Mechanisms underlying retarded emergence of conditioned responding following inhibitory training: Evidence for the comparator hypothesis.

Abstract

The comparator hypothesis posits that conditioned responding is determined by a comparison at the time of testing between the associative strengths of the conditioned stimulus (CS) and stimuli proximal to the CS at the time of conditioning. The hypothesis treats all associations as being excitatory and treats conditioned inhibition as the behavioral consequence of a CS that is less excitatory than its comparator stimuli. Conditioned lick suppression by rats was used to differentiate four possible sources of retarded responding to an inhibitory CS. These include habituation to the unconditioned stimulus (US), latent inhibition to the CS, blocking of the CS-US association by the conditioning context, and enhanced excitatory associations to the comparator stimuli. Prior research has demonstrated the first three phenomena. Therefore, we employed parameters expected to highlight the fourth one--the comparator process. In Experiment 1, our negative contingency training was shown to produce a conditioned inhibitor that passed inhibitory summation and retardation tests. In Experiment 2 we found transfer of retardation from an inhibitory CS to a novel stimulus when the location where retardation-test training occurred was excitatory, which is indicative of contextual blocking and/or comparator effects. In Experiment 3, extinction of the conditioning context was found to attenuate retardation regardless of whether extinction occurred before or after the CS-US pairings of the retardation test. This indicates that much of the present retardation was due to the comparator process rather than to contextual blocking. Experiment 4 demonstrated that habituation to the US did not contribute to retardation in the present case. Collectively, these studies suggest that retardation following inhibitory training can be explained without recourse to any of the traditional mechanisms of conditioned inhibition.

The dual role of the context in postpeak performance decrements resulting from extended training

“…That is, in the absence of the training context, the b process (or activation of the CS into A2, according to SOP) should not have been anticipatory to CS onset. Of note, we used highly distinct contexts that extensive prior research in our laboratory has demonstrated are well discriminated by rats (e.g., Laborda, Witnauer, & Miller, 2011;Schachtman et al, 1987). OPT and SOP predict the PPD effect only if testing is conducted in the same context where training was conducted, a prediction that received support in Experiment 2, but only when the spacing of trials during training was large.…”

“…Subjects in the control condition (Groups 5C and 50C) experienced one daily 5-min exposure to the training context in order to equate subjects for overall handling and retention interval between training and testing. These 5 min of exposure were not expected to have a large impact on the PPD, on the basis of prior research in our laboratory (Schachtman, Brown, Gordon, Catterson, & Miller, 1987) that indicated that at least 480 min of context extinction is necessary for observing retrospective revaluation based on posttraining context extinction.…”

Excitation and inhibition in unblocking.

“…Similarly, the Same cue in Group Down of Experiment 3 (equivalent to Group 5 of Experiment 4) showed reliable excitation in Test 1 and marginal inhibition in Test 2. Holland (1984a) and Schachtman, Brown, Gordon, Catterson, and Miller (1987) have noted other examples of cues simultaneously possessing excitatory and inhibitory powers.…”

The role of US novelty in retention interval effects in single-element taste-aversion learning

“…As a result, the context-illness association should extinguish and less retrieval interference would be present to suppress the taste-illness association. This idea is conceptually sim-ilar to the "comparator hypothesis," which is based on the premise that the conditioned response is determined by the comparisons of the current associative strengths of the CS and any other stimuli that were present at conditioning (e.g., Kasprow, Schachtman, & Miller, 1987;Matzel, Schachtman, & Miller, 1985;Matzel, Shuster, & Miller, 1987;Schachtman, Brown, Gordon, Catterson, & Miller, 1987).…”