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UBC Theses and Dissertations

Words and pictures in a short-term memory task Ternes, Willi 1971

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WORDS AND PICTURES IN A SHORT-TERM MEMORY TASK by WILLI TERNES B.A., Un iver s i t y of B r i t i s h Columbia, 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in the Department of Psychology We accept t h i s thes i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1971 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f • Psychology The U n i v e r s i t y o f B r i t i s h C o l umbia V a n c o u v e r 8, Canada Date May I , 1971 i ABSTRACT The fo l lowing se r i e s of experiments was designed to invest igate verbal and v i sua l coding d i f fe rences fo r v i s u a l l y presented words and t h e i r corresponding p ic tures in a STM task. Results show that verbal and v i sua l short-term coding depends on task requirements. In a f ree r e c a l l s i t u a t i o n , words and p ic tures have to be labe l led f o r the response task, and sub-sequent r e c a l l scores r e f l e c t verbal coding in both cond i t ions . If verbal coding of p i c tures can be reduced, as in a recogni t ion task, evidence for verbal and v i sua l short-term coding processes can be obtained in con-junct ion with verbal in ter ference and rehearsal a c t i v i t i e s during the r e -tent ion i n t e r v a l . The damaging e f f e c t s of verbal in ter ference and the f a c i l i t a t i v e e f f e c t s of verbal rehearsal for the verbal short-term store have been reconfirmed in t h i s experiment. The same interpo lated a c t i v i t i e s , in cont ra s t , have been shown to exert an und i f fe rent i a ted e f f e c t on the v i sua l short-term s tore . The data are interpreted as supporting previous f ind ings of the verbal short-term store c h a r a c t e r i s t i c s . In cont ras t , the p i c tu re recogn i t ion data seem i nd i ca t i ve of a v i sua l short-term s tore . In contras t to the verbal store,, however, the v i sua l s tore shows a lack o f , or at least an Ine f fec t i ve rehearsal mechanism in the given e x p e r i -mental s i t u a t i o n . 11 TABLE OF CONTENTS ABSTRACT 1 TABLE OF CONTENTS 1! LIST OF TEXT TABLES Iv LIST OF APPENDIX TABLES v LIST OF FIGURES v i l l ACKNOWLEDGEMENT i x GENERAL INTRODUCTION ' EXPERIMENT I - I n t r o d u c t i o n 15 Method 17 R e s u l t s and D i s c u s s i o n 22 EXPERIMENT II - I n t r o d u c t i o n 34 Method 34 R e s u l t s and D i s c u s s i o n 35 EXPERIMENT I I I - I n t r o d u c t i o n 38 Method 39 R e s u l t s and D i s c u s s i o n 40 EXPERIMENT fV - I n t r o d u c t i o n 49 Method 49 R e s u l t s and D i s c u s s i o n 50 EXPERIMENT V - I n t r o d u c t i o n 57 Method 5 7 R e s u l t s and D i s c u s s i o n 58 GENERAL DISCUSSION 6 3 i ! : FOOTNOTES 80 REFERENCES . . . . . . . . . 81 APPENDIX I - Instruct ions 84 APPENDIX I j - Tables 87 iv LIST OF TEXT TABLES Table I. Mean Number of Correct Probe Responses with Verbal Interference (Experiment I) 25 Table 2. Mean d' Scores f o r Experiment I 25 Table 3. Mean False Alarm Rate f o r Experiment I 26 Table 4. Mean Latency Scores f o r Experiment I 26 Table 5. Mean Number of d' Scores f o r WW and PP Groups Under Interferences (Experiment I ) , Rehearsal (Experiment I I I ) , and Rehearsal plus Responding to an I n i t i a l Auditory Probe (Experiment IV) 41 Table 6. Mean Number of Co r r e c t Probe Responses f o r WW and PP Groups under Interference (Experiment I ) , Rehearsal (Experiment I I I ) , and Rehearsal plus Responding to an I n i t i a l Auditory Probe ( E x p e r i -ment IV) 41 Table 7. Per Cent C o r r e c t Probe Responses f o r WW and PP Groups i n the Zero Delay Recognition Sequence f o r Experiments I, I I I , IV, and Mixed P r e s e n t a t i o n Groups In Experiment I 51 Table 8. Per Cent Correct Probe Responses at 7.5 Seconds f o r Experiments III and IV 51 Table 9. Mean Rec a l l Scores f o r Zero Delay (Experiment II) and 15 Seconds of Rehearsal o r In t e r -ference (Experiment V) out of a Maximum of 54 items 59 LIST OF APPENDIX TABLES Table I. ANOVA f o r Correct Probe Responses in Experiment I 88 Table 2; A n a l y s i s of Simple E f f e c t s f o r A6 I n t e r a c t i o n with Probe Responses (Experiment I) 89 Table 3. Newman Keuls Test f o r Delay E f f e c t s Using C o r r e c t Probe Responses in Experiment I 90 Table 4. ANOVA f o r d' Scores i n Experiment I 91 Table 5 . A n a l y s i s of Simple E f f e c t s f o r AB I n t e r a c t i o n with d ! Scores 92 Table 6. A n a l y s i s of Simple E f f e c t s f o r AC I n t e r -a c t i o n with d f Scores 93 Table 7. Newman Keuls Test f o r Simple Delay E f f e c t s with d' Scores in Experiment I 94 Table 8. ANOVA f o r Correct Probe Responses in Experiment II I 9 5 Table 9. A n a l y s i s of Simple E f f e c t s f o r AB (Pres e n t a t i o n x Delay) I n t e r a c t i o n with Probe Responses (Experiment I I I ) 96 Table 10. Newman Keuls Test Using Probe Responses f o r Delay Conditions (Experiment I I I ) 97 Table I I . ANOVA f o r d 1 Scores in Experiment I II 98 v i T a b l e 12. Newman K e u l s T e s t U s i n g d' S c o r e s f o r Delay C o n d i t i o n s ( E x p e r i m e n t I I I ) 99 T a b l e 13. ANOVA f o r P e r Cent C o r r e c t Responding t o Probe P o s i t i o n s a t Z e r o Delay f o r E x p e r i m e n t s I and I I I 100 T a b l e 14. A n a l y s i s f o r S i m p l e P o s i t i o n E f f e c t s f o r Z e r o D e l a y C o n d i t i o n s f o r WW and PP Groups i n E x p e r i m e n t s I and I I I 101 T a b l e 15. ANOVA f o r P e r Cent C o r r e c t Responding a t Z e r o Delay f o r P o s i t i o n s One and Two ( E x p e r i m e n t s I and I I I ) 102 T a b l e 16. ANOVA f o r C o r r e c t Probe Responses i n E x p e r i m e n t IV 103 T a b l e 17. Newman K e u l s f o r D e l a y E f f e c t w i t h Probe Responses ( E x p e r i m e n t IV) 104 T a b l e 18. ANOVA f o r d' S c o r e s ( E x p e r i m e n t IV) 105 T a b l e 19. Newman K e u l s f o r Delay E f f e c t w i t h d' S c o r e s ( E x p e r i m e n t IV) 106 T a b l e 20. ANOVA f o r C o r r e c t P e r Cent Responding t o P r o b e P o s i t i o n s a t Z e r o D e l a y ( E x p e r i m e n t IV) 107 T a b l e 21. A n a l y s i s f o r S i m p l e P o s i t i o n E f f e c t s f o r Z e r o Delay C o n d i t i o n s f o r WW and PP i n E x p e r i m e n t IV 108 T a b l e 22. ANOVA f o r R e c a l l S c o r e s In E x p e r i m e n t V 109 v i i Table 23. ANOVA f o r Word-P icture E f f e c t s During Rehearsal in Free Reca l l 110 Table 24. ANOVA f o r Word-P ic ture E f f e c t s A f t e r I n te r fe rence in Free Recal I I l l v i i i LIST OF FIGURES F i gu re I. Mean Number of Probe Responses out of a Maximum of Nine f o r EXP. I 27 F igure 2. d ' Scores f o r EXP. I out of a Maximum of S i x 28 F igure 3. Percent Co r r e c t Probe Responses f o r PP and WW on Zero Delay Recogn i t ion T r i a l s Co l l apsed over EXP. I and III 42 F igure 4. Number of Co r rec t Probe Responses out of Maximum of Nine f o r EXP. I l l 43 F igure 5. d ' Scores f o r EXP. I l l out of a Maximum of S i x 44 F igure 6. Co r rec t Probe Responses f o r EXP. IV 52 F igure 7. d ' Scores f o r EXP. IV 53 F igure 8. Mean Reca l l Scores f o r Zero Delay (EXP. II) and Rehearsal and I n te r fe rence Groups In EXP. V out of a Maximum of 54 items .-.. 60 i x ACKNOWLEDGEMENT I would l i k e t o express my a p p r e c i a t i o n f o r the he l p f u l comments and suggests ions of Dr. J im Johnson and Dr. John Y u i I l e in the w r i t i n g of t h i s paper. I am e s p e c i a l l y indebted to Dr. John Y u i M e f o r h i s con -t inuous support and encouragement which made t h i s research p o s s i b l e . And f i n a l l y , I would l i k e to thank F r i e d a , Ca ro le and Andrea f o r t h e i r pa r t In t yp i n g t h i s paper. GENERAL INTRODUCTION Memory r e s e a r c h w i t h i n t h e l a s t decade has p r o v i d e d s u f f i c i e n t e v i d e n c e i n f a v o u r o f a t r i c h o t o m o u s human memory system p e r s u a d i n g even t h e more t r a d i t i o n a l t h e o r i s t s t o abandon t h e p r e v i o u s l y a c c e p t e d u n i t a r y memory c o n c e p t . W h i l e t h e r e i s l e s s t h a n unanimous agreement on t h e n a t u r e of and n e c e s s i t y t o i n c l u d e p a r t i c u l a r s u b s y s t e m s , s e v e r a l o f t h e s e seem t o r e a p p e a r c o n s i s t e n t l y i n v a r i o u s m o d e l s , though i n s l i g h t l y a l t e r e d f orms. In g e n e r a l , t h e s e b a s i c memory subsystems I n c l u d e a s e n s o r y memory, and a s h o r t term memory system as w e l l as t h e more f a m i l i a r long term memory. Ample s u p p o r t f o r t h e c o n c e p t of a s e n s o r y memory, a t l e a s t i n t h e v i s u a l m o d a l i t y , has acc u m u l a t e d s i n c e S p e r l i n g ' s work w i t h t a c h i s t o s c o p f c s t i m u l u s p r e s e n t a t i o n s ( S p e r l i n g , I960; N e i s s e r , 1967). T h i s l i n e o f r e s e a r c h has e s t a b l i s h e d t h a t a f t e r t h e t e r m i n a t i o n of a v i s u a l s t i m u l u s , some I n f o r m a t i o n c o n t i n u e s t o be a v a i l a b l e t o S_ f o r f u r t h e r p r o c e s s i n g f o r a b r i e f p e r i o d o f t i m e . In g e n e r a l , t h e f i n d i n g s s u g g e s t t h a t t h e v i s u a l s t i m u l u s l e a v e s a b r i e f s e n s o r y t r a c e which r a p i d l y decays d u r i n g a p e r i o d o f s e v e r a l hundred m i l l i s e c o n d s , which Is s u b j e c t t o masking and r e p l a c e -ment by i m m e d i a t e l y s u c c e e d i n g s t i m u l i . A s i m i l a r c a s e has a l s o been made f o r t h e a u d i t o r y m o d a l i t y i n N e i s s e r ' s (1967) e c h o i c memory s y s t e m , and Crowder's (1970) p r e c a t e g o r i c a I a c o u s t i c s t o r a g e . W h i l e s e n s o r y t r a c e s o f t h i s k i n d a l m o s t b o r d e r t h e realm o f p e r -c e p t i o n , and s u b s e q u e n t l y can be e a s i l y i d e n t i f i e d as a d i s t i n c t memory s y s t e m , t h e dichotomy between s h o r t - t e r m memory (STM) and l o n g - t e r m memory (LTM) underwent a more c o n t r o v e r s i a l development. The need t o d i s t i n g u i s h 2 between a p r i m a r y and s e c o n d a r y memory system had a l r e a d y been r e a l i z e d by W i l l i a m James ( 1 8 9 0 ) . Y e t , I t was n o t u n t i l P e t e r s o n and P e t e r s o n (1959) s e t t h e groundwork f o r an o p e r a t i o n a l d i s t i n c t i o n between t h e two systems t h a t t h e o r e t i c a l models emerged which u t i l i z e d t h i s dichotomy (Waugh & Norman, 1965; N e i s s e r , 1967; A t k i n s o n & S h f f f r i n , 1968). The d i s t i n c t i o n between STM and LTM i s ' based l a r g e l y on two c r i t e r i a : f i r s t , t h e o p e r a t i o n a l d e f i n i t i o n d e s c r i b i n g t h e e x p e r i m e n t a l s i t u a t i o n ; s e c o n d , c h a r a c t e r i s t i c s a s c r i b e d t o memory s t r u c t u r e s and p r o c e s s e s o p e r -a t i n g w i t h i n t h e two e x p e r i m e n t a l paradigms. S h o r t - t e r m memory e x p e r i -ments a r e u s u a l l y d e f i n e d as I n v e s t i g a t i n g memory a f t e r s i n g l e , b r i e f s t i m u l u s p r e s e n t a t i o n s and s h o r t r e t e n t i o n i n t e r v a l s . In c o n t r a s t , LTM e x p e r i m e n t s make use of r e p e a t e d t r i a l s and r e l a t i v e l y l o n g e r r e t e n t i o n I n t e r v a l s . B a s i c c h a r a c t e r i s t i c s proposed f o r STM i n c l u d e a l i m i t e d s t o r a g e c a p a c i t y , a r e h e a r s a l mechanism, and a c o d i n g mechanism which r e -l i e s p r e d o m i n a n t l y on v e r b a l - a c o u s t i c f e a t u r e s o f t h e s t i m u l u s m a t e r i a l . In c o n t r a s t , LTM c h a r a c t e r i s t i c s i n c l u d e , among o t h e r s , an u n l i m i t e d s t o r a g e c a p a c i t y , I n d e f i n i t e r e t e n t i o n of s t o r e d i n f o r m a t i o n , and e l a b o r a t e c o d i n g mechanisms. P r o b a b l y t h e most f r u i t f u l c u r r e n t memory model u t i l i z i n g t h e s e subsystems has been d e v e l o p e d by A t k i n s o n & S h l f f r i n ( 1 9 6 8 ) . S u b d i v i d e d I n t o t h e s e n s o r y memory (SM), s h o r t - t e r m s t o r e ( S T S ) , and lo n g - t e r m s t o r e ( L T S ) , t h e model i n t r o d u c e s s e v e r a l i n n o v a t i v e f e a t u r e s w i t h p o t e n t i a l l y f a r r e a c h i n g I m p l i c a t i o n s f o r memory r e s e a r c h and t h e o r y . F o r I n s t a n c e , a c l e a r d i s t i n c t i o n i s made between STM and STS - s i m i l a r l y between LTM and LTS - which i s g e n e r a l l y based on t h e p r e v i o u s l y d i s c u s s e d d e f i n i n g c r i t e r i a 3 o f each subsystem. Hence, STM r e f e r s t o t h e o p e r a t i o n a l d e f i n i t i o n o f t h e e x p e r i m e n t a l s i t u a t i o n and STS t o t h e memory mechanism u n d e r l y i n g t h e p r e v i o u s l y d i s c u s s e d c h a r a c t e r i s t i c s w h i c h may o b t a i n i n a STM t a s k . In a d d i t i o n , t h e r e i s a s t r o n g a t t e m p t t o d i f f e r e n t i a t e between s t r u c t u r a l f e a t u r e s and c o n t r o l p r o c e s s e s , as w e l l as t h e i r i n t e r a c t i o n , w i t h i n each subsystem. T h i s p a r t i c u l a r a s p e c t o f t h e model i s , however, s t i l l a t a h i g h l y t e n t a t i v e s t a g e due t o t h e l a c k and d i f f i c u l t y o f e x p e r i m e n t a l v a l i d -a t i o n . Y e t , t h e model a t l e a s t t a k e s t h e s e n e c e s s a r y r e f i n e m e n t s o f a t h e o r y i n t o c o n s i d e r a t i o n . S i m i l a r l y , though t h e model Is l a r g e l y based on r e s e a r c h w i t h v e r b a l s t i m u l u s m a t e r i a l , i t p r o v i d e s ample room f o r a d d i t i o n s o f n o n - v e r b a l memory p r o c e s s e s , t h e r e b y e n c o u r a g i n g r e s e a r c h i n o t h e r memory m o d a l i t i e s not y e t a d e q u a t e l y i n v e s t i g a t e d . A p a r t from p r e -s e n t i n g a c o m p r e h e n s i v e , w o r k a b l e model f o r c u r r e n t memory r e s e a r c h , A t k i n s o n & S h i f f r i n s u c c e e d i n p r o v i d i n g a t h e o r e t i c a l framework d e s i g n e d t o s t i m u l a t e and I n c o r p o r a t e a v a s t amount of f u t u r e memory r e s e a r c h . E v i d e n c e s u p p o r t i n g t h e t r i c h o t o m y o f human memory i s by no means unambiguous, y e t does p o i n t towards t h e g e n e r a l v a l i d i t y o f t h e c o n c e p t w i t h r e g a r d t o STS c h a r a c t e r i s t i c s , f o r i n s t a n c e , i t sometimes becomes n e c e s s a r y t o r e l y on i n f e r e n c e s from w i d e l y d i v e r g e n t r e s e a r c h In o r d e r t o a r r i v e a t a c c e p t a b l e p o s t u l a t e s . F o r example, s h o r t - t e r m memory c a p a c i t y had long been i n v e s t i g a t e d ( M i l l e r , 1956), though i n a d i f f e r e n t c o n t e x t . Whether e m p l o y i n g d i g i t s , l e t t e r s o r words, M i l l e r found t h e immediate memory span t o be f a i r l y c o n s t a n t i f measured i n terms o f number of i t e m s , i . e . seven items p l u s o r minus two. B u t , i n terms o f i n f o r m a t i o n c o n t e n t , t h i s f i n d i n g does n o t h o l d a c r o s s t y p e s o f s t i m u l u s m a t e r i a l . M i l l e r o v e r -4 c o m e s t h i s p a r a d o x by e x p r e s s i n g t h e b a s i c u n i t o f memory s t o r a g e i n " b i t s o f i n f o r m a t i o n . " T h a t i s , o n e l e t t e r a n d o n e w o r d w i t h s e v e r a l l e t t e r s c o n s t i t u t e e a c h o n e b i t o f i n f o r m a t i o n . A t k i n s o n & S h i f f r i n i n t e r p r e t t h e l i m i t e d s t o r a g e c a p a c i t y o f STS i n t e r m s o f r e h e a r s a l p r o c e s s e s . T h e y p r o p o s e a r e h e a r s a l b u f f e r o f f i x e d s i z e w h i c h i s d e t e r m i n e d by I n p u t a n d r e o r g a n i s a t i o n f a c t o r s o f t h e e x p e r i m e n t a l s i t u a t i o n . M o r e c r i t i c a l t h a n t h e s p e c i f i c s i z e o f t h e r e h e a r s a l b u f f e r , i . e . , STS c a p a c i t y , i s i t s I m p o r t a n t f u n c t i o n a s a r e g e n e r a t i n g m e c h a n i s m o f STS t r a c e s ' ( A t k i n s o n & S h i f f r i n , 1 9 6 8 ) . E v i d e n c e o f t h e f u n c t i o n a l s i g n i f i c a n c e o f t h e r e h e a r s a l m e c h a n i s m d e r i v e s f r o m t w o d i v e r g e n t e x p e r i -m e n t a l o p e r a t i o n s , i . e . i n t r o d u c i n g r e h e a r s a l o r i n t e r f e r e n c e d u r i n g t h e r e t e n t i o n i n t e r v a l i n a STM t a s k . In t h e t y p i c a l i n t e r f e r e n c e p a r a d i g m , i n i t i a t e d by P e t e r s o n a n d P e t e r s o n ( 1 9 5 9 ) , S_ i s p r e s e n t e d w i t h t h e s t i m u l u s , w h i c h i s f o l l o w e d by a t h r e e d i g i t n u m b e r f r o m w h i c h S_ h a s t o c o u n t b a c k -w a r d s by t h r e e s u n t i l c u e d f o r t h e r e s p o n s e t a s k . M u r d o c k ( 1 9 6 3 ) f o u n d r e c a l l o f t r i a d s a n d t r i g r a m s t o d e c r e a s e t o a p r o b a b i l i t y o f . 0 8 a f t e r 15 t o 18 s e c o n d s o f c o u n t i n g b a c k w a r d s . I n c o n t r a s t , i f r e h e a r s a l i s a l l o w e d d u r i n g t h e r e t e n t i o n i n t e r v a l , r e c a l l f o r l e t t e r s , w o r d s , a n d s e n t e n c e s h a s b e e n s h o w n t o i n c r e a s e o v e r a 10 s e c o n d d e l a y ( C r a w f o r d , H u n t & G r a h a m e , 1 9 6 6 ) . C o m b i n i n g t h e t w o o p e r a t i o n s , r e c a l l c a n e f f e c -t i v e l y be m a n i p u l a t e d by i n t r o d u c i n g r e p e t i t i o n s ( H e l l y e r , 1962 ) o r r e -h e a r s a l ( S t o n n e r & M u e n z i n g e r , 1 969 ) b e f o r e t h e o n s e t o f t h e i n t e r f e r e n c e t a s k . In t e r m s o f t h e A t k i n s o n a n d S h i f f r i n m o d e l t h e f o l l o w i n g e v e n t s a r e a s s u m e d t o o c c u r i n t h e s e e x p e r i m e n t a l s i t u a t i o n s . When t h e s t i m u l u s 5 i s p r e s e n t e d i t e n t e r s t h e s e n s o r y memory and i s a t once t r a n s f e r r e d t o t h e STS, where an a t t e m p t i s made t o r e h e a r s e t h e s t i m i i l u s m a t e r i a l . Such a t t e m p t s a r e t e r m i n a t e d when a t t e n t i o n i s g i v e n t o t h e i n t e r f e r e n c e t a s k . The d e c r e a s i n g r e s p o n s e s t r e n g t h w i t h l o n g e r i n t e r f e r e n c e i n t e r v a l s s u b -s e q u e n t l y r e f l e c t s t h e c o n t i n u o u s l o s s o f i n f o r m a t i o n f rom STS i f t h e m a t e r i a l i s n o t r e h e a r s e d . A l m o s t c o m p l e t e l o s s o f i n f o r m a t i o n i n STS i s p o s t u l a t e d t o appea r a f t e r 15 t o 30 s e c o n d s . The o b s e r v a t i o n t h a t re-call p r o b a b i l i t y i s n o t z e r o a f t e r 15 seconds (Murdock , 1963) i s a t t r i b u t e d t o an i n i t i a l b u i l d - u p o f memory t r a c e s i n LTS. T h i s i n i t i a l b u i l d - u p o f t h e LTS t r a c e can be r e g u l a t e d by i n t r o d u c i n g r e p e t i t i o n o r r e h e a r s a l b e -f o r e t h e i n t e r f e r e n c e t a s k . On t h e o t h e r h a n d , i n an e x p e r i m e n t a l s i t u -a t i o n w i t h o u t an i n t e r f e r e n c e t a s k t h e r e w i l l be no l o s s o f i n f o r m a t i o n f r om STS, g i v e n o p t i m a l e x p e r i m e n t a l c o n d i t i o n s , s i n c e t h e r e h e a r s a l mechanism s e r v e s t o r e g e n e r a t e s h o r t - t e r m t r a c e s as w e l l a s t o t r a n s f e r i n f o r m a t i o n t o t h e more permanent LTS. Hence , r e s p o n s e s c o r e s i n t h i s s i t u a t i o n w i l l be f a c i l i t a t e d by STS and LTS. In e f f e c t , t h e f u n c t i o n a l i m p o r t a n c e o f t h e STS r e h e a r s a l mechanism a p p e a r s t o be t h r e e f o l d : i t p r e v e n t s l o s s o f i n f o r m a t i o n i n STS, b u i l d s up s h o r t - t e r m t r a c e s by c o n -t i n u o u s r e g e n e r a t i o n , and i s i n s t r u m e n t a l i n t h e t r a n s f e r o f i n f o r m a t i o n t o LTS. The t h i r d i m p o r t a n t f e a t u r e o f STS i s t h e p r e d o m i n a n t l y v e r b a I-a c o u s t i c e f f e c t s i n STM e x p e r i m e n t s . S p e r l i n g ( I 9 6 0 , 1963) p o s t u l a t e d an " a u d i t o r y i n f o r m a t i o n s t o r a g e " i n immed ia te memory as a r e s u l t o f o b s e r v i n g a l a r g e number o f a u d i t o r y c o n f u s i o n e r r o r s w i t h t a c h i s t o s c o p i c a M y p r e -s e n t e d s t i m u l i . F u r t h e r s u p p o r t f o r v e r b a I - a c o u s t i c e f f e c t s i n STM d e r i v e d from a paradigm which i n v e s t i g a t e s e r r o r s c o r e s a f t e r p r e s e n t i n g s t r i n g s of e i t h e r a c o u s t i c a l l y s i m i l a r o r d i s s i m i l a r i t e m s . The g e n e r a l l y c o n -s i s t e n t f i n d i n g s i n t h i s e x p e r i m e n t a l s i t u