Semantic Priming 453approximately three fourths of LSA’s vocabulary gain from
reading a passage of text was in words not even present in
the paragraph. This finding helps to explain, according to
Landauer and Dumais (1997), why people can have more
knowledge than appears to be present in the information to
which they have been exposed.
Summary
The first models of semantic memory appeared in the late
1960s, and by the mid-1970s at least half a dozen compre-
hensive models had been proposed. The two most influential
models were the network model proposed by Quillian,
Collins, and Loftus (e.g., Collins & Loftus, 1975; Collins &
Quillian, 1969; Quillian, 1967) and the feature-comparison
model proposed by E. E. Smith et al. (1974). These models
became, and largely remain, the canonical models of seman-
tic memory. Although these early models are no longer
considered to be viable accounts of semantic memory, they
remain influential because they provide useful ways of con-
ceptualizing and categorizing memory phenomena.
Distributed network models offered an entirely different
way of thinking about knowledge representations. In tradi-
tional models of semantic memory, concepts were represented
by localized nodes or features, and the relations between
concepts were either stored in the links (network models) or
computed on the fly (feature models). In distributed network
models, however, concepts are represented by patterns of acti-
vation across many units, which participate in representing
other concepts, and knowledge about the relations between
concepts is represented across many connection weights,
which participate in representing other relations. There is no
indication that the influence of these models is flagging.
High-dimensional spatial models also use distributed
representations. In these models, however, the meaning of a
concept is given by the company it keeps, in written and (pre-
sumably) spoken language. Concepts are similar to the extent
that they are used in similar contexts. A virtue of these mod-
els is that they demonstrate how knowledge can be acquired
from specific experiences. A significant challenge for the
developers of these models will be to incorporate processing
architectures that will allow the models to be subjected to rig-
orous testing. It remains to be seen how influential these
high-dimensional spatial models will turn out to be.
SEMANTIC PRIMING
Priming is an improvement in performance in a cognitive task,
relative to an appropriate baseline, as a function of context or
prior experience. Semantic priming refers to the improvement
in speed or accuracy to respond to a stimulus when it is
preceded by a semantically related or associated stimulus rel-
ative to when it is preceded by a semantically unrelated or
unassociated stimulus (e.g.,cat-dogvs. table-dog; D. E.
Meyer & Schvaneveldt, 1971). The stimulus to which re-
sponses are made is referred to as thetarget,and the preceding
stimulus is referred to as theprime. The other kind of priming
examined in this chapter is repetition priming, which refers to
an improvement in speed or accuracy to respond to the second
(or subsequent) occurrence of a stimulus relative to the first
occurrence of the stimulus. Semantic and repetition priming
are probably caused by different mechanisms or by different
processing stages (e.g., Durgunoglu, 1988), but because they
have been so influential in the study of human memory, we re-
view both areas of research in this chapter.
Thesemanticinsemantic primingimplies that priming
is caused by relations of meaning, as exist, for instance,
between the conceptsdogandgoat(mammals, domesticated,
have fur, etc.). In fact, the term has also been used to refer
to priming caused by a mixture of semantic and associative
relations, as exist between the conceptsdogandcat. These con-
cepts are semantically related, but in addition, if people gener-
ate associates todog,they listcatwith high frequency (and vice
versa). In contrast,goatalmost never comes up as an associate
ofdog. Consistent with usage in the field, we shall useseman-
tic primingto refer to both kinds of priming, unless we need to
distinguish the two (as in the section “Associative Versus Pure
Semantic Priming”).Models of Semantic PrimingSpreading Activation ModelsSpreading activation was first incorporated into a model of
memory by Quillian (1967); this model was elaborated and
extended by Collins and Loftus (1975), as described previ-
ously. Spreading activation models were also proposed by
Anderson (1976, 1983). Although these models differ in sev-
eral important ways, they share three fundamental assump-
tions: (a) Retrieving an item from memory amounts to
activating its internal representation; (b) activation spreads
from a concept to associated concepts; and (c) residual activa-
tion accumulating at a concept facilitates its subsequent re-
trieval. For example, the visual presentation of a word, such as
lion, activates its internal representation. This activation
spreads to associated concepts, such astiger. If the wordtiger
appears soon after the wordlion,it can be identified more
quickly than normally because it is already partially activated.
Although Collins and Loftus’s (1975) model and Anderson’s
(1983) ACT* model are similar, they differ in important ways.
The Collins and Loftus model (as well as Anderson’s, 1976,
model) assumes that activation takes time to spread from one