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John A. Greenwood, Kamilla Dombai, Siobhan M. Ludden, Annegret Dahlmann-Noor, Tessa M. Dekker; Distinct patterns of foveal crowding for colour and motion in developmental amblyopia. Journal of Vision 2020;20(11):249. https://doi.org/10.1167/jov.20.11.249.
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© ARVO (1962-2015); The Authors (2016-present)
Crowding is the disruption to object recognition that arises in clutter. Though typically minimal in foveal vision, strong elevations occur during development and with amblyopia. Most theories depict crowding as a singular mechanism that disrupts the recognition of features ranging from colour to motion in the same way. We examined whether this prediction holds for the crowding of colour and motion in the amblyopic and developing fovea.
Children aged 3-9 years with either typical vision (n=32) or strabismic amblyopia (n=24) were shown a foveal ‘cowhide’ target stimulus and judged its direction (left/right of upwards) or hue (blue/green) in a videogame context. Targets were presented either in isolation or crowded by 6 flankers, with stimulus sizes varied using QUEST to determine size-acuity thresholds. On average, typically-developing children showed similar thresholds for colour and motion with unflanked targets, and similar elevations when crowded. These elevations were however stronger for motion than colour in children below 6 years of age. For children with amblyopia, colour thresholds were matched with controls in the fellow eye, with an elevation in the amblyopic eye for unflanked thresholds and further elevation when flanked. In contrast, motion thresholds showed a binocular deficit – in the fellow eye, thresholds were considerably higher than colour for both unflanked and flanked targets. Further elevations were evident in the amblyopic eye, such that flanked motion judgements showed by far the worst performance.
Altogether, amblyopic crowding causes a monocular pattern of disruption for colour perception, similar to that found with letter stimuli, whereas motion crowding exhibits a much stronger set of binocular elevations. Crowding is also stronger for motion than colour in young typically-developing children. These dissociations suggest that crowding is not a singular mechanism within the visual system, but rather that distinct features can be disrupted independently by clutter.
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