Figure 2A.

Macroscopic records of the effect of human isolation upon the sleep-wakefulness rhythm. For the individual, the subjectively estimated time of day and calendar date differ greatly in the isolation of a cave (upper row) from that recorded in societal life (lower row). Waking and sleeping of 3 subjects is plotted on top as a function of subjectively estimated time in isolation and at the bottom as complemented by one-way (cave-to-surface only) telephone to a team outside a cave by Michel Siffre (MS) and two other subjects, TS and JL (top). Note that on returning to society, all 3 subjects thought they had spent much less time in isolation than they actually had. JL readjusted her clock-hour and calendar-date estimate following each menstruation, hence the gaps in the figure on the top right (see also Table 2).