Sleep states and theories of sleep

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  • Created by: ava.scott
  • Created on: 10-04-15 17:04

The stages of sleep 1,2,3,4

Stage 1

  • transition phase
  • low voltage, mixed frequency
  • alpha waves

Stage 2

  • sleep spindles
  • k-complexes
  • theta waves

Stage 3/stage 4

  • high amplitude delta waves in less than 50% of epoch
  • high amplitude delta waves in more than 50% of epoch
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Stages of sleep REM

  • High brain activity
  • Paralysis- so we dont act out the dreams
  • Rapid eye movement- the scanning hypothesis
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Everybody needs to and must go through the sleep stages. You must progress through them to reach REM.

This means we have no free will over our sleep patterns and no control.

Is this a bad thing? Not partiularly, not hugely socially sensitIve or dramatic.

Good things:

  • You can make predictions about what happens if we dont go through these stages- perhaps leading to disruptive behaviour. This could lead to practical applications
  • We could study it is a biological way-- using empirical and controlled ways.
  • Demand characterstics have no effect as we cant control our sleep- however artificality may change the sleep patetrn and sequence.
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Sleep stages research: Dement

  • 19,579 particpants- 5 studied intensively.
  • looked at sleep stages uses EEG, EOGS and EMGS.
  • Identified and isolated three stages.
  • Also found many individual differences between participants.

This study define and establishes the theory. It is very good support due to its objective nature. The nature of sleep has very litle control, so demand characteristics play little role.

HOWEVER- theory does not acocunt for individual differenecs, so this is a weakness.

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Sleep stages research: Sharpio

  • Studied ultra-marathon runners who had studies 57 miles
  • found they slept about an hour and a half longer after the event
  • Lots more sleep devoted to stage 4 sleep (sws)
  • Also, the disruption of stage 4 sleep resulted in muscle and back pain.

This supports the theory that the different stages have different purposes for the body. Stage 4 sleep is involved in body repair and maintenance, as the marathon runner would have put their body under a lot of stress. Therefore the increase in SWS would suggest that stage helps repair and reduce stress on the body.

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Sleep stages research: Borberly

  • Studied REM deprivation
  • Found that those deprived of REM sleep made 31 attempts to reenter REM on the first night.
  • 51 on the second night
  • over 60 on the third night.

This also supports the theory, as its shows that REM stage is a separate phenomenon, to the other stages, as a deprivation was contested by the body. Shows that the human body needs all the stages to operate, and we have evolved to try and gain constant amounts sleep stages.

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  • empirical measurements using EEGS, which increases control and objectivity.


  • Low population validity (Dement = 5 ppts, Sharpio= just marathon runners)
  • Artificial settings- people may sleep differently without being monitored.

Low ecological and populational validity, reducing the generalisablity of the studies.

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Sleep stages wider evaluation

Practical applications

If someone is feeling unwell, this may be due to irregularity in their sleep. The stages can allow better diagnosis and potential practical applications.

Empirical study of sleep has lead to a lot of progress in the field, which is good for the field and psychology.

Individual differences.

Although many differences between indviduals were recorded, it has not been factored into the theory. This means the predictions we make are not going to determinally valid as we would expect. This is a weakness in the theory, as other factors play a role in the sleep stages in people.

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Lifespan changes in sleep: BABIES

Premature Babies:

  • REM accounts for 80% of sleep.


  • REM accounts for 50-60% of sleep
  • sleep around 16 hours a day waking up every hour or so
  • SWS= quiet sleep REM= active sleep
  • circadian rythym established by 12 months.
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Lifespan changes in children and teens


  • 25% of sleep time spent in REM
  • approx. 10 hours spent sleepng but varies
  • sleep cycle lengthens to 90 minutes
  • parasomniacs and night terrors common


  • 20% of time spent in REM
  • 9-10 hours
  • more nocturnal
  • REM is accompanied by 0rgasm and £jaculation
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Lifespan changes in sleep: Adults


  • 25% spent in REM
  • 8 hours average spent sleeping
  • sleep cycle is 90-120minutes long
  • insomnia more likely

60s, 70s + 80s

  • 10% REM
  • less time spent sleeping
  • more naps
  • 50% less stage 3 and stage 4 sleep
  • more difficulty getting to sleep
  • experience phase advance


  • No S3 or S4 Sleep
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Lifespan changes in sleep: IDA


Everybody will experience these changes in sleep as they get older. This means cannot help but experience phase advance as we get older and have less REM sleep.

This can help diagnose sleeping or other disorders if someone has an irregularity.

