Abstract
The utterances made by a moderately language-impaired adult with Down's syndrome, Ken, during 15 minutes of conversation were narrowly transcribed. It was found that pre-pausal rhythm groups containing the nuclear syllable had the best phonation and articulation; and the best rhythm in that a rhythm group whose plausible target was a dactyl (three syllables) or paeon (four) was much less likely to lose a syllable in such a position. Achieved dactyls and paeons were very rare in other prosodic positions, which led to some grammatical deficiencies, such as the inverted operator in a wh-question failing to be realized in any example. Ken often uses pre-pausal nuclear rhythm groups for a tag question which, though perhaps interactionally beneficial, relegates the main content of his utterance to the more distorted head rhythm groups and non-pre-pausal nuclear rhythm groups. These observations are discussed in terms of a speech planning model.