The incentive effect and sleep deprivation.

In order to examine the effect of a small amount of sleep following 3 3/4 days (90 h) of wakefulness, 10 infantry soldiers took part in a laboratory-based experiment. At the end of the vigil, a 2-h sleep was preceded and followed by a cognitive test session consisting of encoding and decoding. In order to simulate a realistic situation, subjects were not told the scheduled length of their vigil until a few hours before their 2-h sleep. Following the test-sleep-test period, 27 h were allowed for sleep and rest. Results indicated that after 3 nights without sleep, performance was, on the average, 55% of the control values. During the test session before the 2-h sleep, performance improved by 30%, to 85% of control values, indicating the considerable effect that incentive can have on even severely sleep-deprived subjects. The reserve mental capacity demonstrable during sleep deprivation indicates the caution that is needed if the effects of "undiluted" sleep loss are sought; it also emphasises once again the lack of knowledge concerning the function of sleep.