Extraversion and electrodermal activity: arousability and the inverted-U

The Eysenck hypothesis that extraverts are less aroused or more inhibited than introverts has been subjected to a number of tests in the psychophysiological literature. Research to date suggests the need to clearly differentiate between tests of overall group differences in arousal or inhibition and studies of the differential reactions of the two groups to arousal manipulations. Psychophysiological studies of overall arousal differences in our laboratories and elsewhere have yielded somewhat inconsistent results for SCL, nonspecific response frequency, trials-to-criterion habituation and initial response amplitude, though dishabituation results are consistent with the expectation of higher amplitudes in introverts. Far more consistent are findings testing the inverted-U hypothesis, which suggests that introverts reach a point of optimal arousal at lower levels of stimulus input than do extraverts and hence should show earlier asymptotes and decrements in arousal measures. Using stimulus intensity and caffeine to manipulate arousal, we have found supportive results for SCL and several phasic measures, including the initial, test, and dishabituation responses. Overall, findings suggest that the two personality groups differ more clearly in arousability than in overall arousal level and that this difference is most consistent when conditions induce a rapid breakdown of inhibition and increase in arousal. Further research is needed to better understand the conditional relationship of extraversion to arousability, and arousal-manipulation paradigms would appear to be a fruitful initial approach to carrying out the needed research.