BRAIN
AND
LANGUAGE
38, 75-104 (1990)
Semantic and Associative Priming in the Cerebral
Hemispheres: Some Words Do, Some Words
Don’t . . . Sometimes, Some Places
CHRISTINE CHIARELLO, CURT BURGESS, LORIE RICHARDS,
AND ALMA POLLOCK
Syracuse
University
This study investigated spreading activation for words presented to the left
and right hemispheres using an automatic semantic priming paradigm. Three
types of semantic relations were used: similar-only (Deer-Pony), associated-only
(Bee-Honey), and similar + associated (Doctor-Nurse). Priming of lexical decisions was symmetrical over visual fields for all semantic relations when prime
words were centrally presented. However, when primes and targets were lateralized to the same visual field, similar-only priming was greater in the LVF than
in the RVF, no priming was obtained for associated-only words, and priming
was equivalent over visual fields for similar + associated words. Similar results
were found using a naming task. These findings suggest that it is important to
lateralize both prime and target information to assess hemisphere-specific spreading activation processes. Further, while spreading activation occurs in either
hemisphere for the most highly related words (those related by category membership and association), our findings suggest that automatic access to semantic
category relatedness occurs primarily in the right cerebral hemisphere. These
results imply a unique role for the right hemisphere in the processing of word
meanings. We relate our results to our previous proposal (Burgess & Simpson,
1988a; Chiarello, 1988~) that there is rapid selection of one meaning and suppression of other candidates in the left hemisphere, while activation spreads more
diffusely in the right hemisphere. We also outline a new proposal that activation
spreads in a different manner for associated words than for words related by
semantic similarity.
0 1990 Academic
Press, Inc.
Lexical-semantic
memory is often conceptualized
as a network, in
which semantically related concepts are closely linked, with more distantly related concepts connected only indirectly or not at all (Collins
This research was supported by NIMH Grant MH43868-01 to the first author and by
NIH Biomedical Support Grant RR-07068-22. We thank Paul Gelling for hardware and
software support and Jessica Senehi for assistance in stimulus preparation. We also thank
Bob Peterson and Mike Tanenhaus for their helpful comments and criticisms.
75
0093-934x190 $3.00
Copyright
0 1990 by Academic
Press. Inc.
All rights of reproduction
in any form reserved.
76
CHIARELLO
ET AL.
& Loftus, 1975). While it is generally agreed that strongly associated
words are linked in the network, it is not clear whether nonassociative
semantic relations are also coded in this structure (Fischler, 1977b; Lupker, 1984). This is an important issue since the automatic activation of
related concepts is thought to occur via lexical connections. When a
word is recognized, its representation is activated (made more available
for processing), and some of this activation spreads through the network
to semantically related words (Collins & Loftus, 1975). This spreading
activation serves to facilitate subsequent recognition of these semantically related items.
In this study we continue our investigation of how spreading activation
operates in each cerebral hemisphere (Chiarello, 1985; Chiarello, Senehi,
& Nuding, 1987; Burgess & Simpson, 1988a). Evidence is accumulating,
from studies of both normal and brain injured individuals, that the right
hemisphere can subserve many aspects of lexical-semantic
processing
(e.g., Chiarello,
1988b). Our previous semantic priming studies have
suggested that spreading activation may be a process which is available
to the right, as well as to the left, hemisphere. A brief review of these
results will set the stage for this investigation.
Semantic priming refers to the facilitation in word recognition which
occurs when a target word is preceded by a semantically related, as
compared to an unrelated, prime word (Fischler, 1977a; Neely, 1976).
Semantic priming can be attributed to an automatic spreading activation
process when it is obtained at short prime-target
stimulus onset asynchronies (SOAs) (Fischler & Goodman, 1978), when the prime is patternmasked (Marcel & Patterson, 1978) or when related primes occur very
infrequently
throughout the experiment (Fischler, 1977a). Under such
conditions visual half-field studies have obtained either equivalent semantic priming effects in each hemisphere (Marcel & Patterson, 1978;
Chiarello et al., 1987; Burgess & Simpson, 1988a) or greater semantic
priming for left visual field (LVF) stimuli (Chiarello, 1985; Michimata,
1987).
The automatic priming effect can be augmented when the experimental
conditions permit subjects to develop expectancies about the occurrence
of semantically related words: with longer SOAs (Neely, 1977) or a high
proportion of semantically related prime-target pairs (Tweedy, Lapinski,
& Schvaneveldt,
1977). Under these controlled processing conditions
priming is greater for stimuli presented to the RVF/left hemisphere (Chiarello, 1985; Chiarello et al., 1987; Michimata,
1987; Burgess & Simpson,
1988a). These result suggest a left hemisphere advantage for some aspect
of semantic processing which requires attention or cognitive control, but
bihemispheric
involvement
for the passive spread of activation through
the lexical network (for discussion see Burgess & Simpson, 1988a, 1988b;
Chiarello, 198%~).
SEMANTIC
AND ASSOCIATIVE
PRIMING
77
It remains to be explained, however, why priming attributable
to
spreading activation should sometimes be greater for words presented
to the right hemisphere. It is theoretically
important to understand the
conditions under which this effect occurs, as this might represent a unique
right hemisphere contribution to the processing of word meanings. Consideration of the methodological
differences between the previous studies
suggests two possibilities for the discrepant automatic priming results:
(1) the position of the prime word-central
or lateral; (2) the basis of
the semantic relationship between related prime-target
pairs-association or semantic similarity. ’
In the study conducted by Chiarello (1985) prime as well as target
words were lateralized to the left or right visual fields, and related primetarget pairs were members of the same semantic category, but not necessarily associated (Horse-Tiger).
Michimata (1987) employed the same
stimuli and also lateralized primes as well as target strings. In the former
study, automatic priming was measured by using a low proportion of
related stimuli, while in the latter, a brief SOA (200 ms) was employed.
In both cases, priming
was significantly
larger in the LVF/right
hemisphere.
In the remaining investigations,
related prime-target
pairs were associated (Police-Jail,
Arm-Leg),
but semantic similarity was not controlled. Prime words were centrally presented in two studies (Chiarello
et al., 1987; Burgess & Simpson, 1988a), but were laterally presented
by Marcel and Patterson (1978). Although each study measured automatic
priming with a different technique (low proportion related, brief SOA,
pattern-masked primes, respectively), all obtained the same result: equivalent priming for targets presented to the LVF and RVF.
These results suggest the intriguing hypothesis that the right hemisphere preferentially has automatic access to nonassociated words which
share semantic features. It is unclear from previous studies what role
simple association plays in priming effects across the cerebral hemispheres. Many of the most highly associated stimuli (Cat-Dog, DoctorNurse) are also members of the same semantic category, and thus are
related by similarity as well as by association. To assess the effects of
association without similarity it is necessary to use dissimilar associates
(Bee-Honey,
Pilot-Plane).
None of the previous lateralization
studies
have examined such stimuli.
It is presently being debated whether automatic spreading activation
can occur via nonassociative semantic relations (Lupker, 1984; Hines,
Czerwinski, Sawyer, & Dwyer, 1986). Several studies using centrally
’ Although semantic similarity can refer to several different dimensions, such as those
arising from the sharing of perceptual or functional features, in this paper the term is used
to refer to membership in the same semantic category.
78
CHIARELLO
ET AL.
presented stimuli have independently
manipulated
associative and semantic relationships. Fischler (1977b) had subjects make lexical decisions
to targets that were preceded by either associatively related primes
(Jump-Rope) or semantically similar related primes (Nurse-Wife).
While
a priming effect was obtained with both relatedness conditions, Lupker
(1984) has questioned these results. He argues that the lexical decision
task has been shown to be sensitive to processes that occur subsequent
to lexical access (see Forster, 1981; West & Stanovich, 1982). Presumably, lexical access involves the parallel activation of information
that
is stored with the lexical item which can include (but is not limited to)
semantic, associative, phonological, and orthographic codes (Seidenberg,
1985). Postlexical processes can influence the selection and integration
of the lexical information.
