The a c c u r a c y o f f e a t u r e r e p o r t a c r o s s t h e two c o n d i t i o n s , c o n j u n c t i o n a n d s e p a r a t e f e a t u r e c o n d i t i o n s was n o t s i g n i f i c a n t l y d i f f e r e n t f o r c o l o r r e p o r t s ( F [ l , l l ] = 1 . 4 2 , p > 0.25) b u t was s i g n i f i c a n t l y d i f f e r e n t f o r l e t t e r r e p o r t s ( F [ l , l l ] = 6.54, p < 0 . 0 3 ) . 42 A c o m p a r i s o n o f t h e f r e q u e n c y o f d i f f e r e n t t y p e s o f e r r o r s was made t o s e e w h e t h e r c o n j u n c t i o n e r r o r s o c c u r more f r e q u e n t l y t h a n one w o u l d e x p e c t i f e r r o r s w e r e s i m p l y t h e r e s u l t o f g u e s s i n g . F o l l o w i n g T r e i s m a n and S c h m i d t ( 1 9 8 2 ) , e r r o r r e s p o n s e s w e r e c o l l a p s e d i n t o c o n j u n c t i o n e r r o r s ( t h o s e e r r o r s w h e r e s u b j e c t s r e c o m b i n e d f e a t u r e s f r o m t h e d i s p l a y , i . e . i l l u s o r y c o n j u n c t i o n s ) , i n t r u s i o n e r r o r s ( e r r o r s w h e r e an i t e m c o n t a i n i n g a f e a t u r e t h a t was n o t p r e s e n t i n t h e d i s p l a y was r e p o r t e d ) , and e r r o r s w h e r e a r e p o r t e d i t e m was p r e s e n t i n t h a t c o m b i n a t i o n e l s e w h e r e i n t h e d i s p l a y . T h e s e l a t t e r e r r o r s w e r e s e p a r a t e d f r o m t h e o t h e r e r r o r s a s t h e y may h a v e b e e n m i s p e r c e p t i o n s o f t h e c u e l o c a t i o n r a t h e r t h a n i l l u s o r y c o n j u n c t i o n s . The d i f f e r e n c e b e t w e e n c o n j u n c t i o n e r r o r s and i n t r u s i o n e r r o r s p r o v i d e s a m e a s u r e o f t h e number o f i l l u s o r y c o n j u n c t i o n s a c t u a l l y b e i n g p r o d u c e d b y . t h e s u b j e c t . The number o f i n t r u s i o n e r r o r s w a s c o r r e c t e d ( w e i g h t e d b y a f a c t o r o f 3) t o c o m p e n s a t e f o r t h e i r r e d u c e d p r o b a b i l i t y o f o c c u r r e n c e , s i n c e o n l y one c o l o r a n d l e t t e r w e r e a b s e n t f r o m e a c h d i s p l a y a n d t h r e e o t h e r ( u n c u e d ) f e a t u r e s w e r e p r e s e n t . T h i s c o r r e c t e d i n t r u s i o n e r r o r m e a s u r e was t h e n c o m p a r e d t o o b t a i n e d c o n j u n c t i o n e r r o r s t h r o u g h a r e p e a t e d m e a s u r e s a n a l y s i s o f v a r i a n c e . Experiment 3: F e a t u r e and C o n j u n c t i o n R e p o r t Observed - P r e d i c t e d D i f f e r e n c e s i.000 Q. O - 0.200 -Q_ 0.100 -0.000 --o. ioo H 1 1 1 1 1 1 1 1 1 1 1 -100 0 100 200 300 400 500 600 700 800 900 1000 1100 S t i m u l u s Onset Asynchrony (ms) F i g u r e 3. 44 The d i f f e r e n c e b e t w e e n c o n j u n c t i o n e r r o r s a nd i n t r u s i o n e r r o r s was s i g n i f i c a n t ( F [ l , l l ] = 10.96, p < 0 . 0 1 ) , w i t h a s i g n i f i c a n t i n t e r a c t i o n w i t h c u e d e l a y ( F [ 4 , 4 4 ] = 2.85, p < 0 . 0 5 ) . T h i s i n t e r a c t i o n was due t o t h e l o w f r e q u e n c y o f e r r o r s a t 0 SOA, and when e r r o r s a t t h i s i n t e r v a l w e r e r e m o v e d f r o m t h e a n a l y s i s t h e i n t e r a c t i o n d i s a p p e a r e d ( s e e F i g u r e 4 ) . A f i n a l a n a l y s i s was t h e c o n s t r u c t i o n o f c o n f u s i o n m a t r i c e s f o r t h e t w o d i m e n s i o n s , c o l o r a nd l e t t e r . T h e p u r p o s e o f t h i s a n a l y s i s was t o d e t e r m i n e i f s u b j e c t s w e r e r e s p o n d i n g t o t h e c o l o r o r t o t h e b r i g h t n e s s o f s t i m u l i . T h e s e w e r e c o n f o u n d e d i n t h e e a r l i e r e x p e r i m e n t s . R e s p o n s e s f r o m a l l i n t e r v a l s e x c e p t 1050, w h e r e r e s p o n s e s i n c l u d e many g u e s s e s , w e r e s o r t e d a c c o r d i n g t o w h a t v a l u e o f a d i m e n s i o n was p r e s e n t e d a n d r e s p o n d e d o n a g i v e n t r i a l . I f s u b j e c t s a r e r e s p o n d i n g b a s e d o n t h e b r i g h t n e s s r a t h e r t h a n c o l o r o f s t i m u l i we s h o u l d s e e more c o n f u s i o n s w i t h i n l u m i n a n c e c a t e g o r i e s t h a n a c r o s s . I t i s a p p a r e n t i n T a b l e I I t h a t t h i s i s n o t t h e c a s e . R a t h e r , s u b j e c t s made t h e p r e d i c t a b l e c o n f u s i o n s b e t w e e n c o l o r s t h a t w e r e m o s t s i m i l a r ( e s p e c i a l l y b e t w e e n b l u e a n d p u r p l e , a n d y e l l o w a n d g r e e n ) . The numbers i n t h e t a b l e r e p r e s e n t p r o p o r t i o n s o f r e s p o n s e s t h a t f e l l i n t o e a c h c e l l . The a c t u a l numbers o f r e s p o n s e s a r e o n l y CO CD CO c o Q. CO cu rx c o \u2022 H +J c_ o a o c_ Q. 0.800 0.750 0.700 0.650 0.600 -0.550 -0.500 -0.450 0.400 H 0.350 0.300 -0.250 -0.200 -0.150 -0.100 -0.050 -0.000 E x p e r i m e n t 3: E r r o r s by t y p e Q Conjunction Errors @ Intrusion Errors ^ Adjusted Intrusion Errors _ Mislocated Conjunction Errors I I l I 1 1 1 1 1 1 , -100 0 100 200 300 400 500 600 700 800 900 1000 1100 S t i m u l u s O n s e t A s y n c h r o n y (ms) F i g u r e 4 46 a p p r o x i m a t e l y e q u a l , s i n c e c u e d i t e m s w e r e c h o s e n r a n d o m l y o n e a c h t r i a l . T a b l e I I C o n f u s i o n M a t r i x f o r c o l o r s . RESPONSE L u m i n a n c e C a t e g o r i e s C a t e g o r y 1 | C a t e g o r y 2 j RED j GREEN | PURPLE ! ! YELLOW ! BLUE j RED J .714 1 -059 j .055 j j .050 j .073 j GREEN | .039 j .696 .059 j j .103 j .104 j PURPLE! .032 j .085 j .530 j j .059 j .295 j YELLOW! .071 ! -139 j .050 j j .652 j .074 j BLUE ! .053 j .080 j .195 j | .040 j .663 | A s i m i l a r a n a l y s i s was p e r f o r m e d on l e t t e r r e s p o n s e s . H e r e i t i s n o t s o c l e a r w h a t p a t t e r n o f c o n f u s i o n s t o e x p e c t , s i n c e l e t t e r s w e r e c h o s e n t o h a v e d i s t i n c t i v e f e a t u r e s . S t i l l , some u n e x p e c t e d c o n f u s i o n s o c c u r r e d f a i r l y f r e q u e n t l y ( s e e T a b l e I I I ) . F o r e x a m p l e , S was more f r e q u e n t l y r e p o r t e d a s N t h a n r e p o r t e d a s O. The m a i n c o n f u s i o n s a r e u n d e r s t a n d a b l e . X was c o n f u s e d w i t h b o t h N a n d S, a n d a l s o was l e a s t a c c u r a t e l y r e p o r t e d o f a l l t h e 47 l e t t e r s . P e r h a p s t h i s i s e v i d e n c e t h a t t h e i n t e r s e c t i o n o f t h e two l i n e s i s n o t a d i s t i n g u i s h i n g f e a t u r e . The o t h e r m a j o r c o n f u s i o n was 0 r e p o r t e d as S, b u t n o t S r e p o r t e d a s 0, w