Linda J. Hesketh

Behavioral phenotype of individuals with Down syndrome.

Evidence is reviewed for a developmentally-emerging behavioral phenotype in individuals with Down syndrome that includes significant delay in nonverbal cognitive development accompanied by additional, specific deficits in speech, language production, and auditory short-term memory in infancy and childhood, but fewer adaptive behavior problems than individuals with other cognitive disabilities. Evidence of dementia emerges for up to half the individuals studied after age 50. Research issues affecting control group selection in establishing phenotypic characteristics are discussed, as well as the possible genetic mechanisms underlying variation in general cognitive delay, specific language impairment, and adult dementia. MRDD Research Reviews 2000;6:84-95. Wiley-Liss, Inc.

Pragmatic development in individuals with mental retardation: Learning to use language in social interactions

Pragmatics is the intentional use of language to achieve interpersonal goals. Pragmatic problems figure prominently in the definition and diagnosis of mental retardation. In this article, we describe the pragmatic development of persons with mental retardation, the ways in which their linguistic, cognitive, and social-emotional limitations influence their pragmatic competence, and the prelinguistic foundations of that competence. Delays in intentional communication during the prelinguistic period are severe and often exceed those in cognitive development. After the transition to language, developmental delays are seen in all components of pragmatics, but the delays are more severe and the final level of achievement lower for some components than for others. Conversational turn-taking is an area of relative strength, although it remains to be determined whether contextual variations in the rules governing turn-taking have been mastered. Individuals with mental retardation have special difficulty in learning to formulate their utterances in ways that make their intended referents clear. Development here often lags behind nonverbal cognitive development. Delays also occur in expressing and understanding speech acts, such as requests and questions. Especially problematic is the task of learning to use linguistic politeness formulae when expressing speech acts. Individuals with mental retardation are also delayed in learning to signal when they have not understood an utterance and in learning how to respond to such signals from others, although the extent of their problems here varies with the nature of the task. They achieve a considerable level of topic-related skill in that they typically produce utterances that are on topic, but the quality of these contributions to the topic is not clear. Pragmatic delays do not appear to be attributable to the language-learning environments provided for individuals with mental retardation by their parents. It is more likely that these delays result from the cognitive, linguistic, and social-emotional limitations that define mental retardation, although there remains much to be learned about the relation between specific pragmatic problems and specific limitations in these other domains. MRDD Research Reviews 1997;3:323–333.