PP1014 - Speech Discrimination Across the Lifespan: MMN Study

Abstract: Aging alters the brain’s ability to process speech even before measurable hearing loss occurs, affecting comprehension and quality of life. This study investigates how automatic speech discrimination changes across the lifespan using mismatch negativity (MMN), a neurophysiological marker of pre-attentive auditory processing. Participants aged 18–74 were divided into five age groups, and EEG responses to nonword stimuli differing in vowel duration were recorded. Preliminary results show larger frontal MMN in younger adults, while older adults exhibited greater central MMN. Analyses of MMN amplitude and latency aim to identify when neural efficiency begins to decline, informing early auditory aging interventions.

Summary: It is well established that speech discrimination abilities decline with age, but the point at which these changes begin and how they progress over time remain unclear. Previous research has often compared only younger and older adults, leaving the gradual neural changes that occur between these stages less understood. The present study aimed to identify when the brain begins to show signs of decline in speech discrimination ability and to map how this ability shifts across the lifespan. To achieve this, we used mismatch negativity (MMN), a neurophysiological marker of pre-attentive auditory processing.
Fifty participants (English monolinguals and Spanish-English bilinguals) aged 18 to 74 were divided into five age groups to examine age-related patterns in MMN responses. Each participant passively listened to a sequence of standard and deviant nonword stimuli differing in vowel duration. Neural activity was recorded using a 32-channel EEG system, and MMN amplitude and latency were analyzed in the frontal and central scalp regions. Additional factors such as hearing loss, language background, and fatigue were also considered to explore their influence on neural efficiency and auditory processing.
Preliminary findings indicate that age, hearing loss, language experience, and fatigue all influence the brain’s ability to automatically discriminate speech sounds. Overall, younger adults showed larger frontal MMN responses, whereas older adults exhibited greater central MMN responses. When analyzed by language background, older monolingual adults demonstrated stronger activation in frontal regions, while older bilinguals exhibited larger responses in the central regions. Younger groups showed smaller differences between frontal and central sites. These results suggest that the differences are not only between younger and older adults but also between monolingual and bilingual listeners.
Participants in their 20s showed the smallest difference between monolinguals and bilinguals, while those in their 30s showed slightly greater differences. The oldest group demonstrated the largest differences between frontal and central regions, as well as across hemispheres (left, central, and right). These findings suggest that older monolingual adults may increasingly rely on frontal brain regions to compensate for reduced auditory processing efficiency in central areas, while bilinguals may engage central regions to maintain efficiency—a possible reflection of neural compensation or resilience linked to language experience.
Importantly, these findings indicate that changes in speech discrimination emerge as early as midlife, even before measurable hearing loss occurs. Including bilingual participants provided valuable insight into how language experience may protect against, or modify, age-related auditory decline. By examining five age ranges instead of comparing only young and older adults, this study captures a more detailed trajectory of how auditory processing evolves throughout adulthood.
Clinically, understanding when these neural changes first appear can guide earlier and more targeted approaches to hearing care and intervention. Electrophysiological measures such as MMN can detect subtle auditory declines that behavioral tests may miss, allowing clinicians to identify at-risk individuals sooner and implement preventive or rehabilitative strategies. Overall, this study enhances our understanding of how aging, hearing loss, language experience, and cognitive factors interact to shape auditory processing across the lifespan.