IMPULSIVITY AND TIME OF DAY - IS RATE OF CHANGE IN AROUSAL A FUNCTIONOF IMPULSIVITY

Impulsivity has been interpreted as a stable mediator of rate of chang e in arousal states. To test this hypothesis, 129 Ss differing in impu lsivity were given placebo or caffeine at 9:00 a.m. or 7:30 p.m. Recog nition memory was tested for the last 20 items from 2 lists of 24 item s and 2 lists of 80 items. Scores from this paradigm reflect sustained attention and are thus sensitive to changes in arousal. A 4-way inter action among impulsivity, time of day, drug, and prior stimuli (p < .0 5) indicated that for those given placebo, recognition memory for long and late lists was poorer the higher the impulsivity in the morning; this pattern reversed in the evening. Caffeine reduced recognition err ors. These results indicate that impulsivity is not a stable predictor of rate of change in arousal states. Instead, susceptibility to atten tional lapses is mediated by impulsivity-related phase differences in diurnal arousal rhythms.