Maldevelopment of visual motion processing in humans who had strabismus with onset in infancy.

Binocular experience in infancy is necessary for the normal development of the visual cortex. However, it is not known whether binocular experience also affects the processing of specific kinds of visual information such as motion. We now report deficits in visual motion processing in 7 adult humans who lacked binocularity in infancy because of strabismus. As probes for assessing visual motion processing, we used the initiation of smooth pursuit eye movements and the judgment of target velocity independent of eye movement. Monocular viewing was essential to reveal the deficits. For horizontal pursuit, strabismic subjects showed nasal-temporal asymmetries, such that nasally directed target motion evoked more vigorous pursuit. For vertical pursuit, strabismics showed up-down asymmetries, such that upward target motion evoked more vigorous pursuit. In addition, strabismics had abnormalities in the relative effectiveness of different parts of the visual field for initiating both horizontal and vertical pursuit. Psychophysical judgements of horizontal target velocity revealed deficits analogous motion was perceived as faster than temporally directed motion, even when the 2 directions of motion were actually presented at the same speed. The magnitude of the motion processing deficits in each subject was correlated with the severity of the clinical signs of the strabismus. Our results suggest 2 possible interpretations. Maldevelopments of visual motion processing may cause strabismus in infancy, or alternatively, strabismus in the critical period for visual development may cause a maldevelopment of visual motion processing.