Down Syndrome Abstract
of the Month: Nov 2002
Predicting longitudinal change in language production and comprehension in individuals with Down syndrome
Chapman RS, Hesketh LJ, Kistler DJ
J Speech Lang Hear Res 2002 Oct;45(5):902-15
Waisman Center, University of Wisconsin-Madison, USA
Abstract:
Longitudinal change in syntax comprehension and production skill, measured four times across a 6-year period, was modeled in 31 individuals with Down syndrome who were between the ages of 5 and 20 years at the start of the study. Hierarchical Linear Modeling was used to fit individual linear growth curves to the measures of syntax comprehension (TACL-R) and mean length of spontaneous utterances obtained in 12-min narrative tasks (MLU-S), yielding two parameters for each participant's comprehension and production: performance at study start and growth trajectory. Predictor variables were obtained by fitting linear growth curves to each individual's concurrent measures of nonverbal visual cognition (Pattern Analysis subtest of the Stanford-Binet), visual short-term memory (Bead Memory subtest), and auditory short-term memory (digit span), yielding two individual predictor parameters for each measure: performance at study start and growth trajectory. Chronological age at study start (grand-mean centered), sex, and hearing status were also taken as predictors. The best-fitting HLM model of the comprehension parameters uses age at study start, visual short-term memory, and auditory short-term memory as predictors of initial status and age at study start as a predictor of growth trajectory. The model accounted for 90% of the variance in intercept parameters, 79% of the variance in slope parameters, and 24% of the variance at level 1. The some predictors were significant predictors of initial status in the best model for production, with no measures predicting slope. The model accounted for 81% of the intercept variance and 43% of the level 1 variance. When comprehension parameters are added to the predictor set, the best model, accounting for 94% of the intercept and 22% of the slope variance, uses only comprehension at study start as a predictor of initial status and comprehension slope as a predictor of production slope. These results reflect the fact that expressive language acquisition continues in adolescence and is predicted by syntax comprehension and its growth trajectory.
My comments: The details of the testing and analysis are fairly complicated and nap-inducing. But the conclusion is one to share with all parents and speech therapists: language development does not plateau in adolescence, but continues on into young adulthood. There was no evidence of any "critical" age period associated with language development.
The paper's authors end with three conclusions: (1) Expressive language skills should continue to be intervention goals for adolescents and young adults with DS, and services should not be curtailed because of any expectation that there willl be no further progress. (2) Progress in speech development can be enhanced by concurrent focus on syntax comprehension (understanding the way words are put together to make sentences) and expressive language goals. (3) Attention should be given to improving short-term memory due to the demands of communication on this function.