Evaluations - A03

• Strength of endogenous pacemakers - supported by research, Morgan removed SCN from hamsters, found circadian rhythm disappeared. Furthermore, when hamsters that were bred with circadian cycle of 20 hours had their SCN transplanted to normal hamsters, the normal hamster display 20 hour cycles too. Demonstrates SCN involved in pace keeping circadian rhythms and changes within SCN also lead to changed in our sleep cycle. Thus supports understanding of role of EP and how internal factors influence biological rhythms.

  C - x unethical, ungeneralisable reducing validity
• Strength of endogenous pacemakers - supported by unique case studies, Michael Siffre spent 7 months in cave despite being fed and active, lacked cues about time of day. Found that sleeping pattern settled at 25 hours. Shows patterns of sleep and waking up internally controlled by EP, not often influenced by changes in external environment. Supports role of biological / endogenous factors on our sleep cycle.

  C - had torchlight which is extraneous variable, impacted results
• Strength of exogenous zeitgebers - supported by research, Burgess found when participants exposed to continuous bright light before long flight to far destination, circadian rhythm shifted by 2.1 hours over course of study. As result, ppts felt sleepy two hours earlier in evening and were well adjusted to local time at their destination upon arrival. Shows influence that external cues (bright light) have over sleep/wake patterns and how changes in such stimuli often alter times we sleep. Supports understanding of role of EZ, used to advise ppl in real world to improve quality of life.
• Strength of exogenous zeitgebers - supported by research on blind people, Skin found that despite blind people lacking visual perception a vast majority of them still able to have some light perception due to functioning of cells containing melanopsin, allows them to reset their circadian rhythms. Fact that despite lack of visual perception, blind people's circadian rhythms influenced by presence of external light shows such EZ have strong influence over sleep/wake cycle. Supports role of light as EZ increasing validity of research.