h i c h a l s o a g r e e s w i t h d a t a f r o m s e a r c h e x p e r i m e n t s t h a t t e r m i n a t o r s a r e d e t e c t e d and c l o s u r e i s n o t ( T r e i s m a n and G o r m i c a n , i n p r e p a r a t i o n ) T a b l e I I I C o n f u s i o n M a t r i x f o r l e t t e r s RESPONSE ! N i 0 s i T ! X N | .714 j .073 .090 j .063 i .065 s O | .067 j .694 .135 | .067 j .037 T j j | | I { j | j M s j .082 ! -055 J .768 | .047 ! .047 U 1 j j j L j { | | U T ! .052 ! -041 ! .053 | .808 ! .046 S ! ; ! | x ! .105 ! .065 .096 j .078 j .655 48 G e n e r a l D i s c u s s i o n Summary o f R e s u l t s What h a v e we l e a r n e d f r o m t h e s e e x p e r i m e n t s ? A r e v i e w a n d c o l l e c t i o n o f t h e r e s u l t s i s t h e f i r s t s t e p i n a n s w e r i n g t h i s q u e s t i o n . T a b l e I V i s a summary o f t h e a n a l y s e s o f t h e d i f f e r e n c e b e t w e e n o b s e r v e d c o n j u n c t i o n p e r f o r m a n c e a n d t h e p r e d i c t e d p e r f o r m a n c e f r o m t h e f e a t u r e a n d t h e w i t h i n s e s s i o n p r e d i c t i o n s . We f i n d a c o n s i s t e n t , t h o u g h s m a l l , a d v a n t a g e f o r o b t a i n e d c o n j u n c t i o n p e r f o r m a n c e a g a i n s t b o t h t y p e s o f p r e d i c t i o n . T h i s d i f f e r e n c e i s s i g n i f i c a n t i n a l l t h r e e e x p e r i m e n t s f o r t h e w i t h i n s e s s i o n p r e d i c t i o n , a n d n o n -s i g n i f i c a n t f o r t h e b e t w e e n s e s s i o n p r e d i c t i o n . The a v e r a g e a d v a n t a g e f o r c o n j u n c t i o n s a c r o s s b o t h t y p e s o f p r e d i c t i o n i s 3.3 p e r c e n t ( 2.0 p e r c e n t f o r b e t w e e n s e s s i o n p r e d i c t i o n a n d 4.6 f o r w i t h i n s e s s i o n p r e d i c t i o n ) . C o l l a p s i n g t h e a d v a n t a g e may p r o v i d e t h e b e s t m e a s u r e o f t h e a c t u a l c o n j u n c t i o n a d v a n t a g e , s i n c e e a c h p r e d i c t i o n on i t s own i s p r o b l e m a t i c . 49 T a b l e I V Summary T a b l e f o r O b s e r v e d P e r f o r m a n c e v s P r e d i c t e d P e r f o r m a n c e ( R e p e a t e d M e a s u r e s A n a l y s i s o f V a r i a n c e ) C o m p a r i s o n d f F E o, \"o D i f f e r e n c e E x p e r i m e n t 1 B e t w e e n s e s s i o n 1,5 1.04 > 0. 30 3.0 SOA ( b e t w e e n ) 6,30 39.29 < 0. 001 W i t h i n s e s s i o n 1,5 3.60 < 0. 01 5.6 SOA ( w i t h i n ) 6,30 34.16 < 0. 001 SOA - W i t h i n S e s s i o n I n t e r a c t i o n 6,30 2.95 < 0. 05 E x p e r i m e n t 2 B e t w e e n s e s s i o n 1,3 0.16 > 0. 70 0.6 SOA ( b e t w e e n ) 5,15 14.16 < 0. 001 W i t h i n s e s s i o n 1,3 16.58 < 0. 05 3.9 SOA ( w i t h i n ) 5,15 7.80 < 0. 001 E x p e r i m e n t 3 B e t w e e n s e s s i o n 1,11 2.92 > 0. 10 2.5 SOA ( b e t w e e n ) 4,44 74.84 < 0. 001 W i t h i n s e s s i o n 1,11 48.81 < 0. 001 4.3 SOA ( w i t h i n ) 4,44 45.97 < 0. 001 SOA - W i t h i n S e s s i o n I n t e r a c t i o n 4,44 3.49 < 0. 05 T h e w i t h i n s e s s i o n p r e d i c t i o n y i e l d s a r e d u c e d p r e d i c t e d c o n j u n c t i o n p e r f o r m a n c e s i n c e b o t h p r e d i c t i o n a n d o b s e r v a t i o n w e r e b a s e d upon t h e same t r i a l . Any f a c t o r a f f e c t i n g t h e s u b j e c t , w h e t h e r i t i m p r o v e s o r d i s r u p t s p e r f o r m a n c e , a c t s o n b o t h f e a t u r e a n d c o n j u n c t i o n p e r f o r m a n c e i n c o n c e r t . I f t h e s u b j e c t b l i n k e d o r l o o k e d away f r o m t h e d i s p l a y b o t h f e a t u r e a n d c o n j u n c t i o n w e r e m i s s e d . The o p e r a t i o n o f m u l t i p l i c a t i o n i n t h e g e n e r a t i o n 50 o f t h e p r e d i c t i o n may c a u s e an a d v a n t a g e f o r c o n j u n c t i o n p e r f o r m a n c e s i m p l y a s a n a r t i f a c t o f t h e c o r r e l a t i o n s i n p e r f o r m a n c e b u i l t i n t o t h i s m e a s u r e . The b e t w e e n s e s s i o n p r e d i c t i o n s u f f e r s f r o m a d i f f e r e n t s e t o f d i f f i c u l t i e s . B e c a u s e p r e d i c t i o n s a r e b a s e d u p o n p e r f o r m a n c e a c r o s s d i f f e r e n t b l o c k s , v a r i a t i o n s i n s t a t e a r e much l a r g e r . I n d e e d , we s e e a l a r g e r v a r i a n c e i n t h i s c o n d i t i o n . A s e c o n d f a c t o r i s t h e l o w e r l o a d i n t h e f e a t u r e r e p o r t b l o c k s . S u b j e c t s w e r e o n l y r e q u i r e d t o r e p o r t one t h i n g a b o u t t h e d i s p l a y i n s t e a d o f t h e two i n t h e c o n j u n c t i o n c o n d i t i o n . A c h e c k t o s e e w h e t h e r t h i s made a n y r e a l d i f f e r e n c e i s t o c o m p a r e t h e l e v e l s o f f e a t u r e p e r f o r m a n c e a c r o s s t h e s e two c o n d i t i o n s ( s e e T a b l e V ) . T a b l e V Summary T a b l e f o r C o l o r P e r f o r m a n c e a n d L e t t e r P e r f o r m a n c e ( R e p e a t e d M e a s u r e s A n a l y s i s o f V a r i a n c e ) C o m p a r i s o n d f F \u00a3 % D i f f e r e n c e E x p e r i m e n t 1 C o l o r 1,5 0.98 > 0.36 2.6 L e t t e r 1,5 2.89 < 0.15 2.5 E x p e r i m e n t 2 C o l o r 1,3 0.03 > 0.88 0.3 L e t t e r 1,3 7.53 < 0.08 2.1 E x p e r i m e n t 3 C o l o r 1,11 1.42 > 0.25 3.8a L e t t e r 1,11 6.54 < 0.03 6.0 a T h i s d i f f e r e n c e was i n t h e o p p o s i t e d i r e c t i o n t o t h e o t h e r s 51 W h i l e c o l o r r e p o r t s b e t w e e n t h e two c o n d i t i o n s a r e n e v e r s i g n i f i c a n t l y d i f f e r e n t ( t h e y a r e e v e n b e t t e r i n t h e c o n j u n c t i o n r e p o r t c o n d i t i o n i n one e x p e r i m e n t ) , l e t t e r s seem t o h a v e an a d v a n t a g e when t h e y a r e r e p o r t e d a l o n e , w h i l e c o l o r s do n o t . T h i s c o n t r a d i c t s t h e d a t a o f C e r a s o ( 1 9 8 5 ) , who f o u n d t h a t l e t t e r s w e r e no b e t t e r r e p o r t e d a l o n e t h a n t h e y w e r e i n c o m b i n a t i o n w i t h c o l o r . The c o l o r - l e t t e r d i f f e r e n c e l i k e l y a r i s e s f r o m two s o u r c e s . C o l o r i s t h e more d i f f i c u l t o f t h e two f e a t u r e s h e r e , w i t h an o v e r a l l l o w e r a c c u r a c y . The o t h e r s o u r c e o f t h e d i f f e r e n c e may be t h e o r d e r o f r e p o r t i n g o f f e a t u r e s i n t h e c o n j u n c t i o n r e p o r t c o n d i t i o n . B e c a u s e i t i s d i f f i c u l t f o r E n g l i s h s p e a k e r s t o p u t a d j e c t i v e s a f t e r n o u n s ( e . g . \"T r e d \" ) , s u b j e c t s a l w a y s r e p o r t e d t h e c o l o r f i r s t a n d t h e n t h e l e t t e r . I f t h e y