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Title: Brain mechanisms determining the dynamics of bistable perception
Author: Fukuda, Megumi
ISNI:       0000 0004 7964 7690
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2016
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The neural correlate of visual perception has been one of the central issues in neuroscience. Bistable perception, two distinct percepts spontaneously alternate in every few seconds while the physical input remains the same, has been used to investigate how our visual system resolves ambiguity in visual information. In this thesis, I interrogate the brain mechanisms of visual bistability in a series of experiments. In chapter 3, I recorded brain activity while participants engaged in a LGN localizer task. Activation in LGN could not be identified successfully, suggesting that we may need to establish a better approach to localize LGN. The experiment in chapter 4 answers how multiple brain regions, two parietal areas and the visual cortex, interact with each other in perceptual switches. Previous TMS studies suggested that the right anterior superior parietal lobule (r-aSPL) and the right posterior superior parietal lobule (r-pSPL) have opposite roles in triggering perceptual reversals. Using dynamic causal modeling (DCM), I found that resolving such perceptual ambiguity was specifically associated with reciprocal interactions between these parietal regions and V5/MT, and the strength of bottom-up coupling between V5/MT to r-pSPL and from r-pSPL to r-aSPL predicted individual mean dominance duration. The third study addressed which functional networks and brain regions would contribute to successful prediction of individual switch frequencies. Applying graph theoretical analysis to resting state data, I found centrality measures, which are used as proxy of hubness of the region in the entire network, predict individual switch frequencies and attack (removal of edges) to fronto-parietal network and visual network decreased prediction accuracy. Finally, in chapter 6 I investigated what determines trial-by-trial dynamics of bistable perception. I have developed a new experimental paradigm to test how an observer forms expectation from statistical information of the stimulus sequence. The subjective percept of ambiguous bistable perception was strongly biased towards expected stimuli, and such expectation quantified by a hierarchical Bayesian model was represented in multiple brain regions, including the fronto-parietal areas as well as the visual cortex. The series of experiments showed that the fronto-parietal network and visual network involve in forming conscious visual percept. My results favor predictive coding theory in bistable perception, which explains formation of consciousness as continuous input from the environment and update of the internal belief.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available