Discuss the evidence from research into the development of infants’ visual perception during the first year of life.
At birth, the infant’s eye is physically immature, as is the nervous system. It is increasingly accepted that infants enter the world with some innate knowledge, which is then built on via experience. There is an interplay, as infants develop, between perception, behaviour and cognition, although this process is not linear, but rather all are part of an integrated system. This essay will examine the four stages of the visual nervous system, and look at studies which have served to increase our understanding of how infants perceive the world, and how this perception develops and matures over the first year of life. It will also focus on the methodology of these studies,
The visual nervous system can be divided into four main parts:
• the retina
• the optic nerve
• the lateral geniculate nucleus
• the visual cortex.
The image formed on the retina, by the lens, of a newborn has about the same clarity and colour as would be formed in an adult’s eye. The infant’s eye, however, is less good at accommodation (the ability to focus the eye on objects at different distances). This inefficiency of accommodation could be due to a lack of retinal sensitivity to fine detail, or may be caused by immaturities in any of the other three parts of the visual nervous system (Oates & Slater, 2005).
Abromov et al, 1982 (cited in Oates & Slater, 2005) studied the migration of cones within the eye as the retina continues to develop following birth. Cones are the part of the eye which are sensitive to fine detail and colour, while rods are more attuned to black and white light. Following birth no new rods or TMA01
cones are formed, however the fovea (central area of the retina) of an infant does not have as high a concentration of cones as the adult fovea, meaning that the infant is less able to perceive detail. The period within which this migration of cones is most active appears to be 2-3 months after birth. It is at this point that acuity seems to make the largest improvement.
Turning to the optic nerve, there is some evidence to show that there is a process of maturation which occurs shortly after birth (Yakovlev and Lecours, 1967, cited in Oates & Slater, 2005). They studied myelin, a form of insulation for nerve cells which improves the speed at which electrical impulses travel. The optic nerve lacks myelination at birth, meaning that the coded electrical impulses carrying data from the retina to the visual cortex move more slowly, and the information gets diffused. In studies, Yakovlev and Lecours showed that the process of myelination is complete by 3 months, and so the infants visual perception is more defined by this point.
The next part of the visual system is the lateral geniculate nucleus (LGN). This is a complex structure, situated at the base of the brain. One of the functions of the LGN is to translate the differing amounts of light between the middle and edge of the retina. Once again, the immaturity of the visual perception system, and lack of myelination means that there is a lack of clarity in the centre of the infant’s visual field (Oates & Slater, 2005).
Finally, the data received from a visual stimulus arrives at the visual cortex. This is a highly complex structure, the mechanics of which are not fully understood. Some of the cells situated here interpret signals for light and dark areas (both lines and boundaries between areas) – these are known as ‘simple’ cells. Other cells, known as ‘complex’ cells, are more sensitive to movement. Size and colour are interpreted by ‘hypercomplex’ cells, which take their data from wider receptive fields (Michael, 1978, in Oates & Slater, 2005). According to evidence from Horton and Hedley-White (1984), the TMA01
organization of these different cells into complex structures continues until at least 6 months of age....
References: Oates, J. and Slater, A. (2005) ‘Sensation and Perception’, in Oates, J., Wood, C. and Grayson, A. (eds) Psychological Development and Early Childhood, Oxford, Blackwell/The Open University.
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