Phasic heart rate responses and cardiac cycle time in auditory choice reaction time

This study investigated the cardiovascular-behavioral interaction under short and long stimulus interval conditions. In addition, the cardiovascular-behavioral interaction was studied as affected by cardiac cycle duration. Fourteen subjects performed a choice reaction time (RT) task employing a mixed speed-accuracy tradeoff design in which reactions were paced to coincide with a signal that occurs randomly at either 200 or 500 msec after the reaction stimulus. The preparatory interval between a warning stimulus and a lead-reaction stimulus complex was also varied (2 vs. 4.5 sec). Anticipatory deceleration occurred within the 4.5 sec interval but not in the 2 sec interval. The depth of anticipatory deceleration did not discriminate between fast and slow reactions; but an earlier shift from deceleration to acceleration was associated with fast reactions. The effect of stimulus timing relative to the R-wave of the electrocardiogram was also analysed. Meaningful stimuli tended to produce cardiac slowing as previously described in the literature. Early occurring stimuli prolong the cycle of their occurrence more than late occurring stimuli. The later prolong the subsequent cycle. Cardiac cycle time effects were absent for unattended stimuli. The results of anticipatory deceleration suggested that the depth of deceleration was regulated by time-uncertainty and speed-accuracy criterion.

The relationship between reaction time and intensity in discrete auditory tasks

The effect of signal intensity upon reaction time (RT) was studied in three auditory RT tasks in which the signal was a tone of high or low frequency. Experiment I showed the well-known negative gradient with intensity of simple RT when the subject was instructed to ignore the frequency and give the same response to both tones. But when the subject had to discriminate the frequency in a choice RT task, the RT/intensity relationship appeared to be U-shaped. Experiment II showed that when the subject was required to make a response to one signal but withhold it for the other, a task which requires discrimination of the frequency of the tone but removes the necessity to choose between overt responses, no increase in RT at high intensities was obtained. The results indicate that it is the response choice stage rather than the stimulus encoding stage which is retarded at higher energy levels. Experiment I also demonstrated that visual and auditory leading signals have similar facilitating effects without affecting the RT/intensity relationships.