Awareness of sleepiness and ability to predict sleep onset: Can drivers avoid falling asleep at the wheel?

ObjectivesRegarding the causes of sleep-related accidents, this study assesses whether individuals can anticipate sleep onset accurately and how individuals acknowledge and use physiological and cognitive cues to make judgments related to sleep onset.MethodsA group of 41 partially sleep-deprived subjects predicted the likelihood of sleep in 30 consecutive two-minute intervals and noted physiological and cognitive signs of sleepiness, including involuntary eye closure, head-nodding, wandering thoughts, yawns, and instances of sleep, collectively referred to as “sleep complaints”. Continuous polysomnographic recording compared these predictions to actual instances of sleep.ResultsSubjects varied in their ability to predict sleep onset. For all subjects, the mean prediction of the likelihood of sleep prior to sleep was significantly higher than the mean prediction of the likelihood of sleep prior to intervals in which no sleep occurred (78% vs. 42%; p < .05). However, subjects tended to predict much lower likelihoods of sleep onset before their first sleep event (55%) than before later sleep events. On average, the rate at which subjects reported miscellaneous sleep complaints (such as head-nodding, eye closure, and wandering thoughts) was higher prior to sleep than prior to intervals in which sleep did not occur.ConclusionSubjects who acknowledged a limited number of physiological and cognitive indicators of sleepiness tended to be poor predictors. Subjects whose physiological and cognitive signs of sleepiness failed to provide a strong indication of whether or not sleep onset would occur also tended to be poor predictors. Inability to judge sleep onset and, hence, susceptibility to sleep-related accidents, may be attributable to both a scarcity of meaningful warning signs and a failure to acknowledge the importance of physiological and cognitive indicators.