Implied Motion From Form Shows Motion Aids the Perception of Global Form in Amblyopia

PURPOSE: Global motion and global form perception have been found to be abnormal in the presence of amblyopia. How such deficits manifest in visual function reliant on the interactions between these two visual processing mechanisms has not been adequately explored. In the current study, we use dynamic Glass patterns (dGlass) to measure implied motion thresholds in variable external noise to investigate the local and global limitations of processing. METHODS: A total of 13 amblyopes (eight strabismic and five anisometropic, mean interocular visual acuity difference 0.30 ± 0.12 logMAR) and six visually normal controls discriminated the overall implied motion of dGlass generated by presenting nine independent sets of static Glass patterns over 0.5 seconds. The orientation of dipole elements was derived from the Gaussian distribution with prescribed mean and standard deviation that served as external noise. Thresholds at varying external noise were fitted to a set of linear amplifier models that were statistically compared to investigate the contribution of local and global processing parameters. RESULTS: The implied motion thresholds were higher for strabismic (4.33° ± 1.34°) compared to anisometropic (2.32° ± 0.76°) amblyopia and controls (2.28° ± 0.50°) in the no-noise condition. The multivariate ANOVA analysis showed no difference between amblyopic and control observers at the no-noise and high-noise levels (P > 0.1). The statistical comparison of nested models showed normal internal noise and sampling efficiency parameters for both strabismic and anisometropic amblyopia (PS >0.50). CONCLUSIONS: The normal thresholds for implied motion in this study would suggest that motion aids the perception of global form cues present in dynamic Glass patterns. Our results challenge the proposed dorsal stream vulnerability in developmental disorders such as amblyopia.