Figure 1.

Protocol for the laboratory phase of the study for the early sleepers and late sleepers. Saliva samples (closed circles) began 5.5 h before scheduled pre-laboratory bedtime (dashed line) and continued until 5 h after scheduled bedtime for each group. Ambient light levels were maintained at <2 lux during the saliva sampling period (gray bars) and participants remained awake in a controlled posture. Black bars illustrate the 3-h sleep period permitted after collection of the final saliva sample, as part of the larger protocol.