Such processes could include subject expectancies or strategies. The lexical decision task necessarily involves lexical
access and potentially involves postaccess processes as well. When contextual variables affect the decision component of lexical decision, the
“lexical”
priming effect (sensitivity in distinguishing
words from nonwords) is confounded with a bias in response criterion (Chumbley &
Balota, 1984). It is argued that the naming task is not as sensitive to
postlexical effects (Seidenberg, 1985).
Exploiting this task difference, Lupker (1984) compared priming with
category instances versus categorically unrelated, but associatively related, word pairs. Priming was found both for categorically and for associatively related word trials when subjects made lexical decisions. A
different pattern of results was obtained when subjects named the target.
Priming was reliably obtained only when word pairs were associated.
Categorically
related words yielded an unreliable, weak effect (6-10
msec) (but c.f., Seidenberg, Waters, Sanders, & Langer, 1984, Expt 4).
The implication of these task differences is that lexical access processes
are strictly associative, and that nonassociative semantic relations do
not have a role in the spreading activation process.
Before we accept this conclusion, an alternative explanation should
be considered. Hines et al. (1986) conducted a relevant series of experiments with two notable findings. First, using a naming task, they found
priming between nonassociated category members, but only when the
prime had high category dominance (Apple-Grape).
Priming was unaffected by category dominance of the targets. These results suggest that
the recognition threshold for targets is lowered by primes with high
category dominance. Only a small proportion of Lupker’s categorical
trials had primes of this sort. Second, the categorical priming effect was
obtained only for subjects with slow naming latencies. While Hines et
al. do not offer an explanation of their interaction between naming latency
and priming magnitude, an obvious candidate is that the rate of spreading
activation varies for different types of information. It is difficult to argue
SEMANTIC
AND
ASSOCIATIVE
PRIMING
79
that deliberate postaccess strategies were operative in the Hines et al.
(1986) experiments given that they used a masking procedure which
prevented conscious recognition of the prime. Thus, the conclusion that
automatic spreading activation does not occur between semantically (i.e.,
categorically) related items may be premature.
A set of experiments by Flores d’Arcais, Schreuder, and Glazenborg
(1985; Schreuder, Flores d’Arcais, & Glazenborg, 1984) is also relevant
to the question of whether activation can automatically
spread between
semantically, but nonassociatively,
related items. They propose that the
rate of activation for perceptual features is faster than for conceptual
features (they consider both to be semantic dimensions). Their distinction
between naming and lexical decision differs from the postaccess explanation of Lupker. Since naming latencies tend to be faster than lexical
decision times (e.g., Theios & Muise, 1977), they hypothesized that this
difference in response speed, rather than the task itself, may be related
to the interaction between task and prime-target
relatedness. In their
experiments subjects were presented with perceptually related (CherryRound) and conceptually related (Tiger-Fierce)
word pairs. With lexical
decision, they found that conceptual priming was eliminated when a 650msec response deadline was used, while perceptual priming did not vary
between deadline and no-deadline conditions. In addition, with naming,
conceptual priming was enhanced when naming latencies were slowed
by the use of a target mask. Again, perceptual priming was maintained
with or without masking. Thus, the simple conclusion that naming is
insensitive to categorical information may not be warranted. Response
latency may influence whether automatic priming for nonassociative semantic relations can be observed. It is interesting to speculate that greater
LVF categorical priming (Chiarello, 1985; Michimata,
1987) may be tied
to the slower processing typically found for words presented to the right
hemisphere.
This study was designed to distinguish the roles of semantic similarity
and association in priming within the cerebral hemispheres. Both lexical
decision (Expt 1) and naming (Expt 2) tasks were employed to determine
whether automatic priming for semantic similarity is task-specific. In
addition, we considered in Expt 1 whether prime location (central vs.
lateral) might influence the size or presence of lateralized automatic
priming effects. It is interesting that the two studies finding greater LVF
priming obtained this result only when prime and target stimuli were
directly presented to the right hemisphere (Chiarello, 1985; Michimata,
1987). Zaidel, White, Sakurai, and Banks (1988) have recently argued
that effects obtained with centrally presented stimuli may not always
reflect simple combinations of left and right hemisphere processing. Thus,
even when the prime-target
interval is sufficient to permit interhemi-
80
CHIARELLO
ET AL.
spheric sharing of information,
lateralized primes may initiate different
processes than do centrally presented stimuli.
To address these issues, subjects were presented with either central
or lateral primes. The type of prime-target
relatedness varied over sessions, the critical stimuli being either similar-only
(Deer-Pony),
associated-only
(Bee-Honey),
or both similar and associated (DoctorNurse). In addition, a neutral prime condition was included to determine
whether priming was due to facilitation (as expected for automatic spreading activation) or facilitation with inhibition (as expected for controlled
priming) (Posner & Snyder, 1975). Since we employed a low proportion
of related trials in order to obtain automatic priming, related trials should
be faster than neutral or unrelated trials, but the latter two conditions
should not differ (i.e., facilitation without inhibition is expected).
If the right hemisphere preferentially
has automatic access to semantically similar words, then greater LVF than RVF priming should
be obtained to Deer-Pony, but not to Bee-Honey.
If this effect depends
on right hemisphere initiation of prime processing, then the asymmetry
should be more prominent with lateral than with central primes. In addition, if nonassociative priming is attributable to postaccess components
of the lexical decision task (Lupker, 1984), then similar-only
priming
should be obtained for lexical decision, but not for naming. On the other
hand, if such priming depends on slower processing speed (Hines et al.,
1986), then we would expect priming for both tasks since slower processing typically follows lateralized tachistoscopic presentation. Finally,
we will investigate whether there is summation of spreading activation
for the similar + associated words, and whether this occurs in each
hemisphere.
Previous studies investigating
spreading activation summation have been inconclusive (Kreusi, 1978; Lupker, 1984; Schreuder
et al., 1984; Klein, Briand, Smith, Smith-Lamothe,
1988). The cumulative
results will provide a more comprehensive
picture of the conditions
governing spreading activation, and thus automatic semantic access, in
the left and right hemispheres.
EXPERIMENT
1: LEXICAL DECISION VARYING PRIME LOCATION
Method
Subjects.Forty-eight right-handed undergraduates (24 male, 24 female) participated. All
were native English speakers with normal vision; none had any immediate left-handed
relatives. Handedness was assessed using a five-item hand preference questionnaire (Bryden, 1982), which yields an index ranging from + 1.00 (extreme right-hand preference) to
- 1.00 (extreme left-hand preference). All participants had an index of at least +0.30 (mean
= +0.73). Subjects received course credit for taking part in the study.
Stimuli.
Three sets of 48 related prime-target noun pairs were created, using published
norms. Similar-only
pairs (Deer-Pony) were rated to be members of the same semantic
category (Battig & Montague, 1969; Hunt & Hodge, 1979; Shapiro & Palermo, 1968). In
addition, these targets were her listed as associates of their primes (Marshall & Cofer,
SEMANTIC
AND ASSOCIATIVE
PRIMING
81
1970; Palermo & Jenkins, 1964; Keppel & Strand, 1970). Associated-only pairs (BeeHoney) had targets which were primary or secondary associates of their primes (Palermo
& Jenkins, 1964; Keppel & Strand, 1970; Shapiro & Palermo, 1968), but were not members
of the same semantic category. Similar + Associated pairs (Doctor-Nurse) were related
via both similarity and association, according to the same normative criteria. All related
prime-target pairs are listed in the Appendix.
Primes and targets for the three semantic relations were equated for mean word length,
imageability (Gilhooly & Logie, 1980; Toglia & Battig, 1978), and log word frequency
(Kucera & Francis, 1967). Means for these dimensions are given in Table I. Stimuli for
the three conditions did not differ in length, imageability, or frequency, as verified by F
tests (all p’s > .15).
In order that the target words appear equally often in the related, neutral, and unrelated
conditions, yet not be repeatedly presented to the same subjects, the related stimulus pairs
for each semantic relation were divided into three sublists (see Appendix). A target which
appeared in the related condition for sublist A (Table-Bed), for example, appeared in the
neutral condition for sublist B (Blank-Bed) and in the unrelated condition of sublist C
(Music-Bed). The word Blank was always used as the neutral prime. Unrelated pairs were
created for each sublist by pairing a related prime from another sublist with an unrelated
target. Since each subject saw only one of the sublists, targets and related/unrelated primes
were counterbalanced over prime conditions, without intrasubject repetition.
