Hearing aid processing of auditory evoked potential stimuli : acoustic effects

Amplification is one of the main interventions used to manage hearing loss in people of all ages. Difficult-to-test populations fitted with amplification may be unable to respond reliably through behavioural methods to evaluate the quality of amplification. In these situations, the use of objective measures, such as auditory evoked potentials (AEP), has been suggested as a means to obtain more information regarding the fitting of the amplification. Recent investigations on aided potentials have been inconsistent in showing more robust responses that would be expected after amplification. This may be in part due to the unpredictable changes that can happen with hearing aid processing. Thus, there is a need to conduct a systematic analysis of the acoustic effects hearing aid processing can have on AEP stimuli to offer possible explanations for the inconsistency. Data were collected using three hearing aids programmed for a mild to moderately-severe sloping hearing loss with linear gain and compression, and stimuli commonly used to elicit brainstem and cortical AEPs at two input intensities. Large changes were noted in stimulus rise times, intensities, signal-to-noise ratios, and modulation depth. The amount of change differed by hearing aid and gain settings (linear or compression). Changes to rise times were also noted with changes to stimulus duration based on the hearing aid as well as the gain setting. These results suggest hearing aid processing can cause many changes to the signal, some of which may affect the morphology of evoked potentials. The changes that occur can also vary widely based on the hearing aid through which the stimuli are processed. Thus, the interpretation of the responses elicited by processed stimuli must be done with caution, and should only be done after taking hearing aid changes into account. Supplementary Material : http://hdl.handle.net/2429/57501Medicine, Faculty ofAudiology and Speech Sciences, School ofGraduat