The interactive effect of personality, time of day, and caffeine: A test of the arousal model

The 1st author and his associates (see record 1976-22426-001) reported that the administration of moderate doses of caffeine (C) hindered performance of introverts and helped performance of extraverts on a cognitive task similar to the verbal test of the Graduate Record Examination. Assuming that C increases arousal, this interaction between introversion-extraversion (I-E) and drug condition supports H. J. Eysenck's I-E theory. The interaction was explored in 5 experiments with 629 undergraduates. The interaction between personality and drug condition was replicated and extended to additional cognitive performance tasks. However, these interactions were affected by time of day and stage of practice, and the subscales of I-E, Impulsivity, and Sociability of the Eysenck Personality Inventory were differentially affected. In the morning of Day 1, low impulsives (LIs) were hindered and high impulsives (HIs) helped by C. This pattern reversed in the evenings of Days 1 and 2. It is concluded that the Day 1 results require a revision of Eysenck's theory. Instead of a stable difference in arousal between LIs and HIs, it appeared that these groups differed in the phase of their diurnal arousal rhythms: LIs were more aroused in the morning and less aroused in the evening than were HIs. (68 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).