Past tense formation in Williams syndrome

It has been claimed that in the language systems of people with Williams sy ndrome (WS), syntax is intact but lexical memory is impaired. Evidence has come from past tense elicitation tasks with a small number of participants where individuals with WS are said to have a specific deficit in forming ir regular past tenses. However, typically developing children also show poore r performance on irregulars than regulars in these tasks, and one of the ce ntral features of WS language development is that it is delayed. We compare d the performance of 21 participants with WS on two past tense elicitation tasks with that of four typically developing control groups, at ages 6, 8, 10, and adult. When verbal mental age was controlled for, participants in t he WS group displayed no selective deficit in irregular past tense performa nce. However, there was evidence for lower levels of generalisation to nove l strings. This is consistent with the hypothesis that the WS language syst em is delayed because it has developed under different constraints, constra ints that perhaps include atypical phonological representations. The result s are discussed in relation to dual-mechanism and connectionist computation al models of language development, and to the possible differential weight given to phonology versus semantics in WS development.