Bilingualism in autism: a neurocognitive investigation of the influence of bilingualism on perspective-taking in autistic adults
Digard, Bérengère Galadriel
Autism spectrum disorder (hereafter autism), is a lifelong neurodevelopmental condition with current prevalence estimates ranging around 1/100 worldwide. Autism is manifest in multiple forms, but always entails differences in communication and interaction behaviours. Consequent difficulties navigating the social world have been linked with altered social cognition, the complex set of cognitive mechanisms used to perceive, process, and respond to social interactions. The development of social cognition draws on social and linguistic inputs received during childhood. Indeed, it is hypothesised that the influence of language may play an additional role in autism, compensating for innate social cognitive difficulties. Thus, it is pertinent to investigate this relationship in an especially varied linguistic environment: bilingualism. Bilingualism is a skill shared by half the world’s population, and encompassing a wide range of language experiences shaped by multiple characteristics. There is considerable interest in the question of whether, and how, bilingualism shapes cognitive processes. Findings suggest that bilingualism does stimulate the development of social cognitive processes in neurotypical children. Does this stimulating effect of bilingualism on social cognition also exist in autism? This question has only been addressed in terms of general social functioning, and only in children or adolescents. Therefore, a dedicated investigation of specific social cognitive processes in adulthood is still lacking. This thesis explores how bilingualism shapes the social cognitive profiles of autistic adults, also capturing their lived social experiences, and investigating the effects of bilingualism at a neural level. I adopted an innovative approach, setting aside the traditional categorical vision of bilingualism, to rely instead on a multidimensional definition taking into account several key features of the bilingual experience. Before investigating the relationship between bilingualism and social cognition in autistic adults, however, it was necessary to address a number of critical gaps. The research currently available in the field of autism describes either early bilingual children, or adult polyglots, which is unlikely to represent the majority of bilingual experiences. Therefore, after an introductory chapter, the second chapter of the thesis provides an unprecedented description of the numerous bilingual experiences of autistic adults, gathering responses from a total of 208 bilingual and multilingual autistic adults via an online survey. This chapter also investigates the link between bilingualism and social life quality in this sample, in comparison with 89 monolingual autistic adults. The results showed that multilingual respondents were more satisfied with their social life than were monolinguals, hinting that linguistic repertoire may shape social functioning in autism. In the third chapter, I take a step back from autism, to first clarify the relationship between bilingualism and the social cognitive process at the centre of this research, perspective-taking, in typical development. Using a sample of 96 participants with a wide range of bilingual profiles, I found that not all forms of perspective-taking respond uniformly to the influence of bilingualism, and that not all bilingual experiences are equally influential. Specifically, cognitive and affective perspective-taking processes are susceptible to the influence of bilingualism, but not visual perspective-taking, and the main driver of this influence is the age of acquisition of the second language. In the fourth chapter, I repeated this analysis with a sample of 39 autistic participants. Crucially, the results mirrored those in the neurotypical population: bilingualism showed in autism a developmental influence on cognitive and affective perspective-taking, but not visual perspective-taking, that endures into adulthood. The fifth chapter is an exploratory investigation of the neural correlates of this developmental influence of bilingualism on perspective-taking. A sample of 15 neurotypical and 17 autistic participants were recruited into early and late bilingual groups. Early and late bilinguals showed in the anterior cingulate gyrus a tendency for distinct activity patterns during cognitive perspective-taking, and autism did not alter this effect, suggesting that the influence of early bilingualism on the neural basis of perspective-taking is similar between autistic and neurotypical populations. My findings are the first to highlight the richness of the bilingual experience of autistic people, and to describe a long-lasting developmental stimulating influence of early bilingualism in autistic and neurotypical adults alike. The research presented in this thesis has implications in numerous academic disciplines, but most importantly will inform practices to support autistic people in their bilingualism journey.