Person. mdicrd. 0~5 Vol. 9, No. 2, pp. 353-360, 1988 0191-8869 SS S3.l?43 +O.OO Printed in Great Britain Pergamon Press plc EXTRAVERSION, NEUROTICISM AND INDIVIDUAL DIFFERENCES IN EVENT-RELATED POTENTIALS VILFREDO DE PASCALIS and ROSARIO MONTIROS% Department of Psychology, University of Rome, “La Sapienza”, Via degli Apuli 8. 00185 Rome. Italy (Received 5 June 1987) Summary-Event-related potentials (ERPs) in response to task-irrelevant tone pips were elicited during meaningful and meaningless speech passages for two groups of subjects selected on the basis of their scores on the extraversion-introversion scale of the Eysenck Personality Questionnaire, ERPs were recorded from two temporal (T3 and T4) and Wernicke (WI and W2) scalp locations. Peak latencies and amplitudes of NI, P2 and N2 components were obtained for each subject during each meaningful and meaningless condition. The extraverts exhibited higher levels of subjective engagement in the meaningful-speech condition than in meaningless condition; the opposite trend was found for introverts. The extraverts showed greater N2 amplitude in the meaningful-speech condition than in the meaningless condition: the reverse trend across conditions was found for introverts. INTRODUCTION Eysenck’s (1967) theory of the biological basis of extraversion, predicted that individual differences along this dimension may be accounted for by individual differences in the functioning of the corticoreticular system that regulates arousal and inhibition processes. According to this theory, the introverts are characterized by greater levels of arousal than extraverts. At the present time, evidence of differences in level of EEG activity between extraverts and introverts is inconsistent. Some studies reported that introverts did not differ from extraverts (e.g. Gale, Coles, Kline and Penfold 1971); others that extraverts are more aroused than introverts (e.g. McAdam and Orme, 1954; Mundy-Castle, 1955; Broadhurst and Glass, 1969); others again reported that extraverts are less aroused than introverts (e.g. Marton, 1972; Savage, 1964; Morris and Gale, 1973). Gale (1973, 1981), attempted to explain the conflicting results by advancing the hypothesis that in the high or low-arousal conditions no differences between extraverts and introverts will be observed, while under moderate arousal conditions (e.g. one in which subjects have to open and shut their eyes) the introverts would be more aroused than extraverts. A recent study by O’Gorman and Mallise (1984) failed to support Gale’s hypothesis, and indeed extraverts were found to be more aroused under opening and closing eyes on instruction. Some previous attempts have been made to examine differences in cortical activity between extraversion groups with event related potentials. One of the first studies (Shagass and Schwartz, 1965) reported increased levels of cortical activity for introverts with the somatosensory evoked response. Attempts to replicate this result have been unsuccessful (Haseth, Shagass and Straamanis, 1969). Stelmack, Achorn and Michaud (1977) found that introverts had greater Nl-P2 amplitude than extraverts on the auditory evoked response elicited by low frequency tones. Danma Karrer and Rosen (1985) examined the possibility that variation in P3 amplitude reflects individual differences in the allocation of attention; these authors found that, during a lengthy stimulus prediction task, the P3 amplitude of the event-related potentials was significantly greater for the introverts than for extraverts. The present paper examined individual differences in ERP responses using the two-tone probe technique described by Shucard, Shucard and Thomas (1977) with auditory stimuli. In this method, ERPs are elicited by irrelevant ‘probe’ tones while subjects are engaged in a task. It is assumed that subjective task engagement and concurrent cognitive activity should influence the processing of such ‘probes’. This study considers two different language conditions within the meaningful-meaningless language dimension. The meaningful task is zyxwvutsrqponmlkjihgfedcbaZYXWVUTS per se more interesting and would be expected to have higher arousal potential than the meaningless task. The differential arousal effects of the meaningful and non-meaningful tasks would be expected to be greater for 353