ABSTRACT
In the past few decades, human chronobiology research has documented rhythms in a variety of biological and physiological functions (e.g., body temperature, blood pressure, metabolic rate, hormonal and digestive secretions) reflecting circadian cycles of approximately 24 hours. Circadian rhythms exhibit pronounced effects on important aspects of everyday life, health, and medical treatment (e.g., Hrushesky, 1989, 1994; Smolensky & D’Alonzo, 1993), as well as on the ability to adapt to shift work (e.g., Monk, 1986; Moore-Ede & Mclntosh, 1993). While extensive research addressing general circadian patterns exists, a far smaller literature concerns the extent to which there are individual differences in these patterns and, in turn, differences in performance at different times of day (e.g., Bodenhausen, 1990; Colquhoun, 1971; Folkard, Knauth, Monk, & Rutenfranz, 1976; Folkard, Weaver, & Wildgruber, 1983). This work shows that individual circadian arousal is indeed correlated with performance on a variety of tasks (e.g., efficiency in reacting to stimuli, performing simple arithmetic, engaging in cognitive activity) such that performance peaks at a certain level of circadian arousal, a peak which occurs more or less regularly at a specific point in the day.
