M e m o r y & Cognition
1 9 9 6 , 2 4 (3), 342-355
P r o c e s s i n g r e s o u r c e c a p a c i t y and the
c o m p r e h e n s i o n o f garden path s e n t e n c e s
GLORIA S. WATERS
McGill U n i v e r s i t y , Montreal, Quebec, C a n a d a
and
DAVID CAPLAN
M a s s a c h u s e t t s General H o s p i t a l , Boston, M a s s a c h u s e t t s
Three e x p e r i m e n t s e x p l o r e d the r e l a t i o n s h i p b e t w e e n verbal working memory capacity and the
c o m p r e h e n s i o n of garden p a t h s e n t e n c e s . In E x p e r i m e n t 1, s u b j e c t s with high, medium, and low work­
ing memory s p a n s made acceptability j u d g m e n t s about garden p a t h and c o n t r o l s e n t e n c e s u n d e r whole
s e n t e n c e and rapid serial visual p r e s e n t a t i o n (RSVP) conditions, There were no significant d i f f e r e n c e s
b e t w e e n s u b j e c t s with different working memory s p a n s in the c o m p r e h e n s i o n of garden p a t h s e n t e n c e s
in either condition. In E x p e r i m e n t s 2A and 2B, s u b j e c t s with high and low working memory s p a n s were
t e s t e d on the same m a t e r i a l s at three RSVP rates. There were no s i g n i f i c a n t d i f f e r e n c e s b e t w e e n sub­
j e c t s with d i f f e r e n t working memory s p a n s in the magnitude of the e f f e c t of garden path s e n t e n c e s at
any p r e s e n t a t i o n rate. The r e s u l t s suggest t h a t working memory capacity, as m e a s u r e d by the Daneman
and C a r p e n t e r (1980) reading span task, is not a major d e t e r m i n a n t of individual differences in the pro­
cessing of g a r d e n p a t h s e n t e n c e s .
Research on sentence c o m p r e h e n s i o n has tended to focus
on the n a t u r e o f the r e p r e s e n t a t i o n s and c o m p u t a t i o n s
that are involved in c o n s t r u c t i n g syntactic s t r u c t u r e s (e.g.,
A l t m a n n & S t e e d m a n , 1988; Frazier, 1990; T r u e s w e l l ,
Tanenhaus, & Garnsey, 1994), with little research on the
p r o c e s s i n g resource r e q u i r e m e n t s o f this function. How­
ever, recently, r e s e a r c h e r s have b e c o m e i n t e r e s t e d in spec­
ifying more clearly the nature o f the p r o c e s s i n g r e s o u r c e or
working m e m o r y s y s t e m involved in s e n t e n c e c o m p r e ­
hension.
Several pieces o f e v i d e n c e suggest that c o m p r e h e n d i n g
s e n t e n c e s requires the a l l o c a t i o n o f p r o c e s s i n g r e s o u r c e s .
Syntactic form affects s u b j e c t s ' accuracy and reaction times
in j u d g i n g the a c c e p t a b i l i t y o f s e n t e n c e s (Waters, C a p l a n ,
& H i l d e b r a n d t , 1987), and r e a d i n g times increase at points
in a s e n t e n c e where m o d e l s o f s e n t e n c e p r o c e s s i n g p r e d i c t
an increased p r o c e s s i n g load (King & Just, 1991). M e m o r y
for u n r e l a t e d m a t e r i a l p r e s e n t e d during sentence c o m p r e ­
hension is affected by syntactic structure (Wanner & Marat­
sos, 1978). Aphasic stroke p a t i e n t s ' c o m p r e h e n s i o n o f sen­
t e n c e s is a f f e c t e d by s y n t a c t i c s t r u c t u r e , in a way t h a t
s u g g e s t s a r e d u c t i o n in p r o c e s s i n g resources available for
This research was s u p p o r t e d by grants from the Medical R e s e a r c h
C o u n c i l of C a n a d a ( M A 9 6 7 1 ) and the N a t i o n a l I n s t i t u t e o f A g i n g
( A G 0 9 6 6 I ). Gloria Waters was s u p p o r t e d by a University R e s e a r c h Fel­
lowship from the Natural Sciences and Engineering Research Council of
Canada. We wish to thank the action editor, Douglas Hintzman, for ex­
tremely detailed and helpful s u g g e s t i o n s regarding the o r g a n i z a t i o n and
style of this paper. D.C. is a f f i l i a t e d with the N e u r o p s y c h o l o g y Labora­
tory at M a s s a c h u s e t t s General. C o r r e s p o n d e n c e c o n c e r n i n g this article
should be addressed to G. S. Waters, School of C o m m u n i c a t i o n Sci­
ences and Disorders, McGill University, 1266 Pine Ave. w., Montreal,
PQ, Canada H3G I A8.
syntactic p r o c e s s i n g ( C a p l a n , Baker, & D e h a u t , 1985; Ca­
plan & H i l d e b r a n d t , 1988).
