Experimental andTheoretical Studies on the Expectancy and Aftereffect of Aversive Stimuli of Different Durations

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The purpose of the present research was to investigate whether or not effects obtained by increasing the intensity of an electric shock would also be obtained by increasing its duration, in a licking conditioned suppression situation with rats. In Experiment 1, the aversiveness of unsignaled grid-socks of five different durations was measured in terms of overall lick suppression. These shocks of five durations were used as USs in Experiment 2, but the US-duration had no effect upon conditioning. In Experiment 3, 0.7-sec and 4.9-sec shocks, which were shown to be significantly different in aversiveness in Experiment 1, were used as USs, and their effects were assessed using both beteen- and within-subjects designs. In agreement with results of Experment 2, shock duration had no effect upon conditioning with the between-subjects design. But conditioned suppression to the CS paired with tje 4.9-sec shock proved to be significantly greater than that to the CS paired with the 0.7-sec shock, with the within-subjects design. This effect was attributed to the fact that, with the latter design, rats had chances to "compare" shocks of two different durations. In Experiment 4, chances rats had to compare shock durations were systematically manipulated by varying the number of within-session transitions from the 0.7-sec shock to the 4.9-sec shock, or vice versa. The results showed that the shock-duration discrimination was facilitated under the condition of greater number of transitions. In the last experiment, the aftereffects of shocks of nine different durations were investigated in terms of their dissuppressing effects upon immediately following conditioned suppression. Longer shocks proved to have greater dissuppressing effect upon following conditioned suppression than shorter shocks. The results as a whole were discussed with reference to contemporary theories of classical conditioning, as well as to the opponent-process theory.