Psychophysiological responding as a function of age: The importance of matching

Abstract

Few studies in the past which have employed psychophysiological measures have controlled for age. We have studied the effects of age on the heart rate, hand surface temperature, cephalic vasomotor response, and frontal electromyographic activity (EMG) of 73 normal individuals who varied in age from 18 to 68 years and were evenly divided into younger, middle, and older age groups. Comparisons were made between groups across eight conditions — baseline, relax body, warm hand, relax facial muscles, mental arithmetic, positive imagery, negative imagery, and cold pressor. Results indicated a direct linear relationship between age and electromyographic activity during relax facial muscles and mental arithmetic conditions. There was also a linear relationship between age and hand surface temperature during stressor conditions. Most important, significant interactions were found for both frontal EMG and heart rate measures with age. Post hoc analyses revealed differences on the frontal EMG levels between younger and older age groups during negative imagery, warm hand, and cold pressor conditions. Heart rate differences were found during positive imagery between the younger age group and the medium age group and during cold pressor between the younger age group and both the medium and the older groups. The implications of these findings are discussed.