Counteracting driver sleepiness: Effects of napping, caffeine, and placebo

Authors

  • J. A. HORNE,

    Corresponding author
    1. Sleep Research Laboratory, Loughborough University, Leicestershire, UK
      Address reprint requests to: J. A. Horne, Sleep Research Laboratory, Loughborough University, Leicestershire, LE11 3TU, UK.
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  • L. A. REYNER

    1. Sleep Research Laboratory, Loughborough University, Leicestershire, UK
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  • This research was supported by the UK Department of Transport. We thank Adrian Bailey, David Harris, Jeff Read, and in particular Hilarie Kemp for their help.

Address reprint requests to: J. A. Horne, Sleep Research Laboratory, Loughborough University, Leicestershire, LE11 3TU, UK.

Abstract

Sleepy drivers should “take a break,” but the efficacy of feasible additional countermeasures that can be used during the break is unknown. We examined a shorter than 15 min nap, 150 mg of caffeine in coffee, and a coffee plalcebo, each given randomly across test sessions to 10 sleepy subjects during a 30-min rest period between two 1-hr monotonous early afternoon drives in a car simulator. Caffeine and nap significantly reduced driving impairments, subjective sleepiness, and electroencephalographic (EEG) activity indicating drowsiness. Blink rate was unaffected. Sleep during naps varied, whereas caffeine produced more consistent effects. Subjects acknowledged sleepiness when the EEG indicated drowsiness, and driving impairments were preceded by self-knowledge of sleepiness. Taking just a break proved ineffective.

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