AO3

• Evidence suggests there are circadian rhythms in cells and organs of the body, which are independent from the SCN. Research with mice found that changing feeding times changed the circadian rhythm of the liver but the SCN was unaffected. This means there are other complex influences on sleep aside from the SCN.
• Ethical issues with the use of animal studies - chipmunks in DeCoursey study were exposed to considerable harm. The question remains as to whether the things we learn from this study justified the aversive techniques involved.
• The influence of exogenous zeitgebers may be overstated and there is evidence that exogenous zeitgebers have little impact on our internal rhythms - Miles et al reported a young man with a circadian rhythm of 24.9 hours that could not be adjusted with social cues.
• People in the Arctic regions show normal sleep parrens despite the sun not setting fully in the summer months and having prolongued exposure to light.
• There are methodological issues in some studies - Campbell and Murphy (light on the knees) study has not been replicated so is not reliable. It was also questioned whether there were issues with confounding variables; other researchers suggested that there was limited exposure of light to the ppt's eyes.
• Only in exceptional circumstances are endogenous pacemakers unaffected by the influence of exogenous zeitgebers. In normal day to day life pacemakers and zeitgebers interact and research that separates the two makes little sense and limited application.
• Studies that separate the two (Siffre's cave study) often involve total isolation and this does not reflect real life. This means the studies lack validity and don't truly measure the effects of endogenous pacemakers and exogenous zeitgebers in the real world.