Thus, each subject viewed 16 related, 16 neutral, and 16 unrelated prime-target pairs.
In order to maintain a low probability of prime-target relatedness, 32 unrelated “filler”
trials were also included. Filler trials were not analyzed. They were included to manipulate
priming probability, while still permitting an equal number of critical trials per prime
condition.
As each list included 80 word target trials (48 critical, 32 filler), 80 orthographically legal
nonword targets (four or five letters) were created by substituting one letter of a real word.
Each letter position was changed equally often, so that visual field asymmetries obtained
with these stimuli could not be attributed to simple acuity gradients (Kirsner & Schwartz,
1986; Chiarello, 1988a). Sixteen nonword targets were preceded by the neutral prime Blank,
and 64 by a unique prime word which did not appear elsewhere in the list.
To match more closely target length and frequency for similar, associated, and similar
+ associated stimuli, a slightly smaller number of trials was used for the lateralized prime
condition (see means in parentheses in Table 1)’ This resulted in 14 related, 14 neutral,
and 14 unrelated prime-target pairs per sublist. Otherwise stimuli were the same in lateralized and in central prime conditions.
We also created practice lists for the similar, associated, and associated + similar
conditions. Each practice list consisted of 25 word and 25 nonword targets, with related,
neutral, and unrelated primes occurring with the same probability as the experimental
trials.
All stimuli were horizontally presented in uppercase. The three- to six-letter strings
subtended 1.4, 1.9,2.4, and 2.9” of horizontal visual angle, respectively, and 0.39” vertically.
Appuratus and procedure. Subjects were seated 175 cm in front of a Hewlett-Packard
1310B vector graphics display equipped with a fast decay phosphor. The display was
interfaced to an LSI 11/23 computer which controlled stimulus presentation and timing
and recorded subject’s responses. Background luminance was 1.46 mL; background +
* The central prime condition was run prior to the lateralized prime condition. In running
the first condition we noticed that subjects had somewhat slower and less accurate performance with the similar-only list. Since targets in this list were (nonsignificantly) longer
and of lower frequency than for the other two lists, we attemped to match the target items
even more closely across lists in the lateral prime condition.
82
CHIARELLO
TABLE
MEAN
WORD
LENGTH,
LOG
FREQUENCY,
AND
Relation
TARGET
ET AL.
1
AND
IMAGERY
FOR CRITICAL
PRIME
WORDS
Length
Log frequency
Imagery
Primes
Similar
Associated
Similar + Associated
4.67 (4.62)
4.92 (4.93)
4.79 (4.88)
1.33 (1.38)
1.07 (1.09)
1.25 (1.22)
5.77 (5.73)
5.71 (5.70)
5.67 (5.65)
Targets
Similar
Associated
Similar + Associated
4.27 (4.16)
4.13 (4.19)
4.06 (4.14)
1.36 (1.48)
1.50 (1.48)
1.44 (1.45)
5.73 (5.71)
5.77 (5.75)
5.76 (5.77)
Note. Values for the lateral prime condition are given in parentheses.
test luminance was 2.32 mL. A chin and head rest was used to stabilize head position.
Subjects registered their decisions by pressing one of two response keys with the index
(word) and middle (nonword) finger of the right hand.
Sessions began with the practice trials, followed by four experimental blocks of 80 trials
each. Each block consisted of 40 word and 40 nonword targets, half appearing in each
visual field. The blocks were separated by brief rest periods during which feedback on
accuracy rate was provided. Stimuli shown in the first 160 trials were unique. These were
repeated in the second half of the experiment, but with visual field of presentation reversed.
Each trial began with a SO-msec 3.75-kHz alerting tone, and simultaneous presentation
of a central fixation marker (+) which remained visible throughout the trial. After 500
msec had elapsed, the prime word was displayed for 75 msec. For the central prime
condition, the prime was centered one degree above the fixation marker. For the lateralized
prime condition, primes also appeared one degree above fixation, but were presented
approximately 2” eccentric from the center of the screen. Following a 500-msec interval,
the target string was presented for 100 msec randomly to the left or right visual field, such
that the inner edge of the string was positioned 2” from the fixation marker. The next trial
was initiated 1.2 set after the subject’s response. Accuracy and reaction time (RT), measured from target onset, were recorded online.
For the lateral prime condition, primes and targets for the critical related, neutral, and
unrelated word trials always appeared in the same visual field. To prevent the prime position
from signalling the target visual field (which might result in anticipatory eye movements),
primes and targets for the “filler” word trials and slightly over half of the nonword trials
were presented in opposite visual fields. Thus, despite the fact that our critical experimental
prime-target pairs were always presented to a single hemisphere, there was no way within
the experiment for target visual field to be predicted from prime location,
Twenty-four subjects received the lateralized prime condition and 24 received the central
prime condition (balanced by sex). Each individual participated in three sessions, separated
by at least one day. Each participant received similar, associated, and similar + associated
lists in separate sessions, with list order counterbalanced across subjects. For each semantic
relation, each sublist was shown to eight central prime and eight lateral prime subjects.
Stimuli were independently randomized for each subject, with the restriction that no more
than three consecutive targets appear in the same visual field or be of the same response
type (word/nonword).
The participants were informed that the experiment investigated how well people could
recognize stimuli they were not looking at directly, and they were told to maintain their
SEMANTIC
AND ASSOCIATIVE
83
PRIMING
gaze on the central cross as long as it was visible. They were instructed to register their
word/nonword
decisions to the second string as quickly and accurately as possible. They
were told that the first (prime) stimulus was a warning signal that the target item was
about to appear.
Results
Although reaction time (RT) was the primary dependent measure,
mixed design analyses of variance were conducted on percentage correct
scores, as well as median RTs to correct responses, for the word target
trials. Trials with response times greater than 3 set were discarded. There
was one between-subjects factor (Prime Location-central,
lateral), and
three within-subjects
factors (Visual Field; Prime Condition-related,
neutral, unrelated; Semantic Relation-similar,
associated, similar + associated). Stimulus items were considered fixed effects since the stimuli
were restricted and did not constitute a random sample of words (Clark,
1973).
Reaction time analyses. Mean RTs are shown in Table 2. As expected,
words in the RVF (680 msec) were recognized faster than those in the
LVF (717 msec) F(1, 46) = 18.25, p < .OOl. In addition, responses were
slower for the Similar list (727 msec) than for either the Associated (683
msec) or Similar + Associated (685 msec) lists, F(2, 92) = 5.10, p <
.Ol. A robust priming effect was also obtained, F(2, 92) = 16.26, p <
.OOl: responses were faster for related trials (679 msec) than for unrelated
(705 msec), t(47) = 5.30, p < .OOl, or neutral (710 msec), t(47) = 6.98,
p < .OOl, trials. However, unrelated and neutral trials did not differ,
t(47) = 1.01, p > .30. In other words, priming was due to facilitation
without inhibition,
which is consistent with an automatic, spreading activation process (Posner & Snyder, 1975).
TABLE
MEAN
REACTION
RELATION,
TIMES
FOR RELATED,
VF,
AND
PRIME
NEUTRAL,
LOCATION
Similar
2
AND
UNRELATED
Ex~r 1
FOR
(LEXICAL
Associated
TRIALS
BY SEMANTIC
DECISION)
Similar +
Associated
LVF
RVF
LVF
RVF
LVF
RVF
Central primes
Related
Neutral
Unrelated
105
109
727
663
689
704
650
695
692
642
668
690
657
691
705
627
612
669
Lateral primes
Related
Neutral
Unrelated
764
778
819
716
747
707
705
738
706
664
689
655
698
751
709
660
698
681
84
CHIARELLO
ET AL.
