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Todd Horowitz, Jeremy Wolfe, Daniel Cohen, Charles Czeisler, Elizabeth Klerman; Quantifying the effects of sleepiness on sustained visual attention. Journal of Vision 2008;8(6):233. doi: 10.1167/8.6.233.
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© ARVO (1962-2015); The Authors (2016-present)
Sleepiness impairs many aspects of performance, but little is known about the effects on visual attention. While typical vigilance tasks require the detection of discrete signals, many important visual behaviors are continuous and cognitive in nature. We measured continuous visual attention using the extended multiple object tracking task (xMOT, Wolfe, Place, & Horowitz, 2007, Psychonomic Bulletin & Review). Eight identical disks moved on independent random non-overlapping trajectories. Participants tracked a subset of four target disks continuously for 7 minutes. At exponentially-distributed intervals (mean = 3 s), participants indicated whether or not a randomly selected probe disk was a target. Sleepiness can arise from extended time awake, adverse circadian phase, or sleep restriction. We analyzed accuracy data from six healthy participants during the forced desynchrony (FD) segment of a 38-day inpatient protocol. The FD procedure allows independent analysis of the effects of time awake and circadian phase. During FD, participants were awake for 32.9 hours and asleep for 10.0 hours for 12 cycles (21 calendar days). This wake:sleep ratio, equivalent to 5.6 hours sleep per 24 hours, produces chronic sleep restriction. The xMOT was administered every 2 h while participants were awake. Results: 1) Accuracy was significantly modulated by circadian phase (based on data from four participants), with a minimum near the melatonin peak (23.7% decrease in accuracy at the middle of the subjective night); 2) Accuracy was constant over the first 10–12 hours of the waking day, then decreased with increasing time awake (18.1% decline); 3) Finally, chronic sleep restriction significantly reduced participants' ability to focus on the tracking task: accuracy declined by 15% over the course of the FD segment. Schedules that do not allow for adequate sleep at the appropriate time impair the ability to sustain attention to visual stimuli. The xMOT method can quantify that impairment.
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