a t i o n a r e : I) s u b s t i t u t i o n e r r o r s t e n d t o be a c o u s t i c a l l y c o n f u s i n g i t e m s ; and 2) t h e r e i s a h i g h e r e r r o r s c o r e w i t h a c o u s t i c a l l y s i m i l a r t h a n d i s s i m i l a r l i s t s . These r e s u l t s h o l d f o r s t r i n g s o f c o n s o n a n t s , whether a u d i t o r i l y p r e s e n t e d and embedded i n n o i s e ( C o n r a d , 1964) o r v i s u a l l y p r e s e n t e d ( W i c k e l g r e n , 1965), and a r e a l s o c o n s i s t e n t f o r words, ( i . e . homophones), i n a r e c a l l ( K i n t c h & Buschke, 1969), o r r e c o g n i t i o n t a s k (Wieke I g r e n , 1966). The l a t t e r f i n d i n g s a r e q u i t e i n c o n t r a s t t o LTM r e s e a r c h where p e r f o r m a n c e i s shown t o be i m p a i r e d by s e m a n t i c but not a c o u s t i c s i m i l a r -i t y ( B a d d e l y , 1966). The i m p l i c a t i o n s o f t h i s l i n e o f r e s e a r c h , t h e r e f o r e , s t r o n g l y s u g g e s t t h a t STS r e l i e s l a r g e l y on a c o u s t i c c o d i n g and i s r e -l a t i v e l y u n a f f e c t e d by t h e s e m a n t i c c o n t e n t o f t h e message t o be s t o r e d . However, s e m a n t i c f a c t o r s may be i m p o r t a n t under g i v e n e x p e r i m e n t a l mani-p u l a t i o n s i n a STM e x p e r i m e n t (Wickens & E c k l e r , 1968). Thus, STM e x p e r i m e n t s e m p l o y i n g a v a r i e t y o f t a s k s and s t i m u l i t e n d t o p r e s e n t c o n s i s t e n t e v i d e n c e i n f a v o u r o f STS as a d i s t i n c t memory system. S t o r a g e c a p a c i t y seems c e r t a i n l y t h e l e a s t d i s p u t a b l e d i s t i n c t i v e f e a t u r e , s i m p l y because of t h e e x p e r i m e n t a l r e q u i r e m e n t s o f t h e r e s p e c t i v e memory t a s k s . The s i g n i f i c a n c e o f t h e r e h e a r s a l mechanism i n p r e v e n t i n g l o s s o f i n f o r m a t i o n from STS and i n impl e m e n t i n g t h e t r a n s f e r p r o c e s s t o LTS has a l s o been a d e q u a t e l y d i s p l a y e d w i t h h e l p o f r e h e a r s a l and i n t e r -f e r e n c e a c t i v i t i e s i n STM e x p e r i m e n t s . F u r t h e r m o r e , a c o u s t i c v e r s u s s e m a n t i c s i m i l a r i t y e f f e c t s on STS and LTS s u g g e s t d i s t i n c t i v e l y d i f f e r e n t 7 c o d i n g mechanisms f o r t h e two s u b s y s t e m s . A t t h e same t i m e , however, i t i s n o t c e r t a i n t h a t STS i s an ex-c l u s i v e l y v e r b a I - a u d i t o r y memory system. E v i d e n c e s u g g e s t i n g n o n - v e r b a l s h o r t - t e r m p r o c e s s e s has been o b t a i n e d i n a v a r i e t y o f e x p e r i m e n t a l s i t u -a t i o n s . In an e x p e r i m e n t c o r r e l a t i n g t h e a b i l i t y t o r e p r o d u c e b r i e f l y exposed f i g u r e s w i t h t h e a b i l i t y t o d e s c r i b e them, Cohen and Granstrom (1969) found a h i g h e r p o s i t i v e c o r r e l a t i o n between p e r f o r m a n c e on t h e two t a s k s f o r complex t h a n f o r s i m p l e f i g u r e s . Cohen and G r a n s t r o m s u g g e s t t h a t t h e d i f f e r e n c e i s due t o v i s u a l memory which p l a y s a g r e a t e r r o l e i n m emorizing s i m p l e f i g u r e s . However, t h e i r e v i d e n c e f o r a v i s u a l STS has t o be e v a l u a t e d i n l i g h t o f two c r i t i c a l f a c t o r s i n t h e e x p e r i m e n t : v i s u a l and v e r b a l a s p e c t s of t h e e x p e r i m e n t a l t a s k a r e n o t e x p e r i m e n t a l l y s e p a r a t e d , and, t h e c o r r e l a t i o n s a r e based on two d i f f e r e n t p a r a d i g m s , i . e . a P e t e r s o n and P e t e r s o n (1959) t a s k f o r r e p r o d u c t i o n v e r s u s a 9 0 -sec. s t i m u l u s e x p o s u r e d u r i n g d e s c r i p t i o n . More c o n v i n c i n g e v i d e n c e f o r a v i s u a l STS i s p r e s e n t e d by P o s n e r ' s ( P o s n e r , 1967; P o s n e r & K o n i c k , 1966) v i s u a l l o c a t i o n t a s k , i n which S_ has t o r e p r o d u c e t h e a n g l e o f a p r e v i o u s l y p r e s e n t e d l i n e segment i n a t y p i c a l P e t e r s o n and P e t e r s o n paradigm. Re-s u l t s show t h a t a r e s t p e r i o d , i . e . t i m e f o r v e r b a l r e h e a r s a l , does n o t f a c i l i t a t e p e r f o r m a n c e , w h i l e a w r i t t e n i n t e r p o l a t e d t a s k lowers t h e a c c u r a c y o f t h e l o c a t i o n r e s p o n s e . In a d d i t i o n a more a c c u r a t e r e s p o n s e l e v e l can be o b t a i n e d by g i v i n g S^  v i s u a l r a t h e r t h a n e x a c t v e r b a l i n f o r m -a t i o n of t h e s t i m u l u s a n g l e . In t h i s s i t u a t i o n t h e s t i m u l u s m a t e r i a l a p p a r e n t l y c a n n o t be r e a d i l y encoded v e r b a l l y . T h e r e f o r e , v e r b a l r e -h e a r s a l and v e r b a I s t i m u l u s i n f o r m a t i o n do n o t iead t o r e s p o n s e f a c i l i t -8 a t i o n . On t h e o t h e r hand, d u r i n g t h e w r i t t e n i n t e r p o l a t e d t a s k , a t t e n t i o n Is d i v e r t e d from t h e STS o f t h e s t i m u l u s p a t t e r n , l e a d i n g t o a decrement In p e r f o r m a n c e . The I m p l i c a t i o n s h e r e a r e s t i l l ambiguous. The d e c r e a s i n g r e s p o n s e l e v e l a f t e r I n t e r f e r e n c e seems t y p i c a l of v e r b a l s t o r a g e . Y e t , t h e s u p e r i o r p e r f o r m a n c e w i t h a v i s u a l l y p r e s e n t e d s t i m u l u s a n g l e o v e r e x a c t v e r b a l i n f o r m a t i o n of t h e s t i m u l u s a n g l e , as w e l l as t h e i n e f f e c t i v e -ness o f v e r b a l r e h e a r s a l , s t r o n g l y s u g g e s t t h a t o t h e r t h a n v e r b a l s h o r t -t e r m p r o c e s s e s a r e i n v o l v e d i n an e x p e r i m e n t o f t h i s t y p e . I t seems d i f f i c u l t , however, t o d e t e r m i n e e m p i r i c a l l y t o what e x t e n t k i n e s t h e t i c o r v i s u a l s h o r t - t e r m p r o c e s s e s a r e u n d e r l y i n g t h e s e r e s u l t s . Up t o t h i s p o i n t , n o n - v e r b a l s h o r t - t e r m p r o c e s s e s have been d i s -c u s s e d w i t h r e s p e c t t o v i s u a l l y p r e s e n t e d s t i m u l u s i n f o r m a t i o n which can n o t be r e a d i l y v e r b a l i z e d . The q u e s t i o n t h e n a r i s e s as t o what happens, when a g i v e n s t i m u l u s c o n f i g u r a t i o n , p r e s e n t e d v i s u a l l y , can be e q u a l l y w e l l encoded v e r b a l l y o r n o n - v e r b a I l y , i . e . , i n a v i s u a l , p h y s i c a l form. Words and d i g i t s , f o r i n s t a n c e can be l a b e l l e d , as w e l l as r e c o g n i z e d , as p h y s i c a l c o n f i g u r a t i o n s . W i l l t h e v i s u a l l y p r e s e n t e d l e t t e r , t h e r e f o r e , be encoded In v e r b a I - a c o u s t i c p r o p e r t i e s o r p h y s i c a I - v i s u a I p r o p e r t i e s o f t h e s t i m u l u s ? The p r e v i o u s l y d i s c u s s e d r e s e a r c h p o i n t s s t r o n g l y t o w a r d s v e r b a I - a c o u s t i c c o d i n g of l e t t e r s i n STM e x p e r i m e n t s . However, under d i f f e r e n t e x p e r i m e n t a l m a n i p u l a t i o n s , as i n a v i s u a l s e a r c h t a s k , G i b s o n and J o n a s (1966) d e m o n s t r a t e d t h a t v i s u a l l y c o n f u s i n g l e t t e r s l e a d t o lower p e r f o r m a n c e t h a n do a c o u s t i c a l l y c o n f u s i n g l i s t s o f l e t t e r s . S i n c e t h e t a s k r e q u i r e m e n t s In t h i s e x p e r i m e n t i n v o l v e a v i s u a l s c a n n i n g of an a r r a y o f l e t t e r s , v i s u a l s t o r a g e o f t h e t a r g e t l e t t e r seems a more e f f i c i e n t 9 w o r k i n g m o d a l i t y f o r t h i s t a s k . Whether t h i s v i s u a l s t o r a g e i s i n STS o r LTS, however, i s u n c l e a r . O t h e r r e s e a r c h s u g g e s t s t h a t t h e r e a r e a l s o m o d a l i t y - s p e c i f i c i n t e r f e r e n c e e f f e c t s . M a r g r a i n (1967) found a s t r o n g e r i n t e r f e r e n c e e f f e c t f o r r e c a l l o f v i s u a l l y p r e s e n t e d words f o l l o w i n g w r i t t e n t h a n v e r b a l i n t e r -p o l a t e d a c t i v i t y . On t h e o t h e r hand, i n an a u d i t o r y shadowing e x p e r i m e n t r e c a l l s u f f e r e d more f o r a u d i t o r i l y t h a n f o r v i s u a l l y p r e s e n t e d l e t t e r s , but o n l y a f t e r a 25-second r e t e n t i o n i n t e r v a l ( K r o l l , P a r k s , P a r k i n s o n , B i e b e r & J o h n s o n , 1970). I n t e r e s t i n g as t h e s e d a t a a r e i n t h e i r i m p l i c -a t i o n s w i t h r e s p e c t t o v e r b a l and n o n - v e r b a l s h o r t - t e r m c o d i n g mechanisms, p o s s i b l e c o n c l u s i o n s from t h i s t y p e o f e v i d e n c e have t o remain t e n t a t i v e u n t i I s u p p o r t e d by f u t u r e r e s e a r c h . F u r t h e r e v i d e n c e s u g g e s t i n g t h a t n o n - v e r b a l e n c o d i n g p r o c e s s e s can be found i n a v a r i e t y o f ''same-different'' r e c o g n i t i o n e x p e r i m e n t s . In a l e t t e r m a t c h i n g t a s k , r e a c t i o n t i m e i s f a s t e r i n a p h y s i c a l t h a n a name match, i f t h e l e t t e r s a r e s e p a r a t e d by up t o one second ( P o s n e r , B o i e s , E i c h e l m a n & T a y l o r , 1969). The s u p e r i o r i t y o f a p h y s i c a l match, however, d i s a p p e a r s w i t h an i n t e r s t i m u I us i n t e r v a l o f two o r more sec o n d s . If s e n s o r y memory i n v o l v e m e n t can be c o n s i d e r e d i n t h i s t a s k , t h e f o l l o w i n g i n t e r p r e t a t i o n w i l l emerge. When t h e t e s t l e t t e r i s p r e s e n t e d b e f o r e v e r b a l e n c o d i n g i s c o m p l e t e d , t h e m a t c h i n g r e s p o n s e i s me d i a t e d by t h e s e n s o r y t r a c e of t h e SM, r e s u l t i n g i n s u p e r i o r p h y s i c a l m a t c h i n g i n t h e s h o r t e r p r e s e n t a t i o n i n t e r v a l s . S i n c e t h e memory t r a c e o f t h e SM decays r a p i d l y , t h e m a t c h i n g r e s p o n s e a f t e r a 2-sec. i n t e r v a l i s me d i a t e d by e q u a l l y e f f i c i e n t a u d i t o r y and v i s u a l s h o r t - t e r m t r a c e s . In e f f e c t , t h e r e seems 10 t o be a s i m i l a r l y e f f i c i e n t i n f o r m a t i o n t r a n s f e r p r o c e s s from t h e s e n s o r y memory t o STS i n t h e v e r b a l and n o n - v e r b a l s h o r t - t e r m system. The e v i d e n c e r e v i e w e d t o t h i s p o f n t i s , however, s t i l l ambiguous. W h i l e t h e r e s u l t s a r e s u g g e s t i v e of n o n - v e r b a l STS, t h e d a t a can a l s o be e x p l a i n e d by o t h e r mechanisms. P r o b a b l y t h e most c o n v i n c i n g a t t e m p t t o s e p a r a t e v e r b a l and v i s u a l c o d i n g mechanisms i n a STM t a s k has been p r e -s e n t e d by T v e r s k y ( 1 9 6 9 ) . In a manner s i m i l a r t o P o s n e r e t aJL (1969) T v e r s k y used a " s a m e - d i f f e r e n t ' : r e c o g n i t i o n t a s k w i t h a l - s e c . i n t e r -s t i m u l u s i n t e r v a l . The s t i m u l i c o n s i s t e d of v i s u a l l y p r e s e n t e d s c h e m a t i c f a c e s and t h e i r w e l l - l e a r n e d names. In each b l o c k of t r i a l s Ss v/ere p r e -s e n t e d w i t h e i t h e r word o r p i c t u r e s t i m u l i . The f i r s t s t a g e was a l w a y s f o l l o w e d by e i t h e r a word o r a p i c t u r e . S t i m u l i i n t h e second s t a g e were always a r r a n g e d i n an e i g h t t o two r a t i o . R e s u l t s showed t h a t r e a c t i o n t i m e was always f a s t e r f o r t h e more f r e q u e n t l y p r e s e n t e d t y p e o f second s t i m u l i , r e g a r d l e s s of whether t h e f i r s t s t i m u l i were words o r p i c t u r e s . Thus, t h e e v i d e n c e from t h i s e x p e r i m e n t s u g g e s t s t h a t v e r b a l m a t e r i a l can be encoded p i c t o r i a l l y , and p i c t o r i a l m a t e r i a l can-be encoded v e r b a l l y . F u r t h e r m o r e , t h e p a r t i c u l a r c o d i n g s t r a t e g i e s c o u l d be e f f e c t i v e l y mani-p u l a t e d by S_'s a n t i c i p a t i o n of t h e r e s p o n s e r e q u i r e m e n t s . A c o m p l e t e l y d i f f e r e n t approach t o d e l i n e a t e v e r b a l and v i s u a l c o d i n g p r o c e s s e s has been t a k e n by P a i v i o and Czapo ( 1 9 6 9 ) . Words and p i c t u r e s o f f a m i l i a r o b j e c t s were p r e s e n t e d a t 5.3 o r 2 items per second and t e s t e d on f o u r r e s p o n s e t a s k s . At t h e f a s t p r e s e n t a t i o n r a t e no modal-i t y d i f f e r e n c e a p p e a r e d , r e g a r d l e s s o f r e s p o n s e t a s k . There was a g e n e r a l i n c r e a s e i n performance f o r a l l g r o u p s a t t h e s l o w e r r a t e , w i t h an a d d i t i o n a l 11 p i c t u r e o v e r word s u p e r i o r i t y f o r r e c a l l and r e c o g n i t i o n s c o r e s . S i n c e t h e f a s t p r e s e n t a t i o n r a t e was d e s i g n e d t o p r e v e n t c r o s s m o d a I i t y e n c o d i n g , i . e . p i c t u r e s encoded v e r b a l l y and v i c e v e r s a , r e s u l t s p r o v i d e f u r t h e r s u p p o r t t h a t under g i v e n e x p e r i m e n t a l c o n d i t i o n s equal a u d i t o r y - v e r b a l and v i s u a l c o d i n g a b i l i t i e s can be d e m o n s t r a t e d . R e c a l l and r e c o g n i t i o n s c o r e s a t t h e slow r a t e a r e , however, q u i t e i n c o n t r a s t t o p r e v i o u s m o d a l i t y e f f e c t s i n STM r e s e a r c h . In l i g h t o f t h e r e s p o n s e r e q u i r e m e n t s , i . e . t h e r e c o g n i t i o n t a s k l a s t i n g 108 s e c o n d s , and s i n c e m o d a l i t y e f f e c t s a r e i n l i n e w i t h LTM c h a r a c t e r i s t i c s ( S h e p a r d , 1967) t h e s e d a t a , however, p r e s e n t l i t t l e argument a g a i n s t p r e v i o u s STM f i n d i n g s , and s h o u l d p r o b a b l y be e v a l u a t e d w i t h i n a LTM framework. To summarize, v e r b a I - a c o u s t i c v a r i a b l e s have been e x t e n s i v e l y used i n STM r e s e a r c h , i n i t i a l l y i n c o n j u n c t i o n w i t h s e m a n t i c v a r i a b l e s t o i s o l a t e STM e f f e c t s , and l a t e r i n c o n j u n c t i o n w i t h v i s u a l - p i c t o r i a l v a r i a b l e s i n o r d e r t o i n v e s t i g a t e v e r b a l and n o n - v e r b a l c o d i n g mechanisms i n STS. The d i f f e r e n t i a l e f f e c t o f s e m a n t i c and a c o u s t i c s i m i l a r i t y i n LTM and STM e x p e r i m e n t s has been one o f t h e more c o n v i n c i n g arguments f o r p o s t u l a t i n g two memory syste m s . The d a t a s t r o n g l y s u g g e s t t h a t STS r e l i e s h e a v i l y on t h e a c o u s t i c c h a r a c t e r i s t i c s o f t h e i n p u t i n f o r m a t i o n , r e g a r d -l e s s o f v i s u a l o r a u d i t o r y p r e s e n t a t i o n , which i s q u i t e i n c o n t r a s t t o LTS c h a r a c t e r i s t i c s . However, a l t e r n a t e c o d i n g mechanisms i n STM e x p e r i m e n t s a l s o have been p o s t u l a t e d . F o r i n s t a n c e , i f t h e v i s u a l i n f o r m a t i o n c a n n o t be r e a d i l y v e r b a l i z e d o r i f t h e t a s k r e q u i r e m e n t s of t h e e x p e r i m e n t a r e not f a c i l i t a t e d by a v e r b a l c ode, s h o r t - t e r m p r o c e s s e s i n o t h e r m o d a l i t i e s may be a v a i l a b l e t o S_. B u t , i n c o n t r a s t t o e v i d e n c e s u p p o r t i n g t h e v e r b a l 12 STS, c o r r e s p o n d i n g n o n - v e r b a l p r o c e s s e s seem s t i l l a t a h i g h l y t e n t a t i v e s t a g e . The major purpose o f t h e p r e s e n t r e s e a r c h was t o e x p l o r e f u r t h e r ways o f c o n t r a s t i n g v e r b a l and n o n - v e r b a l c o d i n g mechanisms i n STM t a s k s . A t t h e same t i m e , t h e r e i s no memory model a v a i l a b l e a t t h i s s t a g e which c l a i m s t o a c c o u n t f o r a l l t h e s e d a t a c o l l e c t e d i n STM e x p e r i m e n t s . W h i l e t h e A t k i n s o n and S h i f f r i n model (1968) p r e s e n t s an adequate frame-work f o r v e r b a I - a u d i t o r y STS p r o c e s s e s , i t i s o n l y t h e l a c k o f c o n s i s t e n t e m p i r i c a l e v i d e n c e which h a s t e n s them t o p o s t u l a t e s i m i l a r n o n - v e r b a l s h o r t - t e r m s t r u c t u r e s and p r o c e s s e s . I t i s p r o b a b l y worth n o t i n g a t t h i s t i m e t h a t most of t h e s u p p o r t f o r a v i s u a l STS has been p r o v i d e d s i n c e t h e i r model was p u b l i s h e d . In any c a s e , n o n - v e r b a l STM systems can be r e a d i l y i n c o r p o r a t e d i n t h e p r e s e n t s t r u c t u r e o f t h e i r m o del, and i t be-comes, t h e r e f o r e , i m p o r t a n t t o i n v e s t i g a t e t h e s e s y s t e m a t i c a l l y t o d e t e r -mine t h e n a t u r e of n o n - v e r b a l STM e f f e c t s . The p r e s e n t r e s e a r c h I s , t h e r e f o r e , d e s i g n e d t o i n v e s t i g a t e s h o r t -term memory p r o c e s s e s w i t h r e s p e c t t o v i s u a l l y p r e s e n t e d words and p i c t u r e s . S i n c e p i c t o r i a l i n f o r m a t i o n i n t h e s e n s o r y s t o r e can be encoded and s t o r e d v e r b a l l y , g i v e n t h e a p p r o p r i a t e e x p e r i m e n t a l s i t u a t i o n , t h e f o l l o w i n g q u e s t i o n emerges. If t h e p i c t o r i a l i n f o r m a t i o n i s p r e v e n t e d from b e i n g 1 encoded v e r b a l l y , does a v i s u a l s h o r t - t e r m mechanism e x i s t which w i l l s t o r e and r e h e a r s e t h e p i c t o r i a l i n f o r m a t i o n o v e r STM r e t e n t i o n i n t e r v a l s ? In o t h e r words, can s i m i l a r s t r u c t u r e s and p r o c e s s e s o f t h e v e r b a I - a u d i t o r y STS be found In t h e v i s u a l STS? Sy p r e s e n t i n g a m a t r i x o f f a m i l i a r o b j e c t s as e i t h e r words o r p i c t u r e s , and t e s t i n g r e c o g n i t i o n a t v a r i o u s i n t e r v a l s , I t i s e x p e c t e d t h a t r e h e a r s a l and i n t e r f e r e n c e e f f e c t s o f p r e v i o u s STM 13 s t u d i e s can be r e p l i c a t e d w i t h v e r b a l m a t e r i a l . The i m p o r t a n t f i n d i n g s In t h i s r e s e a r c h , however, w i l l c e n t e r around r e h e a r s a l and i n t e r f e r e n c e e f f e c t s i n p i c t u r e c o n d i t i o n s . S i n c e t h e r e s u l t s can be i n f l u e n c e d by d i f f e r e n t i a l a c q u i s i t i o n r a t e s i n t h e l e a r n i n g s t a g e , d e f i n i t e p r e d i c t i o n s can n o t be made a t t h i s t i m e , but t h e i m p l i c a t i o n s a r i s i n g from t h e r e -s u l t s w i l l under any c i r c u m s t a n c e s be v a l u a b l e . A c o m p a r i s o n o f t h e I n t e r p o l a t e d a c t i v i t y e f f e c t s a c r o s s word and p i c t u r e p r e s e n t a t i o n s s h o u l d r e v e a l p o s s i b l e d i f f e r e n c e s o r s i m i l a r i t i e s o f t h e two c o d i n g mechanisms, w h i l e a c o m p a r i s o n o f r e h e a r s a l and i n t e r f e r e n c e e f f e c t s i n t h e p i c t u r e g roups s h o u l d throw some l i g h t on t h e u s e f u l n e s s o f t h e c o n c e p t o f a v i s u a l r e h e a r s a l mechanism. However, b e f o r e i t i s assumed t h a t a g i v e n e x p e r i m e n t has exposed v e r b a I - p i c t o r i a I c o d i n g d i f f e r e n c e s of s h o r t - t e r m p r o c e s s e s , s e v e r a l c r i t i c a l a s p e c t s o f t h e d e s i g n w i l l have t o be c a r e f u l l y c o n s i d e r e d . One m ajor problem In a w o r d - p i c t u r e c o m p a r i s o n i s t h e u n c e r t a i n t y as t o what e x t e n t t h e two c o d i n g p r o c e s s e s m i g h t be confounded w i t h i n each o p e r a t i o n a l l y d e f i n e d c o n d i t i o n . T h at i s , how r e a d i l y and how f a s t a r e p i c t u r e s en-coded v e r b a l l y , and words coded p i c t o r i a l l y , t h e r e b y r e f l e c t i n g r e s u l t s w i t h -i n a g i v e n c o n d i t i o n , which m i g h t i n f a c t be m e d i a t e d by p r o c e s s e s i n both m o d a l i t i e s . R e a c t i o n t i m e measures, f o r i n s t a n c e , show v i s u a l e n -c o d i n g of words t o be s l o w e r t h a n v e r b a l e n c o d i n g of p i c t u r e s . A l s o , words can be r e a d f a s t e r t h a n o b j e c t s can be named ( P a i v i o & Czapo, 1969). B u t , e v i d e n c e of t h i s k i n d can o n l y be c o n s i d e r e d as a rough c o r r e l a t i o n of motor and s e n s o r y - m o t o r r e s p o n s e s w i t h t h e i r u n d e r l y i n g p s y c h o l o g i c a l p r o c e s s e s , w i t h o u t r e v e a l i n g d i r e c t e v i d e n c e about t h e a v a i l a b i l i t y o f 14 these memory processes. It becomes necessary, t he re fo re , to cons ider c a r e f u l l y encoding, s torage, and r e t r i e v a l f ac to r s in the design of the experimental task, In order to reduce, if not e l iminate confounding e f f e c t s of cross -modal i ty encoding. 