Contralateral masking in bilateral cochlear implant patients: a model of medial olivocochlear function loss.

Justin M Aronoff,Justin M Aronoff,Qian-Jie Fu,Qian-Jie Fu,David M Landsberger,David M Landsberger,Monica Padilla,Manuel S Malmierca

doi:10.1371/journal.pone.0121591

Abstract

Contralateral masking is the phenomenon where a masker presented to one ear affects the ability to detect a signal in the opposite ear. For normal hearing listeners, contralateral masking results in masking patterns that are both sharper and dramatically smaller in magnitude than ipsilateral masking. The goal of this study was to investigate whether medial olivocochlear (MOC) efferents are needed for the sharpness and relatively small magnitude of the contralateral masking function. To do this, bilateral cochlear implant patients were tested because, by directly stimulating the auditory nerve, cochlear implants circumvent the effects of the MOC efferents. The results indicated that, as with normal hearing listeners, the contralateral masking function was sharper than the ipsilateral masking function. However, although there was a reduction in the magnitude of the contralateral masking function compared to the ipsilateral masking function, it was relatively modest. This is in sharp contrast to the results of normal hearing listeners where the magnitude of the contralateral masking function is greatly reduced. These results suggest that MOC function may not play a large role in the sharpness of the contralateral masking function but may play a considerable role in the magnitude of the contralateral masking function.

Highlights

Presenting a masker to one ear can affect the ability to detect a target signal in the opposite ear
The results indicated that cochlear implant (CI) listeners’ contralateral masking functions are substantially sharper and moderately but significantly smaller in magnitude than their ipsilateral masking functions
Because signals traveling down the medial olivocochlear (MOC) pathway to the outer hair cells do not affect CI perception given the direct stimulation of spiral ganglion cells, these results suggest a role for either the lateral olivocochlear system (LOC) pathway, the ascending auditory pathway, or collateral connections in the descending pathway in the sharpness and magnitude of the masking function

Summary

Introduction

Presenting a masker to one ear can affect the ability to detect a target signal in the opposite ear. This phenomenon, which is known as contralateral masking, is indicative of an interaction in the binaural system. In the normally functioning auditory system, signals travel along two pathways: the ascending pathway that brings signals from the cochlea to the cortex, and the descending pathway that sends signals from the cortex back to the cochlea, modulating the activity of outer hair cells and spiral ganglion cells. Contralateral masking results in a masking pattern that is sharper and has a smaller magnitude than the PLOS ONE | DOI:10.1371/journal.pone.0121591. Contralateral masking results in a masking pattern that is sharper and has a smaller magnitude than the PLOS ONE | DOI:10.1371/journal.pone.0121591 March 23, 2015

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