The child's developing theory of the mind as an interconnected network of beliefs, desires and feelings that govern behaviour provides a cornerstone for social and intellectual life. Recent research has suggested that autistic children have difficulty acquiring such a theory. Although it is speculated that a specific neurological deficit may be responsible for autistic children's difficulties on false belief tasks devised to test a theory of mind, these may also be due to a lack of exposure to conversation about mental states. In this study we explored the development of a theory of mind in a group of 26 signing, prelingually-deaf Australian children of normal intelligence, aged 8-13 years. Results revealed that 65% of these deaf children failed a simple test of false belief which normal preschoolers, mentally retarded children, and other handicapped groups--apart from children with autism--routinely pass at a mental age of 4-5 years. No significant difference emerged between deaf children's performance and that of autistic children tested on the same task in previous research. We discuss the results in terms of a conversational account of the development of a theory of mind in deaf children, and the extent to which this account is applicable to children with autism.

Possession of a "theory of mind" (ToM)--as demonstrated by an understanding of the false beliefs of others--is fundamental in children's cognitive development. A key question for debate concerns the effect of language input on ToM. In this respect, comparisons of deaf native-signing children who are raised by deaf signing parents with deaf late-signing children who are raised by hearing parents provide a critical test. This article reports on two studies (N = 100 and N = 39) using "thought picture" measures of ToM that minimize verbal task-performance requirements. These studies demonstrated that even when factors such as syntax ability, mental age in spatial ability, and executive functioning were considered, deaf late signers still showed deficits in ToM understanding relative to deaf native signers or hearing controls. Even though the native signers were significantly younger than a sample of late signers matched for spatial mental age and scores on a test of receptive sign language ability, native signers outperformed late signers on pictorial ToM tasks. The results are discussed in terms of access to conversation and extralinguistic influences on development such as the presence of sibling relationships, and suggest that the expression of a ToM is the end result of social understanding mediated by early conversational experience.

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What is the nature of our ability to understand and reason about the beliefs of others--the possession of a "theory of mind", or ToM? Here, we review findings from imaging and lesion studies indicating that ToM reasoning is supported by a widely distributed neural system. Some functional components of this system, such as language-related regions of the left hemisphere, the frontal lobes and the right temporal parietal cortex, are not solely dedicated to the computation of mental states. However, the system also includes a core, domain-specific component that is centred on the amygdala circuitry. We provide a framework in which impairments of ToM can be viewed in terms of abnormalities of the core system, the failure of a co-opted system that is necessary for performance on a particular set of tasks, or the absence of an experiential trigger for the emergence of ToM.

This paper summarizes the results of 11 separate studies of deaf children's performance on standard tests of false belief understanding, the results of which combine to show that deaf children from hearing families are likely to be delayed in acquiring a theory of mind. Indeed, these children generally perform no better than autistic individuals of similar mental age. Conversational and neurological explanations for deficits in mental state understanding are considered in relation to recent evidence from studies of deaf, autistic, and normally developing children with varied levels of access to talk about mental states at home with family members during the preschool years.

The purpose of the study reported here was to examine the degree to which delays or deficits in developing a theory of mind are specific to children with autism or extend to other groups of atypical children with varying conversational experience and awareness. The performance of deaf children from a variety of conversational backgrounds was compared with that of autistic and normal hearing children on a range of tasks requiring representation of others' mental states. Native signers, oral deaf children, and normal hearing children scored similarly, and their performance exceeded that shown by signing deaf children from hearing families and children with autism. The latter two groups did not differ significantly from each other. These results point to an interplay among biology, conversation, and culture in the development of a theory of mind.

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A central question in cognitive neuroscience concerns the extent to which language enables other higher cognitive functions. In the case of mathematics, the resources of the language faculty, both lexical and syntactic, have been claimed to be important for exact calculation, and some functional brain imaging studies have shown that calculation is associated with activation of a network of left-hemisphere language regions, such as the angular gyrus and the banks of the intraparietal sulcus. We investigate the integrity of mathematical calculations in three men with large left-hemisphere perisylvian lesions. Despite severe grammatical impairment and some difficulty in processing phonological and orthographic number words, all basic computational procedures were intact across patients. All three patients solved mathematical problems involving recursiveness and structure-dependent operations (for example, in generating solutions to bracket equations). To our knowledge, these results demonstrate for the first time the remarkable independence of mathematical calculations from language grammar in the mature cognitive system. aphasia ͉ language ͉ mathematics