On delay-of-punishment and preexposure time: effects on passive avoidance behavior in rats

Some procedures commonly employed in testing hypotheses of instrumental learning and classical conditioning as applied to the step-through passive avoidance task in rats are examined. In Experiment I, a 'delay-of-punishment gradient', i.e., decreased passive avoidance performance, was obtained by increasing response-shock time intervals (from 0 to 600 s) in training sessions. In Experiment II, decreased passive avoidance behavior was also obtained by submitting animals to nonreinforced preexposure (0 to 600 s) in the shock compartment prior to their receiving shock contingent on the response in training sessions. Experiment III repeated the 'delay-of-punishment gradient' and showed that adequate nonreinforced preexposure time before training decreases passive avoidance performance in animals trained through a noncontingent procedure. The results clearly show that environment training preexposure has a decreasing effect on passive avoidance performance. Increasing response-shock interval also has a decremental effect on this task. With large time intervals the latter effect can be explained as the result of preexposure to the training environment; the possibility of interaction between both processes was not discarded. For smaller time ranges (up to 30 s), the usual interpretation of 'delay-of-punishment gradient', namely decreased response-shock association, seems to be adequate to account for the results.