15 EXPERIMENT I I n t r o d u c t i o n The f i r s t e x p e r i m e n t was d e s i g n e d t o d e t e r m i n e t o what e x t e n t words and p i c t u r e s can be d i f f e r e n t i a l l y encoded In t h e i r r e s p e c t i v e v e r b a l and v i s u a l STS, how e f f e c t i v e t h e two codes a r e In a r e c o g n i t i o n s equence, and how damaging v e r b a l i n t e r f e r e n c e i s on t h e s h o r t - t e r m s t o r a g e i n b oth c o d i n g s y s t e m s . A s e r i e s o f p i l o t s t u d i e s , r a n g i n g from p r e s e n t -i n g one i t e m , t o p r e s e n t i n g n i n e items i n a P e t e r s o n and P e t e r s o n t a s k , l e d t o t h e c h o i c e o f u s i n g s i x Items, p r e s e n t e d f o r 1.2 s e c o n d s , as an o p t i m a l l e a r n i n g t a s k . The t e s t phase of t h e e x p e r i m e n t c o n s i s t e d o f s i x item r e c o g n i t i o n sequences a f t e r 0, 15 and 30 seconds o f v e r b a l i n t e r f e r -ence w h i c h c o u l d be a n a l y s e d w i t h r e s p e c t t o r e c o g n i t i o n and l a t e n c y s c o r e s . The c h o i c e o f p a r t i c u l a r t e mporal and t a s k v a r i a b l e s was l a r g e l y based on p r e v i o u s r e s e a r c h f i n d i n g s and r e s u l t s from p i l o t s t u d i e s . Hence, t h e c o m b i n a t i o n o f i n p u t c a p a c i t y and t e m p o r a l p r e s e n t a t i o n seemed s u f f i c -i e n t l y d i f f i c u l t t o a l l o w f o r e r r o r s r e f l e c t i n g changes due t o t h e i n t e r -p o l a t e d a c t i v i t y , w h i l e a l s o r e m a i n i n g w i t h i n t h e immediate memory span c a p a c i t y ( M i l l e r , 1956). A l t h o u g h t h e r e was no e x p e r i m e n t a l c o n t r o l o v e r t h e t i m e S_ would spend w i t h each item i n t h e m a t r i x , i t was e x p e c t e d t h a t t h e r e q u i r e m e n t s of t h e r e s p o n s e t a s k would f o r c e S_ t o scan o v e r each item In t h e m a t r i x a t an e q u a l l y r a p i d r a t e , i . e . on t h e a v e r a g e 200 m i l l i s e c o n d s , t o r e d u c e , i f not t o e l i m i n a t e c r o s s - m o d a l i t y e n c o d i n g ( P a i v i o & Czapo, 1969; N e i s s e r , 1967). The c h o i c e o f a s i x - i t e m r e c o g n i t i o n sequence was p a r t l y an a r b i t r a r y d e c i s i o n . T h i s t a s k has t h e advantage o f t e s t i n g a 16 l a r g e r p a r t o f t h e memory s t o r e , W h i l e p o s s i b l y i n t r o d u c i n g a d d i t i o n a l d e l a y e f f e c t s f o r most r e c o g n i t i o n r e s p o n s e s . In any c a s e , a r e c o g n i t i o n t a s k w i l l m i n i m i z e r e t r i e v a l problems and, t h e r e f o r e , r e f l e c t r e s p o n s e s c o r e s which a r e more s e n s i t i v e t o memory s t o r a g e . I t a l s o has t h e advantage of a v o i d i n g t h e n e c e s s i t y o f v e r b a l r e s p o n d i n g t o p i c t o r i a l m a t e r i a l . D i f f e r e n t i a l c o d i n g mechanisms f o r v i s u a l l y p r e s e n t e d words and p i c t u r e s can t h e n be a s s e s s e d by r e c o g n i t i o n and l a t e n c y s c o r e s In a f a c t o r i a l d e s i g n u s i n g words and p i c t u r e s i n t h e l e a r n i n g and r e c o g n i t i o n s t a g e . T h i s d e s i g n g e n e r a t e s two s a m e - p r e s e n t a t i o n g r o u p s , i . e . Word-Word (WW) and P i c t u r e - P i c t u r e ( P P ) , and two mixed p r e s e n t a t i o n g r o u p s , i . e . W o r d - P i c t u r e (WP) and P i c t u r e - W o r d (PW). P r e d i c t i o n s as w e l l as r e s u l t s o f t h i s e x p e r i m e n t w i l l have t o be e v a l u a t e d w i t h r e s p e c t t o two q u e s t i o n s : I) i s t h e l e a r n i n g r a t e t h e same f o r p i c t u r e s and words?; 2) how s t r o n g , i f any, a r e t h e e f f e c t s o f c r o s s - m o d a l i t y e n c o d i n g ? The f i r s t q u e s t i o n was t e n t a t i v e l y r e s o l v e d In p i l o t work where r e c a l l and r e c o g n i t i o n s c o r e s , as w e l l as s u b j e c t i v e r e p o r t s o f s c a n n i n g r a t e s seemed t o s u g g e s t s i m i l a r l e a r n i n g r a t e s f o r words and p i c t u r e s . The second problem can be more s a t i s f a c t o r i l y a s s e s s e d by a c o m p a r i s o n of WW-WP and PP-PW g r o u p s . If t h e m i x e d - p r e s e n t a t i o n groups r e v e a l a s i m i l a r i n t e r f e r e n c e e f f e c t as t h e i r r e s p e c t i v e s a m e - p r e s e n t a t i o n groups i t can be s a f e l y i n f e r r e d t h a t t h e I n f o r m a t i o n was s t o r e d i n t h e form of t h e l e a r n i n g phase, i . e . no c r o s s - m o d a l i t y e n c o d i n g . T h i s a n a l y s i s , o f c o u r s e , p r e c l u d e s a d i f f e r -e n t i a l i n t e r f e r e n c e e f f e c t i n WW and PP g r o u p s . G i v e n t h e s e two assump'tions, t h e f o l l o w i n g a s s e s s m e n t of d i f f e r -17 e n t i a l s t o r a g e f o r word and p i c t u r e m a t e r i a l can be made. Z e r o d e l a y r e s -ponses f o r WW and PP groups s h o u l d r e f l e c t t h e most a c c u r a t e s t o r a g e d i f f e r e n c e s due t o v e r b a l and v i s u a l c o d i n g e f f e c t s . Comparisons among WW-WP and PP-PW s h o u l d r e v e a l no d i f f e r e n c e s i n r e c o g n i t i o n s c o r e s u n l e s s t h e s t i m u l u s m a t e r i a l s a r e p o o r l y d e s i g n e d . L a t e n c y s c o r e s i n t h e s e com-p a r i s o n s s h o u l d , however, d i f f e r because of i n c r e a s e d r e t r i e v a l problems i n m i x e d - p r e s e n t a t i o n g r o u p s . I n t e r f e r e n c e e f f e c t s on v e r b a l s t o r a g e s h o u l d l e a d t o lower r e c o g n i t i o n s c o r e s w i t h l o n g e r d e l a y s , w h i l e r e s -ponses i n t h e p i c t u r e groups s h o u l d show t o what e x t e n t t h e v i s u a l s t o r e i s a f f e c t e d by v e r b a l i n t e r f e r e n c e . A com p a r i s o n o f WW-WP and PP-PW groups s h o u l d i n t u r n i n d i c a t e t h e degree o f c r o s s - m o d a l i t y e n c o d i n g under t h e s e e x p e r i m e n t a l c o n d i t i o n s . If t h e s e two a s s u m p t i o n s do not h o l d , d i f f e r e n t r e s u l t s w i l l have t o be e x p e c t e d . D i f f e r e n t i a l l e a r n i n g r a t e s w i l l , o f c o u r s e , r e n d e r t h e a n a l y s i s o f v e r b a l v e r s u s v i s u a l s t o r a g e mechanisms w o r t h l e s s . S i m i l a r l y , c r o s s - m o d a I i t y e n c o d i n g , i f i t o c c u r s i n bo t h d i r e c t i o n s w i l l reduce word-p i c t u r e d i f f e r e n c e s w i t h i n each d e l a y c o n d i t i o n . In e f f e c t t h e n , w h i l e I t m i g h t be i m p o s s i b l e t o s e p a r a t e c o m p l e t e l y v e r b a l and v i s u a l memory p r o c e s s e s i n a g i v e n e x p e r i m e n t a l d e s i g n and, i n t h e end, be a b l e t o p o s t u l a t e p u r e l y v e r b a l and p u r e l y v i s u a l components o f STS, i t can be ex p e c t e d t h a t a t l e a s t t h e r e s u l t s o f t h e d e s i g n w i l l i n d i c a t e t o what e x t e n t t h i s aim has been a c h i e v e d . METHOD S u b j e c t s and D e s i g n S t u d e n t s from i n t r o d u c t o r y p s y c h o l o g y c o u r s e s were c o n t a c t e d by 18 phone and asked to v o l u n t e e r f o r the experiment. Forty males and f o r t y females, ranging in age from 17 to 23 years, p a r t i c i p a t e d in EXP. I. Twenty Ss were assigned t o each group, i . e . WW, WP, PW, PP. Each group was f u r t h e r subdivided i n t o sub-groups of f i v e Ss each r e c e i v i n g a d i f f e r -ent learning I i s t . Delay was added as a w i t h i n - s u b j e c t v a r i a b l e . The three delay p e r i o d s , 0, 15 and 30 s e c , were randomly assigned to the nine t r i a l s in blocks of t h r e e s . Since complete l a t i n i z a t i o n of delay, t r i a l s , and sets of l i s t s seemed unfeasable, two randomly determined delay sequences were used f o r 10 _S_s in each group. No c l a i m can be made about complete random-i z a t i o n of the delay v a r i a b l e . However, s i m i l a r t o the probe p o s i t i o n v a r i a b l e w i t h i n the l i s t s , the complexity of the task l e f t no choice about these p o s s i b l e confounding e f f e c t s . M a t e r i a l A b a s i c pool of 81 items was obtained from stimulus m a t e r i a l used by P a i v i o and Czapo (1969). The items c o n s i s t e d of p i c t o r i a l represent-a t i o n s of f a m i l i a r o b j e c t s in the form of simple l i n e drawings. Consistency of l a b e l l i n g data had been obtained on these drawings ( P a i v i o & Czapo, 1969) to ensure unambiguity of the s t i m u l i . In t h e i r verbal form the items c o n s i s t e d of concrete words with high frequency and meaningfuIness r a t i n g s . For the verbal c o n d i t i o n each word was p r i n t e d on a 4" x 6" card in I - i n . block l e t t e r s . For the p i c t u r e c o n d i t i o n each item appeared as a simple l i n e drawing. Special care had been taken t o keep s i z e and complexity of the drawings equal f o r a l l o b j e c t s . Two sets of items were constructed f o r each t r i a l . S i x items per 19 t r i a l appeared i n the l e a r n i n g phase as a 3 x 2 m a t r i x , t h r e e items h i g h and two a c r o s s . Three items from t h e l e a r n i n g s t a g e (OLD items) and t h r e e NEW items were th e n randomly a r r a n g e d f o r t h e r e c o g n i t i o n sequence. The m a t r i c e s as w e l l as t h e s i n g l e r e c o g n i t i o n items were t h e n photographed i n t h e i r v e r b a l and p i c t o r i a l form. The n e g a t i v e s were mounted as s l i d e s i n w h i c h t h e items appeared as w h i t e o u t l i n e s on a d a r k background. T h e r e were two problems which had t o be c o n s i d e r e d i n c o n s t r u c t i n g t h e l i s t s : (a) t h e p o s i t i o n s of t h e probe items i n t h e m a t r i x as w e l l as i n t h e r e c o g n i t i o n sequence; (b) h i g h a s s o c i a t i o n s o f i t e m s , s e m a n t i c and a c o u s t i c s i m i l a r i t i e s of words as w e l l as s i m i l a r i t i e s o f t h e i r p i c t o r i a l r e p r e s e n t a t i o n s had t o be a v o i d e d w i t h i n each l i s t . S i n c e i t seemed u n f e a s a b l e t o l a t i n i z e c o m p l e t e l y probe p o s i t i o n s and l i s t c o n t e n t , f o u r s e t s of n i n e l i s t s each were c o n s t r u c t e d . The number o f l i s t s used was l a r g e l y l i m i t e d by t h e number of a v a i l a b l e items which c o u l d meet t h e c r i t e r i a o f s t i m u l u s s e l e c t i o n . Two s e t s o f l i s t c o n t e n t and tv/o s e t s of probe p o s i t i o n s were f a c t o r i a l l y combined t o g e n e r a t e f o u r d i f f e r e n t s e t s o f l e a r n i n g l i s t s . S e t l a d i f f e r e d from s e t l b o n l y w i t h r e s p e c t t o t h e p o s i t i o n s o f t h e p r o b e s . S e t I l a and I lb c o n t a i n e d a new arrangement of l i s t c o n t e n t , but had t h e same probe p o s i t i o n s as l a and lb r e s p e c t i v e l y . The r e c o g n i t i o n sequences I and I I , f o l l o w i n g l e a r n i n g l i s t s l a , lb and M a , Mb r e s p e c t i v e l y , d i f f e r e d i n l i s t c o n t e n t , but n o t i n probe p o s i t i o n s . In e f f e c t t h e n , each probe Item i n t h e l e a r n i n g s t a g e was p r e s e n t e d a t two d i f f e r e n t p o s i t i o n s i n t h e m a t r i x , and each probe p o s i t i o n i n t h e l e a r n i n g s t a g e was t e s t e d w i t h two d i f f e r e n t probe i t e m s . 20 The probe p o s i t i o n s in the mat r i ce s and the r e cogn i t i o n sequence were, of cour se , randomly determined, and every p o s i t i o n was equa l l y o f t e n probed. However, s i n ce there are s i x p o s s i b l e p o s i t i o n s and nine t r i a l s , w i th th ree probes In each t r i a l , ha l f of the p o s i t i o n s were ass igned f o u r , the o the r ha l f f i v e probes over a l l nine t r i a l s . The s e l e c t i o n of l i s t content f o r the two s e t s , in c o n t r a s t , was on l y p a r t l y determined by random s e l e c t i o n , s i n ce o ther f a c t o r s seemed of g r ea te r importance. For i n s tance , a c o u s t i c a l l y s i m i l a r items had to be separa ted , e .g . t owe r - f l owe r , a s s o c i a t i o n s l i k e f lower-boy had t o be avo ided, and c a t e g o r i e s , e .g . f r u i t s , animals e t c . had to be evenly d i v i ded over the n ine t r i a l s . At the same t ime i t was c r i t i c a l not to inc lude items w i th p i c t o r i a l s i m i l a r i t y in the same l i s t , e.g. penc i I - a r r ow-c i g a r . In a d d i t i o n , two p r a c t i c e l i s t s were cons t ruc ted to f a m i l i a r i z e S_ w i th the procedure. S ince words and p i c t u r e s were used In the t e s t phase, l e t t e r s of the a lphabet were chosen as f a i r l y neut ra l items f o r the p r a c t i c e s e s s i on . Apparatus A Carousel 850 p r o j e c t o r was connected to an automatic t imer f o r the p re sen ta t i on of the ma t r i x . Recogn i t ion s l i d e s were presented man-u a l l y by p res s ing a button on E_'s pane l . Th i s button a l s o a c t i v a t e d a stop t ime r . The S_'s panel had two but tons , labe led OLD, NEW. When one of these was a c t i v a t e d , i t stopped the t imer and l i t up one of two l i g h t s on E_'s p ane l , i n d i c a t i n g the response cho i ce . E_ was then ab le t o r e c y c l e both panels f o r the next o p e r a t i o n . In a d d i t i o n , IE had a separate t imer to i n d i c a t e delay per iods as wel l as p re sen ta t i on ra te of the r e c o g n i t i o n 21 sequence. Procedure Ss were i n d i v i d u a l l y t e s t e d and randomly assigned t o the four groups. The male-female r a t i o was constant across groups. Upon en t e r i n g the lab, S_ was seated in f r o n t of the response panel e i g h t f e e t from a 3 x 2 f o o t screen. E_ read out a standard s e t of i n s t r u c t i o n s (Appendix), d i f f e r i n g f o r the f o u r groups only with respect t o the p a r t i c u l a r word-p i c t u r e p r e s e n t a t i o n involved. S_ was t o l d he would be presented with a matrix of s i x items f o r one second, followed by a sequence of s i x recog-n i t i o n s l i d e s . Some of the r e c o g n i t i o n s l i d e s were from the previous m a t r i x , and some were new items. As a r e c o g n i t i o n s l i d e appeared on the screen, he was to press, as f a s t as p o s s i b l e , one of the response buttons, i . e . OLD, f o r items from the previous m a t r i x , NEW, f o r Items he had not seen before. Since the matrix was presented f o r a r e l a t i v e l y b r i e f ex-posure, i t was twice emphasized t h a t S_ would have to scan over the s i x items as f a s t as p o s s i b l e in order to maximize h i s r e c o g n i t i o n score. In a d d i t i o n , i f a t h r e e - d i g i t number appeared on the screen a f t e r the matrix d i s p l a y , S_ was i n s t r u c t e d to count backwards by threes from t h a t number, t i l l the f i r s t r e c o g n i t i o n s l i d e was presented. S^did not know how many delay t r i a l s o r when delay t r i a l s o c curred, nor was S_ aware of the OLD-NEW item r a t i o In the r e c o g n i t i o n sequence. I n s t r u c t i o n s were followed by two p r a c t i c e t r i a l s , one with delay the other with immediate r e c o g n i t i o n , to f a m i l i a r i z e S_ with the general procedure. The f o l l o w i n g temporal sequence was maintained throughout the ex-periment. Each t e s t t r i a l s t a r t e d with a 1.2 second presentation of the 22 m a t r i x , followed w i t h i n one second by e i t h e r the f i r s t r e c o g n i t i o n s l i d e o r a number, in case of delay t r i a l s . The p r e s e n t a t i o n r a t e during the r e c o g n i t i o n sequence was 7.5 seconds per s l i d e , which included one second f o r the s l i d e change, f o r a t o t a l of 45 seconds per r e c o g n i t i o n sequence. Since the occasional S_ d i d not respond every time w i t h i n the 6.5 second pr e s e n t a t i o n of the r e c o g n i t i o n item, and no p r o v i s i o n s had been r.-iade t o continue the r e c o g n i t i o n sequence unless S_ had responded, E_ was not able t o adhere s t r i c t l y t o the 7.5 second p r e s e n t a t i o n rate in a l l cases. Yet the time f o r the whole r e c o g n i t i o n sequence, i . e . maximum 45 seconds, was c o n s i s t e n t across a l l Ss. There was a 20 second i n t e r v a l between the end of the r e c o g n i t i o n sequence, i . e . 45 seconds a f t e r the p r e s e n t a t i o n of the f i r s t r e c o g n i t i o n s l i d e , and the onset of the next t r i a l . During the r e c o g n i t i o n sequence E_ scored the response choice as well as latency f o r each OLD and NEW item. RESULTS & DISCUSSION Latency and choice responses were c o l l a p s e d over the f o u r sets of m a t e r i a l . Reaction time measures were almost constant across a l l f o u r groups and delay c o n d i t i o n s (Table 4 ) , which i s q u i t e contrary t o expected r e s u l t s . While these r e s u l t s could i n i t i a l l y be i n t e r p r e t e d in terms of u n d i f f e r e n t i a t e d coding mechanisms across stimulus material and i n t e r -ference c o n d i t i o n s , an i n s p e c t i o n of the choice data i n v a l i d a t e s t h i s c l a i m . In l i g h t of other research i n v e s t i g a t i n g r e a c t i o n time in an STM t a s k , (Posner et aJL , 1969; Tversky, 1969) i t becomes apparent t h a t the u n d e r l y i n g causes f o r the u n d i f f e r e n t i a t e d latency scores can be a t t r i b u t e d to the p a r t i c u l a r experimental task at hand. For instance, Posner et a I. 23 and Tversky used repeated d a i l y sess ions and h i gh l y ove r lea rned t e s t and r e cogn i t i o n ma te r i a l in o rder t o ob t a i n latency d i f f e r e n c e s , in c on t r a s t to new m a t e r i a l , and one se s s ion of n ine r e cogn i t i o n t r i a l s in t h i s ex -per iment. Furthermore, s i n ce S_ in t h i s experiment was g iven 6.5 seconds t o respond i t seems ques t i onab le whether S '^s emphasis was on f a s t r e s -ponding o r c o r r e c t responding. S ince the cho ice data presented c o n s i s t e n t r e c o g n i t i o n d i f f e r e n c e s across c ond i t i o n s and latency scores were f a i r l y con s tan t , they were excluded from f u r t h e r ana lyses in l i g h t of the above mentioned l i m i t a t i o n s o f the exper imental s i t u a t i o n . The cho ice data were analysed wi th re spect t o th ree response measures: ( I ) c o r r e c t probe responses; (2) d ' scores f o r a l l th ree recog-n i t i o n sequences in each delay c o n d i t i o n ; (3) percent c o r r e c t responding to probe items w i th respect to t h e i r p o s i t i o n in the r e c o g n i t i o n sequence. The d ' scores i nc lude a c o r r e c t i o n f o r guess ing. It i s , f o r i n s tance , p o s s i b l e f o r S_ t o respond OLD t o every r e c o g n i t i o n i tem, thereby o b t a i n i n g an e r r o r l e s s score on the probe ana l y s t s which does not r e f l e c t h i s t r ue r e c o g n i t i o n l e v e l . The d ' score was developed to c o r r e c t the data f o r guessing e r r o r s of t h i s type ( K i n t s c h , 1970) by t rans fo rming the number of OLD responses t o OLD items and number of OLD responses t o NEW items t o standard scores on the normal curve. Th i s does not mean, however, t h a t the probe a n a l y s i s should be complete ly ignored, s i n ce d i s c repanc i e s between the two measures w i l l po i n t out exper imental c ond i t i on s which are s u s c e p t i b l e to guess ing. I n i t i a l l y , the t o t a l c o r r e c t and i n c o r r e c t responses f o r OLD and NEW items were computed f o r each S_. The mean c o r r e c t responses f o r OLD 24 and i n c o r r e c t r e s p o n s e s f o r NEW items can be seen i n T a b l e s I and 3. F a l s e a l a r m s c o r e s were s u b s e q u e n t l y a n a l y s e d o n l y i n c o n j u n c t i o n w i t h d' s c o r e s . A 2 x 2 x 3 a n a l y s i s o f v a r i a n c e was p e rformed on d a t a from t h e c o r r e c t probe r e s p o n s e s . The f a c t o r s a r e : s t u d y - p r e s e n t a t i o n (word v s . p i c t u r e ) ; t e s t - p r e s e n t a t i o n (word v s . p i c t u r e ) , and t h r e e d e l a y c o n d i t i o n s as a r e p e a t e d measure ( A p p e n d i x , T a b l e I ) . P r e s e n t a t i o n e f f e c t s a r e s m a l l and n o t s i g n i f i c a n t i n t h e s t u d y o r r e c o g n i t i o n phase. T h e r e i s no main e f f e c t f o r d e l a y . However, t h e s t u d y - p r e s e n t a t i o n x d e l a y i n t e r a c t i o n i s s i g n i f i c a n t ( F = l l . 