c rule in novel sentences" (1989, p. 192). But most behaviorist research has been conducted on adults: "If a factor proven to be effective in increasing [adult] learning in the lab does not exist in the child's natural environment, then that factor cannot be relied upon to explain language acquisition" (1989, pp. 192-3). The so-called communicative approach holds that "when words start getting combined, child language is best described in terms of meaning" (Hakuta, 1985, p. 113). But evidence that syntax and grammar emerge out of meaning and communication is inconclusive (Taylor-Flusberg & Calkins, 1990; Chomsky, 1969. Social-interactionist theory combines features of cognitive and linguistic theory (Bohannon and Warren-Luebecker, 1989, p. 204), with the added feature of the importance of the emotional environment of the language learner, such as the role of "motherese" language.
Questions surrounding language acquisition become vexed, of course, when children fail to accomplish the task. Failure of or delay in language acquisition in children may be attributed to a variety of factors that are grouped under the general category of language or developmental disabilities. Two such attributions are autism and attention deficit disorder (ADD), also sometimes characterized as attention deficit hyperactive disorder (ADHD). Autistic children have language-acquisition problems, and so do children affected by ADD/ADHD. Appropriate diagnosis is an important determinant of proper treatment. Language-acquisition theory and symptom recognition have a role in determining clinical diagnosis as well as treatment modalities. In a study of the psychiatric and behavioral characteristics of several hundred children showing signs of language-development difficulties, Cantwell and Baker (1980) found that those showing evidence of delayed language acquisition tended to be found either mentally retarded or autistic. More than half of those who had acquired ...