Development of Optokinetic Nystagmus in the Human Infant and Monkey Infant: an Analogue to Development in Kittens
One permanent effect of monocular deprivation on visual behaviour in kittens is that optokinetic nystagmus (OKN) in monocular viewing can only be elicited for temporal to nasal field movement; movement of the stimulus nasally to temporally elicits either no response or irregular saccades. In the present study, this condition is called “asymmetrical OKN.” Asymmetrical OKN has also been previously observed in kittens under approximately 4 weeks of age.
In the present study, the development of OKN, with monocular viewing in human infants to random noise patterns, has been investigated. The results of these experiments demonstrate that infants up to about 3 months of age give asymmetrical OKN, although binocularly they give OKN in both directions. There is a gradual change-over to symmetrical OKN between 2 and 3 months of age. Preliminary results on monkey infants show a similar asymmetry over the first two to three weeks of life. Studies of OKN in human clinical cases of early binocular deprivation (strabismus, ptosis), in general, support the idea that early loss of binocularity prevents the normal development of some corticotectal connections controlling OKN.
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