Circadian

• Circadian rhythms last 24 hours
• Circadian rhythms are internal biological clocks lasting 24 hours
• Circadian rhythm - the sleep wake cycle
• The SCN controls the sleep wake cycle and is found in the hypothalamus
• Siffre supports an innate sleep wake cycle by staying in a cave for 6 months with no external cues to guide his sleep cycle. He found that without light cues which usually trigger the SCN, his sleep wake cycle was around 25 hours.
• AO3. Siffre ‘s research is based on one individual. This is a case study, meaning it is ideographic and it is therefore hard for us to generalise these findings to the whole population. This lacks ecological validity. However, as the study was longitudinal it can provide a much deeper insight into the long term effect of the SCN on the sleep wake cycle rather. The study is also qualitative, and provides a lot of data that cannot be found from other studies
• AO3. There are individual differences in the sleep wake cycle. Duffy said that there are morning people who prefer to sleep and wake earlier, and night people that prefer to sleep and wake later. This means that the sleep wake cycle could differ slightly for people, lowering the generalisability of the study.
• AO3. There is issues with the research methodology of Siffre’s study. He was not isolated from artificial light, which could have affected his sleep wake cycle. This lowers the internal validity of the study, casting doubt on his findings.
• AO3. The results of Siffre ‘s study could provide evidence against an innate sleep wake cycle. His sleep wake cycle was slightly over 24 hours when he left the cave, which is not specifically a 24 hour sleep wake cycle. Siffre also thought he spent longer in the cave than he actually did. This means that he felt as though his days were longer than they actually were.