Figure 1.

Schematics of the laboratory study design in the simulated nighttime duty (SND) experimental condition (top) and the simulated daytime duty (SDD) control condition (bottom). Each bar in each schematic represents a day; time of day is indicated above the first bar. Gray bar sections indicate scheduled wakefulness, and black bar sections indicate scheduled sleep. Sleep periods recorded polysomnographically are marked PSG. Dashes indicate the adaptation/baseline period (starting on day 1), 34-hour restart break (starting on day 7), and recovery period (starting on day 13). Periods not marked with dashes represent the simulated duty cycles. Neurobehavioral performance and simulator driving test blocks are indicated by strings of diamonds: 20 test bouts in each of the two duty cycles and three practice bouts during adaptation. Total time scheduled for wakefulness, sleep, duty cycles, restart breaks, and test bouts is equal for the two conditions.