Introduction

Over the last two decades most psychological and neuropsychological research into autism has focused on individuals with Asperger syndrome or high-functioning autism (HFA), rather than on individuals with low functioning autism (LFA) or what is termed autistic disorder in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV; American Psychiatric Association, 1994). The core symptoms of autism, namely impairments of social interaction, communication and behavioural flexibility, are more likely to occur in pure form in people with HFA than people with LFA, and it makes sense, therefore, to focus on HFA to improve understanding of the core impairments.

A consequence of this strategy, however, has been a relative neglect of the impairments of language and intellectual ability that distinguish LFA from HFA. This is regrettable for both practical and theoretical reasons. From a practical point of view the combined effects of cognitive and linguistic impairments with autism are devastating for individuals themselves, and for their families and carers. Better understanding of the additional impairments is needed to provide optimal interventions and care. From a theoretical point of view, familial and genetic studies indicate that vulnerability to language impairment is related to vulnerability to autism (e.g. Bolton et al., 1994; Piven & Palmer, 1997; Folstein et al., 1999; Tomblin, Hafeman & O'Brien, 2003; Bartlett et al., 2004). Understanding the bases of the language impairment in LFA should therefore contribute to understanding autism as a whole.