Language distance & billingual language control : a multimodal neuroimaging study

Abstract

It is known that the constant demand for language control that bilinguals experience can shape the functioning and structure of their brains in significant ways. Evidence of such bilingualism-related neuroplastic changes is in line with the notion of experience-dependant neuroplasticity. However, the experience of being bilingual varies – bilinguals differ on the age of bilingualism-onset, relative language proficiency, exposure, immersion etc. Variation in these bilingualism-related factors generates different language control needs, which in turn triggers an adaptive response in the form of neuroplastic changes of functional and/or structural capacity, especially within the language control network. An important point of variation in the bilingual experience that could also give rise to differing language control needs and drive adaptive changes, is the factor of relative language distance. A reasonable assumption is that the closer a bilingual’s pair of languages are, the greater is the need for managing cross-linguistic interference/conflict between them. The focus of this thesis is to explore how the factor of language distance might influence bilingual language control and in turn contribute towards bilingualism-related adaptive neuroplasticity. Till date, no study has investigated this. Two neuroimaging experiments were devised and conducted on three groups of bilinguals, all homogenous in their bilingual profiles except for the factor of language distance: high-distance Cantonese-English (CE), intermediate distance Hindi-English (HE) and low-distance Dutch-English (DE) speakers. The first study used a translation task to specifically elicit activation within the language control network to uncover adaptive changes in functional activity in the network. The results showed a differential activation of the Anterior Cingulate Cortex (the region implementing conflict control) in the pattern of DE>HE>CE, for identical levels of performance. This suggests that language control regions in bilinguals functionally adapt to different conflict control demands generated by linguistic distance. The second study was aimed at uncovering whether the experience of managing “close” and “distant” languages had induced any adaptive structural changes in the language control networks of the three representative bilingual groups. The results of this structural imaging study (after controlling for potential confounding variables) showed significant bilateral putaminal volume variation between the groups, along the language distance gradient in the pattern of CE>HE>DE. This is attributable to the differing articulatory control needs generated by language distance. This suggests that experience with managing differently overlapping L1-L2 phonemic repertoires could induce adaptive structural changes. The above findings provide emerging evidence of how language distance can differentially affect language control demands and bring into effect different functional and structural adaptive changes within the bilingual language control network. Language distance could be a potential factor that induces important neurocognitive heterogeneity amongst bilinguals, in the way other bilingualism-related variables such as relative language proficiency, L2AoA and immersion/exposure do. Finally, considering the cross-populational nature of this research undertaking, hitherto unavailable norms in Hindi for a picture stimuli set were collected. The norms were necessary for assessing L1 proficiency of the Hindi-English bilinguals who took part in the study. The availability of norms in several world languages can facilitate cross-populational and cross-linguistic research in bilingualism.