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Similarly, Geetha (1989) participated in an experiment referred to as ‘My Life in a Bunker’. Geetha lived in a timeless environment (facility) for thirty-five days with artificial lighting, no zeitgebers and no contact with the outside world other than written notes and with recording apparatus to monitor her behavioural patterns and physiological functions. She was also asked to indicate when she thought two hours had elapsed enabling them to monitor her time awareness ability. Furthermore, during pre-isolation, isolation and post-isolation Geetha had her core body temperature measured regularly. This enabled researchers to get more accurate results, as body temperature rhythms are an indicator of circadian and ultradian rhythms.

In Geetha’s estimation she had been incarcerated for twenty-two days. This was due to her circadian rhythm elongating to a 45.9 hour day, otherwise known as a ‘circa-bidian’ (forty-eight hour day). Conversely her temperature rhythm, like Siffre, remained within the circadian, proving that there is more than one body clock at work. After leaving the facility Geetha’s circadian rhythm soon returned to its natural length, demonstrating that zeitgebers and social cues are a significant factor in re-setting the biological clock. Geetha also discovered that her menstrual cycle synchronised with her temperature rhythm. In other words, the infradian rhythm synchronises with the ultradian rhythm and not the circadian rhythm.

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The ‘Bunker’ experiment was more ecologically valid than Siffre’s because the facility’s design was more natural: an apartment setting compared with a cave environment. Also in her favour is the fact that she had no verbal contact with the outside world and therefore could not receive any ‘accidental’ time indicators. Her sample had a higher validity than Siffre, even though it was limited by being self-selecting and on only one individual, as she repeated the experiment three times, which ruled out any confounding variables which may have impacted on the results. However, her second stay was cut short due to mitigating circumstances and it could be argued that there were demand characteristics, as she knew what to expect from her previous experience.

Research has proven repeatedly that our bodily rhythms are reliant on both endogenous and exogenous factors, ruling out the reductionist theory that there is only one cause accountable for maintaining our bio-rhythms. Evidence shows that if we relied on our endogenous pacemaker alone we would have a naturally longer internal clock and we would not be able to reset or adjust the internal clock to coincide with daylight hours, different time zones, shift work and all individuals would sleep for the same amount of time.

On the other hand if we relied solely on exogenous zeitgebers we would still face difficulties as individuals lead different lives for a variety of reasons such as work schedules, social lives, health issues and age. Due to the complex nature of the human body our internal clocks can be adjusted using zeitgebers, which is ultimately essential to assist us with our modern way of life.


Cromie, W.J. (1999) Human Biological Clock Set Back an Hour, Cambridge, Harvard Gazette. [Online] 18 January 2009,

Geetha, L. (1996) Time in a Timeless Environment: My Life in a Bunker, Resonance, Volume 1 (3) pp 66-77.

Green, S. (1994) Principles of Biopsychology: Sleep, arousal and biological rhythms, Reprint (1995), East Sussex, Lawrence Erlbaum Associates Publishers, pp 130-137.

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