Discuss research into biological rhythms (24 marks)

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Discuss research into biological rhythms (8+16)
Research into circadian rhythms has assessed the effects of isolating participants from their external
time cues (exogenous zietgebers) on our 24 hour cycles, and suggesting that an internal body clock
(endogenous pacemaker) creates a free-running cycle of 25 hours.
For example, Siffre reported a case study of his own experiences in an underground cave for 2
months. Without any exogenous zeitgebers to guide him, his sleep/wake cycle generally adjusted to
25 hours though sometimes changing dramatically up to 48 hours.
Similarly, Aschoff and Weaver (1976) also designed a temporal isolation study by placing participants
in a ww2 bunker without any environmental time cues. They found that the free-running cycle
persisted with a sleep/wake cycle of 25 hours, though sometimes increasing to 29.
A weakness into research of circadian rhythms is that they can be argued to lack internal validity.
Although natural light sources have been removed, there is still artificial light from cameras and
torches which has been shown to also reset endogenous pacemakers, thus interfering as an
extraneous variable.
This is exemplified through Czielser et al (1999) who altered participants' circadna rhythms down to
22 hours and up to 28 using only dim lighting to alter the release of melatonin from the pineal gland.
As a result, the findings do not reflect true isolation and lack internal validity, so the rhythms
measured may not have settled so well in an environment of true isolation.
Similarly, Siffre's study is criticised as being a case study which reflects only his personal individual
differences which cannot be generalised across to the wider public (for instance his motivation to be
isolated, and his bodily history of cave exploring).
Other research has investigated a possible circadian cognitive performance link to the core body
temperature cycle. It's lowest around 4:30a.m (36 degrees) and highest at around 6:00p.m (38
degrees) with a slight trough after lunchtime.
Folkard (1977) investigated the learning ability of young teenagers by asking them to recall a story a
week after it being read to them (either in the morning or evening). The higher afternoon
temperature group showed superior recall and understanding, suggesting that cognitive
performance might be superior with higher body temperature.
This research into cognitive performance rhythms has real world applications into education because
it's implied that learning would be more successful at particular times (possibly copying countries
such as Span where students go home at lunch and return in the afternoon), as reflected in the PISA
country education rankings with Spain scoring higher than England.
The lack of reliability in this area however means that caution must be taken when implementing
applications until conclusive research has determined why students wield conflicting results.
The main flaw of research into circadian rhythms is that studies often fail to account for individual
differences within 24 hour rhythms, especially how people are far from `average' given differing
health, customs and socioeconomic backgrounds. Research by Siffre showed that his body clock
slowed with age, isolation studies have shown that people react differently and research has shown
people differ in their chronotype (a `morning' or an `evening' person).
This is a problem for research in this area because it limits the applications of the findings; for
example knowledge about what time is best to perform cognitively will depend on the individual.

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Without further high quality research on the differences between people's cycles, our knowledge is
limited and applications may be useless or harmful to those who don't have a `typical' cycle.
Alternatively, infradian rhythms repeat themselves over a greater period of time- rhythms that las
longer for a day, such as weekly, monthly or even annually (circannual rhythm). For example, bird
migration and the female menstrual cycle are two infradian rhythms.…read more


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