However it ignores individual differences, and this could provoke anxiety if someone does not fit the normal pattern. This makes the theory less generalisable, as the differences between people may be more signfiicant than the similarities across an age group.

Biological pproach

easy to test empircally, creating more valid conclusions 

many practical applications and assists in diagnosis of conditions.

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Lifespan research: Breedlove's babies

  • Suggested that a high level of REM sleep that happens before and after birth helps the brain grow and become organised.
  • This is because babies are learning so much.

This supports the idea that people need less sleep as they get older, as they have already developed an organised perception about the world, and are learning a lot less for the first time. Therefore, they need less time in REM sleep to organise this.

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Lifespan research: Wolfson and Carskadon (teens)

  • 3000 american high school students
  • found that on average 7.3 hours sleep a night,
  • one quarter were getting 6.5 hours or less
  • Those who were achieving mainly As went to bed earlier and got on average an hour longer
  • those with sleep disturbances were more likey to get bad grades


This supports the idea that sleep plays a big role in cognition, as the teens who slept more achieved better academic grades. This suggest they have more REM sleep, and are therefore more organised.

CONTROL-- other variables may link the two- young carers dont have time to sleep or study

Ties in with restoration theory, as the REM sleep allows organisation of the mind and nervous system after each day.

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Lifespan research: Schools

Monkseaton high school-

  • Started lessons at 10am
  • 800 pupils 13-19yrs old
  • general absenteesim reduced by 8%, and persistent absenteesism by 27%

Israeli kids by Lufi et al

  • middle schools delayed starting time by 1 hour
  • childrens slept 55 minutes longer every night

APPLICATIONS: This research could be used to adjust school and college policies, to encourage phase delay. This will encourage students to sleep more allowing sufficient amounts of REM sleep allowing better organisation and grades, and less absenteesim. It could also encourage better health in students.

However, not all age groups may benefit from this,such as younger children, or schools for adults. More research is needed before wide spread changes occur.

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Lifespan research: older people

  • Sleep 3 and 4 declines in quantity with age.
  • Young sufferers of dementia have very little stage 3 and 4 sleep.

This suggests that s3 and s3 sleep is vital for brain function, development and health. They are not passive parts of sleep.

CONTRADICTS- The restoration theory suggested that the release of human growth hormone during stage 3 and 4 sleep meant those stages were just for physical restoration, not nervous system. HOWEVER the brain is physical, so may promote the growth and creation of neurones.

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Lifespan research: Ancoli-isreali

Older people and sleeping problems

  • older people report problems such as waking up more, going to sleep earlier and more naps.
  • Ancoli-Isreal suggestsed that healthy older adults dont have sleeping problems, so perhaps it is the illness , and its treatment, that is more likely to come with age that is causing poor sleep, and not the poor sleep causing illness.

This displays the difficulty in studying life span changes, as cause and effect is very difficult to isolate and establish.

  • There are many factors effecting sleep, and many things that sleep effects.
  • Different age groups may have similarities that effect sleep, and it is more social than biological differences that define the sleep patterns.
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Lifespan research evaluation

CAUSALITY + CONTROL- effecting internal validity and prediction abilities of the research/theory. The studies do not establish cause and effect, as sleep and social effects  are so intertwined e.g.

  • The lower grades found in Wolfson and Carskadon study may be due to the childrens background e.g. those who sleep more my have parents that encourage more revision/reading. The children who sleep less may have more time consuming hobbies or responsibilities, affecting their schoolwork, not the amount of sleep.
  • What about older people who engage in learning and new activities? Do they have more or less REM?
  • Monkseaton high school may have shown improvements because children woke up earlier nd were able to fulfill more school work/activities, improving their well being.
  • Dementia sufferers- dementia causing poor sleeping, or poor sleeping casuing dementia???
  • MAY NOT BE PHYSICAL AGE causing difference, but the social differences if the age groups causing variety in sleeping patterns-- perhaps having young children makes you sleep more?

Makes the stages less convincing as a deterministic apsect of human sleep- maybe social changes would result in different sleep patterns. Therefore, the theory does not have temporal, or prediction validity.

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Lifespan changes wider evaluation

Individual differences/reductionism

Webb (Univeristy of Florida) found marked differences between particpants. Data was consistent for individuals but not between participants.

This shows we cannot generalise within age groups,as the individual differences are more significant than the similarities.

Practical applications-apart from school times

Those showing early signs of dementia may be given sleep-inducing medicine, and this could help reduce progression of the condition. 

