Motion and form processing along the functionally differentiated dorsal and ventral stream is reported to be abnormal in amblyopia; however limitations in previous stimuli have made analogous comparison of the outputs from these two streams difficult. In the current study, we characterise both functions in amblyopia using equivalent stimuli for fine global motion and orientation discrimination in the presence of noise. Anisometropic (n = 6) and strabismic (n = 6) amblyopes, and 12 visually normal subjects monocularly estimated the mean direction of motion of random dot kinematogram (RDK) and orientation of Glass pattern (Glass), whose directions/orientations were drawn from normal distributions with a range of means and variances that served as external noise. Two levels of noise were tested to obtain direction/orientation discrimination threshold in the absence of noise then threshold variance at the multiples of the direction/orientation threshold. For all subjects the thresholds for Glass were higher than RDK. The direction/orientation thresholds were higher for amblyopic eye (AE) in the strabismic group compared to the fixing eye (FE) and normal observers (NE) but not for anisometropic group. The MANOVA for the strabismic group revealed significant effect of both eyes (p < 0.01) and stimulus type (p < 0.01) but no interaction p > 0.1), with thresholds significantly higher for the AE than both FE and NE (ps < 0.05) on pairwise analysis. The MANOVA for the anisometropic group showed no significant effect of eyes p > 0.1) but a significant effect of stimulus type (p < 0.001) with no interaction p > 0.1). Our results show a deficit in motion and form perception only in subjects with dense strabismic amblyopia, irrespective of noise levels. The thresholds will be modelled to parse out the influence of local and global processing mechanisms in the respective streams.
- form perception
- motion perception