Semantic Priming 457and reported a reliable pure semantic priming effect. However,
several subsequent studies (e.g., Lupker, 1984; Moss, Ostrin,
Tyler, & Marslen Wilson, 1995; Shelton & Martin, 1992)
failed to find pure semantic priming under certain conditions;
indeed, Shelton and Martin (1992) concluded that automatic
priming was associative, not semantic. Recent experiments by
McRae and Boisvert (1998) indicate that previous failures to
find pure semantic priming can be attributed to the use of
prime-target pairs that were weakly semantically related.
A recent meta-analysis may bring order to this apparent
chaos. Lucas (2000) examined the results of 26 studies
in which purely semantically related prime-target pairs were
used as stimuli in lexical decision or naming (including
Stroop) tasks. Most of these studies also included asso-
ciatively related primes and targets. The average effect size
(J. Cohen, 1977), weighted by the number of subjects in each
sample, was .25 for pure semantic priming and .49 for asso-
ciative priming. There was clear evidence therefore that pure
semantic priming was present in the studies reviewed and
that associative priming was substantially larger than seman-
tic priming. Because associatively related primes and targets
were usually related semantically, the larger effect size is best
interpreted as an associative boost to priming. Further analy-
ses indicated that the effect size for pure semantic priming
was not influenced by the particular type of lexical decision
task used, RP, or SOA, suggesting that pure semantic priming
was not strategically mediated.
Lucas (2000) also examined whether pure semantic prim-
ing varied with type of semantic relation. Category coordi-
nates (e.g., bronze-gold), synonyms, antonyms, and script
relations (e.g., theater-play) had similar average effect sizes,
ranging from .20 to .27. In contrast, functional relationships
(e.g.,broom-sweep) had an average effect size of .55. This re-
sult supports the hypothesis that functional relations are cen-
tral to word meaning (e.g., Tyler & Moss, 1997). Perceptually
related prime-target pairs, in which primes and targets share
referent shape (e.g., pizza-coin), had a very low effect size of
.05. This estimate must be treated with caution, however, be-
cause only two studies in the corpus examined perceptual
priming of this kind.
In summary, although the evidence on pure semantic prim-
ing has been mixed, with some studies finding evidence of
such priming and others not, Lucas’s (2000) meta-analysis
shows that pure semantic priming does occur and, moreover,
indicates that it may vary as a function of the type of semantic
relation. This conclusion is important because distributed net-
work models of priming strongly predict semantic priming. A
subset of these models can also explain associative priming
(Moss et al., 1994; Plaut & Booth, 2000). Distributed network
models that do not include an associative component will
need to be modified to account for the associative boost to
priming. Spreading-activation and compound-cue models can
easily explain both semantic and associative priming as long
as the appropriate relations are represented in memory.Mediated Versus Direct PrimingMediated priming involves using primes and targets that
are not directly associated or semantically related but in-
stead are related via other words. For example, based on free-
association norms (e.g., McNamara, 1992b), maneandtiger
are not associates of each other, but each is an associate of
lion. The associative relation between a prime and a target
can be characterized in terms of the number of associative
steps or links that separate them: 1-step, or directly related
(e.g.,tiger-stripes), 2-step (e.g., lion-stripes), 3-step (e.g.,
mane-stripes), and so on. Models of priming are distin-
guished based on whether or not they predict priming through
mediated relations.
Early experiments suggested that 2-step mediated priming
occurred in naming but not in lexical decision (e.g., Balota &
Lorch, 1986; de Groot, 1983). Subsequent studies showed
that 2-step, and even 3-step, priming could be obtained in
lexical decision if the task parameters were selected so as
to minimize strategic processing (e.g., McNamara, 1992b;
McNamara & Altarriba, 1988; Shelton & Martin, 1992).
Mediated priming is strongly predicted by spreading acti-
vation models. Certain versions of compound-cue models can
account for 2-step priming, but none predicts 3-step priming
(McNamara, 1992a, 1992b). Most distributed network mod-
els cannot account for mediated priming of any kind. Possible
exceptions are the models proposed by Moss et al. (1994) and
by Plaut and Booth (2000). These models learn associative
relations between words that co-occur frequently during
learning. It is possible that other distributed network models
could be augmented with similar mechanisms.
A serious problem exists, however, in interpreting the
mediated priming results. Although researchers have made
valiant efforts to show that mediated primes and targets
are not directly associated and not semantically related (e.g.,
McNamara, 1992b), there is the nagging possibility that
residual associations or semantic relations still exist. This is a
big problem because if the primes and targets are directly re-
lated in some fashion, all models predict priming between
them. The best way to address this issue is in the context of a
particular model. For example, McNamara (1992b) showed,
using the memory model SAM (Gillund & Shiffrin, 1984),
that if direct associations between 3-step primes and targets
were high enough to produce priming of the magnitude ob-
served, then these primes and targets would have appeared as