Neuroimaging of binocular vision in human amblyopia

Amblyopia is a visual developmental condition that usually occurs when one eye receives abnormal input. For many years amblyopia was thought to be untreatable beyond 8 years old, after which the visual system would become functionally monocular. Recent research has shown that binocular mechanisms do remain intact in amblyopia and therefore investigating the nature of the deficit is crucial for understanding where neural problems arise and how they can be treated. Chapter 3 used population receptive field (pRF) modelling to further understand the cortical problems caused by amblyopia. Findings suggest that neurons responding to the amblyopic eye have reduced spatial resolution within striate and extrastriate areas. Chapters 4 and 5 aimed to test the predictions of different computational models of amblyopia using functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), within the same group of participants. This is the first study to use a model driven approach to directly compare both neuroimaging methods within the same participants. The pattern of fMRI responses from the amblyopic eye showed evidence of a response gain effect and unbalanced interocular suppression, whereas EEG responses showed evidence of a contrast gain shift. Finally, Chapter 6 used EEG to objectively measure visual improvements, following treatment for amblyopia in children and adults. Measurable steady-state EEG responses were found for both groups; however, there was no convincing evidence of improvements in amblyopic eye responses throughout treatment. The studies undertaken in this thesis contribute to the wider understanding of the neural basis of amblyopia. Two different neuroimaging methods are compared, which has enabled insight into how current computational models of amblyopia could be improved. It is hoped that this research will further the development of treatments for amblyopia, by providing more insight into how binocular visual processes break down between the eyes.