Eayrs, Joshua O; (2018) Individual differences in visual perception capacity and related brain morphology. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Limited capacity for perception results in various phenomena of inattentional blindness in task conditions that load perceptual capacity. These effects have been extensively studied under the load theory framework, with numerous demonstrations spanning a wide variety of perceptual load manipulations. Research also established contrasting effects of loading perception versus cognitive control functions (e.g. working memory). The convergence of findings across different manipulations of perceptual load together with the contrasting effects of cognitive control load suggests a generalised capacity for perception, which is distinct from general cognitive capacity. The purpose of this thesis was to examine this hypothesis further, using an individual differences approach and relating traditional visual perception and awareness paradigms to the phenomenon of subitizing: the ability to detect a limited number of items in parallel from a brief exposure that has traditionally been studied within the enumeration literature. The research first extended perceptual load effects to measures of unattended processing in an enumeration paradigm, demonstrating that distractor effects are only found within subitizing capacity but not in set sizes that exceed capacity (Chapter 2). A series of individual differences experiments then revealed significant correlations between tasks involving subitizing, motion tracking, ‘change blindness’ and ‘inattentional blindness’. These relationships were furthermore established to withstand controls for non-perceptual factors, establishing perceptual capacity as distinct from working memory capacity or general cognitive effort (Chapters 3-4). Finally, voxel-based morphometry analyses of structural brain images established distinct correlates of grey matter density for perceptual capacity across tasks (Chapter 5). Taken together, the results of this thesis establish individual differences in perceptual capacity across a diverse range of paradigms and stimuli, demonstrating a common, general capacity limit for perception which correlates with individual differences in performance and grey-matter density and is independent from other cognitive constructs such as number estimation abilities and executive working memory.

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