At each visit, participants will receive a different treatment. During these visits, participants will remain awake for up to 40 hours at a time, while their eye movements, and brain, muscle, heart, and breathing activity are monitored. Urine and saliva will be collected, and participants will undergo various cognitive performance testing measures. At 3-week intervals between each visit, participants will record sleep habits and will wear the activity and light exposure monitoring device. A sleep diary will also be maintained by participants for 3 weeks following the end of the last visit.