Williams Syndrome, specific language impairment and modularity.

It has been widely claimed that the language abilities in individuals with Williams Syndrome
(WS) provide evidence for dissociations between verbal and non-verbal cognitive processes,
thereby supporting the modularity hypothesis. Although previous research has delineated a
variety of skills and weaknesses in the WS profile, the reported results have been conflicting
and inconsistent. It has also been claimed that WS is the 'opposite' of Specific Language
Impairment (SLI), that is, that, in contrast to SLI, individuals with WS have relatively well
preserved linguistic abilities in the face of cognitive deficits. However there have not been any
studies that have directly compared the two populations on verbal and non-verbal tasks.
The aims of the present thesis are: to investigate whether individuals with WS show
superior verbal abilities in comparison to their non-verbal cognitive functioning; to investigate
whether the individuals with WS show the 'opposite' profile to that of individuals with SLI; and
to address the question of whether WS offers support for modular views of language.
Case study series of five participants with WS and five participants with SLI were
carried out. The study not only gathered information from a range of standardised verbal and
non-verbal tests but, most importantly, combined these results with analysis of conversational
interaction and narrative discourse, which has not been done previously. The results suggest
there is a wide variability among individuals with WS (and those with SLI), and that the
linguistic abilities of individuals with WS can often be severely impaired, sometimes being even
inferior to those of children with SLI. Furthermore, there seems to be no statistically significant
difference between the WS and the SLI profile with regard to their linguistic abilities, although
the two profiles are clearly distinct regarding their non-verbal abilities.
The results are discussed in light of the relevant literature and the current theoretical
debates on modularity.