Second-order optic flow deficits in amblyopia

PURPOSE. Amblyopic observers show deficits for global motion discrimination that cannot be accounted for by their contrast sensitivity impairment. The processing of first- and second-order translational global motion is deficient, as is the processing of first- order optic flow, suggesting that cortical function in extrastriate areas is impaired. The authors sought to determine whether amblyopes show impairment in the processing of optic flow defined by second-order motion, whether these deficits are comparable in the two eyes, and whether these deficits are correlated with first- order deficits. METHODS. Eight amblyopic subjects (three strabismic, three strabismic-anisometropic, one anisometropic, one deprivation; mean age, 29 years) were tested. The authors used random dot kinematograms in which the dots were luminance or contrast modulations of background noise. The global pattern of dot motion within the stimulus area was translational, radial, or rotational. Coherence thresholds for direction discrimination were obtained across a range of dot modulation depths, allowing the separation of contrast and motion deficits. RESULTS. The present study showed that deficits in second-order optic flow processing were equivalent to those for first-order stimuli and that these were unrelated to the extent of the amblyopic contrast sensitivity deficit and were comparable in both eyes. Radial optic flow was more affected than rotational optic flow. CONCLUSIONS. Global motion impairment appeared to have a high-level binocular locus and was independent of the depth of the contrast deficit. Results also support the idea that global motion and optic flow processing are form-cue invariant.