Language skills of children and adolescents with Down syndrome: II. Production deficits.

Hypotheses that children and adolescents with Down syndrome show (a) a specific expressive language impairment, (b) a "critical period" for language acquisition, (c) a "simple sentence syntactic ceiling" in production, and (d) deficit in grammatical morphology were investigated cross-sectionally. Conversational and narrative language samples from 47 children and adolescents with Down syndrome (Trisomy 21), aged 5 to 20 years, were compared to those from 47 control children aged 2 to 6 years matched statistically for nonverbal mental age. Children with Down syndrome appear to have a specific language impairment, compared to control children, in number of different words and total words (in the first 50 utterances) and in mean length of utterance (MLU). Total utterance attempts per minute were more frequent in the Down syndrome group. Narrative samples contained more word tokens, more word types, and longer MLU than conversation samples, for both groups. Intelligibility of narratives was significantly poorer for the Down syndrome group than controls. Analyses of narrative language sample by age sub-group showed no evidence of a critical period for language development ending at adolescence, nor of a "syntactic ceiling" at MLUs corresponding to simple sentences for the Down syndrome group. Omissions of word tokens and types were more frequent in the older Down syndrome than the younger control sample, matched on MLU.