Sleepiness is not always perceived before falling asleep in healthy, sleep-deprived subjects

To test whether subjects spontaneously signal sleepiness before falling asleep under monotonous conditions. Twenty-eight healthy students were deprived of sleep for one night and then underwent a “maintenance-of-wakefulness test” (MWT) consisting of four 40-min trials. They were told to give a signal as soon as they felt sleepy and to try to stay awake as long as possible. In a first series of tests, the subjects were given no reward (nr); in a...