Elizabeth F. Loftus. University of Washington. Introduction. If I were to ask the average English-speaking adult to name an animal, or a yellow fruit, or a flower ...
SEMANTIC MEMORY R E T R I E V A L : SOME DATA AND A MODEL E l i z a b e t h F. Loftus U n i v e r s i t y of W a s h i n g t o n Introduction If I w e r e to a s k the a v e r a g e E n g l i s h - s p e a k i n g adult to n a m e an a n i m a l , o r a yellow f r u i t , o r a flower beginning with the l e t t e r " D " , he would o r d i n a r i l y be able to give m e a c o r r e c t a n s w e r in l e s s t h a n a few s e c o n d s .
P r o d u c i n g a piece of i n f o r m a t i o n t h a t one h a s
l e a r n e d s o m e t i m e ago and knows v e r y well r e q u i r e s v e r y l i t t l e e f f o r t indeed. we do i t ?
But, how do
By what p r o c e s s do we r e a c h into the huge s t o r e of i n f o r m a t i o n in m e m o r y and
produce a r e s p o n s e t h a t i s a p p r o p r i a t e to a given q u e s t i o n .
T h e r e i s no doubt t h a t we a r e
v e r y good a t doing t h i s , but at the m o m e n t we know r e l a t i v e l y l i t t l e about how we do it. Although it is too e a r l y to p r o v i d e d e t a i l s of the r e t r i e v a l m e c h a n i s m , we c a n m a k e c e r t a i n g e n e r a l d i s t i n c t i o n s a m o n g p o s s i b l e types of p r o c e s s e s .
F o r e x a m p l e , we can c l a s -
sify p r o c e s s e s of m e m o r y - a c c e s s in t e r m s of the e x t e n t to w h i c h they involve s u c c e s s i v e a s opposed to s i m u l t a n e o u s c o n s u l t i n g of the m e m o r y s t o r e .
This basic distinction has many
i m p o r t a n t c o n s e q u e n c e s : one of t h e m c o n c e r n s the effect of s i z e of the a r r a y to be s e a r c h e d on s e a r c h i n g t i m e .
To the e x t e n t t h a t the r e t r i e v a l p r o c e s s i n v o l v e s s u c c e s s i v e c o n s u l t a t i o n
of the m e m o r y s t o r e , r e t r i e v a l t i m e should be a function of the m e m b e r of i t e m s in the a r r a y to be s e a r c h e d .
C o n v e r s e l y , to the e x t e n t t h a t s i m u l t a n e o u s c o n s u l t a t i o n ( o r " p a r a l l e l
p r o c e s s i n g " ) i s involved, r e t r i e v a l t i m e should be r e l a t i v e l y unaffected by the n u m b e r of i t e m s in the a r r a y . Previous Research In m o s t of the e a r l i e r r e s e a r c h dealing with the e f f e c t of a r r a y o r c a t e g o r y size on r e t r i e v a l t i m e , s u b j e c t s have been given a r e c o g n i t i o n o r i d e n t i f i c a t i o n t a s k .
Typically they
m u s t decide w h e t h e r a g i v e n i n s t a n c e i s a m e m b e r of a p a r t i c u l a r a r r a y , c l a s s o r c a t e g o r y . Most of t h i s w o r k h a s d e a l t with r e l a t i v e l y s m a l l , newly l e a r n e d c a t e g o r i e s t h a t a r e t y p i c a l l y defined s o l e l y by an e n u m e r a t i o n of i n s t a n c e s (e. g . , N e i s s e r , 1963; P o l l a c k , 1963; R a b b i t t , 1959; S t e r n b e r g , 1966).
F o r e x a m p l e , S t e r n b e r g ( 1 9 6 6 ) gave s u b j e c t s a g r o u p of d i g i t s (e. g . ,
4, 8, 3, 5) and a s k e d t h e m w h e t h e r a n o t h e r digit (e. g . , 3) was a m e m b e r of t h a t set.
This
r e s e a r c h on " s h o r t - t e r m m e m o r y " h a s g e n e r a l l y found r e s p o n s e t i m e for b o t h p o s i t i v e a n d n e g a t i v e i n s t a n c e s to be a d i r e c t function of the size of the c a t e g o r y .
This result has been
i n t e r p r e t e d a s e v i d e n c e for the e x i s t e n c e of a s u c c e s s i v e and p e r h a p s e v e n e x h a u s t i v e s c a n ning process for retrieval from short-term memory. W h a t happens when l a r g e r and b e t t e r - l e a r n e d c a t e g o r i e s a r e u s e d ?
For example,
suppose we a s k a s u b j e c t to decide w h e t h e r a "dog" i s a n " a n i m a l " ? L a n d a u e r and F r e e d m a n
42
(1963) found that s u b j e c t s took l o n g e r to decide that an i t e m was not a m e m b e r of a l a r g e c a t e g o r y than to decide that it was not a m e m b e r of a s m a l l c a t e g o r y .
F o r e x a m p l e , it took
l o n g e r to decide that a " d e s k " was not an " a n i m a l " than to decide that it was not a "dog". T h e r e was a slight, but n o n s i g n i f i c a n t , d i f f e r e n c e in d e c i s i o n t i m e s for the p o s i t i v e i n s t a n c e s . Collins and Quillian (1969) and M e y e r (1970), using s o m e w h a t d i f f e r e n t p r o c e d u r e s , a l s o r e p o r t that r e t r i e v a l t a k e s l o n g e r for l a r g e r c a t e g o r i e s . Although L a n d a u e r and F r e e d m a n , Collins and Quillian~ and M e y e r all find an e f f e c t of c a t e g o r y s i z e , the e f f e c t is v e r y s m a l l r e l a t i v e to the s i z e of the c a t e g o r i e s u s e d .
For
e x a m p l e , L a n d a u e r and F r e e d m a n r e p o r t that the c o r r e c t identification of n e g a t i v e i n s t a n c e s took 53 m s e c . l o n g e r for l a r g e than f o r s m a l l c a t e g o r i e s .
arrays to be searched,
in order for such small differences to be caused
time it takes to scan the larger categories, mously
Given the r e l a t i v e s i z e of the
rapid, on the order of 1,000 words
the successive
by the additional
scanning would have to be enor-
per sec., which seems
improbable.
The authors
accordingly conclude that the small differences should probably not be interpreted as evidence for the existence of a successive scanning process. some
Thus,
effect of category size on retrieval from semantic
been interpreted in terms of successive processing. small that they seem processing of some
to argue
for a mechanism
previous research
memory,
has sho~a
but it has generally not
On the contrary,
the differences are so
consisting largely if not entirely of parallel
sort.
The Original Experiment In 1969 I conducted an experiment Freedman
at Stanford University.
on this problem
in collaboration with Jonathan
Since subsequent experiments
have used a semilar meth-
odology, and have in general been designed to test a model of retrieval that we proposed the publication growing out of that research
(Freedman
to describe the original experiment
detail.
The experiment mechanism
was designed to provide more
with particular emphasis
sing is involved.
in some
to decide whether
memory
information about the retrieval
One major departure from previous work is that rather than study identifi-
ject could actually produce a word himself,
it is simple,
1971), it is appropriate
on the question of the extent to which successive proces-
cation time as had been done before, this experiment
duce a member
and Loftus,
in
it was a member
concerned
the speed with which a sub-
Instead of giving him a stimulus and asking him
of a category,
of it. The identification procedure
he was given a category and asked to prohas been used in the past largely because
convenient and yet obviously involves the retrieval of information from the
store.
The production procedure
is more
complicated
and less convenient because
|n a sense it involves a higher level of retrieval--the individual must not only reach into the store and find information relating to a stimulus,
he must actually produce an item from that
43 store.
