Neural Measures of Visual Attention and Suppression as Biomarkers for ADHD- associated Inattention Rebecca Elizabeth Townley PhD University of York Psychology August 2019 Abstract Abstract Whilst there is a wealth of literature examining neural differences in those with ADHD, few have investigated visual-associated regions. Given extensive evidence demonstrating visual-attention deficits in ADHD, it is possible that inattention problems may be associated with functional abnormalities within the visual system. By measuring neural responses across the visual system during visual-attentional tasks, we aim to explore the relationship between visual processing and ADHD-associated Inattention in the typically developed population. We first explored whether differences in neural responses occurred within the superior colliculus (SC); an area linked to distractibility and attention. Here we found that Inattention traits positively correlated with SC activity, but only when distractors were presented in the right visual field (RVF) and not the left visual field (LVF). Our later work followed up on these findings to investigate separate responses towards task-relevant targets and irrelevant, peripheral distractors. Findings showed that those with High Inattention exhibited increased responses towards distractors compared to targets, while those with Low Inattention showed the opposite effect. Hemifield differences were also observed where those with High Inattention showed increased RVF distractor-related signals compared to those with Low Inattention. No differences were observed for the LVF. Finally, we examined attention and suppression-related neural responses. Our results indicated that, while attentional responses were similar between Inattention groups, those with High Inattention showed weaker suppression responses towards the unattended RVF. No differences were found when suppressing the LVF. Findings across all studies suggest that differences in neural responses between those with High and Low levels of Inattention exist within the visual system. Such differences appear to relate to suppression of task-irrelevant distractors rather than attention towards task-relevant targets, suggesting such mechanisms are differentially affected in those with frequent Inattention problems. We also show a clear relationship between Inattention traits and visual suppression of the RVF. 2 Abstract List of Contents Abstract ................................................................................................................... 2 Abbreviations .......................................................................................................... 6 List of Tables ............................................................................................................ 7 List of Figures........................................................................................................... 8 Acknowledgements................................................................................................ 11 Declaration ............................................................................................................ 12 Chapter One: Introduction ...................................................................................... 13 1.1 Overview .......................................................................................................... 13 1.2 Attention Deficit Hyperactivity Disorder ............................................................ 13 1.2.1 ADHD Symptoms and Diagnosis criteria.............................................................................. 13 1.2.2 Diagnostic Tools ................................................................................................................... 16 1.2.3 Prevalence ........................................................................................................................... 18 1.3 Visual Attention in ADHD .................................................................................. 19 1.3.1 Sustained attention ............................................................................................................. 19 1.3.2 Visual field differences in Attention .................................................................................... 28 1.3.3 Attentional Load .................................................................................................................. 32 1.4 The Visual System and ADHD ............................................................................. 35 1.4.1 Functional Differences ......................................................................................................... 36 1.4.2 Structural Differences .......................................................................................................... 40 1.4.3 Superior Colliculus ............................................................................................................... 43 1.5 Concluding Remarks .......................................................................................... 57 Chapter Two: Assessing ADHD in the typical population ......................................... 61 2.1 Participant Recruitment .................................................................................... 61 2.2 Ethics of measuring ADHD ................................................................................. 62 2.3 Measuring ADHD traits using the CAARS ............................................................ 64 Chapter Three: Evidence for hyperactivity in the superior colliculus in ADHD ........... 75 3.1 Abstract ............................................................................................................ 75 3.2 Introduction ...................................................................................................... 76 3.3 Methodology .................................................................................................... 78 3.3.1 Participants .......................................................................................................................... 78 3.3.2 Saccade tasks ....................................................................................................................... 79 3.3.3 Functional imaging: Stimuli and Task .................................................................................. 81 3.3.4 MRI acquisition .................................................................................................................... 83 3.3.5 Analyses of MRI data ........................................................................................................... 83 3.4 Results .............................................................................................................. 85 3.4.1 Saccade task ........................................................................................................................ 85 3.4.2 fMRI: Sustained Attention Task and Inattention Traits ....................................................... 85 3 Abstract 3.4.3 fMRI: Superior colliculus and Inattention ........................................................................... 86 3.5 Discussion ......................................................................................................... 89 Chapter Four: Characterising Visual EEG responses in Inattention: exploring the effects of Hemifield and Attentional load. ............................................................... 93 4.1 Abstract ............................................................................................................ 93 4.2 Introduction...................................................................................................... 94 4.2.1 Perceptual Load ................................................................................................................... 94 4.2.2 Sensory Competition ........................................................................................................... 96 4.2.3 Asymmetrical Spatial Attention .......................................................................................... 96 4.2.4 The Steady State Visual Evoked Potential and its application to research on attention.... 97 4.2.5 Hypotheses and predictions ................................................................................................ 99 4.3 Methods ........................................................................................................... 99 4.3.1 Participants.......................................................................................................................... 99 4.3.2 EEG Apparatus ................................................................................................................... 102 4.3.3 Stimuli and experimental procedure ................................................................................ 102 4.3.4 Eye tracking apparatus and analysis ................................................................................. 106 4.3.5 EEG Analysis ...................................................................................................................... 107 4.4 Results .............................................................................................................110 4.4.1 Central target Fixation....................................................................................................... 110 4.4.2 Behavioural Task ..............................................................................................................