448 Semantic Memory and Priming
memory are not independent systems (e.g., McKoon,
Ratcliff, & Dell, 1986), the distinction has been extremely
influential in the field of memory and is useful for organizing
memory phenomena, tasks, and models.
A complete theory of semantic memory should be able to
explain the following phenomena (e.g., E. E. Smith, 1978):
First, a theory of semantic memory should explain how the
meanings of words are mentally represented. It might specify,
for example, that meaning is represented as a collection of
features, some of which are essential and others of which are
just typical (e.g., forbird, animate,andcan fly,respectively).
Second, it should be able to explain how the meanings of in-
dividual words can be combined to form more complex units.
How, for example, is the meaning of a simple noun combina-
tion, such aspet bird,constructed from the meanings of its
constituents,petandbird? Third, the theory should specify
the permissible inferences that can be made from word and
sentence meanings. What can you infer about a grampus if
you know that it is a mammal? This goal is, of course, closely
tied to the first. Fourth and finally, a theory of semantic mem-
ory should explain the connection between word meaning
and the world, between semantic representations and percep-
tual systems. For example, it should explain how we recog-
nize an object from a description, or describe an object based
on perceptual input (e.g., vision, taction, etc.).
As a matter of history, theories of semantic memory have
dealt primarily with the first goal, specifying how word
meanings are mentally represented. There has been a fair
amount of research on how word meanings are combined, but
it has been carried out under the guise of investigations of
concepts and categorization (see the chapter by Goldstone &
Kersten). Very little attention has been given to the third and
the fourth goals by cognitive psychologists. Our goal in this
section of the chapter is to review some of the major theoret-
ical and empirical developments in the field of semantic
memory. We begin by summarizing the models developed
during the late 1960s and the 1970s, the golden age of se-
mantic memory research. We then turn to a brief review of
some of the major empirical challenges posed during that
time. We close with a brief review of recent models of
semantic memory.
Early Models of Semantic Memory
The early models of semantic memory were of three basic
types: network models (e.g., Collins & Loftus, 1975; Collins &
Quillian, 1969; Glass & Holyoak, 1974; Quillian, 1967); set-
theoretic models (D. E. Meyer, 1970); and feature models
(e.g., McCloskey & Glucksberg, 1979; E. E. Smith, Shoben, &
Rips, 1974). Two of these models turned out be extremely
influential: the spreading-activation theory of Collins and
Loftus (1975) and the feature-comparison theory of E. E.
Smith et al. (1974). We focus our attention on these two mod-
els. For a comprehensive review of the other models, consult
E. E. Smith (1978).Spreading-Activation Theory of Semantic ProcessingThe spreading-activation theory of semantic processing pro-
posed by Collins and Loftus (1975) is an elaboration of the
hierarchical network model proposed by Quillian and Collins
(e.g., Collins & Quillian, 1969; Quillian, 1967). A unique fea-
ture of the model, at least in the context of psychological mod-
els of semantic memory, is that it distinguishes knowledge of
the meanings of concepts from knowledge of their names.
The conceptual network is organized according to seman-
tic similarity. Concepts are assumed to be represented as
nodes in a network. The more properties two concepts have in
common, the more links that exist between the two nodes. For
example,carandtruckwould have many links between them,
whereascarandapplewould have few links. In the original
hierarchical network model, several types of links were dis-
tinguished (e.g., superordinate and subordinate, modifiers,
disjunctive sets, etc.). This rich array of link types allowed the
model to account for a wide variety of semantic decisions
(e.g., Quillian, 1969). However, the different link types did
not play an important role in the elaborated theory.
The names of concepts are stored in a lexical network or-
ganized according to phonemic similarity. Thus, for example,
several links would exist between the nodes for carandbar,
but no links would exist between the nodes for carandbus.
Each node in the lexical network is connected to at least one
node in the conceptual network.
The fundamental retrieval mechanism is spreading activa-
tion. Concepts are activated by being mentally processed in
some manner; for example, thinking about or seeing apples
would activate the corresponding concept in semantic mem-
ory. Activation spreads from a concept along links through-
out the network and decays with distance in the network; that
is, the farther the activation spreads, in terms of number of
links traversed, the less arrives at the destination. Activation
also requires more time to spread greater distances. Activa-
tion is released from a concept as long as it is processed, but
only one concept can be actively processed at any one time,
and therefore only one concept can be a source of activation.
Activation gradually decays with time if no concepts in the
network are being processed.
Several ancillary processing assumptions are made to han-
dle particular semantic judgments. One such assumption is
that people can control whether to activate the conceptual