Auditory and executive determinants of phonetic processing and lexical acquisition in older adults with mild hearing impairment and cognitive decline

Age-related pure-tone hearing loss (HL) frequently co-occurs with central auditory processing deficits and cognitive decline and is commonly associated with speech processing difficulties. To examine how inter-individual differences in central auditory processing and cognitive capacities contribute to speech processing and lexical acquisition, we investigated the neural encoding and acquisition of novel words using phonetic stimuli as a proxy for speech processing abilities. These stimuli were presented at 80 dB SPL to minimize audibility-related confounds and ensure that differences in learning were not primarily driven by peripheral hearing sensitivity. Older adults with mild-to-moderate peripheral HL and signs of cognitive decline (N = 21) completed an attentive listening and associative word learning task with Thai words while EEG was recorded, alongside comprehensive psychometric, audiometric, and auditory assessments. Neural markers of word learning were preserved in this population, as reflected in the N400 and late positive component (LPC) event-related potentials (ERPs), with LPC amplitudes predicting word learning performance. Multiple linear regression models controlling for age and HL examined whether sensory ERPs (P50, N100, P200), behavioral auditory-audiometric measures (OLSA, PTA 4000, d-primes for attentive listening), or cognitive variables (attention, language, memory, perception, executive function, n-back, Stroop) predicted learning outcomes. Age accounted for the largest proportion of variance in word learning performance. Sensory ERPs and cognitive measures also emerged as significant predictors, whereas, as expected given the high stimulus intensity, peripheral HL showed a non-significant effect. Larger N100 amplitudes explained variance in sensory ERP models, while executive functions were the strongest predictors in cognitive models. Superior word learning performance was associated with younger age, enhanced central auditory processing, and stronger executive functions. These findings indicate that central auditory processing and executive functions are key determinants of speech learning in older adults with mild-to-moderate peripheral HL and cognitive decline when audibility is controlled.