9 9 ; df=2, 152; p <. 0 1 ) . An a n a l y s i s o f s i m p l e e f f e c t s ( A p p e n d i x , T a b l e 2) p o i n t s o u t t h a t s t u d y - p r e s e n t a t i o n e f f e c t s a ppear o n l y a t z e r o d e l a y (F=26.26; df=2, 152; p<.OI). A Newman-KeuIs t e s t ( A p p e n d i x , T a b l e 3) f u r t h e r c l a r i f i e d t h e n a t u r e of t h i s i n t e r a c t i o n . A f t e r 15 seconds o f d e l a y , p r e s e n t a t i o n d i f f e r e n c e s d i s a p p e a r due t o a s i g n i f i c a n t d e c r e a s e f o r v e r b a l and s i g n i f i c a n t I n c r e a s e f o r p i c t u r e s t u d y g r o u p s . In e f f e c t , t h e r e a r e o n l y random d i f f e r e n c e s between t h e f o u r g r o u p s a t 15-and 3 0 -sec. d e l a y c o n d i t i o n s . A 2 x 2 x 3 a n a l y s i s of v a r i a n c e f o r d' s c o r e s ( A p p e n d i x , T a b l e 4) p r e s e n t s some changes i n t h e r e s p o n s e p a t t e r n ( F i g . I & 2 ) . There i s a s i g n i f i c a n t s t u d y x t e s t p r e s e n t a t i o n i n t e r a c t i o n (F=I0.89; d f = l , 7 6 ; p<.01). R e c o g n i t i o n s c o r e s i n both m i x e d - p r e s e n t a t i o n and PP g r o u p s a r e s i g n i f i c a n t l y lower t h a n f o r t h e WW g r o u p , as i n d i c a t e d by an a n a l y s i s o f s i m p l e e f f e c t s ( A p p e n d i x , T a b l e 5 ) . The p r e v i o u s s t u d y - p r e s e n t a t i o n x d e l a y i n t e r a c t i o n i s , however, a l s o r e p l i c a t e d w i t h d' s c o r e s (F=8.42; df=2, 152; p<.OI). A Newman-Keuls t e s t ( A p p e n d i x , T a b l e 7) r e v e a l s o n l y m i n o r d i s c r e p a n c i e s between t h e two a n a l y s e s a t 30 seconds d e l a y . Y e t TABLE 1 Mean Number of Correct Probe Responses with Verbal Interference (Experiment I) Delay in Seconds 0 15 30 WW 7.75 6.70 7.60 WP 7.50 6.85 6.95 PW 6.60 6.95 7.20 PP 5.90 7.40 7.45 TABLE 2 Mean d' Scores f o r Experiment I Delay in Seconds 0 15 30 WW 3.97 3.37 3.17 WP 3.17 2.37 2.30 PW 2.42 2.79 2.95 PP 2.64 3.59 2.95 26 TABLE 3 Mean False Alarm Rate f o r Experiment I Q Delay in Seconds 0 15 30 WW .1 .1 .9 WP .7 1.2 2.00 PW 1.2 .9 1.3 PP .6 .6 1.1 TABLE 4 Mean Latency Scores f o r Experiment I Note: Reaction Time measures include a constant of one second f o r s l i d e change. Delay in Seconds 0 15 30 WW 2.35 2.66 2.49 WP 2.54 2.66 2.82 PW 2.51 2.66 2.48 PP 2.48 2.34 2.35 27 2 0 15 30 Delay in Seconds FIG, 2. d' Scores f o r EXP.- I out of a Maximum of S i x . 29 both analyses agree t h a t s t udy -p re sen ta t i on e f f e c t s appear on ly in the zero delay c o n d i t i o n , f o l l owed by a s i g n i f i c a n t convergence of s tudy -p re sen ta t i on e f f e c t s over de lay . S ince d i s c repanc i e s between the two response measures can be a t t r i b u t e d to the c o r r e c t i o n f a c t o r f o r guessing in the d ' s co re s , a com-par i son of the response pa t te rn ( F i g . I & 2 ) , F r a t i o s (Appendix, Tables I & 4 ) , and f a l s e alarm r a t e s , should po i n t out d i f f e r e n t i a l guess ing rates f o r some of the exper imental c o n d i t i o n s . High agreement between the r e -sponse measures should i n d i c a t e exper imental c ond i t i on s in which Ss f e l t f a i r l y c on f i den t about what they have learned, whereas d i s c repanc i e s w i l l des ignate c ond i t i o n s in which Ss d id not f ee l as con f i den t about d i f f e r -e n t i a t i n g between probe and d i s t r a c t o r items in the r e c o g n i t i o n sequence. An i n spec t i on of F i g . I and 2 suggest t ha t l i t t l e guess ing occurred f o r WW and PP groups, e s p e c i a l l y a t zero de lay . The d i f f e r e n t response pa t te rn s f o r the mixed p re sen ta t i on groups, e s p e c i a l l y a f t e r longer de l ay s , in c o n t r a s t , suggest two independent f a c t o r s which seem to encourage guessing i . e . m ixed-p resenta t ion and de lay . Th i s i s f u r t h e r s ub s t an t i a t ed by the d i f f e r e n t s i g n i f i c a n t F r a t i o s of both ana ly ses . Even though latency scores d id not support the c l a im f o r i n c rea s i ng r e t r i e v a l problems in PW and WP, d i s c repanc i e s between probe responses and d ' scores suggest t h a t the h igher guess ing ra te in these groups could be due to i n c rea s i ng e r r o r s i f words have to be recognized as p i c t u r e s and v i c e ve r sa . On the o the r hand, i t seems not too s u r p r i s i n g t o f i n d longer i n t e r f e r ence a s soc i a ted wi th increased guess ing. An a d d i t i o n a l f a c t o r c o n t r i b u t i n g to increased guess ing dur ing delay c ond i t i o n s can be a t t r i b u t e d to the exper imental 30 des ign . That i s , de lay was used as a w l t h i n - S v a r i a b l e . There fo re , a p a r t i c u l a r response se t t o f i n d an equal number of o l d responses in each r e c o g n i t i o n sequence might have developed In Ss, leading to h igher guessing rates in these c o n d i t i o n s . O v e r a l l word -p i c tu re p re sen ta t i on e f f e c t s are a t t h i s stage s t i l l f a i r l y ambiguous. The s t udy -p re sen ta t i on e f f e c t s of the f i r s t a n a l y s i s w i l l have to be a t t r i b u t e d to guessing e r r o r s inherent in the raw da ta , in l i g h t of the d i f f e r e n t s i g n i f i c a n t main e f f e c t s found in both ana ly ses . Even the study x t e s t - p r e s e n t a t i o n i n t e r a c t i o n of the d ' scores has t o be q u a l i f i e d by a s t rong s t udy -p re sen ta t i on x delay i n t e r a c t i o n . S ince zero delay responses are the most accurate i n d i c a t o r s of STS, the c o n s i s t e n t wo rk -p i c tu re d i f f e r e n c e , a t l e a s t f o r the learn ing s tage , presents f a i r l y s t rong support f o r the predominantly v e r b a l - a c o u s t i c coding mech-anism of STS. Even t h i s f i n d i n g has t o be q u a l i f i e d by subsequent c l a r i -f i c a t i o n of p o s s i b l e d i f f e r e n t i a l l ea rn ing ra te s f o r p i c t u r e s and words. Delay e f f e c t s in c o n t r a s t are more c o n s i s t e n t , y e t , even more p u z z l i n g f o r the p i c t u r e study groups. As p r e d i c t e d , verba l i n t e r f e r ence damages the r e c o g n i t i o n leve l of ve rba l m a t e r i a l . Whi le i n t e r f e r ence e f f e c t s cou ld be expected t o be lower f o r the v i s u a l s t o r e , an increase in r e c o g n i t i o n leve l c e r t a i n l y seems c o n t r a d i c t o r y to prev ious r e s u l t s and would not be expected on the bas i s of any cu r ren t t h e o r e t i c a l framework. It Is important to note though t ha t i n t e r f e r ence e f f e c t s f o r mixed-p re sen ta t i on groups are always c o n s i s t e n t w i th t h e i r r e spec t i ve same moda l i t y group, which prov ides some evidence aga in s t c ro s s -moda l i t y en -coding in the lea rn ing phase. 31 In order to invest igate f u r the r the nature of the d i f f e r e n t i a l Interference e f f e c t s f o r words and p i c tu re s , responses In the recogni t ion sequence w i l l be analyzed In more d e t a i l . The recogn i t ion task i t s e l f lasted 45 seconds, thereby cons t i tu t i ng an addi t iona l delay component f o r f i v e out of s i x recogni t ion Items in each sequence. That Is, the temporal arrangement of the recogni t ion task could be a f ac to r determining the unexpected Interference e f f e c t s . Probe responses were, the re fo re , converted into percentages of co r rec t responding per pos i t i on in the sequence. While the data are analyzed In conjunct ion with the resu l t s from EXP. I l l ( F i g . 3) and are discussed in more de ta i l at that stage, It s u f f i c e s to mention here that apart from random f luc tua t ions within cond i t i ons , only one cons i s tent pattern emerged. Probe responses f o r the f i r s t pos i t i on at zero delay are almost e r r o r l e s s , I.e. 85% and 90% f o r PP and WW re spec t i ve l y , and are fol lowed by a s i g n i f i c a n t <!rop to a constant recogni t ion level fo r the remaining po s i t i on s . Su rpr i s i ng l y though, the word-picture d i f f e rence s t i l l remains even for the small d i f f e rence in the f i r s t pos i t i on when analyzed in conjunction with a l l pos i t ions of the sequence. In any case, the c r i t i c a l f i nd ing here is the s i g n i f i c a n t drop from the f i r s t pos i t i on to the rest of the sequence. Probe pos i t i on percentages were a l so computed fo r WP and PW groups (Table 7) but were excluded from fur ther ana lys i s s ince mixed presentat ion groups were e l iminated from fur ther i nves t i ga t i on . In s p i t e of several l im i ta t ions of the percentage data, i . e . percentages are based on only one or two data points per probe pos i t i on and are not corrected f o r guessing, a new Interpretat ion of the e x p e r i -32 mental t a s k , at l e a s t f o r the zero delay c o n d i t i o n s , becomes p l a u s i b l e a t t h i s stage. The previous word-picture d i f f e r e n c e s a t zero delay, col lapsed over a l I r e c o g n i t i o n p o s i t i o n s , c l e a r l y support the verbal super-i o r i t y In STM experiments. The small modality d i f f e r e n c e , i . e . 85% and 90%, and temporal c o n s i d e r a t i o n of the f i r s t p o s i t i o n response are more in l i n e with previous research i n v e s t i g a t i n g v e r b a l - v i s u a l d i f f e r e n c e s using very short temporal parameters. In a p a r t i a l r e c a l l experiment of a 4 x 4 matrix of l e t t e r s , s u b s t i t u t i o n e r r o r s , f o r instance, were found to be predominantly v i s u a l (Rudov, 1966). With a s i m i l a r approach Turvey (1967) found a l s o no a c o u s t i c confusion e f f e c t s . In a d d i t i o n , Posner e t aj_. (1969) presented convincing evidence f o r equal v i s u a l o r name matching under given c o n d i t i o n s . Unrelated as these experiments might seem, they do show t h a t s i m i l a r as w e l l as d i f f e r e n t coding a b i l i t i e s of v i s u a l and verbal m a t e r i a l can be obtained depending on given temporal parameters. N e i s s e r (1967) concludes from h i s research t h a t words or drawings do not d i f f e r as long as the " i c o n i c s t o r e " has not been encoded v e r b a l l y . Furthermore, research in t a c h I s t o s c o p i c r e c o g n i t i o n leaves l i t t l e doubt t h a t v i s u a l impressions are b r i e f l y a v a i l a b l e f o r f u r t h e r processing even a f t e r the termination of the v i s u a l s t i m u l u s . The duration of t h i s sensory d i s p l a y depends l a r g e l y on the duration and i n t e n s i t y of the v i s u a l d i s p l a y as well as the type of post exposure f i e l d ( S p e r l i n g , I960, 1963). While some t h e o r i s t s are not as outspoken about the e f f e c t s of the sensory memory in a wide range of experimental s i t u a t i o n s due t o the lack of s u f f i c i e n t e m p i r i c a l v a l i d a t i o n (Atkinson & S h i f f r i n , 1968), 33 Ne l s se r (1967, p. 20) c la ims t h a t under idea l c ond i t i on s , : t he Icon remains l e g i b l e as long as f i v e seconds. " Whether the exper imental task a t hand q u a l i f i e s as an " i d e a l c o n d i t i o n " i s , of cour se , que s t i onab le . C e r t a i n l y , the s t imu lu s Is presented r e l a t i v e l y long, the whi te o u t l i n e s on a dark background seem of adequate i n t e n s i t y , and most of a l l , there i s no masking e f f e c t before the f i r s t r e c o g n i t i o n s l i d e . But, on the o the r hand, eye movements and phy s i ca l scanning of the d i s p l a y d e f i n i t e l y comp l i ca te the analogy. More important, however, Is the s i g n i f i c a n t drop in r e c o g n i t i o n l eve l f o l l o w i n g the f i r s t r e cogn i t i on s l i d e . Though masking e f f e c t s have on ly been i n ve s t i g a ted with t a c h i s t o s c o p i c s t imu lus p r e sen ta t i on s , the exper imental task and the r e s u l t s s t r ong l y resemble a masking e f f e c t of the sensory s t o r e dur ing the f i r s t r e c o g n i t i o n s l i d e . In e f f e c t , I t ?s conce i vab le t h a t data in the zero delay c o n d i t i o n are based on responses from two d i s t i n c t memories. The f i r s t p o s i t i o n response i s mediated by the sensory s t o r e , subsequent responses are based on STS. S ince i t i s c r i t i c a l t o the i n t e r p r e t a t i o n of zero delay con-d i t i o n s to e s t a b l i s h whether the r e c o g n i t i o n sequence i s in f a c t mediated by d i f f e r e n t memory systems i t becomes necessary t o i n v e s t i g a t e f u r t h e r t h i s p r o p o s i t i o n . There are two separate exper imental man ipu lat ions a v a i l a b l e t o determine sensory memory involvement in t h i s p a r t i c u l a r t a s k : an immediate f r e e reca l I task and a r e cogn i t i o n sequence wi th an aud i t o r y p re sen ta t i on of the f i r s t probe. I t can be expected t h a t both approaches in con junc t i on w i l l p rov ide an adequate assessment of the under l y ing que s t i on . 34 EXPERIMENT I I I n t roduct ion The f o l l o w i n g experiment was inc luded t o determine to what ex tent an Immediate f r e e r e c a l l task can be used t o i n v e s t i g a t e sensory memory e f f e c t s in t h i s exper imental s i t u a t i o n . Assuming tha t the s t imu lus p r e -s en t a t i on in t h i s experiment f a l l s w i t h i n N e l s s e r ' s (1967, p. 20) d e f i n -i t i o n of an " i d e a l v i s u a l d i s p l a y , ' 1 a f t e r a l l , du ra t i on and i n t e n s i t y are s u f f i c i e n t and the re i s no masking e f f e c t , i t can be expected t h a t sensory t r ace s w i l l be a v a i l a b l e to S_ f o r a sho r t per iod of t ime a f t e r t e rm ina t i on of the mat r i x d i s p l a y . S ince s i x items can e a s i l y be c a l l e d out w i t h i n severa l seconds, i t can be expected t h a t r e c a l l scores f o r word and p i c t u r e p re sen ta t i on are equa l l y h i gh , assuming, of cour se , as in EXP. I s i m i l a r scanning ra te s In both m o d a l i t i e s . The assessment of the expected r e s u l t s i s , however, f u r t h e r compl icated by the necessary verba l coding o f p i c t u r e s f o r t h i s response task . METHOD Subject s and Design Twenty-e ight Ss from the same sub jec t pool as in EXP. I vo lunteered f o r EXP. I I. Fourteen Ss were randomly ass igned t o e i t h e r word o r p i c t u r e group. The male-female r a t i o was kept constant across a l l groups. The fou r sets o f l ea rn ing mate r i a l were con secu t i ve l y a l t e r n a t e d in b lock s of f ou r w i t h i n each moda l i t y . MaterI a I A l l f our sets of l ea rn ing mat r i ces from EXP. I were used in t h i s experiment in t h e i r verba l and p i c t o r i a l forms. 35 Apparatus A Carousel 850 p r o j e c t o r was a c t i v a t e d by an automat ic t imer f o r a 1.2 second d i s p l a y of each ma t r i x . Procedure Ss were i n d i v i d u a l l y t e s t ed and randomly ass igned to e i t h e r word o r p i c t u r e study c o n d i t i o n . The general procedure and i n s t r u c t i o n s were s i m i l a r to EXP. I , except mod i f ied f o r an immediate f r e e r e c a l l t a sk . That i s , l ea rn ing mat r i ces were presented f o r 1.2 seconds, f o l l owed by S.'s o r a l r e c a l l . To keep the temporal con s i de ra t i on s f a i r l y constant w i th respect to EXP. I, a 60 second i n t e r t r i a l i n t e r v a l was employed in t h i s ta sk . Aural responses were checked o f f on a s co r i ng sheet , and a l i b e r a l s co r i n g method f o r the p i c t u r e c o n d i t i o n was used, s i n ce ob jec t s l i k e s h i p , d o l l , oven cou ld e q u a l l y be l a b e l l e d boat, g i r l , s tove r e s -p e c t i v e l y . RESULTS & DISCUSSION Reca l l scores were co l l ap sed over the fou r se t s of l ea rn ing l i s t s f o r word and p i c t u r e groups. The mean r e c a l l scores were 36.67 and 36.57 f o r p i c t u r e s and words r e s p e c t i v e l y (Table 9 ) . The lack of wo rd -p i c tu re d i f f e r e n c e s of the r e c a l l data as we l l as E_fs ob se rva t i on t h a t most items were r e c a l l e d w i t h i n severa l seconds a f t e r the te rm ina t i on of the s t imu lu s d i s p l a y , f a l l in l i n e w i th p r e d i c t i o n s made from con s i de ra t i on s of sensory memory e f f e c t s . However, the d i f f e r e n t task demands in the two e x p e r i -ments cannot be ignored as p o t e n t i a l confounding v a r i a b l e s . P i c t u r e r e -c a l l r equ i re s verba l cod ing , whereas p i c t u r e r e c o g n i t i o n does not neces-s a r i l y demand a s i m i l a r process . Y e t , i f l a b e l l i n g p i c t u r e s and v e r b a l -36 I z l n g words leads t o equal r e c a l l , d i f f e r e n t i a l l e a r n i n g rates i n the r e c o g n i t i o n task should be minimal, assuming s i m i l a r l e a r n i n g s t r a t e g i e s f o r both response tasks. However, t h i s l a t t e r assumption seems a l s o questionable. I t I s , f o r instance, necessary to scan over the whole stimulus d i s p l a y t o maximize r e c o g n i t i o n scores, whereas d e b r i e f i n g sessions in the r e c a l l experiment suggested t h a t i t i s more advantageous f o r S_ t o concentrate on a few items and subsequently be a b l e t o r e c a l l these, than to look a t a l l s i x items and f o r g e t h a l f of them. However, a c l a r i f i c a t i o n of t h i s p o i n t has to wait f o r a d d i t i o n a l evidence. S t i l l , the complementary evidence from the r e c a l l data and the response patte r n of the percentage data f o r zero delay c o n d i t i o n s , do support the Idea t h a t word-picture d i f f e r e n c e s of the zero delay sequence can be i n t e r p r e t e d with reference to sensory memory e f f e c t s . Hence, the f i r s t p o s i t i o n response seems mediated by SM processes, while subsequent p o s i t i o n s r e f l e c t r e c o g n i t i o n scores from STS. This STS r e c o g n i t i o n le v e l i s , however, not a t r u e estimate of short-term storage s i n c e i t i s modi-f i e d by the v i s u a l masking e f f e c t In SM. With t h i s new i n t e r p r e t a t i o n of the zero delay sequence In mind, even the increase of r e c o g n i t i o n scores f o r p i c t u r e groups over delay a l s o appears i n a new l i g h t . If the low r e c o g n i t i o n le v e l at zero delay can be, at l e a s t p a r t l y , a t t r i b u t e d t o the masking e f f e c t of the i n i t i a l sensory t r a c e , the d i f f e r e n c e between zero and 15 seconds delay f o r p i c t u r e groups subsequently does not n e c e s s a r i l y r e f l e c t an increase per se, but merely points t o a r e l a t i v e d i f f e r e n c e due to d i f f e r e n t i a l i n t e r f e r e n c e e f f e c t s under the two c o n d i t i o n s . That i s , the v i s u a l masking e f f e c t f o r 37 p i c t u r e s torage a t zero delay i s more det r imenta l to r e cogn i t i o n than 15 seconds of count ing backwards. There i s , of cour se , no masking e f f e c t f o r the 15 second delay c o n d i t i o n , s i n ce the SM t r a c e on l y l a s t s f o r a b r i e f du ra t i on and t r a n s f e r from SM t o verba l STS i s complete by then. Whi le the WW group a l s o s u f f e r s from v i s u a l masking, i t i s unc lea r to what ex -t e n t the zero delay r e c o g n i t i o n leve l i s due t o a s u p e r i o r learn ing r a te o r a s m a l l e r masking e f f e c t . In any case, i t seems sa fe to s t a t e t h a t verba l r e c o g n i t i o n s u f f e r s more from count ing backwards f o r 15 seconds than from the masking e f f e c t a t zero de lay . A summary of f i n d i n g s a t t h i s po i n t s t i l l presents an ambiguous p i c t u r e . There are no moda l i t y d i f f e r e n c e s a t zero delay f o r a r e c a l l t a sk . Yet in a r e cogn i t i on task performance on words i s s u p e r i o r to t ha t on p i c t u r e s . At the same t i m e , t h i s d i f f e r e n c e cannot be a t t r i b u t e d t o d i f f e r e n t i a l sho r t - te rm storage because of the masking e f f e c t and p o s s i b l e d i f f e r e n c e s in l ea rn ing r a t e s . Without a v a l i d re ference po i n t a t zero delay f o r STS, i n t e r f e r ence e f f e c t s can a l s o not be a c c u r a t e l y eva lua ted . Before con t i nu ing to i n v e s t i g a t e SM i m p l i c a t i o n s w i th an aud i t o r y f i r s t probe p r e s e n t a t i o n , the next s t ep , t h e r e f o r e , w i l l be t o rep lace the i n t e r f e r e n c e task w i th a rehearsa l i n t e r v a l , in o rder t o assess i n t e r -ference e f f e c t s with respect t o rehearsa l c o n d i t i o n s . 