Abstract
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.
Acknowledgements
This research was supported by EC NEST grant 029008 (ANALOGY).
Notes
1. For a discussion of the use of repeated measures in ANCOVA, see http://www.psyc.bbk.ac.uk/research/DNL/stats/Repeated_Measures_ANCOVA.html/.
2. While no task in the biological general knowledge battery appeared to make particular metacognitive demands, two of the five tasks of the folk-biological concepts battery may have done so (Death, as part of which participants were asked several open-ended questions about death, such as ‘What happens to a person when they die?’; and Species Transformations, in which stories were told of animals being transformed to look like other animals—for example, a tiger into a lion—either by dressing-up or by surgery, and participants were asked, for example, ‘Is it a tiger or a lion?’). Despite these concerns, the same basic pattern of results held across all five tasks of the folk-biological concepts battery.