D e s p i t e its d i f f i c u l t i e s , the use of t h i s p r o c e d u r e s e e m e d to be j u s t i f i e d b e c a u s e it is
an i m p o r t a n t f o r m of r e t r i e v a l a n d p r o v i d e s additional i n f o r m a t i o n about the r e t r i e v a l p r o c e s s . The b a s i c p r o c e d u r e was to p r e s e n t the s u b j e c t with a s t i m u l u s c o n s i s t i n g of a noun c a t e g o r y p a i r e d with e i t h e r a l e t t e r o r an a d j e c t i v e , and a s k h i m to p r o v i d e a w o r d t h a t b e longed in the o v e r l a p defined by the p a i r .
F o r e x a m p l e , s u b j e c t s who w e r e p r e s e n t e d with
the p a i r " f r u i t - P " m i g h t s a y " p e a c h " , " p e a r " , o r " p l u m " , a m o n g o t h e r p o s s i b i l i t i e s .
A
c o r r e c t r e s p o n s e would be any word b e g i n n i n g w i t h " P " t h a t n a m e s a kind of fruit. R e s p o n s e s s u c h a s " a p p l e " o r "pony" would be i n c o r r e c t . As d e s c r i b e d above, the m a i n focus of the study was on the e x t e n t to w h i c h the r e t r i e v a l m e c h a n i s m involved s u c c e s s i v e scanning.
The effect of size of the a r r a y to be
s e a r c h e d on r e t r i e v a l t i m e was an i n d i c a t i o n of the p r e s e n c e o r a b s e n c e of s u c c e s s i v e p r o c e s sing.
The e f f e c t of a r r a y size w a s i n v e s t i g a t e d by s e l e c t i n g m a n y noun c a t e g o r i e s t h a t r a n g e d
in s i z e f r o m v e r y s m a l l (e. g . , s e a s o n s , gems) to e x t r e m e l y l a r g e (words, f i r s t n a m e s ) . A n o t h e r c o n s e q u e n c e of s u c c e s s i v e p r o c e s s i n g c o n c e r n s the effect of the a r r a y defined by the o v e r l a p of the noun c a t e g o r y with the a d j e c t i v e or l e t t e r r e s t r i c t o r , o r e q u i v a l e n t l y , the n u m b e r of p o s s i b l e c o r r e c t r e s p o n s e s .
The s i z e of the o v e r l a p v a r i e d f r o m a m i n i m u m
of one ( " a n i m a l - Z " , with " z e b r a " b e i n g the only c o r r e c t r e s p o n s e in m o s t p e o p l e ' s m e m o r y s t o r e ) to v e r y l a r g e ( " f i r s t n a m e - J " , with dozens of n a m e s being p o s s i b l e r e s p o n s e s ) .
To
the e x t e n t t h a t s u c c e s s i v e s c a n n i n g plays a r o l e in r e t r i e v a l , it s e e m s l i k e l y t h a t the l a r g e r the n u m b e r of p o s s i b l e r e s p o n s e s , the s o o n e r a s u b j e c t will find and p r o d u c e one. The study thus p r o v i d e s two ways of a s s e s s i n g the e x t e n t to w h i c h s u c c e s s i v e s c a n n i n g o c c u r s in the r e t r i e v a l p r o c e s s : the effect of s i z e of the c a t e g o r y on r e a c t i o n t i m e a n d the e f f e c t of o v e r l a p of the c a t e g o r y a n d m o d i f i e r on r e a c t i o n t i m e . Method F o r t y s u b j e c t s w e r e individually told t h a t we w e r e conducting a study of how m e m o r y worked, t h a t they would s e e i t e m s c o n s i s t i n g of c a t e g o r i e s and e i t h e r a d j e c t i v e s o r l e t t e r s , and t h a t they should r e s p o n d with a w o r d that was an a p p r o p r i a t e m e m b e r of the c a t e g o r y . They w e r e given e x a m p l e s , and told to r e s p o n d a s quickly a s p o s s i b l e , but to avoid e r r o r s . D u r i n g the e x p e r i m e n t , the s u b j e c t s a t in f r o n t of a s c r e e n in w h i c h w a s a window c o v e r e d by h a l f - s i l v e r e d g l a s s .
An index c a r d c o n t a i n i n g the s t i m u l u s w a s p l a c e d in a d a r k
e n c l o s u r e behind the m i r r o r and was p r e s e n t e d by i l l u m i n a t i n g the e n c l o s u r e .
A microphone
was p l a c e d in f r o n t of the s u b j e c t a n d he r e s p o n d e d by s p e a k i n g into it. A t r i a l c o n s i s t e d of the following.
As a c a r d with t h e i t e m p r i n t e d in l a r g e type was
p l a c e d in the d a r k e n e d e n c l o s u r e behind t h e h a l f - s i l v e r e d m i r r o r , t h e e x p e r i m e n t e r s a i d " R e a d y " , a n d p r e s s e d a button t h a t i l l u m i n a t e d the f i r s t m e m b e r of the s t i m u l u s p a i r .
After
a n i n t e r v a l of a t l e a s t . 5 s e c . , the second m e m b e r of the s t i m u l u s p a i r w a s a u t o m a t i c a l l y
44 illuminated, and s i m u l t a n e o u s l y an e l e c t r i c t i m e r with a DC clutch was s t a r t e d .
The s u b -
j e c t ' s v e r b a l r e s p o n s e a c t i v a t e d a voice key that stopped the clock and t e r m i n a t e d the t r i a l . E a c h s u b j e c t r e c e i v e d a r a n d o m s e q u e n c e of 96 s t i m u l i with the c a t e g o r y p r e c e d i n g the r e s t r i c t e r on half the t r i a l s and following it on the o t h e r half. Results The two r e s u l t s that b e a r on the s u c c e s s i v e s c a n n i n g i s s u e a s a s follows. 1) T h e r e was a n o n s i g n i f i c a n t c o r r e l a t i o n of -. 22 between c a t e g o r y s i z e and r e a c t i o n t i m e . Thus, c o n t r a r y to e x p e c t a t i o n s f r o m a s u c c e s s i v e scanning model, the amount of t i m e to r e t r i e v e a w o r d f r o m a l a r g e c a t e g o r y i s not g r e a t e r than for a s m a l l c a t e g o r y - - r a t h e r t h e r e is little r e l a t i o n s h i p b e t w e e n s i z e and l a t e n c y and what t h e r e is i n d i c a t e s that l a r g e r c a t e g o r i e s take l e s s t i m e than s m a l l c a t e g o r i e s . 2) T h e r e was a n o n s i g n i f i c a n t c o r r e l a t i o n of . 02 b e t w e e n the n u m b e r of p o s s i b l e c o r r e c t r e s p o n s e s and r e a c t i o n time~ a l s o c o n t r a r y to e x p e c t a t i o n s f r o m a s u c c e s s i v e s c a n n i n g model. Although size of c a t e g o r y and o v e r l a p do not affect r e a c t i o n t i m e , o t h e r v a r i a b l e s do. 1) R e c a l l t h a t e a c h s t i m u l u s c o n s i s t e d of a noun and e i t h e r a l e t t e r o r an a d j e c t i v e ; and that the noun c a m e e i t h e r f i r s t o r s e c o n d . R e a c t i o n t i m e was significantly f a s t e r when the noun c a m e f i r s t r a t h e r than s e c o n d (1.87 vs. 2.12 s e c . ) .
R e a c t i o n t i m e w a s a l s o significantly f a s -
t e r when the s t i m u l u s included an adjective r a t h e r than a l e t t e r ( 1 . 8 4 v s . 2.15 s e c . ) . 2) A s e c o n d v a r i a b l e involves the f r e q u e n c y in E n g l i s h of the p o s s i b l e c o r r e c t r e s p o n s e s . Specifically the f r e q u e n c y in E n g l i s h of the one c o r r e c t r e s p o n s e that had the h i g h e s t such f r e quency w a s r e l a t e d to r e a c t i o n t i m e . have f a s t e r r e a c t i o n t i m e s .
