Complex grammar in Williams syndrome.

This study investigated knowledge of binding and raising in two groups of children with Williams syndrome (WS), 6-12 and 12-16-years-old, compared to typically developing (TD) controls matched on non-verbal MA, verbal MA, and grammar. In typical development, difficulties interpreting pronouns, but not reflexives, persist until the age of around 6, while raising is not mastered until about the age of 8 or 9. If grammar in WS is delayed, but develops in a fashion parallel to TD population, similar patterns of difficulties may be expected, although it has not been established whether the grammatical development is ever complete in the individuals with this disorder. Knowledge of the principle of binding which states that a reflexive must have a c-commanding antecedent, was found to be intact in all the participants, in line with previous reports in the literature. In contrast, children with WS younger than 12 showed a poorer performance on personal pronouns, like two groups of younger matched TD controls, suggesting a previously unreported delay in the acquisition of constraints regulating coreferential interpretation of pronouns. Both groups of children with WS showed an extremely limited comprehension of raised, as opposed to unraised structures. The revealed patterns indicate that, like in unimpaired populations, different aspects of grammar mature at distinct stages of language development in WS: reflexive binding is acquired earlier than constraints governing coreference. However, development of raising seems exceptionally delayed, and perhaps even unattainable, as data from several adults with WS studied in Perovic and Wexler (2006) show. If, as hypothesized by Hirsch and Wexler, the late development of raising is related in TD children to lack of maturation of the knowledge of A-chains or defective phases, it seems reasonable to hypothesize that the even later development of these structures in WS is related to an even later (if ever) maturation of the knowledge of these grammatical forms.