Oscillatory brain activity in response to familiar and unfamiliar languages in monolingual and bilingual young adults

This study investigated how bilingual experience modulates neural oscillations during spoken language processing as a function of language familiarity. Two groups of English-speaking young adults-monolinguals and simultaneous bilinguals-actively listened to long passages (∼30 s) in either a familiar (English) or unfamiliar (Hebrew) language while their EEG activity was recorded. To characterize the cognitive processes underpinning spoken language processing, we analyzed spectral power across a broad frequency spectrum (1-80 Hz), spanning delta to gamma bands, and conducted time-frequency analyses to capture neural dynamics during sustained listening. Results revealed that bilingual experience was associated with differential oscillatory patterns, particularly in alpha and theta frequencies. Bilinguals exhibited stronger alpha suppression when processing the unfamiliar language, reflecting experience-dependent engagement of attentional and control-related processes. Additionally, greater home exposure to non-English languages was linked to higher theta power during familiar language processing, consistent with enhanced attention and increased working memory load. Reduced beta power in response to the unfamiliar language suggested limited maintenance of stable representational states and prediction during novel input processing. However, no significant effects were observed in gamma or delta power, nor in the time-frequency analyses. Altogether, these findings suggest that bilingual experience shapes brain responses to spoken language primarily through attention- and memory-related processes. Furthermore, our results underscore the importance of approaching bilingualism as a continuous variable beyond binary categories.