Roulston, B.W.; (2008) Integration and disintegration of human visual awareness. Doctoral thesis , University of London.

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Abstract

The neuronal underpinnings of visual awareness has recently become the primary question of interest for many researchers, with many theories suggesting distinct mechanisms. The aim of this thesis was to test predictions of the low-level modular theory of visual awareness. This modular view is encapsulated in the 'microconsciousness' framework (Zeki & Bartels, 1999) in which each visual processing system, such as that for colour, is capable of generating a conscious correlate autonomously in parallel across space, within each of the different functionally specialised areas of the visual brain, and across time, with different attributes perceived at different times. Given the scope of this topic, we approached it from three diverse angles: (1) Two psychophysical experiments investigated temporal aspects of visual perception - in particular these addressed the issue of whether the timing of awareness is an 'online* phenomenon rather than integrated into a temporal buffer zone prior to awareness. We measured the relative perceptual times of different magnitudes of direction changes and investigated the 'flash-lag' effect (Nijhawan, 1994) and related illusions of positional localisation. (2) The first two fMRI experiments examined the necessity of frontal and parietal areas for visual awareness in the context of bistable figures, combined with dynamic causal modelling (Friston et al., 2003), and perception outside the focus of attention. (3) We looked to extend the concept of modularity of awareness to that of 'access consciousness', that is the ability to give a report of a conscious experience (Block, 1996), in addition to the previous studies on phenomenal consciousness. To this end, we combined psychophysics with fMRI to investigate the interaction between report modality and visual perception. We conclude that the low-level modular theory of stands up to direct tests of its predictions and remains a viable theory of visual awareness.

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