Skin conductance as a measure of tonic and phasic arousal

Abstract

This paper offers a number of suggestions, that are inspired by current experimental literature and neurophysiological findings. It seems possible to distinguish a tonic arousal and a phasic arousal, as neurophysiological states of the organism. Notwithstanding their functional interaction, in experiments both types of arousal can be very well independently studied. Tonic arousal is an organistic state of vigilance of a relatively permanent character and not within short time-ranges dependent upon stimulus conditions. Phasic arousal is a respondent state of vigilance increment of short endurance and dependent upon the stimulus conditions of novelty and others. There are a number of reasons for a preference to measure both types of arousal peripherally by skin conductance measurement, instead of measurement by EEG. Evidence has been collected, that the BLC is an appropriate measure of tonic arousal. We have been able to demonstrate the well-known inverted U-shape function of performance variables in relation to degree of BLC. Phasic arousal seems to be measurable by skin conductance changes. In experimental practice data on skin conductance changes (EDR) are reported in a variety of scales: absolute change in conductance, change as a ratio of the basic conductance level (BLC), and log conductance change. Explorative studies in our laboratory have shown that the respective relationships of these EDR scales with the BLC are different. It is very necessary that these relationships will be further studied. In the use of data on phasic arousal for inferences on activation-level (tonic arousal) the nature of the experimental variables and the scales used, require serious consideration.