“Language and Communicative Development in Williams Syndrome”, 2007-02-26 ():
Williams syndrome, a genetic disorder caused by a microdeletion of ~25 genes on chromosome 7q11.23, is associated with mild to moderate intellectual disability or learning difficulties. Most individuals with Williams syndrome evidence a cognitive profile including relative strengths in verbal short-term memory and language, and considerable weakness in visuospatial construction. The syndrome has often been argued to provide strong evidence for the independence of language from other aspects of cognition.
We provide a brief history of early research on the language abilities of individuals with Williams syndrome and then review contemporary studies of language and cognition in Williams syndrome, beginning with a consideration of performance on standardized assessments.
In the remainder of the article, we first consider early language acquisition, with a focus on speech production and perception, vocabulary acquisition, and communicative/pragmatic development and then consider the language abilities of school-age children and adolescents, focusing on semantics, grammar, and pragmatics. We argue that rather than being the paradigm case for the independence of language from cognition, Williams syndrome provides strong evidence of the interdependence of many aspects of language and cognition.
[Keywords: Williams syndrome, language acquisition, intellectual disability, autism spectrum disorder, modularity]
…General Intellectual Ability: The Kaufman Brief Intelligence Test (KBIT) [1990] is the most commonly used measure of general intellectual ability in studies of English-speaking individuals with Williams syndrome. Our laboratory has tested 306 children aged 4–17 years on this test. The distribution of standard scores is shown in Figure 1. As is clear from this figure, the description of general intelligence as “barely measurable” is highly inaccurate. Mean Composite intelligence quotient (IQ) is 69.32, which is at the top of the range for mild intellectual disability, with a range from 40 (the lowest possible standard score) to 112. For 47% of the participants, Composite IQ was 70 or higher. Only 3.6% earned the lowest possible IQ (40, which is at the bottom of the moderate intellectual disability range). The standard deviation was 15.36, which is similar to the standard deviation of 15 for the general population. Thus, the distribution of IQ in Williams syndrome has the same shape and variability as for the general population, but is depressed by about two standard deviations. Mean verbal IQ was 71.35 and mean nonverbal (matrices) IQ was 1 point higher, 72.47.
The KBIT does not assess visuospatial construction, the area of greatest weakness for individuals with Williams syndrome. When IQ is measured by a fullscale assessment that includes spatial ability as well as verbal ability and nonverbal reasoning ability, overall IQ is considerably lower. For example, on the Differential Ability Scales, School Age version, mean GCA (similar to IQ) for a sample of 119 children aged 8–17 years tested by our laboratory was 58.29, toward the lower end of the mild intellectual disability range [2007], with a standard deviation of 12.77 and a range from 24 (the lowest possible GCA using the extended norms) to 94. Despite the 10-point difference between KBIT composite IQ and DAS GCA, the mean standard scores for the DAS Verbal Cluster (70.18) and Nonverbal Reasoning cluster (67.43) were similar to the Verbal and Nonverbal IQs for the KBIT; the primary reason for the lower GCA was very weak performance on the Spatial cluster (mean standard score: 55.54). Mean GCA was not a valid indicator of intellectual ability for the majority of children with Williams syndrome. For 80%, Verbal cluster standard score, Nonverbal Reasoning cluster standard score, or both was substantially higher than expected for GCA [; see also Meyer-Lindenberg et al 200618ya]. Once again, “general intelligence” is clearly measurable.