Neurophysiology and Personality

The first domain to test Eysenck s biological model of personality is hi neurophysiology. If, as Eysenck proposed, introverts have lower thresholds of arousal than do extraverts, then they should be more reactive (i.e., sensitive) to sensory stimulation. One way to test this idea is to present both groups with varying intensities of stimulation and measure their physiological reactivity. If Eysenck s theory is to be supported, then hitroverts should be more reactive than extroverts.

Over the last 30 years, a substantial amount of research has explored cognitive, behavioral, and physiological measures of reactivity in relationship to extraversion-hitroversion (Eysenck, 1990; Stelmack, 1990, 1997). In general, Eysenck s assumption that hitroverts are more reactive (have lower thresholds) than extraverts has been supported, with the qualification that it is reactivity rather than baseline activity levels that distinguishes introverts from extraverts. For instance, Anthony Gale (1983) summarized the findings from 33 studies examining EEG and extraversión and found that introverts showed greater cortical arousal than did extraverts hi 22 of the 33 studies. Later, Robert Stelmack (1997), a major figure hi testing Eysenck s neu-rophysiological 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 correspond well with their greater spontaneity, social disinhibition, and impulsiveness. In a study by Cynthia Doucet and Stehnack (2000), however, it was only motoric response rate—not cognitive processing speed—that differentiated introverts and extraverts. Extraverts were faster motorically but not cognitively. Extraverts may move faster but they do not think faster than introverts.

Optimal level of arousal is another of Eysenck s hypotheses that has generated some research. Eysenck theorized that hitroverts should work best hi environments of relatively low sensory stimulation, whereas extraverts should perform best under conditions of relatively high sensory stimulation (Domic & Ekehammer, 1990). In an important study conducted by Russell Geen (1984), hitroverted and extraverted participants were randomly assigned to either a low noise or high noise condition and then given a relatively shnple cognitive task to perform. Results showed that introverts outperformed extraverts under conditions of low noise, whereas extraverts outperformed introverts under conditions of high noise. These findings not only support Eysenck s theory but also suggest that people who prefer to study in public places (like a dorm study area) are more likely to be extraverts. Introverts, on the other hand, find such noisy environments distracting and therefore tend to avoid them.

In summary, research on Eysenck s theories suggests that highly creative people, whether they are artists or scientists, are more introverted, open, dominant, driven, impulsive, hostile, and sensitive than less creative people are. hi addition, research tends to support Eysenck s notion that personality factors have a biological basis and are not simply dependent on a particular culture.

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