Shock-Duration Reduction as Negative Reinforcement

Abstract

In two experiments, rats were shocked every 30 sec. Before a response, a bar press, shocks were long (2 sec); for 3 min after a response, shocks were short (0.1, 0.5, or 1 sec). When responding reduced shocks from 2 to 0.1 sec, bar pressing was acquired, and the shorter the shocks the more time spent with the short-shock condition in effect. In another procedure, the duration of individual shocks following a response was controlled so that the first shock was as long as those before the response (2 sec), but the remaining shocks in the 3-min period were short (0.1 sec). Bar pressing was maintained in some rats and acquired in others showing that, even when delayed, a reduction in shock duration is reinforcing. The latter findings question the generality of a two-factor, safety-signal interpretation of negative reinforcement. These results plus others imply that to predict responding in aversive situations it is necessary to integrate, for at least several minutes, the parameters of aversive events that follow a response.