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

ABSTRACT

Objectives

Regarding 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.

Methods

A 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.

Results

Subjects 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.

Conclusion

Subjects 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.

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From the full-text paper:

·        “The results of this study establish that people do have a limited ability to predict the onset of sleep. The wide variation in predictions both before episodes of sleep and before episodes of no-sleep establishes that subjects certainly do fall asleep at times when they think sleep is highly unlikely and fail to fall asleep at times when they think sleep is highly likely” (p78)

·        “The mean prediction before subjects’ first sleep was low, suggesting that subjects in general judged sleep to be fairly unlikely on first occurrence. Mean predictions prior to future episodes of sleep, however, were significantly higher than mean predictions prior to future episodes of no-sleep. Stated differently, subjects learned how to more accurately predict sleep onset over the course of the study” (p78)

·        “Since there is a significant chance that a sleepy driver will not be alive to experience his or her second, third, or fourth sleep attack, predictions made prior to the first sleep event are of particular importance in the current study. There was a wide variation in subjects’ ability to predict their first sleep onset. Predictions prior to the first sleep event ranged from as high as 93.3% to as low as 4.9% on the prediction scale” (p78)

·        It’s noted that while this was a lab study with controlled conditions “subjects may have even greater difficulty accurately predicting the likelihood of sleep in real-world situations such as driving” (p78)

·        “There are many reasons why the ability to predict sleep onset may be limited. First, the information people receive by way of physiological and cognitive signs of sleepiness is imperfect” (p78)

·        “There is some positive relationship between the sleep complaints measured in the study (eyes, head, thoughts, and prior sleep) and imminent sleep onset (see Table 3), but this relationship is imperfect in the sense that there are times, particularly during extended periods in which an individual is struggling to stay awake, when sleep can occur suddenly and without clear preemptive warning signs” (p78)

·        Data showed that based on obvious warning signs of sleep “yawning was more frequent prior to no-sleep intervals than to intervals in which sleep occurred, and the experience of miscellaneous sleep complaints did not differ between sleep and no-sleep episodes. Thus, physiological and cognitive cues may not always accurately predict sleep onset, even when acknowledged by the sleepy individual” (p78, emphasis added)

This study also has some useful graphs on the relationship between how well people could predict when they were about to fall sleep versus their performance *actually* predicting onset to sleep.

Link in comments.

Authors: Kaplan, K. A., Itoi, A., & Dement, W. C. (2007). Sleep Medicine, 9(1), 71-79.