Definitions versus categorization: assessing the development of lexico-semantic knowledge in Williams syndrome
Article first published online: 16 MAY 2011
© 2010 Royal College of Speech & Language Therapists
International Journal of Language & Communication Disorders
Volume 46, Issue 3, pages 361–373, May-June 2011
How to Cite
Purser, H. R. M., Thomas, M. S. C., Snoxall, S., Mareschal, D. and Karmiloff-Smith, A. (2011), Definitions versus categorization: assessing the development of lexico-semantic knowledge in Williams syndrome. International Journal of Language & Communication Disorders, 46: 361–373. doi: 10.3109/13682822.2010.497531
- Issue published online: 16 MAY 2011
- Article first published online: 16 MAY 2011
- Received 13 October 2009; accepted 26 May 2010
- Williams syndrome;
Background: Williams syndrome (WS) is associated with relatively strong language abilities despite mild to moderate intellectual disability, particularly when language is indexed by vocabulary.
Aims: The aim of the study was twofold: (1) to investigate whether reported lexical anomalies in WS can be explained with reference to anomalous semantic development; and (2) to assess whether receptive vocabulary skills in WS, a relative strength, are underpinned by commensurate semantic knowledge.
Methods & Procedures: The development of lexical–semantic knowledge was investigated in 45 typically developing individuals (chronological age range = 5–10 years, mental age range = 5–13 years) and 15 individuals with WS (chronological age range = 12–50 years, mental age range = 4–17 years) by means of (1) a categorization task and (2) a definitions task, which was expected to make additional metacognitive demands.
Outcomes & Results: At younger ages, the performance level of typically developing individuals and individuals with WS did not differ on the definitions task. However, the WS group's ability to define words fell away from the level predicted by the typically developing group at older ages, as more sophisticated definitions were expected. The results of the categorization task indicated that individuals with WS had less lexical–semantic knowledge than expected given their level of receptive vocabulary, although from this lower level the knowledge then developed at a similar rate to that found in typical development.
Conclusions & Implications: It is concluded, first, that conventional vocabulary measures may overestimate lexical–semantic knowledge in WS; and, second, concerns about the metacognitive demands of the definitions task when used with atypical populations may be well founded.