----However, the research isn't that strong and it could easily be that the dementia is causing worse sleep not vice versa.

Babies needs to get enough sleep for cognitive development.

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Evolutionary theories of sleep: Hiberantion


Sleep gives a survival advantage because it helps conserve energy by:

  • reducing energy spent on behavioural activity because we are asleep

  • reducing energy spent as heat since sleep causes a drop in body temp and metabolic rate

Hibernation theory predicts that sleep will increase when the potential for energy loss is great whilst awake- e.g. when it is cold energy is needed to stay warm. Sleep should also increase when energy intake is low- scarce food- because energy needs conserving even more.

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Evolutionary: PREDATION theory

PREDATION THEORY: explains amount of sleep needed by:

  • threat of predators and safe habitat
  • need for food and metabolic activity

Animals that are at risk and cannot find a safe place to sleep , generally have high metabolic rates and need to eat a lot- this means they sleep very little

  • e.g. SHORT TAILED SHREWS sleep around 2 HOURS, even with a safe burrow, because of their high metabolic activity.
  • Prey animals such as sheep dont have a safe burrow and eat all day sleep around 4 HOURS.
  • Lions sleep a lot as they have very little threat from predators, and eat infrequently.
  • Animals sleep still so as to avoid attention from predators.

predicts WHEN animals sleep

  • poor vision (humans) sleep at night as they cannot see predators and keeps them out of trouble.
  • Cats can see well so stay awake during the night as it gives them an advantage.
  • This is adaptive behaviour.
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Evolutionary theory of sleep: IDA

Evolutionary approach:


  •  logical explanation

  • see patterns amongst mammals and animals


  • Impossible to test empirically
  • We can never postively justify/prove the theory
  • HIGH BRAIN ACTIVITY when sleeping as shown by EEG's-- this uses energy?

Makes the theory less compelling and reliable. 

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Evolutionary resaerch: Alison and Cichetti

Alison and Cicchetti

  • analysed the sleep patterns of 39 species and found a relationship between a risk of predation and amount of sleep.
  • Animal at high risk sleep less.

This supports the predation theory as animals as high risk would not be able to run away or protect themselves from predators whilst asleep, so it is adaptive behaviour to stay awake. Those who stayed awake are more likely to survive and pass on their advantageous genes to offspting.

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Evolutionary research: Hibernation observation

  • In winter, when food is more scarce, some species hibernate.

This supports the hibernation theory, as energy loss would be high during the winter, as it is cold, and with scare food, this could result in weight loss or death.

Therefore, animals who had the tendency to hibernate, and therefore preserving energy, would survive and pass on these genes to offspring, resulting in a species with an overall ability to hibernate.

HOWEVER- predation theory would say that it also helps animals hide from predators.

Restoration theory could also say that is helps bodily restoration and nervous system organisation, so this observation does not just justify the hibernation theory alone.

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Evolutionary research: sleep deprivation

The severe effect sleep deprivation had on Tripp, Gardner and Cork (death!) shows that sleep plays a larger role than just energy conservation and hiding from predators.

If these theories were true, people at no risk would be able to continue forever without sleep as long as they had a large, constant amount of food available. This isn't possible.

Therefore, this research does not support the evolutionary theories, reducing their validity and usefulness.

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Evolutionary research: Sharpio and Borberly

  • The ultra marathon runners needed a lot more sleep- this could be due to the huge expenditure of energy causing the body to believe it now needs to preserve energy.
  • This supports the hibernation theory.
  • Increased back pain after disruption of stage 4 sleep- neither evolutionary theory explains this.
  • The stages should have no effect, as all sleep is for the same purpose.
  • found that attempts to reenter REM increased when it was dirsupted.
  • This shows the theory is not detailed and overlooks key aspects of sleep and its uses.


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Evolutionary research evaluation

Low reliability

  • the studies are mainly observational and natural studies, and lack experiemental control and settings.
  • Therefore, no cause and effect can be established.
  • e.g. maybe the small amounts of sleep lead to a high metabolic rate and little focus of developing safe burrows, rather than the other way round.
  • The hibernation observation could have many explanations, not just evolutionary.
  • The more reliable studies (sharpio and borberly) either support other theories more, or don't support evolutionary theory at all.

This is bad for the theories, as they just say there is a relationship between species and the amount fo sleep, but not explaining the details of the relationship. Scientifically valid studies aren't supportive of the theories, suggesting they are innacurate.

