The representation of global spatial structure in amblyopia

Visual processing is thought to involve initial local analyses that are subsequently integrated globally to derive functional representations of structure that extends over large areas of visual space. Amblyopia is a common deficit in spatial vision that could be based on either unreliable local estimates of image structure, irregularities in global image integration or a combination of errors at both these stages. The purpose of this study was to quantify the integration of local spatial information in amblyopia with global orientation discrimination and inter-ocular matching tasks. Stimuli were composed of pseudo-random arrays of highly visible and resolvable features (Gabor patches) whose local orientation and position were drawn from global distributions whose mean and variance statistics were systemically varied. Global orientation discrimination thresholds in both the amblyopic and fellow eye were elevated. The orientational and positional variances perceived by the amblyopic eye were matched by stimuli with higher variances perceived in the fellow eye. It would appear that amblyopes are able to integrate orientation information across visual space but the global representation of local structure shows greater variability compared to normal. It is this increased spatial uncertainty that underlies the spatial deficit in amblyopia.