Comment

``The personality theories of H. J. Eysenck andJ. A. Gray: a comparative review.'' G. Matthews and

K. Gilliland (1999), Personality and Individual Di�erences,26, 583±626

p

John Brebner

Department of Psychology, University of Adelaide, 5005, Australia

In their comprehensive comparison of Hans Eysenck's and Je�rey Gray's theories, GerryMatthews and Kirby Gilliland wrote the following. ``Extraverts tend to show faster responseon short tasks, riskier speed-accuracy trade-o� and lower response criterion'' (Eysenck, 1967).A series of RT studies conducted by Brebner and Cooper (1985) suggested that extravertsappear to be ``geared to respond'' and introverts seem ``geared to inspect''. However, e�ects ofE on responsiveness do not seem to be very reliable across di�erent tasks and are not apparentin many well-designed studies (Amelang & Ullwer, 1991; Matthews 1992).

The point that is made here is that the ``geared to respond/inspect'' di�erence was invokedin discussing a transit RT task where the stimulus rate was as low as 1 per 18 sec. With timeon task extraverts became sleepy and slower than introverts who remained alert (Brebner &Cooper, 1974). In this task extraverts also tended to miss signals but introverts did not.Changing the signal rate to 1 per 2.3 sec (except when catch trials occurred) altered theresponsiveness of extraverts who produced more commissive errors than the introverts(Brebner & Flavel, 1978).

The conclusion that extraverts' responsiveness is not reliable across tasks is probably correctsimply because, unless a task is unbalanced to demand one or the other, i.e. being high on thedemand for stimulus analysis or response organisation, and low on the other, no di�erencebetween extraverts and introverts would be expected. In many tasks extraverts maintain theirresponsiveness because of the degree of response organisation required, while introverts remainresponsive because of the level of stimulus analysis in the same task. Only when unbalanced

Personality and Individual Di�erences 28 (2000) 1191±1192

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tasks are used can di�erences between them be shown, and manipulated to be in eitherdirection.If press reports stating that Jonathon Evans of Bristol University, U.K. has identi®ed the

gene 5HT2c as an impulsiveness gene in a DNA study he led, are correct (The Australian 21September, 1998 citing the Sunday Times) extraverts' responsiveness would seem likely to belinked to their impulsiveness. This might even be why extraverts appear to be ``geared torespond''.

References

Amelang, M., & Ullwer, U. (1991). Correlations between psychometric measures and psychophysiological as well asexperimental variables in studies on extraversion and neuroticism. In J. Strelau, & A. Angleitner, Explorations in

temperament. New York: Plenum.Brebner, J., & Cooper, C. (1974). The e�ect of a low rate of regular signals upon the reaction times of introverts

and extraverts. In H. J. Eysenck, Reprinted in the measurement of personality. Lancaster: Medical Technical

Publishing Company.Brebner, J., & Cooper, C. (1985). A proposed uni®ed model of extraversion. In J. T. Spence, & C. E. Izard,

Motivating emotion and personality. Amsterdam: North-Holland.

Brebner, J., & Flavel, R. (1978). The e�ect of catch-trials on speed and accuracy among introverts and extraverts ina simple RT task. British Journal of Psychology, 69, 9±15.

Eysenck, H. J. (1967). The biological basis of personality. Spring®eld, IL: Thomas.Matthews, G. (1992). Extraversion. In A. P. Smith, & D. M. Jones, Handbook of human performance, Vol 3, State

and trait. London: Academic Press.

J. Brebner / Personality and Individual Di�erences 28 (2000) 1191±11921192