Figure 1 displays the overall priming effects (RT unrelated-RT
related)
by VF for central vs. lateral primes, separately for each semantic relation.3 It can be seen that the size of this priming effect varied with
Prime Location, F(2, 92) = 4.45, p < .05. With lateralized primes, an
overall priming effect of 12 msec was obtained, while with central primes
41 msec of priming was observed. There was also a Prime Condition X
VF x Semantic Relation interaction which just missed statistical significance, F(4, 184) = 2.27, p = .06. Although there were no VF differences in priming for the Associated and Similar + Associated lists,
for the Similar list priming was greater in the LVF (+ 39 msec) than in
the RVF (+ 16 msec). However, the Prime Location x Prime Condition
X VF
x
Semantic Relation interaction, F(4, 184) = 2.83, p < .05,
indicated that the priming asymmetry for the Similar list occurred only
when primes were lateralized. To further investigate the higher order
interaction, separate three-way (Prime Location x Prime Condition
x
VF) ANOVAs were run for Similar, Associated, and Similar + Associated Lists.
Similar Only
Priming was obtained for words related only by semantic similarity,
F(2, 92) = 4.20, p < .05. As mentioned above, these effects differed in
each visual field, F(2, 92) = 3.88, p < .05. The Prime Location x Prime
Condition x VF interaction, F(2, 92) = 4.53, p < .05, was also significant. Post-hoc analyses for this list verified that with central primes,
priming did not interact with VF (F < 1) while with lateral primes this
interaction was highly significant, F(2, 92) = 7.81, p < .OOl. Thus, when
both prime and target are lateralized, facilitation for categorically related
primes is found only for words input to the right hemisphere.
Associated Only
Priming was also obtained for words related only via association, F(2,
92) = 7.81, p < .OOl. The Prime Location x Prime Condition interaction,
F(2, 92) = 5.25, p < .OOl indicated that these effects varied with prime
position. While robust priming occurred with central primes, this effect
disappeared when primes were lateralized. Since there were no VF interactions, this indicates that when associated prime information is available to both hemispheres, equal priming occurs in each VF. But, when
the same associated primes are directed to either the left or the right
3 In conformity with most other investigators, we use RT related-RT unrelated as our
measure of priming, rather than RT neutral-RT related. It is our experience that latencies
in the neutral condition are more variable
than those in either the related or unrelated
condition. Thus, a larger number of neutral trials is necessary to obtain stable RTs than
is present in the smallest cells of our design.
SEMANTIC
I
AND ASSOCIATIVE
SIMILAR
\SSOCI
85
PRIMING
SIM + ASSOC.
ATED
u
CENTRAL
LATERAL
:ENTRAL
LATERi
CENTRAL
LATERAL
FIG. 1. Overall priming effect (RT unrelated - RT related) in each visual field for the
three semantic relations with central and lateral primes (Expt I).
hemisphere, neither hemisphere displays any facilitation.
this surprising result further below.
We will discuss
Similar + Associated
RT priming was also obtained for words related by both similarity and
association, F(2, 92) = 11.44, p < .OOl. However, this effect did not
interact with either VF (F < 1) or Prime Location (p > .12). Thus,
priming for these most strongly related words occurred regardless of
whether the prime was immediately
available to both hemispheres or to
either hemisphere alone. Further, these effects did not differ over visual
fields.
Percentage Correct Analyses
Mean accuracy scores are shown in Table 3. Overall, greater accuracy
was obtained for words in the RVF (85.6%) than for words in the LVF
(80.0%), F(1, 46) = 10.85, p < .Ol. In addition, performance was worse
for the similar list (81.2%) than for either the associated (83.9%) or
similar + associated (83.3%) lists, F(2, 92) = 3.85, p < .OS. There were
also significant priming effects, F(2, 92) = 15.91, p < .OOl: accuracy
was higher for related trials (85.6%) than for unrelated (81.4%), t(47) =
5.37, p < .OOl, or neutral (81.5%) trials, t(47) = 5.21, p < .OOl . However,
performance on neutral and unrelated trials did not differ (t < 1). Thus,
as was found with RT, priming was entirely due to facilitation for related
primes; no inhibition with unrelated primes was found.
As with RT, greater priming was obtained with central (+ 6.7%) than
with lateral (+ 1.8%) primes, F(2, 92) = 5.26, p < .Ol. No other inter-
86
CHIARELLO
ET AL.
TABLE
3
MEAN PERCENTAGE CORRECT FOR RELATED, NEUTRAL, AND UNRELATED
SEMANTIC RELATION, VF, AND PRIME LOCATION FOR EXPT 1 (LEXICAL
TRIALS BY
DECISION)
Similar
+
Associated
Associated
LVF
RVF
LVF
RVF
LVF
RVF
Central primes
Related
Neutral
Unrelated
81.0
76.6
76.8
87.2
86.2
85.4
87.5
81.0
80.2
89.2
86.5
82.2
91.1
85.4
79.9
92.4
87.4
83.6
Lateral primes
Related
Neutral
Unrelated
79.2
72.6
78.9
87.8
81.5
81.5
81.8
79.5
82.7
85.4
86.9
84.2
77.1
73.8
75.6
87.8
81.0
85.4
actions with Prime Condition were obtained (all Fs < 1.3). Thus, the
small accuracy priming effects we found were constant over VFs and
semantic relations.
Individual
Differences
in Priming
To further investigate the finding that priming via semantic similarity
is greatest for those individuals with the slowest RTs (Hines et al., 1986),
each subject’s overall RT (summed over words, nonwords and visual
fields) for each session was correlated with his or her RT priming effect
(RT unrelated-RT
related) in that session, separately for each visual
field. If the slowest individuals do obtain the largest priming, then these
correlations should be significant and positive. The resulting correlation
coefficients are shown in Table 4. In general, we replicated the finding
of Hines et al. (1986) that similarity priming varies with processing speed.
TABLE
4
CORRELATION COEFFICIENTS FOR INDIVIDUAL’S
OVERALL REACTION TIME AND SIZE OF PRIMING
(RT UNRELATED
- RT RELATED) BY VISUAL FIELD AND CONDITION
FOR EXPT 1 (LEXICAL
DECISION)
Central
LVF
RVF
primes
Lateral
LVF
RVF
primes
* p < .02.
Similar
Associated
Similar
+ Associated
.51*
.62*
.21
.35
.24
.21
.85*
.16
-.I5
- .06
.24
- .25
SEMANTIC
AND ASSOCIATIVE
PRIMING
87
However, it is clear that there is no strong relationship between overall
RT and associated, or similar + associated, priming. In addition, covariation of similarity priming with processing speed was moderate and symmetrical with central primes, but strong and highly asymmetrical,
with
lateral primes. That is, when both primes and targets were lateralized
to the LVF, overall processing speed accounted for 72% of the variance
in priming, yet no relationship was found for the same stimuli lateralized
to the RVF.
Discussion
The low proportion of related primes used in Expt 1 was successful
in obtaining automatic priming. That is, these effects were due to facilitation without inhibition (Posner & Snyder, 1975). In addition, both the
location of the prime (central vs. lateral) and the nature of the semantic
priming relation influenced whether asymmetrical priming effects were
observed. In most conditions, priming was equivalent over visual fields.
However, when both prime and target were lateralized to the same
hemisphere and prime-target
pairs were categorically (but not associatively) related, there was a LVF/right
hemisphere predominance
for
priming. The issues of prime location and semantic relation will each be
discussed in turn.
Prime Location
There were two major effects of prime location: (I) in general, larger
relatedness effects were obtained with central than with lateral primes;
(2) priming asymmetry was observed only with lateral primes. The first
result may seem to compromise our interpretation that automatic priming
was measured. Since automatic effects do not depend on the subject’s
attention to the prime, simply displaying the prime within a visual hemifield should not affect the size of the priming effect. However, it is
important to remember that the smaller lateral priming was due to two
conditions in which priming was completely absent: similar-only primes
presented to the RVF and associated primes in either VF (recall that
with similar + associated primes the priming effect was statistically
equivalent across prime locations). We will argue below that the absence
of RVF priming for semantic similarity indicates that spreading activation
via this relation is a specialized process of the right hemisphere. The
absence of associated-only
priming with lateralized primes is puzzling
(see discussion below). However, since all lateralized priming effects
were not smaller than their corresponding values with central primes,
we would argue that lateralized primes produce more selective effects,
rather than smaller effects in general. Since we obtained no empirical
support for nonautomatic priming (i.e., no inhibition on unrelated trials)
for either prime location, variation in the size of priming with prime
location need not implicate nonautomatic processing with central primes.
