Distinction between directed or intelligent thought, and undirected or autistic thought, appears to have been made in general terms by Bleuler in 1912. Directed thought is conscious and can be communicated by language. Autistic thought is subconscious and is (typically) incommunicable by language, whether spoken or unspoken. Over the course of the twentieth century, the definition has been refined, and autism exhibits a variety of symptoms. However, language acquisition problems, as well as cognitive problems, are important features of diagnosis. In particular, autism is marked by an absence of or developmental delay in the acquisition of linguistic speech plus an absence of nonverbal communication cues. To the degree language does appear to have been acquired, the autistic child falls into repetitive speech patterns (echolalia) or otherwise fails to sustain an effective track of verbal or nonverbal communication (APA, DSM-IV, 1994). Asperger's syndrome is the name given to a less severe autism of communication and delayed language acquisition. Autistics who fail to acquire language by the age of six are unlikely to do so at any time during life, and those who acquire words but not sentences during that period are likely never to develop linguistic communication skills (Williams, 1990). Although symptoms of autism, such as impaired language, may decline or disappear as the child gets older, social impairments such as failure to communicate effectively may not necessarily disappear (LeCouteur & Others, 1996).

Stephens, L. A. (1993). Measurement of formal thought disorder and its relationship to receptive language deviancy in children. Dissertation Abstracts International, 54 (3), 1698-B.

Nippold, M. A. & Fey, S. H. (1984, July). Metaphoric understanding in preadolescents having a history of language acquisition difficulties. Language, Speech, and Hearin