The Measurement of Autonomic Arousal Some Basic Issues Illustrated by the Covariation of Heart Rate and Skin Conductance

Empirical evidence is presented to demonstrate that there is no true relationship between such physiological measures as heart rate and skin conductance, but that (depending on circumstances) heart rate and skin conductance covary directly, inversely, or not at all. It is contended that a solution to the general measurement of arousal will not be found by transforming single measures, by innovations in data reduction, or by combining measures. Instead, the solution lies in learning more about the unique properties of different physiological sys-tems by establishing how they vary as a function of the parameters of stimulus input—such as intensity, rate of stimulation, and time since stimulus onset. TLHE FINDING of low intercorrelations among physiological measures (cf. Ax1 and Lacey and Lacey10) has been a source of disturbance to a number of psychologists seeking an index of general arousal. Lazarus and colleagues11 state that low correlations are "embarrassing to those who propose a general activa-tion or arousal syndrome." To deal with this problem, two gen-eral solutions have been proposed, one of which is to use multiple measures. Duffy2 states: "it is probable that a combinatio