88
CHIARELLO
ET AL.
Of greater interest is the appearance of lateralized automatic priming
only when both primes and targets were directed to a single hemisphere.
Thus, at least part of the differing results of previous studies (e.g.,
Chiarello, 1985, vs Chiarello et al., 1987) may be attributable to whether
a single hemisphere initially has sole access to prime information. Theoretically, the prime-target
interval (500 msec) used in this study is sufficient to allow diffusion of prime information to either hemisphere from
central or lateral primes, and visual field differences in priming should
then be a function of target visual field alone. Yet the results (with similar
primes) do not support this interpretation.
It appears that when there
are hemisphere differences in spreading activation, use of a central prime
allows the “inferior”
hemisphere to share in the facilitation produced
by the “superior”
hemisphere. There seems no other way to explain
why priming via semantic similarity occurred for RVF targets with central
primes, but not when the same primes were directly presented to the
RVF. Thus, the most sensitive measure of hemisphere differences in
priming requires lateralization
of prime, as well as target, information.
Semantic
Relation
Since evidence for lateralized spreading activation was found only with
lateral primes, we will focus our discussion on the latter condition. Our
major finding was hemisphere equivalence in priming for words related
via both similarity and association, but right hemisphere predominance
for priming based on similarity alone. The latter result confirms the
previous findings of Chiarello (1985) and Michimata
(1987), while the
former result suggests that not all spreading activation is greater for
stimuli input to the right hemisphere. Our findings indicate that the right
hemisphere alone may have automatic access to semantic category
relatedness.
Our right hemisphere results partially confirm the findings of Hines et
al. (1986) that activation can spread between nonassociated words related
by category membership.
However, Hines et al. found this effect only
for primes of very high category dominance. That is, they obtained
priming for the most highly dominant category member, but not for the
fifth most dominant item. We did not select our similar-only primes based
on category dominance, which resulted in quite a broad range on this
scale (approximately
two-thirds were ranked between 1 and 5 in category
dominance, while one-third had even lower dominance). Thus, it is unlikely that our LVF similar priming result depended on only very dominant category members. It will be interesting to systematically
vary
category dominance in future lateralization
studies to ascertain whether
evidence for left hemisphere similarity priming could be found if only
the most highly dominant category members were used.
Our results do support the finding of Hines et al. that categorical (i.e.,
SEMANTIC
AND ASSOCIATIVE
PRIMING
89
similar-only) priming is related to overall response time. Subjects having
the slowest latencies also had the largest priming effects. This suggests
that for fast responders lexical access may be complete before activation
has had time to spread between members of the same semantic category.
Since neither associative nor similar + associative priming was related
to response latency in our study, we may speculate that spreading activation for these relationships is fast enough to produce priming in even
the faster responders. We will consider these issues further after presenting the results of Expt 2.
Priming for words related by similarity and association was never
greater than that for either relationship alone. Thus, there was no evidence for additivity or summation of spreading activation in either hemisphere. However, conclusions about lack of additivity
when lateral
primes were used must remain tentative since no priming, in either VF,
was found for words related only via association. This was an unexpected
and surprising result. Robust associated-only priming has been found in
several studies using central presentation of primes and targets (e.g.,
Seidenberg et al., 1984; Lupker, 1985) and in this investigation when
central primes were shown. Thus, it is unlikely that there was something
peculiar about the particular set of stimuli we used. Before attempting
to “explain”
this finding, it is important to determine whether it is
replicable. Thus, we postpone further discussion until after presenting
the results of Expt 2.
The results of Expt 1 do not speak to the issue of possible task differences in priming. It could still be argued that our finding of similarity
priming in Expt 1 was due not to spreading activation, but to postaccess
processing which can occur in the lexical decision task (Lupker, 1984).
To answer this criticism we repeated the lateral prime condition of Expt
1 using naming, rather than lexical decision, as our measure of word
recognition. If categorical priming reflects postaccess semantic integration, rather than automatic spreading activation, then no priming should
be observed in this condition using a naming task (Seidenberg, 1985).
However, if spreading activation does occur via semantic similarity in
the right hemisphere, then we should observe equivalent priming across
tasks. In experiment 2 we used the naming task to test this hypothesis
and to determine the reliability of our other priming results with a new
sample of subjects.
EXPERIMENT 2: NAMING
Method
Subjects.
Twenty-four right-handed members of the university community (undergraduates, graduate students, and volunteers; 12 male, 12 female) participated for a small
monetary payment. They were all native English speakers with no immediate left-handed
relatives; none had participated in Expt 1. Mean handedness index was +0.76.
Stimuli. Stimuli consisted of the word pairs used in the lateral prime condition of Expt 1.
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CHIARELLO
ET AL.
Apparatus and procedure.
Stimulus display apparatus was the same as that employed
in Expt 1. Subject responses were recorded via a Sound Grabber microphone (Crown
International Model 12 SG) which was interfaced to the laboratory computer. Primes were
laterally presented for 100 msec; after a SOO-msec interstimulus interval, target words were
shown for 100 msec. Instructions were similar to those for Expt 1, except that subjects
were asked to pronounce the target word as quickly and accurately as possible, guessing
if necessary. Vocal reaction time, measured from target onset, and response accuracy
were recorded on-line. The latter was determined by the experimenter who was in a separate
room monitoring performance via headphones. As soon as the subject responded, the
experimenter entered an accuracy code into the computer. In the event of a spurious vocal
response (a cough, for example), a zero was entered, and such trials were not analyzed.
Results
Mean reaction time to correct responses, and overall priming effects,
are given in Table 5, and percentage correct scores in Table 6. As
indicated in these tables priming results for naming were similar to those
obtained in lexical decision. We first report analyses for the naming task
(Expt 2): repeated measures ANOVAs examining VF, Prime Condition,
and Semantic Relation. Next, to permit examination of possible task
differences, the results from this naming experiment and those from the
lateral prime condition of Expt I (lexical decision)
were compared
via
mixed design analyses of variance. Task was a between-subjects factor,
and Visual Field, Prime Condition, and Semantic Relation were withinsubjects factors.
Naming
As expected, words in the RVF (775 msec) were named faster than
those in the LVF (798 msec), F(1, 23) = 7.45, p < .02. There was also
a significant RT priming effect, F(2, 46) = 4.50, p < .02: responses were
faster for related trials (777 msec) than for unrelated (792 msec) t(23) =
2.91, p < .005, or neutral (791 msec), t(23) = 2.54, p < .02, trials.
Unrelated and neutral trials did not differ, t < 1. Thus, as in Expt 1,
priming was attributable to facilitation without inhibition.
The priming
MEAN
OVERALL
REACTION
PRIMING
TIMES
EFFECT,
TABLE
(msec)
5
FOR RELATED,
BY SEMANTIC
RELATION
NEUTRAL,
AND UNRELATED
TRIALS,
AND
AND VISUAL
FIELD FOR EXPT 2 (NAMING)
Similar
LVF
Similar +
Associated
Associated
RVF
LVF
RVF
LVF
RVF
783
780
-770
-13
782
812
-806
+24
760
795
-790
+30
Related
Neutral
Unrelated
774
794
-811
765
760
-773
796
803
-802
Priming
+37
+8
f6
SEMANTIC
MEAN
AND
ASSOCIATIVE
TABLE
PERCENTAGE CORRECT FOR RELATED,
SEMANTIC RELATION AND VISUAL
Similar
Related
Neutral
Unrelated
91
PRIMING
6
NEUTRAL, AND UNRELATED
FIELD FOR Expr 2 (NAMING)
TRIALS, BY
Similar +
Associated
Associated
LVF
RVF
LVF
RVF
LVF
RVF
81.1
91.1
89.0
89.7
84.6
83.8
86.0
92.4
90.7
89.2
83.0
83.0
84.8
94.0
90.5
91.1
78.7
80.5
effect differed over the three semantic relations, F(4, 92) = 2.81, p <
.05. Priming was obtained for words related only via similarity (+ 22
msec), F(l, 69) = 6.96, p < -02, and for words which were both similar
and associated (+ 28 msec), F( 1, 69) = 10.49, p < .005. However, there
was no priming for words related only by association (- 4 msec, F <
1). There were no other significant findings for reaction time.