How s p e c i a l i z e d is the p r o c e s s i n g r e s o u r c e system re­
q u i r e d for s e n t e n c e c o m p r e h e n s i o n ? Many l i n g u i s t s and
psycho linguists have argued that the p r o c e s s e s involved in
s e n t e n c e c o m p r e h e n s i o n are distinct from those involved
in other v e r b a l l y m e d i a t e d functions, such as r e a s o n i n g
and problem s o l v i n g (e.g., Fodor, 1983). C l a i m s r e g a r d i n g
the " m o d u l a r i t y " o f sentence processing have generally been
r e s t r i c t e d to i n f o r m a t i o n - p r o c e s s i n g a s p e c t s o f this func­
tion. However, a p a r a l l e l question arises about the process­
ing r e s o u r c e s i n v o l v e d in s e n t e n c e c o m p r e h e n s i o n : are
they s p e c i f i c to s e n t e n c e c o m p r e h e n s i o n (or to aspects o f
the sentence c o m p r e h e n s i o n process) or are the same pro­
cessing r e s o u r c e s used in s e n t e n c e c o m p r e h e n s i o n and
other verbal tasks?
Just and C a r p e n t e r (1992) have a p p r o a c h e d the question
o f the nature o f the p r o c e s s i n g r e s o u r c e s used in s e n t e n c e
c o m p r e h e n s i o n by a t t e m p t i n g to d e t e r m i n e w h e t h e r indi­
vidual d i f f e r e n c e s in p e r f o r m a n c e on a task that was de­
signed to m e a s u r e verbal working m e m o r y c a p a c i t y - t h e
Daneman and C a r p e n t e r (1980) reading span t a s k - a r e re­
lated to i n d i v i d u a l d i f f e r e n c e s in the a b i l i t y to s t r u c t u r e
sentences syntactically. They have i n t e r p r e t e d the results
o f a variety o f e x p e r i m e n t s as showing that individuals with
lower reading spans are less e f f i c i e n t at s t r u c t u r i n g sen­
tences s y n t a c t i c a l l y than are subjects with higher spans.
On this basis, they have argued that the working m e m o r y
system that is m e a s u r e d by the r e a d i n g span task is in­
volved in syntactic processing during sentence comprehen­
sion. We have q u e s t i o n e d this " c a p a c i t y t h e o r y " on several
grounds. At an e m p i r i c a l level, many results that form the
basis for Just and C a r p e n t e r ' s claims are not s t a t i s t i c a l l y
C o p y r i g h t 1996 P s y c h o n o m i c Society, Inc. 342

WORKING MEMORY AND C O M P R E H E N S I O N OF G A R D E N PATH S E N T E N C E S 343
s i g n i f i c a n t , and, at a t h e o r e t i c a l level, t h e i r mode~ does not
generate clear p r e d i c t i o n s (Waters & C a p l a n , In press).
Just and C a r p e n t e r ' s (1992) c a p a c i t y t h e o r y is also con­
tradicted by studies o f two different types o f b r a i n - d a m a g e d
patients. P a t i e n t s with r e d u c e d w o r k i n g m e m o r y ~ e . g . , y a ­
tients with A l z h e i m e r ' s d i s e a s e ) are not more i m p a i r e d
than n o r m a l s in c o m p r e h e n d i n g s y n t a c t i c a l l y more com­
plex s e n t e n c e s ( R o c h o n , Waters, & Ca~lan, 1994), even
under dual-task c o n d i t i o n s that load working m e m o r y (Wa­
ters, Caplan, & Rochon, 1995). Conversely, pati.ent~ with
aphasia due to stroke, who suffer from a reductlO~ I n the
p r o c e s s i n g r e s o u r c e s that are n e e d e d for s y n t a c t i c pro­
cessing, are not more a f f e c t e d by a digit load than normals
when c o m p r e h e n d i n g syntactically more complex sentences
(Caplan & Waters, 1994). Both these r e s u l t s s~gg~st that
the r e s o u r c e s y s t e m used in s y n t a c t i c p r o c e s s i n g I~ sen­
tence c o m p r e h e n s i o n is s e p a r a t e from that u s e d I n the
D a n e m a n and C a r p e n t e r (1980) r e a d i n g span task.
