A cross-sectional analysis of developmental trajectories of vocabulary comprehension among children and adolescents with Down syndrome or intellectual disability of undifferentiated aetiology

ABSTRACT

Background In this work we sought to expand our knowledge of developmental trajectories of subcomponents of the language systems of individuals with intellectual disability (ID). We aimed to explore how general and relational vocabularies evolve as a function of cognitive level.

Method Developmental trajectories of general and relational vocabulary comprehension were compared among typically developing (TD) children and children and adolescents with ID of undifferentiated aetiology (UND) or Down syndrome (DS).

Results Comparisons between TD participants and participants with UND showed no interaction between cognitive level and diagnostic status for general vocabulary, and only a very weak interaction for relational vocabulary. Comparisons between TD participants and participants with DS failed to reveal group-specific trajectories. Performance in general vocabulary was higher than in relational vocabulary for participants with UND and DS.

Conclusion The developmental trajectories of vocabulary appear to be globally comparable for participants with or without ID.

KEYWORDS:

• intellectual disability
• Down syndrome
• language
• lexical development
• developmental trajectory

Acknowledgements

We are grateful to John M. Belmont for his helpful comments on this manuscript. We also thank the students and psychologists who helped with data collection. We extend our deepest gratitude to the special education facilities and schools that permitted us to conduct this study, and to all the children and adolescents who participated.

Conflicts of interest

None of the authors has any conflicts of interest with any company or other organisation regarding the material discussed in the manuscript.

Notes

1. The vocabulary evaluated by tests such as the PPVT is sometimes called concrete vocabulary (e.g., Mervis & John, 2008). However, we much prefer the term general vocabulary because the PPVT actually evaluates knowledge of abstract as well as concrete words.

Additional information

Funding

This work was supported by a grant from the French National Research Agency (Agence Nationale de la Recherche, ANR, LANG & HANDICAPS, Project no. ANR-09-ENFT-019). David Magis is a Research Associate of the Fonds de la Recherche Scientifique (FNRS) (Belgium).