Ultradian rhythms of reaction times in performance in vigilance tasks.

This study examined the presence of rhythmic fluctuations in vigilance tasks. The hypothesis was that individual attentional performance is subject to rhythmic variation beyond a linear decrease over time. In the first study the reaction times to an acoustic stimulus were recorded. The analysis of the individual periodograms indicated a rhythm in attentional capacity with periods ranging from 5 to 30 min. These findings indicate that considerable individual variation can be accounted for by considering individual periodicity in performance. Although marked individual differences between subjects are present, the rhythmic fluctuations are stable within each subject and between experimental sessions.