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Abstract

Data were collected in 48 experiments from subjects who lived singly in an underground isolation unit without any temporal cues. By recording the sleep-wake cycle and rectal temperature, two states of the circadian system could be distinguished: internal synchronization with equal periods for the sleep-wake cycle and the rhythm of temperature (n = 33), and internal desynchronization either by a lengthening of the sleep-wake cycle to more than 28 h (n = 12) or by a shortening to less than 22 h (n = 3). Due to desynchronization, the duration of wake time varied within the limits from about 10 to more than 30 h. The subjects were asked to press a button whenever they thought that one hour had passed. The intervals produced in this manner were longer than 1 h, and varied in strong proportionality to the duration of wake time. This relationship held intraindividually as well as between subjects. It is concluded that the passage of subjective time is closely coupled to the sleep-wake cycle.