Conditioned suppression of avoidance behaviour in rats.

Abstract

Six rats were exposed to schedules of free-operant shock avoidance. For three of these, auditory or visual stimuli were present continuously throughout each experimental session. For the remaining three rats, these stimuli were presented only 5 sec. before an avoidable shock, and were removed by any operant response to be emitted during their presence. For these latter rats, the stimuli developed strong discriminative control over the emission of operant responses. When the avoidance behaviour had stabilized, the effects were studied of a stimulus which preceded an unavoidable shock of the same intensity as that maintaining the avoidance responding. These effects were studied in the following conditions: against the ongoing avoidance behaviour; with no avoidance stimuli present; and against extinction of avoidance behaviour. With the animals exposed to continuous schedule stimuli, all these experimental conditions resulted in an acceleration of responding during the signal which preceded an unavoidable shock. The rats with the strong stimulus control of avoidance responding afforded by the discontinuous schedule stimuli never showed such an acceleration; indeed all three animals showed suppression of their operant responding in the final experimental condition. It therefore appears that experience of shock avoidance per se is not sufficient to produce the acceleration effect: the discriminative control of behaviour, or lack of it, is also implicated.