Figure 2B.

The amplitude of a circadian rhythm in a mental function, time (2-minute) estimation, is much smaller under conditions of desynchronization vs. that under 24-hour synchronized conditions. Note that in all subjects, during isolation, there is a peak in the spectrum away from the vertical line that corresponds to exactly 24 hours. In TS and JL, who had continued to record sleep-wakefulness during the days after isolation, the amplitude is much smaller in isolation than under a societal routine.