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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.
Aim
Siffre aimed to find out what would happen to a person’s circadian rhythms if they were cut off from all zeitgebers, such as light, dark and an awareness of time, and how this would affect their reliance on their endogenous pacemaker to tell them when to eat and sleep.
Method
The only participant in the experiment was Siffre himself. He spent 179 days and nights in an underground cave. He had no lights, clocks or radios to give him any indication of what time it was and so his only influence was his internal body clock, which had a ‘free run’ to do what felt natural.
His only link to the outside world was a telephone where he could keep in touch and was also monitored by video camera and by wires attached to his body that monitored how he was functioning.
Results
- At first, Siffre’s sleep-wake patterns were very erratic
- After a while, they settled into a 25-hour pattern rather than 24 hours, which is the time a human considers to be a full day and therefore how long a sleep-wake cycle should last
Conclusion
Siffre concluded that humans do have a natural sleep-wake cycle, but without the influence of external zeitgebers it naturally settles into a 25-hour pattern, so an hour longer than what people would experience normally.
Strengths of the study
- The study gives validation to the idea that humans’ sleep-wake cycles are regulated by endogenous pacemakers
- The study lasted a long time so Siffre’s rhythms were allowed to settle into a natural pattern
- Similar studies that have been carried out with rats have also found that the sleep-wake cycle increases, which supports the findings
Weaknesses of the study
- The sample size here was just one person so findings are not generalisable
- A cave is not where humans would naturally go to sleep and so the study lacks ecological validity
- It has been suggested that other factors, such as loneliness, may have affected Siffre’s sleep-wake cycle
