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AoA shapes neural mechanisms of selective attention in bilinguals through delta-band tracking
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
Pepita Alex1,2, Stéphen Theron-Grimaldi1, Anastasia Klimovich-Gray2, Mirjana Bozic1; 1University of Cambridge, 2University of Aberdeen
Introduction: Bilingualism modulates how listeners encode speech during dichotic listening (e.g., Olguin et al., 2019). However, it remains unclear whether/how these neural adaptations are further modulated by Age of Acquisition (AoA). Specifically, earlier bilingual exposure may promote more efficient mechanisms for segregating competing speech streams due to prolonged experience in managing multilingual input. Here, we examined how AoA shapes neural mechanisms of auditory selective attention using naturalistic dichotic listening. We focused on low-frequency neural encoding, specifically in the delta (1-4Hz) and theta (4-8Hz) bands, due to their roles in tracking prosodic and syllabic parsing of speech, with delta additionally linked to higher-order attentional modulation (e.g., Molinaro & Lizarazu, 2018). Method: 27 Early (AoA < 6y) and 22 Late (AoA > 11y) Spanish-English bilinguals (mean age = 28.3; 30 female), matched on L2 proficiency and exposure, attended to children’s stories in their native Spanish language in one ear while ignoring interference in the other ear. There were three interference conditions: Musical Rain (MuR; acoustically-matched non-linguistic interference), Unknown language (non-intelligible linguistic interference), and Native language (intelligible linguistic interference), as well as Single Talker condition (ST). 128-channel EEG was recorded, pre-processed, and decomposed into delta and theta bands. Neural tracking of speech was decoded using backward temporal response function (TRF) modelling, which reconstructs attended/unattended speech envelope from EEG, measuring the fidelity of cortical tracking of speech signal. Attention modulation index (AMI) was calculated as the standardised difference in reconstruction accuracies between attended and unattended streams, where higher values reflect greater preferential tracking towards attended stream. We expected Early bilinguals to show greater AMI, corresponding to more effective differentiation of competing streams. Results: Early and Late bilinguals showed no differences in reconstruction accuracy of attended speech in the baseline ST condition, suggesting comparable speech encoding under standard listening. However, under dichotic listening, significant Group and Group*Condition effects emerged in delta-band AMI: Early bilinguals showed both greater attentional selectivity and more flexible modulation compared to Late bilinguals, with group differences most pronounced in the MuR condition. Further analyses revealed these Group effects were driven by differences in the encoding of attended speech, whereas unattended speech tracking showed no AoA-related modulation. No effects of Group or Condition were observed in theta band. Discussion: These findings suggest that AoA modulates how bilinguals encode goal-relevant speech during selective attention, rather than influencing general speech processing or passive encoding of unattended input. AoA-related effects were selectively expressed in delta-band tracking, consistent with findings that delta activity supports top-down attentional control under challenging listening conditions (e.g., Molinaro & Lizarazu, 2018; Park et al., 2015). Early bilinguals separated competing streams more flexibly, particularly when the interference was non-linguistic (and therefore less disruptive), while Late bilinguals found all types of interference equally challenging. This suggests early bilingualism may foster more adaptable auditory attention systems in managing listening demands.
Topic Areas: Multilingualism, Control, Selection, and Executive Processes