Previous research has suggested that high impulsive individuals perform better in the evening than in the morning because of differential variations in diurnal arousal rhythms. The current study was designed to determine if these findings could be replicated without external manipulation of arousal level. Forty subjects (20 high impulsive and 20 low impulsive as classified by the Barratt impulsiveness scale) were tested twice, once between 8.00 and 10.00 a.m. and once between 6.00 and 8.00 p.m. A variety of performance and cognitive tempo measures were employed in the study. No significant interactions between level of impulsivity and time of day on performance were observed. However, the results did reveal a greater variability of performance and a faster cognitive tempo in high impulsives as compared to low impulsives, a finding that is consistent with previous research. Time of day differences were also discovered on tasks requiring attention, with all subjects performing better in the evening on those tasks.
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