title: Forward Masking in Cochlear Implant Users: Electrophysiological and Psychophysical Data Using Pulse Train Maskers.
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 rapid-recovery process due to refractory properties of the auditory nerve and a slow-recovery process arising from more central structures. In the present study, we investigate whether the use of different maskers between eCAP and psychophysical measures, specifically single-pulse versus pulse train maskers, may have been a source of confound.In experiment 1, we measured eFM using the following: a single-pulse masker, a 300-ms low-rate pulse train masker (LTM, 250 pps), and a 300-ms high-rate 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 single-pulse probe were measured for masker-probe intervals ranging from 1 to 512 ms. Recovery from masking was much slower for pulse trains than for the single-pulse masker. When presented at Φ level, HTM produced more and longer-lasting masking than LTM. However, results were inconsistent when LTM and HTM were compared at Ψ level. In experiment 2, masked detection thresholds of single-pulse 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 level.Our results confirm the presence of slow-recovery 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 paradigms.
authors.affiliation: Aix Marseille Université, CNRS, Centrale Marseille, LMA, 4 Impasse Nikola Tesla CS 40006, 13453, Marseille Cedex 13, France. youssef.adel@kgu.de.|Audiological Acoustics, Department of Otorhinolaryngology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany. youssef.adel@kgu.de.
authors.forename: Youssef
authors.identifier: http://orcid.org/0000-0002-8968-5995
authors.initials: Y
authors.lastname: Adel
authors.affiliation: Aix Marseille Université, CNRS, Centrale Marseille, LMA, 4 Impasse Nikola Tesla CS 40006, 13453, Marseille Cedex 13, France.
authors.forename: Gaston
authors.initials: G
authors.lastname: Hilkhuysen
authors.affiliation: Laboratoire Neurosciences Intégratives et Adaptatives, UMR CNRS 7260 and Aix-Marseille Université, Fédération de Recherche 3C, Marseille, France.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Noreña
authors.affiliation: Laboratoire Neurosciences Intégratives et Adaptatives, UMR CNRS 7260 and Aix-Marseille Université, Fédération de Recherche 3C, Marseille, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Cazals
authors.affiliation: Department of Pediatric Otorhinolaryngology Head and Neck Surgery, La Timone Children's Hospital, Aix Marseille Université, 264 rue Saint-Pierre, 13385, Marseille Cedex 5, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Roman
authors.affiliation: Aix Marseille Université, CNRS, Centrale Marseille, LMA, 4 Impasse Nikola Tesla CS 40006, 13453, Marseille Cedex 13, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Macherey
mesh_terms: D000200:Action Potentials; D000222:Adaptation, Physiological; D000328:Adult; D000368:Aged; D003054:Cochlear Implants; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged
keywords: detection threshold; electrical stimulation; electrically evoked compound action potential; neural adaptation; recovery from forward masking; stimulation rate