Human visual development over the first 6 months of life. A review and a hypothesis.

The behavioural changes that occur in visual development in the first 6 months of human life are discussed in relation to the possible underlying changes in neurophysiological mechanisms, with inter-species comparisons being made when appropriate. Recent data on the developing infant's changing capacity to discriminate various stimulus attributes is considered. It appears that orientation discrimination and cortically related visual evoked potentials are present at, or soon after, birth. However, data on colour discrimination, field differences in detection tasks and control of visual attention suggest a subcortical site for control of behaviour for the first month of life. The improvements in spatial and temporal resolution depend on maturation of both peripheral and central structures in the visual pathway and so do not provide a clear distinction between cortical and subcortical function. There is clear evidence that binocular function in the cortex does not emerge until three months postnatally. A hypothesis is proposed that maturation of a number of pathways between cortex and subcortical structures underlies the observed behavioural changes starting at around 2 months of age. The initial immaturity of connections between cortex and pretectum may give rise to asymmetrical monocular OKN. Maturation of pathways from cortex to colliculus could account for improvements in convergence, allowing development of cortical binocularity, and for the developing ability to control shifts of visual attention.