Profiles and paths: Effects of language impairment and bilingualism on children's linguistic and cognitive development

Research on children with language impairment (LI) and bilingual children is important for both clinical and theoretical reasons (Paradis, 2010). For example, identifying similarities and differences between the two child populations can support the clinical challenge of diagnosing LI in bilingual children, but can also inform us about the nature of LI. Additionally, such research can determine whether effects of bilingualism and LI accumulate and whether bilingualism aggravates or alleviates the symptoms of LI, strengthening our knowledge of children who are both dual language learners and diagnosed with LI. In the past few years, there has been a growing body of work that tackled these issues, focusing mostly on children’s language abilities. The current dissertation contributes to this body of work by investigating the effects of LI and bilingualism on children’s skills in both linguistic and cognitive domains, including studies that evaluated promising clinical tools, that made cross- and within-domain comparisons, and that took a developmental perspective. In doing so, we aimed to (1) support a reliable diagnosis of LI in bilingual contexts, (2) identify the risks and strengths of bilingual children with LI, and (3) provide insight into the origins of the partially overlapping language profiles of bilingual children and children with LI. The results of the studies in the present dissertation show that three recently developed instruments can contribute to a reliable diagnosis of LI in (monolingual and) bilingual learning contexts. Combining parental report on a child’s early language development with the child’s performance on a quasi-universal nonword repetition task and a narrative task testing macrostructure demonstrated excellent clinical accuracy, irrespective of the linguistic background of the child (or parents). In addition, our results indicate that vocabulary may be a particular risk area for bilingual children with LI, as the effects of bilingualism aggravated the effects of LI in this domain. In contrast, working memory was found to be a relative strength of bilingual children with LI, who performed better in this area than monolingual peers with LI when controlling for language ability. Finally, our findings suggest that the overlapping language profiles of children with LI and bilingual children may be explained by the weakened ability of children with LI to maintain attention to the stream of linguistic information, interfering with how well incoming language is processed. While reductions in input frequency cause language delays in bilingual children, the functional equivalent, i.e., incomplete processing of input, may impair the language proficiency of children with LI