Olivocochlear Efferent Function: Associations with Hearing in Noise and Listening Effort - PROJECT SUMMARY/ABSTRACT Between 25–44 million U.S. adults are estimated to have difficulties hearing in background noise despite having normal audiometric thresholds. These difficulties can negatively impact health and quality of life. Currently, there is no consensus on how to diagnose or treat these individuals. The long-term objective of this research program is to translate knowledge of the auditory mechanisms underlying speech-in-noise (SIN) recognition to improve the diagnosis and treatment of difficulties hearing in background noise. One potential mechanism is the medial olivocochlear (MOC) reflex, an ear-brain network in which the brainstem reduces the response of the inner ear to background noise. Previous studies in humans have yielded conflicting results regarding the association between the MOC reflex and SIN recognition. These discrepant findings may be due, in part, to lack of inclusion of individuals with SIN recognition difficulties. It is also possible that the reduction in masking produced by the MOC reflex reduces listening effort in the presence of background noise, but this area has not been investigated thoroughly. Finally, the contribution of the afferent (ascending) drive to the measured MOC reflex strength remains unknown. The proposed studies will address these gaps in knowledge through three aims. Two groups of age- and sex-matched adults with normal hearing will be recruited (n=104 per group). One group will have self-reported SIN recognition difficulties and one group will have no self-reported SIN recognition difficulties, as assessed using a validated questionnaire. Aim 1 will determine the ability of MOC reflex strength to predict self- reported SIN recognition difficulties. The strength of the MOC reflex will be assessed using contralateral inhibition of otoacoustic emissions, a non-invasive measure of efferent control of the inner ear. We hypothesize that MOC reflex strength is a significant predictor of SIN recognition group classification. Aim 2 will determine the association between MOC reflex strength and listening effort. The same participants from Aim 1 will perform a word recognition in noise task at two signal-to-noise ratios. Listening effort will be quantified by verbal response time and self-report. It is hypothesized that MOC reflex strength is a significant predictor of listening effort, and the strength of the association between MOC reflex strength and listening effort depends on the signal-to-noise ratio of the speech task. Aim 3 will determine the contribution of afferent drive to MOC reflex strength. The same participants from Aim 1 will undergo auditory brainstem response testing and MOC reflex testing. Afferent drive will be quantified as the amplitude of wave I of the auditory brainstem response. Associations between afferent drive and MOC reflex strength will be assessed using correlational analyses. This aim is exploratory in nature. The results of these studies will lead to an improved mechanistic understanding of the functional role of the MOC reflex. Additionally, the results will contribute to the development of better diagnostic tests and interventions for difficulties with SIN recognition and listening effort.