The only significant finding for accuracy was a main effect of VF, F( 1,
23) = 29.14, p < .OOl. Words shown in the RVF were named more
accurately than those in the LVF (90.9% vs. 82.8%, respectively).
Lexical Decision and Naming Compared
Reaction time analyses. Responses were faster to words presented in
the RVF (733 msec) than to those presented in the LVF (769 msec), F( 1,
46) = 28.16, p < -001. There was also a nonsignificant trend for subjects
in lexical decision to respond faster (716 msec) than those in naming
(786 msec), F(1, 46) = 3.27, p = .08. A Task x Semantic Relation
interaction, F(2, 92) = 3.02, p = .05, indicated that for lexical decision,
slowest responses occurred for the similar list, F(2, 92) = 4.39, p < .05,
while there were no differences between lists for naming (F < 1). There
was also a Task x VF interaction, F(l, 46) = 3.90, p = -05: a larger
RVF advantage was obtained for lexical decision (50 msec), than for
naming (24 msec).
A robust priming effect was observed, F(2, 92) = 11.91, p < .OOl.
Responses were faster for related trials (739 msec) than for unrelated
(752 msec), t(47) = 3.00, p < .Ol or neutral (762 msec), t(47) = 5.09,
p < .OOl, trials. Neutral trials were also slower than unrelated, t(47) =
2.15, p < .05. Thus, as in Expt 1, there was no evidence for inhibition
on unrelated trials.
Priming was not equivalent for the three semantic relations, F(4, 184)
= 3.27, p < .02. Post-hoc contrasts indicated that there was no reliable
priming for the associated list (- 4 msec), F < 1, while priming was
obtained for the similar (+ 22), F(l, 276) = 7.69, p < .Ol, and the similar
+ associated (+22 msec) lists, F(l, 276) = 7.15, p < .Ol. However,
92
CHIARELLO
ET AL.
these effects were modified by a Semantic Relation x Prime Condition
x VF interaction,
F(4, 184) = 2.53, p < .OS. Post-hoc analyses indicated
that priming did not differ over VFs for either Associated or Similar +
Associated lists, Fs < 1; however, priming was highly asymmetrical for
the Similar list, F(1, 276) = 10.05, p < .Ol. It is important to note that
this priming asymmetry was reliable over tasks; there was no interaction
involving Task, Prime Condition, and Semantic Relation (F < 1). Nor
was there an interaction of these variables with VF ($ > .lO). Thus,
although categorical priming was limited to LVF stimuli, it was not taskdependent, occurring to an equivalent extent in naming as in lexical
decision.
Percentage correct analyses. Words were recognized more accurately
in the RVF (87.7%) than in the LVF (80.4%) F(l, 46) = 27.21, p >
.OOl. Subjects in the naming task were more accurate (86.8%) than those
in lexical decision (81.3%), F(1, 46) = 4.44, p < .05. However, there
were no other effects involving task. A small priming effect was obtained
for accuracy, F(2, 92) = 6.99, p < .Ol: there was a nonsignificant tendency for higher accuracy on related trials (85.4%) than on unrelated trials
(84.1%), t(47) = 1.82, p = .07. Accuracy was poorer on neutral trials
(82.6%) than on either related, t(47) = 3.88, p < .OOl, or unrelated, t(47)
= 2.13, p < .05, trials. The latter effect was primarily due to LVF
scores, F(2, 92) = 3.26, p < .05. That is, accuracy was poorer for
neutral, as opposed to unrelated, trials in the LVF, t(47) = 2.50, p <
.05, but not in the RVF (t < 1). Thus, as we saw for reaction time, there
was no evidence for inhibition on unrelated trials in either VF. None of
the higher order interactions were significant (Fs < 1). Thus, the very
small accuracy priming effects were constant over semantic relations and
tasks.
Zndividual differences in priming. Correlations between each subject’s
overall RT and their reaction time priming effect were computed for the
naming task (Expt 2), as was previously done for the lexical decision
tasks (Expt 1). Table 7 shows the resulting correlation coefficients. None
reached acceptable levels of statistical significance. Based on the results
of Expt 1, we would have expected a much larger correlation in the LVF
for the similar list. Although this correlation coefficient is in the expected
TABLE
I
CORRELATION COEFFICIENTS FOR INDIVIDUAL’S
OVERALL REACTION TIME (msec) AND SIZE
OF PRIMING (RT UNRELATED - RT RELATED) BY VISUAL FIELD AND CONDITION FOR Exm 2
Similar
LVF
RVF
.37
- .22
Associated
-.04
- .36
Similar + Associated
.14
.18
SEMANTIC
AND
ASSOCIATIVE
PRIMING
93
direction, the relationship between size of categorical priming and overall
response time was not nearly as strong for naming as for lexical decision.
Discussion
The results of Expt 2 can be summarized very succinctly. The priming
effects we obtained in Expt 1 were replicated. No interactions with task
were found. Our combined analyses demonstrate that similarity priming
was greater in the LVF than the RVF, associative priming was not found
in either VF, and similar + associative priming was equivalent over
VFs. These results provide further evidence for a spreading activation
interpretation
of our priming effects. The finding of similarity priming
using a naming response makes it unlikely that these effects may have
been due to postaccess processing.
In our lateralization
paradigm naming responses were not faster than
lexical decisions. This is in contrast to the results obtained with central
presentation, where lexical decision latencies are typically slower than
those for naming (Theios & Muise, 1977). Chiarello, Nuding, and Pollock
(1988), using lateralized presentation,
also reported no differences in
response speed for these tasks. Our similar response latencies for naming
and lexical decision were accompanied by comparable priming effects
across tasks, even for categorically related words. This suggests that
task differences in automatic priming, when they occur, may be attributable to slower lexical decision latencies (Flores d’Arcais et al., 1985)
rather than to postaccess semantic integration for lexical decisions (Lupker, 1984).
The only major difference in the results of naming and lexical decision
was the correlation of response speed with similarity priming for the
latter, but not the former. Although there was a trend in the same direction, no strong relationship for naming could be found. Whether this
reflects a true task difference, or simply a different range of variability
among two groups of subjects, cannot be determined at this point. However, since Hines et al. (1986) found the correlation using a naming task,
task differences do not seem a likely candidate for our failure to obtain
this result in Expt 2.
GENERAL DISCUSSION
The purpose of this study was to investigate the spreading activation
process within each cerebral hemisphere, and to ascertain the conditions
under which lateral differences in automatic priming would occur. Most
previous studies had obtained equivalent automatic semantic priming
over visual fields (Marcel & Patterson, 1978; Chiarello et al., 1987; Burgess & Simpson, 1988a). Yet two studies reported greater LVF than
RVF automatic priming (Chiarello, 1985; Michimata,
1987). We investigated two possible sources for these discrepancies: the location of the
94
CHIARELLO
ET AL.
prime word and the nature of the semantic relationship between prime
and target. In addition, we considered whether any of our priming effects
might be task-dependent. Although no task differences were found, both
prime location and semantic relation proved to be important determinants
of lateralized priming,
and by inference, hemisphere differences in
spreading activation. We will now consider the thoeretical significance
of each of our major findings.
Priming
for Lexical Decision
vs. Naming
The similarity of our priming results over tasks is significant because
task differences have played an important role in elucidating the mechanism responsible for priming (c.f. Seidenberg et al., 1984). It had been
argued that because lexical decision involves a binary decision process,
semantic relatedness could influence this postaccess judgment in addition
to producing spreading activation (Forster, 1981; West & Stanovich,
1982). Since naming does not include such a decision component, priming
effects for naming have been taken to be a “purer” measure of spreading
activation. Indeed, a number of priming results have been reported for
lexical decision, but not for naming (Seidenberg et al., 1984; Lupker,
1984).
In our study no task differences were observed, which offers no support for the postaccess interpretation.
