Yong, KXX; (2014) The visual basis of reading impairment in posterior cortical atrophy. Doctoral thesis , UCL (University College London).

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Abstract

This thesis explores the nature of reading impairment in posterior cortical atrophy (PCA), a degenerative syndrome most commonly caused by Alzheimer’s disease (AD) pathology. PCA is characterised by cognitive deficits associated with posterior brain atrophy, including disruption to various visual domains, with relatively spared episodic memory function. Acquired dyslexia is an early and debilitating symptom of PCA; however, there is a lack of group investigations of reading dysfunction. Through a better understanding of dyslexia, including the contribution of visual deficits, the optimal conditions for PCA patients’ reading might be revealed. A series of studies were conducted to characterise reading and other visual deficits in PCA patients, typical AD (tAD) patients and healthy controls, accompanied by a consistent and comprehensive battery of neuropsychological tests. One form of early visual processing deficit that has been proposed to crucially limit reading in normal peripheral vision is crowding. Behavioural and neuroimaging investigations confirmed the qualitative similarity between crowding and deficits in identifying centrally presented flanked stimuli in PCA. Assessments of single word recognition and passage reading were carried out through behavioural, eye movement and neuroimaging analysis. Perceptual and spatial factors primarily determined single word and passage reading ability in PCA, not tAD. One counter-intuitive finding was how PCA patients demonstrated particular difficulty reading text in large font. Results also identified two patients who demonstrate remarkably preserved reading despite showing grave visual impairment; this discrepancy poses problems for general visual accounts of reading deficits. The two patients were followed longitudinally, revealing how the development of enhanced crowding effects coincided with loss of reading ability. Insights from the thesis informed the development of two interventions which intended to provide the optimal conditions for reading in PCA; both interventions resulted not only in consistent gains in reading accuracy, but also in improvements in self-reported reading ease and comprehension.

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