Psychol. ©
Res.
38,
23
-
by Sprin'ger-Verlag
36
(1975)
1975
Functional Aspects of Information Processing in Human Memory GUNTER
SCHULTER"
I n s t i t u t fur P s y c h o l o g i e der U n i v e r s i t ~ t Graz A - 8010 Graz, S c h u b e r t s t r a S e 6a, A u s t r i a Received
April
4, 1975
SUMMARY. This study was d e s i g n e d to i n v e s t i g a t e the a s s u m p t i o n of t w o - s t o r a g e t h e o r i e s of human m e m o r y that i n f o r m a t i o n after b e i n g p r e p r o c e s s e d in a sensory r e g i s t e r is d i r e c t l y t r a n s f e r r e d into a s h o r t - t e r m storage system. To test this a s s u m p t i o n a r e a c t i o n - t i m e task was used. Ss had to scan the contents of their s h o r t - t e r m store. Some of the elements of s h o r t - t e r m m e m o r y target sets w e r e a s s o c i a t e d w i t h test stimuli by learning trials p r e c e d ing the m e m o r y search. On the t h e o r e t i c a l basis of a t w o - s t o r a g e m o d e l like that p r o p o s e d by A t k i n s o n and S h i f f r i n (1968), s c a n n i n g of s h o r t - t e r m store should be p o s s i b l e w i t h o u t the i n v o l v e m e n t of the l o n g - t e r m storage system; however, in the p r e s e n t study, search a n d / o r d e c i s i o n p r o c e s s e s w e r e a f f e c t e d by a s s o c i a t i v e factors, i.e. by contents of l o n g - t e r m memory. The f u n c t i o n a l r e l a t i o n b e t w e e n S e n s o r y r e g i s t e r and s h o r t - t e r m store p o s t u l a t e d in t w o - s t o r a g e m o d e l s of h u m a n m e m o r y is questioned. An a l t e r n a t i v e m o d e l is p r o p o s e d w h i c h is c o m p a t i b l e w i t h the e x p e r i m e n t a l data.
~ The author is indebted to G. Gletthofer, P. Urban and N. Lyon for their valuable assistence in gathering the data and preparing the manuscript.
23
INTRODUCTION A l t h o u g h the s y s t e m a t i c e x a m i n a t i o n of m e m o r y p h e n o m e n a dates b a c k to the initial stages of e x p e r i m e n t a l p s y c h o l o g i c a l research, it is only d u r i n g the last d e c a d e that a series of a t t e m p t s h a v e b e e n m a d e to i n t e g r a t e the n u m e r o u s i n d i v i d u a l results p e r t a i n i n g to this p r o b l e m a r e a into a c o m p r e h e n s i v e t h e o r y of h u m a n memory. The v a r i o u s d i f f e r e n t t h e o r e t i c a l p r o p o s i t i o n s o f f e r e d have in c o m m o n a d i s t i n c t i o n b e t w e e n long- and s h o r t - t e r m memory. Fundam e n t a l d i f f e r e n c e s a l r e a d y exist in the q u e s t i o n w h e t h e r shortand l o n g - t e r m m e m o r y p e r f o r m a n c e s are m e r e l y d i f f e r e n t p r o c e s s e s in one and the same s t o r a g e m e c h a n i s m ("dual-process system") or w h e t h e r they are b a s e d on s e p a r a t e s t o r a g e systems ( " d u a l - s t o r a g e system"). A q u e s t i o n of p a r t i c u l a r i m p o r t a n c e for the latter m o d e l seems to have not b e e n resolved: that is, how the s e q u e n c e of s t o r a g e p r o c e s s e s is to be conceived. In o t h e r words, w h a t f u n c t i o n a l r e l a t i o n s exist b e t w e e n the p o s t u l a t e d m e m o r y systems. E v e n the t h e o r y of i n f o r m a t i o n t r a n s f e r as c o n t a i n e d in such a c o m p r e h e n s i v e and d e t a i l e d t h e o r e t i c a l m o d e l of h u m a n m e m o r y as p r o p o s e d by A t k i n s o n et al. (Atkinson and Shiffrin, 1968, 1971; S h i f f r i n and A t k i n s o n , 1969) has b e e n c r i t i c i z e d on several occasions and, as a c o n s e q u e n c e , has b e e n m o d i f i e d by the a u t h o r s in i m p o r t a n t respects. The initial p r o p o s i t i o n of this t h e o r y pred i c t e d that all information, after b e i n g coded in a p e r i p h e r a l s e n s o r y r e g i s t e r (PSS), is i m m e d i a t e l y and e x c l u s i v e l y transf e r r e d into a s o - c a l l e d s h o r t - t e r m store (STS) and is o n l y t h e n c o p i e d into the l o n g - t e r m store (LTS). This c o n c e p t u a l i z a t i o n was then m o d i f i e d by a s s u m i n g t r a n s f e r of c o n t e n t s of PSS immed i a t e l y into the l o n g - t e r m s t o r a g e m e c h a n i s m as w e l l as into the STS (Atkinson, H e r r m a n n and Wescourt, 1973). T h a t the transfer of s t i m u l u s i n f o r m a t i o n into the LTS does not n e c e s s a r i l y h a v e to p r o c e e d t h r o u g h the STS is s u g g e s t e d by a series of experiments. Thus, for example, B r e l s f o r d and A t k i n s o n (1968) had to o b s e r v e that the type of r e h e a r s a l d i d indeed i n f l u e n c e short-term memory performance; however, there was no e f f e c t on l o n g - t e r m s t o r a g e of m e m o r i z e d m a t e r i a l . These r e s u l t s are supported by e x p e r i m e n t s by Reed (1970) and J a c o b y and Bartz (1972). C r a i k and W a t k i n s (1973) and S c h u l t e r (!973) showed that longt e r m r e t r i e v a l of a m e m o r y c o n t e n t is also i n d e p e n d e n t of the a m o u n t of time it was p r e s e n t in STS. In addition, S h a l l i c e and W a r r i n g t o n (1970) have shown that patients, w i t h intact s h o r t - t e r m memory, w h o a p p a r e n t l y w e r e u n a b l e to r e t a i n n e w inf o r m a t i o n on a l o n g - t e r m basis, w e r e n e v e r t h e l e s s able to a c q u i r e l o n g - l a s t i n g m e m o r y traces, a l t h o u g h o n l y under c e r t a i n l e a r n i n g conditions: a l t h o u g h p a t i e n t s w i t h such m e m o r y d i s t u r b a n c e s cannot r e t a i n l e a r n i n g m a t e r i a l by m e m o r i z a t i o n , i.e. by "internal r e p e t i t i o n " , they succeed w i t h r e p e a t e d e x t e r n a l p r e s e n t a t i o n of the m a t e r i a l . F u r t h e r m o r e their p e r f o r m a n c e a p p r o a c h e s that of n o r m a l s u b j e c t s w h o h a v e b e e n p r e v e n t e d from rehearsing. 24
