BINOCULARITY IN INFANCY

A variety of behavioural and electrophysiological studies agree that t he onset of functional binocular interaction in human visual cortex no rmally occurs between 10 and 16 weeks of age. Measures of sensitivity to binocular correlation and to disparity agree closely, and behaviour al and visual evoked potential measures on the same infant show onset of binocularity within about a 2 week range. Beyond the initial onset, the maximum disparity to which infants are sensitive increases steadi ly and stereoacuity is found to increase very rapidly. The initial dev elopment of binocularity does not appear to be a consequence of improv ing alignment of the eyes and occurs even in the presence of strabismu s. However, the connections subserving binocularity are plastic in ear ly childhood; they can be disrupted by unilateral strabismus, although in some strabismic children who use both eyes for fixation, they can adapt to serve stereo function at the angle of deviation and re-adapt, albeit temporarily, to the surgical alignment of the eyes. These find ings allow us to pose some as yet unanswered questions about the devel opment of binocularity, including: How is the infants visual system or ganised before the establishment of binocularity? How does the pre-bin ocular infant maintain vergence? And what neural changes underlie the increase in performance for small and large disparities following the initial onset of binocular function?