Functional lateralization of tool-sound and action-word processing in a bilingual brain

BACKGROUND The impact of bilingualism on lateralized brain functions such as praxis - the control of skilled actions - and language representations themselves, particularly in the auditory domain, is still largely unknown. Recent studies suggest that bilingualism affects both basic (fundamental frequency) sound and action-related speech processing. Whether it can impact non-verbal action sound processing is a question of debate. PARTICIPANTS AND PROCEDURE Here we examined twenty bilinguals using a dichotic listening paradigm, in which in addition to repeating the just heard action words, participants named - in Polish or English - one of two simultaneously presented tool sounds from attended ears. The results were compared with data from these same participants tested with reading the same words in a visual-half field paradigm. RESULTS In contrast to typical outcomes from monolinguals, the laterality indices of action-related sound processing (verbal and non-verbal) were not left lateralized but hemispherically balanced. Notably, despite similar organization of tool- and action-word sound processing, their auditory (balanced) and visual-language (left-lateralized) representations might be independent because there were no significant correlations between any of their laterality indices. CONCLUSIONS This indicates that bilingualism might involve reshuffling/reorganization of typically lateralized brain functions and such plasticity will have consequences for second language learning strategies, as well as for neurorehabilitation.