Physiological Foundations
The Four Modes
Introversion and Extraversion
Why is the BTSA Different?
Introversion and Extraversion According to the work of Hans Eysenck, PhD and Zenith Petrie, PhD, our arousal system establishes the basis for our level of extraversion. Each of us has a natural, stable level of arousal when awake. However, arousal levels vary from person to person. Those who have a very high level of arousal (i.e. they are naturally very alert when they are awake), are seen as introverted because they take in so much information second per second that they typically select environments as optimal that have lower volumes of stimulation occurring (e.g. a library, research lab, nature, a back office). By contrast, those who have a very low level of arousal are naturally barely awake and subsequently seek out sources of stimulation (e.g. a crowd, a front office, the pit in a stock exchange, competition or an argument with another person) in order to achieve an optimal level of inner wakefulness.

Petrie labels introverts “diminishers” because in many situations they need and seek to diminish the intensity of stimulation, to suit their naturally hyper alert arousal level and preclude their needing to shut down due to being overwhelmed. She labels extraverts “augmenters” because in the majority of situations they need to increase the level of activity or stimulation in order to achieve sufficient wakefulness.

This type of insight is invaluable. For many years people have had difficulty distinguishing between the interest in people demonstrated by feeling types and by extravert’s. Indeed, many people regularly confuse the two to such an extent that many people have taken to calling someone “extraverted” who showed a keen interest in people. Here, at last, we have a solid, scientific model for distinguishing the two.

Another ah-ha provided by Eysenck and Petrie’s work is the clear understanding that both extraverts and introverts say yes to life. Informally, many Jungians and others have distinguished extraversion from introversion by saying: Introverts say no to life; Extraverts say yes to life. With Eysenck’s new structure, we see that both say yes to life: the extravert in small bites due to the heavy filters their naturally low level of arousal creates; the introvert in big gulps due to the tremendous openness of their arousal system.

As important, are the insights concerning the distribution of extraversion and introversion in the population. In recent decades, as counselors and therapists have worked with Jung’s model, they have sought to apply Jung’s model rigorously; labeling each person as either an extravert or an introvert. How amazing to learn from Eysenck that by far and away the majority of individuals are balanced. His research showed that people are distributed along a continuum of arousal levels, from low to high, based on a normal curve. Thus, only about 15% of the population is extremely aroused (introverted) and only 15% minimally aroused (extraverted).

This insight actually confirms the experiences of many who have tried to peg everyone as either extraverted or introverted. Namely, that many people are in between.

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