The r e p o r t e d results of e x p e r i m e n t a l and c l i n i c a l r e s e a r c h suggest that c o r r e s p o n d i n g e x c i t a t i o n p r o c e s s e s are d i r e c t l y t r i g g e r e d in the LTS by external stimulation, that is w i t h o u t the m e d i a t i n g f u n c t i o n of the STS. Therefore, as M e l t o n (1963) assumed, it seems P O S s i b l e that every p e r c e p t i o n brings about structural, i.e. lasting, m e m o r y i m p r e s s i o n s even w i t h o u t the further p e r s i s t e n c e of c o n s o l i d a t i o n p r o c e s s e s that r e s u l t from active m e m o r i z a t i o n . As a c o n s e q u e n c e the p o s t u l a t e c o n c e r n i n g the t r a n s f e r of inform a t i o n f r o m PSS into STS is put into question. This p o s t u l a t e seems v e r y p l a u s i b l e i n t r o s p e c t i v e l y and is, p r o b a b l y for this reason, p r o p o s e d in all d u a l - s t o r a g e systems of human memory. The n e c e s s i t y of p o s t u l a t i n g such a f u n c t i o n a l r e l a t i o n s h i p between PSS and STS m a y be seen as superfluous, since an e x p l a n a t i o n of m e m o r y p h e n o m e n a o b s e r v e d in normal i n d i v i d u a l s as well as in p e r s o n s w i t h m e m o r y d i s t u r b a n c e s seems to be p o s s i b l e w i t h o u t this assumption. Moreover, it is n e c e s s a r y to ask how the t r a n s f e r of i n f o r m a t i o n into the STS is at all p o s s i b l e w i t h o u t the p a r t i c i p a t i o n of the l o n g - t e r m store; or in w h a t form those c o n t e n t s of s h o r t - t e r m m e m o r y w h i c h i m m e d i a t e l y come from the PSS are coded. Is this code e x c l u s i v e l y a r e p r e s e n t a t i o n of the p h y s i c a l m o d a l i t y of the s t i m u l u s m a t e r i a l (called "perceptual code" by A t k i n s o n et al., 1973)? Is the c o r r e s p o n d i n g e x c i t a t i o n p a t t e r n a c t i v a t e d in the LTS m e r e l y a c o n s e q u e n c e of this p e r c e p t u a l code w h i c h rep r e s e n t s the n e u r o p h y s i o l o g i c a l s u b s t r a t e of the "meaning" of a stimulus ("conceptual code"; A t k i n s o n et al., 1973) and transferred into the STS? The p r e s e n t e x p e r i m e n t was c o n c e i v e d on the basis of these considerations. It a t t e m p t e d to e x a m i n e e m p i r i c a l l y the a s s u m p t i o n that there is a f u n c t i o n a l r e l a t i o n s h i p b e t w e e n the PSS and the STS. This kind of e x a m i n a t i o n seems p o s s i b l e w h e n m e m o r y tasks are defined: I.
w h i c h deal e x c l u s i v e l y w i t h the STS, i.e. w h i c h a c c o r d i n g to the p r o p o s i t i o n s of the s o - c a l l e d d u a l - s t o r a g e theories can be m a n a g e d by the s h o r t - t e r m m e m o r y alone;
2.
in w h i c h it is p o s s i b l e that l o n g - t e r m i n f l u e n c e the c r i t e r i o n p e r f o r m a n c e ;
3.
which, however, m u s t be so c o n c e i v e d that, in o r d e r to m a n a g e the n e c e s s a r y p r o c e s s i n g of a g i v e n information, the o p t i m a l s o l u t i o n is a r r i v e d at by the i n v o l v e m e n t of the p o s t u l a t e d d i r e c t r e l a t i o n s h i p b e t w e e n the PSS and the STS.
In the c o n c r e t e e x p e r i m e n t a l s i t u a t i o n r e a l i z e d in the f o l l o w i n g way: ad I.:
memory
these
contents
conditions
were
The Ss' task c o n s i s t e d in stating w h e t h e r or not a p a r t i c ular c o n s o n a n t ("test item") was p r e s e n t in a c o n s o n a n t t r i g r a m ("positive set") w h i c h the Ss saw i m m e d i a t e l y bef o r e h a n d and w h i c h was, therefore, still in STS. 25
ad 2.:
The p o s s i b l i l i t y Of i n f l u e n c i n g the r e q u i r e d r e a c t i o n by c o n t e n t s in LTS e x i s t e d i n s o f a r as c e r t a i n s e q u e n c e s of letters, w h i c h h a d to be l e a r n e d in a f i r s t p h a s e of the e x p e r i m e n t w e r e p a r t i a l l y p r e s e n t in the t r i g r a m s u s e d as p o s i t i v e sets.
ad 3.:
The r e q u i r e d p o s i t i v e or n e g a t i v e d e c i s i o n h a d to be m a d e as q u i c k l y as p o s s i b l e by p r e s s i n g a p p r o p r i a t e r e s p o n s e b u t t o n s ; the Ss w e r e m o t i v a t e d to g i v e t h e i r b e s t indiv i d u a l p e r f o r m a n c e by the E's c o n t i n u o u s f e e d b a c k of t h e Ss' r e a c t i o n times.
T h e q u e s t i o n w a s n o w w h e t h e r , u n d e r the g i v e n c o n d i t i o n s , an i n f l u e n c e of the r e q u i r e d p e r f o r m a n c e s by l o n g - t e r m m e m o r y c o n t e n t s w o u l d be o b s e r v e d . If this is the case, t h e n the p o s t u l a t e conc e r n i n g t h e f u n c t i o n a l r e l a t i o n s h i p of b o t h s t o r a g e m e c h a n i s m s (PSS --~ STS) is q u e s t i o n a b l e and an a l t e r n a t i v e m o d e l m u s t be c o n s i d e r e d w h i c h e x p l a i n s t h e s e results, since, in the c o n c r e t e e x p e r i m e n t a l s i t u a t i o n , an o p t i m a l s o l u t i o n to the g i v e n t a s k s e e m s p o s s i b l e w i t h o u t the p a r t i c i p a t i o n of the LTS, i.e. by the p o s t u l a t e d 'direct' r e l a t i o n s h i p b e t w e e n PSS and STS.
