Attention and cardiac activity: heart rate responses during a variable foreperiod, disjunctive reaction time task.

A variable foreperiod disjunctive reaction time task was used to evaluate the effects of stimulus discriminability on cardiac activity. In two sessions, 20 male undergraduates received easy or difficult auditory discrimination trials in blocked and random series. In the random session only, when the warning stimulus provided information about the difficulty of the subsequent discrimination, difficult trials were associated with greater foreperiod deceleration. Cardiac accelerations also tended to be greater in the foreperiods of difficult trials. There was an effect of both warning and imperative stimuli on the heart rate of the cycle in which the stimuli occurred which depended on the difficulty of the trial. The results are discussed in terms of the psychological significance of the different heart rate responses.