The effects of changing the phase and duration of sleep

The relative effects of extended sleep, reduced sleep, and shifts of habitual sleep time on subsequent performance and mood were studied. Ten healthy male university students who regularly sleep 9.5-10.5 hr were the subjects. Measurements were obtained from a 45-min auditory vigilance task, a 5-min experimenter-paced addition task and a mood adjective check list 30 min after awakening, at midday, and in the evening following five electroencephalographically recorded nights of sleep. The experimental treatments compromised at 9.5-10.5 hr habitual sleep condition and four conditions in which the regular sleep period was lengthened, reduced, delayed, and advanced by 3hr. Following each 3-hr altered condition of sleep there was an equivalent decline in vigilance performance and in subjective arousal as measured by the mood scales. Together with other recent evidence, the present results support the hypothesis that acute disruption of the 24-hr sleep-wakefulness cycle produces degradations in human performance largely independent of total sleep time.