38 EXPERIMENT I I I I n t r o d u c t l o n E x p e r i m e n t a l e v i d e n c e has q u i t e c o n s i s t e n t l y shown t h e f a c u l t a -t i v e e f f e c t s of r e h e a r s a l i n STM e x p e r i m e n t s u t i l i z i n g v e r b a l m a t e r i a l ( H e l l y e r , 1962; C r a w f o r d e t a].., 1969). Bu t r e h e a r s a l e f f e c t s on t h e v i s u a l STS have not been c o n v i n c i n g l y d e m o n s t r a t e d . P o s n e r (1967) found no improvement o f t h e v i s u a l l o c a t i o n r e s p o n s e a f t e r a 20 second r e h e a r s a l p e r i o d . M i l n e r ( 1 9 6 8 ) , In c o n t r a s t , o b t a i n e d a lower r e c o g n i t i o n l e v e l f o r nonsense f i g u r e s , l i g h t f l a s h e s , and c l i c k s u s i n g both a r e h e a r s a l p e r i o d and an I n t e r f e r e n c e t a s k . S t i m u l i o f t h i s t y p e c a n , of c o u r s e , n o t be r e a d i l y v e r b a l i z e d and a r e , t h e r e f o r e , w e l l s u i t e d f o r t h e i n v e s t i g a t i o n o f n o n - v e r b a l r e h e a r s a l p r o c e s s e s . S i n c e c r o s s - m o d a l i t y e n c o d i n g has been shown t o p l a y a n e g l i g i b l e r o l e i n t h i s e x p e r i m e n t a l t a s k , word and p i c t u r e groups c a n , t h e r e f o r e , be e x p e c t e d t o r e f l e c t a d i f f e r e n t i a l r e -h e a r s a l e f f e c t , as w e l l as p r o v i d e a v a l i d r e f e r e n c e p o i n t t o a s s e s s t h e I n t e r f e r e n c e d a t a from EXP. I r e l a t i v e t o r e h e a r s a l c o n d i t i o n s . In o r d e r t o reduce g u e s s i n g e r r o r s i n t h e d a t a , mixed p r e s e n t a t i o n g r o u p s and t h e 30 second d e l a y c o n d i t i o n were e l i m i n a t e d from f u r t h e r i n v e s t i g a t i o n . Thus, r e h e a r s a l e f f e c t s w i l l be I n v e s t i g a t e d i n WW and PP g r o u p s a t 0, 7.5 and 15 seconds o f d e l a y . The s p e c i f i c p r e d i c t i o n s under t h e s e e x p e r i m e n t a l c o n d i t i o n s a r e t h e f o l l o w i n g . Z e r o d e l a y r e s p o n s e s from WW and PP g r o u p s i n EXP. I s h o u l d be r e p l i c a t e d . R e h e a r s a l e f f e c t s s h o u l d lead t o a h i g h e r r e c o g -n i t i o n l e v e l f o r WW, e i t h e r w i t h r e s p e c t t o t h e i n t e r f e r e n c e c o n d i t i o n o r even w i t h r e s p e c t t o t h e z e r o d e l a y c o n d i t i o n . R e h e a r s a l e f f e c t s f o r PP 39 group cannot be p r e d i c t e d , but a comparison of the r e c o g n i t i o n leve l a f t e r i n t e r f e r e n c e o r rehearsa l a c t i v i t y should lead t o a t e n t a t i v e statement about the f r u i t f u l n e s s of the concept of a v i s u a l sho r t - te rm rehearsa l mechanism. METHOD Subjects and Design Fo r ty S_s from the same s ub jec t pool p a r t i c i p a t e d in EXP. I I I . Ss were t e s t ed in groups and randomly ass igned t o WW and PP groups. The th ree r e c o g n i t i o n i n t e r v a l s , 0, 7.5, and 15 seconds, were randomly ass igned to the nine t r i a l s in b locks of t h r e e s , and were constant across groups. Mater ia I Only one s e t of the fou r lea rn ing l i s t s in EXP. I was randomly s e l e c t e d f o r the group p r e s e n t a t i o n . Apparatus As in EXP. I a Carousel 850 p r o j e c t o r was a c t i v a t e d by an a u t o -mat i c t ime r . Instead of the response bu t ton , Ss rece ived a response sheet t o mark down t h e i r cho i ce s . Procedure Ss were te s ted in groups of t e n . Two sess ions each were requ i red t o f i l l both groups. Procedures and i n s t r u c t i o n s were i d e n t i c a l t o EXP. I except f o r two changes: one, Ss were encouraged to rehearse the l ea rn ing mate r i a l dur ing de l ay ; two, s co r i n g sheets were prov ided and Ss were In-s t r u c t e d to answer wi th " 0 " ( f o r o l d ) i f the r e cogn i t i o n item was from the prev ious m a t r i x , and " N " ( f o r new) i f the item had not been presented be fo re . 40 RESULTS & DISCUSSION R e c o g n i t i o n s c o r e s were a g a i n t a b u l a t e d as i n EXP. I. F i g . 4 and 5 r e v e a l h i g h l y c o n g r u e n t r e s p o n s e p a t t e r n s f o r c o r r e c t probe r e s p o n s e s and d' s c o r e s , i n d i c a t i n g t h a t a r e d u c t i o n i n g u e s s i n g e r r o r s has been a c h i e v e d i n t h i s d e s i g n . A c o m p a r i s o n o f r e s p o n s e means ( T a b l e s 5 and 6) w i t h EXP. I shows t h a t s i m i l a r z e r o d e l a y d i f f e r e n c e s have been o b t a i n e d a g a i n and r e c o g n i t i o n s c o r e s t e n d t o i n c r e a s e i n both m o d a l i t i e s . A 2 x 3 a n a l y s i s o f v a r i a n c e f o r both r e s p o n s e measures was p e r -formed w i t h f a c t o r s : (a) p r e s e n t a t i o n (word v s . p i c t u r e ) ; (b) t h r e e d e l a y c o n d i t i o n s as a r e p e a t e d measure. The a n a l y s i s o f probe r e s p o n s e s ( A p p e n d i x , T a b l e 8) r e v e a l s a s i g n i f i c a n t s u p e r i o r i t y o f word o v e r p i c t u r e r e c o g n i t i o n ( F = I 8 . 6 I ; d f = l , 38; p < . 0 l ) , as w e l l as a s i g n i f i c a n t i n c r e a s e o v e r d e l a y (F=8.40, df=2, 76; p < . 0 l ) . The d e l a y e f f e c t , howevor, has t o be f u r t h e r q u a l i f i e d by a p r e s e n t a t i o n x d e l a y i n t e r a c t i o n (F=5.37; df= 2, 76; p < . 0 l ) . A Newman-Keuis t e s t c l a r i f i e s t h e n a t u r e o f t h i s i n t e r -a c t i o n ( A p p e n d i x , T a b l e 10). T h a t i s , word r e c o g n i t i o n Is c o n s i s t e n t l y s u p e r i o r t o p i c t u r e r e c o g n i t i o n . But t h e r e i s no increc.se d u r i n g r e -h e a r s a l f o r WW, w h i l e t h e i n c r e a s e f o r PP o c c u r s o n l y between 0 and 7.5 s e c o n d s . An a n a l y s i s o f d' s c o r e s ( A p p e n d i x , T a b l e I I ) shows an e d / i a l l y s t r o n g p r e s e n t a t i o n e f f e c t (F=I6.07, d f = l , 38; p <.01) and Improved r e c o g -n i t i o n o v e r r e h e a r s a l p e r i o d s (F=5.03; df=2, 76; p < . 0 l ) . As opposed t o t h e p r e v i o u s a n a l y s i s , t h e i n t e r a c t i o n i s n o t s i g n i f i c a n t . B u t , s i m i l a r t o t h e probe r e s p o n s e s , a Newman-Keuis t e s t f o r t h e d e l a y e f f e c t shows an I n c r e a s e due t o r e h e a r s a l o n l y between 7.5 and 15 seconds ( A p p e n d i x , TABLE 5 Mean Number of d'Scores f o r WW and PP Groups Under Interference (Experiment I ) , Rehearsal (Experiment I I I ) , and Rehearsal plus Responding to an I n i t i a l Auditory Probe (Experiment IV) Delay in Seconds 0 7.5 15 30 Experiment I 3.97 - 3.37 3.17 WW Experiment III 3.73 3.51 4.33 Experiment IV 2.51 3.46 3.14 Experiment I 2.42 - 2.79 2.95 PP Experiment M l 2.46 2.75 3.05 Experiment IV 2.19 2.71 2.94 TABLE 6 Mean Number of Correct Probe Responses f o r WW and PP Groups under Interference (Experiment I ) , Rehearsal (Experiment I I I ) , and Rehearsal plus Responding to an I n i t i a l Auditory Probe (Experiment IV) Delay in Seconds 0 7. .5 15 30 Exper iment 1 7.75 6.70 7.60 WW Exper iment 1 1 1 7.55 7 ,25 7.05 -Experiment IV 6.25 6, ,95 6.75 -Exper iment 1 5.90 7.40 7.45 pp Experiment 1 1 1 5.30 6, ,35 6.90 -Experiment IV 5.60 6, .80 7.05 -42 l O O i R e c o g n i t i o n S l i d e Number FIG. 3. P e r c e n t C o r r e c t P r o b e Responses f o r PP'and WW on Z e r o D e l a y R e c o g n i t i o n T r i a l s C o l l a p s e d Over EXP. I and I I I . DeI ay i n Seconds FIG. 4. Number o f C o r r e c t Probe Responses o u t o f Maximum o f N i n e I f o r EXP. I I I . , 7 . 5 15 Delay in Seconds FIG. 5.. d ' Scores f o r EXP. I l l out of a Maximum of S i x . 45 Table 12). An ana lys i s of probe pos i t ions again revealed a s i m i l a r pattern as in EXP. I (Table 7). Since there were only minor d i f fe rences between zero delay condi t ions of EXP. I and III, i . e . group t e s t i n g , and only one set of material was used, a 2 x 2 x 6 ana lys i s of var iance (Appendix, Table 13) was performed f o r zero delay responses. The factors are: (a) Experiment (EXP. I vs. EXP. I l l ) ; (b) presentat ion (WW vs. PP); (c) s i x pos i t i ons of the zero delay sequence as a repeated measure. Results c l e a r l y show there is no d i f f e rence between the two experiments (F=.17; d f= l , 76; p>.05). Word-picture e f f e c t s are highly s i g n i f i c a n t (F=24.95; d f= l , 76; p <• 01) with WW recogn i t ion super ior to PP. Most important, however, i s the pos i t i on e f f e c t (F=4.88; df=5, 380; p<.0l). A Newman-Keuls t e s t (Appendix, Table 14) fu r ther c l a r i f i e s t h i s pos i t i on e f f e c t . Recognition f o r the f i r s t pos i t i on is s i g n i f i c a n t l y higher than the r e -maining f i v e p o s i t i o n s , with no s i g n i f i c a n t d i f fe rences among them (F ig . 3). The overa l l re su l t s of the experiment r e f l e c t , in e f f e c t , high agreement with the p red i c t i on s . Zero delay responses have been r e p l i c a t e d . Rehearsal leads to a s i g n i f i c a n t increase in recogn i t i on , and, because of the rehearsal e f f e c t , a s i g n i f i c a n t main e f f e c t f o r word-picture present-at ion emerges. But, a c l o se r inspect ion of the re su l t s s t i l l leaves an ambiguous p i c tu re . The probe po s i t i on ana l y s i s , fo r instance, favours a SM i n t e r -pre ta t ion f o r the zero delay recogn i t ion sequence. The s i g n i f i c a n t drop a f t e r the f i r s t recogn i t ion response in word and p i c tu re groups appears 46 t o be a t y p i c a l masking e f f e c t caus ing the c o n s i s t e n t l y lower r e c o g n i t i o n leve l f o r the remaining p o s i t i o n s . Y e t , i f SM involvement i s po s tu l a ted f o r the zero delay c o n d i t i o n , the increase dur ing rehearsa l should occur a l ready between 0 and 7.5 seconds and not between 7.5 and 15 seconds, s i n ce SM t r a ce s can be expected to have d i s s i p a t e d by then. Indeed, the percentage data f o r probe p o s i t i o n s f o r the 7.5 second c o n d i t i o n on ly r e -vea l random f l u c t u a t i o n s , w i th on ly 65$ c o r r e c t f o r the f i r s t probe p o s i t i o n (Table 8 ) . In c o n t r a s t , the p re sen ta t i on x delay i n t e r a c t i o n o f the probe a n a l y s i s p laces the increase between 0 and 7.5 seconds f o r PP group. But because the a n a l y s i s i s based on uncorrected raw data no v a l i d i n fe rences can be drawn from i t . Word-p ic ture d i f f e r e n c e s are equa l l y ambiguous. Whi le the re i s a c o n s i s t e n t s u p e r i o r i t y of word over p i c t u r e c o n d i t i o n which can be a t t r i b u t e d t o d i f f e r e n t i a l rehearsa l c a p a c i t i e s in the two m o d a l i t i e s f o r the 7.5 and 15 second c o n d i t i o n , the re i s no v a l i d re fe rence po i n t f o r sho r t - te rm s to rage , s i n ce the data a t zero delay are confounded by the i n i t i a l masking e f f e c t . Although p re sen ta t i on d i f f e r e n c e s are c on s i s t en t across a l l p o s i t i o n s a t zero de l a y , i t must be remembered t h a t word-p i c t u r e s u p e r i o r i t y i s on ly % f o r the f i r s t p o s i t i o n versus 22% f o r the remaining f i v e p o s i t i o n s . An i n t e r p r e t a t i o n of p re sen ta t i on e f f e c t s in terms of l ea rn ing r a te d i f f e r e n c e s appears, t h e r e f o r e , on weak grounds. At the same t ime, however, the s t a t i s t i c a l a n a l y s i s d id not r e f l e c t a d i f f e r e n t i a l masking e f f e c t f o r words and p i c t u r e s . To compl i cate the r e s u l t s , a separate a n a l y s i s us ing on l y the f i r s t two p o s i t i o n s a t zero delay was a l s o performed. Th i s a n a l y s i s revea led no moda l i t y d i f f e r e n c e , 47 on ly a s i g n i f i c a n t p o s i t i o n e f f e c t (Appendix, Table 15). In e f f e c t then , whMe moda l i t y e f f e c t s are h i gh l y s i g n i f i c a n t , the under l y i ng processes are by no means c l e a r . Rehearsal e f f e c t s , in c o n t r a s t , render a more s a t i s f a c t o r y i n t e r -p r e t a t i o n . Though there i s s t i l l no assessment of abso lu te increases due to r e h e a r s a l , because there i s no reference po i n t f o r STS, a compar-ison wi th EXP. I conf i rms the e f f e c t i v e n e s s of verba l rehearsa l in STM exper iments. The p a r a l l e l increase f o r PP group, however, d i f f e r s on l y s l i g h t l y from EXP. I. That i s , between zero and 15 seconds, p i c t u r e recog -n i t i o n increases 1.45 and 1.60 mean items dur ing i n t e r f e r e n c e and rehearsa l r e s p e c t i v e l y . The r e s u l t s perhaps suggest t h a t whatever has been oper -a t i o n a l l y de f ined as i n t e r f e r e n c e o r rehearsa l seems q u i t e i r r e l e v a n t t o the under l y ing processes . Atk inson & S h i f f r i n ' s (1968) t e n t a t i v e hypo-t h e s i s about the lack of a v i s u a l rehearsa l mechanism, t h e r e f o r e , seems to be conf i rmed aga i n , i n s p i t e of two unanswered problems, i . e . d i f f e r -e n t i a l l ea rn ing rates and the s p e c i f i c temporal locus of the increase dur ing r e h e a r s a l . With a l l the l i m i t a t i o n s of the r e s u l t s in mind, the re are s t i l l two important f i n d i n g s t o r e p o r t . A comparison of the 15 second delay c o n d i t i o n s f o r WW and PP in EXP. I and III c l e a r l y suggest the e f f e c t i v e -ness of the verba l rehearsa l mechanism and the lack of a s i m i l a r f a c i I i t -a t l v e process in the v i s u a l STS in t h i s p a r t i c u l a r exper imental ta sk . To what ex tent rehearsa l and i n t e r f e r e n c e a c t i v i t i e s modify the i n i t i a l STS of both m o d a l i t i e s cannot be adequately assessed in the present e x p e r i -mental s i t u a t i o n . S ince the i n i t i a l STS s u f f e r s from the p re sen ta t i on of 48 the f i r s t v i s u a l probe, i t can be expected t ha t by removing the masking s t imu lu s a more accura te r e c o g n i t i o n leve l of the STS can be ob ta ined . The next experiment i s designed to i n v e s t i g a t e t h i s p r o p o s i t i o n . 49 EXPERIMENT IV I n t r o d u c t i o n If t h e f i r s t r e c o g n i t i o n r e s p o n s e i s indeed m ediated by SM e f f e c t s as s u g g e s t e d by t h e p o s i t i o n d a t a and r e s u l t s from f r e e r e c a l l , r e p l a c i n g t h e v i s u a l w i t h an a u d i t o r y p r e s e n t a t i o n o f t h e f i r s t probe i n an i d e n t i c a l d e s i g n t o EXP. I l l s h o u l d f u r t h e r c l a r i f y t h i s p r o p o s i t i o n . W h i l e i t i s not c l e a r what a d d i t i o n a l c o m p l i c a t i o n s an a u d i t o r y p r e s e n t a t i o n m i g h t i n t r o d u c e , t h e r e Is no doubt t h a t a t l e a s t t h e v i s u a l masking e f f e c t w i l l be e l i m i n a t e d . By i n t r o d u c i n g t h i s change I n t o t h e b a s i c d e s i g n o f EXP. I l l two s e p a r a t e p r e d i c t i o n s can be made. S i n c e t h e r e i s no masking s t i m u l u s a f t e r t h e m a t r i x d i s p l a y , t h e probe p o s i t i o n a n a l y s i s a t z e r o d e l a y s h o u l d not show a s i g n i f i c a n t b reak i n r e s p o n s e l e v e l between p o s i -t i o n one and t h e r e m a i n i n g f i v e p o s i t i o n s . A t t h e same t i m e , s i n c e r e s -ponses do n o t s u f f e r from m a sking d u r i n g SM, an o v e r a l l h i g h e r r e c o g n i t i o n l e v e l f o r z e r o d e l a y can be e x p e c t e d . I t f o l l o w s from t h i s p r e d i c t i o n t h a t r e h e a r s a l e f f e c t s s h o u l d be s m a l l e r t h a n i n EXP. I I I . METHOD S u b j e c t s and D e s i g n F o r t y Ss from t h e same s u b j e c t pool p a r t i c i p a t e d i n t h i s e x p e r i -ment. There were a g a i n two g r o u p s , i . e . WW and PP, w i t h d e l a y c o n -d i t i o n s as In EXP. I I I . M a t e r i a l and A p p a r a t u s The same s e t o f s t u d y and t e s t m a t e r i a l was used as i n EXP. I l l , and p r e s e n t e d w i t h t h e same a p p a r a t u s . 50 Procedure Four groups of f i v e Ss each were randomly ass igned t o PP and WW c o n d i t i o n s . Procedure and i n s t r u c t i o n s were i d e n t i c a l t o EXP. II I except f o r one m o d i f i c a t i o n : Ss were t o l d t ha t the f i r s t r e c o g n i t i o n item in each sequence would be presented a u d i t o r i l y . RESULTS & DISCUSSION Recogn i t ion responses were again analyzed w i th respect t o : ( I ) c o r r e c t probe responses; (2) d ' s co re s ; (3) probe p o s i t i o n percentages. As can be seen in Tables 5 and 6 response pat te rns d i f f e r from EXP. I l l , y e t , not in the p red i c ted d i r e c t i o n . The analyses of va r i ance f o r both response measures (Appendix, Tables 16 and 18) show t h a t word -p i c tu re d i f f e r e n c e s have disappeared (F=.32; d f = l , 38; p>.05 f o r probe responses; F=2.29; d f = l , 38; p>.05 f o r d ! s c o r e s ) . But the re i s s t i l l a s i g n i f i c a n t delay e f f e c t (F=9.54; df=2,76; p<.01 f o r probe responses; F=5.20; df=2, 76; p <. 01 f o r d ' s c o r e s ) . A Newrnan-Keu I s t e s t in both cases p laces the i n -crease between 0 and 7.5 seconds in c o n t r a s t to EXP. I l l (Appendix, Tables 17 and 19). The analyses of probe p o s i t i o n s (Appendix, Table 20) f u r t h e r sub-s t a n t i a t e s the iack of word -p i c tu re d i f f e r e n c e s at zero delay (F=l.54; d f = l , 38; p>.05). A s i g n i f i c a n t p o s i t i o n e f f e c t appears again (F=3.53; df=5, 190; p< .0 l ) , but cont ra ry t o EXP. I and I I I , a Newrnan-KeuIs t e s t (Appendix, Table 21) shows t ha t the re i s no loss of r e c o g n i t i o n a f t e r the f i r s t probe response. Instead the re seems t o be a f a i r l y l i n e a r d e c l i n e throughout the sequence wi th the on l y s i g n i f i c a n t d i f f e r e n c e being be-tween p o s i t i o n one and s i x . TABLE 7 Per Cent Correct Probe Responses f o r WW and PP Groups in the Zero Delay Recognition Sequence f o r Experiments I, I I I , IV, and Mixed Presentation Groups in Experiment I Experiment I WW Experiment I I I Experiment IV P o s i t I 2 3 90.00 82.50 87.50 95.00 85.00 85.00 85.00 67.50 85.00 i cn 4 5 6 65.00 87.50 75.00 80.00 80.00 80.00 65.00 60.00 50.00 Experiment i PP Experiment I I I Experiment IV Experiment ! ^ 85.00 70.00 62.50 90.00 67.50 50.00 60.00 70.50 62.50 •100.00 95.00 85.00 80.00 70.00 82.00 55.00 57.50 67.50 65.00 52.50 45.00 60.00 52.50 50.00 45.00 82.50 87.50 65.00 S2.50 57.50 TABLE 8 Per Cent C o r r e c t Probe Responses at 7.5 Seconds f o r Experiments 111 and IV -os i t i on 3 4 WW Experiment III 82.50 85.00 90.00 50.00 75.00 90.00 Experiment IV 82.50 77.50 95.00 45.00 80.00 75.00 Exceriment III 65.00 57.50 100.00 50.00 Experiment IV 92.50 67.50 90.00 60.00 90.00 55.00 82.50 45.00 52 _ J ; 1_ 7.5 15 Delay in Seconds FIG. 6. Correct Probe Responses for EXP. IV. 53 Delay i n Seconds FIG. 7. d' S c o r e s f o r EXP. IV. i I I 54 Though the r e s u l t s are hard ly in agreement wi th p r e d i c t i o n s made from a SM i n t e r p r e t a t i o n , severa l i n t e r e s t i n g i m p l i c a t i o n s emerge aga in . As p r e d i c t e d , the drop in r e c o g n i t i o n l eve l a f t e r the f i r s t probe a t zero delay d id not occu r . But, wh i l e t h i s cou ld be a t t r i b u t e d to the absence of a masking s t i m u l u s , the o v e r a l l response leve l does not i n -crease because of the absence of the masking e f f e c t . Moreover, r ecog -n i t i o n leve l f o r WW group has decreased to the extent of e l i m i n a t i n g the p rev i ou s l y c o n s i s t e n t word -p i c tu re e f f e c t . In s p i t e of the decrease of WW r e c o g n i t i o n , f i r s t p o s i t i o n responses are comparable t o the prev ious r e s u l t s , i . e . 