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ABSTRACT This study examined the effects of restricting sleep to the first or second half of the night on the composition of sleep and on performance. Eight young women who regularly slept for 8–8.5 hrs a night had their sleep restricted to the first or second half of the night for two consecutive nights. Performance of a 20‐min unprepared simple reaction time task was measured at fixed times of day for the two restricted sleep conditions and for a full night sleep control condition. Restricting sleep to the second half of the night produced higher amounts of REM sleep and Stage 4 sleep and lower amounts of Stage 2 sleep compared to restricting sleep to the first half of the night. Both restricted sleep conditions impaired performance relative to the full night sleep control, and performance was worse after two nights of restricted sleep than after one night of restricted sleep. The results show that the effects of a restricted sleep regime on the composition of sleep are partly a function of the time of night to which sleep is restricted. It is suggested that the performance deficits are due to loss of sleep per se rather than due to any change in the composition of sleep.
Tilley et al. (Sun,) studied this question.