Research On The Neural Mechanism Of Bilingual Language Control

Bilinguals exhibit a feat to control their two languages in conversation. The neural substrates of bilingual language control have been well investigated with language switching paradigm. Yet, most of those studies have taken single lexical items (i.e., words outside a context) as the investigative tool. In the present study, we examined the neural substrates of in-context language control in unbalanced bilinguals with a sentence-end switching paradigm. Our results showed that in-context language control in bilinguals recruited the neural mechanisms that were similar in kind to those responsible for cognitive control in general. When the direction of switching was considered, we found that backward switching called for more cognitive/language control relative to forward switching. Behaviorally, symmetric switching costs were found regardless of the switching factor (switching vs. non-switching) and the language factor (L1 vs. L2). We interpreted our imaging and behavioral results as the effects of context when unbalanced bilinguals controlled their two languages in a context.In a bilingual context, the speaker exhibits an adept feat to select between languages in response to external demand (forced language selection) or to select by his/her own volition (free language selection). The neural substrates underlying free and forced language selection may differ. While the neural substrates underlying forced language selection have been well explored mainly with language switching paradigms, those underlying free language selection have remained unclear. Using a modified digit-naming switching paradigm, we addressed the neural substrates underlying free language selection by contrasting free language switching with forced language switching. Chinese-English bilingual subjects successively named each visually-presented digit in pairs in Chinese or English on external demand (forced language selection) or did by their own volition (free language selection). The results revealed activations in the frontal-parietal regions which mediated volition of language selection. Further, we found that both free and forced language switching engaged cognitive control function and showed switching costs. However, free language switching demonstrated different patterns of activation and reduced switching costs as compared to forced language switching, suggesting differences between the mechanisms underlying free and forced language switching. As such, the current study suggested the interactive functions between control of volition and control of language selection in free language selection (or control), providing insights into the models of bilingual language control.