Learned helplessness theory predicts that animals exposed to inescapable shock acquire an expectancy of response-reinforcer independence, which proactively interferes with learning of response-reinforcer dependence. The theory also predicts that this expectancy can increase sensitivity to subsequent instances of response-reinforcer independence. These experiments test the latter prediction in a paradigm that minimizes the confounding effects of shock-induced activity deficits. Rats were trained to respond for food, then given either escapable, inescapable, or no shock. Subsequently, they received two sessions of response-contingent food followed by sessions of noncontingent food deliveries. During this phase, inescapably shocked animals decreased responding faster than did controls. Experiment 2 replicated this finding with a different schedule of food delivery and a procedure that more directly minimized the possibility that the outcome is due to either direct or indirect shock-induced activity changes. These results support the prediction that uncontrollable aversive events can increase an animal's sensitivity to noncontingent response-reinforcer relationships.

In experiments 1 and 2, we examined the learned helplessness and immunization effects using a test in which appetitive responding was extinguished by delivering noncontingent reinforcers. Contrary to learned helplessness theory, "immunized" animals showed performance virtually identical to that of animals exposed only to inescapable shock, and different from nonshocked controls. Experiment 2 suggests that the helplessness effect and the lack of immunization are not due to direct response suppression resulting from shock. In Experiment 3, where the immunization effect was assessed by measuring the acquisition of a response to obtain food when there was a positive response-reinforcer contingency, immunization was observed. These results cannot be explained on the basis of proactive interference, but suggest that animals exposed to the immunization procedure acquire an expectancy of response-reinforcer independence during inescapable shock. Thus, immunization effects may reflect the differential expression of expectancies, rather than their differential acquisition as learned helplessness theory postulates.

The present experiments investigated the role of signals for pellet delivery in the development of polydipsia on random time schedules. In Experiment 1, when an explicit signal or auditory stimulation from pellet dispenser operation was available to the rats, polydipsia developed in all ofthe animals. In Experiment 2, animals receiving signaled pellet deliveries developed polydipsia more quickly than those receiving unsignaled pellet deliveries. Furthermore, behavioral observations suggested that animals showing polydipsia in the unsignaled group may have been able to detect the operation of the pellet dispenser despite our attempt to mask such cues. In Experiment 3, the information value of pellet-dispenser cues was degraded by the operation of an empty pellet dispenser during the interpellet interval. Under these conditions, almost all animals did not develop polydipsia and the data suggest that for the few that did, pellet-dispenser cues were probably not responsible. Thus, the present findings suggest two conclusions: (1) In studies reporting polydipsia on random schedules, the animals may have been inadvertently provided with cues for pellet availability, and (2) although Pavlovian conditioning may be an important modulator of adjunctive behavior, other factors must also be considered.

No abstract

No abstract