Time of day effects on extroversion and salivation.

A circadian rhythm in the biological basis of extroversion-introversion (E-I) was hypothesized. Eighty subjects had their EPI E-I scores and lemon juice test (LJT) scores assessed at a.m. and at p.m. Results showed that : (a) there were high intra-test correlations for EPI E-I and LJT; (b) a significant correlation between EPI E-I and LJT was only found for a.m. and not for p.m.; and (c) there were large individual differences in LJT scores. It was concluded that a circadian rhythm of E-I could not be detected by these measures, and that applicability of the LJT to E-I depends upon the time of day of assessment and the measurement procedure employed.