Human heart-rate responses during experimentally induced anxiety: Effects of instructions on acquisition.

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Abstract
Base-level measurements of cardiac activity were made while 12 subjects watched the sequence of No. 1-12 appear on a memory drum. Each subject was then told that he would sometimes receive a shock during 1 of the numbers. Each subject received 10 shocks on No. 10 during the 15 shock-anticipation trials. An acceleration in rate during No. 1-8 appeared on the 1st trial and gradually decreased in amplitude over trials, whereas a deceleration in rate during No. 10 appeared only near the end of the trials.