The introduction provides a theoretical analysis of a conceptual link between the ability to predict action based upon a false belief, and the ability to describe the contents of a misrepresenting representational artefact. This justifies an empirical comparison of these two abilities in three and four year old normally developing children, and high functioning children with autism (those having a Verbal Mental Age greater than four years). The first half of the empirical work describes the development and investigation of two procedures that test non-mental misrepresentation (false models and misleading direction signs). These are compared with performance on established false belief tasks to examine both levels of absolute difficulty, and developmental coincedence in task ability. It is found that there is a strong relationship in normally developing children between the ability to pass a false belief task, and to interpret the contents of a misrepresenting artefact. This close relationship is not found in children with autism, where tasks in the mental domain present greater difficulty than, and are unrelated to, the tasks in the non-mental domain. This suggests that the children with autism do not follow the same conceptual developmental course as normal children. Two subsequent experiments examine the abilities of children with autism in understanding the appearance reality distinction. It is found that this group and normally developing children are better at a colour transformation task than a deceptive objects task. An existing suggestion in the literature that children with autism produce a majority of phenomentist errors was not replicated. Experiment 6 exploited children's good performance on the colour transformation task in a new paradigm to produce a genuinely misrepresenting photograph. This task was of equal difficulty and highly correlated with false belief in the normally developing group. For children with autism this task was easier than and uncorrelated with false belief. These findings are discussed in relation to existing theories of normal development and the condition of autism.

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