Hearing aid use, audiovisual integration, and speech performance: probing the interplay

Perception is based on information arriving from different sensory modalities, such as audition and vision, and our brain has the capability to combine these different inputs to form a coherent percept. This process of multisensory integration may lead to an enhanced processing of stimuli and thus, prove beneficial for the interaction with the environment. A plethora of multisensory processes in general and audiovisual phenomena in particular have been studied at both the behavioral and neural level in different populations. For instance, studies have repeatedly shown altered multisensory processing in the elderly. This has been extended to cochlear implant (CI) patients, with a number of studies pointing towards enhanced audiovisual integration abilities of CI patients compared to normal-hearing individuals. In contrast, the effects of hearing aid usage on audiovisual processing in milder hearing impairment have been largely neglected.
We aimed at filling this gap by a recent study, where we found differences in audiovisual integration capacities (measured with the sound-induced flash illusion, SIFI) as a function of hearing aid experience in elderly individuals with mild hearing impairment (PTA 26-40 dB HL). Specifically, hearing aid users displayed greater audiovisual integration than their age-matched peers with the same hearing impairment who were not using hearing aids. A parallel study showed increased McGurk illusions in elderly, mild-to-moderately hearing-impaired listeners compared to age-matched normal-hearing individuals.

A recurring question is how those results may link to audiovisual speech understanding. Typical speech performance tests, as used to evaluate hearing aid benefits for instance, assess outcomes in auditory-only conditions. To address this issue, we focus here on the interplay between audiovisual integration and potential effects of hearing aids. We investigate mild-to-moderately hearing-impaired elderly individuals without hearing aid experience in an interventional, longitudinal 6-month study, whereby a treatment group fitted with hearing aids is compared to a waiting control group. Investigating their audiovisual integration (SIFI, McGurk), cognitive performance, as well as potential changes in brain structure using MRI, and relating those to audiovisual speech performance, we hope to help clarify how hearing aid experience affects audiovisual integration, possible cross-modal re-organization in the brain, and potentially associated benefits in audiovisual speech perception.
First results will be presented at the conference.