Selective Attention and Perceptual Load in Autism Spectrum Disorder Anna Remington University College London A thesis submitted for the degree of Doctor of Philosophy September 2009 1 Declaration I, Anna Remington 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. A Remington 2 Abstract This thesis examines selective attention in young adults with Autism Spectrum Disorder (ASD). Existing literature regarding this issue is mixed; some research suggesting an overly-focused attentional style (Rincover & Ducharme, 1987) while others highlight an abnormally broad attentional lens (Burack, 1994). The research presented here has, for the first time, examined selective attention in individuals with ASD using a theoretically-led approach based on Lavie’s Load Theory of attention and cognitive control (Lavie et al., 2004). Load theory states that the perceptual load (amount of potentially task relevant information) of a task affects selective attention. This theory may explain the equivocal findings in the current data on selective attention and ASD. Using behavioural measures, the pattern of selective attention under various levels of load was explored in individuals with ASD and matched controls. The results provide evidence of increased perceptual capacity in ASD. This means that, at any one time, individuals with ASD may be able to process more information from the visual environment. This increase in capacity was evident on tasks of both unconscious and conscious perception. In light of the social deficits observed in the condition, the work in this thesis also explored selective attention in the presence of social distractor stimuli. Results indicated that faces are less salient for individuals with ASD and, unlike for typical adults, are not processed in an automatic and mandatory fashion. These results bring together findings on selective attention with work on social processing in an attempt to find basic abnormalities which might be fundamental in explaining the disorder. 3 For Guy 4 Contents Abstract ...................................................................................................................3 List of Tables ...........................................................................................................8 List of Figures .........................................................................................................9 List of Abbreviations ............................................................................................ 10 Acknowledgments ................................................................................................. 10 Chapter 1: Autism Spectrum Disorder ................................................................ 12 Social Impairment ........................................................................................... 12 Communication Deficit ................................................................................... 13 Repetitive and Rigid Behaviour ....................................................................... 13 Asperger Syndrome and Autism Spectrum Disorder ...................................... 14 Prevalence ......................................................................................................... 14 Biological Theories of ASD ............................................................................... 15 Neuroanatomical Abnormalities ...................................................................... 16 Biochemical Abnormalities ............................................................................. 19 Genetics of Autism .......................................................................................... 21 Psychological Approach .................................................................................... 22 Theory of Mind ............................................................................................... 23 Executive Dysfunction .................................................................................... 29 Weak Central Coherence ................................................................................. 33 Systemizing, Empathizing and the Extreme Male Brain .................................. 36 Summary ........................................................................................................... 37 Chapter 2: Selective Attention and Perceptual Load .......................................... 40 Selective Attention ............................................................................................ 41 Autism and Attention ........................................................................................ 49 Arousal ........................................................................................................... 50 Sustained Attention ......................................................................................... 51 Orienting, Disengaging and Attention Shifting ................................................ 52 Selectivity and Filtering .................................................................................. 54 Visual search ................................................................................................... 58 Chapter 3: Selective Attention and Perceptual Load in ASD ............................. 62 Introduction ...................................................................................................... 62 Participants and Diagnosis ............................................................................... 63 Ethical Considerations ..................................................................................... 65 Methodology ...................................................................................................... 65 Apparatus and Stimuli ..................................................................................... 65 Procedure ........................................................................................................ 67 Results ............................................................................................................... 68 Search Slopes .................................................................................................. 71 Accuracy data ................................................................................................. 72 Discussion .......................................................................................................... 73 Chapter 4: Perceptual Load and Conscious Perception in ASD ......................... 76 Introduction ...................................................................................................... 76 5 Participants ....................................................................................................... 79 Methodology ...................................................................................................... 80 Apparatus and Stimuli ..................................................................................... 80 Procedure ........................................................................................................ 82 Results ............................................................................................................... 84 Letter Search ................................................................................................... 84 Letter search error analysis .............................................................................. 85 CS Detection ................................................................................................... 86 Percentage Detection ....................................................................................... 87 False alarm rate ............................................................................................... 88 Detection sensitivity ........................................................................................ 89 Response Bias ................................................................................................. 91 Error Analysis ................................................................................................. 91 Control Block .................................................................................................. 92 Discussion .......................................................................................................... 92 Mixed trial paradigm. ....................................................................................... 94 Participants ....................................................................................................... 94 Methods ............................................................................................................. 95 Results ............................................................................................................... 95 Letter Search ................................................................................................... 95 CS Detection ................................................................................................... 97 Percentage Detection ....................................................................................... 97 False alarm rate ............................................................................................... 99 Detection sensitivity (d’) 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