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 speech processing varied by language familiarity. Two groups of English-speaking young adults— monolinguals and simultaneous bilinguals—actively listened to long passages (~30 seconds) in either a familiar (English) or unfamiliar (Hebrew) language, while their EEG activity was recorded. To characterize cognitive processes underpinning speech processing, we analyzed spectral power across a broad frequency spectrum (1–80 Hz), from delta through gamma bands. Further, time-frequency analyses were performed to capture the 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, indicating heightened attentional demands relative to the familiar language. Additionally, greater home exposure to non-English languages was linked to higher theta power during familiar language processing, reflecting enhanced attention and increased working memory load. Lower beta power in response to the unfamiliar language suggested greater demands of cognitive state maintenance during novel speech perception. 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 speech as reflected in attention- and memory-related processes. Furthermore, our results also underscore the importance of approaching bilingualism as a continuous variable beyond the binary categorization.