Overshadowing-like effects between potential comparator stimuli: Covariation in comparator roles of context and punctate excitor used in inhibitory training as a function of excitor salience

Abstract

Water-deprived rats served in a conditioned lick suppression paradigm designed to probe the associative structure underlying a partially reinforced Pavlovian inhibitor (i.e., A+ AX± ) when Stimulus A (a flashing light) was either of high or low salience. Following inhibition training, subjects received either extinction of A, extinction of the training context alone, or remained in their home cages. The inhibitory potential of Stimulus X (white noise) was then assessed in a neutral context using both a summation test with an excitor other than Stimulus A (Experiment 1) and a retardation test (Experiment 2). When A was of high salience, the inhibitory potential of Stimulus X was directly related to the excitatory value of A and not the excitatory value of the training context. But when A was of low salience, the inhibitory potential of X was directly related to the excitatory value of the training context rather than the excitatory value of A. Although the high salience A, relative to the low salience A, overshadowed the context's role as a modulator of responding to Stimulus X, it did not appreciably overshadow context's potential to directly elicit conditioned responding; thus, a dissociation was seen in the ability of a punctate CS to overshadow a context as a function of the behavioral index of overshadowing. These results are discussed in the framework of the comparator hypothesis.