A neural signature of automatic lexical access in bilinguals

Abstract

Bilingualism is often associated with beneficial effects on cognitive control and top-down processes. The present study aimed at bypassing these processes to assess automatic visual word recognition in bilinguals. Using fast periodic visual stimulation, we recorded frequency-tagged word-selective EEG responses in French monolinguals and late bilinguals (German native, French as second language). Words were presented centrally within rapid (10 Hz) sequences of letter strings varying in word-likeness, i.e., consonant strings, non-words, pseudo-words, while participants performed an orthogonal task. Automatic word-selective brain responses in the occipito-temporal cortex arose almost exclusively for the languages mastered by participants: two in bilinguals vs. one in monolinguals. Importantly, the amplitude of bilinguals’ responses to words within consonant strings were unaffected by the native vs. late-learnt status of the language. Furthermore, for all and only known languages, word-selective responses were reduced by embedding them in pseudo-words relative to non-words, both derived from the same language as the words. This word-likeness effect highlights the lexical nature of the recorded brain visual responses. A cross-language word-likeness effect was observed only in bilinguals and only with pseudo-words derived from the native language, indicating an experience-based tuning to language. Taken together these findings indicate that the amount of exposure to a language determines the engagement of neural resources devoted to word processing in the occipito-temporal visual cortex. We conclude that automatic lexical coding occurs at early visual processing in bilinguals and monolinguals alike, and that language exposure determines the competition strength of a language. Significance Statement Bilingualism and its possible impact on automatic processes have rarely attracted interest, contrary to bilingualism and its mutual relation with the executive functions. We assessed automatic visual word recognition in bi- and monolingual individuals while purposively bypassing executive functions. Visual brain potentials frequency tagged to words, that were flashed in rapid trains of strings with varying word-likeness degrees, exposed the automatic encoding of word-form as well as language identity at early stages of visual word processing within the occipito-temporal visual cortex. The mechanisms involved in both encoding processes reflect experience-based activity as the one characterizing tight-tuned neurons in the VWFA. Our findings provide a novel framework to understand the mechanisms behind the incredible efficiency of bilinguals in handling multiple languages.