Stimuli that have h i g h e r f r e q u e n c y r e s p o n s e s tend to
This finding i s a f u r t h e r d e m o n s t r a t i o n of the f r e q u e n c y - r e a c t i o n
t i m e r e l a t i o n s h i p found by M a r b e quite long ago (Thumb and M a r b e , 1901; c i t e d in Woodworth and S c h l o s b e r g , 1954). 3) A n o t h e r i m p o r t a n t v a r i a b l e involves the likelihood that a p a r t i c u l a r r e s p o n s e will be given when s u b j e c t s a r e a s k e d to n a m e w o r d s that fit a p a r t i c u l a r c a t e g o r y . n a n c e " of a r e s p o n s e within a c a t e g o r y .
We call this the " d o m i -
R a t h e r than the f r e q u e n c y in the E n g l i s h language in
g e n e r a l , " d o m i n a n c e " r e f e r s to the f r e q u e n c y with which a w o r d i s given a s an e x a m p l e of a category.
I n f o r m a t i o n on dominance was obtained f r o m Battig and Montague (1969).
c l e a r that high dominance p r o d u c e s f a s t e r r e a c t i o n t i m e s .
It is
Within the " f r u i t " category~ for
e x a m p l e , "apple" i s m o r e d o m i n a n t than " l e m o n " ; thus t h e r e i s a t e n d e n c y to r e s p o n d to " f r u i t - A " m o r e quickly than to f r u i t - L " . Discussion The m a j o r focus of this study was the question of w h e t h e r the p r o c e s s of r e t r i e v a l f r o m s e m a n t i c m e m o r y involved s u c c e s s i v e scanning to any a p p r e c i a b l e e x t e n t .
To the d e g r e e that
45 s u c c e s s i v e s c a n n i n g of i t e m s in the m e m o r y s t o r e o c c u r s , r e a c t i o n t i m e should be l o n g e r when m o r e i t e m s have to be s c a n n e d .
When a s u b j e c t is a s k e d to p r o d u c e an i t e m f r o m an
a r r a y o r c a t e g o r y , the l a r g e r the c a t e g o r y , the l o n g e r the r e a c t i o n t i m e should be.
T h u s , if
r e a c t i o n t i m e s a r e l o n g e r f o r l a r g e r c a t e g o r i e s , it s u g g e s t s t h a t s u c c e s s i v e s c a n n i n g i s o c c u r r i n g ; if r e a c t i o n t i m e s a r e not l o n g e r for l a r g e r c a t e g o r i e s , i t s u g g e s t s t h a t s u c c e s s i v e s c a n n i n g i s not o c c u r r i n g .
The p r e s e n t study did not find a p o s i t i v e r e l a t i o n s h i p between
c a t e g o r y s i z e and r e a c t i o n t i m e .
F u r t h e r m o r e , to the e x t e n t t h a t s u c c e s s i v e s c a n n i n g plays
a r o l e in r e t r i e v a l , r e a c t i o n t i m e should b e s h o r t e r when t h e r e a r e a l a r g e n u m b e r of p o s s i b l e c o r r e c t r e s p o n s e s (the m o r e c o r r e c t r e s p o n s e s , the e a s i e r it should be to find one). The p r e s e n t study did not find a n e g a t i v e r e l a t i o n s h i p b e t w e e n the n u m b e r of p o s s i b l e e o r r e e t r e s p o n s e s and r e a c t i o n t i m e .
T h u s , all of the e v i d e n c e i n d i c a t e s t h a t the p r o c e s s of r e t r i e v a l
i n v o l v e s l i t t l e o r no s u c c e s s i v e s c a n n i n g of the m e m o r y s t o r e . We m i g h t m e n t i o n a t t h i s point t h a t the i t e m s b e i n g r e t r i e v e d w e r e e x t r e m e l y w e l l learned.
It m a y well be t h a t with r e l a t i v e l y o b s c u r e i t e m s , o r with e a s y i t e m s t h a t for s o m e
reason are
not found quickly, a s u b j e c t e v e n t u a l l y r e s o r t s to s u c c e s s i v e s c a n n i n g .
However,
it a p p e a r s t h a t with t h e s e o v e r l y - l e a r n e d i t e m s , the n o r m a l , s u c c e s s f u l p r o c e s s of r e t r i e v a l does not involve s u e e e s s i v e s c a n n i n g of the m e m o r y s t o r e . A R e t r i e v a l Model If the r e t r i e v a l p r o c e s s d o e s not involve s u c c e s s i v e s c a n n i n g , of w h a t does it c o n s i s t ? One m o d e l t h a t a p p e a r s to fit m u c h of the data i n v o l v e s a h i e r a r c h i c a l o r g a n i z a t i o n , b y w h i c h we m e a n a s y s t e m t h a t is divided into a n u m b e r of i n t e r c o n n e c t e d s u b s y s t e m s , e a c h of the latter being hierarchical itself.
Specifically, o u r b a s i c conception i s t h a t of a m e m o r y o r g a n -
ized into a c o m p l e x h i e r a r c h y c o m p o s e d of c a t e g o r i e s (e. g . , a n i m a l s ) with s u b s e t s of e a c h (e. g . , b i r d s , dogs) and s u p e r s e t s (e. g . , l i v i n g things).
The s e a r e h p r o c e s s n e e d not b e g i n
a t the top and w o r k down until the a p p r o p r i a t e s u b s e t is found ( a s s u g g e s t e d , for e x a m p l e , by G r e e n , e t a l . , 1963 a n d L i n d s a y , 1963). can be e n t e r e d d i r e c t l y .
R a t h e r , e a c h c a t e g o r y h e a d s i t s own h i e r a r c h y t h a t
T h u s , to find a b i r d the c a t e g o r y " b i r d s " i s e n t e r e d ; to find a n a n i -
m a l , the c a t e g o r y " a n i m a l s " i s e n t e r e d ; and so on. In o r d e r to explain the l a c k of e f f e c t of c a t e g o r y s i z e , additional a s s u m p t i o n s a r e necessary.
Within e a c h c a t e g o r y it s e e m s l i k e l y t h a t a v a r i e t y of s u b s e t s e x i s t .
Some a r e
noun c a t e g o r i e s t h a t a r e s p e c i a l i z e d m e m b e r s of the l a r g e r s e t (e. g . , b i r d s and dogs a r e s u b s e t s of a n i m a l s ) . b e r of r e a s o n s .
Some a r e c l u s t e r s of w o r d s t h a t a r e highly a s s o c i a t e d for any of a n u m -
T h e y m a y have q u a l i t i e s in c o m m o n (e. g . , a l l begin with the l e t t e r " S " o r
all have long n a m e s o r all r h y m e ) .
They m a y be a s s o c i a t e d with e a c h o t h e r in the i n d i v i d u a l ' s
e x p e r i e n c e (e. g . , all be a n i m a l s in the P o o h books).
These clusters are probably more
i d i o s y n c r a t i c than the m a i n , noun c a t e g o r i e s , but a r e s o m e w h a t c o n s i s t e n t a c r o s s i n d i v i d u a l s .
46 And finally, u n d e r e a c h c a t e g o r y i s an u n d i f f e r e n t i a t e d e n u m e r a t i o n of e x e m p l a r s .
