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INVESTIGATION of HUMAN VISUAL SPATIAL ATTENTION with Fmri AND INVESTIGATION OF HUMAN VISUAL SPATIAL ATTENTION WITH fMRI AND GRANGER CAUSALITY ANALYSIS by Wei Tang A Dissertation Submitted to the Faculty of The Charles E. Schmidt College of Science in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Florida Atlantic University Boca Raton, FL December 2011 Copyright by Wei Tang 2011 ii ACKNOWLEDGEMENTS I would like to thank all those who have helped to make this thesis reach its final com- pletion. My utmost gratitude goes to Dr. Steven Bressler, who has been advising me for five years. Without his knowledge and insights, and especially his enormous patience, I would have lost the battle against all those complicated problems. My appreciation goes to our collaborators at Washington University at St. Louis: Drs. Maurizio Corbetta, Gordon Shulman and Chad Sylvester, who designed and conducted the behavioral experiments and generously provided us the fMRI data, together with discussions on the results. I thank my friends from the laboratory, Tracy Romano, Marmaduke Woodman and Timothy Meehan, for giving valuable suggestions on the analysis methods. I also thank the Scientific Squir- rels Club of China for letting me present my work to general audience in my home country. At last, I would like to thank my parents and my sister, who have always been there with deep love to encourage and support me chasing my dream. iv ABSTRACT Author: Wei Tang Title: Investigation of Human Visual Spatial Attention with fMRI and Granger Causality Analysis Institution: Florida Atlantic University Dissertation Advisor: Dr. Steven L. Bressler Degree: Doctor of Philosophy Year: 2011 Contemporary understanding of human visual spatial attention rests on the hypothesis of a top-down control sending from cortical regions carrying higher-level functions to sen- sory regions. Evidence has been gathered through functional Magnetic Resonance Imaging (fMRI) experiments. The Frontal Eye Field (FEF) and IntraParietal Sulcus (IPS) are can- didates proposed to form the frontoparietal attention network for top-down control. In this work we examined the influence patterns between frontoparietal network and Visual Occipital Cortex (VOC) using a statistical measure, Granger Causality (GC), with fMRI data acquired from subjects participated in a covert attention task. We found a directional asymmetry in GC between FEF/IPS and VOC, and further identified retinotopically spe- cific control patterns in top-down GC. This work may lead to deeper understanding of goal-directed attention, as well as the application of GC to analyzing higher-level cognitive functions in healthy functioning human brain. v DEDICATION To Xuxu, Yark and The Mad Mountain, who keep reminding me how important and joyful it is to keep creative. INVESTIGATION OF HUMAN VISUAL SPATIAL ATTENTION WITH fMRI AND GRANGER CAUSALITY ANALYSIS List of Tables . ix List of Figures . .x Introduction . 1 A Brief Historical Account . 1 The Role of FEF and IPS in Attentional Control . 5 The Large-Scale Cortical Network Approach . 10 Scenario of Current Study . .13 Top-Down Control of Visual Cortex by Frontal and Parietal Cortex in Anticipatory Visual Spatial Attention . 15 Introduction . 16 Materials and Methods . 18 Results . 24 Discussion . 29 Measuring Granger Causality Between Cortical Regions from Voxelwise fMRI BOLD Signals with LASSO . 32 Introduction . 33 Materials and Methods . 38 vii Results . 47 Discussion . 58 Retinotopically Oriented Top-Down Modulation of the Visual Cortex during Visual Spatial Attention . 63 Introduction . 63 Materials and Methods . 65 Results . 68 Discussion . 80 Discussion and Conclusions . 85 Relate Findings to Theory: A Biased-Competition Model . 86 Spatiotopic Maps: A Control Mechanism without Agency . 87 Technical Issues Concerning GC Application to fMRI . 91 Summary and Conclusions . 93 Bibliography . 95 viii LIST OF TABLES 3.1 The Fraction of Non-Zero Coefficients in Each of the 4 Submatrices for Each of the 56 Simulation Models . 48 4.1 Paired-Sample t Tests for the Difference Between Groups of Summary GC Scores ...................................................................70 4.2 Repeated-Measures ANOVA for Retinotopy Effect (Pre-Target Condition) . 71 4.3 Repeated-Measures ANOVA for Retinotopy Effect (Control Condition 1) . .74 4.4 Repeated-Measures ANOVA for Retinotopy Effect (Control Condition 2) . .74 4.5 Repeated-Measures ANOVA for Retinotopy Effect (Post-Rarget Ttest Condition) 78 4.6 Repeated-Measures ANOVA for Cue Effect (Pre-Target Test Condition) . 79 ix LIST OF FIGURES 1.1 Schematic Depiction of Four Influential Accounts of Selective Attention . .3 1.2 Lateral View of the Left Hemisphere of Human and Monkey Brain Showing the Location of FEF . 7 1.3 Lateral View of Macaque Monkey Brain and Human Brain Showing the Location ofIPS .....................................................................9 2.1 Visual Spatial Attention Behavioral Paradigm . .19 2.2 Top-Down and Bottom-Up Granger Causality F -statistic Histograms for a Representative ROI Pair in One Subject . 25 2.3 Top-Down Versus Bottom-Up Granger Causality . 26 2.4 Top-Down Granger Causality Before Correct Versus Incorrect Performance . .28 3.1 Simple Driving Patterns That Can Lead to Spurious Identification of Significant Granger Causality . .36 3.2 Schematic Illustration of the Computation of Summary Statistics f and W for Hypothetical Submatrix Byx ............................................46 3.3 Granger Causality Patterns Between Simulated ROIs . 49 3.4 Comparison of Model Estimation by LASSO-GC and Pairwise-GC Methods for One Simulation Model . 51 x 3.5 Comparison of LASSO-GC and Pairwise-GC Methods in Recovering the f Summary Statistic . 52 3.6 Comparison of LASSO-GC and Pairwise-GC Methods in Recovering the W Summary Statistic . 53 3.7 Comparison of Connectivity Patterns with LASSO-GC and Cross-Correlation Measures . .55 3.8 Functional Connectivity Analysis of Dorsal Attention Network and Visual Occipital Cortex in Visual Spatial Attention . 57 4.1 Illustration of the Locations of Randomly Sampled ROIs Outside FEF, IPS and VOC .....................................................................67 4.2 Mean of the Summary Scores Over Subjects . 69 4.3 Time Plots Showing the Retinotopy × Direction Interaction in the Pre-Target Test Condition . 72 4.4 Time Plots Showing the Retinotopy × Direction Interaction in Control Condition 1 . 73 4.5 Time Plots Showing the Retinotopy × Direction Interaction in Control Condition 2 . 75 4.6 Time Plots Showing the Retinotopy × Direction Interaction in the Post-Target Test Condition . 76 4.7 Summary Time Plot for the Test Condition . 77 4.8 Invariant Time and Cue Effect in the Preparatory Period . 80 xi CHAPTER 1. INTRODUCTION Everyone knows what attention is. It is the taking possession by the mind in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought...It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrained state. William James (1890) Everyone knows what attention is, yet no one knows exactly how it works. Introspec- tively, as William James put it, it is easy to find the subjective feeling about attention as a means of reallocating mental resources to bypass the capacity limit of information pro- cessing. Such feeling can commonly arise from two different situations: when a prominent event in the outside world draws our attention toward it, or when an endogenous goal di- rects us to events of our own interest. Cognitively what lead to this phenomenon remains a puzzle far from resolved. A Brief Historical Account There has been a long quest in psychology trying to pin down the.
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