Competition for associative strength between a punctate signal and contextual stimuli: Effect of signal preexposure versus context preexposure.

Preexposures to a punctate stimulus or to an external context were examined for their effect on the competition for associative strength between context and stimulus in subsequent aversive classical conditioning. Using rats as subjects and freezing as the index of conditioned responding, Experiment 1 showed that preexposure to a tone retarded the subsequent acquisition of responding to the tone, but enhanced the acquisition of freezing to the conditioning context. Experiment 2 examined whether the enhanced contextual freezing in Experiment 1 was based on the formation of an association between the preexposure context and the tone. A tone was preexposed in one context and conditioned in another. A subsequent of fear for the preexposure context failed to support the notion of an association between context and tone. In Experiment 3, context preexposure was given prior to tone conditioning in that context. The acquisition of contextual freezing was impaired but the exposure treatment had no augmenting effect on freezing to the tone. Collectively, the results suggest that preexposure reduced the associability of both the punctate stimulus and contextual stimuli. More importantly, the reduced associability of the punctate stimulus resulted in a reduced overshadowing of contextual stimuli by the punctate stimulus, whereas the reduced associability of the context did not result in a reduced overshadowing of the punctate stimulus by the context.