Language Immersion Enhances Attentional Speech Processing via Low-Frequency Neural Tracking

Language experience is a powerful driver of neurocognitive plasticity, shown to modulate attentional and executive processing in speakers of multiple languages. This paper investigated how immersion in a second-language environment shapes attentional processing of speech. Fifty-eight bilingual Chinese-English speakers matched on their English language proficiency listened to competing continuous speech streams in a naturalistic listening task. They were immersed either in their native language environment (Beijing, China), or in the second language environment (Cambridge, UK). In an identical EEG experiment across the two immersion contexts, we assessed the listeners cortical tracking of attended and unattended speech and task-related attentional allocation using Temporal Response Function (mTRF) and Power Spectral Density (PSD) analyses. Behavioral comprehension of the attended narratives was uniformly high. PSD analyses showed no group difference in task-related attentional allocation, but mTRF results revealed robust differences in cortical tracking, with increased tracking of attended - but not unattended - streams in the immersed group, driven by the delta band (1-4 Hz). This boost in tracking of the attended signal declined with prolonged immersion, indicative of changes to attentional speech processing as the language environment stabilizes and consistent with the expansion-renormalization framework of neurocognitive adaptation. Jointly, these data imply that immersion in second-language environments shapes the way listeners encode speech, sharpening the brains ability to extract target auditory information from background noise. They furthermore suggest that, rather than being static or monotonous, this modulation reflects a flexible and dynamic process that is continuously shaped by changes in environmental demands and their duration. Key pointsO_LISecond language immersion boosts cortical tracking of attended speech, driven by the delta band (1-4 Hz). C_LIO_LIThis boost decreases with prolonged immersion, reflecting the dynamic, expansion-renormalization adaptation trajectory. C_LIO_LIImmersion does not influence task-related attentional allocation. C_LI