w e r e r e p o r t i n g f r o m a r a p i d l y d e c a y i n g t r a c e t h e i n f o r m a t i o n a b o u t t h e l e t t e r m i g h t h a v e d e c a y e d b e f o r e t h e y c o u l d r e p o r t i t . C e r a s o ( 1 9 8 5 ) , h o w e v e r , f o u n d no e f f e c t o f o r d e r o f r e p o r t o n a c c u r a c y f o r c o l o r a n d l e t t e r r e p o r t . T h e s e two f a c t o r s w o u l d i n f l a t e t h e d i f f e r e n c e b e t w e e n t h e two l e t t e r c o n d i t i o n s w h i l e k e e p i n g c o l o r p e r f o r m a n c e more o r l e s s t h e same. B e c a u s e o f t h e d i f f e r e n c e on l e t t e r s , I c a n n o t be c o n f i d e n t t h a t t h e b e t w e e n s e s s i o n p r e d i c t i o n d o e s n o t o v e r p r e d i c t c o n j u n c t i o n p e r f o r m a n c e ( i . e . t h e m e a s u r e 52 u n d e r e s t i m a t e s f e a t u r e p e r f o r m a n c e ) . F o r t h e s e r e a s o n s t h e c o m b i n e d e s t i m a t e o f c o n j u n c t i o n a d v a n t a g e seems t h e b e s t m e a s u r e o f a c t u a l c o n j u n c t i o n a d v a n t a g e . I n e x p e r i m e n t 1 a c l e a r p a r t i a l r e p o r t s u p e r i o r i t y was o b t a i n e d up t o 600 ms SOA f o r c o n j u n c t i o n p e r f o r m a n c e . W h i l e t h e t o t a l r e p o r t p e r f o r m a n c e f r o m e x p e r i m e n t 1 c a n n o t be s t a t i s t i c a l l y c o m p a r e d t o t h e p a r t i a l r e p o r t i n t h e o t h e r two e x p e r i m e n t s t h e a c t u a l numbers o b t a i n e d may be r o u g h l y c o m p a r e d . S i n c e t h e t r i a l s f r o m w h i c h t h e t o t a l r e p o r t m e a s u r e was t a k e n a r e t h o s e w here s u b j e c t s saw t h e l o n g e s t d u r a t i o n d i s p l a y s a n d w e r e t h e most p r a c t i c e d a t t h e t a s k i t i s r e a s o n a b l e t o a s sume t h a t t o t a l r e p o r t u n d e r an y o f t h e o t h e r c o n d i t i o n s w o u l d n o t e x c e e d t h a t o b t a i n e d h e r e . I f t h i s i s t h e c a s e we h a v e a p a r t i a l r e p o r t a d v a n t a g e a c r o s s a l l e x p e r i m e n t s a t a l l SOAs up t o 600 ms. C e r t a i n l y , t h e r e i s a c l e a r p a r t i a l r e p o r t a d v a n t a g e t o 300 ms SOA ( s e e T a b l e V I ) . A p a r t i a l r e p o r t a d v a n t a g e may a l s o be i n f e r r e d f r o m t h e h i g h l y s i g n i f i c a n t e f f e c t o f c u e d e l a y i n a l l e x p e r i m e n t s ( s e e T a b l e I V ) . 53 T a b l e V I Summary T a b l e f o r P a r t i a l R e p o r t P e r f o r m a n c e o n C o n j u n c t i o n s A c r o s s E x p e r i m e n t s SOA a v e r a g e number o f SD i t e m s r e p o r t e d W hole R e p o r t 2.05 0.444 E x p e r i m e n t 1 -200 7.96 0.098 0 6.24 1.979 200 3.11 1.329 300 3.00 1.387 400 2.83 1.440 600 2.88 2.007 1100 2.52 1.823 E x p e r i m e n t 2 0 6.00 1.876 70 4.80 2.473 100 4.46 1.833 140 3.48 1.447 320 3.12 1.450 1020 2.46 0.790 E x p e r i m e n t 3 0 6.53 0.996 125 4.58 0.963 200 4.25 1.151 300 3.75 1.086 1050 2.67 0.892 54 The Conjunction Advantage The major hypothesis of t h i s t h e s i s was not s t r o n g l y supported by the r e s u l t s . The advantage f o r c o n j u n c t i o n r e p o r t s o v e r what was p r e d i c t e d by i n d e p e n d e n t f e a t u r e r e p o r t s i s 3.3 p e r c e n t a v e r a g e d o v e r both types of p r e d i c t i o n . The d i r e c t i o n of t h i s d i f f e r e n c e i s c o n s i s t e n t a c r o s s experiments and types of p r e d i c t i o n , and so i t seems l i k e l y t o be r e l i a b l e . Subjects are r e p o r t i n g more than they s h o u l d be a b l e t o i f a l l they have access t o a r e separate f e a t u r e maps, y e t at the same time the advantage i s q u i t e a s m a l l one, and i s not s i g n i f i c a n t across both types of p r e d i c t i o n . A p o s s i b l e source of the c o n j u n c t i o n advantage (other than the e x i s t e n c e of a c o n j o i n e d r e p r e s e n t a t i o n ) may be found i n the nature of the task s u b j e c t s performed. Feature i n t e g r a t i o n t h e o r y s t a t e s t h a t f e a t u r e s may be d e t e c t e d w i t h o u t k n o w l e d g e o f t h e i r e x a c t l o c a t i o n s , w h i l e c o n j u n c t i o n s must be l o c a t e d to be r e p o r t e d . A t t e n t i o n i n t h i s paradigm i s s e l e c t i n g items on the b a s i s of t h e i r s p a t i a l l o c a t i o n s , so i n d i v i d u a l f e a t u r e s may not be more a v a i l a b l e than combinations of f e a t u r e s . T h i s would l e a d t o an u n d e r - r e p o r t i n g of f e a t u r e s r e l a t i v e to c o n j u n c t i o n s and r e l a t i v e t o t h e i r t r u e a v a i l a b i l i t y . Since r e p o r t of a 55 c o r r e c t c o n j u n c t i o n d e p e n d s o n t h e c o r r e c t e x t r a c t i o n o f b o t h f e a t u r e s c o m p o s i n g t h e i t e m , f e a t u r e r e p o r t s h o u l d a l w a y s e x c e e d c o n j u n c t i o n r e p o r t , a n d t h i s i s t r u e o f t h e p r e s e n t d a t a . H o w e v e r , i f f e a t u r e s a r e b e i n g u n d e r - r e p o r t e d i n r e l a t i o n t o t h e i r t r u e a v a i l a b i l i t y , t h e n t h e p r e d i c t i o n o f c o n j u n c t i o n p e r f o r m a n c e o b t a i n e d f r o m t h e p r o d u c t o f t h e o b s e r v e d f e a t u r e p e r f o r m a n c e a c t u a l l y u n d e r p r e d i c t s t h e e x p e c t e d c o n j u n c t i o n p e r f o r m a n c e . S i n c e t h e o b t a i n e d c o n j u n c t i o n a d v a n t a g e was s o s m a l l , a n d o n l y one t y p e o f p r e d i c t i o n was s i g n i f i c a n t , t h i s p o s s i b i l i t y c a n n o t be r e j e c t e d . I t i s p o s s i b l e t h a t o n c e more p e r m a n e n t r e p r e s e n t a t i o n s a r e e s t a b l i s h e d , c o m b i n a t i o n s o f f e a t u r e s a r e t i e d t o g e t h e r i n a h o l i s t i c r e p r e s e n t a t i o n . The o b j e c t f i l e s p r o p o s e d b y K a h n e m a n a n d T r e i s m a n ( 1 9 8 4 ) p r o v i d e a t e m p o r a r y r e p r e s e n t a t i o n t h a t c o u l d s e r v e t h i s p u r p o s e . Do we h a v e a n y r e a s o n t o b e l i e v e t h a t f e a t u r e s do n o t c o n t i n u e t o be r e p r e s e n t e d i n d e p e n d e n t l y ? C e r a s o ( 1 985) s u g g e s t e d t h a t l e t t e r s a n d c o l o r s a r e a l w a y s s t o r e d i n d e p e n d e n t l y . He s u g g e s t e d t h i s b e c a u s e l e t t e r - c o l o r c o m b i n a t i o n s d i d n o t show t h e same p a t t e r n o f r e s p o n s e s a s o t h e r s h a p e - c o l o r c o m b i n a t i o n s w hen s u b j e c t s w e r e a s k e d t o r e p o r t them. R