Three main theories have attempted to characterise autism at the cognitive level: theory of mind, executive function and central coherence but none are able to account for all the behavioural manifestations seen across different children. This thesis is concerned with heterogeneity within the autism spectrum that might exist at the cognitive level and how this relates to behaviour. 57 high-functioning 7-12 year olds with autism spectrum disorder (ASD) and 28 normally-developing children participated in tasks tapping into these three cognitive domains, as well as intelligence and head size. Their parents completed interviews concerning their behavioural symptoms. Support for the relevance of all three theories to ASD was found, with significant group differences between the ASD and control groups. Approximately 50% of the children with ASD displayed a detectable theory of mind impairment, 33% executive dysfunction and 20% weak central coherence, and all possible combinations of impairment were found. A further puzzling 40% of children displayed no detectable impairment, indicating either a misdiagnosis, that the tests were not sensitive enough, or that there was an additional cause not investigated here. Theory of mind and executive function abilities were found to be closely related, whilst central coherence was independent of these skills, indicating that at least two cognitive subtypes were present in the current sample. The emerging hypothesis was that theory of mind impairment adversely affected performance in unstructured executive function tests through a lack of understanding of implicit task demands. Only theory of mind and verbal ability were found to predict specific aspects of the behavioural triad. In addition, the presence of weak central coherence was related to the increased head size found in 20% of ASD cases, providing a possible endophenotype for this cognitive skill.

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Managing feeding problems and gastrointestinal (GI) symptoms in children with Autism Spectrum Disorders (ASD) is a challenging process for professionals and parents especially if they become persistent and longstanding. These problems may have psychosocial and financial impacts on family life. To date, there is no structured questionnaire available to assist community professionals to identify these problems in a systematic manner. The primary aim of this research was to develop an interviewer-based questionnaire for community professionals (the ‘Brief structured questionnaire for the Early identification of Feeding problems and GI symptoms in primary school children with ASD (BEFGASD)). The secondary aim was to evaluate the psychometric properties of the BEFGASD. The development process of the BEFG-ASD included a comprehensive literature review, items and scales construction, specialist review, a modified Delphi technique and a pre-testing with professionals and parents. 42 items within 15 sub-domains of feeding problems, GI symptoms and the impact were selected. The panel experts in the Delphi technique (n=20) rated the items as either ‘important’ or ‘very important’ (Mean score: 1.0-2.0). The final draft of the BEFG-ASD was field-tested with 48 professionals and 74 parents of primary schoolchildren with ASD (aged 4-11) in North East England. Responses from the field-testing were used to evaluate the psychometric properties of the BEFGASD. Face validity and content validity was established. Internal consistency of the 42 items was good (Cronbach’s alpha: 0.85) but varied across domains. Test-retest reliability and inter-rater reliability of domains and items was satisfactory. Criterion validity and construct validity of the BEFG-ASD also varied across domains and sub domains. The BEFG-ASD is the first questionnaire developed for use by community professionals. Further research and clinical practice will increase our understanding of its properties and utility in different population and settings.