Subtypes in the autism spectrum : relating cognition to behaviour
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.