Within all
s u b s e t s , c l u s t e r s and the e n u m e r a t i o n , the i n s t a n c e s will be l i s t e d in a m o r e o r l e s s c o n s t a n t o r d e r , a c c o r d i n g to t h e i r f r e q u e n c y in the language o r d o m i n a n c e in the c a t e g o r y . U s i n g t h i s as a g e n e r a l m o d e l , we c a n begin to d e s c r i b e how a p e r s o n m a n a g e s the t a s k t h a t he h a s b e e n g i v e n i n t h e a b o v e e x p e r i m e n t . ginning with the l e t t e r " P " .
He m u s t , f o r e x a m p l e , find a f r u i t b e -
It s e e m s r e a s o n a b l e to a s s u m e t h a t the p r o c e s s of r e t r i e v a l h a s
a t l e a s t two m a j o r s t e p s : 1) e n t e r i n g an a p p r o p r i a t e c a t e g o r y - - " f r u i t s " ; and 2) finding an a p p r o p r i a t e m e m b e r of t h a t e a t e g o r y - - " p e a c h " (plus, of c o u r s e , the t i m e r e q u i r e d to p r o duce the r e s p o n s e v e r b a l l y ) .
T h e s e two s t e p s m a y e a c h be divided into s u b s t e p s , but for the
m o m e n t we have no i n f o r m a t i o n on t h a t . It c a n be s e e n t h a t nothing in the model would i m p l y t h a t r e t r i e v M would take l o n g e r for l a r g e r c a t e g o r i e s .
Step 1 i s a s s u m e d to be equally e a s y for l a r g e and s m a l l c a t e g o r i e s ,
s i n c e the p a r t i c u l a r c a t e g o r y is e n t e r e d d i r e c t l y . step 2 need not be affected by c a t e g o r y s i z e . the c a t e g o r y that fits the r e s t r i c t i o n i m p o s e d .
S i m i l a r l y , but s o m e w h a t l e s s obviously,
The c r u c i a l p r o b l e m is finding an i n s t a n c e of Once the c a t e g o r y is e n t e r e d , the next s t e p
( p r e s u m a b l y a substep) is to find an a p p r o p r i a t e c l u s t e r of i t e m s .
U n d e r f r u i t , a c l u s t e r of
" f r u i t s b e g i n n i n g with P " e x i s t s , is e n t e r e d , and the f i r s t e n t r y is r e a d out.
If i n s t e a d the
t a s k w e r e to find a g e m whose c o l o r was g r e e n , the s m a l l e r s e t " g e m s " would be e n t e r e d d i r e c t l y , the s u b s e t " g r e e n g e m s " found a n d the f i r s t e n t r y r e a d out, a huge s e t with a huge s u b s e t , the s a m e p r o c e s s i s r e p e a t e d .
And to find " N o u n - Y " ,
In all c a s e s , it c o n s i s t s of
finding a m a i n s e t and a s u b s e t , and does not involve s e a r c h i n g t h r o u g h au a r r a y of i n s t a n c e s . T h i s m o d e l of the r e t r i e v a l p r o c e s s a c c o u n t s f o r the l a c k of effect of c a t e g o r y s i z e , and, it s e e m s to us, is quite p l a u s i b l e . c l u s t e r s exist.
It s e e m s unlikely t h a t e v e r y c a t e g o r y c o n t a i n s s e p a r a t e c l u s t e r s for e a c h
l e t t e r and a d j e c t i v e . clusters.
The one i m p l a u s i b i l i t y i s the notion t h a t so m a n y
However, t h e r e a r e two a r g u m e n t s in f a v o r of the e x i s t e n c e of s u c h
F i r s t , when a s u b j e c t i s a s k e d to n a m e s e v e r a l f r u i t s b e g i n n i n g with a p a r t i c u l a r
l e t t e r , he h a s l i t t l e difficulty in p r o d u c i n g m a n y c o r r e c t r e s p o n s e s , v e r y r a p i d l y (if, in fact, m a n y c o m m o n r e s p o n s e s exist). p a u s e and then say " p l u m " .
T h a t is, he does not s a y " p e a c h " , p a u s e and then say " p e a r "
The typical p a t t e r n we have found in i n f o r m a l t e s t i n g i s a s p u r t
of s e v e r a l r e s p o n s e s , p e r h a p s followed by a p a u s e and then s e v e r a l m o r e r e s p o n s e s , etc. This s u g g e s t s t h a t t h e s e w o r d s a r e c l u s t e r e d in s o m e s o r t of functional r e l a t i o n s h i p .
The
s e c o n d a r g u m e n t in f a v o r of t h e e x i s t e n c e of c l u s t e r s is t h a t when m u l t i d i m e n s i o n a l s c a l i n g and c l u s t e r i n g p r o c e d u r e s a r e applied to c a t e g o r y r e t r i e v a l data, c e r t a i n c a t e g o r y m e m b e r s t h a t have q u a l i t i e s in c o m m o n tend to c l u s t e r t o g e t h e r (Shepard, 1972). In t h i s model, we have m a d e the a s s u m p t i o n t h a t the m e m o r y s t o r e is o r g a n i z e d p r i m a r i l y into noun c a t e g o r i e s .
It a l m o s t c e r t a i n l y i n c l u d e s g r o u p s of i t e m s t h a t have q u a l i -
47 t i e s in c o m m o n (e. g . , w a r m , r e d , e t e . ) and mac- e v e n have g r o u p s that have initial l e t t e r s in c o m m o n (e. g . , all w o r d s s t a r t i n g with P).
In fact, we can handle the fact that r e t r i e v a l
t i m e is f a s t e r when a noun is p a i r e d with an adjective r a t h e r than a l e t t e r by postulating that the main c l u s t e r s a r e i t e m s that have q u a l i t i e s in c o m m o n and within t h e s e c l u s t e r s a r e groupings of i t e m s that have initial l e t t e r s in c o m m o n .
The m a j o r , useful o r g a n i z a t i o n ,
h o w e v e r , is thought to be in t e r m s of noun g r o u p i n g s .
The significance of t h i s a s s u m p t i o n
i s that the f i r s t s t e p of the r e t r i e v a l p r o c e s s would c o n s i s t of locating and e n t e r i n g the a p p r o p r i a t e noun c a t e g o r y .
The p r e s e n t e x p e r i m e n t p r o v i d e s s o m e data that a r e c o n s i s t e n t with
this model and that provide an e s t i m a t e of the duration of the f i r s t s t e p in the p r o c e s s . E a c h s t i m u l u s p a i r was p r e s e n t e d with the noun e i t h e r f i r s t o r s e c o n d . When the noun c o m e s s e c o n d , the total r e t r i e v a l p r o c e s s begins only a f t e r its p r e s e n t a t i o n . When the noun c o m e s f i r s t , s t e p 1 can be begun b e f o r e the s e c o n d half of the p a i r , any d i f f e r e n c e due to o r d e r can be a s s u m e d to be c a u s e d by that p a r t of the p r o c e s s that i s c o m p l e t e d b e f o r e the s e c o n d half i s shown.
Thus, the d i f f e r e n c e b e t w e e n noun f i r s t and noun s e c o n d i s an i n d i c a -
tion of the e x i s t e n c e of s t e p 1 and of its duration. When nouns a r e p r e s e n t e d f i r s t , the m e a n r e a c t i o n t i m e is 1.87 s e c . , with noun second it i s 2.12 s e c . ditions.
T h i s d i f f e r e n c e of . 25 i s quite stable a c r o s s s o m e w h a t d i f f e r e n t c o n -
With n o u n - l e t t e r p a i r s , it i s . 27 s e c . ; with n o u n - a d j e c t i v e p a i r s it i s . 23 s e c .
