Protocol
napping
POSITIVE
Participants completed all four conditions in a repeated-measures design: no nap, 10 min nap, 30 min nap, and 60 min nap. A balanced Latin square procedure was used to counterbalance the order of conditions and stimuli. Participants were not informed of the order of conditions or the nap condition they would undergo until arrival at the sleep laboratory at each visit.Participants were instructed to keep habitual sleep habits throughout the experimental period (nocturnal sleep of 6–6.5 hr and sleep and wake times between 23:00 and 08:00, respectively) and to avoid napping on the day of each session. Participants wore an Actiwatch (Actiwatch 2, Philips Respironics Inc., Pittsburgh, PA) and filled in sleep diaries 3 days prior to each session to verify adherence with these instructions. Average TIB was 6.32 ± 0.48 hr and total sleep time (TST) was 5.23 ± 0.61 hr, durations that are typical in Singaporean young adults. Participants were asked to refrain from medication, nicotine, alcohol, caffeine, and vigorous exercise 24 hr prior to each session. They were instructed to have a normal-sized lunch by 11:30 before they arrived at the laboratory at 12:00. After their actigraphy and sleep diary records were verified, polysomnography was applied (including the wake group).For each session, the pre-nap test was administered at approximately 13:15 (Study protocol. Participants completed all 4 conditions in a fully within design: no nap, 10 min nap, 30 min nap, and 60 min nap. The pre-nap test battery (Karolinska Sleepiness Scale, Digit Symbol Substitution Test, Positive and Negative Affect Scale, 3-min Psychomotor Vigilance Task) was administered at 1315. In the 10 min nap, 30 min nap, and 60 min nap conditions, lights-off times were 1420, 1400, and 1330, respectively. Post-nap tests were conducted at intervals of 5 min (to assess sleep inertia), 30 min, 60 min, and 240 min. The encoding session for the picture encoding task began 90 min after waking from the nap, and retrieval took place 210 min after encoding.At the end of each session, participants were given a new sleep diary and provided with an Actiwatch for the next session which was scheduled at least 1 week later. At the end of the experiment, participants were debriefed and reimbursed accordingly.