PP1012 - Neural Signatures of Vowel Discrimination in Younger and Older Tagalog-English Bilinguals

Abstract: Aging affects auditory processing and speech perception, but bilingualism may help maintain neural efficiency. This study examined mismatch negativity (MMN) responses in younger and older Tagalog–English bilinguals and American English monolinguals using EEG. A fatigue effect was observed in older adults. Older bilinguals showed enhanced MMN amplitudes after a cognitive task, especially at central sites, whereas older monolinguals showed reduced responses and degraded waveforms. These findings suggest that bilingual experience may promote neural resilience and preserve automatic auditory discrimination with age, highlighting bilingualism’s potential role in mitigating age-related auditory decline and supporting healthier cognitive aging.

Summary: Background
Aging is associated with declines in auditory processing, cognition, speech discrimination, and memory, increasing the risk of comprehension difficulties that impact communication and quality of life. Structural changes in the aging brain are linked to cognitive reserve, which may help preserve auditory and linguistic processing. Native phonetic contrasts are typically processed automatically with minimal attentional demand, supporting efficient native-language speech perception.

Mismatch negativity (MMN)—an automatic neural response measured via electroencephalography (EEG)—reflects pre-attentive auditory discrimination and provides insight into automatic speech processing (Näätänen et al., 2012; Bartha-Doering et al., 2015; Partanen et al., 2011). A prior study comparing American English monolinguals and Spanish–English bilinguals revealed age-related differences in MMN amplitude and latency, suggesting that bilingual experience may promote resilience in speech perception with aging.

Building on these findings, the present study examines Tagalog–English bilinguals to determine whether similar neural patterns emerge in a typologically distinct bilingual group. It investigates the effects of aging and bilingual experience on vowel discrimination and electrophysiological responses compared to American English monolinguals. Specifically, it explores how language background influences neural sensitivity to speech sound differences. We hypothesized that younger bilinguals would show larger and earlier MMN responses than older bilinguals, and that bilinguals overall would elicit stronger MMNs than monolinguals.

Methods
Neural encoding of acoustic features and auditory discrimination were measured using a modified oddball paradigm. Participants included younger (18–39 years) and older (50+ years) adults. MMN responses (amplitude and latency) were recorded using a 32-channel BrainVision actiCAP system (Brain Products GmbH). A phonological memory repetition task was administered between two EEG sessions (Part 1 and Part 2) to examine the effects of cognitive load on auditory discrimination. Participants also completed the Quick Speech-in-Noise (QuickSIN) test and the Montreal Cognitive Assessment (MoCA) to explore relationships between neural and behavioral performance.

Results
Preliminary analyses revealed patterns consistent with those in the Spanish–English study. Bilinguals elicited larger MMN responses than monolinguals in both Parts 1 and 2 across frontal and central sites, though with later latencies. A fatigue effect was observed in older adults: older bilinguals showed larger MMN amplitudes in Part 2 than in Part 1, especially at central sites, while older monolinguals showed the opposite pattern. Neural responses in older bilinguals appeared more affected by the repetition task, possibly increasing cognitive load or fatigue and leading to enhanced MMN amplitudes indicative of retained sensitivity to speech sounds.

Conclusion
Findings suggest that bilingual experience may enhance neural resilience in aging auditory systems, helping preserve sensitivity to speech sounds. Older bilinguals demonstrated neural plasticity through enhanced MMN responses following a cognitive task, whereas older monolinguals exhibited reduced amplitudes and degraded waveform morphology. These results indicate that bilingualism may mitigate age-related declines in speech perception and support more robust auditory processing, advancing understanding of how linguistic experience and aging interact to shape auditory neural mechanisms.

This study advances knowledge of auditory processing in aging individuals with cognitive decline and second-language English speakers, with the goal of optimizing outcomes in auditory rehabilitation and aural therapy.