Comparing sleep-loss sleepiness and sleep inertia: lapses make the difference.

To compare the behavioral effects of sleep-loss sleepiness (performance impairment due to sleep loss) and sleep inertia (period of impaired performance that follows awakening), mean response latencies and number of lapses from a visual simple reaction-time task were analyzed. Three experimental conditions were designed to manipulate sleepiness and sleep-inertia levels: uninterrupted sleep, partial sleep reduction, and total sleep deprivation. Each condition included two consecutive nights (the first always a night of uninterrupted sleep, and the second either a night of uninterrupted sleep, a night when sleep was reduced to 3 h, or a night of total sleep deprivation), as well as two days in which performance was assessed at 10 different time points (08:00, 08:30, 09:00, 09:30, 10:00, 11:00, 14:00, 17:00, 20:00, and 23:00 h).