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Title: A common framework for visual crowding in typical and amblyopic vision
Author: Kalpadakis-Smith, Alexandra V.
ISNI:       0000 0004 8507 7778
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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Amblyopia is a developmental disorder of vision characterised by reduced acuity in one eye despite optical correction. When associated with strabismus, foveal vision is impaired by crowding: objects that are readily recognised in isolation become indistinguishable in clutter. In typical vision, crowding is minimal in the fovea and increases in the visual periphery. According to pooling accounts, the increase of crowding in the periphery arises from the integration of adjacent objects to promote perceptual homogeneity where sampling is insufficient and neurons have large receptive fields. It is unclear whether amblyopic crowding represents the same process. In this thesis I characterise amblyopic crowding, and investigate whether it can be understood within the same pooling framework as peripheral crowding. First, I show that amblyopic crowding systematically shifts the appearance of crowded objects to promote perceptual homogeneity, matching the perceptual effects in the periphery. A model simulating pooled responses of populations of visual neurons accurately characterises these effects in amblyopic and peripheral crowding, suggesting a common underlying mechanism. Second, I investigate the pattern of amblyopic crowding across the visual field and its neural correlates. I show that amblyopic crowding is elevated relative to typical vision in both fovea and periphery. At a group level, the increase of crowding in amblyopia and the typical periphery matches the increase of fMRI population receptive field (pRF) estimates in V1, V2, and V3, but at an individual level there is no correlation. Finally, I investigate the effects of higher-level grouping processes by examining whether uniformity in global clutter configuration modulates amblyopic crowding. I find that in most cases, clutter disrupts recognition in amblyopia regardless of global configuration, suggesting that contrary to the periphery, amblyopic crowding is largely unaffected by higher-level grouping processes. Therefore, on the whole pooling provides a successful framework for both amblyopic and peripheral crowding.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available