Psychomotor performance as a function of time of day

Previously reported data on mirror tracking were reexamined for time-of-day (TOD) effects on performance and for the interaction of these effects with sex and practice effects. Analyses showed a significant linear decline of mean score from 0900 through 1300 hours, a sharp postlunch recovery at 1400 hours, and another significant linear decline from 1400 through 1700 hours. These effects were orthogonal to sex and practice effects. Discussion emphasized the importance of control for time of day in experimental design and suggested several hypotheses about the decremental effects of time of day.