Phonological investigation of verbal autistic and mentally retarded subjects.

A review of the pertinent literature indicates that autistic children are likely to show normal but delayed development of speech sounds. In contrast, atypical phonological development is suggested by experiments demonstrating that autistic subjects are deficient in their ability to extract the components of structured auditory input. A systematic investigation of the speech sound systems of verbal autistic and mentally retarded children reveals a delay in phoneme acquisition, as well as a relative uniformity of error types in both groups. The autistic subjects, however, differ significantly from the mentally retarded in the phonemic substitutions which they make. Autistic subjects are also characterized by a high correlation between frequency of phonological errors and level of overall language development. The findings are interpreted as supporting the hypothesis that the autistic group shows a more global delay in language development.