Figure 5.

The three-pulse PRC to 0.5 mg (solid curve) and 3.0 mg (dashed curve) of exogenous oral melatonin generated from subjects free-running during 3 d of an ultradian light/dark cycle (LD 2.5:1.5). Phase shifts of the circadian clock, measured by the DLMO, are plotted against the time of administration of the melatonin pill relative to the midpoint of each individual’s assigned baseline sleep schedule at home before the laboratory sessions. The vertical lines show the average assigned baseline bedtime and wake time.