“A sure sign”: Reinforcing effects of stimuli correlated with shock-frequency reduction

The primary objective of this study is to determine whether there is a difference between the reinforcing effects of stimuli correlated with avoidance and extinction schedules in rats, with the aim of analyzing the role of these aversive contingencies in the acquisition of observing behavior. Five rats were exposed to a multiple-schedule procedure with two components —one of avoidance and another of extinction— each correlated with a discriminative and a delta stimulus, respectively. During avoidance, lever-presses reduced shock-frequency from 0.35 per 2 s to 0.10 per 2 s. During extinction, lever-presses were ineffective at reducing shock-frequency and extended the time of the extinction period. Once multiple-schedule performance was established, rats were exposed to an observing procedure. The same two components operated in a mixed-schedule, and activation of the correlated stimuli was contingent on responses on a separate lever (i.e., observing responses). Observing responses produced (a) both the discriminative and delta stimuli, (b) only the discriminative stimulus, or (c) only the delta stimulus. Subjects showed discrimination across components of the multiple-schedule. Although rats overall displayed low observing responses rates across all experimental conditions, they showed higher response rates when the discriminative stimulus was the only stimulus contingent on observing responses. The delta stimulus had a reinforcing effect on observing responses only in the phase in which it was produced together with the discriminative stimulus. These results were analyzed from the conditioned-reinforcement account and the notion of relative aversiveness.