METHOD
~
~
~
:
~
:
<~. ~
~~
Subjects The Ss w e r e 24 s t u d e n t s f r o m the p s y c h o l o g y d e p a r t m e n t of the U n i v e r s i t y of Graz. T h e y w e r e i n d i v i d u a l l y t e s t e d and c h o s e to p a r t i c i p a t e in this e x p e r i m e n t in p a r t i a l f u l f i l l m e n t of a c o u r s e requirement. Material T h e m a t e r i a l u s e d in the f i r s t p a r t of the e x p e r i m e n t ("learning phase") c o n s i s t e d of 7 d i f f e r e n t C C C - t r i g r ~ m s , in w h i c h 7 c o n s o n a n t s w e r e r a n d o m l y s e l e c t e d in s u c h a w a y t h a t e a c h two cons o n a n t s w e r e in the same o r d e r f r o m t r i g r a m to trigram. The f o l l o w i n g 7 t r i g r a m s ( d e s i g n a t e d as " l e a r n i n g - s e t s , ) w e r e used: NFS, FSL, SLX, LXR, XRH, R H N a n d HNF. In a s e c o n d e x p e r i m e n t a l p h a s e ("testing phase") the m a t e r i a l c o n s i s t e d in 18 C C C - t r i g r a m s ( d e s i g n a t e d as " s t i m u l u s se£s" a c c o r d i n g to the t e r m i n o l o g y of r e a c t i o n - t i m e e x p e r i m e n t s ) . T h e r e w e r e t h r e e g r o u p s of 6 w h i c h c o n t a i n e d e i t h e r two (Condit i o n 2), one ( C o n d i t i o n I) or n o n e (Condition O) of t h o s e cons o n a n t s u s e d in the f i r s t p a r t of the e x p e r i m e n t . The p o s i t i o n of e a c h c o n s o n a n t w i t h i n e a c h t r i g r a m w a s s y s t e m a t i c a l l y varied, a l t h o u g h the s e q u e n c e of c o n s o n a n t s , in C o n d i t i o n 2, r e m a i n e d the same. R e p e t i t i o n of s i n g l e l e t t e r s and d i g r a m s w a s avoided. In a d d i t i o n 18 3 - d i g i t n u m b e r s w e r e c o n s t r u c t e d f r o m the n u m b e r s I to 9 w i t h o u t r e p e t i t i o n and w e r e u s e d as p r a c t i c e m a t e r i a l for the r e a c t i o n t i m e task. 2G
Design and Procedure In the f i r s t p a r t of the e x p e r i m e n t the Ss w e r e i n d i v i d u a l l y s h o w n the l e a r n i n g sets on a m e m o r y d r u m (exposure time: 2 sec. per trigram). The Ss w e r e a s k e d to r e a d the g i v e n m a t e r i a l a l o u d i m m e d i a t e l y a f t e r its a p p e a r a n c e in the w i n d o w of the m e m o r y d r u m and to r e t a i n it as w e l l as p o s s i b l e . F o l l o w i n g this, l e a r n i n g w a s c o n t i n u o u s l y m o n i t o r e d by the a n t i c i p a t i o n m e t h o d by pres e n t i n g the f i r s t l e t t e r of a t r i g r a m and r e q u i r i n g S to p r o d u c e the r e m a i n i n g two. This w a s c o n t i n u e d u n t i l a c r i t e r i o n of 1OO% c o r r e c t w a s a c h i e v e d in e a c h of two c o n s e c u t i v e trials. Next, the Ss had to p e r f o r m a s i m p l e a d d i t i o n t a s k d u r i n g two p e r i o d s of two m i n u t e s each. A f t e r e a c h t w o - m i n u t e p e r i o d the Ss w e r e a g a i n t e s t e d by the a n t i c i p a t i o n m e t h o d in o r d e r to be sure t h a t the l e a r n i n g m a t e r i a l h a d r e a l l y b e e n r e t a i n e d in l o n g - t e r m memory. Next, the Ss w e r e i n s t r u c t e d that this p a r t of the task, w h i c h s e r v e d to m e a s u r e the i n d i v i d u a l l e a r n i n g p e r f o r m a n c e - w a s o v e r and t h a t now, i n d e p e n d e n t of this first part, t h e i r r e a c t i o n s p e e d w o u l d be tested. This s e c o n d part of the e x p e r i m e n t w a s c a r r i e d out in an a d j o i n i n g e x p e r i m e n t a l room. The Ss w e r e s h o w n all the 18 t r i g r a m s ("stimulus sets") in r a n d o m o r d e r on a slide projector. F o l l o w i n g the p r e s e n t a t i o n of e a c h t r i g r a m a s i n g l e c o n s o n a n t was p r o j e c t e d . The Ss' t a s k was to r e p o r t w h e t h e r or not the c o n s o n a n t s h o w n h a d b e e n p r e s e n t in the i m m e d i a t e l y p r e c e d i n g trigram. T h e r e q u i r e d d e c i s i o n was to be m a d e as q u i c k l y as p o s s i b l e by p r e s s i n g one of the two r e a c t i o n b u t t o n s for positive o r n e g a t i v e r e s p o n s e s . The p o s i t i o n of the b u t t o n s (left or right) w a s a l t e r n a t e d f r o m p e r s o n to person. T h e e x p e r i m e n t p r o c e e d e d i n d i v i d u a l l y in the f o l l o w i n g way: the p r o j e c t i o n of e a c h t r i g r a m (from the g r o u p of 18 s t i m u l u s sets) l a s t e d two seconds. A two second i n t e r v a l w i t h no p r e s e n t a t i o n f o l l o w e d w h i c h e n d e d by the p r e s e n t a t i o n of a tone (400 Hz, approx. 40 db, d u r a t i o n : I sec.). Immediately a f t e r the c e s s a t i o n of the tone a t e s t item, i.e. a s i n g l e c o n s o n a n t , was p r o j e c ted by m e a n s of a n e l e c t r o n i c a l l y t i m e d t a c h i s t o s c o p e (Compurelectronic-m CN-1533). S i m u l t a n e o u s l y w i t h the o n s e t of p r o j e c t i o n an e l e c t r o n i c timer was started, w h i c h w a s s t o p p e d w h e n S p r e s s e d the r e a c t i o n button. T h e r e s u l t i n g r e a c t i o n times w e r e a u t o m a t i c a l l y r e g i s t e r e d a f t e r each trial b y the t i m e r p r i n t o u t (Kienzle D i g i t a l d r u c k e r D 44). S i n c e 18 d i f f e r e n t t r i g r a m s w e r e u s e d as s t i m u l u s sets, 18 p o s i t i v e (single c o n s o n a n t p r e s e n t in the trigram) and 18 n e g a t i v e (single c o n s o n a n t not p r e s e n t in the trigram) test items w e r e c o n s t r u c t e d w i t h r e s p e c t to the 7 l e a r n i n g sets in the f o l l o w i n g manner:
