Audiovisual deficits in older adults with hearing loss: biological evidence.

OBJECTIVE To examine the impact of hearing loss (HL) on audiovisual (AV) processing in the aging population. We hypothesized that age-related HL would have a pervasive effect on sensory processing, extending beyond the auditory domain. Specifically, we predicted that decreased auditory input to the neural system, in the form of HL over time, would have deleterious effects on multisensory mechanisms. DESIGN This study compared AV processing between older adults with normal hearing (N = 12) and older adults with mild to moderate sensorineural HL (N = 12). To do this, we recorded cortical evoked potentials that were elicited by watching and listening to recordings of a speaker saying the syllable "bi." Stimuli were presented in three conditions: when hearing the syllable "bi" (auditory), when viewing a person say "bi" (visual), and when seeing and hearing the syllables simultaneously (AV). Presentation level of the auditory stimulus was set to +30 dB SL for each listener to equalize auditory input across groups. RESULTS In the AV condition, the normal-hearing group showed a clear and consistent decrease in P1 and N1 latencies as well as a reduction in P1 amplitude compared with the sum of the unimodal components (auditory + visual). These integration effects were absent or less consistent in HL participants. CONCLUSIONS Despite controlling for auditory sensation level, visual influence on auditory processing was significantly less pronounced in HL individuals compared with controls, indicating diminished AV integration in this population. These results demonstrate that HL has a deleterious effect on how older adults combine what they see and hear. Although auditory amplification vastly improves the communication abilities in most hearing impaired individuals, the associated atrophy of multisensory mechanisms may contribute to a patient's difficulty in everyday settings. Our findings and related studies emphasize the potential value of multimodal tasks and stimuli in the assessment and rehabilitation of hearing impairments.