Lexical skills in Williams Syndrome: a cognitive neuropsychological analysis

Abstract

Williams syndrome is a genetic disorder associated with learning disabilities. Although language has been reported as well developed in comparison to other skills, recent studies have also shown focal impairments within the language system. This study reports performance on a range of lexical skills in WS. Children with WS had elevated levels of receptive vocabulary, in relation to mental age, on the BPVT ( Dunn, Dunn, Whetton & Pintilie, (1982). The British picture vocabulary scale, Windsor, Berks: NFER-Nelson ) in which a spoken word has to be matched to a picture from an array with three distracters. However, impairments in receptive vocabulary became apparent when required to select from multiple, semantically-related distracters, so that more detailed semantic specification of the word was required. Oral fluency performance was also characterised by elevated performance levels, yet there were atypical selections with significantly increased proportions of items of low frequency. There were naming difficulties, particularly for the older children and for all the children with WS, naming errors were atypical. Yet, when naming was accurate it was faster than that of mental age controls. We propose that the parameters governing lexical access in WS have a looser criterion for target identification but more rapid arrival at selected targets. The results are discussed in relation to other contemporary studies of WS and a model of lexical processing. The results require the rejection of the on-line/off-line theory of performance in WS ( Tyler et al., (1997). Do individuals with Williams syndrome have bizarre semantics? Evidence for lexical organisation using an on-line task. Cortex, 33, 515–27 ) but are compatible with both the Clahsen and Almazan ( Clahsen & Almazan, (1998). Syntax and morphology in children with Williams Syndrome. Cognition, 68, 167–98; (2001). Compounding and inflection in language impairment: evidence from Williams syndrome (and SLI). Lingua, 110, in press ) studies of selective impairment in morphology in WS and developmental studies of early lexical development in WS (Stevens & Karmiloff-Smith, (1997). Word learning in a special population: do individuals with Williams Syndrome obey lexical constraints. Journal of Child Language, 24, 3737–65).