Perceptual Psychology: Nativism Vs. Empiricism

Comparing the evidence for theories of Nativist, Empiricist, and Constructivist theories of perceptual psychology.

The debate between nativism and empiricism is the basis of all research into the development of perception. Nativists believe that humans are born with all their perceptual functions ready to be used, while empiricists believe that perceptual abilities have to be learned and adapted to. In general, theories which support nativism are bottom up theories of perception while evidence in favour of nativism tends to support the top down idea. There are five ways in which psychologists have attempted to study this debate: by studying human babies, or neonates, by studying cataract patients, by studying animals, by studying different cultures and by studying adaptation.

Human Neonate Studies: It is an obvious principle that the earlier a human is in possession of a skill, the greater the likelihood of this skill being genetically innate rather than learned as a result of the environment. A good starting point is to see whether the baby is in possession of a fully developed visual system at birth, if it is then they are likely to have a well developed perceptual system as well. As it is, human babies do not have fully developed visual systems at birth, having a weak optic nerve and undeveloped rods and cones in the retina. They are unable to track a moving object and do not blink if something moves towards their eyes. However, the majority of these abilties develop within three or four months, with the exception of focus, which is often not 20:20 until the age of twelve. The early age at which the system develops indicates that it is probably developed as a result of genetic time switches, with the abilities developing only when they are likely to be needed.

Perceptual ability is a different matter however, as its development is unrelated to the develpment of the visual system. Studies of human babies by Fantz reveal that they show a preference for complex shapes at an early age, meaning that they have colour, shape and brightness perception. Fantz maintained that babies had an inborn preference for human faces over other shapes, which his own studies marginally supported. However, other psychologists dispute this,although babies of 12 months do show a preference for faces deemed to be 'good-looking' even at an age when this should not matter. While it is not generally denied that babies can do simple perception like shape and so on, it is a matter of much debate whether they can percieve distance. Gibson's 'visual cliff' was intended to discover this, consisting of a raised surface half opaque and half transparent. A baby which could percieve depth would not go on the transparent side. Gibson and Walk found that babies did tend to show fear of the transparent side, but this does not prove that depth is an innate perceptual ability because at six months these were babies old enough to have learned to crawl, and thus arguably to have learned to percieve depth.

Animal Studies: like babies animals are unable to tell us what they percieve but unlike babies we can legally carry out much more dangerous research on them. Most animal studies focus on the effects of deprivation. Riesen raised chimps in total darknss and found that their systems had decayed. He then filtered light through opaque goggles on chimps and found that while they could percieve size shape and colour they could not differentiate between patterns or percieve depth, implying that these more compex elements are learned.

Held and Hein placed two kittens in the 'kitten carousel' a device which let one cat move it while the other followed around but was not in control of the motion. This meant that both cats had the same visual experience.The immobile kittens were unable to blink and didn't stretch out their paws when lowered to the ground. However, when allowed free movement they quickly learned the ability, implying that the perception of depth is learned and related to the motor system.

Blakemoor and Cooper rasied kittens in environments consisting entirely of horizontal or vertical lines. The cats were unable to track objects along the path they had been prescribed, and rarely to track diagonally, again implying learning was required.

Human Cataract Patients: This is similar to investigating babies in that then visual use is new and unfamiliar, but cataract patients are able to communicate effectively what they can percieve. However, their abilities may be distorted by a reliance on their other senses which has built up while they have been blind. Hebb correlated almost all investigation on the subject in 1944, and found that overall the patients could percieve shapes but not give them meanings or implications without resorting to the other senses, particularly touch.

Adaptation Studies: These studies aim to find out whether we can adapt to a consistent change in our visual array, for example in colour or orientation. This would show that we are able to adapt and thus that much perceptual ability is learned, whereas a failure would support the assertion that perception is innate. Stratton inverted his vision with lenses in 1896, and found that he was soon able to adapt and carry out complicated procedures like writing and pouring drinks with ease, although better with his eyes closed. Most human subjects are able to adapt after a short period of disorientation, significantly better if they move around. This both implies that human perception is learnt and that the motor system plays an important part.

Animals however often fail to adapt,for example chickens will go on pecking at corn tht is in fact ten centimetres away until they are forcibly removed, no matter how many times they peck air. This shows that humans adapt more than most animals, which seems to make sense since human lives are much less easy to predict genetically.

Cross-Cultural Studies: If human perception is the result of learning then there should be a difference in perceptual skills between humans raised in different environments.

It has been found that some African tribes who are not used to buildings and a world composed of rectangles are less subject than westerners to illusions like the Muller-Lyer. Also a tribe of jungle pygmies were taken by Jahota to the plains, where they thought the distant buffalo were ants because in the jungle they had never been able to see depth on that scale.

Overall the evidence is that some parts of perception are learned and some innate, and although it tends to be the more complex ones that are learned, there is still no total certainty as to which are inate and which rely on experience.

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