e c a l l o f l e t t e r - c o l o r c o m b i n a t i o n s d i d n o t d i f f e r when p r e s e n t e d e i t h e r i n t h e same o b j e c t o r i n two d i f f e r e n t o b j e c t s . When s u b j e c t s p e r f o r m e d t h e same t a s k w i t h 56 g e o m e t r i c a l f o r m s a n d c o l o r s t h e y w e r e more a c c u r a t e when t h e f e a t u r e s w e r e c o m p o n e n t s o f t h e same s t i m u l u s r a t h e r t h a n l o c a t e d i n s e p a r a t e i t e m s . T h e s e r e s u l t s s u p p o r t o t h e r e v i d e n c e o n t h e p r i m a c y o f o b j e c t s f o r t h e g e o m e t r i c a l f o r m s ( e . g . Kahneman & H e n i k , 1 9 8 1 ) , b u t c o n t r a d i c t them i n t h e c a s e o f l e t t e r s . The r e s u l t s h o l d f o r b o t h a r e c a l l t e s t a n d f o r a s t r a i g h t f o r w a r d r e p o r t f r o m b r i e f d i s p l a y s ( i . e . l e s s t h a n 50 m s ) . C e r a s o s u g g e s t e d t h a t l e t t e r s h a v e a d u a l n a t u r e . A s w e l l a s b e i n g f o r m s , t h e y h a v e m e a n i n g a s s y m b o l s , a n d map o n t o t h e p h o n e t i c s t r u c t u r e o f t h e l a n g u a g e s t h a t u s e them. F o r l i t e r a t e p e o p l e , l e t t e r s may be v e r y e a s i l y e n c o d e d i n r e p r e s e n t a t i o n s t h a t a r e s i m p l e r t o r e c a l l t h a n o t h e r l e s s m e a n i n g f u l s h a p e s . T h i s r e p r e s e n t a t i o n i s d i f f e r e n t f r o m a f e a t u r e map, b u t s t i l l m a y b e q u i t e i n d e p e n d e n t o f o t h e r a t t r i b u t e s o f t h e s t i m u l u s , s i n c e t h e s y m b o l i c v a l u e o f t h e i t e m i s w h a t i s e x t r a c t e d . T h e r e i s n o e v i d e n c e i n t h e p r e s e n t d a t a t h a t a n y c o n j o i n e d r e p r e s e n t a t i o n o f t h e f e a t u r e s i n t h e d i s p l a y becomes more a v a i l a b l e o v e r t i m e . A t l e a s t f r o m a b o u t 100 ms SOA, t h e r e i s l i t t l e c h a n g e i n t h e a d v a n t a g e o f c o n j u n c t i o n s o v e r t h e p r e d i c t e d v a l u e . T h i s l a c k o f e f f e c t o f SOA o n t h e o b s e r v e d - p r e d i c t e d d i f f e r e n c e i s somewhat s u r p r i s i n g . The d i f f e r e n c e i s more o r l e s s c o n s t a n t o v e r a l l SOAs e x c e p t w h e r e n e a r p e r f e c t p e r f o r m a n c e o n a l l t h e 57 r e p o r t i n g c o n d i t i o n s r e d u c e s t h e o b s e r v e d - p r e d i c t e d d i f f e r e n c e t o n e a r l y z e r o . I f e i t h e r a f o r m i n g o r a d e c a y i n g c o n j u n c t i o n r e p r e s e n t a t i o n i s assumed, one w o u l d e x p e c t t o s e e some c h a n g e i n t h e r e l a t i v e a d v a n t a g e o f c o n j u n c t i o n r e p o r t s . O t h e r e v i d e n c e i n d i c a t e s t h a t , a t l e a s t i n s h o r t - t e r m memory, i n f o r m a t i o n a b o u t t h e i d e n t i t y o f i t e m s a nd t h e i r l o c a t i o n s i n t h e v i s u a l f i e l d a r e s t o r e d t o g e t h e r (Cumming & C o l t h e a r t , 1 9 6 9 ) . T h i s d a t a i s f o r t h e r e t e n t i o n o f i n f o r m a t i o n a b o u t s i n g l e f e a t u r e s , h o w e v e r , r a t h e r t h a n o f c o n j u n c t i o n s o f f e a t u r e s . So we do n o t s e e s t r o n g s u p p o r t f o r t h e n o t i o n t h a t a n e n d u r i n g c o n j o i n e d r e p r e s e n t a t i o n i s e s t a b l i s h e d o v e r t i m e . T h i s c o n c l u s i o n d o e s n o t f i t w e l l w i t h p h e n o m e n o l o g y . We a r e a ware o f o b j e c t s i n t h e e n v i r o n m e n t a s c o h e r e n t w h o l e s , a n d t h e same i s t r u e o f r e c a l l o f a remembered o b j e c t . E r r o r s The d e t a i l e d e r r o r a n a l y s i s i n e x p e r i m e n t 3 a l l o w s us t o r e a c h s e v e r a l c o n c l u s i o n s r e l e v a n t t o c u r r e n t i s s u e s i n i c o n i c memory. One s u c h i s s u e i s t h e r o l e t h a t i d e n t i t y a n d l o c a t i o n i n f o r m a t i o n p l a y i n t h e r e t e n t i o n a n d l o s s o f i n f o r m a t i o n f r o m i c o n i c memory. 58 T h e r e i s some e v i d e n c e t h a t i d e n t i t y a n d l o c a t i o n i n f o r m a t i o n may n o t f o l l o w t h e same t i m e c o u r s e . C l a r k , ( 1 9 6 9 ) f o u n d t h a t h e r s u b j e c t s w e r e n o t a b l e t o r e p o r t c o l o r s b y t h e i r l o c a t i o n i n a d i s p l a y , b u t w e r e a b l e t o r e p o r t t h e p r e s e n c e o f i t e m s o f a c e r t a i n c o l o r . Townsend ( 1 9 7 3 ) f o u n d t h a t s u b j e c t s p r o d u c e d n o p a r t i a l r e p o r t a d v a n t a g e when a r e c o g n i t i o n r a t h e r t h a n a r e c a l l p a r a d i g m was u s e d . The u s e o f r e c o g n i t i o n i n s t e a d o f r e c a l l i s p r o b l e m a t i c , s i n c e i t i s u n l i k e l y t h a t t h e same p r o c e s s e s a r e u s e d i n b o t h , w h i c h makes c o m p a r i s o n s b e t w e e n t h e two d i f f i c u l t t o a s s e s s . I n T o w n s e n d ' s d e s i g n ( l e t t e r r e c o g n i t i o n ) i t i s p o s s i b l e t h a t s u b j e c t s w e r e m a t c h i n g s t i m u l i t o p r o b e l e t t e r s b a s e d upon d i s t i n c t i v e f e a t u r e s r a t h e r t h a n i d e n t i t y , s o t h e l a c k o f e f f e c t may show t h a t i n f o r m a t i o n a b o u t t h e s t i m u l u s i s m a i n t a i n e d , b u t n o t t h e e x a c t n a t u r e o f t h a t i n f o r m a t i o n . Townsend c o n c l u d e d t h a t s p a t i a l a n d i d e n t i t y i n f o r m a t i o n w e r e s t o r e d i n d e p e n d e n t l y a n d f o l l o w a d i f f e r e n t t i m e c o u r s e . I n a d d i t i o n , T o w n s e n d c o m p a r e d l o n g a n d s h o r t c u e d u r a t i o n s . A l o n g d u r a t i o n c u e (900 ms) harmed, r a t h e r t h a n i m p r o v e d , p e r f o r m a n c e when r e p o r t was c u e d b y l o c a t i o n . T h i s was somewhat s u r p r i s i n g , s i n c e a p l a u s i b l e r e a s o n f o r t h e e x i s t e n c e o f l o c a t i o n e r r o r s i s m i s p e r c e p t i o n o f t h e c u e l o c a t i o n e x a c e r b a t e d b y s h o r t c u e d u r a t i o n s . The p r e s e n t r e s u l t ( e x p e r i m e n t 3 ) , w h i c h e m p l o y e d a 500 ms c u e f o r one 59 h a l f o f t h e s u b j e c t s a n d a 50 ms c u e f o r t h e o t h e r h a l f , s howed no d i f f e r e n c e i n p e r f o r m a n c e b e t w e e n t h e 50 ms and t h e 500 ms c u e s . T h i s a p p e a r s t o c o n t r a d i c t T o w n s e n d ' s r e s u l t , b u t 900 ms i s a much l o n g e r c u e d u r a t i o n a n d may hamper p e r f o r m a n c e f o r o t h e