Burton, EA; (2016) Extrastriate form and motion processing in cone dysfunction and normal vision. Doctoral thesis , UCL (University College London).

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Abstract

Cone disorders result in poor visual acuity and colour blindness. While previous studies have investigated low-level vision, little is known about how cone loss impacts on extrastriate vision. This thesis used behavioural psychophysics and steady-state VEP (SSVEP) to examine effects of cone loss on coherent form, coherent motion and biological motion perception. Chapter one introduces the topic and background literature. Chapter two outlines the methods used within this thesis. Chapter three investigates the impact of simulated low-vision on form and motion perception. Normally sighted participants completed behavioural and SSVEP tests under blurred conditions. Blur led to reductions in perceptual sensitivity and coherence-related cortical signals in all three tasks, with coherent form perception faring the worst. Chapter four describes collection of control data for subsequent comparison with patient groups: behavioural and SSVEP measures under differing light levels chosen to stimulate rods and/or cones. The fifth and sixth chapters examine extrastriate vision in patients with stationary and progressive cone disorders. Comparisons of patients and controls on scotopic performance, mediated by rods reveal the extent to which cortical visual processing may have developed atypically in this group. Behavioural results in chapter 5 show that even at scotopic levels, cone disorder patients show some perceptual and SSVEP impairments compared to controls. Progressive patients show scotopic impairments on all three tests while stationary patients have impairments on coherent form and motion but not biological motion tests. Scotopic contrast sensitivity was also measured to check if extrastriate deficits could be explained by low-level deficits. Chapter six examines SSVEP results in the stationary patient group. Patients showed reduced VEP amplitudes relative to controls and there was some evidence of atypical motion topography. Results suggest that atypical photoreceptor function can affect the development and function of extrastriate vision. Potential advances in treatments for genetic visual disorders raise questions regarding neural plasticity, including the extent to which cortical visual processing can be reorganised following restoration of photoreceptor function.

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