The impact of developmental visuospatial learning difficulties on British Sign Language.
There has been substantial research interest in recent years in the relationship between the development of language and cognition, especially where dissociations can be seen between them. Williams syndrome, a rare congenital disorder characterized by a fractionation of higher cortical functions, with relatively preserved language but marked difficulties with visuospatial constructive cognition, has been extensively studied. The case of Heather, who is remarkably similar to the characteristic phenotype of Williams syndrome in physical appearance and cognitive abilities, but who is also congenitally deaf and a user of British Sign Language, provides the first opportunity to explore the consequences of specific visuospatial learning difficulties on the linguistic system when the language used is visuospatial. Heather shows a pattern of impaired drawing ability and visual form discrimination, but preserved ability to discriminate faces. She has a large vocabulary in British Sign Language, and overall presents a picture of relative competence in British Sign Language grammar. However, she shows specific deficits in those areas of British Sign Language which directly rely on spatial representations for linguistic purposes. A number of theories as to the nature of her impairments and those found in Williams syndrome are discussed, using models of the relationship between language and visuospatial cognition based on data from this unique case.