The extent of the dorsal extra-striate deficit in amblyopia.

Previously, we have shown that humans with amblyopia exhibit deficits for global motion discrimination that cannot be simply ascribed to a reduction in visibility or contrast sensitivity. Deficits exist in the processing of global motion in the fronto-parallel plane that suggest reduced extra-striate function (i.e., MT) in amblyopia. Here, we ask whether such a deficit also exists for rotation and radial components of optic flow that are first processed at higher sites along the dorsal pathway (i.e., MSTd). We show that similar motion processing deficits occur in our amblyopic group as a whole for translation, rotation, and radial components of optic flow and that none of these can be solely accounted for by the reduced visibility of the stimuli. Furthermore, on a subject-by-subject basis there is no significant correlation between the motion deficits for radial and rotational motion and those for translation, consistent with independent deficits in dorsal pathway function up to and including MSTd.