From categorization to classification: a comparison among individuals with autism, mental retardation, and normal development.

Free-sorting, matrix, and class-inclusion tasks were administered to 16 participants with autism, 16 participants with mental retardation (MR), and 16 normal children, matched for mental age. On perceptual matrices, participants with MR performed less well than those with autism, who performed less well than normal children. On functional matrices, participants with autism and those with MR performed less well than normal children. Participants with autism performed less well than participants with MR and normal children in free-sorting representational objects and in the class-inclusion tasks, which require higher operational thought. These results suggest that individuals with autism have difficulties with tasks that necessitate internal manipulation of information. This impairment is discussed in relation to the cognitive deficit characterizing autism.