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UNIVERSITY of LONDON THESIS Yearfyrof Y 2809688258 REFERENCE ONLY UNIVERSITY OF LONDON THESIS YearfyrOf Name of Author COPYRIGHT This is a thesis accepted for a Higher Degree of the University of London. It is an unpublished typescript and the copyright is held by the author. All persons consulting this thesis must read and abide by the Copyright Declaration below. COPYRIGHT DECLARATION I recognise that the copyright of the above-described thesis rests with the author and that no quotation from it or information derived from it may be published without the prior written consent of the author. LOANS Theses may not be lent to individuals, but the Senate House Library may lend a copy to approved libraries within the United Kingdom, for consultation solely on the premises of those libraries. Application should be made to: Inter-Library Loans, Senate House Library, Senate Hpuse, Malet Street, London WC1E 7HU. REPRODUCTION University of London theses may not be reproduced without explicit written permission from the Senate House Library. Enquiries should be addressed to the Theses Section of the Library. Regulations concerning reproduction vary according to the date of acceptance of the thesis and are listed below as guidelines. A. Before 1962. Permission granted only upon the prior written consent of the author. (The Senate House Library will provide addresses where possible). B. 1962-1974. In many cases the author has agreed to permit copying upon completion of a Copyright Declaration. C. 1975-1988. Most theses may be copied upon completion of a Copyright Declaration. D. 1989 onwards. Most theses may be copied. y This copyThis copy has been has been deposite< deposited in the Library of This copy has been deposited in the Senate House Library, Senate House, Malet Street, London WC1E 7HU. Integration and Disintegration of Human Visual Awareness Barrie W. Roulston University College London Ph.D. Thesis UMI Number: U591330 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U591330 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Declaration I, Barrie Roulston, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. 2 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 ‘microconsciousness5 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. 3 Acknowledgements The immense, taxing, daunting, frustrating, and ultimately stimulating, rewarding and inspiring challenge of my PhD could not have taken place without a group of individuals who provoked, questioned, contended, and ultimately encouraged, educated and inspired me to produce what is contained within this thesis. Firstly, there is Professor Semir Zeki, my supervisor, who above all always ensured that I kept the fundamental questions in mind, sought deeper and more profound meaning from science, and provided the most assured and cultivated advice on matters scientific, philosophical and aesthetic. Next there is my second supervisor, Professor Karl Friston, who consistently provided the most meticulous and meaningful answer to any question posed, and who taught the true meaning of 'orthogonal*. I must also thank Stuart Shipp, who was always able to inject a note sobriety and insightfulness into any matter, and whose unrivalled knowledge of anatomy always reminded me that the brain is a real physical entity and not a philosophical construct. John Romaya and Thomas Muller without fail could resolve any technical hitches, provide culinary advice and fire off a joke each time I walked into their office. Anton Burdakov for being an all round PA/artist/scientist and without whom this thesis would never be examined. I would also like to thank my fellow students without whom I certainly could not have finished my studies. Matt Self for his vastly superior knowledge of brain imaging, psychophysics, programming and dodgy bars in Clerkenwell, as well as in-depth discussions about recent trends in the British indie scene. Richard Lewis simply for being Richard Lewis. Anyone who has met him will know what I mean. Ollie Hulme for his passionate musings on consciousness and dodgy bars in Shoreditch, and whose daily high-five which was always able to lift my spirits. Ulrich Kirk for his calming and serene Danish existentialist outlook and unforgettable 4 rendition of U2’s ‘One’. Velia Cardin for her vivacity, charm and capacity to inject some Latin flair into us reserved Brits, especially a dour Scots one like myself. Finally, I must give thanks to my family who always supported me in my academic pursuits and never questioned my own choices, despite their bemusement at this whole mysterious neuroscience subject, and Loma Elcock, my girlfriend, who has had to tolerate years of obscure rants and late nights, for her utter faith in my ability that has always been a steady crutch, and for that can of Diet Coke that she is about to give me. 5 TABLE OF CONTENTS Part 1: Page INTRODUCTION 12 1.1 Overview 13 1.2 What is consciousness? 15 1.3 Is consciousness a neurobiological problem? 16 1.4 The neural basis of visual perception 19 1.5 Subjective perception as an objective phenomenon 24 1.5.1 Neuropsychology 25 1.5.2 Electrophysiology 31 1.5.3 Human brain imaging 41 1.5.4 Human single-unit recording 47 1.5.5 Psychophysics 49 1.6 Current theories of visual aw areness 52 1.6.1 Microconsciousness 52 1.6.2 Feedback to VI 53 1.6.3 Neuronal synchrony 54 1.6.4 Thalamo-cortical interactions 55 1.6.5 Brainstem enabling 56 1.6.6 Global workspace 57 1.6.7 An emerging theme: global-integrated vs. local-modular 58 1.7 Thesis aims 60 Part 2: PSYCHOPHYSICS 61 2.1 Perceptual asynchrony from direction changes 62 2.1.1 Introduction 62 2.1.2 Methods 64 2.1.3 Results 68 2.1.4 Discussion 72 2.2 Perceptual compression of space through position integration 79 2.2.1 Introduction 79 2.2.2 Methods 82 6 2.2.3 Results 88 2.2.4 Discussion 96 Part 3: FUNCTIONAL BRAIN IMAGING 102 3.1 Bistable and stable figures: top-down and bottom-up interactions 103 assessed with dynamic causal modelling 3.1.1 Introduction 103 3.1.2 Methods 106 3.1.3 Results 115 3.1.4 Discussion 123 3.2 Neural correlates of conscious perception in the near absence of 128 attention 3.2.1 Introduction 118 3.2.2 Methods 132 3.2.3 Results 137 3.2.4 Discussion 146 3.3 Modularity of response modes and visual awareness 155 3.3.1 Introduction 155 3.3.2 Methods 160 3.3.3 Results 164 3.3.4 Discussion 172 Part 4: CONCLUSIONS J80 Part 5: APPENDICES 183 A.l Appendix 1: Object localisers 184 A.2 Appendix 2: Retinotopic mapping 189 Part 6: BIBLIOGRAPHY 1% 7 LIST OF FIGURES 1.4.1 Schematic diagram of simple and complex cells. 1.4.2 Parallel processing in the primate visual system. 1.5.1 Direction discrimination task and neural responses. 1.5.2 Population average responses for cells in macaque VI during figure- ground detection task. 1.5.3 Mean BOLD activated in the PPA and FFA during binocular rivalry. 1.5.4 Meta-analysis of frontal and parietal areas that correlate with visual awareness. 1.6.1 Schematic diagram of the sensorimotor pathway. 2.1.1 Direction of motion over time of the reference and test squares. 2.1.2 Stimuli for each trial of pairing judgements and temporal order judgements.
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