85 and 80 percent f o r WW and PP versus 90 - 85 and 95 - 90 percent f o r EXP. I and III r e s p e c t i v e l y . The importance of d i f f e r e n t i a l l ea rn ing ra tes c o n t r i b u t i n g t o moda l i ty d i f f e r e n c e s seems, t h e r e f o r e , even less acceptab le a t t h i s s tage. It seems f a i r l y c l e a r t hen , t ha t by removing the hypothes ized v i s u a l masking e f f e c t an even s t ronger damaging e f f e c t on STS has been s imul taneous ly i n t roduced. I n t e r e s t i n g l y enough, the e f f e c t seems to be moda l i t y s p e c i f i c . Return ing t o the p r e v i ou s l y mentioned memory model of A tk in son and S h i f f r i n (1968) a p l a u s i b l e exp l ana t i on f o r under l y ing processes becomes a v a i l a b l e . As the mat r i x of words, f o r i n s t ance , i s p r e -sented the S_ s t a r t s a cont inuous rehearsa l c y c l e , wh i l e a t the same t ime w a i t i n g , i . e . , g i v i n g a t t e n t i o n , f o r the aud i to r y probe. As the aud i to r y probe enter s the STS, items in the s t o r e can be knocked out of STS o r can be l o s t in the search process invo lved in r e t r i e v a l . With increased rehearsa l more items can be expected to enter LTS. Subsequent ly, recog -n i t i o n scores are lowest f o r the zero delay c o n d i t i o n , s i n ce l i t t l e 55 r e o r g a n i z a t i o n a n d r e h e a r s a l h a s o c c u r r e d when t h e a u d i t o r y p r o b e i s a d d e d t o S T S . A t t h e s ame t i m e t r a n s f e r t o LTS i s m i n i m a l a t t h i s s t a g e . A s r e h e a r s a l c o n t i n u e s , r e c o g n i t i o n w i l l i m p r o v e b e c a u s e o f i n c r e a s e d t r a n s -f e r t o LTS a n d b e t t e r r e o r g a n i z a t i o n o f S T S , b u t w i l l a l w a y s s u f f e r f r o m t h e a u d i t o r y p r e s e n t a t i o n , t h e r e b y l e a d i n g t o l o w e r p e r f o r m a n c e w i t h r e s p e c t t o EXP. I I I . T h e p i c t u r e c o n d i t i o n s c a n n o t b e a s e a s i l y e x -p l a i n e d , m a i n l y b e c a u s e o f z e r o d e l a y r e s p o n s e s . I t s e e m s u n s a t i s f a c t o r y t o c l a i m t h a t b y c o i n c i d e n c e r e s p o n d i n g t o a v i s u a l o r a u d i t o r y f i r s t p r o b e l e a d s t o t h e same r e c o g n i t i o n l e v e l , a n d o n l y t h e n a t u r e o f t h e d e -c r e a s e i s d i f f e r e n t i n b o t h c a s e s . I t s e e m s a l s o u n s a t i s f a c t o r y t o c l a i m t h a t p i c t u r e s h a v e b e e n e n c o d e d v e r b a l l y a n d , t h e r e f o r e , s u f f e r t o t h e s ame e x t e n t a s w o r d s , i n l i g h t o f t h e d a t a a r g u i n g a g a i n s t c r o s s m o d a l i t y e n c o d i n g . T h e m o s t p a r s i m o n i o u s , y e t p r o b a b l y e q u a l l y u n s a t i s f a c t o r y , e x p l a n a t i o n c o u l d b e i n c o n s i d e r i n g t h e d i v e r s i o n o f a t t e n t i o n w h i c h i s d e m a n d e d f r o m S_ a t t h e p r e s e n t a t i o n o f t h e f i r s t p r o b e . T h a t I s , i f a t t e n t i o n i s d i v e r t e d d u r i n g t h e t r a n s f e r p r o c e s s f r o m SM t o S T S , e . g . , z e r o d e l a y r e s p o n s e s , l e s s i n f o r m a t i o n w i l l e n t e r S T S . I f t h e a t t e n t i o n i s d i v e r t e d a f t e r t h e t r a n s f e r p r o c e s s m o r e i n f o r m a t i o n c a n b e e x p e c t e d t o b e s t o r e d i n S T S . T h e r e h e a r s a l e f f e c t i n EXP. I l l a n d IV f o r p i c t u r e g r o u p s a r e q u i t e i n l i n e w i t h t h i s d e s c r i p t i v e a n a l y s i s . S i n c e p i c t u r e s a r e s t o r e d v i s u a l l y , t h e a u d i t o r y p r e s e n t a t i o n o f t h e f i r s t p r o b e w i l l e n t e r t h e a u d i t o r y - v e r b a l STS a n d , t h e r e f o r e , h a v e no d a m a g i n g e f f e c t o n t h e v i s u a l s t o r e . F a r f e t c h e d a s t h e s e i n t e r p r e t a t i o n s m i g h t b e , t h e y d o f i t i n t o t h e A t k i n s o n a n d S h i f f r i n ( 1 9 6 8 ) memory m o d e l . F o r t h e w o r d c o n d i t i o n , 56 f u r t h e r support can be found in N e i s s e r ' s (1967) " e c h o i c memory" system and Crowder ' s (1970) " p r e c a t e g o r i c a l a c o u s t i c s to rage. 5 ' While both t h e o r i s t s avo id the term aud i to r y sensory memory, t h e i r i n v e s t i g a t i o n s do cente r around exper imental c ond i t i on s which can be desc r ibed as such. Crowder ' s p a r t i c u l a r exper imental man ipu l a t i on s , f o r i n s tance , inc lude r e c a l l of s t r i n g s of items presented e i t h e r w i th a p r e f i x o r s u f f i x . Summarizing the r e s u l t s of t h i s type of research he concludes t ha t the s u f f i x i s be l i e ved t o remove the advantage aud i t o r y p re sen ta t i on has ( i . e . , p r e ca t ego r i c a l a c o u s t i c s torage t r ace s ) over v i s u a l p r e s e n t a t i o n . That i s , an a d d i t i o n a l aud i to ry input damages the a cou s t i c s torage t r a ce s of the i n i t i a l l y s to red m a t e r i a l . Whi le the analogy t o t h i s p a r t i -c u l a r task c e r t a i n l y has to be s t r e t c h e d , i t i s encouraging to f i n d s i m i l a r e f f e c t s under a wide v a r i e t y of exper imental man ipu la t i on s . S t i l l , the experiment f a i l e d in i t s o r i g i n a l purpose. There i s s t i l l no v a l i d re fe rence po i n t f o r STS moda l i t y e f f e c t s and, con s i de r i ng the exper imental task a t hand, attempt ing to i s o l a t e f u r t h e r t h i s e f f e c t seems ra the r f u t i l e a t t h i s s tage. I n te r fe rence and rehearsa l e f f e c t s can, subsequent ly , on ly be assessed wi th respect to each o t h e r . The remaining problem then cente r s around the f r e e r e c a l l data of EXP. II. S ince the o r i g i n a l data were used as support f o r SM Invo lve -ment in the zero delay r e c o g n i t i o n sequence, and s i n ce SM e f f e c t s f o r t h i s c o n d i t i o n are s t i l l ambiguous, i t becomes c r i t i c a l to i n v e s t i g a t e f u r t h e r r e c a l l responses under i n t e r f e r e n c e and rehearsa l c ond i t i o n s in o rde r t o throw some l i g h t on the nature of word -p i c tu re e f f e c t s obta ined in EXP. I I. 57 EXPERIMENT V I n t r o d u c t i o n The p r e s e n t e x p e r i m e n t i s , t h e r e f o r e , d e s i g n e d t o i n v e s t i g a t e pos-s i b l e d i f f e r e n t i a l e n c o d i n g , s t o r a g e , and r e t r i e v a l p r o c e s s e s w i t h r e s p e c t t o t h e two t a s k v a r i a b l e s . D i f f e r e n t i a l c o d i n g and/or s t o r a g e p r o c e s s e s f o r words and p i c t u r e s have been e s t a b l i s h e d i n t h e r e c o g n i t i o n t a s k em-p l o y i n g i n t e r f e r e n c e and r e h e a r s a l a c t i v i t i e s . W i t h t h e use o f t h e same i n t e r p o l a t e d a c t i v i t i e s , i t can be e x p e c t e d t h a t r e c a l l s c o r e s w i l l r e v e a l a s i m i l a r p a t t e r n . T h a t i s , t h e r e w i l l be an i n c r e a s e and d e c r e a s e due t o r e h e a r s a l and i n t e r f e r e n c e r e s p e c t i v e l y f o r w o r d - r e c a l l and no d i f f e r -ence between i n t e r f e r e n c e and r e h e a r s a l f o r p i c t u r e s , i f p i c t u r e s and words a r e coded d i f f e r e n t l y . S i n c e t h e r e s p o n s e t a s k i n t h e p i c t u r e c o n d i t i o n demands v e r b a l l a b e l l i n g , i t c o u l d a l s o be e x p e c t e d t h a t m o d a l i t y s p e c i f i c c o d i n g d i f f e r e n c e s become n e g l i g i b l e . In t h i s c a s e w o r d - p i c t u r e r e c a l l a f t e r r e h e a r s a l and i n t e r f e r e n c e would be u n d i f f e r e n t i a t e d . R e t r i e v a l problems a r e , of c o u r s e , g e n e r a l l y i n c r e a s e d i n a r e c a l l t a s k b u t c a n n o t be a s s e s s e d u n t i l s t o r a g e d i f f e r e n c e s a r e known. The p e r s i s t e n t q u e s t i o n o f d i f f e r e n t i a l l e a r n i n g r a t e s f o r words and p i c t u r e s w i l l a l s o be i n v o l v e d a g a i n In t h i s t a s k b u t can o n l y be c o n s i d e r e d i n c o n j u n c t i o n w i t h t h e r e s u l t s . METHOD S u b j e c t s and D e s i g n Ten Ss from t h e same s u b j e c t pool were a s s i g n e d t o each o f t h e f o u r groups i n a f a c t o r i a l d e s i g n w i t h two l e v e l s o f p r e s e n t a t i o n (word v s . p i c t u r e ) and two l e v e l s of i n t e r p o l a t e d a c t i v i t y ( I n t e r f e r e n c e v s . R e h e a r s a l ) . R e c a l l was al w a y s t e s t e d a f t e r a 15-sec. r e t e n t i o n i n t e r v a l . 58 M a t e r i a l and Apparatus The same study mate r i a l and apparatus were used as in EXP. II. Procedure The general procedure was i d e n t i c a l t o EXP. II. The same r e c a l l i n s t r u c t i o n s were g iven aga in , but mod i f i ed t o e x p l a i n i n t e r f e r e n c e o r rehearsa l c o n d i t i o n s . RESULTS & DISCUSSION The mean reca l I scores f o r the f ou r groups can be seen in con -j u n c t i o n wi th the data from EXP. II (Table 9 ) . I t should be mentioned here t h a t four randomly s e l e c t e d Ss were excluded from the data of EXP. II t o s i m p l i f y the l a t e r ana ly ses . Noteworthy a t t h i s po i n t i s the lack of wo rd -p i c tu re d i f f e r e n c e s under any exper imental c o n d i t i o n ( F i g . 8 ) , which i s q u i t e oppos i te t o r e s u l t s f o r the r e c o g n i t i o n t a sk . Three separate ana lyses of va r i ance were performed wi th the s i x independent groups. An a n a l y s i s of p re sen ta t i on and i n t e r p o l a t e d a c t i v i t y e f f e c t s a f t e r 15 seconds of delay (Appendix, Table 22) leaves no doubt about equal r e c a l l f o r p i c t u r e s and words under both c o n d i t i o n s (F=2.24; df= I, 36; p>.05). The decrease in performance due to i n t e r f e r ence in tu rn i s h i g h l y s i g n i f i c a n t (F=63.99; d f = l , 36; p<.01). The a n a l y s i s i n v e s t i -ga t ing r e c a l l a t zero and 15 seconds of rehearsa l f o r both p re senta t ions (Appendix, Table 23) again revea l s no word -p i c tu re d i f f e r e n c e (F=l.73; d f = l , 36; p>.05). There i s a small main e f f e c t f o r rehearsa l (F=5.53; d f = l , 36; p<.05), but con t ra ry to r e c o g n i t i o n scores rehearsa l leads t o a smal l decrease in performance. A s i m i l a r a n a l y s i s f o r i n t e r f e r e n c e e f f e c t s (Appendix, Table 24) was performed which again negates any word-59 TABLE 9 Mean Rec a l l Scores f o r Zero Delay (Experiment II) and 15 Seconds of Rehearsal or Interference (Experiment V) out of a Maximum of 54 I terns Delay in Seconds 0 15 Interfarence RehearsaI Word 37.60(36.67)* 23.20 36.00 P i c t u r e 37.60(36.57)* 23.00 32.10 ^ I n d i c a t e s mean reca II f o r a l l 14 S_s in Experiment I I . 60 40T 35^ If) CD l _ o u to ro u a> cr c ro 30i 251 20- RehearsaI Interference Delay in Seconds 15 FIG. 8. Mean Recal l S co re s ' f o r Zero Delay (EXP. II) and Rehearsal and Interference Groups in EXP. V out of a Maximum of 54 Items. 6! p i c t u r e d i f f e r e n c e s in r e c a l l (F=.OOI; d f = l , 36; p>.05) wh i l e support ing the prev ious damaging e f f e c t s of i n t e r f e r ence (F=I02.99; d f = l , 36; p<.OI). The c o n s i s t e n t lack of a s i g n i f i c a n t word -p i c tu re d i f f e r e n c e leaves l i t t l e doubt t ha t r e c a l l of words and p i c t u r e s does not d i f f e r under any of the exper imental man ipu la t i on s . P o s s i b l e reasons f o r t h i s w i l l be d i scussed w i th re fe rence t o the i n t e r p o l a t e d a c t i v i t i e s e f f e c t s . The smal l increase a f t e r 15 seconds of rehearsa l remains we l l w i t h i n p r e -d i c t i o n s , e s p e c i a l l y w i th respect t o the large decrease due t o verba l i n t e r f e r e n c e . With respect t o rehearsa l e f f e c t s in the r e c o g n i t i o n t a s k , the d i f f e r e n c e can be exp la ined in terms of g rea te r r e t r i e v a l problems in the r e c a l l t a sk . Furthermore, the r e c o g n i t i o n task never r e f l e c t e d a v a l i d re fe rence p o i n t f o r zero de l ay , the reby , leav ing the r e l a t i v e increase due to rehearsa l on ques t i onab le grounds. I n te r fe rence e f f e c t s , in c o n t r a s t , are h i g h l y s i g n i f i c a n t and q u i t e in agreement w i th expected r e s u l t s . If p re sen ta t i on e f f e c t s are cons idered in l i g h t of rehearsa l and i n t e r f e r e n c e e f f e c t s i t becomes q u i t e apparent t h a t , con t ra ry to the r e c o g n i t i o n t a s k , the lea rn ing mate r i a l f o r words and p i c t u r e s has been v e r b a l l y coded. Th i s i s e s p e c i a l l y ev ident in the u n d i f f e r e n t i a t e d r e -hearsa l and i n t e r f e r e n c e e f f e c t s in both m o d a l i t i e s . As opposed t o r e -c o g n i t i o n scores rehearsa l and i n t e r f e r ence have the same e f f e c t on word and p i c t u r e s to rage. The d i f f e r e n t i n t e r p o l a t e d a c t i v i t y e f f e c t s f o r words and p i c t u r e s dur ing r e c o g n i t i o n have been i n t e r p r e t e d in terms of d i f f e r e n t i a l ve rba l and v i s u a l cod ing. S ince in the r e c a l l task no d i f f e r e n t i a l i n t e r p o l a t e d a c t i v i t y e f f e c t s become apparent i t w i l l have 62 t o be assumed tha t words and p i c t u r e s have been encoded v e r b a l l y . If words and p i c t u r e s are r e c a l l e d equa l l y w e l l , i t cou ld be assumed t h a t l ea rn ing ra te s are a l s o s i m i l a r . Y e t , i f reading words and l a b e l l i n g p i c t u r e s proceed at an equal r a t e , d i f f e r e n t i a l l ea rn ing ra te s f o r the r e c o g n i t i o n ta sk can be p r a c t i c a l l y i gnored, i f not assumed t o favour p i c t u r e s u p e r i o r i t y . But lea rn ing ra tes a l s o have to be cons idered wi th re spect t o d i f f e r e n t study s t r a t e g i e s in the two response t a s k s , as d i s -cussed in EXP. I I , which makes in ferences from learn ing r a te s in r e c a l l t o l ea rn ing ra tes in r e c o g n i t i o n almost wor th le s s . Furthermore, s i n ce the d i f f e r e n t p re sen ta t i on e f f e c t s in r e c a l l and r e c o g n i t i o n are shown t o be under l y ing d i f f e r e n t sho r t - te rm storage mechanisms, r e s u l t s in EXP. II which were used in support of SM involvement because of word-p i c t u r e e q u a l i t y , have to be r e j e c t e d as such. In e f f e c t , the response task becomes a c r i t i c a l v a r i a b l e In t h i s exper imental c o n d i t i o n . It leads to d i f f e r e n t i a l learn ing s t r a t e g i e s t o maximize performance in each t a s k , which a t the same time w i l l i n f l u -ence l ea rn ing r a te s in each p re sen ta t i on c o n d i t i o n . Subsequent ly, be-cause of the d i f f e r e n t task requi rements, i . e . p i c t u r e s have to be l a b e l l e d in r e c a l l , d i f f e r e n t i a l s torage system f o r words and p i c t u r e s a re on l y obta ined in r e c o g n i t i o n , but not in a r e c a l l t a sk . 63 GENERAL DISCUSSION Before the data can be p roper l y eva luated and t h e i r i m p l i c a t i o n s cons idered in a t h e o r e t i c a l framework i t becomes necessary t o c l a r i f y severa l quest ions in o rde r t o e s t a b l i s h the meaningfuIness of the r e s u l t s . That i s , t o what ex tent do the o p e r a t i o n a l l y de f ined cond i t i o n s r e f l e c t t h e i r po s tu l a ted under ly ing processes. F i r s t of a l l , in showing d i f f e r -e n t i a l coding mechanisms f o r words and p i c t u r e s , does the exper imental ta sk In f a c t q u a l i f y as an adequate research t oo l t o i n v e s t i g a t e verba l and v i s u a l coding d i f f e r e n c e s of the STS? The argument support ing t h i s c l a im i s the f o l l o w i n g . If the g i ven exper imental task i s used to r e p l i -cate r e s u l t s of we l l e s t a b l i s h e d v a r i a b l e s , e.g. i n t e r f e r e n c e and r e -hearsal e f f e c t s on verba l r e c o g n i t i o n , the exper imental task can be con -s i de red as a v a l i d research approach f o r STM exper iments. Whether i t can be gene ra l i z ed t h a t the research t o o l f o r words, i s e q u a l l y s u i t a b l e f o r p i c t u r e s , i s of cour se , an open que s t i o n , y e t , in the l i g h t of the r e s u l t s seems perhaps t o be answered p o s i t i v e l y . Assuming t h i s p o s i t i v e answer can be accepted, i t must be e s t ab -IIshed how c o n f i d e n t l y cross moda l i ty encoding can be r e j e c t ed as a con -founding v a r i a b l e in word -p i c tu re d i f f e r e n c e s . EXP. I has c o n v i n c i n g l y demonstrated t h a t d i f f e r e n t i a l i n t e r f e r e n c e e f f e c t s f o r mixed p re sen ta t i on groups were always in l i n e of same p re sen ta t i on groups (Tables I and 2 ) . These r e s u l t s imply s t r o n g l y t ha t the s t imu lus ma te r i a l in a l l groups had been coded in the form of the study m a t e r i a l . S i m i l a r l y , i f p i c t u r e s were encoded v e r b a l l y , the r e s u l t s of the p i c t u r e group in EXP. I l l should have 64 shown some i n c r e a s e due t o v e r b a l r e h e a r s a l ( T a b l e s 5 and 6 ) . In a d d i t i o n , t h e i n t e r p r e t a t i o n o f r e s u l t s i n EXP. IV shows t h e a u d i t o r y p robe t o be an e f f e c t i v e i n t e r f e r e n c e c o n d i t i o n f o r v e r b a l s t o r a g e . If p i c t u r e s were coded v e r b a l l y i n t h i s e x p e r i m e n t , a l ower r e c o g n i t i o n l e v e l wou ld have t o be e x p e c t e d w i t h r e s p e c t t o EXP. I I I . More e v i d e n c e a g a i n s t c r o s s m o d a l i t y e n c o d i n g can be f ound i n a c o m p a r i s o n o f r e c o g n i t i o n and r e c a l l d i f f e r e n c e s . I n t e r p o l a t e d a c t i v i t y e f f e c t s r ema i ned c o n s t a n t f o r word and p i c t u r e r e c a l l ( T a b l e 9 ) . The r e a s o n f o r t h i s l i e s i n t h e n e c e s s a r y v e r b a l l a b e l l i n g o f p i c t u r e s t i m u l i i n a r e c a l l t a s k . In c o n t r a s t , i n t e r p o l a t e d a c t i v i t i e s e x e r t e d a d i f f e r e n t i a l e f f e c t on word and p i c t u r e c o n d i t i o n s i n t h e r e c o g n i t i o n t a s k ( T a b l e s 5 and 6 ) . T h e r e f o r e , t h e l e a r n i n g m a t e r i a l i n t h e d i f f e r e n t p r e s e n t a t i o n g r oup s must have been s t o r e d i n s e p a r a t e , v e r b a I - v i s u a I s t o r a g e mechan i sms , o t h e r w i s e , i n t e r p o l a t e d a c t i v i t y e f f e c t s s h o u l d have been s i m i l a r f o r word and p i c t u r e r e c a l l . In e f f e c t , t h e d a t a s t r o n g l y s u g g e s t t h a t t h e o p e r a t i o n a l l y d e f i n e d c o n d i t i o n w h i c h was d e -s i g n e d t o i n v e s t i g a t e v i s u a l s h o r t - t e r m mechanisms has a c h i e v e d t h i s a i m , b u t o n l y i n t h e r e c o g n i t i o n e x p e r i m e n t . A n o t h e r c o n f o u n d i n g f a c t o r u n d e r l y i n g p r e s e n t a t i o n d i f f e r e n c e s i s p o s s i b l e d i f f e r e n t i a l l e a r n i n g r a t e s f o r word and p i c t u r e m a t r i c e s . W h i l e t h i s p r o b l e m has been m e n t i o n e d t h r o u g h o u t t h e d i s c u s s i o n o f t h e e x p e r i -m e n t s , a summary o f t h e a rgument s p r e s e n t s t h e f o l l o w i n g p i c t u r e . L e a r n i n g r a t e d i f f e r e n c e s had been shown t o be n e g l i g i b l e i n p i l o t work u s i n g p i c t u r e s and words as a w i t h i n - S _ v a r i a b l e . S u b j e c t i v e r e p o r t s f r om S_s i n t u r n i n d i c a t e d p e r s o n a l p r e f e r e n c e s , b u t no c o n s i s t e n t t r e n d i n e i t h e r d i r e c t i o n . C o n s i d e r i n g t h e f i r s t r e c o g n i t i o n r e s p o n s e a t z e r o d e l a y as 65 the most accurate e s t imate of l ea rn ing r a t e , a l l t h ree r e c o g n i t i o n e x p e r i -ments show c o n s i s t e n t word over p i c t u r e s u p e r i o r i t y . But , the d i f f e r e n c e i s c o n s i s t e n t l y on l y f i v e percent , which in con junc t i on w i th the o the r f i v e probes r e s u l t s in a s i g n i f i c a n t word -p i c tu re d i f f e r e n c e in EXP. I and I I I , yet not in EXP. IV. Furthermore, a separate a n a l y s i s of the f i r s t two probe p o s i t i o n s in EXP. I and III r evea l s no word -p i c tu re d i f -f e rences . In a d d i t i o n , l ea rn ing r a te s f o r words and p i c t u r e s seem t o be equal in a r e c a l l t a s k , in s p i t e of the necessary l a b e l l i n g of p i c t u r e s . Bu t , because of d i f f e r e n t i a l l ea rn ing s t r a t e g i e s to maximize performance in the two response t a s k s , any in ferences from r e c a l l experiments seem i napp rop r i a t e . In e f f e c t , the in fo rmat ion about d i f f e r e n t i a l l ea rn ing rates is ambiguous. In l i g h t of the s m a l l , i f not i n c o n s i s t e n t , d i f f e r -ences, however, i t seems sa fe to assume t h a t i t i s not the c r i t i c a l v a r i -ab le under l y i ng wo rd -p i c tu re d i f f e r e n c e s . With these arguments in mind, the i n t e r p r e t a t i o n of verba l and v i s u a l coding d i f f e r e n c e s becomes more accep tab le . D i f f e r e n t i a l s h o r t -term coding f o r words and p i c t u r e s can be pos tu la ted in l i g h t of t h e i r r e l a t i v e d i f f e r e n c e in r e cogn i t i o n scores a f t e r 15 seconds of i n t e r f e r -ence o r rehearsa l (Tables 5 and 6 ) . That i s , the p re sen ta t i on of words leads t o verba l encoding and subsequent storage in the verba l STS. The amount of s to red in fo rmat ion a f t e r a 15 second r e t e n t i o n i n t e r v a l can be e f f e c t i v e l y manipulated by count ing backwards o r r ehea r s i ng . To what ex tent the i n te r ven ing a c t i v i t i e s change the i n i t i a l verba l STS can, how-eve r , not be assessed because the experiment f a i l e d t o ob ta i n a pure STS r e c o g n i t i o n leve l a t zero de lay. In any case, the s i g n i f i c a n t d i f f e r e n c e 66 between word r e c o g n i t i o n a f t e r the two i n t e r p o l a t e d a c t i v i t i e s under l i ne s the importance of the verba l rehearsa l mechanism in STS, as we l l as p ro -v ides ev idence f o r the damaging e f f e c t s of verba l i n t e r f e r ence on ve rba l STS. In c o n t r a s t , the lack of i n t e r p o l a t e d a c t i v i t y e f f e c t s f o r the p i c t u r e c o n d i t i o n suggests , f i r s t of a l l , t h a t p i c t u r e s have not been coded v e r b a l l y , o therwi se one cou ld expect s i m