Visual search performance across 40 h of continuous wakefulness: Measures of speed and accuracy and relation with oculomotor performance

The aim of the study was to estimate the sensitivity of a brief self-paced visual search task to increased levels of sleepiness as a consequence of 40 h of steep deprivation. Time-of-day effects on this task, on subjective sl eepiness and on oculomotor performance changes, were also assessed. Eight n ormal subjects slept for three nights in the laboratory (adaptation, baseli ne, recovery). Baseline and recovery nights were separated by a period of 4 0 h of continuous wakefulness, during which subjects were tested every 2 h from 10:00 to 22:00 h on both days preceding and following the sleep depriv ation night, as well as from 24:00 to 08:00 h during the deprivation period . At the same time, subjects filled in a visual analogue sleepiness scale a nd the Stanford Sleepiness Scale (SSS). As regards cognitive performance, s ignificant effects were found on speed measures, while accuracy was not aff ected. The number of explored rows was higher after the baseline night than after the sleepless night, and showed a consistent time-of-day trend. Omis sions ratio (OR), false positives ratio (FPR) and hits ratio (HR) did not s how any significant effect. Subjective ratings of sleepiness varied accordi ng to speed measures, being affected by sleep deprivation and time of day. Since similar effects were found with an oculomotor task, detrended functio ns for all variables across the 40 It of continuous wakefulness were calcul ated. A circadian effect was found, in which speed measures seem to be more affected than accuracy ones in both visual search and oculomotor tasks. It is concluded that 40 h of prolonged wakefulness significantly impairs perf ormance in a brief cognitive visual search task. Such a performance worseni ng is evident on speed, but not on accuracy indices, and is strictly relate d to the deterioration of oculomotor performance, indicating a clear circad ian effect. (C) 2001 Elsevier Science Inc. All rights reserved.