Given the r e s u l t s o f the studies o f b r a i n d a m a g e d pa­
tients the d i f f e r e n c e s in sentence p r o c e s s i n g that Just, Car­
p e n t e r and their c o l l e a g u e s claim to have found in ? o r m a l
s u b j e c t s with d i f f e r e n t readin.g spans provide. c r u c i a l em­
pirical s u p p o r t for the c a ? a c l t y theory. ~n th~s p~~e.r, we
focus on one a s p e c t o f this support: s u b j e c t s a b i l i t i e s to
c o m p r e h e n d s e n t e n c e s with s y n t a c t i c g a r d e n paths. Gar­
den path s e n t e n c e s are locally a m b i g u o u s s y n t a c t i c struc­
tures whose u l t i m a t e r e s o l u t i o n is t o w a r d an u n f a v o r e d
s y n t ; c t i c r e p r e s e n t a t i o n . R e a d e r s and l i s t e n e r s are fre­
quently m i s l e d as to the s y n t a c t i c s t r u c t u r e o f garden path
c o n s t r u c t i o n s . P e r h a p s the best known g a r d e n path struc­
ture is i l l u s t r a t e d in ( I ) (Bever, 1970):
I. The boat floated down the river sank.
Readers ( a n d l i s t e n e r s ) g e n e r a l l y a s s i g n the boat as the
subject o f f l o a t e d in ( I ) , and have consi~erab~e d i f f i c u l t y
revising this a s s i g n m e n t in favor o f one I n w h i c h t~e boat
is the s u b j e c t o f sank, and f l o a t e d down the river IS a re­
duced relative clause.
G a r d e n path s e n t e n c e s are o f i n t e r e s t wit~ resp~ct to t?e
role o f p r o c e s s i n g r e s o u r c e s , since they are i n t u i t i v e l y ~If­
ficult and w o u l d be e x p e c t e d to r e q u i r e more p r o c e s s i n g
resources to be i n t e r p r e t e d correctly than would unaI?~i~­
ous s e n t e n c e s with the same s t r u c t u r e . T h e r e f o r e , if indi­
vidual differences in the availability o f p r o c e s s i n g resources
affect s e n t e n c e c o m p r e h e n s i o n , there s h o u l d be differ­
ences in the a b i l i t y o f subjects with high and low p r o c e s s ­
ing c a p a c i t y to i n t e r p r e t these s e n t e n c e s .
M a c D o n a l d , Just, and C a r p e n t e r ( 1 9 9 2 ) have e x p l o r e d
the p r o c e s s i n g o f the type o f g a r d e n y a t h s e n t e n c e s ill~s­
trated in ( I ) by r e a d e r s who have high and low working
m e m o r y c a p a c i t i e s as m e a s u r e d by the D a n e m a n and Car­
penter (1980) r e a d i n g span task. M a c D ? n a l d . e t al. used a
s e l f - p a c e d w o r d - b y - w o r d r e a d i n g task, I n which each sen­
tence was followed by a question. They p r e s e n t e d garden
path s e n t e n c e s such as (2a) and n o n - g a r d e n path control
s e n t e n c e s such as (2b).
2a. The e x p e r i e n c e d soldiers warned about the dangers con­
ducted the m i d n i g h t raid.
2b. The e x p e r i e n c e d soldiers who were told about the dan­
gers c o n d u c t e d the m i d n i g h t raid.
