AP PSYCHOLOGY

Detailed explanation-1: -In 1962, a French speleologist named Michel Siffre spent two months living in total isolation in a subterranean cave, without access to clock, calendar, or sun.

Detailed explanation-2: -French researcher Michel Siffre conducted several experiments where he confined himself to a cave, where there was no natural light, in an attempt to find out the effects that this would have on his sleep cycle and therefore how reliable his internal body clock was.

Detailed explanation-3: -He then organized several similar underground experiments for other speleologists. In 1972, Siffre went back underground for a six-month stay in a cave in Texas. He found that without time cues, several people including himself adjusted to a 48-hour rather than a 24-hour cycle.

Detailed explanation-4: -Siffre (1975) found that the absence of external cues significantly altered his circadian rhythm: When he returned from an underground stay with no clocks or light, he believed the date to be a month earlier than it was.

Detailed explanation-5: -Diurnal (night and day) Circadian (24 hours) Ultradian (less than 24 hours) Infradian/Circalunar (1 month)