Patricia V Aguiar, Brandon T Paul
Older adults with age-related hearing loss (OAHL) are more strongly influenced by vision during audiovisual perception tasks compared to typical-hearing older adults, suggesting a greater weighting of visual input in the former group. This visual "bias" has been argued to arise through compensatory, top-down cross-modal neuroplasticity that strengthens visual perceptual processing in response to hearing loss. However, current behavioural evidence does not convincingly demonstrate that cross-modal plasticity confers a visual benefit to OAHL, and existing methods do not untangle top-down influences of visual processing from low-level audiovisual integration. Here, we tested for evidence of enhanced visual speech processing in OAHL using a cross-modal lexical matching task designed to bypass low-level integration and isolate higher-level visual influences. Forty-nine adults aged 59-81 years completed a task where auditory-only and visual-only words were presented separately and serially in either audio-then-visual (A-V) or visual-then-audio (V-A) order under no noise, 0 dB speech-to-noise ratio (SNR), and -10 dB SNR conditions. Half of the trials contained mismatching word pairs. Participants judged whether audio and visual words matched or mismatched while eye-tracking recorded visual attention to the speaker's face. OAHL were expected to benefit more from the V-A order if visual speech provided stronger perceptual predictions. We found that mismatch detection was stronger in the A-V relative to V-A condition in no-noise and 0 dB SNR conditions, but there was no difference at -10 dB SNR. More hearing loss was associated with worse overall perceptual sensitivity, and contrary to our predictions, was not associated with enhanced performance in the V-A condition. Hearing loss was also not associated with gaze differences to the speaker's eyes and mouth. Overall, these findings do not support that the visual bias in OAHL arises through high-level visual speech processing.