Data are derived from polysomnography and represent minutes (mean + SEM) unless indicated otherwise, for the Morning Sleep (0800 – 1600; n = 14) and Evening Sleep (1400 – 2200; n = 16) groups. Note that prior to Day Sleep 1, the Morning Sleep group had been awake for 26 hours while the evening sleep group for 32 hours. The symbols ‘*’ and ‘∼’ represent a comparison to baseline sleep at the p < 0.01 and p < 0.05 level respectively (paired t-test). The symbol ‘#’ represents a comparison between the Evening and Morning Sleep groups at the p<.01 (unpaired t-test). Sleep latencies were log-transformed for statistical comparisons. The reported comparisons between Sleep groups and Sleep Conditions were done when the corresponding main effect or interaction in the two-way ANOVA with the factors Sleep Group and Sleep Condition were significant.