Williams Syndrome is a rare genetic disorder, first identified in 1961, that is characterized by, among other things, outgoing personalities and deficits in processing and adaptive behavior skils. These individuals frequently have comparatively low IQs with comparatively high language skills. While initially the facts of the preceding sentence were eagerly seized by proponents of the separation of intelligence and language, the accumulation of research has (as it so often does) muddied the picture. Williams Syndrome and Specific Language Impairment (SLI) have frequently been used as converse examples of evidence to support the dissociation between cognition and language. The cognitive scientist, Steven Pinker, has made this argument in several popular books. In 1999 he wrote,
Overall, the genetic double dissociation is striking, suggesting that language is both a specialisation of the brain and that it depends on generative rules that are visible in the ability to compute regular forms. The genes of one group of children [SLI] impair their grammar while sparing their intelligence; the genes of another group of children [WS] impair their intelligence while sparing their grammar.
Subsequent assertions by Pinker leaning more toward an inextricable relationship between genes and environment seem not to have been as widely read as his earlier work.
Comparisons of SLI and Williams Syndrome hinge on the notion that SLI is inherited. While the research does suggest that at least a predisposition toward SLI is inherited, the complexity of its causes makes any comparisons like that of apples and oranges. The exact cause of Williams Syndrome is known: it is the result of missing genetic material on chromosome seven. SLI is likely the result of a stew of ingredients, with varied recipes, and varied results. Individuals with Williams Syndrome are gregarious. They enjoy talking. Is it any wonder that they may become relatively proficient at something they enjoy? As with other human behaviors and skills, language acquisition will likely never be reduced to one cause. Similarly, the fact that these individuals are poor puzzle solvers is more likely related to visual-spacial deficits than an impairment in some “puzzle solving” gene.
Anette Karmiloff-Smith has done a lot of great work on Williams Syndrome, much with a focus on accurately describing its characteristic language skills and deficits. Many of her publications are available for download on her personal web site. Language log has published an interesting post on the science and state of language research in Williams Syndrome, found here: Language Log link.