Thilo, Kai Volker; (2001) Physiological correlates of visually induced self-motion perception. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A striking manifestation of visual-vestibular interaction in the central nervous system is the ability of large-field visual motion to induce the perception of contra-directional self-motion (vection) in a stationary observer. The work of this thesis investigated the presence and nature of changes in several physiological and perceptual markers correlating with the subjective perception of visual motion as object- or self-motion. During circularvection, the beating field of torsional as well as horizontal optokinetic nystagmus was found to deviate in the direction of perceived self- motion. This anticipatory deviation is present at several stimulus velocities as well as body orientations with respect to gravity and presumably reflects a reorientation of spatial attentional resources in the direction of perceived self-motion. Using fMRI, it was found that during rollvection early motion-sensitive occipital and parieto-insular vestibular cortex deactivated whereas higher- order temporo- and parieto-occipital areas maintained identical, elevated, activity levels as during object-motion perception. However, event-related analysis showed that these areas were activated transiently during perceptual transitions reflecting their potential involvement in perceptual switching. Reduced primary visual cortex excitability during circularvection was also found using pattern-reversal visually evoked potentials and is likely to be mediated by feedback processes originating in higher visual and multimodal cortical areas. The measurement of cardiovascular activity identified a generalised pressor response following real self-motion in roll. Although of similar perceptual quality, no systematic autonomic adjustments were observed following the perception of circularvection demonstrating a differential effect of visual- vestibular interaction on conscious perception versus autonomic regulation. Measuring perceived postural verticality, it was confirmed that optokinetic stimulation in roll biases the perceived direction of gravity towards the direction of stimulus motion. However, no differential perception of postural verticality was obtained across perceptual states which can be explained by a functional segregation of visual-vestibular subsystems in the brainstem processing the perception of tilt and rotation.

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