r r e a s o n s . The r e s u l t t h a t was r e p l i c a t e d was t h e l a c k o f a n a d v a n t a g e f o r t h e l o n g e r c u e d u r a t i o n . I s I c o n i c Memory P r e - c a t e g o r i c a l o r p o s t - c a t e g o r i c a l ? Can t h e e r r o r a n a l y s i s i n e x p e r i m e n t 3 s h e d an y l i g h t o n t h e d e b a t e a b o u t w h e r e a t t e n t i o n i n t e r v e n e s i n i c o n i c memory? I b e l i e v e i t c a n , b u t o n l y i n d i r e c t l y . I f we assume t h a t a l l i t e m s i n a d i s p l a y a r e a u t o m a t i c a l l y e n c o d e d and i d e n t i f i e d t h e n a l l i t e m s p r e s e n t i n a d i s p l a y s h o u l d be p r o c e s s e d w h e t h e r o r n o t t h e y a r e a t t e n d e d . I f i d e n t i t y i n f o r m a t i o n ( p o s t - p r o c e s s i n g ) d e c a y s , t h e n we w o u l d e x p e c t t o s e e t h e number o f i n t r u s i o n e r r o r s i n c r e a s e r e l a t i v e t o t h e number o f l o c a t i o n e r r o r s . C o n v e r s e l y , i f l o c a t i o n i n f o r m a t i o n d e c a y s we e x p e c t a n i n c r e a s e i n l o c a t i o n e r r o r s . T h i s l a t t e r p o s i t i o n i s t h e o n e w h i c h has b e e n s u p p o r t e d b y s e v e r a l t h e o r i s t s ( T o wnsend, 1973; B u t l e r , 1 9 8 0 ) . T r e i s m a n a n d G e l a d e ( 1 9 8 0 ) f o u n d t h a t l o c a t i o n i n f o r m a t i o n p l a y e d a d i f f e r e n t r o l e when a t a s k r e q u i r e d d e t e c t i n g a f e a t u r e i n a b r i e f l y p r e s e n t e d d i s p l a y t h a n i t d i d when t h e t a s k r e q u i r e d t h e d e t e c t i o n o f a c o n j u n c t i o n . T r e i s m a n a n d G e l a d e l o o k e d a t t h e c o n d i t i o n a l p r o b a b i l i t i e s f o r c o r r e c t d e t e c t i o n o f a 60 t a r g e t g i v e n t h a t i t was m i s l o c a t e d . M i s l o c a t i o n d i d not a f f e c t t h e a c c u r a c y w i t h w h i c h f e a t u r e t a r g e t s were r e p o r t e d , but i t d i d a f f e c t the accuracy f o r c o n j u n c t i o n t a r g e t s . In the pr e s e n t study we can take a f i n e - g r a i n e d look a t e r r o r s s u b j e c t s are making. Some l o c a t i o n e r r o r s are indeed m i s l o c a t i o n s of e n t i r e items, where c o l o r and l e t t e r move to g e t h e r . These, however, occur l e s s f r e q u e n t l y than the a d j u s t e d i n t r u s i o n e r r o r s . The most f r e q u e n t l y o c c u r r i n g e r r o r i s one where both c o l o r and l e t t e r are m i s l o c a t e d w i t h i n the d i s p l a y , but they are independently m i s l o c a t e d . These are c o n j u n c t i o n e r r o r s , or i l l u s o r y c o n j u n c t i o n s , s i n c e they are combinations of f e a t u r e s t h a t were not i n f a c t p r e s e n t i n the d i s p l a y (see F i g u r e 4). The presence of t h i s l a r g e number of c o n j u n c t i o n e r r o r s suggests t h a t i c o n i c memory does not c o n t a i n a u n i t i z e d and i d e n t i f i e d r e p r e s e n t a t i o n of the items i n a d i s p l a y . Rather, i t lends support to the i d e a t h a t what i s s t o r e d i s an independent r e p r e s e n t a t i o n of the f e a t u r e s p r e s e n t and s e p a r a t e i n f o r m a t i o n a b o u t t h e i r l o c a t i o n s . T h i s i n f o r m a t i o n must be combined a t a l a t e r p o i n t f o r the c o n j u n c t i o n t o be c o r r e c t l y r e p o r t e d . I t a l s o confirms the r e s u l t t h a t i n f o r m a t i o n about items i n a d i s p l a y , be t h a t i n f o r m a t i o n a b out f e a t u r e s or the i d e n t i t i e s of e n t i r e o b j e c t s , has a d i f f e r e n t time course. 6 1 E x t e n s i o n s o f t h e r e s e a r c h A s h b y a n d Townsend (1986) p r o p o s e d a s e r i e s o f t e s t s t h a t p r o v i d e c o n v e r g i n g e v i d e n c e f o r p e r c e p t u a l i n d e p e n d e n c e . T h e t e s t s s t a r t w i t h a t e s t o f s a m p l i n g i n d e p e n d e n c e , a n d p r o g r e s s t o a c h e c k o f t h e c o n d i t i o n a l p r o b a b i l i t i e s o f g e t t i n g a f e a t u r e c o r r e c t g i v e n e a c h p o s s i b l e v a l u e o n a s e c o n d d i m e n s i o n . I f t h e d a t a s e t p a s s e s a l l o f t h e i r p r o p o s e d t e s t s , i t i s a s s u m e d t o d e m o n s t r a t e t h e e x i s t e n c e o f p e r c e p t u a l i n d e p e n d e n c e f o r t h e d i m e n s i o n s a n d p r o c e s s u n d e r c o n s i d e r a t i o n . S i n c e p e r c e p t u a l i n d e p e n d e n c e m u s t b e i n f e r r e d r a t h e r t h a n o b s e r v e d o n l y a s t r o n g c a s e b a s e d o n c o n v e r g i n g e v i d e n c e c a n j u s t i f y a c o n c l u s i o n o f p e r c e p t u a l i n d e p e n d e n c e . The p r e s e n t a n a l y s e s r e f l e c t a s t e p o f A s h b y ' s and Townsend's p r o c e d u r e , b u t n o t t h e c o m p l e t e s e r i e s . A l o g i c a l e x t e n s i o n o f t h i s r e s e a r c h i s t o r e - r u n t h e same p a r a d i g m u s i n g i n t e g r a l f e a t u r e s i n s t e a d o f s e p a r a b l e o n e s . I f i n t e g r a l f e a t u r e s a r e u n i t a r y a s i s c l a i m e d , t h e n we s h o u l d s e e a s u b s t a n t i a l a d v a n t a g e f o r c o n j u n c t i o n r e p o r t o v e r f e a t u r e r e p o r t . I f t h e s e s t i m u l i a r e t r u l y h o l i s t i c , t h e n i t may be d i f f i c u l t f o r s u b j e c t s t o r e p o r t f e a t u r e s i n d e p e n d e n t l y a n d f e a t u r e r e p o r t may a c t u a l l y be l o w e r i n a c c u r a c y t h a n c o n j u n c t i o n r e p o r t . 62 A s e c o n d e x t e n s i o n i s a s i m p l e c h e c k t o s e e i f t h e t y p e o f a t t e n t i o n a l m a n i p u l a t i o n i n v o l v e d i n t h i s t a s k i s t h e o n l y one t h a t w o u l d w o r k . B r i a n d and K l e i n (1987) c l a i m t h a t o n l y d r a w n a t t e n t i o n ( o r i e n t i n g ) , w h i c h t h e y c o n t e n d i s a u t o m a t i c a l l y a t t r a c t e d t o p e r i p h e r a l l y a p p e a r i n g s t i m u l i , a f f e c t s f e a t u r e i n t e g r a t i o n . T h e y f o u n d t h a t c e n t r a l l y d i r e c t e d a t t e n t i o n ( i . e . w i t h a d i r e c t i o n a l p o i n t e r ) d i d n o t i m p r o v e t h e c o n j o i n i n g o f f e a t u r e s , w h i l e p e r i p h e r a l a t t e n t i o n a l c u e s d i d . A s i m p l e r e p l i c a t i o n o f t h e p r e s e n t r e s u l t s w i t h c e n t r a l c u e s t o r e p o r t s h o u l d show no a d v a n t a g e f o r t h e c o n j u n c t i o n r e p o r t c o n d i t i o n i f t h e y a r e r i g h t . I f t h e y