T h e s e data s u p p o r t the idea that step 1 c o n s i s t s of e n t e r i n g the noun c a t e g o r y , and s u g g e s t that the duration of s t e p 1 is a p p r o x i m a t e l y . 25 s e c . f o r the p r o c e d u r e e m p l o y e d h e r e . To s u m m a r i z e , we have p r e s e n t e d a h i e r a r c h i c a l s t o r a g e m o d e l , and have p r o p o s e d that the r e t r i e v a l p r o c e s s f r o m s e m a n t i c m e m o r y c o n s i s t s of two d i s t i n c t s t e p s ( e n t e r i n g the a p p r o p r i a t e c a t e g o r y and then finding an a p p r o p r i a t e
m e m b e r of that c a t e g o r y ) .
This g e n e r -
al model is c o n s i s t e n t with the lack of r e l a t i o n s h i p b e t w e e n c a t e g o r y s i z e and r e t r i e v a l t i m e , and is given s o m e s u p p o r t by the d i f f e r e n c e in r e a c t i o n t i m e s when the noun is p r e s e n t e d f i r s t and second.
That d i f f e r e n c e o f . 25 s e c . a l s o s e r v e s a s an indication of the d u r a t i o n of s t e p
1 of the r e t r i e v a l p r o c e s s . E x p e r i m e n t a l Support for the Model Now let me p r e s e n t s o m e e v i d e n c e supporting t h r e e d i f f e r e n t a s p e c t s of the model. 1) The s e m a n t i c m e m o r y s t o r e i s o r g a n i z e d p r i m a r i l y into noun c a t e g o r i e s . The a s s u m p t i o n that the m a j o r o r g a n i z a t i o n i s in t e r m s of noun c a t e g o r i e s h a s s e v e r a l important implications.
One o b s e r v a b l e c o n s e q u e n c e c o n c e r n s the n u m b e r of w o r d s that a
s u b j e c t can produce in a given amount of t i m e u n d e r v a r i o u s c o n d i t i o n s . If we p r e s e n t a noun c a t e g o r y and give a s u b j e c t , say, one minute to w r i t e down any i t e m s that belong in the c a t e gory, he should be able to produce m o r e i t e m s than if we p r e s e n t him with an adjective and ask him to w r i t e any i t e m s w h i c h have the i n h e r e n t quality of that a d j e c t i v e .
A c c o r d i n g to the
48 model~ when a s u b j e c t i s p r e s e n t e d with a noun c a t e g o r y , he e n t e r s that c a t e g o r y in his s e m a n t i c m e m o r y and begins to n a m e m e m b e r s of the c a t e g o r y that a r e s t o r e d t h e r e .
When
he s e e s an a d j e c t i v e , h o w e v e r , he m u s t s t i l l e n t e r the m e m o r y s t o r e at s o m e noun c a t e g o r y , w h e r e u p o n he can n a m e m e m b e r s of that c a t e g o r y which have the i n h e r e n t quality of the p r e s e n t e d a d j e c t i v e . When he has n a m e s a s many m e m b e r s a s he can, he m u s t shift to a n o t h e r c a t e g o r y and begin to n a m e i t e m s f r o m it.
Thus, when p r e s e n t e d with an a d j e c t i v e f e w e r
i t e m s should be p r o d u c e d for two r e a s o n s : (a) The s u b j e c t m u s t decide which c a t e g o r y to e n t e r f i r s t , and this d e c i s i o n takes t i m e , and (b) he m u s t shift f r o m one c a t e g o r y to a n o t h e r w h e n e v e r he n e e d s to, and shifting takes t i m e An e x p e r i m e n t w a s d e s i g n e d to d e t e r m i n e w h e t h e r the n u m b e r of r e s p o n s e s given to a noun i s d i f f e r e n t f r o m the n u m b e r of r e s p c a s e s given to an a d j e c t i v e .
Two hundred s t u d e n t s
w e r e told that they would s e e s t i m u l i c o n s i s t i n g of e i t h e r a noun o r an a d j e c t i v e .
If the s t i m -
ulus w e r e a noun c a t e g o r y , they w e r e to w r i t e down a s many i t e m s a s they could that b e longed to that c a t e g o r y ,
F o r e x a m p l e , s u b j e c t s who w e r e p r e s e n t e d with the s t i m u l u s " s e a -
food" might say " o y s t e r ~', " c l a m " , and " s h r i m p " , a m o n g o t h e r p o s s i b i l i t i e s . If the s t i m u l u s w e r e an a d j e c t i v e , the s u b j e c t was to w r i t e down a s many i t e m s a s he could that had the i n h e r e n t quality of the a d j e c t i v e .
F o r e x a m p l e , if the s t i m u l u s w e r e " h a r d " , the s u b j e c t m i g h t
say " b r i c k " , ~'roek", " w o o d ' , e t c .
Details about the p r o c e d u r e can be found in Loftus (1972).
The m e a n n u m b e r of r e s p o n s e s given in one minute to noun s t i m u l i w a s 12.03 and to adjective s t i m u l i it w a s 9.15.
M o r e d e t a i l e d a n a l y s e s of the r e s p o n s e p r o t o c o l s indicated
that when the s t i m u l u s w a s a noun, a l m o s t all the r e s p o n s e s w e r e i n s t a n c e s of that noun c a t e gory.
However, when the s t i m u l u s was an a d j e c t i v e , s u b j e c t s tended to n a m e a n u m b e r of
i t e m s f r o m one c a t e g o r y , shift to a n o t h e r c a t e g o r y and n a m e a n u m b e r of i t e m s f r o m that c a t e g o r y , shift again, and sG on.
One s u b j e c t ' s r e s p o n s e p r o t o c o l to the s t i m u l u s " s m a l l "
i l l u s t r a t e s this tendency: " r a t , m o u s e , c a n a r y , p a r a k e e t , toe, f i n g e r , eye, e a r " . j e c t , i t can be s e e n , n a m e d two a n i m a l s , two b i r d s , and four p a r t s of the body.
This s u b -
These re-
stilts a r e c o n s i s t e n t with a m o d e l that d e s c r i b e s m e m o r y a s being o r g a n i z e d p r i m a r i l y into noun c a t e g o r i e s .
Only a f t e r a s u b j e c t has e n t e r e d a noun c a t e g o r y d o e s he find c l u s t e r s of
i t e m s that have qualities in c o m m o n .
In o t h e r w o r d s , a f t e r c o m p l e t i n g the f i r s t s t e p of the
r e t r i e v a l p r o c e s s {category e n t r y ) , the s u b j e c t may find a c l u s t e r of i n s t a n c e s to which a given adjective a p p l i e s . The second piece of evidence in s u p p o r t of the a s s u m p t i o n that the m e m o r y s t o r e is o r g a n i z e d p r i m a r i l y into noun c a t e g o r i e s g r e w out of a c o n v e r s a t i o n with Allan Collins at a 1971 m e e t i n g of the E a s t e r n V e r b a l I n v e s t i g a t o r ' s League.
We w e r e d i s c u s s i n g the finding
that r e a c t i o n t i m e is significantly f a s t e r when a noun c a t e g o r y c o m e s b e f o r e the a d j e c t i v e o r letter restrietor.
This finding is s o m e w h a t s u r p r i s i n g in view of the fact that E n g l i s h language
49 h a b i t s f a v o r an a d j e c t i v e - n o u n o r d e r .
We talk about a "yellow b i r d " but n e v e r a " b i r d yellow".
The q u e s t i o n a r i s e s a s to w h e t h e r t h e r e a r e s p e c i a l a d j e c t i v e s s u c h t h a t r e a c t i o n t i m e in a production t a s k would be f a s t e r if the a d j e c t i v e p r e c e d e d the noun.
P e r h a p s if we could find
a d j e c t i v e s t h a t w e r e m o r e c l o s e l y r e l a t e d to p a r t i c u l a r i n s t a n c e s than w e r e the s u p e r o r d i n a t e s of t h o s e i n s t a n c e s , a r e v e r s a l would o c c u r .
