For each session, the study participants spent eight hours in bed one night, were only allowed two hours of sleep the second night, and then were allowed to have unlimited sleep the third night. But the sessions differed this way: For one of the sessions, the participants were not allowed to take any naps after the night of two hours’ sleep. But for the other session, the participants were able to take two 30-minute naps during the day following the night of two hours’ sleep