The stability of physiological reactivity over multiple sessions.

Although individual response stereotypy (IRS) has been a subject of research for many years, the stability of the phenomenon, though often assumed, has not been adequately proven. The present study evaluated stability of reactivity profiles of eight variables (heart rate, heart rate variability, integrated muscle tension, skin resistance level, skin resistance response, systolic blood pressure, diastolic blood pressure, and pulse transit time) over four sessions of laboratory tasks in comparison to two subsequent sessions of rest periods. The two major characteristics of IRS--stability and uniqueness--were fulfilled. On the other hand, the first session was found to be an inadequate predictor of the stable composite profiles. Thus the IRS profiles which are determined from multiple observations over time are different from those which are calculated in the traditional manner with a single recording session.