They found that s u b j e c t s t o o k l o n g e r to rea~ the final
words and made more errors in a n s w e n n g questions about
g a r d e n p a t h s e n t e n c e s (2a) than in a n s w e r i n g q u e s t i o n s
a b o u t n o n - g a r d e n path s e n t e n c e s , c o n f i r m i n g the diffi­
culty o f these garden path s e n t e n c e s . L o w - c a p a c i t y sub­
j e c t s m a d e more errors in a n s w e r i n g q u e s t i o n s about gar­
den p a t h than about n o n - g a r d e n path s e n t e n c e s , ~hile
h i g h - c a p a c i t y subjects took l o n g e r to read the ~ords I n the
final p h r a s e s o f garden p a t h s e n t e n c e s than I n t h o s e o f
n o n - g a r d e n path s e n t e n c e s . M a c D o n a l d et al. i n t e r p r e t e d
these r e s u l t s as c o n s i s t e n t with the c a p a c i t y theory o f sen­
tence c o m p r e h e n s i o n . They argued that both low- and high­
span r e a d e r s a t t e m p t to c o n s t r u c t both the prefe~red and
the u n p r e f e r r e d s y n t a c t i c s t r u c t u r e s in s e n t e n c e s like (2a),
but that low-span subjects c a n n o t m a i n t a i n both s t r u c t u r e s
in working memory. Therefore, low-capacity subjects make
more e r r o r s on g a r d e n path s e n t e n c e s , b e c a u s e they do not
have the u n p r e f e r r e d syntactic s t r u c t u r e available at the end
o f t h e s e n t e n c e , w h e r e a s h i g h - s p a n s u b j e c t s take l o n g e r to
read the words in the final phrases o f garden path sentences,
b e c a u s e they m a i n t a i n both the p r e f e r r e d and the unpre­
ferred syntactic structures t h r o u g h o u t the sentence.
However, there are several p r o b l e m s with this i n t e r p r e ­
tation o f M a c D o n a l d et al.'s ( 1 9 9 2 ) results. First, the ef­
fects d e s c r i b e d above were not r e l i a b l e s t a t i s t i c a l l y over
subjects. Second, there were only six sentences in each con­
d i t i o n , and s u b j e c t s made e r r o r s on 3 5 % - 5 0 % o f the gar­
den path s e n t e n c e s , so that the r e a c t i o n time a n a l y s i s for
g a r d e n p a t h s e n t e n c e s was b a s e d on d a t a for a p p r o x i ­
m a t e l y three s e n t e n c e s . Third, presum~bly bec~us.e o f the
small n u m b e r o f sentences o f each type, Item statistics were
not r e p o r t e d . Finally, the p a t t e r n o f results could s~mply
have r e f l e c t e d d i f f e r e n t s p e e d - a c c u r a c y t r a d e o f f s I n the
high- and l o w - s p a n groups.
B e c a u s e o f the a m b i g u i t y o f the M a c D o n a l d et al.
( 1 9 9 2 ) r e s u l t s , we u n d e r t o o k f u r t h e r study o f the r e l a t i o n ­
ship between working m e m o r y and c o m p r e h e n s i o n o f ~~r­
den p a t h s e n t e n c e s . In E x p e r i m e n t I we tested the abl~lty
o f 65 s u b j e c t s to p r o c e s s garden path s e n t e n c e s : The stim­
uli in this e x p e r i m e n t c o n s i s t e d o f s e n t e n c e s With r e d u c e d
relative clauses, as had been t e s t e d in the M a c D o n a l d et ~1.
s t u d y and two a d d i t i o n a l s y n t a c t i c s t r u c t u r e s - s e n t e n t i a lcom~lements and e m b e d d e d c1auses-w~ich have been
shown to result in garden path e f f e c t s . S u b j e c t s made sen­
tence a c c e p t a b i l i t y j u d g m e n t s a b o u t a c c e p t a b l e and u n a c ­
c e p t a b l e g a r d e n path s e n t e n c e s and two types o f n~n­
g a r d e n path s e n t e n c e s under two diff~r.ent p r e s e n t a t I o n
c o n d i t i o n s . In the whole s e n t e n c e c o n d i t i o n , the s e n t e n c e
r e m a i n e d on the screen until the s u b j e c t had r e s p o n d e d . In
the RSVP ( r a p i d serial visual p r e s e n t a t i o n ) c o n d i t i o n , the
words o f the s e n t e n c e were p r e s e n t e d s e q u e n t i a l l y in the
c e n t e r o f a c o m p u t e r screen. Miyake, Carpenter, and Just
( 1 9 9 4 ) have argued that the severe time c~nstraints im­
p o s e d by this t e c h n i q u e r e d u c e the p r o c e s s l ? g resour~es
available for syntactic processing. Moreover, SInce the stim­
ulus is not p r e s e n t for the s u b j e c t to review in the RSVP