Conditioned suppression, heart rate and pulse volume: effects of instructions on extinction

Two experimental groups of undergraduate volunteers received five classical aversive conditioning trials with a tone conditioned stimulus (CS) and shock unconditioned stimulus (UCS). Control groups received either the CS alone or UCS alone. Subjects from one experimental group were subsequently instructed that they would not receive further shocks, while the other experimental group received no such instructions. The CS alone was then presented once to all four groups while subjects were engaged in a button-pressing task maintained by slide reinforcement. During this latter phase rate of button pressing was measured as well as heart rate and pulse volume. The last two measures being employed as indices of autonomic arousal. The results indicated that while instructions as to the absence of the UCS completely abolished the conditioned suppression of button-pressing, they had no effect upon the pulse volume CR. A heart rate CR was not obtained. These results reflect unfavourably upon theoretical formulations of conditioned suppression that emphasize the causal interdependence of motor and autonomic events or the primacy of either one.