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Title: Exploring the neural basis of visual crowding
Author: Soo, Leili
ISNI:       0000 0004 7961 2690
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2019
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Human visual system deals with an immense amount of information at any given time to achieve adaptive behaviour. Due to capacity limitations only a small selection of information is processed fully. One of the bottlenecks of visual processing is crowding - a breakdown of object recognition in clutter. The behavioural outcome of crowding has been thoroughly investigated, yet, the underlying mechanisms leading to crowding are still debated. The present thesis employed a combination of psychophysical and electrophysiological research techniques to investigate (1) how jointly co-varied stimulus factors affect the spatial extent of flanker interference in crowding; and (2) how targets and flankers are processed in the visual cortex as a function of their distance and similarity. First, we found that the combination of two manipulations modulated the spatial extent of crowding non-additively. This challenges the currently dominating view of a fixed spatial bottleneck of crowding. However, a simple transformation of the measurement scale to critical resolution allowed all effects to become additive. Critical resolution is proportional to the inverse of the smallest flanker free area surrounding the target object necessary for its unimpaired identification. Secondly, we found that target processing in the visual cortex is hindered in clutter. This reduction is alleviated when targets are dissimilar to flankers. Correspondingly, the flankers that are similar to targets are processed less compared to dissimilar flankers in close flanker distances. These findings indicate that crowding is a result of cortical competition between targets and flankers leading to integrated processing of similar objects. Overall, the results suggest that crowding can be understood in the context of biased competition model of attention, which proposes that all stimuli in the visual field compete for neural representation. Hence, the neural basis of crowding is an inability to bias processing resources in favour of a target.
Supervisor: Andersen, Søren K. ; Chakravarthi, Ramakrishna Sponsor: Biotechnology and Biological Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Visual perception ; Psychophysics ; Electrophysiology