A comparator view of Pavlovian and differential inhibition

Abstract

In 3 experiments using rats as subjects, the authors varied trial spacing to investigate the conditions under which Pavlovian and differential inhibition are observed. Experiment 1 compared Pavlovian and differential inhibition with spaced training trials. Spaced trials resulted in only the Pavlovian inhibitor passing both summation and retardation tests. Conversely, Experiment 2 compared these 2 types of inhibition with massed training trials. This training resulted in only the differential inhibitor passing both tests for conditioned inhibition. Finally, in Experiment 3 all subjects experienced Pavlovian inhibition training with massed trials. Although this training by itself did not result in behavior indicative of inhibition, subjects that also experienced posttraining extinction of the training context did pass both tests for inhibition. Overall, these results are anticipated by the extended comparator hypothesis (Denniston, Savastano, & Miller, 2001) but are problematic for most contemporary associative learning theories.

Figure 1

A schematic representation of the extended comparator hypothesis (Denniston et al., 2001) applied to Pavlovian conditioned inhibition. Here, the training excitor A is depicted as the target cue’s first-order comparator stimulus and the training context serves as the target cue’s second-order comparator stimulus. As it applies to differential inhibition, the context replaces A as the first-order comparator stimulus, given the absence of an X–A association, and there is no significant second-order comparator stimulus. Rectangles are physical stimuli and responses, ovals are stimulus representations, and the diamond is the actual comparator process.

Figure 2

Mean times to complete 5 cumulative seconds of drinking upon presentation of the target CS in Experiment 1. Left: Results of the summation test. Right: Results of the retardation test. Note that subjects that served as controls for the summation test (Ret groups) were the target groups for the retardation test, and vice versa. The actual test stimuli are indicated within parentheses. See Table 1 for the treatments of the four groups.

Figure 3

Mean times to complete 5 cumulative seconds of drinking upon presentation of the target CS in Experiment 2. Left: Results of the summation test. Right: Results of the retardation test. Note that subjects that served as controls for the summation test (Ret groups) were the target groups for the retardation test, and vice versa. See Table 1 for the treatments of the four groups.

Figure 4

Mean times to complete 5 cumulative seconds of drinking upon presentation of the target CS in Experiment 3. Left: Results of the summation test. Right: Results of the retardation test. Note that subjects that served as controls for the summation test (Ret groups) were the target groups for the retardation test, and vice versa. All subjects received Pavlovian inhibition training. See Table 2 for treatments of the four groups.