27
C o n d i t i o n O: N o n e of the 7 c o n s o n a n t s w h i c h w e r e u s e d in the c o n s t r u c t i o n of the l e a r n i n g sets w a s p r e s e n t in the 6 s t i m u l u s sets w h i c h c o m p r i s e d this c o n d i t i o n . The 6 p o s i t i v e t e s t items c o n s i s t e d of one c o n s o n a n t each. Each single consonant was also p r e s e n t in one of the 6 s t i m u l u s sets in first, s e c o n d o r t h i r d p o s i t i o n ; the 6 n e g a t i v e t e s t items w e r e c o n s o n a n t s w h i c h h a d n e v e r b e e n u s e d in the e x p e r i m e n t . Example: S t i m u l u s set: B Z G P o s i t i v e test item: Z N e g a t i v e test item: W C o n d i t i o n I: In the 6 s t i m u l u s sets in this c o n d i t i o n o n e of t h o s e c o n s o n a n t s p r e s e n t h a d b e e n u s e d in the c o n s t r u c t i o n of the l e a r n i n g sets (this c o n s o n a n t w i l l be d e n o t e d as the " c r i t i c a l " letter). T h e s e c o n s o n a n t s c o m p r i s e d the 6 p o s i t i v e t e s t items. T h o s e c o n s o n a n t s w h i c h i m m e d i a t e l y p r e c e d e d the c r i t i c a l l e t t e r in the c o r r e s p o n d i n g l e a r n i n g set w e r e u s e d as n e g a t i v e t e s t stimuli. T h e n e g a t i v e test s t i m u l i w e r e s u p p o s e d l y in s t r o n g a s s o c i a tive c o n n e c t i o n w i t h the r e s p e c t i v e c r i t i c a l l e t t e r s b e c a u s e of the Ss' p r e v i o u s e x p e r i e n c e w i t h t h e m in the l e a r n i n g trials. Example: S t i m u l u s set: CJF P o s i t i v e t e s t item: F N e g a t i v e t e s t item: N HNF and N F S w e r e l e a r n i n g sets in w h i c h N p r e c e d e d l e t t e r (F, u n d e r l i n e d in the s t i m u l u s set).
the c r i t i c a l
C o n d i t i o n 2: The 6 s t i m u l u s sets c o n t a i n e d two c r i t i c a l c o n s o n a n t s e a c h w h i c h w e r e in the same s e q u e n c e they w e r e in d u r i n g the f i r s t l e a r n i n g trial. O n e c o n s o n a n t in e a c h c r i t i c a l c o n s o n a n t p a i r w a s s e l e c t e d r a n d o m l y as a p o s i t i v e t e s t s t i m u l u s . The 6 n e g a t i v e test items c o n s i s t e d of t h o s e c o n s o n a n t s w h i c h p r e c e d e d the two c r i t i c a l l e t t e r s in the l e a r n i n g set. Example: S t i m u l u s set: L_XXC P o s i t i v e t e s t item: L N e g a t i v e t e s t item: S The l e a r n i n g set in w h i c h S p r e c e d e s (LX, u n d e r l i n e d in the s t i m u l u s set)
the two c r i t i c a l w a s SLX.
letters
T h e r e f o r e , a t o t a l of 6 x 3 x 2 t e s t t r i a l s (6 s t i m u l u s sets in e a c h of 3 c o n d i t i o n s for p o s i t i v e and n e g a t i v e t e s t items) r e s u l t e d , w h i c h w e r e p r e s e n t e d to e a c h i n d i v i d u a l S. The sequence of t e s t t r i a l s w a s r a n d o m l y d e t e r m i n e d . The time i n t e r v a l b e t w e e n t r i a l s was 5 sec. B e f o r e s t a r t i n ~ the a c t u a l e x p e r i m e n t a ! p h a s e two p r a c t i c e s e s s i o n s (each c o n s i s t i n g of 18 trials) w e r e c a r r i e d out. As m e n t i o n e d earlier, the m a t e r i a l c o n s t r u c t e d for this p u r p o s e c o n s i s t e d of 18 3 - d i g i t numbers, w h i c h w e r e p r e s e n t e d as s t i m u l u s sets t h r e e times p e r s e s s i o n in r a n d o m order, and the n u m b e r s 1 t h r o u g h 9 as t e s t items. O t h e r w i s e , the p r o c e d u r e of this t r a i n i n g p h a s e w a s i d e n t i c a l w i t h the a c t u a l t e s t i n g phase. T h e g o a l of this t r a i n i n g p h a s e was, on the o n e hand, to f a m i l 28
i a r i z e the Ss w i t h the e x p e r i m e n t a l situation, i.e. the r e a c t i o n t i m e task, and on the o t h e r hand, to s t i m u l a t e t h e m to m a x i m a l i n d i v i d u a l p e r f o r m a n c e , which, in light of the r e q u i r e m e n t s form u l a t e d in P o i n t 3 of the i n t r o d u c t i o n , seems to be of s p e c i a l importance. In o r d e r to b r i n g a b o u t the d e s i r e d i n c r e a s e in p e r f o r m a n c e m o t i v a t i o n the m e d i a n of the r e a c t i o n times of all the c o r r e c t r e s p o n s e s o b t a i n e d from each S to p o s i t i v e and n e g a tive s t i m u l i d u r i n g the p r a c t i c e s e s s i o n w a s c a l c u l a t e d . This m e d i a n s e r v e d as the i n d i v i d u a l p e r f o r m a n c e limit for the f o l l o w ing s e c o n d p r a c t i c e session. B e f o r e b e g i n n i n g the s e c o n d p r a c t i c e p h a s e the Ss w e r e i n f o r m e d that t h e i r f u t u r e p e r f o r m a n c e s w o u l d o