Spatial vision deficit underlies poor sine-wave motion direction discrimination in anisometropic amblyopia

For five anisometropic amblyopes and five normal controls, contrast sensitivities in both grating motion direction discrimination and moving grating detection were measured with the same moving sine-wave stimuli over a wide range of spatial and temporal frequencies. We found that the apparent local motion deficits in anisometropic amblyopia can be almost completely accounted for by deficits in moving grating detection. Furthermore, the differences between the amblyopic and the nonamblyopic eyes are nonspecific to temporal frequency in both motion direction discrimination and moving grating detection and are quantitatively identical to the differences in their contrast sensitivities. The observations on motion direction discrimination and its relationship to the contrast sensitivity function were replicated with an additional five anisometropic amblyopes and four normal controls. Complementing an earlier study on strabismic amblyopia (R. F. Hess & S. J. Anderson, 1993), these results suggest that local motion-sensitive mechanisms are largely intact in anisometropic amblyopia; the apparent local motion deficits in anisometropic amblyopia can be modeled with deficits in contrast sensitivity functions.