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Word learning in a special population: do individuals with Williams syndrome obey lexical constraints?



Williams syndrome (WS), a rare neurodevelopmental disorder, is of special interest to developmental psycholinguists because of its uneven linguistico-cognitive profile of abilities and deficits. One proficiency manifest in WS adolescents and adults is an unusually large vocabulary despite serious deficits in other domains. In this paper, rather than focus on vocabulary size, we explore the processes underlying vocabulary acquisition, i.e. how new words are learned. A WS group was compared to groups of normal MA-matched controls in the range 3–9 years in four different experiments testing for constraints on word learning. We show that in construing the meaning of new words, normal children at all ages display fast mapping and abide by the constraints tested: mutual exclusivity, whole object and taxonomic. By contrast, while the WS group showed fast mapping and the mutual exclusivity constraint, they did not abide by the whole object or taxonomic constraints. This suggests that measuring only the size of WS vocabulary can distort conclusions about the normalcy of WS language. Our study shows that despite equivalent behaviour (i.e. vocabulary test age), the processes underlying how vocabulary is acquired in WS follow a somewhat different path from that of normal children and that the atypically developing brain is not necessarily a window on normal development.


Corresponding author

Address for correspondence: Tassos Stevens or Annette Karmiloff-Smith, MRC-CDU, 4 Taviton Street, London WC1H 0BT, UK.


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This study forms part of the PhD thesis of Tassos Stevens entitled ‘Language acquisition in Williams syndrome: lexical constraints and semantic organisation’, under the supervision of Karmiloff-Smith. We would particularly like to thank Julia Grant for checking the text, appendices, tables and references, and for many forms of assistance during the preparation of the thesis on which this paper is based. Useful comments from two anonymous reviewers on the earlier version are gratefully acknowledged. We wish to express our sincere gratitude to the Williams Syndrome Foundation UK for putting us in touch with families whom we warmly thank for their participation in the research. For their help with setting up the testing of the normal control groups, we thank Mr Paul Smith of Holloway School for Boys, as well as Mr Christopher Hotham and the staff and pupils of Tufnell Park Primary School.


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Word learning in a special population: do individuals with Williams syndrome obey lexical constraints?



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