Effects of a pre-shock stimulus on temporal control of behavior.

Rats were exposed to a situation in which a response on lever B was followed by reinforcement if a preceding response on lever A had been made at least 5, 10, or 15 sec before. The effects of signalled unavoidable shock were studied on the behavior maintained by this procedure. All rats made fewer A-to-B sequences during the periods of pre-shock stimulus. In addition, when the A-to-B delay was 10 or 15 sec, the distribution of A-to-B times changed, there being more shorter intervals. However, for animals where the A-to-B delay was 5 sec, the distribution of A-to-B times was not changed during the pre-shock stimulus. In all cases, there was an increased proportion of inappropriate B responses (i.e., with no preceding A response) during the pre-shock stimulus; this was most marked with animals exposed to a 15-sec A-to-B delay.