ABSTRACT
Heart rate and blood pressure may increase or decrease, or, indeed, may exhibit no change in response to stimulation or as concomitants of the performance of various tasks. Most importantly, the direction of blood pressure and heart rate changes may reveal parasympathetic-like responses while other simultaneously recorded responses reveal sympathetic-like responses, such as digital vasoconstriction, pupillary dilation, and decrease in skin resistance. The principle of temporal proximity, concerned with the improvement in the ability of single heart beats to predict reaction time as the beats become more proximate to the response-eliciting sensory input, emphasizes the importance of the single cardiac cycle in sensorimotor integration. Directional fractionation was demonstrated in several experiments in that cardiac deceleration was accompanied by simultaneous sympathetic-like responses in finger volume, skin conductance, or pupillary diameter. Significant relationships between physiological responses and task difficulty were restricted, however, to the cardiac variables. Studies of cycle effects are usually concerned with the dependence of responses on momentary physiological state.