n l y then be "valid" w h e n they w e r e u n d e r a c e r t a i n time limit w h i c h was c a l c u l a t e d on the b a s i s of t h e i r p e r f o r m a n c e in the f i r s t p r a c t i c e phase. If, d u r i n g this s e c o n d p r a c t i c e session, r e a c t i o n times w e r e o b s e r v e d w h i c h w e r e a b o v e the median, £he E i m m e d i a t e l y i n f o r m e d the S and stated that this p a r t i c u l a r res p o n s e d i d n ' t count. In the a c t u a l e x p e r i m e n t a l p h a s e the E p r o v i d e d no m o r e p e r f o r m a n c e feedback, a l t h o u g h the Ss w e r e i n s t r u c t e d to react as q u i c k l y as p o s s i b l e , since n o w t h e i r r e a c t i o n speed w a s a c t u a l l y m e a s u r e d and p e r f o r m a n c e s a b o v e a c e r t a i n time limit w o u l d similarly be "invalid", i.e. w o u l d d i s p r o p o r t i o n a t e l y r e d u c e t h e i r total p e r f o r m a n c e . T h e e x p e r i m e n t w a s c o n c l u d e d by p r e s e n t i n g the Ss w i t h a q u e s t i o n n a i r e c o n c e r n i n g l e a r n i n g s t r a t e g i e s i.e. n u m b e r and type of m n e m o n i c d e v i c e s w h i c h they u s e d d u r i n g the m e m o r i z a t i o n of the l e a r n i n g sets in the first e x p e r i m e n t a l phase. RESULTS First, a m e a n r e a c t i o n time for all c o r r e c t d e c i s i o n s was d e t e r m i n e d for each S, w i t h s e p a r a t e m e a n s for each e x p e r i m e n t a l cond i t i o n and p o s i t i v e or n e g a t i v e response. The few e x t r e m e l y long r e a c t i o n times (more than I sec.) o b s e r v e d w e r e omitted. The further t r e a t m e n t of the i n d i v i d u a l m e a n s w a s c a r r i e d out by a n a l y s i s of v a r i a n c e (l-factorial d e s i g n for r e p e a t e d m e a s u r e s ) , s e p a r a t e d a c c o r d i n g to r e s p o n s e class (positive or n e g a t i v e ) . The corres p o n d i n g t o t a l c o m p o s i t e m e a n s (N = 24) are p r e s e n t e d in T a b l e I.
W h i l e no s i g n i f i c a n t d i f f e r e n c e s in m e a n r e a c t i o n times w e r e o b s e r v e d b e t w e e n the t h r e e e x p e r i m e n t a l c o n d i t i o n s for p o s i t i v e r e s p o n s e s (F < I), t h e s e d i f f e r e n c e s w e r e v e r y s i g n i f i c a n t for n e g a t i v e r e s p o n s e s (F = 6,11; df I = 2, df 2 = 46; P < O,O1). T h e r e is a s t a t i s t i c a l l y s i g n i f i c a n t i n c r e a s e in m e a n r e a c t i o n t i m e in C o n d i t i o n I (t = 3,4; df = 46) as w e l l as in C o n d i t i o n 2 (t = 2,4; df = 46) c o m p a r e d w i t h C o n t r o l C o n d i t i o n O.
29
Table i. Mean latency (msec.) of positive and negative responses, according to experimental condition Type of response required
Experimental Condition (Number of consonants in learning sets, which were present in the stimulus set) 0 I 2
Positive Negative
542 545
556 6O2
L
J
547 585
~significant mean differences (p < 0,O1; t-test for related samples) for each of the response classes across experimental conditions are marked by connecting lines. B o t h C o n d i t i o n s I and 2 are c h a r a c t e r i z e d b y the fact that the r e s p e c t i v e s t i m u l u s sets c o n t a i n e d 'critical' letters, i.e. l e t t e r s also p r e s e n t in the l e a r n i n g sets, and the t e s t i t e m c o n s i s t e d in o n e c o n s o n a n t , which, a l t h o u g h not p r e s e n t in the c o r r e s p o n d i n g s t i m u l u s set, p r e c e d e d the c r i t i c a l letter(s) in the l e a r n i n g set. S i n c e the Ss h a d to m e m o r i z e the l e a r n i n g sets to a I O O % - c r i t e r i o n in the f i r s t e x p e r i m e n t a l p h a s e and a l s o r e p r o d u c e the m a t e r i a l two and f o u r m i n u t e s a f t e r c o m p l e t i n g the l e a r n i n g a c t i v i t y , it m a y be a s s u m e d t h a t the l e a r n i n g sets w e r e w e l l e s t a b l i s h e d in the Ss' l o n g - t e r m store. That implies that between the single c o n s o n a n t s s t r o n g and s u p p o s e d l y d i r e c t e d a s s o c i a t i o n s (the d i r e c t i o n w a s d e t e r m i n e d by the s p e c i a l c o n s t r u c t i o n of the l e a r n i n g sets) w e r e b u i l t up w i t h r e s p e c t to t h e i r s e q u e n c e in the t r i g r a m s . A c c o r d i n g to the a s s u m p t i o n s of d u a l - s t o r a g e t h e o r i e s of m e m o r y concerning functional relationships between storage mechanisms it can be e x p e c t e d that, in s o l v i n g the r e q u i r e d r e a c t i o n t i m e t a s k t h e s h o r t - t e r m m e m o r y is e x c l u s i v e l y involved. M o r e s p e c i f i cally, the o p t i m a l s o l u t i o n s t r a t e g y in the c o n c r e t e e x p e r i m e n t a l s i t u a t i o n , i.e. u n d e r e x t r e m e p r e s s u r e to r e a c t as q u i c k l y as p o s s i b l e , m a y be r e p r e s e n t e d in the f o l l o w i n g p r o c e s s i n g s e q u e n c e : presented
test
peripheral
item
sensory
store
short-term store ( c o m p a r i s o n of test i t e m w i t h c o n s o n a n t s in the s t i m u l u s set) positive
or n e g a t i v e
decision.
