EXTROVERSION, HEMISPATIAL BIAS, AND EYEBLINK RATES

Two experiments were conducted in order to explore the relationship be tween extraversion and brain activity. In Experiment 1, subjects were randomly assigned to receive either caffeine or placebo. Higher levels of extraversion were associated with more frequent eyeblinking, which is an indirect index of central dopaminergic activity. The strength o f the association between eyeblinking and extraversion was stronger am ong females than among males, and did not differ appreciably between t he caffeine and placebo conditions. Higher levels of extraversion also tended, on average, to be associated with greater relative left hemis phere activation, as measured by the Chimeric Faces Task. However, the strength of the association appeared to vary as a function of both ge nder and caffeine/placebo condition. Experiment 2 attempted to replica te the finding that extraversion is associated with hemispatial bias. Subjects completed the Chimeric Faces Task in the evening and then aga in the following morning. The correlations between hemispatial bias an d extraversion were generally rather strong for both males and females , with more extraverted individuals exhibiting greater relative left h emisphere activation. The strength of the association did not vary app reciably as a function of the time of day at which subjects completed the Chimeric Faces Task.