However, little attention has been
given to task differences in response speed as a possible explanatory
factor. In this study, naming was not faster than lexical decision and the
expected task differences in categorical priming did not occur. It is
important to point out that our average response times were quite a bit
slower than those which are typically found under standard viewing
conditions which employ longer target durations. Presumably lexical access is slowed by the data limitations which accompany lateralized presentation. Because target word processing is slowed, information activated
by the prime will have more time to spread before a response to the
target becomes available. This will increase the temporal “window”
during which priming effects can be manifested. Our results suggest that
it is this temporal window which is responsible for the occurrence of
automatic priming effects, rather than task-specific processing requirements. By allowing a longer than normal window, we were able to
observe priming effects for naming which are typically seen only for
lexical decision. Flores d’Arcais et al. (1985) found a similar result when
they masked target words in a naming task. Thus, we infer that when
response times are equated, task differences in automatic priming will
not occur.
Central vs. Lateral Primes
One important result of this study was the demonstration that laterally
presented primes yield a different profile of hemispheric processing than
SEMANTIC
AND ASSOCIATIVE
PRIMING
95
do centrally presented primes. Evidence for hemisphere-specific
automatic priming occurred only when both prime and target information
were directed to the same cerebral hemisphere. Thus, future investigations of spreading activation within the cerebral hemispheres should
employ lateralized primes.
But why should prime location make a difference when the ptimetarget interval (500 msec) greatly exceeds interhemispheric
transfer time?
Theoretically,
prime information
should be available to either hemisphere, regardless of prime location, by the time the target word is shown.
One would then expect that lateralized effects would depend only on
target visual field. However, it appears that lateralized effects may depend on the initiation of prime processing in one or both hemispheres,
rather than whether interhemispheric
transfer can occur once processing
has been initiated.
With tachistoscopic
presentation,
central primes
would immediately
stimulate each hemisphere, but each hemisphere
would receive different, and incomplete, informaton (i.e., the left hemisphere would receive letters at, and to the right of, fixation, while the
right hemisphere would receive letters at, and to the left of, fixation).4
Thus, interhemispheric
sharing of prime information would be necessary
to produce a complete percept. This need not occur when the prime is
presented entirely within one visual half-field. We can speculate that the
process of combining prime information across hemispheres also induces
interhemispheric
sharing of the activation produced by the prime. In
contrast, it may be that when primes are lateralized, activation initiated
by a single hemisphere is not shared with the other. This would then
give us a more accurate picture of how spreading activation operates
within each individual hemisphere.
Similar, Associative,
and Similar + Associative Priming
Since evidence for hemisphere-specific
priming occurred only with
lateral primes, we will focus our discussion of the three semantic relations
on this condition. Our most theoretically
important result was the differential effect of type of semantic relatedness on priming within the left
and right hemispheres. Before discussing the implications of the similar
and similar + associated conditions, we need to discuss the surprising
absence of priming for associated-only words. This result was replicable
over tasks, and thus cannot be ignored.
Only a few previous investigators have examined priming for words
that are associated, but not semantically similar (Kreusi, 1978; Lupker,
4 There is little consensus on the extent of bilateral representation of the fovea, although
l-1.5” is a frequently cited figure (McKeever, 1986). Since our primes ranged between 1.4
and 2.9”, it is reasonable to assume that, in most cases, complete information was not
directly transmitted to both hemispheres.
96
CHIARELLO
ET AL.
1984; Seidenberg et al., 1984) and none used lateralized presentation.
It should be reiterated that although most priming studies use associated
words, many of these are also categorically related (Cat-Dog, DoctorNurse). Thus, there is remarkably little data on the conditions under
which purely associative priming can be demonstrated.
However, the
three previous studies, and our own using central primes, all produced
robust associative priming. It is all the more surprising, then, that this
effect vanished when primes were laterally presented.
Two interpretations
can be considered. One seemingly unlikely possibility is that interhemispheric
sharing of prime information is needed
for associative priming to occur. That is, both hemispheres must “combine forces” for this effect to be manifest. We have already argued that
this is less likely to occur when primes are lateralized. While this account
is consistent with our data, it has no a priori theoretical basis. However,
it should be noted that in the only investigation of semantic priming with
split-brain patients, no consistent priming was observed in either isolated
hemisphere (Zaidel, 1983). Although the primes used in the Zaidel study
were said to be associated, we do not know how many, if any, were
also semantically similar. Thus, at the moment, we are left with some
weak empirical support for the interhemispheric
sharing view, but no
compelling theoretical rationale.
A second possiblity focuses on the fact that, when stimuli are lateralized, they also undergo significant data limitations
(Sergent, 1983).
Perhaps associative priming requires a more stable percept (i.e., higher
stimulus quality) than does priming for similar + associated words. We
suggest a theoretical rationale for this position below. This view does
lead to some testable predictions. One could employ a central prime,
but directly manipulate stimulus quality by masking, blurring, or filtering.
If associated-only priming was more vulnerable to such manipulations
than similar + associated priming, then this interpretation could be supported. Alternatively,
one could employ lateral primes, but increase their
perceptual salience by increasing their size, contrast, or exposure duration. The perceptual quality interpretation
would be supported if associative priming could be demonstrated in either visual field under less
limited conditions. On the other hand, if none of the above manipulations
produced associative priming then the interhemispheric
sharing view
would receive some indirect support.
We did observe significant priming with words related via similarity
or similarity
+ association. In the former case, priming was asymmetrical, with a LVF/right hemisphere predominance, while in the latter case
the effects were symmetrical over visual fields. This suggests that spreading activation via categorical links is a function of the right cerebral
hemisphere. However, spreading activation in general is not greater for
words input to the right hemisphere since priming for similar words which
SEMANTIC
AND
ASSOCIATIVE
PRIMING
97
are also associated was equivalent across hemispheres. Thus, it is the
categorical relationship per se, rather than some more general semantic
phenomenon,
for which a unique right hemisphere role is implicated.
These findings provide an explanation for why greater LVF automatic
priming was found only occasionally in previous studies (Chiarello, 198.5;
Michimata,
1987).
It is important at this point to consider the theoretical implications
of
our results regarding the cognitive architecture of the cerebral hemispheres. But first we will clarify our view of the relationship between
lexical and semantic memory with respect to the representation of meaning. In our view, lexical and semantic memory are separate structures
(see also Collins & Loftus, 1975). Lexical memory contains the phonological and orthographic codes required to create a form-based representation from the perceptual input. These form-based lexical units serve
as pointers to their corresponding semantic units, but the representation
of meaning, except for associative relations,’ is not part of lexical memory
(for a related view see Fodor, 1983).
We will discuss our results in the context of how we think the processing of these semantic representations varies between the two hemispheres. Important to our proposal is the notion of semantic flexibility.
That is, that a word is composed of a constellation of semantic features
and that the retrieval and/or selection of the meaning of a word depends
on contextual factors. We propose separate accounts for semantic (i.e.,
categorical) and associative priming effects. Priming attributable to semantic feature similarity occurs as a result of spreading activation between similar features in semantic memory. Associative priming is a
function of the associative relationship that exists between the lexical
form of the prime and target.
Figure 2 presents a schematic representation of lexical and semantic
memory for our three prime-target
relationships. Words are represented
at the semantic and lexical levels. At the lexical level the word consists
of its orthographic (and phonological) code. The nature of the representation is different at the semantic level, where a word consists of a
constellation of semantic features, rather than a single word node. For
example, in Fig. 2a, Lawyer is represented as a single node lexically,
but is a constellation
of four (an arbitrary number) semantic features.
The direction of activation flow in memory is designated by directional
links between nodes and/or features. Note in Fig. 2a that Lawyer and
Nurse share a feature which designates the featural overlap between
’ Another
exception
includes
those lexical
parser and have redundant
semantic features.
for a low-level
lexical feature that may guide
part of the semantic
code.
features
that may provide
guidance
to the
For example,
animacy
would be a candidate
thematic
role assignment,
but would also be
CHIARELLO
98
ET AL.
a
SEMANTIC
EFFECTS
b
SEMANTIC
+ ASSOCIATIVE
EFFECTS
1
semantic
2
3
4
5
3
4
5
6
\/PU
ACSSOCIATIVE
semantic
lexical
EFFECTS
1
2
/farmer/-
7
8
/Plow/
FIG. 2. Fragment of the proposed lexical and semantic networks for the three semantic
relations. Numbers represent the semantic features which make up the word’s meaning,
and a word’s lexical (form-based) representation is shown immediately below. Arrows
denote the hypothesized flow of activation, and not necessarily the direction of association.
these two words. It is also possible for activation to spread between two
lexical nodes, as shown by the link between Farmer and Plow in Fig.
