Extraversion and alcohol: Eysenck's drug postulate revisited.

Within the framework of Eysenck's drug postulate alcohol is frequently used as an example for a depressant drug that should shift a person's position on the extraversion-introversion axis in the direction of lower arousability. However, only little experimental evidence for differential effects of alcohol on extraverts and introverts appears to exist. Therefore, a placebo-controlled study was designed to investigate the effects of 0.65 g/kg alcohol on temporal discrimination, time estimation, reaction time, movement time, critical flicker fusion frequency (CFF), as well as feelings of activity, alertness, drowsiness, joyfulness, and relaxation in introverts and extraverts. While a main effect of alcohol could be shown for temporal discrimination (p < 0.05), reaction time (p < 0.05), CFF (p = 0.01), and feelings of alertness (p < 0.001) and joyfulness (p < 0.01), significant interactive effects of alcohol and extraversion were only found for time estimation (p < 0.001) and feelings of relaxation (p < 0.01). Extraversion-related differences in movement time (p = 0.05) proved to be insensitive to alcohol. Results are discussed with regard to the pharmacological profile of alcohol and the validity of the drug postulate.