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Evolutionary wider evaluation


  • Theorie fails to explain intricacies of sleep, and why some people may have issues sleeping.
  • As we have evolved our sleeping patterns, they must be universal and stable. However research has shown that sleep patterns change with era/ times e.g. the one-two hour period humans used to wake up in the night- how does the theory explain this?


  • Humans have no predators and a constant supply of food- they should sleep all day to conserve as much energy as possible.
  • lifespan changes unexplained.
  • sleep stages unexplained
  • REM- uses alot of energy STAGE 4- human growth hormone released, so sleep cannot be for just conservation of energy.
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Restoration theories: Oswald and Horne


  • REM allowed the organsiation and restoration of the nervous system
  • NREM involves the restoration and repair of the body via release of human growth hormone/
  • HGH is release during the day but even more during stage 4 sleep.
  • this suggests this stage is for bodily repair.


  • Sleep is needed for psychological recovery
  • optional sleep (stages 1-3) and core sleep (stage 4 and REM)
  • Core sleep is critical for  function as the brain restores and organises itself after activities of the day.
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Restoration theories: IDA

Biological approach as it looks at the role of growth hormones and restoration of the nervous system and body.


  • easily tested using empirical method, giving reliable and valid conclusions.
  • giving more effective and useful practical applictions.
  • ALTERNATIVELY--- sleep deprivation is unethical so STILL hard to research


  • reductionist- the theory suggests there is no social side of sleep, whenthere are cultural and temporal variations.
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Restoration research: sleep deprivation

Peter Tripp

  • Stayed awake for 8 days
  • suffered hallucinations and delusions
  • didn't ever fully recover
  • Hornes theory-- as brain function disintegrated, because it couldnt repair and organise itself after the day.

Randy Gardner

  • 17 years old
  • awake for 11 days
  • suffered disorganised speech and blurred vision and paranoia
  • Oswald theory- physical symptoms are prevalent, suggesting not enough human growth hormone was emmitted to repair and restore functioning  of the body and nervous system.

Michael Cork- fatal familial insomnia.

  • He died!
  • shows that sleep is absolutely vital to our life and wellbeing.
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Restoration research: Sharpio + Empson


  • studied ultra-marathon runners
  • They slept on average and 1.5 hours longer after the marathon.
  • They also spent a much larger proportion of sleep in stage 4.


  • disruption of stage 4 sleep in healthy people resulted in back and muscle pain/stiffness.

These studies support mainly Oswalds theory, as physical exertion lead to more stage 4, sleep showing it is a repsonse to help repair body after strain. Lack of stage 4 sleep also causes reduced physical wellbeing. This may be because human growth hormone isn't being released enough, as no stage 4, so the body canot grown new cells and repair itself.

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Restoration research: Dement + Borberly


  • REM-deprived participants were more irritable, more aggressive and more unable to concentrate on tasks compared to particpants deprived of NREM.

Borberly 1986

  • Found that REM-deprived particpants tried to reenter REM 31 times on the first night or deprivation, 51 times on the second night and 60+ times on the third night.

These studies support both Oswald and Hornes theories, as they show how REM (within core sleep) is vital to brain function, as deprivation lead to ill effects on behavior. The body is also designed to attain a constant amount of REM, as particpants tried to reenter it. 

However, doesn't distinguish between theories as HGH wasn't measured, and the psychological effects recorded may be due to poor physical feeling, and not just mental tiredness. 

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Restoration: wider evaluation


  • Doesn't explain why sometimes doing nothing, such as travelling, is tiring. Why does boredom provoke sleepiness/restlessness?
  • Why does non-core sleep exist when the core stages is so important? Evolutionarily, shouldn't all sleep be core?
  • Why do predators/lions sleep alot when they don't do much? Not much exercise= little damage to body and nervous system.


  • more energy spent awake > more wear and tear on brain and body >> more sleep to repair.


  • greater REM needed in babies, and less in older people.
  • sleep variation between species: humans need lots of sleep despite lack of predators, because of high brain function.

PRATICAL- HGH tablets to improve repair during nights sleep.

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Restoration: research evaluation


  • Lab studies so high level of control over variables, giving good cause and effect.
  • Artificial settings- not ecologically valid??
  • low populational validity. effects of no sleep on western men many be different to other target populations- case studies. SHARPIO- just marathon runners.


  • Case studies are impossible to replicate.

Despite low populational validity and artifical settings, the lack of control over what sleep we have makes it easier to generalise these studies.

The research is relatively compelling, as it displays clearly the negative ffects sleep deprivation has on us, and also ways the body tries to tackle it. More research needed before we can fully justify either Oswald or Hornes theory, although they do overlap.

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