FIGURE 1.

Schematic representation of study protocols for an individual with a habitual sleep time from midnight to 8:00 a.m. (clock time is provided on the x-axis). For protocol 1, (A) a baseline night of sleep at this habitual time is followed by a baseline day of wakefulness (11-hours). After baseline assessments, the circadian protocol is introduced which evenly distributes behaviors across all circadian phases with 10 identical consecutively recurring 5-hour 20-minute cycles (2-hour and 40-minute of scheduled wakefulness and 2-hour and 40-minute of a scheduled sleep opportunity) across 5 days. For protocol 2, (B) two nights of sleep at the participant’s habitual sleep time with 16-hour scheduled wakefulness in between, is followed by a circadian protocol with reoccurring 18-hour “days” (12-hour wake and 6-hour sleep cycles) across 7 days. Black boxes indicate scheduled sleep opportunities in darkness (<0.1 lux), gray bars indicate scheduled wakefulness in dim light (∼3 lux), and white boxes represent regular room light used when participants are admitted or discharged from the study.