Sleepiness, alertness and performance during a laboratory simulation of an acute shift of the wake-sleep cycle.

Monitoring the presence of sleepiness on the job and its effects on performance is of primary importance for improving schedule systems of shiftworkers. Shiftworkers, often involved in night-time operations and irregular work schedules, frequently complain of nocturnal sleepiness especially in conditions of abrupt shift of the wake-sleep cycle. In this study, the authors evaluated the effects of a laboratory simulation of acute night-shift changes on sleepiness, vigilance and performance, using Maintenance of Wakefulness Test, Multiple Sleep Latency Test and three pencil and paper tests: Digit Symbol Substitution Test, 'Deux Barrages' Test and a 3-Letter Cancellation Task. All of the tests were administered four times at 2-hourly intervals during the night after daytime sleep. Results showed that the ability to maintain wakefulness and to perform simple visuo-attentive tasks is substantially spared during the night. On the other hand, sleep tendency and performance on a more complex and monotonous task (Letter Cancellation Task) reveal, respectively, increasing sleepiness and degrading performance.