Chapter 14 Eysenck’s Biologically Based Factor Theory 425thresholds) than extraverts has been supported, with the qualification that it is reac-
tivity rather than baseline activity levels that distinguishes introverts from extraverts.
For instance, in a recent study, Beauducel and colleagues (2006) predicted
that extraverts would be less cortically aroused and show worse performance on a
boring and monotonous task. The researchers selected students who scored either
very low or very high on the Eysenck Personality Questionnaire–Extraversion scale.
They then presented the participants with a series of tones every 3 seconds for
60 minutes. Participants had to press a button as soon as possible after they heard
a target tone. Computers measured both the speed (reaction time) and accuracy of
responses. The task was meant to be tedious and boring, and it was. The idea is
that extraverts will do worse at the tone task because it is so understimulating.
Finally, the participants’ cortical activity was measured via EEG throughout the
entire tone task. The predictions again were that extraverts would have lower cor-
tical arousal and would do worse on the monotonous task. Beauducel and col-
leagues found support for both of these hypotheses, which support two of the most
basic of Eysenck’s assumptions about the biological basis of personality traits.
Similarly, Anthony Gale (1983) summarized the findings from 33 studies
examining EEG and extraversion and found that introverts showed greater cortical
arousal than did extraverts in 22 of the 33 studies. Later, Robert Stelmack (1997),
a major figure in testing Eysenck’s neurophysiological hypothesis, reviewed the
literature and came to two basic conclusions: First, introverts are more reactive
than extraverts on various measures of arousal; and second, extraverts are quicker
to respond on simple motor tasks. The faster motoric response rates of extraverts
Preferring to be alone at times is one way that introverted people regulate their optimal level
of arousal. © Image Source/Getty Images