Neural substrates of bilingual processing in a logographic writing system: An fMRI study in Chinese Cantonese-Mandarin bilinguals.

Logographic-logographic bilingualism is lacking in bilingual researches. Cantonese and Mandarin are two Chinese languages that belong to the logographic writing system and share the same set of Chinese characters. Cantonese-Mandarin bilinguals employ logographic-logographic bilingualism, and thus provide a unique population for bilingual studies. In Cantonese-Mandarin bilinguals, it remains unclear whether the second language (L2) phonological processing conforms to the assimilation or accommodation hypothesis and whether the brain mechanisms underlying Cantonese and Mandarin phonological processing are similar. Differential brain mechanisms of Mandarin as first language (L1) and L2 also needs to be clarified. Task-modality functional magnetic resonance imaging (fMRI) was used to explore these questions in Cantonese-Mandarin bilinguals and native Mandarin speakers. Univariate analysis, activation similarity analysis, brain-behavioral analysis and psychophysiological interaction (PPI) analysis were conducted. Novel evidence for accommodation was observed in the L2 processing of Cantonese-Mandarin bilinguals, indicating that small language distance leads to the accommodation of L2 processing, which is absolutely distinct to alphabetic bilingualism. We speculated that the role of language distance in the balance between assimilation and accommodation may be regulated by L1. Notably, we found Cantonese processing relied more on orthography-to-phonology mapping, phonological processing, language control and inhibition while Mandarin relied more on memory extraction. And Mandarin processing as L1 and L2 in our study are highly similar, suggesting the stability of brain regions processing Mandarin.