Figure 6.13: Decline and rise in vigilance during sleep deprivation In this experiment, university students were kept awake for 42 hours before the start of testing. Just before testing, some received a strong dose of caffeine, others received one of three doses of another stimulant drug, modafinil, and still others received a placebo. In the test of vigilance, conducted every hour, the subjects watched a time display on a computer screen and were instructed to press a button as quickly as possible each time it began to increment. The measure was response speed (the reciprocal of response time). As shown in the graph, in the placebo group vigilance declined steadily from midnight to 8 a.m. and then began to increase. This is consistent with other evidence that the circadian rhythm of sleepiness and wakefulness continues even after long periods of sleep deprivation. There was no such decline in the groups receiving caffeine or in those receiving high doses of modafinil.
(Based on data from Wesensten et al., 2002.)