Psychology Sleep



Spent 6 months in a Texan cave without any external cues, he just ate and slept when he felt like it. His natural circadian rhythm settled to just over 24 hours but sometimes this would change to up to 48 hours.


  • Being alone for so long could lead to depression and sleep deprivation, hence the longer rhythms.
  • Only an individual case study.
  • Patterns were recorded for a long period of time so is reliable.
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BIOLOGICAL RHYTHMS - Folkard et al (1985)

12 volunteers in a cave agreed to go to bed at 11:45am and wake at 7:45am. They gradually quickened the clock over 3 weeks to a 22 hour day but all except one stuck to a 24 hour cycle.


  • Fairly small sample size.
  • The one who stuck to the timings may have done so to please the researchers.
  • Issues of informed consent as the participants would not have known that the clock would be quickened.
  • Suggests sleep-wake patterns are fixed by internal mechanisms (determinist approach).
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Performance on IQ tests was best at 7pm, where core body temperature is highest, compared to 9am or 2pm.


  • Participants may have been able to practise the same test if they had done it three times. If different participants were used for each test, there may have been individual differences in the groups by chance.
  • May have been due to fluctuating cortisol levels, which is a hormone related to making us alert.
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BIOLOGICAL RHYTHMS - Friedman and Fisher (1967)

Observed a clear 90-minute cycle in eating and drinking behaviour.


  • This may be a form of timing to ensure biological processes work in unison.
  • Sleep stages may be part of a continuum.
  • Real-world application - We can only concentrate for a certain amount of time and fluctuate between high and low alertness. Changing our work routine to fit this may be beneficial.
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BIOLOGICAL RHYTHMS - Russell et al (1980)

Rubbed sweat from one woman's armpit onto the upper lip of another 11. They were kept separate, yet their menstrual cycles synchronised.


  • This is probably due to the action of pheromones.
  • Others suggest menstural synchronicity is due to changes in food or awareness of cycles.
  • Fairly small sample size.
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ENDOGENOUS/EXOGENOUS - Albus et al (2005)

The ventral suprachiasmatic nucleus (SCN) is relatively quickly reset by external cues, whereas the dorsal SCN is much less affected by light.


  • Artificial lighting may disrupt circadian rhythms and thus melatonin production.
  • Women in industrialised societies are more likely to develop breast cancer, perhaps because of this disruption.
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ENDOGENOUS/EXOGENOUS - Buhr et al (2010)

Daily changes in body temperature entrain other circadian rhythms.


  • Determinist approach - Rhythms may be altered exogenously.
  • Desynchronising temperature and sleep rhythms lead to symptoms of jet lag, as seen in the case study of Kate Aldcroft, who spent 25 days in a cave.
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Bred 'mutant' hamsters so they had 20 hour circadian rhythms, then transplanted their SCNs into normal hamsters who displayed the new rhythms.


  • Ethical issues - May have caused distress to the hamsters.
  • May not be generalisable to humans.
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DISRUPTION - Knutsson et al (1986)

Long term shift workers were 3 times more likely to develop heart disease that non-shift workers.


  • It may be that a certain personality would choose to work night shifts, and they may make certain life choices increasing the chance of heart disease.
  • Social disruption may lead to stress and then to heart disease.
  • Sleep in the daytime may be affected by external cues.
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DISRUPTION - Gold et al (1992)

To reduce the harmful effects of shift working, non-fluctuating shifts may be less disruptive as the individual can get used to one sleep-wake cycle.


  • Supported by evidence that found unhappy shift workers had changing rhythms.
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DISRUPTION - Recht et al (1995)

Over 3 years, baseball teams who travelled east to west won 44% of their games, whereas those travelling west to east won just 37%.


  • Studied over fairly long period of time.
  • Real-world application - Should be taken into account in sporting competitions.
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DISRUPTION - University of California (2010)

Twice a week for four weeks, hamsters experienced 6 hour time shifts, creating a jet lag period. They had trouble learning simple tasks compared to a control group.


  • Suggests external cues, such as alcohol and coffee, noisy passengers and low oxygen, don't have a large impact.
  • Using animals has issues of ethics and generalisability.
  • Real-world application - Impaired cognitive ability could lead to accidents.
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NATURE OF SLEEP - Wolfson and Carskadon (2005)

Schools should begin their day later to accomodate the poor attention span of adolescents early in the morning.


  • Supported by the fact that hormones are primarily released at night, leading to sleep deprivation. Lack of sleep leads to impairments in cognitive ability.
  • Hormonal changes result in delayed sleep phase syndrome: teenagers feel naturally more awake at night and find it difficult to wake in the morning.
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NATURE OF SLEEP - Kripke et al (2002)

Those sleeping for 6 or 7 hours had a reduced mortality risk, at 8 hours there was a 15% increase in risk, and at 10 hours the risk was over 30%.


  • Underlying illness may have led to the need for more sleep.
  • Those who sleep more may have more demanding and tiring jobs, which may be more stressful.
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NATURE OF SLEEP - van Cauter et al (2000)

Reduction in SWS leads to reduced production of growth hormone, explaining the symptoms of lack of energy and low bone density.


  • Lack of energy may also be linked to the fact that reducing SWS means they are more easily woken by noise and sleep disorders such as sleep apnoea.
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NATURE OF SLEEP - Laberge et al (2000)

The prevalence of occasional sleepwalking is 40% in 6 to 16 year olds, which declines after age 10.


  • Developmental approach emphasised the changes in patterns.
  • Sleepwalking may be more common in children as the system inhibiting motor activity in SWS is not sufficiently developed.
  • Other parasomnias common in children such as insomnia may be caused by fears, for instance the dark, and 'monsters'.
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SWS enables body repair and REM enables brain recovery.