B e c a u s e o f this, c o n t e n t s the c o u r s e of i n f o r m a t i o n 3O
of the LTS s h o u l d processing.
h a v e no i n f l u e n c e o n
If, o n t h e c o n t r a r y , l o n g - t e r m m e m o r y d o e s p a r t i c i p a t e in t h e p r o c e s s i n g of i n f o r m a t i o n b y t h e a s s o c i a t i o n b e t w e e n t e s t i t e m and "critical" letter(s) (which w a s b u i l t u p d u r i n g t h e l e a r n i n g t r i a l s a n d e s t a b l i s h e d in t h e L T S ) , in t h e c a s e of n e g a t i v e d e c i s i o n s (test i t e m w a s n o t p r e s e n t in t h e s t i m u l u s set, b u t w a s s t r o n g l y a s s o c i a t e d w i t h s i n g l e c o n s o n a n t s of the s t i m u l u s set) a r e a c t i o n t e n d e n c y i n t e r f e r i n g w i t h t h e c o r r e c t r e s p o n s e (pressi n g t h e ' n e g a t i v e ' b u t t o n ) is to be e x p e c t e d , w h i c h is e x p r e s s e d b y a d e l a y of r e a c t i o n t i m e s . T h e r e s u l t s r e p o r t e d in T a b l e I c l e a r l y s u p p o r t t h e l a t t e r p r o position: even under experimental conditions which, on the theor e t i c a l b a s i s of a d u a l - s t o r a g e m o d e l as w a s c o n c e i v e d b y A t k i n s o n et al. (1973), p r i n c i p a l l y s e e m to p e r m i t t h e s o l u t i o n of t h e g i v e n t a s k w i t h t h e e x c l u s i v e p a r t i c i p a t i o n of s h o r t - t e r m m e m o r y , t h e c o n t e n t s of t h e L T S h a v e b e e n o b s e r v e d to i n f l u e n c e s e a r c h o p e r a t i o n s w i t h i n t h e STS. T h i s f a c t is s u p p o r t e d b y a f u r t h e r r e s u l t : it c o n c e r n s a p a r t i a l i n f l u e n c e of the i n d i v i d u a l s t r a t e g i e s u s e d to m e m o r i z e the l e a r n i n g s e t in t h e f i r s t p h a s e of the experiment. O n t h e b a s i s of t h e q u e s t i o n n a i r e w h i c h w a s i s s u e d a f t e r t h e c o m p l e t i o n of t h e e x p e r i m e n t a l p h a s e s c o n c e r n i n g t h e n u m b e r a n d t y p e of p o s s i b l y u s e d m n e m o n i c d e v i c e s , a t o t a l of ~ 12~S was ~elected wh~ had~used'Such &n~id during~the~acq~i~ition of o n e of t h e t r i g r a m s (e.g. t h e p r o p e r n a m e 'Rhein' for t h e trigram RHN etc.). T h e m e a n r e a c t i o n t i m e s w h i c h w e r e o b s e r v e d in t h i s g r o u p of Ss w e r e c o m p a r e d w i t h e a c h o t h e r a c c o r d i n g to t h e t y p e of m e m o r i z a t i o n in t h e l e a r n i n g p h a s e ( l e a r n i n g set l e a r n e d w i t h or w i t h o u t a m n e m o n i c aid). T h i s f u r t h e r s t a t i s t i c a l a n a l y s i s is l i m i t e d to t h e n e g a t i v e d e c i s i o n s in C o n d i t i o n 2 (2 c o n s o n a n t s of a l e a r n i n g s e t w e r e p r e s e n t in the c o r r e s p o n d i n g s t i m u l u s set), s i n c e o n l y in t h i s c a s e a c l e a r p a i r i n g of c o r r e s p o n d i n g l e a r n i n g and stimulus sets was possible. I T w o m e a n r e a c t i o n t i m e s (for t r i g r a m s l e a r n e d w i t h or w i t h o u t a m n e m o n i c aid) w e r e c a l c u l a t e d for e a c h S a n d t e s t e d for s i g n i f i c a n t d i f f e r e n c e s a c r o s s all t w e l v e Ss ( t - t e s t for r e l a t e d s a m p l e s ) .
iThis may be clarified by an example: one of the consonants was repeatedly used in the learning set, for instance, "N" in the trigrams RHN; HNF; NFS° If the stimulus set now contained only one critical letter (Condition i), then this letter was present in the three given learning sets; for example, one was memorized with a m n e m o n i c device, another was not etc. In Condition 2 the pairing is similarily ambiguous in the case of positive responces: if the positive test item was, for instance, "R", the stimulus set "DXR", then the combination of X and R was found in the learning set LXR as well as in XRH. 31
On the a v e r a g e the r e a c t i o n t i m e in C o n d i t i o n 2 for n e g a t i v e d e c i s i o n s w h i c h c o n c e r n e d l e a r n i n g sets m e m o r i z e d w i t h the h e l p of m n e m o n i c aids w a s 544 msec.; for t h o s e l e a r n e d w i t h o u t m n e m o n i c aids the m e a n r e a c t i o n t i m e w a s 589 msec. T h i s d i f f e r e n c e in the m e a n s is s t a t i s t i c a l l y s i g n i f i c a n t (t = 2,38, df = 11; p < 0,05). T h i s r e s u l t can be seen as f u r t h e r e v i d e n c e that the m e m o r y contents of the LTS h a v e i n f l u e n c e d the r e q u i r e d s e a r c h and d e c i s i o n p r o c e s s e s of the STS: it m a y be a s s u m e d that the a s s o c i a t i o n s bet w e e n the e l e m e n t s in a trigram, i.e. between single consonants, w e r e m o r e s t r o n g l y e s t a b l i s h e d in the LTS w i t h o u t the u s e of a m n e m o n i c d e v i c e d u r i n g the l e a r n i n g p r o c e d u r e and t h e r e f o r e , i n f l u ences i n t e r f e r i n g w i t h c o r r e c t r e a c t i o n c o u l d be m o r e e f f e c t i v e . D e l a y in r e a c t i o n time m a y be d u e to t h e s e i n t e r f e r i n g i n f l u e n c e s which, however, do not r e s u l t in an i n c r e a s e in i n c o r r e c t responses. A l t h o u g h the f r e q u e n c y of e r r o r s is too low to p e r f o r m s t a t i s t i c a l c o m p a r i s o n s (the m e a n v a l u s of 2,16 for p o s i t i v e and 1,13 for n e g a t i v e d e c i s i o n s account, r e s p e c t i v e l y , for 12,0 a n d 6,3% of all o b t a i n e d r e s p o n s e s ) , the n u m b e r of errors, for example, for C o n d i t i o n O and 2 w a s e q u a l for n e g a t i v e d e c i s i o n s (the m e a n v a l u e in b o t h cases w a s 0,33, w h i c h a c c o u n t e d for 5,5% of all obtained responses).
