362 Conditioning and Learning
trials. However, when cues or outcomes sometimes occur
by themselves during the training sessions, conditioned re-
sponding to the cue (reflecting the outcome) is often slower
to develop (measured in number of cue-outcome pairings)
and is asymptotically weaker (Rescorla, 1968).
There are four possibilities for each trial in which a di-
chotomous cue or outcome might be presented, as shown in
Figure 13.1:
1.Cue–outcome.
2.Cue–no outcome.
3.No cue–outcome.
4.No cue–no outcome.
The frequencies of trials of type 1, 2, 3, and 4 are a,b,c,
andd, respectively. The objective contingency is usually de-
fined in terms of the difference in conditional probabilities of
the outcome in the presence (a/[a+b]) and in the absence
(c/[c+d]) of the cue. If the conditional probability of the
outcome is greater in the presence rather than absence of
the cue, the contingency is positive; conversely, if the condi-
tional probability of the outcome is less in the presence than
absence of the cue, the contingency is negative. Alternatively
stated, contingency increases with the occurrence of a-and
d-type trials and decreases with b-andc-type trials. In terms
of stimulus control, excitatory responding is observed to in-
crease and behavior indicative of conditioned inhibition (see
this chapter’s later section on that topic) is seen to decrease
with increasing contingency, and vice versa with decreasing
contingency. Empirically, the four types of trials are seen to
have unequal influence on stimulus control, with Type 1 trials
having the greatest impact and Type 4 trials having the least
impact (e.g., Wasserman, Elek, Chatlosh, & Baker, 1993).
Note that although we previously described the effect of
spaced versus massed cue-outcome pairings as a qualifier of
contiguity, such trial spacing effects are readily subsumed
under objective contingency because long intertrial intervals
are the same as Type 4 trials, provided these intertrial inter-
vals occur in the training context.
Conditioned responding can be attenuated by presentations
of the cue alone before the cue-outcome pairings, intermin-
gled with the pairings, or after the pairings. If they occur be-
fore the pairings, the attenuation is called theCS-preexposure
(also calledlatent inhibition)effect(Lubow & Moore, 1959);
if they occur during the pairings, they (in conjunction with the
pairings) are calledpartial reinforcement(Pavlov, 1927); and
if they occur after the pairings, the attenuation is calledex-
tinction(Pavlov, 1927). Notably, the operations that produce
the CS-preexposure effect and habituation (i.e., presentation
of a single stimulus) are identical; the difference is in how
behavior is subsequently assessed. Additionally, based on the
two phenomena being doubly dissociable, Hall (1991) has
argued that habituation and the CS-preexposure effect arise
from different underlying processes. That is, a change in con-
text between treatment and testing attenuates the CS-preexpo-
sure effect more than it does habituation, whereas increasing
retention interval attenuates habituation more than it does the
CS-preexposure effect.
Conditioned responding can also be attenuated by presen-
tations of the outcome alone before the cue-outcome pairings,
with the pairings, or after the pairings. If they occur before
the pairings, the attenuation is called theUS-preexposure
effect(e.g., Randich & LoLordo, 1979); if they occur during
the pairings, it (in conjunction with the pairings) is called the
degraded contingency effect(in the narrow sense, as any
presentation of the cue or outcome alone degrades the objec-
tive contingency, Rescorla, 1968); and if they occur after the
pairings, it is an instance ofretrospective revaluation(e.g.,
Denniston, Miller, & Matute, 1996). The retrospective reval-
uation effect has proven far more elusive than any of the other
five means of attenuating excitatory conditioned responding
through degraded contingency, but it occurs at least under
select conditions (Miller & Matute, 1996).
If compounded, these different types of contingency-
degrading treatments have a cumulative effect on condi-
tioned responding that is at least summative (Bonardi & Hall,
1996) and possibly greater than summative (Bennett, Wills,
Oakeshott, & Mackintosh, 2000). A prime example of such
a compound contingency-degrading treatment is so-called
learned irrelevance, in which cue and outcome presentations
truly random with respect to one another precede a series of
cue-outcome pairings (Baker & Mackintosh, 1977). This
pretraining treatment has a decremental effect on condi-
tioned responding greater than either CS preexposure or US
preexposure.Figure 13.1 Two-by-two contingency table for dichotomous variables; a,
b,c, and dare the frequencies of trial types 1, 2, 3, and 4. See text for details.