Leslie, 1992; Frith et al., 1994). Various experimental tasks and procedures used to investigate this capacity generally indicate that many somewhat more able (e.g., verbal) children with autism do indeed lack the capacity to infer mental states. This capacity is viewed as one aspect of a more general difficulty in “metarepresentation” (Leslie, 1987) that is presumed to be expressed in younger children by difficulties with understanding communicative gesture and joint attention (Baron-Cohen, 1991). While not all children with autistic spectrum disorders entirely lack a theory of mind (Klin et al., 1992), they may be impaired to some degree (Happe, 1994). There appear to be strong relationships between verbal ability and theory of mind capacities in autism (e.g., Ozonoff et al., 1991), though many language-impaired non-autistic children can normally acquire these skills (Frith et al., 1991). The theory of mind hypothesis has been a highly productive one in terms of generation of research, and in focusing increased attention on the social aspects of autism, including deficits in joint attention, communication, and pretense play (see Happe, 1995, for a summary). However, specific behaviors that evidence a deficit in theory of mind are not by themselves sufficient to yield a diagnosis of autism, which can be associated with other cognitive deficits. In addition, research in which theory of mind concepts were taught to individuals with autism did not result in general changes in social behavior, suggesting that links between theory of mind and sociability are not simple (Hadwin et al., 1997).

A second body of work has focused on deficits in executive functioning, that is, in forward planning and cognitive flexibility. Such deficits are reflected in difficulties with perseveration and lack of use of strategies (see Prior and Ozonoff, 1998). Tests such as the Wisconsin Card Sort (Heaton, 1981) and the Tower of Hanoi (Simon, 1975) have been used to document these difficulties. In preschool children, the data on executive functioning deficits are more limited. McEvoy and colleagues (1993) used tasks that required flexibility and response set shifting, and noted that younger children with autism tended to exhibit more errors in perseveration than either mentally or chronologically age-matched control children. More recently, others did not find that the executive functioning in preschoolers with autistic spectrum disorders differed from that in other children (Griffith et al., 1999; Green et al., 1995).

A third area of theoretical interest has centered on central coherence theory, in which the core difficulties in autism are viewed as arising from a basic impairment in observing meaning in whole arrays or contexts (Frith, 1996; Jarrold et al., 2000). As Frith (1996) has noted, it is likely that a number of separate cognitive deficits will be ultimately identified and related to the basic neurobiological abnormalities in autism.

Neuropsychological assessments are sometimes of help in documenting sensory-perceptual, psychomotor, memory, and other skills. The util-



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