a r e n o t , t h e r e s u l t s s h o u l d n o t d i f f e r f r o m t h o s e r e p o r t e d h e r e . A n o t h e r e x t e n s i o n o f t h e p r e s e n t w o r k i s t o d e v e l o p a p a r a d i g m t h a t w i l l a l l o w t h e measurement o f b o t h f e a t u r e a n d c o n j u n c t i o n r e p o r t w i t h o u t n e c e s s i t a t i n g t h a t e a c h o f t h e s e be l o c a t e d b e f o r e t h e y a r e r e p o r t e d . U s i n g a s i m p l e r e c o g n i t i o n p a r a d i g m i s n o t t h e b e s t s o l u t i o n . T h i s h a s b e e n t r i e d b y o t h e r r e s e a r c h e r s , b u t a d i r e c t c o m p a r i s o n o f r e c o g n i t i o n a n d r e c a l l i s p r o b l e m a t i c . The c r e a t i o n o f a d i r e c t l y c o m p a r a b l e s i t u a t i o n i s d i f f i c u l t ; t o u s e t h e c u r r e n t p a r a d i g m one w o u l d n e e d e q u a l numbers o f f e a t u r e e l e m e n t s p r e s e n t a n d a b s e n t f r o m a d i s p l a y ( o t h e r w i s e t h e t a s k c a n b e c o m e \" m a t c h t h e m i s s i n g e l e m e n t \" ) . T h i s r e q u i r e m e n t i s i m p o s s i b l e t o s a t i s f y w i t h c o l o r e d l e t t e r s a s 63 s t i m u l i . E i t h e r t h e number o f c o l o r s r e q u i r e d makes them become i n d i s c r i r a i n a b l e o r t h e d i s p l a y s i z e s must be k e p t s o s m a l l t h a t t h e t a s k i s much t o e a s y . A p o s s i b l e p a r a d i g m i s a m o d i f i c a t i o n o f t h e one w h i c h E r i k s e n a n d C o l l i n s (1967) u s e d . They p r e s e n t e d s u b j e c t s w i t h two d i s p l a y s o f a p p a r e n t l y random d o t s . I f s u b j e c t s c o u l d i n t e g r a t e t h e two d i s p l a y s , t h e y saw a t h r e e l e t t e r n o n s e n s e s y l l a b l e . I f t h e y c o u l d n o t , t h e y saw o n l y r andom d o t s . S t i m u l i c o u l d be c r e a t e d t o p r o d u c e a p a t t e r n t h a t i s o n l y d i s c r i m i n a b l e when i n t e g r a t e d , and t h i s p a t t e r n c o u l d be c o m p o s e d o f e i t h e r f e a t u r e o r c o n j u n c t i o n s t i m u l i . I f c o n j u n c t i v e l y d e f i n e d i t e m s c a n be i n t e g r a t e d t o f o r m a p a t t e r n , t h e n a u n i t a r y r e p r e s e n t a t i o n o f t h e f i r s t d i s p l a y s t i m u l i w o u l d be i m p l i e d . T h i s w o u l d be s t r o n g s u p p o r t f o r a n e a r l y i n t e g r a t e d c o n j u n c t i o n r e p r e s e n t a t i o n . C o n c l u s i o n To e n d t h e d i s c u s s i o n , I w i l l s u m m a r i z e t h e c o n c l u s i o n s d r a w n f r o m t h i s r e s e a r c h . I n t h e p r e s e n t i n v e s t i g a t i o n I f o u n d a s u b s t a n t i a l a n d s i g n i f i c a n t p a r t i a l r e p o r t a d v a n t a g e f o r b o t h c o n j u n c t i o n s a n d f e a t u r e s t h a t w e r e c u e d b y s p a t i a l l o c a t i o n . T h i s s u p e r i o r i t y e x t e n d e d t o 600 ms SOA, w h i c h i s l o n g e r t h a n i s u s u a l l y t h e c a s e . A c r o s s t h e t h r e e e x p e r i m e n t s I o b s e r v e d a s l i g h t a d v a n t a g e f o r c o n j u n c t i o n r e p o r t s r e l a t i v e t o t h e p r e d i c t e d 64 v a l u e f r o m t h e i n d e p e n d e n t f e a t u r e r e p o r t s . The a d v a n t a g e a v e r a g e d a b o u t t h r e e p e r c e n t and was n o n - s i g n i f i c a n t f o r t h e b e t w e e n s e s s i o n p r e d i c t i o n , b u t s i g n i f i c a n t f o r t h e w i t h i n s e s s i o n p r e d i c t i o n . The message f r o m t h e s e m e a s u r e s i s t h u s e q u i v o c a l . H o w e v e r , t h i s r e s u l t i s b a l a n c e d b y t h e o b s e r v a t i o n t h a t s u b j e c t s a r e m a k i n g a l a r g e number o f c o n j u n c t i o n e r r o r s r e l a t i v e t o i n t r u s i o n e r r o r s and m i s l o c a t e d c o n j u n c t i o n s . T h e h y p o t h e s i s t h a t i s b e s t s u p p o r t e d b y t h e s e r e s u l t s i s t h e c o m p r o m i s e p o s i t i o n d i s c u s s e d i n t h e i n t r o d u c t i o n . T h i s i s t h e p o s s i b i l i t y t h a t b o t h i n d e p e n d e n t and h o l i s t i c r e p r e s e n t a t i o n s e x i s t . A p u z z l e i s w h y c o n j u n c t i o n s d o n o t e x h i b i t a c l e a r e r a d v a n t a g e t h a n t h e t h r e e p e r c e n t i n d i c a t e d h e r e . I t i s p o s s i b l e t h a t s u b j e c t s a r e r e p o r t i n g c o n j u n c t i o n s f r o m a v e r y e a r l y r e p r e s e n t a t i o n , p e r h a p s e v e n f r o m maps t h a t e n c o d e c o m b i n a t i o n s o f c o l o r and o r i e n t a t i o n . 65 R e f e r e n c e s A l l p o r t , D. A., A n t o n i s , B., & R e y n o l d s , P. ( 1 9 7 2 ) . On t h e d i v i s i o n o f a t t e n t i o n : A d i s p r o o f o f t h e s i n g l e c h a n n e l h y p o t h e s i s . Q u a r t e r l y J o u r n a l o f E x p e r i m e n t a l P s y c h o l o g y , 24, 225-235. A n d e r s o n , N . H. ( 1 9 8 1 ) . F o u n d a t i o n s o f I n f o r m a t i o n  I n t e g r a t i o n . New Y o r k : A c a d e m i c P r e s s . A s h b y , F. G., & T o w n s e n d , J . T. (19 8 6 ) . V a r i e t i e s o f P e r c e p t u a l I n d e p e n d e n c e . P s y c h o l o g i c a l R e v i e w , 93 ( 2 ) , 1 5 4 - 1 7 9 . A v e r b a c h , E., & C o r i e l l , A. S. ( 1 9 6 1 ) . S h o r t - t e r m memory i n v i s i o n . The B e l l S y s t e m s T e c h n i c a l J o u r n a l , 40, 309-328. B i e d e r m a n , I . , & C h e c k o s k y , S. F. ( 1 9 7 0 ) . P r o c e s s i n g r e d u n d a n t i n f o r m a t i o n . J o u r n a l o f E x p e r i m e n t a l  P s y c h o l o g y , 8 3 , 486-490. B u t l e r , B. E. ( 1 9 8 0 ) . S e l e c t i v e a t t e n t i o n a n d s t i m u l u s l o c a l i z a t i o n i n v i s u a l p e r c e p t i o n . C a n a d i a n J o u r n a l o f  P s y c h o l o g y , 34, 119-133. B u t l e r , B. E. , B r o w s e , R. A., & M e w h o r t , D . J . K . ( 1 9 8 6 ) . Do l e t t e r f e a t u r e s m i g r a t e ? : I t d e p e n d s on t h e t a s k . P a p e r p r e s e n t e d a t t h e m e e t i n g o f t h e C a n a d i a n P s y c h o l o g i c a l A s s o c i a t i o n , T o r o n t o , O n t a r i o , J u n e , 1986. C e r a s o , J . ( 1 9 8 5 ) . U n i t f o r m a t i o n i n p e r c e p t i o n a n d memory. The P s y c h o l o g y o f L e a r n i n g a n d M o t i v a t i o n , 1 9, 1 7 9 - 2 1 0 . C l a r k , S. E. ( 1 9 6 9 ) . R e t r i e v a l o f c o l o r i n f o r m a t i o n f r o m p r e p e r c e p t u a 1 m e m o r y . J o u r n a l o f E x p e r i m e n t a l  P s y c h o l o g y , 82 ( 2 ) , 263-266. C o l t h e a r t , M. ( 1 9 8 0 ) . I c o n i c m e m o r y a n d v i s i b l e p e r s i s t e n c e . P e r c e p t i o n a n d P s y c h o p h y s i c s , 27, 1 8 3 -228. C o l t h e a r t , M. ( 1 9 8 3 ) . I c o n i c memory. P h i l o s o p h i c a l  T r a n s a c t i o n s o f t h e R o y a l S o c i e t y o f L o n d o n ( S e r i e s B ) , 302, 2 8 3-294. 