i l a r i n t e r p o l a t e d a c t i v i t y e f f e c t s ; second ly , whatever has been o p e r a t i o n a l l y de f ined as an i n t e r -ference o r rehearsa l c o n d i t i o n does not a f f e c t the storage of p i c t u r e s t i m u l i d i f f e r e n t i a l l y . There fo re , verba l s torage can hard ly be invo lved under these c ond i t i o n s and r e s u l t s w i l l have to be i n t e rp r e t ed as r e -f l e c t i n g a sepa ra te , non-verbal STS. The lack of an adequate re ference po i n t f o r p i c t u r e r e c o g n i t i o n a t zero de l a y , in con junc t i on w i th the ab -sence of a d i f f e r e n t i a l i n t e r p o l a t e d a c t i v i t y e f f e c t , int roduces even f u r t h e r comp l i ca t i on s in a s ses s ing the r e l a t i v e e f f e c t i v e n e s s of the v i s u a l STS over r e t e n t i o n i n t e r v a l s . S ince the re i s no v a l i d re fe rence po i n t f o r verba l and v i s u a l STS a t the zero delay c o n d i t i o n , no statement can be made about the s u p e r i o r -i t y of words o r p i c t u r e s in an immediate r e c o g n i t i o n sequence. Word recog-n i t i o n i s s i g n i f i c a n t l y s upe r i o r t o p i c t u r e r e c o g n i t i o n a f t e r 15 seconds of rehear sa l (EXP. I l l ) , but , r e c o g n i t i o n scores f o r the two m o d a l i t i e s a re u n d i f f e r e n t i a t e d a f t e r verba l i n t e r f e r ence (EXP. I ) . Whether t h i s u n d i f f e r e n t i a t e d response leve l a f t e r a 15 second r e t e n t i o n i n t e r v a l f o r words and p i c t u r e s in EXP. I and p i c t u r e s in EXP. I l l i s the r e s u l t of s i m i l a r STS processes o r d i f f e r e n t STS processes converging t o a s i m i l a r 67 r e c o g n i t i o n leve l i s , of cour se , a j u s t i f i e d que s t i o n , wh ich, a t the same t ime , seems unanswerable a t t h i s p o i n t . Fu r the r support f o r separate verba l and v i s u a l s torage systems can be obta ined from the complimentary evidence of the r e c a l l data . S ince verba l l a b e l l i n g i s demanded f o r words and p i c t u r e s in f r e e r e c a l l , no d i f f e r e n c e s emerge due to i n t e r p o l a t e d a c t i v i t i e s because words and p i c t u r e s are s to red in the same STS. If the same i n t e r p o l a t e d a c t i v i t i e s in a r e cogn i t i o n task produce word -p i c tu re d i f f e r e n c e s , i t i s safe t o assume tha t words and p i c t u r e s , under these c o n d i t i o n s , were s to red in d i f f e r e n t sho r t - te rm systems. In e f f e c t , the p re sen ta t i on of ve rba l mate r i a l in a r e c a l l o r r e c o g n i t i o n task always leads t o verba l cod ing. Subsequently verba l i n t e r -ference and rehearsa l w i l l i n f l uence the response leve l of the verba l s t o re a f t e r 15 seconds as p r e d i c t e d . When p i c t u r e s are requ i red to be coded v e r b a l l y , as in a f r e e r e c a l l t a s k , the verba l s torage of the p i c t u r e s t i m u l i w i l l be a f f e c t e d dur ing the i n t e r p o l a t e d a c t i v i t i e s in the same way. P i c t u r e s torage in a r e cogn i t i o n t a s k , in c o n t r a s t , i s not a f f e c t e d d i f f e r e n t i a l l y by the i n t e r p o l a t e d a c t i v i t i e s , and, t h e r e f o r e , i s po s tu la ted t o be s to red in a sepa ra te , v i s u a l STS. Rehearsal e f f e c t s are q u i t e c o n s i s t e n t throughout the exper iments. The increase of word r e c o g n i t i o n due to rehearsa l was s i g n i f i c a n t in EXP. I l l as we l l as in EXP. IV, though the o v e r a l l response leve l was lower due t o the aud i t o r y f i r s t probe in the l a t t e r experiment. However, s i n ce rehearsa l e f f e c t can on ly be a c cu r a t e l y assessed wi th re spec t t o i n t e r -fe rence e f f e c t s , the data from EXP. IV cannot be cons idered because there 68 Is no comparable re ference p o i n t . A d d i t i o n a l support f o r the rehearsa l e f f e c t can be found in EXP, V where r e c a l l scores show a h i gh l y s i g n i f i c a n t increase over delay pe r i od s . S ince r e c a l l scores do have a v a l i d r e f e r -ence p o i n t a t zero de lay , the small decrease between zero and 15 seconds r e t e n t i o n , though in c on t r a s t t o r e cogn i t i on s co re s , s t i l l supports the f a c i l i t a t i v e e f f e c t s of the verba l rehearsa l mechanism w i th re fe rence to the i n t e r f e r e n c e e f f e c t . The r e l a t i v e increase in p i c t u r e r e c a l l a f t e r rehearsa l has a l ready been a t t r i b u t e d to verba l coding of p i c t u r e mate r i a l in t h i s exper imental c o n d i t i o n . Rehearsal e f f e c t s on the v i s u a l s t o re can, t h e r e f o r e , on l y be assessed in the r e c o g n i t i o n ta sk . S ince the apparent i n c rea se , w i th r e s -pect t o zero de l ay , dur ing rehearsa l in EXP. I l l and IV does not d i f f e r from the Increase dur ing i n t e r f e r e n c e (EXP. I ) , a comparable v i s u a l r e -hearsal mechanism seems, t h e r e f o r e , i n e f f e c t i v e under the g i ven e x p e r i -mental c o n d i t i o n s . The data from the r e c o g n i t i o n and reca l I exper iments , t h e r e f o r e , support prev ious f i n d i n g s of the f a c i l i t a t i v e e f f e c t s of the verba l r e -hearsa l mechanism in STM exper iments , as we l l as p rov ide a d d i t i o n a l e v i d -ence aga in s t the e x i s t ence o r e f f e c t i v e n e s s of a s i m i l a r f a c i l i t a t i v e mechanism in the v i s u a l STS. The e f f e c t s of ve rba l i n t e r f e r e n c e have a l s o shown a c o n s i s t e n t p a t t e r n throughout the exper iments. S ince i n t e r f e r ence data w i l l have t o be eva luated again w i th re spec t to rehearsa l c o n d i t i o n s , i n t e r f e r e n c e e f f e c t s w i l l merely be a complementary aspect of the p r e v i ou s l y d i scussed rehearsa l e f f e c t s . That i s , verba l i n t e r f e r e n c e has a damaging e f f e c t on 69 v e r b a l s t o r a g e i n both r e s p o n s e t a s k s , w h i l e t h e v i s u a l s t o r e i n t h e r e c o g -n i t i o n t a s k i s u n a f f e c t e d by c o u n t i n g backwards. However, i t seems a p p a r e n t t h a t c o u n t i n g backwards was n o t t h e o n l y i n t e r f e r e n c e a c t i v i t y i n v o l v e d i n t h i s e x p e r i m e n t . Though no t d e f i n e d as s u c h , r e s p o n d i n g t o t h e i n i t i a l v i s u a l o r a u d i t o r y probe f o l l o w i n g s t i m u l u s t e r m i n a t i o n e x e r t e d a more damaging e f f e c t on STS t h a n some of t h e o p e r a t i o n a l l y d e f i n e d i n t e r f e r e n c e c o n d i t i o n s . The word c o n d i t i o n seemed e s p e c i a l l y s e n s i t i v e t o t h e v a r i o u s t y p e s of i n t e r f e r e n c e s , w h i c h makes i t p o s s i b l e t o rank o r d e r t h e d i f f e r e n t t y p e s o f i n t e r f e r e n c e s a c r o s s t h e t h r e e r e c o g n i t i o n e x p e r i m e n t s ( T a b l e s 5 and 6 ) . Responding t o an a u d i t o r y probe i m m e d i a t e l y a f t e r s t i m u l u s p r e s e n t a t i o n r e s u l t s i n t h e s t r o n g e s t damaging e f f e c t of t h e v e r b a l STS (EXP. I V ) . C o u n t i n g backwards f o r 15 seconds i s l e s s damaging t o t h e v e r b a l s t o r e , y e t i s e q ual t o r e s -p o n d i ng t o an a u d i t o r y probe a f t e r a 15 second r e h e a r s a l p e r i o d (EXP. I v s . EXP. I V ) . The l e a s t damaging o f t h e i n t e r f e r e n c e e f f e c t s on v e r b a l s t o r a g e i s r e s p o n d i n g t o a v i s u a l probe a t z e r o d e l a y (EXP. I and I I I ) . F i f t e e n seconds of r e h e a r s a l l e a d , of c o u r s e , t o t h e h i g h e s t r e c o g n i t i o n I eve I. The p i c t u r e c o n d i t i o n s seem t o be l e s s i n f l u e n c e d by t h e s e p a r t i -c u l a r t a s k demands. In f a c t , t h e r e a r e o n l y two d i s t i n c t r e c o g n i t i o n l e v e l s , one a t z e r o and t h e o t h e r a t 15 seconds d e l a y . An immediate r e c o g n i t i o n r e s p o n s e l e a d s t o e q u a l l y s t r o n g i n t e r f e r e n c e e f f e c t whether t h e probe i s p r e s e n t e d v i s u a l l y o r a u d i t o r i l y (EXP. I and I I I v s . EXP. I V ) . On t h e o t h e r hand, c o u n t i n g backwards, r e h e a r s i n g , o r r e h e a r s i n g p l u s a u d i t o r y probe r e s u l t s i n an e q u a l l y h i g h r e c o g n i t i o n l e v e l (EXP. I, I I I & 70 IV). With t h i s new i n t e r p r e t a t i o n of the va r ious i n t e r f e r i n g task de-mands in hand, a r e - e v a l u a t i o n of the data leads to s e v e r a l , i n t e r e s t i n g i m p l i c a t i o n s . I t seems f a i r l y c l e a r t ha t any type of ve rba l f a c i l i t a t i o n o r i n t e r f e r e n c e has l i t t l e e f f e c t on the v i s u a l s t o r e , once p i c t u r e s are encoded v i s u a l l y . The response l e ve l f o r p i c t u r e c ond i t i o n s a f t e r a 15 second r e t e n t i o n i n t e r v a l in EXP. I, III and IV leaves l i t t l e doubt about t h i s assumption. More d i f f i c u l t to e x p l a i n i s the equa l l y damaging e f f e c t in the zero delay cond i t i on s due t o responding t o a v i s u a l or aud i t o r y probe. 'Why the v i s u a l STS a t t h i s p a r t i c u l a r temporal l o c a t i o n , i . e . dur ing the t r a n s f e r process of i n fo rmat ion from SM t o STS, s u f f e r s equa l l y in e i t h e r p r e sen ta t i on moda l i ty of the f i r s t probe, has been t e n t a t i v e l y answered in terms of the damaging e f f e c t s on STS by d i v e r t i n g a t t e n t i o n dur ing the t r a n s f e r process. But , even t h i s answer seems h i gh l y u n s a t i s -f a c t o r y in l i g h t of d i f f e r e n t i a l responses in the word c o n d i t i o n under the same c i rcumstances . In g e n e r a l , the word c o n d i t i o n leads to more p rovoca t i ve s p e c u l -a t i o n s . The verba I -aud i tory as we l l as the v i s u a l task demands, seem to e xe r t c o n s i s t e n t l y damaging e f f e c t s on the verbal STS. I t i s important t o n o t i c e though, t h a t every one of the a u d i t o r y - v e r b a l task demands, i . e . , responding t o an immediate aud i t o r y probe, count ing backwards, and r e -hears ing p lus responding t o an aud i t o r y probe, are more damaging t o the verba l s t o r e than are the v i s u a l ta sk demands, i . e . , responding t o an immed-i a te v i s u a l probe. No c l a im can be made at t h i s stage about c o n s i s t e n t s torage s p e c i f i c i n t e r f e r ence e f f e c t s . That i s , i t might be specu lated 71 t ha t verba I -aud i tory i n t e r f e r e n c e i s more det r imenta l to ve rba l s torage and v i s u a l i n t e r f e r ence i s more damaging t o the v i s u a l s t o r e . Some ex -amples f o r STS s p e c i f i c i n t e r f e r e n c e e f f e c t s can be e x t r a c t ed from the exper iments. For i n s tance , responding to a v i s u a l probe a t zero delay i s more damaging f o r p i c t u r e s than words (EXP. I and I I I ) , whereas f o r the word c o n d i t i o n , a lower r e c o g n i t i o n leve l i s obta ined by responding to an aud i t o r y f i r s t probe than to a v i s u a l l y presented f i r s t probe (EXP. IV v s . EXP. I and I I I ) . However, there are a l s o data which show tha t count ing backwards r e s u l t s in a lower r e c o g n i t i o n score f o r p i c t u r e s than does r e s -ponding to a v i s u a l probe a t zero delay f o r words (EXP. I ) . On the o ther hand, i t might seem more reasonable to c l a s s i f y i n t e r -f e r i n g cond i t i on s w i th respect to t h e i r temporal occurrance dur ing the response ta sk . That i s , one could con s i de r responding immediately, as one type of i n t e r f e r i n g a c t i v i t y , d i v e r t i n g a t t e n t i o n dur ing the r e t e n t i o n I n te rva l as another type. However, f o r t h i s k ind of a n a l y s i s the data are incomplete s i n ce there i s no v i s u a l i n t e r f e r e n c e task dur ing the r e t e n t i o n i n t e r v a l . Even wi th the a v a i l a b l e i n t e r f e r ence c o n d i t i o n s , verba l i n t e r f e r e n c e p lus responding to an aud i to ry probe i s mis s ing from the da ta . As a r e s u l t of t h i s , verbal and v i s u a l STS s p e c i f i c and task demand s p e c i f i c i n t e r f e r e n c e e f f e c t s cannot be comprehensively assessed. Some aspects of the da ta , however, do po i n t towards a p o s s i b l e t rend of s p e c i f i c i n t e r f e r e n c e cond i t i o n s f o r the verba l and v i s u a l STS. A comparison of r e c a l l and r e c o g n i t i o n data has t o s t a r t w i th an e v a l u a t i o n of the d i f f e r e n t response demands in each t a s k , which in t u rn have led t o an unexpected s e r i e s of ta sk s p e c i f i c adjustments. Learning 72 s t r a t e g i e s have been shown to d i f f e r in the two response t a s k s . Though the evidence i s l a r ge l y based on s u b j e c t i v e r e p o r t s , the tesk s p e c i f i c learn ing s t r a t e g i e s appear by no means c o u n t e r i n t u i t i v e . A f t e r a l l , why should i n a r e c a l l task look a t a l l items in the mat r i x on l y t o f o r ge t some of them i f he can ob ta in a h igher r e c a l l score by concent ra t i ng on a few of the items. Subsequently, learn ing rates f o r the two tasks can be expected t o d i f f e r a l s o . Learning ra tes w i t h i n each task f o r words and p i c t u r e s , however, appear to be f a i r l y cons tant , i f zero delay responses can be used as an adequate i n d i c a t o r . There i s no wo rd -p i c tu re d i f f e r e n c e in the r e c a l l experiment at t h i s s t age , and word -p i c tu re d i f f e r e n c e s in the r e c o g n i t i o n experiments are s m a l l , yet ambiguous in t h e i r i n t e r p r e t a t i o n across exper iments. At the same t ime , verbal l a b e l l i n g of p i c t u r e s i s requ i red in the r e c a l l t a s k , whereas l i t t l e c ros s moda l i ty encoding has been evidenced in the r e c o g n i t i o n t a sk . Hence, i f l ea rn ing ra tes f o r words and p i c t u r e s are the same with cross moda l i t y encoding, i . e . , r e -c a l l , l ea rn ing ra tes wi thout c ross modal i ty encoding, i . e . , r e c o g n i t i o n , should be even f a s t e r f o r p i c t u r e s than words. However, t h i s might be a r a the r i napp rop r i a te e x t en t i on of the argument in l i g h t of the d i f f e r e n t lea rn ing s t r a t e g i e s across the two response t a s k s . In summary, i t seems f a i r l y c l e a r t h a t Ss use d i f f e r e n t s t r a t e g i e s to maximize t h e i r response scores in the two t a s k s . It seems less c l e a r whether p i c t u r e s and words are learned at a d i f f e r e n t r a te w i t h i n each s t r a tegy . However, there i s ample evidence t h a t words and p i c t u r e s are s to red d i f f e r e n t l y in the two types of experiments because of response demands. In s p i t e of these l i m i t a t i o n s of the data a comparison of r e c a l l 73 and r e c o g n i t i o n r e s u l t s c on t r i bu te s c r i t i c a l ev idence f o r the ex i s t ence of a v i s u a l STS. If the response task demands verba l l a b e l l i n g of p i c t u r e s , the s t imu lu s i n fo rmat ion w i l l be s to red v e r b a l l y . Subsequently the re i s no d i f f e r e n c e between word and p i c t u r e r e c a l l under rehearsa l and i n t e r -fe rence c o n d i t i o n s . If Ss are prevented from l a b e l l i n g p i c t u r e s v e r b a l l y , as in the r e c o g n i t i o n t a s k , they w i l l be s to red in a separate STS, and w i l l show d i f f e r e n t e f f e c t s w i th respect t o word r e c o g n i t i o n under the two i n -t e r p o l a t e d a c t i v i t i e s . In e f f e c t , the negat ive outcome of the r e c a l l experiments can be used as complimentary ev idence f o r the ex i s t ence of a v i s u a l STS in the r e c o g n i t i o n ta sk . It should be noted though a t t h i s s tage t h a t the i n t e r p o l a t e d a c t i v i t i e s were introduced as a within-S_ v a r i a b l e in the r e c o g n i t i o n exper iments , and as a between-S v a r i a b l e in the r e c a l l t a sk . To what ex tent t h i s procedural d i f f e r e n c e cou ld be con -founding the data i s , of cour se , unknown. Throughout the d i s cu s s i on of the p r e s e n t a t i o n , i n t e r p o l a t e d a c t i v i t y , and response task e f f e c t s , severa l p e r s i s t e n t problems have been, a t t imes , ignored and w i l l be d i scussed now in more d e t a i l . The most c r i t i c a l of these i s the f a i l u r e of the s e r i e s of experiments to ob-t a i n a r e c o g n i t i o n leve l f o r the immediate STS in words and p i c t u r e s . Subsequent ly, no statement can be made about the r e l a t i v e e f f i c i e n c y of the verba l and v i s u a l sho r t - te rm s to rage. Furthermore, because of t h i s f a i l u r e , i n t e r p o l a t e d a c t i v i t y e f f e c t s cou ld be assessed on ly w i th r e s -pect t o each o t h e r , and the abso lu te amount of change which occurs in STS due to rehearsa l and i n t e r f e r e n c e i s s t i l l unknown. At t h i s stage i t seems c l e a r , t h a t under l y ing t h i s f a i l u r e was the s p e c i f i c r e c o g n i t i o n 74 task s e l e c t e d . The damaging e f f e c t on STS due t o responding t o the i n i t i a l probe in the zero delay c o n d i t i o n unexpectedly introduced an i n t e r f e r e n c e f a c t o r which cou ld not be reso lved in the g iven exper imental s i t u a t i o n ; and though the nature of t h i s damaging e f f e c t has not been s a t i s f a c t o r i l y answered, i t s pe r s i s t ency s t r ong l y evidences the importance of the under-l y i n g phenomena. That i s , responding dur ing the t ime of the po s tu l a ted t r a n s f e r process of i n fo rmat ion from SM to STS has been shown to be a c r i t i c a l i n t e r f e r e n c e paradigm. S ince responding immediately a f t e r s t imu lu s p re sen ta t i on leads to a decrease of r e c o g n i t i o n f o r the remainder of the sequence, the 7.5 second delay c o n d i t i o n in EXP. I l l should be the next c l o s e s t i n d i c a t o r of the pure STS e s t ima te , a t l e a s t f o r the p i c t u r e group. A f t e r a l l , the t r a n s f e r process from SM t o STS should be completed by then , and i t has been shown tha t ve rba l rehearsa l does not f a c i l i t a t e the v i s u a l s t o r e . If r e s t r i c t i n g the d i s c u s s i o n t o d ' scores o n l y , the data present again a c o n t r a d i c t o r y p i c t u r e . In EXP. I l l t he re i s no increase in p i c t u r e o r word r e cogn i t i o n between zero and 7.5 seconds of r e h e a r s a l , fo l l owed by a s i g n i f i c a n t increase f o r the 15 second c o n d i t i o n . In EXP. IV, the increase occurs between zero and 7.5 seconds i n s t ead . But the on ly d i f f e r e n c e in the exper imental s i t u a t i o n i s the replacement of the v i s u a l w i th an aud i to ry f i r s t probe. Y e t , how t h i s exper imental man ipu l -a t i o n i s r e l a t e d to the changing locus of the increase in r e c o g n i t i o n scores i s by no means e v i d e n t , and t r y i n g t o e x p l a i n i t w i th unwieldy s pecu l a t i on s seems equa l l y f u t i l e . I t should be added here t h a t , s i n ce d ' scores in EXP. I l l suggested 75 an increase f o r PP between zero and 7.5 seconds, f u r t h e r post hoc analyses were a p p l i e d in an attempt t o eva luate s t a t i s t i c a l l y t h i s p r o p o s i t i o n . However, a homogeneity of v a r i ance and a s i gn t e s t d id not change the s t a t i s t i c a l i n t e r p r e t a t i o n . Moreover, i t became apparent, t h a t the d ' score in i t s e l f might not be the most accurate assessment of the da t a , s i n ce the t r an s fo rmat i on of the raw data to a normal curve was based on a r e l a t i v e l y smaI I N. A f u r t h e r data po i n t which i n v i t e s s pecu l a t i on s i s the c o n s i s t e n t response leve l f o r the 15 second delay c ond i t i o n s f o r p i c t u r e s and words in EXP. I and IV r e s p e c t i v e l y . Though the data po i n t s a re h i gh l y s i m i l a r , they are c l e a r l y r e f l e c t i n g two d i f f e r e n t processes , i . e . , count ing back-wards f o r EXP. I and rehearsa l p lus an aud i t o r y probe in EXP. IV. The p i c t u r e cond i t i on s g i v e data po i n t s of 7.40, 6.90 and 7.05 f o r count ing backwards, rehearsa l and rehearsa l p lus aud i t o r y probe. These data have been i n t e r p r e t e d in terms of the v i s u a l STS being unaf fected by the g iven i n t e r p o l a t e d a c t i v i t i e s . However, looking a t a l l f i v e data p o i n t s , the d i f f e r e n c e s are extremely s m a l l , and i t becomes reasonable to wonder whether the data po i n t s are indeed mediated by the d i f f e r e n t po s tu la ted processes , o r whether the data po in t s are i n d i c a t i v e of one s i n g l e under-l y i n g process . That i s , under