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  • Created by: Amira
  • Created on: 13-01-14 20:57

Discuss the role of exogenous zeitgebers in one or more biological rhythms. (8+16)m.


Exogenous zeitgebers, literally means external light givers. This is a psychology term used to describe external factors that have impact on biological rhythms.


The most famous research on exogenous zeitgebers is Michel Siffre’s case study. He spent long periods of time in caves trying to figure out his biological rhythm. When he was awake, he would have a bright light with him (which was artificially) that he kept on when he was awake, and he would turn this light off when he was asleep. His rhythm settled down to approximately 25 hours, but sometimes it would change dramatically to 48 hours. This suggests that without exogenous zeitgebers, (such as light), we frequently lose the ability to maintain a sleep-wake cycle.


This study is criticised because Siffre used artificial light. Czeisler found that using just dim light alone, could shift a free running cycle down to 22 hours and up to 28 hours. This threatens the validity of Siffre’s study as it was tampered using dim lighting, hence the circadian rhythm of Siffre may have been adjusted and changed accordingly.


Alongside this criticism for validity, Siffre’s study was a case study which meant his cycle may or may not have been typical of all people, and living in caves may have had effects on his behavior (he was depressed, which may have led to increase in sleeping- which would change his sleep-wake cycle). This makes his study ungeneralisable.


Siffre’s study is supported by Asch and Wever


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