Sign-tracking behavior in aversive conditioning: Its acquisition via a Pavlovian mechanism and its suppression by operant contingencies

Abstract

When rats are presented with Pavlovian backward pairings in which shock is the unconditioned stimulus (US) and an elevated platform the conditioned stimulus (CS), they show a strong tendency to approach the platform. Attempts were made at evaluating the nature of the associative mechanisms responsible for the acwuisition and maintenance of the approach behavior. In Experiment 1, following a baseline period when platform presentations were given in the absence of shocks, first (training I), approach to the platform was prevented and subjects were exposed to either backward, forward, or random presentations of shock and platform: this procedure attempted to minimize the effects of response learning on the acquisition of approach behavior. Then (training II), all subjects received backward shock-platform pairings and had access to the platform. Approach to the platform was stronger in animals previously exposed to backward pairings than in the animals of the other two groups. Also, animals preexposed to forward platform-shock pairings showed suppression of approach behavior on the first trial of training II relative to their performance on the last trial of baseline. These data suggest that a stimulus-reinforcer learning mechanism alone is sufficent for the acquisition of approach. Experiments 2a and 2b evaluated the effects of “punishing” operant contingencies on Pavlovian-produced approach behavior. The results showed that approach can be eliminated, but only after repeated exposure to an operant contingency which consisted of the immediate closure of the platform upon approach responding. These data suggest that approach behavior produced by Pavlovian contingencies can be modified by operant contingencies. Taken together, these data provide additional support for a sign-tracking notion in aversive conditioning.