66 Cumming, G., & C o l t h e a r t , M. ( 1 9 6 9 ) . S h o r t - t e r m memory: A r e i t e m a n d p o s i t i o n i n f o r m a t i o n s t o r e d i n d e p e n d e n t l y ? . P s y c h o n o m i c S c i e n c e , 15 ( 4 ) , 216-218. D a v i d s o n , M. L., F o x , M. J . , & D i c k , A. 0. ( 1 9 7 3 ) . E f f e c t s o f e y e movements o n b a c k w a r d m a s k i n g a nd p e r c e i v e d l o c a t i o n . P e r c e p t i o n a nd P s y c h o p h y s i c s , 14, 110 - 1 1 6 . De V a l o i s , R. L., & De V a l o i s , K. K. ( 1 9 8 0 ) . S p a t i a l v i s i o n . A n n u a l R e v i e w o f P s y c h o l o g y , 3 1 , 3 0 9 - 3 4 1 . D i L o l l o , V. ( 1 9 7 7 ) . T e m p o r a l c h a r a c t e r i s t i c s o f i c o n i c memory. N a t u r e , 267 , 241-243. E r i k s e n , C. W. , & C o l l i n s , J . F. ( 1 9 6 7 ) . Some t e m p o r a l c h a r a c t e r i s t i c s o f v i s u a l p a t t e r n p e r c e p t i o n . J o u r n a l  o f E x p e r i m e n t a l P s y c h o l o g y , 74, 476-484. E r i k s e n , C. W. , & S c h u l t z , D. W. ( 1 9 7 8 ) . T e m p o r a l f a c t o r s i n v i s u a l i n f o r m a t i o n p r o c e s s i n g : A t u t o r i a l r e v i e w . I n J . R e q u i n ( E d . ) , A t t e n t i o n a n d P e r f o r m a n c e V I I , H i l l s d a l e , N . J . : E r l b a u m . G a r n e r , W. R. ( 1 9 7 4 ) . The p r o c e s s i n g o f i n f o r m a t i o n a n d  s t r u c t u r e . P o t o m a c , M.D.: L a w r e n c e E r l b a u m . G a r n e r , W. R., & F e l f o l d y , G. L. ( 1 9 7 0 ) . I n t e g r a l i t y o f s t i m u l u s d i m e n s i o n s i n v a r i o u s t y p e s o f i n f o r m a t i o n p r o c e s s i n g . C o g n i t i v e P s y c h o l o g y , 1, 2 2 5 - 2 4 1 . G i b s o n , J . J . ( 1 9 5 9 ) . P e r c e p t i o n a s a f u n c t i o n o f s t i m u l a t i o n . I n S. K o c h ( E d . ) , P s y c h o l o g y : A s t u d y o f  a s c i e n c e , 1, 4 5 6 - 5 0 1 . H a b e r , R. N. ( 1 9 8 3 ) . The i m p e n d i n g d e m i s e o f t h e i c o n : A c r i t i q u e o f t h e c o n c e p t o f i c o n i c s t o r a g e i n v i s u a l i n f o r m a t i o n p r o c e s s i n g . The B e h a v i o r a l a n d B r a i n  S c i e n c e s , J 5 , 1-11. H u b e l , D. H. , & W i e s e l , T. N. ( 1 9 5 9 ) . R e c e p t i v e f i e l d s o f s i n g l e n e u r o n s i n t h e c a t ' s s t r i a t e c o r t e x . J o u r n a l o f  P h y s i o l o g y , 148, 5 7 4 - 5 9 1 . H u b e l , D. H., & W i e s e l , T. N. ( 1 9 6 8 ) . R e c e p t i v e f i e l d s a n d f u n c t i o n a l a r c h i t e c t u r e o f m o n k e y s t r i a t e c o r t e x . J o u r n a l o f P h y s i o l o g y , 1 9 5 , 2 1 5 - 2 4 3 . 67 K a h n e m a n , D. ( 1 9 7 3 ) . A t t e n t i o n a n d E f f o r t . E n g l e w o o d C l i f f s , N . J . : P r e n t i c e - H a l l . Kahneman, D. & H e n i k , A. ( 1 9 8 1 ) . P e r c e p t u a l o r g a n i z a t i o n a n d a t t e n t i o n . I n M. K u b o v y a n d J . R. P o m e r a n t z ( E d s . ) , P e r c e p t u a l O r g a n i z a t i o n . H i l l s d a l e , N . J . : E r l b a u m . Kahneman, D. , & T r e i s m a n , A. ( 1 9 8 4 ) . C h a n g i n g v i e w s o f a t t e n t i o n a n d a u t o m a t i c i t y . I n R. P a r a s u r a m a n , R. D a v i e s , a n d J . B e a t t y ( E d s . ) , V a r i e t i e s o f A t t e n t i o n , New Y o r k : A c a d e m i c P r e s s . L o c k h e a d , G. R. ( 1 9 6 6 ) . E f f e c t s o f d i m e n s i o n a l r e d u n d a n c y o n v i s u a l d i s c r i m i n a t i o n . J o u r n a l o f E x p e r i m e n t a l  P s y c h o l o g y , 7 2 , 95-104. L o c k h e a d , G. R. (19 7 2 ) . P r o c e s s i n g d i m e n s i o n a l s t i m u l i . P s y c h o l o g i c a l R e v i e w , 79 ( 5 ) , 410-419. M e r i k l e , P. M. ( 1 9 8 0 ) . S e l e c t i o n f r o m v i s u a l p e r s i s t e n c e b y p e r c e p t u a l g r o u p s a n d c a t e g o r y m e m b e r s h i p . J o u r n a l o f  E x p e r i m e n t a l P s y c h o l o g y : G e n e r a l , 109, 279-295. P a s h l e r , H. ( 1 9 8 4 ) . E v i d e n c e a g a i n s t l a t e s e l e c t i o n : S t i m u l u s q u a l i t y e f f e c t s i n p r e v i e w e d d i s p l a y s . J o u r n a l o f E x p e r i m e n t a l P s y c h o l o g y : Human P e r c e p t i o n  a n d P e r f o r m a n c e , 10 ( 3 ) , 429-448. P r i n z m e t a l , W. , P r e s t i , D. , & P o s n e r , M. ( 1 9 8 6 ) . Does a t t e n t i o n a f f e c t v i s u a l f e a t u r e i n t e g r a t i o n ? . J o u r n a l  o f E x p e r i m e n t a l P s y c h o l o g y : Human P e r c e p t i o n a n d  P e r f o r m a n c e , 12 ( 3 ) , 361-369. S p e r l i n g , G. ( 1 9 6 0 ) . The i n f o r m a t i o n a v a i l a b l e i n b r i e f v i s u a l p r e s e n t a t i o n s . P s y c h o l o g i c a l M o n o g r a p h s , 74 (11) . S p e r l i n g , G. ( 1 9 6 7 ) . S u c c e s s i v e a p p r o x i m a t i o n s t o a m o d e l f o r s h o r t - t e r m memory. A c t a P s y c h o l o g i c a , 27, 2 8 5 - 2 9 2 . T o w n s e n d , V. M. ( 1 9 7 3 ). L o s s o f s p a t i a l and i d e n t i t y i n f o r m a t i o n f o l l o w i n g a t a c h i s t o s c o p i c e x p o s u r e . J o u r n a l o f E x p e r i m e n t a l P s y c h o l o g y , 98 ( 1 ) , 113-118. T r e i s m a n , A. M. ( 1 9 6 9 ) . S t r a t e g i e s a n d m o d e l s o f s e l e c t i v e a t t e n t i o n . P s y c h o l o g i c a l R e v i e w , 7 6 , 282-299. 68 T r e i s m a n , A. M. ( 1 9 8 2 ) . F o c u s e d a t t e n t i o n i n t h e p e r c e p t i o n a nd r e t r i e v a l o f m u l t i d i m e n s i o n a l s t i m u l i . P e r c e p t i o n  a nd P s y c h o p h y s i c s , 22 ( 1 ) , 1-11. T r e i s m a n , A. M. ( 1 9 8 6 ) . P r o p e r t i e s , p a r t s , a n d o b j e c t s . I n K. R. B o f f , L. K a u f m a n , & J . P. Thomas, ( E d s . ) Handbook  o f P e r c e p t i o n a n d Human P e r f o r m a n c e : C o g n i t i v e  P r o c e s s e s a n d P e r f o r m a n c e , ( V o l . 