the g iven exper imental c o n d i t i o n s , t h i s i s the abso lu te minimum r e c o g n i t i o n leve l which w i l l be always ob t a i ned , regard le s s of exper imental man ipu la t i on s . The only argument aga in s t t h i s l a t t e r i n t e r p r e t a t i o n i s the even lower response leve l f o r p i c t u r e s a t 7.5 seconds of rehearsa l in EXP. I I I . Hence, the ques t ion whether the same o r d i f f e r e n t processes are under l y ing t h i s common r e c o g n i t i o n leve l 76 c a n be s a t i s f a c t o r i l y answered i n t h e two word c o n d i t i o n s , i s l e s s c l e a r i n t h e t h r e e p i c t u r e c o n d i t i o n s , and becomes v e r y m e a n i n g f u l i n a word-p i c t u r e c o m p a r i s o n , y e t a g a i n i s c o n t r a d i c t e d by t h e even lower r e c o g -2 n l t i o n l e v e l f o r t h e p i c t u r e c o n d i t i o n a t 7.5 seconds of r e h e a r s a l . The r e m a i n i n g problem c e n t e r s around t h e i n v o l v e m e n t o f s p e c i f i c memory sub-systems i n t h e i r c o n t r i b u t i o n t o o v e r a l l r e c o g n i t i o n s c o r e s . As p r e v i o u s l y p o s t u l a t e d t h e immediate r e c o g n i t i o n r esponse a f t e r s t i m u l u s p r e s e n t a t i o n seems t o be m e d i a t e d by SM i n v o l v e m e n t . T h i s SM e f f e c t a p p a r e n t l y h o l d s f o r v i s u a l and a u d i t o r y p r e s e n t a t i o n s of t h e i n i t i a l p r o b e . S i n c e t h e r e c o g n i t i o n sequence l a s t e d 45 s e c o n d s , and under d e l a y c o n d i t i o n s Ss were s t i l l r e s p o n d i n g a f t e r 60 o r 75 seconds f o l l o w i n g s t i m u l u s p r e s e n t a t i o n , i t a l s o becomes r e a s o n a b l e t o ask whether r e s p o n s e s under t h e s e c o n d i t i o n s can be c o n s i d e r e d as r e f l e c t i n g s h o r t - t e r m s t o r a g e . P r e v i o u s e v i d e n c e (among o t h e r s , A t k i n s o n & S h i f f r i n , 1968) s t r o n g l y s u g g e s t t h a t s h o r t - t e r m t r a c e s do not l a s t f o r more t h a n 15 t o 30 s e c o n d s . In e f f e c t t h e n , most of t h e r e c o g n i t i o n r e s p o n s e s i n t h e s e e x p e r i m e n t s have been o b t a i n e d o u t s i d e o f t h e normal c o n f i n e s o f STM. On t h e o t h e r hand, a l l of t h e e x p e r i m e n t a l m a n i p u l a t i o n s , i . e . , i n t e r f e r e n c e and r e -h e a r s a l , have been c o n f i n e d w i t h i n t h e t e mporal l i m i t s of STM d u r a t i o n . W i t h r e s p e c t t o t h e p r e v i o u s l y d i s c u s s e d A t k i n s o n and S h i f f r i n model, t h e f o l l o w i n g p r o c e s s e s a r e p o s t u l a t e d t o o c c u r . The s t i m u l u s i n f o r m a t i o n e n t e r s t h e SM and i s i m m e d i a t e l y t r a n s f e r r e d t o STS. In t h e r e c a l l ex-p e r i m e n t s t h i s i n f o r m a t i o n i s e i t h e r r e p r o d u c e d i m m e d i a t e l y , r e h e a r s e d , o r i n t e r f e r e d w i t h . Subsequent r e c a l l s c o r e s r e f l e c t r a t h e r a d e q u a t e l y t h e u n d e r l y i n g p r o c e s s e s i n STS. In t h e r e c o g n i t i o n t a s k , however, most 77 of the data po in t s are obta ined beyond the accepted du ra t i on of STS p r o -cesses . Hence, most of the data po i n t s can be expected t o r e f l e c t STS o r LTS processes. Y e t , s i n ce LTS capac i t y depends on the a b i l i t y of STS t o t r a n s f e r Information i n to LTS, and s i n ce a l l experimental man ipu la t ions occurred dur ing STS temporal l i m i t s , the obta ined r e cogn i t i o n s co re s , whether they r e l y on STS o r LTS are s t i l l i n d i c a t i v e of STS f unc t i on s as determined by the exper imental v a r i a b l e s . For example, r e c o g n i t i o n scores in the word c o n d i t i o n a f t e r verba l rehearsa l are r e l a t i v e l y h i gh , but not on ly because verba I -aud i tory t r a ce s in STS have been cont inuous l y regenerated and a r e , t h e r e f o r e , r e l a t i v e l y s t r ong , but a l s o because of the cont inuous t r a n s f e r process t o LTS, which made a high response level a t 60 seconds a f t e r s t imulus p re sen ta t i on s t i l l p o s s i b l e . In e f f e c t t hen , w h i l e some of the r e cogn i t i o n response might not have been mediated pure ly by STS, they s t i l l r e f l e c t t o what ex tent STS was ab le t o f u n c t i o n under the exper imental c o n d i t i o n s . SUMMARY In s p i t e of problems in the design and va r i ou s c o n t r a d i c t o r y r e s u l t s w i t h i n a g iven and across the th ree response measures f o r the s e r i e s of exper iments , severa l worthwhi le f i n d i n g s can s t i l l be repor ted . The r e c o g n i t i o n experiments have shown t h a t words and p i c t u r e s w i l l be s to red d i f f e r e n t i a l l y i f c ross moda l i t y encoding can be expe r imenta l l y reduced. Subsequently, the ve rba l STS w i l l s u f f e r from verba l i n t e r -ference and w i l l be f a c i l i t a t e d by r e h e a r s a l . The po s tu l a ted v i s u a l STS seems t o be unaf fec ted under s i m i l a r exper imental c o n d i t i o n s . In a d d i t i o n , responding t o a r e c o g n i t i o n Item immediately a f t e r s t imu lu s p re sen ta t i on 78 exe r t s a damaging e f f e c t on the verba l and v i s u a l STS. Here aga in , the damaging e f f e c t seems moda l i ty s p e c i f i c f o r the verba l STS, i . e . , an aud i to r y probe i s more damaging than a v i s u a l probe, wh i l e the v i s u a l STS s u f f e r s t o the same ex tent under both c o n d i t i o n s . At the same t ime, verba l and v i s u a l coding s t r a t e g i e s seem to be ta sk s p e c i f i c . In the r e c a l l exper iments, f o r i n s tance , where p i c t u r e s must be l a b e l l e d f o r the response t a s k , word and p i c t u r e study groups do not d i f f e r f o r immedi-ate r e c a l l nor a f t e r rehearsa l o r verba l i n t e r f e r e n c e . That i s , when p i c t u r e s are coded v e r b a l l y , r e c a l l scores r e f l e c t s i m i l a r response p a t -te rn s f o r word and p i c t u r e p re sen ta t i on s a t zero delay and a f t e r both i n -t e r p o l a t e d a c t i v i t i e s . The s e r i e s o f exper iments , however, f a i l e d to o b t a i n any ev idence about ve rba l o r v i s u a l STS s u p e r i o r i t y . The reasons f o r t h i s f a i l u r e are the f o l l o w i n g : the equal r e c a l l scores f o r word and p i c t u r e study groups a t zero delay had to be i n t e rp re ted i n terms of verba l coding in both groups; in c o n t r a s t , the d i f f e r e n t i a l r e cogn i t i o n scores f o r WW and PP a t zero delay had t o be eva luated w i th respect to the damaging e f f e c t s of responding t o the i n i t i a l r e cogn i t i o n i tem. With re ference t o the o r i g i n a l ques t ion asked in the i n t r o d u c t i o n , i . e . , i f verba l coding Is not demanded f o r p i c t o r i a l m a t e r i a l , does a non-verbal sho r t - te rm mechanism e x i s t with s i m i l a r p r o p e r t i e s as the verba l STS, the answer seems to support Atk inson and S h i f f r i n ' s (1968) t e n t a t i v e hypothes i s . The experiments have confirmed prev ious f i n d i n g s of the damaging e f f e c t of verba l i n t e r f e r ence and f a c i l i t a t i v e e f f e c t s of the rehearsa l a c t i v i t y in the verba l STS. The lack of a d i f f e r e n t i a l e f f e c t of the i n t e r p o l a t e d a c t i v i t i e s in the p i c t u r e cond i t i on s in con-79 j u n c t i o n with the r e l a t i v e l y high r e c o g n i t i o n lev e l a f t e r a f i f t e e n second r e t e n t i o n i n t e r v a l , on the other hand, i n d i c a t e t h a t there i s a v i s u a l STS. In l i g h t of the i n e f f e c t i v e n e s s of the rehearsal c o n d i t i o n the data f u r t h e r suggest t h a t the postulated v i s u a l STS lacks a corresponding r e -hearsal mechanism, or at l e a s t show th a t the v i s u a l rehearsal mechanism i s I n e f f e c t i v e in f a c i l i t a t i n g r e c o g n i t i o n scores in t h f s p a r t i c u l a r ex-perimental s i t u a t i o n . 80 FOOTNOTES The term " t r a c e " i s here used as In the Atk inson and S h i f f r i n model, i . e . , as an In terna l r ep re sen ta t i on of the to-be-remembered m a t e r i a l . Subsequent research has shown tha t count ing backwards p lus responding t o an aud i to r y f i r s t probe leads to no increase in r e c o g n i t i o n scores from zero t o f i f t e e n seconds of de iay . 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The r o l e of v e r b a l i z a t i o n in the memorizing of convent iona l f i g u r e s . Journal of Verbal Learning and Verbal Behav io r , 1969, 8_, 380-383. Conrad, R. A cou s t i c confus ion in immediate memory. B r i t i s h Journa l of Psychology, 1964, 55, 75-84. Crowder, R. G. The r o l e of one ' s own v o i c e in immediate memory. Cogn i t i ve Psycho Ioqy, 1970, ± , 157-178. G ibson, E. J . & Yonas, A. A developmental study of the e f f e c t s of v i s u a l and aud i to r y i n t e r f e r ence on a v i s u a l scanning t a sk . Psychonomic S c i ence , 1966, 5, 163-154. H e l I y e r , S. Frequency of s t imu lus p re sen ta t i on and sho r t - te rm decrement I n reca I I. Journa I of Experimenta I Psychology, 1962, 64_, 650. James, W. P r i n c i p l e s of Psychology, H o l t , New York, 1890. 82 K i n t s c h , W. Learn lng , Memory, and Conceptual Processes. John Wiley and Sons, New York, 1970. K i n t s c h , W. & Buschke, H. 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Recogn i t ion memory f o r words, sentences, and p i c t u r e s . Journa l of Verbal Learning and Verbal Behav ior , 1967, 6_, 156-163. S p e r l i n g , G. The in format ion a v a i l a b l e in b r i e f v i s u a l p r e sen ta t i on s . Psychology Monographs, I960, 74 (Whole No. 498). S p e r l i n g , G. A model f o r v i s u a l memory t a s k s . Human Fac t o r s , 1963, 5_, 19-31. Turvey, M. I. Phonemic coding and the v i s u a l perceptua l system. Journa l of Experimental Psychology, 1967, 74, 289-293. Tversky , B. P i c t o r i a l and verba l encoding in a shor t - te rm memory t a sk . Pe rcept i on and Psychophys ics , 1969, £ 5 , 225-233. Waugh, N. C. & Norman, D. A. Primary memory. P sycho log i ca l Review, 1965, 72_, 89-104. W icke l g ren , W. A. A cou s t i c s i m i l a r i t y and i n t r u s i o n e r r o r s in s h o r t -term memory. Journal of Experimental Psychology, 1965, 70, 102-108. 84 APPENDIX I 85 INSTRUCTIONS Th i s i s an experiment in STM. In each t r i a l you w i l l be presented wi th a mat r i x of s i x words which you are t o remember f o r a subsequent r e c o g n i t i o n t a sk . Each t r i a l w i l l s t a r t w i th the p re sen ta t i on of the s i x words f o r 1.2 seconds. Now, 1.2 seconds i s a very shor t du ra t i on to learn s i x words. The re fo re , you w i l l have to scan over the whole d i s p l a y as r a p i d l y as p o s s i b l e , in o rder to know a l l of the words. Make su re , t ha t you d o n ' t miss any one of the words dur ing the shor t p r e sen ta t i on t i m e , because some of the words w i l l reappear in the subsequent r e c o g n i t i o n t a sk . The r e c o g n i t i o n task i t s e l f w i l l c o n s i s t of s i x s l i d e s , w i th one word each, presented at a r a te of one s l i d e every 7.5 seconds. Some of these words in the r e cogn i t i o n sequence w i l l be from the p r e v i ou s l y p r e -sented m a t r i x , and some of them w i l l be new, unre la ted words. Your task w i l l be, as the r e c o g n i t i o n s l i d e appears, to decide whether the word had been In the prev ious mat r i x o r not. If you t h i n k the word i s from the prev ious m a t r i x , press the button "OLD." If you th i nk the word had not been in the m a t r i x , press "NEW.'1 S ince I am i n t e r e s t e d in r e a c t i o n t ime , you should press the cho ice button as f a s t as p o s s i b l e . In a d d i t i o n , on severa l t r i a l s , the r e cogn i t i o n ta sk w i l l not be immediately f o l l o w -ing the p re sen ta t i on of the m a t r i x , instead a th ree d i g i t number w i l l appear, and you are t o count backwards by threes from t h i s number t i l l I I n i t i a t e the r e cogn i t i o n sequence. To summarize. There w i l l be nine t r i a l s . Each t r i a l w i l l s t a r t w i th a 1.2 second p re sen ta t i on of s i x words, fo l lowed e i t h e r by the f i r s t r e c o g n i t i o n s l i d e , o r by a number, in which case you count backwards t i l l I i n i t i a t e the r e cogn i t i o n sequence. 86 Your task i s to make sure you see every word in the m a t r i x , and to r e s -pond as f a s t as p o s s i b l e in the r e cogn i t i o n task by p re s s i ng the a p p r o p r i -a te but ton. Are there any quest ions? 87 APPENDIX I I i TABLE 1 ANOVA f o r Co r rec t Probe Responses in Experiment I. Source of Var iance SS df MS F p Between Subjects 153.50 79 A (Study P re sen ta t i on ) 6.34 1 6.34 3.33 -B (Recogn i t ion Presentat ion) - .70 1 .70 .36 -AB 1 .71 1 1.71 .90 -Subjects w i t h i n Groups 144.75 76 1 .90 Wi th in Subjects 270.00 160 2.08 C (Delay) 6.01 2 3.00 -AC 33.97 2 16.89 1 1 .79 <.01 BC 7.06 2 3.53 2.45 -ABC 3.56 2 1 .78 1.23 -C x Subject s w i t h i n 'Groups 219.40 152 1 .44 Tota l 423.50 239 89 TABLE 2 A n a l y s i s of Simple E f f e c t s f o r AC I n t e r a c t i o n With Probe Responses (Experiment I) C1 C 2 S A 1 (Word) 7.62 6.82 7.27 A 2 ( P i c t u r e ) 6.25 7.17 7.32 Source C f o r A A A f o r 0 Er r o r Within df 2 2 1 1 1 152 MS 6.43 13.56 37.81 2.45 0.05 i . 44 F 4.47 9.41 26.26 1 .70 0.03 P .05 .01 .01 TABLE 3 Newman Keuls Test f o r Delay E f f e c t s Using Correct Probe Responses in Experiment I 2 Sxq .95 .7512 .9014 Sxq .99 .9927 1.1268 )rder Treatments in Order of C f o r A 1 b c a C f o r A 1 6-82 7.27 7.62 b c a C f o r A "2 a b .•80* .35 ,45 b , 92* ,07* ,15 TABLE 4 ANOVA f o r d ' Scores in Experiment I Source of Var iance SS df MS F p Between Subjects 185.61 79 A (Study P re sen ta t i on ) 1 .74 1 1 .74 .82 -B (Recogn i t ion P re sen ta t i on ) 4.60 1 4.60 2.23 -AB 22.48 1 22.48 I 0.89 .01 Subject s w i t h i n Groups 156.79 76 2.06 W i th i n Subject s 235.22 160 C (Delay) 2.20 2 1.10 .81 -AC 22.87 2 1 1 .43 8.42 .01 BC 1.10 2 .55 .40 -ABC 2.54 2 1 .27 .94 -C x Subjects w i t h i n Groups 206.48 152 1.35 Tota l 420.84 239 92 TABLE 5 A n a l y s i s of Simple E f f e c t s f o r AB I n t e r a c t i o n with d f Scores Aj (Word Study) 3^ (Word Recognition) ( P i c t u r e Recognition) 3.50 2.61 A„ ( P i c t u r e Study) 2.72 3.06 z Source df MS F p B f o r A 1 1 23.7185 11.49 .01 /\n 1 3.3701 1.63 z. A f o r B1 1 18.3691 8.90 .01 B 2 1 5.8565 2.34 E r r o r Between 76 2.0630 93 TABLE 6 A n a l y s i s of Simple E f f e c t s f o r AC I n t e r a c t i o n with d' Scores A 1 (Word Study) A 2 ( P i c t u r e Study) 3.57 2.53 C 2 2.87 3.19 C 3 2.73 2.94 Source C f o r A 1 A, A f o r C, df 2 2 MS 8.0759 4.4652 21.6736 2.0865 .8569 F 5.94 3.29 15.95 1 .54 .63 P .01 .05 .01 Err o r Within 152 1.3584 TABLE 7 Newman Keuls Test f o r Simple Delay E f f e c t s with d' Scores in Experiment I 2 3 Sxq .95 .5160 .6192 Sxq .99 . .6818 .7740 Order 1 2 3 Treatments in Order of C f o r A^  c b a C f o r A 1 2.73 2.87 3.57 c b a c - .7022** .8367** b -• - .1345 Treatments in Order of C f o r A ? a c b C f o r A 0 2.5337 2.9450 3.1955 a c b a - .6618* .4113 c - .2505 95 TABLE 8 ANOVA f o r Co r rec t Probe Responses in Experiment III Source of Var iance SS df MS F p Between Subjects 170. 53 39 A (WW vs. PP) 56. 03 1 56. 03 18.61 <.01 Subjects w i t h i n Groups 114. 50 38 3. 01 With in Subject s 113. 34 80 B (Delay) 18. 32 2 9. 16 8.40 <.01 AB 11 . 72 2 5. 86 5.37 <.01 B x Subject s w i t h i n Groups 83. 30 76 1 . 09 Tota l 283. 87 119 TABLE 9 Ana l y s i s of S imple E f f e c t s f o r AB (Presentation x Delay) I n t e r a c t i o n with Probe Responses (Experiment I I I ) A 1 (Word) A ? ( P i c t u r e ) B 7.55 5.30 2 7.25 6.35 "3 7.85 6.90 Source B f o r A A. A f o r B J1 3 df 2 2 E r r o r Wi t h i n MS 1 .80 13.22 50.62 8.10 9.03 1 .07 F 1 .68 12.35 47.31 7.57 8.43 Sxq .95 Sxa QQ B f o r A. ,6545 ,8696 . 7864 .9899 2 1 .05** 1 .60** .55 TABLE 10 Newman Keuls Test Usinq Probe Responses f o r Delay Conditions (Experiment i l l ) De I ay C ^  C C-^  6.42 6.80 7.37 .4666 .5606 .6200 .7057 2 3 ,3750* .9500** .5750* 98 TABLE 11 ANOVA f o r d' Scores in Experiment I I I Source of Var iance SS df MS F p Between Subjects 123.25 39 A (WW vs . PP) 36.64 1 36.64 16.07 <.01 Subject s w i t h i n Groups 86.61 38 2.27 W i th in Subjects 77.91 80 B (Delay) 8.90 2 4.45 5.03 • <.01 AB 1 .78 2 .89 1.01 B x Subjects w i t h i n Groups 67.22 76 .38 Tota l 201.16 119 TABLE 12 Newman Keuls Test Using d' Scores f o r Delay Conditions (Experiment III C1 C 2 C 3 3,09 3.13 3.69 2 3 Sxq .95 .4208 .5056 Sxq .99 .5591 .6320 1 - .0422 .5977* 2 - .5555* 100 TABLE 13 ANOVA f o r Per Cent Co r rec t Responding t o Probe P o s i t i o n s a t Zero Delay f o r Experiments I and III Source of Var iance SS df MS F r\ Between Subjects 1,875.83 79 A (Experiment 1 vs. Experiment I I I ) 3.33 1 •••3.'33 . 17 -B (WW vs . PP) 460.20 1 460.20 24.95 <.01 AB 10.22 1 10.22 .55 -Subject s w i t h i n Groups 1 ,402.08 76 18.44 W i th in Subjects 5,216.67 400 <.0I C ( P o s i t i o n ) 305.87 5 61 .17 4.98 AC 84.80 5 16.96 1 .38 BC 119.18 r, 23.83 1 .94 ABC 42.89 5 8.57 .69 C x Subject s w i t h i n Groups 4,662.92 380 12.27 Tota l 7,092.50 479 101 TABLE 14 A n a l y s i s f o r Simple P o s i t i o n E f f e c t s f o r Zero Delay Conditions f o r WW and PP Groups in Experiments I and 111 Order Treatment i n Order of P o s i t i o n s 66.25 66.87 71.25 71.87 76.25 90.00 Truncated Range 2 3 4 5 6 SXQ .95 10.844 12.958 14.211 15.111 15.777 Sxq .99 14.250 16.168 17.226 18.009 18.635 c a d b e f c - 0.625 5.000 5.625 10.000 23.750** a ' - - 4.375 5.000 9.375 23.125** d - 0.625 5.000 18.750** b - - - - 4.375 18.125** e - - 13.750** 102 TABLE 15 ANOVA f o r Per Cent Co r r e c t Responding a t Zero Delay f o r P o s i t i o n s One and Two (Experiments I and I I I ) Source of Var iance SS df MS F p Between Subjects 1,069. 39 79 • A (Experiment 1 v s . Experiment I I I ) 2. 50 1 2. 50 .18 -B (W vs'. P) 40. 00 1 40. 00 2.95 ns AB 63 1 . 63 .04 -Subject s w i t h i n Groups 1.026. 25 76 13. 50 W i t h in Subject s 725. 00 80 C ( P o s i t i o n 1 v s . P o s i t i o n 2) 75. 63 1 75. 63 9.03 <.01 AC 2. 50 1 2. 50 .29 -BC 10. 00 1 10. 00 1 .19 -ABC 62 1 » 62 .07 -C x Subject s w i t h i n Groups 636. 25 76 8. 37 Tota l 1 ,794. 38 159 103 TABLE 16 ANOVA f o r Correct Probe Responses in Experiment IV Source of Variance SS df MS F P Between Subjects A (W vs. P) 119 1 39 1 i .32 Subjects w i t h i n Groups 118 38 3.10 Within Subjects B (Delay) AB 129 25 4 80 2 2 12.50 2.00 9.54 1 .52 . <.oi B x Subjects w i t h i n Groups 100 76 1 .31 Tota 1 258 119 TABLE 17 Newman-Keuis f o r Delay E f f e c t w i th Probe Responses (Experiment I V ) De I ay 0 7.5 15 X Co r rec t 5.9250 6.8750 6.900 Sxq Sxq .95 .99 .5116 .6798 ,6147 ,7738 3 1 - .9500** .9750** 2 - - .0250 105 TABLE 18 ANOVA f o r d ' Scores (Experiment IV) Source of Variance SS df MS c P Between Subjects 93.55 39 A (W vs. P) 5.33 1 5.33 2.29 -Subjects w i t h i n Groups 88.21 38 2.32 Within Subjects 114.64 80 B (Delay) 13.61 2 8.60 5.20 <.01 AB 1 .59 n .79 .60 -B x Subjects w i t h i n Groups 99.42 76 1.30 Total 2.08. 19 119 TABLE 19 Newrnan-Keu I s f o r Delay E f f e c t with d ? Scores (Experiment IV) Delay 0 7.5 15 X d' scores 2.35 3.08 3.5 ' 2 3 Sxq .95 .5116 .6147 Sxq .99 .6798 .7738 1 2 3 1 - .73* * 1.19** 2 .45 TABLE 20 ANOVA f o r Correct Per Cent Responding to Probe P o s i t i o n s at Zero Delay (Experiment IV) Source of Variance SS df MS F Between Subjects 501.57 39 A (W vs. P) 23.44 1 23.44 1 .54 Subjects w i t h i n Groups 578.13 38 15.21 Within Subjects 3,337.50 200 B ( P o s i t i o n ) 280.96 5 56. 19 3.53 AB 38.44 5 12.37 .77 B x Subjects w i t h i n Groups 3,018.12 190 15.83 Total 3,939.07 239 108 TABLE 21 A n a l y s i s f o r Simple P o s i t i o n E f f e c t s f o r Zero Delay Conditions f o r WW and PP in Experiment IV Order 1 2 3 4 5 6 Treatment in Order of P o s i t i o n s a b c e d f 50.00 58.20 62.50 68.70 73.80 82.50 Truncated Range . 2 3 4 5 6 Sxa .95 17.451 20.853 22.869 24.318 25.389 Sxa .99 22.932 25.956 27.720 28.980 29.988 a c e 8.2 12.5 18.7 23.8 32 .5 * * b - 4.3 10.5 15.6 24.3 6.2 11.3 20.0 5.1 14.8 d _ _ _ _ _ 8.7 109 TABLE 22 ANOVA f o r Reca l l Scores in Experiment V Source of Var iance SS df MS F A (W vs . P) B ( I n t . vs . Re I.) AB Subject s w i t h i n Groups 42.03 1,199.03 34.22 674.50 1 1 1 36 42.03 1 ,199.03 34.22 18.73 2.24 63.99-1 .82 <.01 Tota l ,994.78 39 TABLE 23 ANOVA f o r Word P i c t u r e E f f e c t s During Rehearsal i n Free RecaI I 10 Source of Variance SS df MS F A (W vs. P) B (RehearsaI) AB Subjects w i t h i n Groups 39.03 126.03 38.02 819.70 1 1 1 36 39.03 126.03 38.02 22.76 1.71 5.53 1 .67 <.05 Total 1,021.78 TABLE 24 ANOVA f o r Word-Picture E f f e c t s A f t e r I interference i n Free RecaI I Source of Variance SS df MS F p A (W vs. P) .10 1 .10 .0048 B ( i n t e r f e r e n c e ) 2J02.10 1 2,102.10 102.99 .01 AB .50 1 .50 .0244 Subjects w i t h i n Groups 735.00 36 20.41 Total 2,837.1 39 

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