Phasic heart rate changes in reaction time and time estimation.

The phasic cardiac changes of two groups of Ss were compared, with one group performing a reaction time task and the other a time estimation task. The cardiac changes of the two groups were very similar with both groups showing deceleration shortly before they made their motor responses. The reaction time task group showed this to a greater extent than the time estimation group. It was concluded that the anticipatory deceleration observed under reaction time conditions is not wholly attributable to the direction of attention.