2c. The precise implications
of these three network arrangements are
discussed below.
(I) Semantic relationships. The similar-only effect was isolated in the
right hemisphere, while similar + associated priming did not vary with
VF/hemisphere.
Since we did not find associative priming in either hemisphere we would not expect it to be contributing to the priming obtained
in the similar + associated condition. Consequently we are required to
distinguish between the semantic relationships in these two conditions.
It has been implicit in previous priming studies that the degree of semantic
similarity was comparable in the two conditions. However, we suggest
that there is more semantic feature overlap between prime and target
for similar + associated pairs than for similar-only
stimuli. This is il-
SEMANTIC
AND
ASSOCIATIVE
PRIMING
99
lustrated in Figs. 2a and 2b. Intuitively
this can be seen by comparing
stimuli from the similar-only (Lawyer-Nurse,
Lamp-Chair,
Arm-Nose)
and the similar + associated (Doctor-Nurse,
Sofa-Chair,
Arm-Leg)
lists. It appears that pairs such as Doctor-Nurse
have a higher degree
of semantic similarity than do pairs such as Lawyer-Nurse.
That is, the
former share more semantic features than the latter. We propose that
hemispheric asymmetries in semantic retrieval may depend on these
variations in feature overlap.
We have suggested elsewhere that left hemisphere semantic processing
operates in a focal manner, with rapid selection of one meaning and
suppression of other potential candidates, while right hemisphere semantics operate more diffusely, with activation spreading to a broader
range of semantic candidates over an extended time course (Burgess &
Simpson, 1988a; Burgess & Rosen, 1988; Chiarello, 1988~). Within this
framework relationships defined by less featural overlap may not have
an opportunity to emerge in the left hemisphere. Assuming that the left
hemisphere is a rapid “winner-take-all”
system (McClelland
& Rumelhart, 1981), activation may not be maintained for items with minimal
overlap since targets with less feature overlap will tend to be inhibited
as a result of the activation of stronger candidates. However, priming
will be observed for targets which share a high proportion of semantic
features with the prime. Conversely, the right hemisphere uses slower
and less selective processes which allow priming between items with
little featural overlap. Consistent with this interpretation
is the finding
that our slower subjects tended to be those who showed LVF categorical
priming.
However, slow processing speed, in and of itself, cannot entirely account for our results. Recall that with central primes, responses were
faster in general than with lateralized primes. Yet RVF categorical priming was obtained in the former, but not in the latter, condition. If response
speed were the only determining
factor the opposite result would be
expected. Thus, we argue that it is processes specific to the right hemisphere that allow for the maintenence of activation.
(2) Associative
relationships.
The lack of an associative priming effect
(in either VF) when the prime is lateralized is counterintuitive.
Our
proposal, while speculative, suggests that prime information
must be
sufficiently processed to enable the prime to reach threshold before activation spreads to associated items. This assumes a crucial difference
with respect to the point at which activation spreads from a lexical node
either to a set of semantic features or to another lexical node. As the
lexical representation of the prime is activated, some threshold must be
reached for activation to spread to the associates of the prime. In contrast, activation spreads continuously to the prime’s corresponding semantic features. In other words, activation quickly passes to semantic
100
CHIARELLO
ET AL.
features via a cascaded process (McClelland,
1979), while some threshold
must be met before activation will spread to associated lexical nodes.
We conjecture that the lateralized prime did not allow the lexical threshold to be reached. Hence no associative priming effects were seen.
While this proposal is admittedly speculative, it is easily testable. When
primes are presented subliminally
(or at least under severe data limits)
no associative priming should be seen. As soon as the prime can be
clearly perceived we would expect the usual relatedness effect. With
respect to hemispheric processing, we would expect this associative
effect to obtain in the left hemisphere since there is a close correspondence between these overlearned sequential associations and language
production (and comprehension).
The role of right hemisphere processing
with these relationships is less clear, and will require further investigation
(Miller, 1969).
To summarize, our preliminary
conclusion is that the hemispheres
differ in how semantic representations are automatically
accessed, although we need not postulate structural differences in the lexical or
semantic networks available to each hemisphere. Despite a redundancy
in the general semantic stores of the two hemispheres, characteristic
differences in selection and/or retrieval processes may result in a different set of meanings being accessible to each hemisphere.6 In particular,
our data suggest that relationships due to semantic feature similarity
without association are primarily processed by the right hemisphere. This
extends our previous contention (Burgess & Simpson, 1988b; Burgess
& Hollbach,
1988; Chiarello, 1988~) that there is a unique role for the
right hemisphere in the processing of word meanings.
APPENDIX
Related Prime-Target
Pairs for the Three Semantic
Separated by Sublists
Similar-Only
Sublist A
Table-Bed
Circle-Cross
Roof-Door
Hair-Fur
Pants-Hat
Fox-Horse
Brass-Iron
Velvet-Linen
Relations,
Sublist B
Sublist C
Music-Art
Pan-Bowl
Steel-Brass
House-Cabin
Carrot-Corn
Birch-Elm
Coat-Gown
Apple-Grape
Flea-Ant
Train-Canoe
Lamp-Chair
Bear-Cow
Tulip-Daisy
Burlap-Felt
Ear-Foot
Shoe-Glove
6 We acknowledge that an account
positing hemisphere differences in the structure of
the semantic network is also consistent with our data.
SEMANTIC
Oak-Maple
Garlic-Mint
Arm-Nose
Bean-Onion
Street-Path
Lemon-Pear
Jeep-Plane
Shark-Trout
Associated-only
Sublist A
Cradle-Baby
Waist-Belt
Alley-Cat
Circus-Clown
Miner-Coal
Cloth-Dress
Decoy-Duck
Rug-Floor
Stove-Heat
Hockey-Ice
Rake-Leaf
Wave-Ocean
Book-Page
Onion-Tears
Spider-Web
Sheep-Wool
Similar + Associated
Sublist A
Ale-Beer
Sofa-Chair
Jacket-Coat
Wolf-Dog
Inch-Foot
Moth-Fly
Steel-Iron
Sword-Knife
Army-Navy
Doctor-Nurse
Pot-Pan
Ounce-Pound
Figure-Shape
Boot-Shoe
Coffee-Tea
Cotton-Wool
AND ASSOCIATIVE
PRIMING
101
Head-Leg
Drums-Piano
Deer-Pony
Car-Ship
Cotton-Silk
Bacon-Steak
Desk-Stool
Orchid-Tulip
Lawyer-Nurse
Banana-Peach
Stem-Petal
Knife-Pot
Dagger-Rifle
Sugar-Salt
Floor-Wall
Gin-Wine
Sublist B
Sublist C
Mug-Beer
Nest-Bird
Button-Coat
Bone-Dog
Key-Door
Candle-Flame
Bee-Honey
Camel-Hump
Crown-King
Hammer-Nail
Artist-Paint
Farmer-Plow
Shell-Sea
Crew-Ship
Rubber-Tire
Train-Track
Mold-Bread
Engine-Car
Hermit-Cave
Flea-Dog
Gallon-Jug
Cow-Milk
Crater-Moon
Cheese-Mouse
Usher-Movie
Pilot-Plane
Star-Sky
Grocer-Store
Apple-Tree
Fish-Water
Floor-Wood
Harbor-Boat
Sublist B
Sublist C
Uncle-Aunt
Butter-Bread
Mint-Candy
Dog-Cat
Brush-Comb
Nickel-Dime
Silver-Gold
Coat-Hat
Arm-Leg
Tiger-Lion
Road-Path
Pepper-Salt
Basin-Sink
Blouse-Skirt
Lizard-Snake
Sleet-Snow
Ball-Bat
Lotion-Cream
Knife-Fork
Jelly-Jam
Queen-King
Engine-Motor
Dirt-Mud
Tack-Nail
Sea-Ocean
Mouse-Rat
String-Rope
Frown-Smile
Oven-Stove
Shirt-Tie
Brandy-Wine
Man-Woman
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