  • Lack of sleep doesn't always result in damage and there is no need to recover.
  • Much supporting research is based on case studies.
  • Supported by the fact that growth hormone is secreted during SWS, which stimulates growth and enables protein synthesis.
  • Research suggests both REM and SWS may be important for consolidation of memory.
  • Environmental pressures may be a better explanation.
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The amount of REM sleep in any species is proportional to the immaturity of the offspring at birth.


  • Supported by the fact that premature human babies have more REM sleep than those non-premature.
  • The platypus (immature at birth) needs 8 hours REM sleep, whereas the dolphin (can swim at birth) has almost none.
  • More REM sleep is needed as the brain is developing by forming neurotransmitters and memories.
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RESTORATION EXPLANATIONS - Williams et al (1959)

When participants were deprived of sleep for more than 72 hours, they had short periods of microsleep whilst awake.


  • May be why lack of sleep doesn't always lead to damage and there is no need to recover.
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RESTORATION EXPLANATIONS - Rechtschaffen et al (19

Woke rats when they were about to sleep on a rotating disc. After 33 days, all rats died.


  • This may have been due to stress, leading to reduced immune functioning.
  • Ethical issues - Causing harm and distress.
  • Rat and human physiology is different.
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RESTORATION EXPLANATIONS - Breedlove et al (2007)

Found no relationship between the length of sleep and activity levels prior to sleep.


  • May suggest that environmental pressures may be a better explanation.
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Suggested the hibernation theory of sleep. It is used to provide a period of forced inactivity for energy conservation.


  • Smaller animals (higher metabolic rates) have been found to sleep more than large ones.
  • However, the sloth is an exception.
  • Brain activity only drops in NREM sleep, so this is probably most important for energy conservation.
  • We only have a small proportion of information about animal sleep patterns.
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Suggested the waste of time hypothesis. Sleep helps animals stay still when they have nothing better to do with their time.


  • If animals are awake, they are more likely to be injured.
  • They would also be more likely to attract the attention of predators if awake.
  • However, they may be more at risk of predation if they are not awake and alert. Therefore, it is more likely that sleep would have a purpose.
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EVOLUTIONARY EXPLANATIONS - Capellini et al (2008)

There was a negative correlation found between metabolic rates and sleep, supporting foraging requirements but not energy conservation. Predation risk is complex - those sleeping in exposed conditions slept less, but so did those sleeping socially, which is safer.


  • They claimed that previously used methods for data collection were not standardised, whereas theirs were.
  • Those sleeping socially, such as meerkats, are probably more prone to predation risk anyway so double their protection by sleeping less.
  • Correlation does not necessarily show cause and effect.
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Correlations only show association not cause and effect. Many studies are done in artificial environments such as zoos. Evolutionary explanations also cannot tell us which is the most important factor determining sleep patterns. However, it is not a reductionist explanation as it takes into account environment.


  • It is difficult to study animals' behaviour over long periods of time in the wild.
  • It may be a combination of all explanations that determines sleep patterns.
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SLEEP DISORDERS - Zammit et al (1999)

Found patients with insomnia scored lower on the Medical Outcomes Study Cognitive Scale than contol participants, demonstrating problems with concentration, memory, reasoning and problem solving.


  • Certain personality may be associated with insomnia and these people may have lower abilities with reason and problem-solving, which would make sense with primary insomnia.
  • Real-world application - Those with insomnia may be more likely to have accidents.
  • Scoring may be subjective to the researcher.
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SLEEP DISORDERS - Spielman and Glovinsky (1991)

Came up with a model to explain insomnia.

Predisposing factors: Genetic vulnerability. Insomniacs are more likely to experience hyperarousal.

Precipitating factors: Events triggering insomnia.

Perpetuating factors: Maintain the insomnia.


  • 50% of the variance in risk is attributed to genetic factors.
  • Perpetuating factors may be key to chronic insomnia.
  • Not reductionist as it takes into account the environment.
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SLEEP DISORDERS - Lehrman and Weiss (1943)

Sudden sleepiness in narcolepsy disguises sexual fantasies.


  • There is no supporting evidence.
  • This is difficult to test.
  • Psychodynamic explanation.
  • It may be a way of coping with them to minimise the anxiety and distress they may cause.
  • The disorder has clear physiological elements.
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SLEEP DISORDERS - Stanford Medical Center (2012)

Found that more than 90% of narcoleptic cataplexy sufferers have the HLA variant HLA-DQB1*0602.


  • This has also been found to be reasonably common in the general population.
  • Cataplexy is associated with REM sleep so this may be an alternative explanation.
  • 10% don't have this variant.
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SLEEP DISORDERS - University of Tokyo

Discovered a genetic link of narcolepsy. There was a 79% increase in Japanese people, and a 40% chance in other ethnic groups.


  • Suggests a determinist approach may be reductionist: though unlikely, culture may actually have an impact.
  • Other research has found that it doesn't run in families and isn't seen in twins.
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SLEEP DISORDERS - Zadra et al (2008)

Applied the diathesis-stress model to sleep walking. Studied 40 patients suspected of sleep walking, and prevented them from sleeping. On the first night 50% showed signs of sleep walking, and 90% on the second night. Therefore, the sleep deprivation acted as the 'stressor' in those vulnerable to sleep walking.


  • Can be applied to the fact that children have more SWS, leading to more sleep walking.
  • Sample size could have been larger for more accurate results.
  • They weren't confirmed sleepwalkers, and obtaining the participants may have been down to self-reported sleep walking, which may not have been the case.
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