Figure 2.

Average neurocognitive performance and alertness by day (psychomotor vigilance test [PVT] and Karolinska Sleepiness Scale [KSS]). Average of the two common test batteries scheduled 8 and 10 hours after wake time for the reciprocal mean reaction time (RT) (A), fastest 10% mean RT (B), and number of lapses (C) from the PVT, and KSS ratings (D). Better performance is represented by smaller values for all measures. The first, second, and third cycles of sleep deficiency are represented by filled circles, unfilled squares, and filled triangles, respectively. See the text for x-axis definitions.