ABSTRACT
The effect of lapses on performance varies with the nature of the task, however, such that subject-paced tasks show response slowing when lapses occur, while experimenter-paced tasks show increased errors when lapses occur. Despite the lack of demonstrated pathophysiology associated with human sleepiness, operationalizing sleepiness has become an increasingly important issue in the fields of sleep and human chronobiology. At any given time, sleepiness is the composite result of different temporal patterns for the effects of prior wakefulness, sleep disturbance, the preceding state, and the circadian phase. Boredom, heat, a large meal, and an uninteresting task are the most common contexts in which attributions of sleepiness are made, but they do not always result in sleepiness. The occurrence of voluntary sleep onsets and increased sleep tendency in the middle of the night and the middle of the day should, if they are indicative of increased daytime sleepiness, be accompanied by involuntary sleep onsets at these same times.