DISCUSSION T h e o v e r w h e l m i n g m a j o r i t y of t h e o r e t i c a l p r o p o s i t i o n s of h u m a n m e m o r y is b a ~ e d o n the a s s u m p t i o n t h a t two s e p a r a t e s t o r a g e m e c h a n i s m s are i n v o l v e d in s h o r t - and l o n g - t e r m m e m o r y p r o c e s s e s . The m o d e l p r e s e n t e d in s i m p l i f i e d f o r m in Fig. I d e s c r i b e s the f u n c t i o n a l s e q u e n c e of i n f o r m a t i o n p r o c e s s i n g in h u m a n m e m o r y as it w a s c o n c e i v e d in the t h e o r e t i c a l c o n c e p t p r o p o s e d by A t k i n s o n and others. In the l a t e s t m o d i f i c a t i o n of the m o d e l (Atkinson et al., 1973), it is p o s t u l a t e d that t r a n s f e r of i n f o r m a t i o n f r o m the PSS into the LTS ( d e s i g n a t e d a in Fig. I) w i t h o u t the p a r t i c i p a t i o n of the STS a l s o takes place. The o r i g i n a l a n d i n t r o s p e c t i v e l y v e r y p l a u s i b l e a s s u m p t i o n of a conn e c t i o n of PSS m STS m L T S r e m a i n s u n a f f e c t e d by this m o d i f i c a t i o n a n d is f u r t h e r e n d o r s e d by the authors. a) External Stimulation '
Peripheral sensory store (PSS)
I Short-term store (STS)
> -~
Long-term store (LTS)
b)
[ eoc ion moc onis s I. Fig. i. Graphical representation of the essential aspects of dual-storage models of human memory 32
As was a l r e a d y m e n t i o n e d there are some d a t a w h i c h suggest the e x i s t e n c e of such a f u n c t i o n a l r e l a t i o n b e t w e e n PSS and LTS. These data w e r e p r o d u c e d by e x p e r i m e n t s w h i c h showed that, under c e r t a i n e x p e r i m e n t a l conditions, l o n g - t e r m m e m o r y p e r f o r m a n c e is not determ i n e d by p r o c e s s e s in s h o r t - t e r m m e m o r y and w h i c h support the assumption that p r i n c i p a l l y all i n f o r m a t i o n can be t r a n s f e r r e d into the LTS w i t h o u t the p a r t i c i p a t i o n of the STS. B e c a u s e of this, the f u n c t i o n o r i g i n a l l y a s c r i b e d to s h o r t - t e r m m e m o r y - an i n t e r m e d i a t e storage s y s t e m r e s p o n s i b l e for the t r a n s f e r of i n c o m i n g i n f o r m a t i o n into l o n g - t e r m m e m o r y - is s e r i o u s l y doubted. Therefore, the pos£ u l a t e d c o n n e c t i o n of P S S - - - ~ S T S (designated b in Fig. I) is put into question. S c h u l t e r (1974) has p r o p o s e d a m o d e l w h i c h does not include this a s s u m p t i o n but opens up new p o s s i b i l i t i e s of interp r e t i n g results of e x p e r i m e n t a l and c l i n i c a l m e m o r y r e s e a r c h w h i c h cannot be r e c o n c i l e d w i t h e x i s t i n g t h e o r e t i c a l p r o p o s i t i o n s . This m o d e l is p r e s e n t e d in Fig. 2. The i n t e n t i o n of the e x p e r i m e n t r e p o r t e d was to find e m p i r i c a l d a t a s u g g e s t i n g that the p o s t u l a t e d f u n c t i o n a l r e l a t i o n b e t w e e n PSS and STS, as p r o p o s e d by A t k i n s o n et al. (1973) and all o t h e r p r o p o n e n t s o f a d u a l - s t o r a g e s y s t e m of human memory, does not exist. Moreover, it a t t e m p t e d to show that all i n f o r m a t i o n e n t e r i n g f r o m the sensory organs, e v e n w h e n it is r e t a i n e d o n l y b r i e f l y (i.e. can be r e t r i e v e d o n l y d u r i n g a brief p e r i o d of time), leads to the d e v e l o p m e n t of l o n g - l a s t i n g m e m o r y traces as w e l l as to the r e a c t i v a t i o n of contents w h i c h a l r e a d y exist in LTS (contents c o r r e s p o n d i n g to as well as a s s o c i a t e d w i t h the coded information) b e f o r e this i n f o r m a t i o n enters the STS. One i m p l i c a t i o n of this a s s u m p t i o n is that l o n g - t e r m m e m o r y m u s t a l s o i n f l u e n c e a task s i t u a t i o n w h o s e mastery, a c c o r d i n g to the d u a l - s t o r a g e m o d e l s (Fig.l), should be p o s s i b l e by means of the e x c l u s i v e p a r t i c i p a t i o n of STS and, therefore, should show no such
Rehearsal pr
External Stimulation-------~
PSS separated according to sensory organ (visual, acoustical ...)
