Forward Masking in Cochlear Implant Users Electro

Authors: Youssef Adel Gaston Hilkhuysen Arnaud Noreña Yves Cazals Stéphane Roman Olivier Macherey

Publish Date: 2017/02/21

Volume: 18, Issue: 3, Pages: 495-512

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Abstract

Electrical stimulation of auditory nerve fibers using cochlear implants CI shows psychophysical forward masking pFM up to several hundreds of milliseconds By contrast recovery of electrically evoked compound action potentials eCAPs from forward masking eFM was shown to be more rapid with time constants no greater than a few milliseconds These discrepancies suggested two main contributors to pFM a rapidrecovery process due to refractory properties of the auditory nerve and a slowrecovery process arising from more central structures In the present study we investigate whether the use of different maskers between eCAP and psychophysical measures specifically singlepulse versus pulse train maskers may have been a source of confoundIn experiment 1 we measured eFM using the following a singlepulse masker a 300ms lowrate pulse train masker LTM 250 pps and a 300ms highrate pulse train masker HTM 5000 pps The maskers were presented either at same physical current Φ or at same perceptual Ψ level corresponding to comfortable loudness Responses to a singlepulse probe were measured for maskerprobe intervals ranging from 1 to 512 ms Recovery from masking was much slower for pulse trains than for the singlepulse masker When presented at Φ level HTM produced more and longerlasting masking than LTM However results were inconsistent when LTM and HTM were compared at Ψ level In experiment 2 masked detection thresholds of singlepulse probes were measured using the same pulse train masker conditions In line with our eFM findings masked thresholds for HTM were higher than those for LTM at Φ level However the opposite result was found when the pulse trains were presented at Ψ levelOur results confirm the presence of slowrecovery phenomena at the level of the auditory nerve in CI users as previously shown in animal studies Inconsistencies between eFM and pFM results despite using the same masking conditions further underline the importance of comparing electrophysiological and psychophysical measures with identical stimulation paradigmsWe would like to thank all subjects for their participation We would also like to thank the editors and two anonymous reviewers for their insightful comments and helpful suggestions This study was funded by the Agence Nationale de Recherche ANR11PDOC0022 and by the Mission pour l’interdisciplinarité du CNRS Project DEFISENS Parts of this work were presented at the 8th International Symposium on Objective Measures in Auditory Implants October 15–18 2014 in Toronto Ontario Canada and at the Conference on Implantable Auditory Prostheses July 12–17 2015 in Granlibakken Lake Tahoe CA USA

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