456 Semantic Memory and Priming
However, the absence of a relation may or may not be infor-
mative depending on the construction of the test list. One
measure of the informativeness of the absence of a semantic
relation is the nonword ratio (NR), which is the conditional
probability that the correct response isnonwordgiven that the
(word) prime and the target are unrelated (Neely et al., 1989).
As the nonword ratio deviates from .5, the absence of a se-
mantic relation between the prime and the target becomes in-
creasingly informative, signaling a nonword response when it
is above .5 and a word response when it is below .5.
The variables that control semantic matching are not well
understood. Neely et al. (1989) manipulated the RP and the
NR independently in a lexical decision task in which primes
were category names and targets were exemplars. The RP
was correlated most strongly with priming for typical exem-
plars (e.g., robinforbird). The NR, however, was correlated
with priming for both typical and atypical (e.g., penguin) ex-
emplars, and with nonword facilitation (defined as faster re-
sponses to nonwords primed by words than to nonwords
primed by a neutral prime). They argued that the effect of RP
on priming for typical exemplars was a true expectancy ef-
fect, as subjects would be likely to generate typical but not
atypical exemplars to category primes. According to Neely
et al., the effect of NR was due to semantic matching. The
nonword facilitation effects are especially consistent with
this interpretation, as, when NR is high, nonword targets will
benefit from a bias to respond nonwordto targets unrelated to
their word primes.
It seems likely that semantic matching is influenced by the
RP and the NR. As the RP increases, semantic relations be-
come more noticeable, and as the NR increases, the absence
of semantic relations becomes more informative. It is worth
pointing out that standard experimental procedures often lead
to NRs over .5, as investigators often use equal numbers of
word and nonword targets, but only use word primes; hence,
the number of word prime–nonword target trials exceeds the
number of unrelated word prime–word target trials.
Semantic matching is probably also influenced by the task
used. Tasks such as lexical decision that require accumulation
of information to make a binary decision are probably more
susceptible to semantic matching than are tasks, such as nam-
ing, that do not involve an explicit decision (e.g., Seidenberg
et al., 1984). McNamara and Altarriba (1988; see also
Shelton & Martin, 1992) have argued that semantic match-
ing, as well as expectancy, can be minimized by using a task
in which the relations between primes and targets are not ap-
parent to subjects. One method of achieving this goal is to use
a sequential or single-presentation lexical decision task. In
this task, stimuli are displayed one at a time, and participants
respond to each as it appears. Primes precede targets in the
test list, but their pairings are not apparent to subjects. Shel-
ton and Martin found that inhibition and backward priming
(e.g., primehop,targetbell;discussed later) did not occur in
the single-presentation task.
Neely and Keefe (1989) have proposed a three-process hy-
brid theory of semantic priming that incorporates expectancy,
automatic spreading activation, and semantic matching. Not
surprisingly, this theory can account for a greater variety of re-
sults than can any one mechanism alone (Neely, 1991). The
important contribution of this theory is that it combines a
model of automatic, attention-free priming with strategic, at-
tention-laden processes. Viewed in this way, one can see that
any of the models of priming outlined earlier in this chapter
could be combined with expectancy and semantic matching
processes.
In summary, two principal types of strategic processes
have been identified, expectancy and semantic matching. Ex-
pectancy is minimized at short SOAs and low RPs; semantic
matching is minimized with an NR of .5 and, we suspect, low
RP as well. Put another way, an investigator interested in the
automatic component of priming would be well served by
using an SOA less than 300 ms, RP of .20 or less, and NR
of .50.
In closing, we should acknowledge that Plaut and Booth
(2000) have shown that it may be possible to account for the
dependence of inhibition on SOA without invoking an ex-
pectancy process. Given all of the evidence implicating the
role of strategic processes in semantic priming, it seems
likely that any model of priming must incorporate strategic
processes of some kind. However, Plaut and Booth’s analysis
suggests that a single-mechanism account of priming may be
able to explain at least some of the phenomena previously at-
tributed to strategic processing.Associative Versus Pure Semantic PrimingAs noted earlier, the term semantic primingis a catch-all
phrase that includes priming caused by many different kinds
of relations, including both associative relations and true re-
lations of meaning. Associatively related words are those
produced in response to each other in free-association tasks,
and they may be semantically related (e.g., dog-cat) or not
(e.g.,stork-baby). Pure semantically related pairs share se-
mantic features or are members of a common category but
are not associatively related (e.g., goose-turkey).
It is well documented that associatively related words
prime each other in lexical decision, naming, and similar tasks.
The controversial issue has been whether priming occurs in the
absence of association. The evidence is mixed. Fischler
(1977b) first investigated priming in the absence of association