exogenous zeitgeber

• -confounding variables. campbell and murphy research. being woken up from heat from the light which cause disruption to circadian rhythm. as other researchers were unable to replicate findings therefore the research has low reliability and external validity as unable to be applied
• social cues:

  newborn random circadian rhythm 6 weeks. 16 weeks entrained by parents through determined meal and bedtimes. jet lag avoided by adopting meal and bedtimes of the place travelling to when travelling long distances
• external environmental factors that affect the brain and entrain biological rhythms
• light:

  resets the main bodys endogenous pacemaker. scn maintains circadian rhythm. light indirect influence on processes such as hormone secretion and blood circulation
• campbell and murphy 1988:

  demonstrated light can be detcted by skin receptors even though not detected by eyes. 15 pps woken various times during the night and light pod shone on back of leg. researchers managed to produce deviation in pps usual circadian rhythm by 3hrs
• evidence suggested that ppl have age related insomnia due to poor quality sleep due to age. may be due to falling asleep earlier and having broken sleep during the night (duffy 2015). but studies suggested that exogenous factors are responsible for changes in sleep patterns in elderly. hood 2004 found management of insomnia was improved in elderly if they were more active and higher exposure to light
• miles 1977 recount the study of a young man blind from birth who had abnormal circadian rhythm of 24.9hrs despite exposure to social cues e.g meal times but circadian rhythm unable to be adjusted. the findings show the importance of scn and light in maintaining a regular circadian rhythm. but should be noted that the individual managed to keep a circadian rhythm despite the absence of light. suggesting a free running circadian rhythm largely governed my endogenous pacemakers
• the experience of ppl who live with little light winter and little dark summer such as the artic circle have similar patterns of sleep all year round despite spending nearly 6 month in complete darkness. shows the overwhelming influence of endogenous pacemakers on circadian rhythm despite exogenous changes. but can be explained by the manipulation exogenous factors such as having regular meal times to entrain cycles. difficult to separate influence of endogenous and exogenous factors