F o r e x a m p l e , if " s o u r " i s m o r e c l o s e l y
r e l a t e d to " l e m o n " than i s " f r u i t " , then p e r h a p s p r e s e n t i n g " s o u r " f i r s t and " f r u i t " s e c o n d would r e s u l t in a f a s t e r " l e m o n " . We u s e d the Kent and R o s a n o f f (1910) n o r m s a s one c o u r s e of a d j e c t i v e s . n o r m s a r e the a s s o c i a t i o n s of 1000 s u b j e c t s to 100 f a m i l i a r E n g l i s h w o r d s .
These
In the Kent and
R o s a n o f f n o r m s , the listing of r e s p o n s e s to " s o u r " i n d i c a t e s t h a t " l e m o n " o r " l e m o n s " i s the second most common response.
The only w o r d g i v e n m o r e often i s " s w e e t " .
In the B a t t i g
and Montague (1969) n o r m s , h o w e v e r , the r e s p o n s e s to " f r u i t " i n d i c a t e t h a t " l e m o n " is the ninth most common response. " l e m o n " than i s " f r u i t " .
T h u s , in s o m e s e n s e , " s o u r " i s m o r e c l o s e l y r e l a t e d to
Even in c a s e s s u c h a s t h e s e , h o w e v e r , r e a c t i o n t i m e is s h o r t e r
when the noun i s p r e s e n t e d f i r s t .
The r e t r i e v a l model p r o p o s e d a c c o u n t s for t h i s fact by
a s s u m i n g t h a t m e m o r y i s o r g a n i z e d p r i m a r i l y into a c o m p l e x h i e r a r c h y of noun c a t e g o r i e s and t h a t the f i r s t step of the r e t r i e v a l p r o c e s s is to e n t e r one of t h e s e noun c a t e g o r i e s . 2. E a c h c a t e g o r y in the h i e r a r c h i c a l o r g a n i z a t i o n c a n be e n t e r e d d i r e c t l y . A portion of a h y p o t h e t i c a l m e m o r y s t r u c t u r e m i g h t c o n s i s t s of " l i v i n g t h i n g " with " a n i m a l " and " v e g e t a b l e " a s s u b s e t s of it, the s u p e r s e t " b i r d " and " s n a k e " a s s u b s e t s of " a n i m a l " , a n d " c a n a r y " and " r o b i n " a s i n s t a n c e s of the s u b s e t " b i r d " .
Suppose f o r a m o m e n t
t h a t a c a t e g o r y n a m e c a n n o t be l o c a t e d d i r e c t l y , but m u s t be found by b e g i n n i n g a t the top of the s e m a n t i c h i e r a r c h y and s e a r c h i n g don w a r d t h r o u g h the h i e r a r c h y .
I t follows t h a t the
t i m e r e q u i r e d to r e t r i e v e an i n s t a n c e of any c a t e g o r y should r e f l e c t the n u m b e r of s u p e r s e t s t h r o u g h which the s u b j e c t m u s t move b e f o r e finding the a p p r o p r i a t e c a t e g o r y .
T h u s , we
would e x p e c t the t i m e t a k e n to r e t r i e v e an i n s t a n c e of the c a t e g o r y " b i r d " to be g r e a t e r t h a n the t i m e to r e t r i e v e an a n i m a l , b e c a u s e the s u b j e c t m u s t move t h r o u g h at l e a s t one e x t r a s u p e r s e t to l o c a t e the c a t e g o r y " b i r d " .
Note that we have o p e r a t i o n a l l y d e s c r i b e d the h i e r -
a r a c h y by a s s u m i n g that, f o r a s n p e r o r d i n a t e - s u b o r d i n a t e p a i r of c a t e g o r i e s s u c h a s a n i m a l b i r d , the s u p e r o r d i n a t e (which i n c l u d e s e v e r y t h i n g t h a t belongs in the s u b o r d i n a t e category) will b e h i g h e r on the h i e r a r c h y .
F o r any s u p e r o r d i n a t e - s u b o r d i n a t e p a i r , t h e n , r e t r i e v i n g
an i n s t a n c e of the s u p e r o r d i n a t e c a t e g o r y should take l e s s t i m e , a c c o r d i n g the view t h a t e a c h c a t e g o r y c a n n o t be locate d i r e c t l y . A l t e r n a t i v e l y , suppose that when a s e a r c h p r o c e s s b e g i n s with a p a r t i c u l a r c a t e g o r y n a m e , t h a t n a m e is d i r e c t l y a c c e s s i b l e by s o m e c e n t r a l p r o c e s s o r , i n s t e a d of b e i n g a c c e s s i b l e only via a s e a r c h along a h i e r a r c h i c a l path.
In t h i s c a s e , t h e r e i s no r e a s o n to e x p e c t
50 any d i f f e r e n c e in the t i m e t a k e n to r e t r i e v e a n i n s t a n c e of the c a t e g o r y " b i r d " and the t i m e t a k e n to r e t r i e v e an a n i m a l . We have d e s i g n e d au e x p e r i m e n t to d e t e r m i n e w h e t h e r the t i m e r e q u i r e d to n a m e an i n s t a n c e of a c a t e g o r y is d e p e n d e n t upon the position of the c a t e g o r y in a s e m a n t i c h i e r a r c h y . In d e s i g n i n g the e x p e r i m e n t , a c e n t r a l p r o b l e m was to e n s u r e that c a t e g o r i e s u s e d could be c l a s s i f i e d a c c u r a t e l y a c c o r d i n g to t h e i r r e l a t i v e position in the h i e r a r c h y .
This was accomp-
l i s h e d by u s i n g p a i r s of n e s t e d c a t e g o r i e s in w h i c h the s u p e r o r d i n a t e c a t e g o r y included by definition e v e r y t h i n g t h a t belonged in the s u b o r d i n a t e c a t e g o r y .
F o r e x a m p l e , the c a t e g o r y
" b e v e r a g e s " c o n t a i n s all a l c o h o l i c b e v e r a g e s , " m u s i c a l i n s t r u m e n t s " c o n t a i n s all s t r i n g e d i n s t r u m e n t s , and " a n i m a l s " c o n t a i n s a l l b i r d s .
In t h i s e x p e r i m e n t the s u b j e c t was p r e s e n t e d
w i t h both a s u p e r s e t n a m e (e. g . , b e v e r a g e ) , and r e q u i r e d to give a m e m b e r of t h a t c a t e g o r y , and a s u b s e t n a m e (e. g . , alcoholic b e v e r a g e ) and r e q u i r e d to give a m e m b e r of it.
This
allowed a d i r e c t c o m p a r i s o n of the t i m e t a k e n to produce m e m b e r s of s u p e r s e t s and s u b s e t s . F o r a d d i t i o n a l d e t a i l s , s e e Loftus, e t al. (1970). Subjects took a n a v e r a g e of 1.60 s e e . to p r o d u c e a m e m b e r of a s u p e r o r d i n a t e c a t e g o r y , and 1 . 4 9 s e c . to p r o d u c e a m e m b e r of a s u b o r d i n a t e c a t e g o r y .
This nonsignificant
d i f f e r e n c e is i n c o n s i s t e n t with the view t h a t a s e a r c h p r o c e s s b e g i n s at the top of the h i e r a r c h y and follows pathways downward t h r o u g h the n e t w o r k .
Such a view would p r e d i c t l o n g e r
t i m e s for a s u b s e t c a t e g o r y than for a s u p e r s e t c a t e g o r y s i n c e the s u b s e t is l o c a t e d c l o s e r to the b o t t o m of the h i e r a r c h y . opposite d i r e c t i o n .
