A-Level心理学-睡觉的功能Functions of Sleep
    Revision: Functions of Sleep

　　Ecological perspective

　　AO1:

　　Meddis (1975) believed that sleep behavior shown by any species depends on their need to adapt to environmental threats and dangers. Sleep serves the function of keeping animals fairly immobile and safe from predators. However, species that are in danger from predators sleep relatively little to remain vigilant.

　　Warm blooded animals need lots of energy to maintain body temperature. Animals with high metabolic rates use more energy. Sleep provides a period of inactivity, thereby reducing physiological demands and conserving energy. This is known as hibernation theory (Webb 1982)

　　Herbivores eat plants, which are fairly low in nutrients. Therefore they must eat more time eating and consequently less time sleeping. Carnivores eat food that is high in nutrients, so do not need to eat continuously. They can afford to rest and conserve energy.

　　Unilateral sleep occurs in animals such as dolphins and birds. One half od the animal's brain is in NREM at a time, while the other is awake. The two hemispheres of the brain swap every 2-3 hours. In dolphins, this adaptation allows them to surface for air.

　　AO2:

　　Zepelin and Rechtshaffen (1974) studied the relationship between sleep length and metabolic rate across 53 mammalian species. There was a negative correlation between body size and total sleep time, thereby supporting the theory that animals with high metabolic rate sleep for longer. This does not apply to all animals; sloths are large and slow and should not need much sleep, but sleep on average 20 hours a day.

　　Allison and Cicchetti (1976) studied relationship between sleep time in their laboratory and degree of danger typically experienced by the species. In 39 species the amount of sleep correlated negatively with danger. However, this does not apply to all species. Rabbits sleep as much as moles, even though rabbits have a much higher danger rating than moles. Both studies demonstrate correlational relationships, rather than causation.

　　The ecological theory is difficult to prove false, as animals that are in danger of predation either sleep to keep themselves immobile or stay awake to stay vigilant. It is also hard to apply to human sleep.

　　All research is based on observations of animals, but the behavior of some animals is yet to be recorded.

　　Restoration perspective

　　AO1:

　　Proposes that sleep is to save energy and permit the restoration of tissue. Oswald identified SWS as being important in the recovery process, and has been linked to release of growth hormone and protein synthesis. Adam and Oswald found that tissue growth of new cells in the skin is quicker when we are asleep.