Divergence of verbal expression and embodied knowledge: Evidence from speech and gesture in children with specific language impairment

It has been suggested that phonological working memory serves to link speech comprehension to production. We suggest further that impairments in phonological working memory may influence the way in which children represent and express their knowledge about the world around them. In particular, children with severe phonological working memory deficits may have difficulty retaining stable representations of phonological forms, which results in weak links with meaning representations; however, nonverbal meaning representations might develop appropriately due to input from other modalities (e.g., vision, action). Typically developing children often express emerging knowledge in gesture before they are able to express this knowledge explicitly in their speech. In this study we explore the extent to which children with specific language impairment (SLI) with severe phonological working memory deficits express knowledge uniquely in gesture as compared to speech. Using a paradigm in which gesture-speech relationships have been studied extensively, children with SLI and conservation judgement-matched, typically developing controls were asked to solve and explain a set of Piagetian conservation tasks. When gestures accompanied their explanations, the children with SLI expressed information uniquely in gesture more often than did the typically developing children. Further, the children with SLI often expressed more sophisticated knowledge about conservation in gesture (and in some cases, distributed across speech and gesture) than in speech. The data suggest that for the children with SLI, their embodied, perceptually-based knowledge about conservation was rich, but they were not always able to express this knowledge verbally. We argue that this pattern of gesture-speech mismatch may be due to poor links between phonological representations and embodied meanings for children with phonological working memory deficits.