The p r e s e n t r e s u l t a c t u a l l y i n d i c a t e s a s l i g h t d i f f e r e n c e in the
T h e s e data a r g u e in f a v o r of a m o d e l in which e a c h c a t e g o r y can be
located directly. 3,
The r e t r i e v a l p r o c e s s c o n s i s t s of two m a j o r s t e p s .
In t h i s s e c t i o n , we d i s c u s s two e x p e r i m e n t s t h a t w e r e o r i g i n a l l y d e s i g n e d to p r o v i d e m o r e i n f o r m a t i o n a s to why s o m e i t e m s a r e r e s p o n d e d to quickly while o t h e r s r e q u i r e a c o n siderably longer response time.
F o r e x a m p l e , s u b j e c t s take l e s s than 1.00 sec. to n a m e a
c o l o r , but they take n e a r l y twice a s long to n a m e a building (Loftus, et a l . , 1970).
If e a c h
c a t e g o r y i s e n t e r e d d i r e c t l y , the r e a s o n t h a t s o m e c a t e g o r i e s a r e l e s s a c c e s s i b l e than o t h e r s c a n n o t be due to the n e c e s s i t y of s e a r c h i n g t h r o u g h m o r e of the h i e r a r c h y to r e a c h t h o s e categories. One possible answer
to the question of why the speed of producing instances of some
categories is faster than others is suggested by the effect of word frequency on identification time.
It is well established that reaction times to identify high frequency words
than for low frequency words nition may
(Rubenstein,
et al., 1970).
are faster
This difference in ease of recog-
account for difference in the speed of producing instances of a category.
51
C l e a r l y , s t i m u l u s r e c o g n i t i o n i s a l o g i c a l l y n e c e s s a r y s t e p in p r o d u c t i o n of a r e s p o n s e from memory.
In o t h e r w o r d s , when a s u b j e c t i s a s k e d to n a m e a m e m b e r of a p a r t i c u l a r
c a t e g o r y , he m u s t " r e c o g n i z e " the s t i m u l u s w o r d (in t h i s c a s e , the c a t e g o r y n a m e ) b e f o r e h e c a n find and produce a m e m b e r of the c a t e g o r y .
T h u s , the p r o d u c t i o n of the r e s p o n s e " p e a c h "
to the s t i m u l u s " f r u i t " depends not only on the e x i s t e n c e in m e m o r y of a link b e t w e e n " p e a c h " and '*fruit", but a l s o upon the s e m a n t i c i d e n t i f i c a t i o n of " f r u i t " when it is p r e s e n t e d .
The
r e c o g n i t i o n o r s e m a n t i c i d e n t i f i c a t i o n of a c a t e g o r y n a m e m a y be e q u i v a l e n t o r a t l e a s t a p a r t of w h a t we have b e e n c a l l i n g " c a t e g o r y e n t r y " o r s t e p i of the r e t r i e v a l p r o c e s s . If the f i r s t s t e p in the r e t r i e v a l p r o c e s s is indeed r e c o g n i t i o n of the c a t e g o r y n a m e and if r e c o g n i t i o n s p e e d is a function of the f r e q u e n c y in the language of t h a t n a m e , then t h i s step of the p r o c e s s should c l e a r l y take l o n g e r for c a t e g o r i e s whose n a m e s a r e low f r e q u e n c y words.
O t h e r things b e i n g equal, then, the t o t a l t i m e to n a m e a m e m b e r of a c a t e g o r y with
a h i g h - f r e q u e n c y n a m e should be s h o r t e r than the t i m e to n a m e a m e m b e r of a l o w - f r e q u e n c y category. An e x p e r i m e n t was conducted in w h i c h s u b j e c t s w e r e p r e s e n t e d w i t h a s e r i e s of c a t e g o r y n a m e s , and had to r e s p o n d with the f i r s t word t h a t they could think of belonging to the c a t e g o r y .
We will r e f e r to t h i s as E x p e r i m e n t I; m o r e c o m p l e t e d e t a i l s c a n be found in
Loftus and F r e e d m a n (1972),
The m e a n t i m e to produce a m e m b e r of a c a t e g o r y w h o s e ~ a m e
is a high f r e q u e n c y word w a s i . 64 sec° and to p r o d u c e a m e m b e r of a c a t e g o r y w h o s e n a m e is a low f r e q u e n c y word was i . 89 s e c .
The d i f f e r e n c e was highly s i g n i f i c a n t , i n d i c a t i n g
c l e a r l y t h a t the f r e q u e n c y of the c a t e g o r y n a m e is a s s o c i a t e d w i t h s p e e d of p r o d u c i n g a n i n s t a n c e of t h a t c a t e g o r y .
We have s u g g e s t e d t h a t t h i s is due to the g r e a t e r t i m e r e q u i r e d
m e r e l y to identify the l o w e r f r e q u e n c y n a m e .
The p o s s i b i l i t y r e m a i n s , h o w e v e r , t h a t the
f r e q u e n c y of the n a m e a l s o a f f e c t s the s e c o n d p a r t of the r e t r i e v a l p r o c e s s - - t h a t p a r t w h i c h o c c u r s a f t e r the n a m e h a s b e e n identified.
In o t h e r w o r d s , once the s t i m u l u s h a s b e e n fully
" r e c o g n i z e d " , it m a y s t i l l take l o n g e r to n a m e a m e m b e r of a c a t e g o r y with a low f r e q u e n c y name.
A s e c o n d e x p e r i m e n t , w h i c h we r e f e r to a s E x p e r i m e n t H, w a s d e s i g n e d to t e s t t h i s
possibility. In the s e c o n d e x p e r i m e n t , the p r o b l e m w a s to d e s i g n a p r o c e d u r e t h a t would e l i m i n a t e d i f f e r e n c e s due to the f i r s t ( r e a d i n g and identification) p a r t of the r e t r i e v a l p r o c e s s but t h a t would e n a b l e us to m e a s u r e the s p e e d of the r e s t of the p r o c e s s (finding and producing the correct response).
The f i r s t r e q u i r e m e n t w a s m e t by giving the s u b j e c t the c a t e g o r y n a m e a
full 3 sec. b e f o r e he had to m a k e any r e s p o n s e .
Since the f i r s t step t a k e s c o n s i d e r a b l y l e s s
than 3 s e c . p r e s u m a b l y t h i s p r o v i d e d a m p l e t i m e for the s u b j e c t to r e a d and identify any c a t e g o r y n a m e , and thus e l i m i n a t e d any d i f f e r e n c e s in r e s p c u se t i m e due to d i f f e r e n c e in r e a d i n g speed.
It was e s s e n t i a l a t t h i s point to p r e v e n t the s u b j e c t f r o m i m m e d i a t e l y b e g i n -
52 ning the r e s t of the r e t r i e v a l p r o c e s s until we in e s s e n c e told him to s t a r t .
This w a s
a c c o m p l i s h e d by r e q u i r i n g a v a r i e t y of r e s p o n s e s to the c a t e g o r y n a m e so that the s u b j e c t did not know ahead of time which r e s p o n s e he would have to give and a c c o r d i n g l y would not know for which to begin s e a r c h i n g .
The idea was that u n d e r t h e s e c i r c u m s t a n c e s the s u b j e c t
would wait until he was a s k e d for a p a r t i c u l a r r e s p o n s e to begin the a p p r o p r i a t e r e t r i e v a l process.
The s u b j e c t was given a c a t e g o r y n a m e and w a s r e q u i r e d to a n s w e r s e v e r a l q u e s t i o n s about that c a t e g o r y .
