Degraded contingency revisited: posttraining extinction of a cover stimulus attenuates a target cue's behavioral control

Abstract

In a Pavlovian conditioning situation, unsignaled outcome presentations interspersed among cue-outcome pairings attenuate conditioned responding to the cue (i.e., the degraded contingency effect). However, if a nontarget cue signals these added outcomes, responding to the target cue is partially restored (i.e., the cover stimulus effect). In 2 conditioned suppression experiments using rats, the effect of posttraining extinction of the cover stimulus was examined. Experiment 1 found that this treatment yielded reduced responding to the target cue. Experiment 2 replicated this finding, while demonstrating that this basic effect was not due to acquired equivalence between the target cue and the cover stimulus. These results are consistent with the extended comparator hypothesis interpretation of the degraded contingency and cover stimulus effects.

Figure 1

The extended comparator hypothesis (Denniston, Savastano, & Miller, 2001) account of the role of a cover stimulus in a degraded contingency preparation. Ovals depict stimulus representations; solid rectangles depict physical events; diamonds represent the comparator process. In accordance with the comparator hypothesis’s account of the relationship between the cover stimulus and the target stimulus, the only second-order comparator stimulus depicted is that for Link 3. CS = conditioned stimulus; S = surrogate outcome.

Figure 2

Experiment 1: Mean time to complete 5 cumulative seconds of licking in the presence of the target CS (X) in Context 2. See Table 1 for treatments. Error bars denote standard error of means. Acq = Acquisition; Cover-Ext = Cover Stimulus-Extinction.

Figure 3

Experiment 2: Mean time to complete 5 cumulative seconds of licking in the presence of the target CS (X) in Context 2. See Table 2 for treatments. Error bars denote standard error of means. Degrade = Degraded Contingency; Cover = Cover Stimulus; Cover-Ext = Cover Stimulus-Extinction; Ctx-Ext = Context Extinction.

Figure 4

Experiment 3: Mean time to complete 5 cumulative seconds of licking in the presence of the surrogate outcome (S) in Context 2. See Table 3 for treatments. Error bars denote standard errors of mean. Acq-S = Acquisition Test S; Degrade-S = Degraded Contingency Test S; Cover-S = Cover Stimulus Test S; and Cover-Ext-S = Cover Stimulus-Extinction Test S.

Figure 5

Simulation of the groups from Experiments 1 and 2 after Stout and Miller’s (2007) implementation of the extended comparator hypothesis. All parameters were the same as those used by Stout and Miller, and the numbers of trials were the same as those used in Experiments 1 and 2 of the present experiments. Acq = Acquisition; Degrade = Degraded Contingency; Cover = Cover Stimulus; Cover-Ext = Cover Stimulus-Extinction; Ctx-Ext = Context Extinction.