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Feature and conjunction information from brief visual displays Grabowecky, Marcia F. 1987

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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 © 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 •r-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 • 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 £ % 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. 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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. 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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 . 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