Mimicking the unmasking effects of the medial olivo-cochlear efferent reflex with cochlear implants

Abstract

In healthy ears, cochlear sensitivity and tuning are not fixed; they vary depending on the state of activation of medial olivo-cochlear (MOC) efferent fibers, which act upon outer hair cells modulating the gain of the cochlear amplifier. MOC efferents may be activated in a reflexive manner by ipsilateral and contralateral sounds. Activation of the MOC reflex (MOCR) is thought to unmask sounds by reducing the adaptation of auditory nerve afferent fibers response to noise. This effect almost certainly improves speech recognition in noise. Furthermore, there is evidence that contralateral stimulation can improve the detection of pure tones embedded in noise as well as speech intelligibility in noise probably by activation of the contralateral MOCR. The unmasking effects of the MOCR are unavailable to current cochlear implant (CI) users and this might explain part of their difficulty at understanding speech in noise compared to normal hearing subjects. Here, we present preliminary results of a bilateral CI sound-coding strategy that mimics the unmasking benefits of the ipsilateral and contralateral MOCR. [Work supported by the Spanish MINECO and MED-EL GmbH.]