Abstract
For children with strabismic amblyopia (a developmental disorder of vision linked with ocular deviation), foveal vision can become affected by crowding: objects that are visible in isolation become indistinguishable in clutter. Crowding also affects the visual periphery of adults, where it produces systematic errors in object identification: the target object appears to be either averaged with the flanker identities (assimilation), or replaced by them (substitution). If the same mechanisms underlie crowding in amblyopia and the adult periphery, then errors in amblyopic crowding should be similarly systematic. Alternatively, amblyopic errors may be random, driven by factors such as perceptual distortions. To examine these perceptual effects we tested children, aged 3-9, with strabismic amblyopia. Children wore stereoscopic shutter-glasses and reported the orientation of a target 'Vac-Man, similar to a Landolt-C. We first measured acuity (threshold size) and the spatial extent of foveal crowding. Then, to investigate the perceptual effects of crowding, we used a matching task: children adjusted a reference Vac-Man to indicate the perceived target orientation. To examine the effect of target-flanker similarity, target-flanker differences were set at 30- and 90-degrees. These tests were also conducted on adults with normal vision. We find that the addition of flankers impairs matching performance in both children and adults. Flankers with a 30-degree difference were most disruptive, while 90-degree offsets allowed more accurate matching and a partial release from crowding. Children's precision was strongly affected under crowded conditions, with random errors common. However, we find strong evidence of substitution, with children frequently reporting the identity of the flankers. Although less often than adults, children also report orientations around the target-flanker average, showing evidence of assimilation. We thus argue that despite an increase in random errors, the perceptual outcomes of amblyopic crowding generally resemble those in the adult periphery, suggesting a common underlying mechanism.
Meeting abstract presented at VSS 2016