The q u e s t i o n s ( i n s t r u c t i o n s ) w e r e : (a) " f i r s t l e t t e r " , in which the s u b -
j e c t r e s p o n d e d with the f i r s t l e t t e r of the c a t e g o r y n a m e ; (b) " l a s t l e t t e r " , in which c a s e the s u b j e c t r e s p o n d e d with the l a s t l e t t e r of the c a t e g o r y n a m e ; (c) " l e n g t h " , in w h i c h c a s e the s u b j e c t r e s p o n d e d with the n u m b e r of l e t t e r s in the c a t e g o r y ; and (d) " m e m b e r " , in w h i c h c a s e the s u b j e c t r e s p o n d e d with the f i r s t w o r d that he could think of that n a m e d an object that belonged in the c a t e g o r y .
We took p r e c a u t i o n s to e n s u r e that the s u b j e c t s would not always
e x p e c t to produce a m e m b e r of any given c a t e g o r y .
F o r d e t a i l s the r e a d e r is r e f e r r e d to
Loftus and F r e e d m a n (1972). The data of i n t e r e s t w e r e the r e s p o n s e t i m e s of c o r r e c t r e s p o n s e s to the " m e m b e r " question.
The m e a n t i m e to p r o d u c e a m e m b e r of a c a t e g o r y
w h o s e n a m e is high f r e q u e n c y
was 1.48 s e c . and to produce a m e m b e r of a c a t e g o r y w h o s e n a m e is low f r e q u e n c y was 1.67 s e c . , a highly s i g n i f i c a n t d i f f e r e n c e .
Thus e v e n a f t e r the s u b j e c t has had a m p l e t i m e to r e a d
and identify the c a t e g o r y than a high f r e q u e n c y c a t e g o r y . What do we make of t h e s e r e s u l t s ?
R e c a l l that in the o r i g i n a l e x p e r i m e n t , s u b j e c t s
w e r e p r e s e n t e d with a noun c a t e g o r y plus a r e s t r i c t i n g l e t t e r o r a d j e c t i v e , and p r o d u c e d an i n s t a n c e of the c a t e g o r y w h i c h s a t i s f i e d the r e s t r i c t i o n i m p o s e d . When the c a t e g o r y n a m e was p r e s e n t e d f i r s t , the m e a n r e a c t i o n t i m e was 1.87 s e c . ; with the c a t e g o r y n a m e p r e s e n t e d second, it was 2.12 s e c .
The d i f f e r e n c e o f . 25 s e c . was quite stable a c r o s s s o m e w h a t d i f -
f e r e n t conditions, and was taken as e v i d e n c e that the d u r a t i o n of c a t e g o r y e n t r y , or s t e p 1 of the r e t r i e v a l p r o c e s s , was a p p r o x i m a t e l y . 25 s e c . The two e x p e r i m e n t s just d i s c u s s e d a l s o provide an e s t i m a t e of the duration of s t e p 1. In E x p e r i m e n t 1 the m e a n r e a c t i o n t i m e was 1.89 for low f r e q u e n c y c a t e g o r i e s and t . 64 s e c . f o r high f r e q u e n c y c a t e g o r i e s . 1.48 s e c . , r e s p e c t i v e l y .
In E x p e r i m e n t II the c o r r e s p o n d i n g t i m e s w e r e 1.67 s e c . and
Since E x p e r i m e n t I included identification t i m e (i. e . , included c a t e -
g o r y entry') ~hile E x p e r i m e n t II did not, the d i f f e r e n c e s in r e a c t i o n t i m e between the two e x p e r i m e n t s provide s o m e indication of identification t i m e .
F o r low f r e q u e n c y c a t e g o r i e s the
d i f f e r e n c e is . 22 s e c . (1.89 - 1.67) and for high f r e q u e n c y c a t e g o r i e s it i s . t6 s e c . (1.64 1.48).
A s e x p e c t e d , identification o r e n t r y of a low f r e q u e n c y c a t e g o r y t a k e s l o n g e r than for
a high f r e q u e n c y c a t e g o r y .
The m e a n for all c a t e g o r i e s is . t9 s e c .
Thus, although the
53
p r e s e n t p r o c e d u r e s a r e quite d i f f e r e n t f r o m t h a t u s e d in the o r i g i n a l e x p e r i m e n t and involve r e l a t i v e l y s i m p l e ( u n r e s t r i c t e d ) r e s p o n s e s , the e s t i m a t e s of t h e d u r a t i o n of s t e p t o b t a i n e d i n the two p a p e r s is quite c o m p a r a b l e (. 25 sec. v s . .
19 s e e . ) .
Conclusion Our b a s i c conception of h u m a n m e m o r y i s t h a t of a s t o r e c o n s i s t i n g of a l a r g e n u m b e r of i n t e r c o n n e c t e d and c r o s s - r e f e r e n c e d a s s o c i a t i v e and c a t e g o r y n e t w o r k s .
According
to the model, m e m o r y is o r g a n i z e d into a complex h i e r a r c h y c o m p o s e d of c a t e g o r i e s (e. g . , a n i m a l s ) with s u b s e t s of e a c h (e. g . , b i r d s , dogs) and s u p e r s e t s (e. g . , living things).
Fur-
t h e r m o r e , when a s e a r c h b e g i n s with a p a r t i c u l a r c a t e g o r y n a m e , t h a t c a t e g o r y c a n be e n t e r e d d i r e c t l y , without f i r s t s e a r c h i n g t h r o u g h o t h e r c a t e g o r i e s .
T h u s , to find a b i r d , the
c a t e g o r y " b i r d s " is e n t e r e d ; to find an a n i m a l , the c a t e g o r y " a n i m a l s " i s e n t e r e d , and s o on. A g e n e r a l m o d e l of the r e t r i e v a l p r o c e s s a s s u m e s t h a t the e n t i r e p r o c e s s c o n s i s t s of at l e a s t two m a j o r s t e p s : (a) e n t e r i n g an a p p r o p r i a t e c a t e g o r y and (b) finding and p r o d u c i n g a n a p p r o p r i a t e m e m b e r of t h a t c a t e g o r y , We have p r e s e n t e d the r e s u l t s of s e v e r a l e x p e r i m e n t s to s u p p o r t v a r i o u s a s p e c t s of the model.
F o r e x a m p l e , s u p p o r t for the view t h a t the r e t r i e v a l p r o c e s s c o n s i s t s of at l e a s t
two m a j o r s t e p s c o m e s f r o m the r e d u c t i o n in t o t a l r e a c t i o n t i m e o b t a i n e d w h e n a s u b j e c t h a s a l r e a d y r e a d and " i d e n t i f i e d " the c a t e g o r y n a m e .
T h i s r e d u c t i o n r a n g e s f r o m . 19 to . 25,
depending on the t a s k , and it s e r v e s as an i n d i c a t i o n of the d u r a t i o n of the f i r s t s t e p o2 the process. F u r t h e r d e v e l o p m e n t and t e s t i n g of t h i s model is badly needed, model is m o r e like a l o o s e outline t h a n a s p e c i f i c t h e o r y ,
At t h i s point t h e
Much m o r e r e s e a r c h will be
n e e d e d b e f o r e we c a n a c t u a l l y t r a n s l a t e t h i s outline into a c o n c r e t e model.
Even more re-
s e a r c h will be n e c e s s a r y b e f o r e we c a n build a r e a l i s t i c m o d e l t h a t t r u l y d e s c r i b e s t h e c h a r a c t e r i s t i c s of h u m a n m e m o r y .
One fruitful d i r e c t i o n would involve a r e f i n e d a n a l y s i s of d a t a
f r o m individual s u b j e c t s r a t h e r t h a n a n a l y s i s of d a t a a v e r a g e d a c r o s s s u b j e c t s , b e c a u s e the h i e r a r c h i c a l o r g a n i z a t i o n s u r e l y v a r i e s a c c o r d i n g to individual u s a g e and e x p e r i e n c e f r o m s u b j e c t to s u b j e c t .
We plan to t u r n to s u c h individual a n a l y s e s in f u t u r e w o r k .
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