Endogenous Pacemakers and Exogenous Zeitgebers

• A limitation of research into endogenous pacemakers is the use of animal studies.
• For example, there is an issue in generalising findings from research into the sleep/wake cycle using a chipmunk study because cognitive factors (e.g. animals lack a cerebral cortex) may be more significant in humans.
• Furthermore, ethical concerns arise from Decoursey's study as well, due to the animals' SCNs being destroyed and exposing them to great harm and potential risk when returning them back to their natural habitats.
• This weakens both the appropriateness and support for research into endogenous pacemakers as these issues and ethical concerns may not be easily justified.
• A limitation of research into exogenous zeitgebers is methodological issues.
• For example, Campbell and Murphy's study has been criticised as there may have been some light exposure to participants' eyes, which acts as a major confounding variable.
• Also, isolating one exogenous zeitgeber (light) in this way doesn't give insight into the many other zeitgebers that influence the sleep/wake cycle.
• This weakens both the internal validity and support for research into exogenous zeitgebers given that some studies may have ignored or underplayed the way in which different exogenous zeitgebers interact.
• A limitation of research into endogenous pacemakers and exogenous zeitgebers is that they interact.
• For example, only in exceptional circumstances do endogenous pacemakers free-run unaffected by exogenous zeitgebers.
• Total isolation experiences (e.g. Siffre's cave study) are extremely rare and present an unrealistic view of how the system works.
• This weakens both the ecological validity and support for research into endogenous pacemakers and exogenous zeitgebers as they both interact in real life and so it makes no sense to separate them just for research purposes.