2 ) , New Y o r k : J o h n W i l e y . T r e i s m a n , A. M., & G e l a d e , G. ( 1 9 8 0 ) . A f e a t u r e i n t e g r a t i o n t h e o r y o f a t t e n t i o n . C o g n i t i v e P s y c h o l o g y , 12, 97-136 T r e i s m a n , A. M. , & G o r m i c a n , S. ( i n p r e p a r a t i o n ) . F e a t u r e a n a l y s i s i n e a r l y v i s i o n : E v i d e n c e f r o m s e a r c h a s y m m e t r i e s . T r e i s m a n , A. M. , R u s s e l l , R. , & G r e e n , J . ( 1 9 7 5 ) . B r i e f v i s u a l s t o r a g e o f s h a p e and movement. I n P. M. A. R a b b i t t & S. D o r n i c ( E d s . ) , A t t e n t i o n and P e r f o r m a n c e V, L o n d o n : A c a d e m i c P r e s s . T r e i s m a n , A. M. , & S c h m i d t , H. ( 1 9 8 2 ) . I l l u s o r y c o n j u n c t i o n s i n t h e p e r c e p t i o n o f o b j e c t s . C o g n i t i v e  P s y c h o l o g y , 14 1 0 7 - 1 4 1 . T r e i s m a n , A. M. , S y k e s , M. , & G e l a d e , G. ( 1 9 7 7 ) . S e l e c t i v e a t t e n t i o n a n d s t i m u l u s i n t e g r a t i o n . I n S. D o r n i c ( E d . ) , A t t e n t i o n a n d P e r f o r m a n c e , V I , H i l l s d a l e New J e r s e y : L a w r e n c e E r l b a u m . V o n W r i g h t , J . M. ( 1 9 6 8 ) . S e l e c t i o n i n v i s u a l i m m e d i a t e memory. Q u a r t e r l y J o u r n a l o f E x p e r i m e n t a l P s y c h o l o g y , 20, 6 2 - 6 8 . ","attrs":{"lang":"en","ns":"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note","classmap":"oc:AnnotationContainer"},"iri":"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note","explain":"Simple Knowledge Organisation System; Notes are used to provide information relating to SKOS concepts. There is no restriction on the nature of this information, e.g., it could be plain text, hypertext, or an image; it could be a definition, information about the scope of a concept, editorial information, or any other type of information."}],"Genre":[{"label":"Genre","value":"Thesis\/Dissertation","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/hasType","classmap":"dpla:SourceResource","property":"edm:hasType"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/hasType","explain":"A Europeana Data Model Property; This property relates a resource with the concepts it belongs to in a suitable type system such as MIME or any thesaurus that captures categories of objects in a given field. It does NOT capture aboutness"}],"IsShownAt":[{"label":"DOI","value":"10.14288\/1.0097265","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/isShownAt","classmap":"edm:WebResource","property":"edm:isShownAt"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/isShownAt","explain":"A Europeana Data Model Property; An unambiguous URL reference to the digital object on the provider\u2019s website in its full information context."}],"Language":[{"label":"Language","value":"eng","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/language","classmap":"dpla:SourceResource","property":"dcterms:language"},"iri":"http:\/\/purl.org\/dc\/terms\/language","explain":"A Dublin Core Terms Property; A language of the resource.; Recommended best practice is to use a controlled vocabulary such as RFC 4646 [RFC4646]."}],"Program":[{"label":"Program (Theses)","value":"Psychology","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeDiscipline","classmap":"oc:ThesisDescription","property":"oc:degreeDiscipline"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeDiscipline","explain":"UBC Open Collections Metadata Components; Local Field; Indicates the program for which the degree was granted."}],"Provider":[{"label":"Provider","value":"Vancouver : University of British Columbia Library","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/provider","classmap":"ore:Aggregation","property":"edm:provider"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/provider","explain":"A Europeana Data Model Property; The name or identifier of the organization who delivers data directly to an aggregation service (e.g. Europeana)"}],"Publisher":[{"label":"Publisher","value":"University of British Columbia","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/publisher","classmap":"dpla:SourceResource","property":"dcterms:publisher"},"iri":"http:\/\/purl.org\/dc\/terms\/publisher","explain":"A Dublin Core Terms Property; An entity responsible for making the resource available.; Examples of a Publisher include a person, an organization, or a service."}],"Rights":[{"label":"Rights","value":"For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https:\/\/open.library.ubc.ca\/terms_of_use.","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/rights","classmap":"edm:WebResource","property":"dcterms:rights"},"iri":"http:\/\/purl.org\/dc\/terms\/rights","explain":"A Dublin Core Terms Property; Information about rights held in and over the resource.; Typically, rights information includes a statement about various property rights associated with the resource, including intellectual property rights."}],"ScholarlyLevel":[{"label":"Scholarly Level","value":"Graduate","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#scholarLevel","classmap":"oc:PublicationDescription","property":"oc:scholarLevel"},"iri":"https:\/\/open.library.ubc.ca\/terms#scholarLevel","explain":"UBC Open Collections Metadata Components; Local Field; Identifies the scholarly level of the author(s)\/creator(s)."}],"Title":[{"label":"Title ","value":"Feature and conjunction information from brief visual displays","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/title","classmap":"dpla:SourceResource","property":"dcterms:title"},"iri":"http:\/\/purl.org\/dc\/terms\/title","explain":"A Dublin Core Terms Property; The name given to the resource."}],"Type":[{"label":"Type","value":"Text","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/type","classmap":"dpla:SourceResource","property":"dcterms:type"},"iri":"http:\/\/purl.org\/dc\/terms\/type","explain":"A Dublin Core Terms Property; The nature or genre of the resource.; Recommended best practice is to use a controlled vocabulary such as the DCMI Type Vocabulary [DCMITYPE]. To describe the file format, physical medium, or dimensions of the resource, use the Format element."}],"URI":[{"label":"URI","value":"http:\/\/hdl.handle.net\/2429\/26822","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#identifierURI","classmap":"oc:PublicationDescription","property":"oc:identifierURI"},"iri":"https:\/\/open.library.ubc.ca\/terms#identifierURI","explain":"UBC Open Collections Metadata Components; Local Field; Indicates the handle for item record."}],"SortDate":[{"label":"Sort Date","value":"1987-12-31 AD","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/date","classmap":"oc:InternalResource","property":"dcterms:date"},"iri":"http:\/\/purl.org\/dc\/terms\/date","explain":"A Dublin Core Elements Property; A point or period of time associated with an event in the lifecycle of the resource.; Date may be used to express temporal information at any level of granularity. Recommended best practice is to use an encoding scheme, such as the W3CDTF profile of ISO 8601 [W3CDTF].; A point or period of time associated with an event in the lifecycle of the resource.; Date may be used to express temporal information at any level of granularity. Recommended best practice is to use an encoding scheme, such as the W3CDTF profile of ISO 8601 [W3CDTF]."}]}