/ "--~
ocess
Control - and !iilration unit lwith limited capacity
I
Reaction mechanisms
Fig. 2. Graphical representation of the model suggested by Schulter (1974) in the form of a flow chart. The arrows indicate the sequence of information processing and indicate the postulated functional relationships in the 33 memory system
i n f l u e n c e by the LTS. The r e s u l t s o b t a i n e d under the e x p e r i m e n t a l c o n d i t i o n s d e s c r i b e d in this r e p o r t c l e a r l y d e m o n s t r a t e the effects of LTS on p r o c e s s e s o c c u r r i n g in the STS. Nevertheless, the p r e s e n t study c a n n o t be v i e w e d as a c r u c i a l e x p e r i m e n t conc e r n i n g the e x i s t e n c e of a f u n c t i o n a l r e l a t i o n s h i p b e t w e e n PSS and STS. In the p r e s e n t a u t h o r ' s opinion, p l a n n i n g such an exp e r i m e n t is d i f f i c u l t if not i m p o s s i b l e since the d u a l - s t o r a g e m o d e l p r o p o s e d by A t k i n s o n et al. (1973), as far as the f u n c t i o n al i n t e r c o n n e c t i o n s of the storage s u b s y s t e m s are concerned, is so g e n e r a l l y o u t l i n e d that s u p p o s e d l y any r e s u l t w h i c h c o n c e r n s the s e q u e n c e of i n f o r m a t i o n p r o c e s s i n g can be e x p l a i n e d by it. Even the r e s u l t s o b t a i n e d in the p r e s e n t study c o u l d in p r i n c i p l e be r e c o n c i l e d w i t h the A t k i n s o n t h e o r y which, however, w o u l d r e q u i r e additional assumptions. B e f o r e d i s c u s s i n g these a s s u m p t i o n s it seems n e c e s s a r y to deal w i t h some p o s s i b l e r e p r e s e n t a t i o n s of i n f o r m a t i o n in the m e m o r y s y s t e m as p r o p o s e d by A t k i n s o n et al. (1973). The authors dist i n g u i s h the p e r c e p t u a l code, r e p r e s e n t e d by the p h y s i c a l c h a r a c t e r i s t i c s of stimuli, from the c o n c e p t u a l code, w h i c h c o n s i s t s of the v a r i o u s c h a r a c t e r i s t i c s of the m e a n i n g of the stimuli. The c o n c e p t u a l code r e p r e s e n t s the a t t r i b u t e s of a stimulus e s t a b lished in the l o n g - t e r m store. This c o n c e p t i o n of c o d i n g p r o c e s s e s implies that the t r a n s f e r of i n f o r m a t i o n f r o m the PSS into the STS is solely b a s e d on the c o d i n g of the p h y s i c a l c h a r a c t e r i s t i c s of the stimulus. If hhe m a s t e r i n g of the r e a c t i o n time task used in the p r e s e n t study took p l a c e on this level of coding, i.e. by a c o m p a r i s o n of p e r c e p t u a l codes w i t h i n the STS (which in p r i n c i p l e seems to be possible), then the o b s e r v e d i n f l u e n c e of l o n g - t e r m m e m o r y c o n t e n t s on r e a c t i o n times c a n n o t be explained. If, on the o t h e r hand, the r e q u i r e d d e c i s i o n was m a d e on the basis of c o n c e p t u a l codes, then the e x p l a n a t i o n of the r e p o r t e d r e s u l t s m a k e s additional p r o p o s i t i o n s n e c e s s a r y w h e n seen w i t h i n the f r a m e w o r k of the m o d e l s u g g e s t e d by A t k i n s o n et al. (1973). These assumptions w o u l d have to concern, for example, the s i g n i f i c a n c e and f u n c t i o n of the p e r c e p t u a l code in STS; the type of coding, on w h i c h the r e q u i r e d s e a r c h and d e c i s i o n p r o c e s s e s are b a s e d ; t h e time c h a r a c t e r i s t i c s under w h i c h i n f o r m a t i o n is t r a n s f e r r e d f r o m one s t o r a g e s y s t e m into another; the r e l a t i o n of p r o c e s s e s in the STS a n d c o r r e s p o n d i n g c o n s c i o u s processes. If a p a r t i c u l a r c o n t e n t in the STS is seen as i d e n t i c a l to the m o m e n t a r y state of c o n s c i o u s n e s s of a p e r s o n (as A t k i n s o n and o t h e r s assume) then, w i t h r e s p e c t to the p e r c e p t i o n of a word, for example, this p e r c e p t i o n s h o u l d first of all c o m p r i s e just the image of the word, i.e. l e t t e r forms and size, t y p e s t y l e , etc., and o n l y t h e n s h o u l d the a p p r o p r i a t e m e a n i n g enter c o n s c i o u s n e s s , w i t h a c e r t a i n l a t e n c y w h i c h should be p e r c e p t i b l e by the individual. This seems not to be the case on the basis of i n t r o s p e c t i v e experience. On 34
t h e c o n t r a r y , as m a n y r e s u l t s of e x p e r i m e n t a l r e s e a r c h d e m o n s t r a t e , i n f l u e n c e s - s o m e t i m e s r a t h e r s t r o n g - of e x p e r i e n c e a n d s t a t e of m o t i v a t i o n o n t h e p e r c e p t i o n of v a r i o u s k i n d of s t i m u l i h a v e been observed. H o w e v e r , if t h e i n t e r p r e t a t i o n of t h e r e s u l t s o b t a i n e d in t h e p r e s e n t s t u d y is b a s e d on t h e m o d e l s h o w n in Fig. 2, t h e n t h i s i n t e r p r e t a t i o n is p o s s i b l e w i t h o u t f u r t h e r assumptions. A f t e r t h e p r e s e n t a t i o n of a s t i m u l u s , an i n i t i a l p e r c e p t u a l c o d i n g of t h i s s t i m u l u s o c c u r s . The coded information is t h e n t r a n s f e r r e d f r o m t h e P S S to t h e L T S and, b y r e a c t i v a t i o n of t h e m e m o r y t r a c e s w h i c h a r e a s s o c i a t e d w i t h it, t r a n s f o r m e d i n t o a c o m p l e x e x c i t a t i o n p a t t e r n , w h i c h r e p r e s e n t s the t o t a l information available concerning the stimulus. This specific c o n s t e l l a t i o n of e x c i t a t i o n s n o w c a u s e s c o n s o l i d a t i o n a c t i v i t y in t h e L T S a n d s i m u l t a n e o u s l y , a c o p y of t h i s e x c i t a t i o n p a t t e r n is c o n v e y e d to t h e STS a n d r e p r e s e n t s t h e b a s i s of t h e c o n t e n t s of c o n s c i o u s n e s s as w e l l as t h a t of s e a r c h o p e r a t i o n s . The s t i m u l u s i n f o r m a t i o n is t h u s t r a n s f o r m e d i n t o a c o n c e p t u a l c o d e w h i c h is o n l y t h e n i d e n t i c a l to t h e p e r c e p t u a l c o d e w h e n t h e r e h a s b e e n no p r e v i o u s e x p e r i e n c e w i t h r e s p e c t to t h e s t i m u l u s situation. If, h o w e v e r , s u c h p r i o r e x p e r i e n c e h a s o c c u r r e d (as w a s t h e c a s e in t h e g i v e n e x p e r i m e n t a l s i t u a t i o n by t h e m e m o , r i z a t i o n of the l e a r n i n g sets), t h e n t h e m e m o r y t r a c e s a l r e a d y e x i s t i n g in L T S a r e c o d e d a l o n g w i t h r e l a t e d i n c o m i n g s t i m u l i in t h e c o u r s e of i n f o r m a t i o n p r o c e s s i n g , p r o d u c i n g i n t e r f e r e n c e s b e tween the excitation patterns underlying the search and decision processes, T h e o b s e r v e d i n c r e a s e d r e a c t i o n t i m e s a r e to be i n t e r p r e t e d to be a r e s u l t of s u c h i n t e r f e r e n c e s .
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