German psychologist Hans Eysenck’s Model of Nervous System Temperament links temperament traits, specifically introversion and extraversion to the Central Nervous System. Introverted people are typically quiet, reserved, and timid whereas extraverts are active, sociable, and outgoing (151). According to Eysenck, introverts have high levels of brain arousal, which is controlled by the ascending reticular activating system (ARAS). Therefore, introverts do not need to seek external arousal leading them to be more reserved. Contrastingly, he argues that extraverts have lower levels of brain arousal and therefore are more sensation seeking in order to make up for it. In this paper, I will aim to synthesize and summarize some of the research regarding introversion and extraversion and their link to the central nervous system and states of arousal. I will synthesize this information to support the idea that while introversion and extraversion are on some level linked to states of arousal, Eysenck’s arousal hypothesis is not alone sufficient to explain the biological differences between introverted and extraverted individuals and their behaviors as such.
Gerald Matthews, D. Roy Davies, and Jackie L. Lees conducted a series of three experiments to test this Eysenck’s arousal hypothesis of introversion and extraversion. The first of the experiments, which consisted of two parts (A and B) is most germane to this argument. According to Eysenck’s hypothesis, extraverts are low in arousal and therefore should seek stimulation in the morning. However, in accordance to Matthew’s experiment, the opposite actually happens. In part A of this experiment, the participants were 50 males and 50 females ranging in age from 18 to 36 with normal vision. They were tested for extraversion by the Sixteen Personality Questionnaire and were put into either the extraverted or introverted group and either a low arousal or high arousal group accordingly. The subjects were shown 540 single digits on a microcomputer. The subjects were to press a key when one of the 135 target digits was shown on the screen. Introverts who were low on arousal performed the worst while introverts high on arousal performed the best.
In part B of this experiment, the subjects were 20 males and 20 females aged 18-22. These 40 were the 20 most introverted and 20 most extraverted from a group of 60 when tested with the Eysenck Personality Inventory. The subjects were to press one of two keys when either a target or nontarget stimulus was presented. The results showed that there was no significant difference between introverts and extraverts. According to Matthews, Davies, and Lees, “the extraversion data were inconsistent with arousal-mediation theories of extraversion effects on performance” (158). In conclusion, differences in arousal are not strongly related to the cognitive processes associated with extraversion, and therefore, this experiment refutes Eysenck’s theory.
A study by Dirk Hagemann...