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A common framework for visual crowding in typical and amblyopic vision

Kalpadakis-Smith, Alexandra V; (2019) A common framework for visual crowding in typical and amblyopic vision. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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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

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: A common framework for visual crowding in typical and amblyopic vision
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10085190
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