Orientation anisotropies in human visual cortex

Representing the orientation of features in the environment is a fundamental operation of the early stages of the human visual system. Previous research has demonstrated that the properties of such representations can vary with the particular orientation of the visual stimulus—they can show anisotropies. However, such research is equivocal regarding both the presence and nature of orientation anisotropies in human visual cortex.e aim of this thesis was to elucidate how the responses of the human visual system are modulated by stimulus orientation. To achieve this aim, this thesis relates three experiments in which functional magnetic resonance imaging (fMRI) was used to infer the neural activity of human visual cortex while subjects viewed oriented stimuli.e rst experiment reported in this thesis demonstrated that the presence of a bias towards local orientations radial to the point of xation is not necessary for the accurate classication of stimulus orientation based on the multivariate patterns of fMRI activity in the early visual areas.e second experiment quantied the cortical responses to a sinusoidal grating which varied in orientation, and revealed an anisotropy in which horizontal orientations evoked the least activity, vertica