Electrophysiological Correlates of Visual Search in the Autism Spectrum Stephanie Dunn A thesis submitted for the degree of Doctor of Philosophy (PhD) The University of Sheffield Department of Psychology March 2016 Publications arising from this thesis: Dunn, S.A., Freeth, M., & Milne, E. (2016). Electrophysiological evidence of atypical spatial attention in those with a high level of self-reported autistic traits. Journal of Autism and Developmental Disorders, 46(6), 2199-2210. i Contents Chapter 1 : Selective Attention and the Autism Spectrum ........................................................ 1 Autism Spectrum Conditions ................................................................................... 1 Autistic Traits in the Typically Developed Population ........................................ 2 Theories of ASC ....................................................................................................... 3 Weak Central Coherence ...................................................................................... 3 Enhanced Discrimination and Reduced Generalisation........................................ 4 Enhanced Perceptual Functioning ........................................................................ 4 Enhanced Perceptual Capacity .............................................................................. 5 Neural Under-Connectivity................................................................................... 5 Selective Attention in ASC ...................................................................................... 6 Embedded Figures Task........................................................................................ 8 Visual Search ........................................................................................................ 9 Which Theory Best Explains Superior Visual Search in ASC? ......................... 10 Visual Processing and Autistic Traits .................................................................... 11 The Cognition of Visual Search ............................................................................. 12 Neural Basis of Visual Search ................................................................................ 13 N2pc .................................................................................................................... 14 N2pc, Target Selection and Distracter Suppression ........................................... 15 Computing the N2pc ........................................................................................... 17 Summary ................................................................................................................ 18 Chapter 2 : ERP indices of spatial attention: Investigating the N2pc in those with high and low levels of autistic traits ......................................................................................... 20 Introduction ............................................................................................................ 20 Using the Autism Quotient ..................................................................................... 21 Ethical Considerations ............................................................................................ 23 Participants ............................................................................................................. 24 Methodology .......................................................................................................... 24 Stimuli and Procedure ......................................................................................... 24 Spatial Attention Task (based on Luck et al., 1997) ........................................... 25 Visual Search Task (Based on Plaisted et al., 1998) .......................................... 26 EEG Recording and Data Processing ................................................................. 27 ii ERP Processing ................................................................................................... 28 ERP Analyses ..................................................................................................... 30 Results .................................................................................................................... 30 Behavioural Results ............................................................................................ 30 ERP Results ........................................................................................................ 34 Additional ERP Analyses ................................................................................... 38 Simon Effect ....................................................................................................... 40 Discussion .............................................................................................................. 41 N2pc Amplitude .................................................................................................. 43 Chapter 3 : ERP correlates of spatial selective filtering in those with high self- reported levels of autistic traits ................................................................................................ 45 Introduction ............................................................................................................ 45 Experiment Two: The neural correlates of target and distracter processing in those with high or low levels of autistic traits ................................................................. 46 Participants ............................................................................................................. 46 Methodology .......................................................................................................... 47 Stimuli ................................................................................................................. 47 Procedure ............................................................................................................ 48 Data Processing and Analysis ............................................................................. 50 ERP Processing ................................................................................................... 51 Results .................................................................................................................... 53 Behavioural Results ............................................................................................ 53 Event Related Potentials ..................................................................................... 56 Additional ERP Analyses ................................................................................... 66 Discussion .............................................................................................................. 69 Chapter 4 : Electrophysiological evidence for reduced selectivity in those with high levels of autistic traits compared to those with low levels of autistic traits ............................. 72 Introduction ............................................................................................................ 72 Experiment Three: Is reduced selectivity in those with high levels of autistic traits compared to those with low levels of autistic traits a consistent and reliable finding? ................................................................................................................... 73 Participants ............................................................................................................. 73 Methodology .......................................................................................................... 73 Stimuli and Procedure ......................................................................................... 73 Procedure ............................................................................................................ 74 iii Data Processing and Analysis ............................................................................. 75 Results .................................................................................................................... 77 Behavioural Results ............................................................................................ 77 Event Related Potentials ..................................................................................... 79 Additional ERP analyses .................................................................................... 90 Discussion .............................................................................................................. 93 Chapter 5 : General Discussion ................................................................................................ 96 Motivation for Research ......................................................................................... 96 Summary of Findings ............................................................................................. 98 Implications for Selective Attention in ASC ........................................................ 100 Visual Search and Autistic Traits ......................................................................... 102 Visual Search Superiority in ASC ........................................................................ 103 Building a Profile of Autistic Traits ..................................................................... 104 N2pc Amplitude is Affected by Stimulus Characteristics .................................... 105 Further Study .......................................................................................................