Auditory Performances With Different Stimulation Depths in Cochlear Implanted Subjects Using a Fine Structure Strategy

Overview

Main objective: Investigate on new cochlear implanted patients whether the FineHearing strategy of the MED-EL cochlear implant gives better results on musical perception if the depth of stimulation (stimulation or not of the apical areas) is greater. Secondary objectives: Evaluate the effect of stimulation depth on vocal audiometric results, results of differential frequency threshold test and on qualitative sound perception.

Introduction: Conventional stimulation strategies in cochlear implants (e.g. ACE, CIS) use the place of the electrode to code the frequency by sending low frequency information on the apical electrodes and high frequency information on the basal electrodes. The stimulation rate of the electrodes is constant. The pitch is only partially transmitted by these conventional strategies which would explain the poor results of cochlear implants in the perception of music. In the FineHearing strategy of the MED-EL implant, the rate of stimulation on the low-frequency electrodes is related to the frequency of the sound and makes it possible to code the frequency information temporally. Rader \& al. 2016 have studied the contribution of adding to the tonotopic coding of the frequency (classical strategy) a temporal coding of the information by varying the stimulation rate. The results obtained show that providing this frequency information by time coding makes it possible to obtain perceived pitch much closer to the expected pitch (of normal-hearing) and less variability, especially at low frequencies. With fixed stimulation rate (classical strategy) low frequencies are poorly coded, whereas with the variable stimulation rate they are better coded. In addition, Landsberger et al. \[2018\] studied in six subjects with a MED-EL implant the perception of a temporal coding according to the position of the electrodes with a long insertion: middle or apical position. The results seem to show that the temporal coding of the frequency would be more reliable than the spatial coding (related to the position of the electrode) at the apex, and the reverse on the electrodes in the middle position. Studies have shown that the FineHearing strategy can provide benefits over the classic HDCIS strategy in tasks involving the fundamental F0 such as speech recognition in noise (after a certain learning time) \[Kleine Punte \& al. 2014 ; Vermeire \& al. 2010\], the perception of music \[Roy \& al. 2015 ; Roy \& al. 2016\] or the perceived quality of pitch \[Müller \& al. 2012\]. The results obtained seem to depend on the position of the electrode: a deep insertion to reach the apical zone of the cochlea would allow better coding of the information. MED-EL's FineHearing coding strategy with stimulation of the apical areas of the cochlea (long insertion of electrodes) could therefore allow better transmission of musical pitch and in particular improve the subjective quality of music compared to the same stimulation strategy without reaching the apical areas (short insertion). Objective of the study: The objective of the study is to evaluate if the FineHearing strategy of MED-EL with stimulation of the apical zones allows to better transmit musical pitch and in particular to improve the subjective quality of the music compared to the same stimulation strategy without apical stimulation. Main objective: Show that the FineHearing strategy of MED-EL with stimulation of the apical zones allows to obtain a better perceptual quality of music in newly implanted cochlear patients than the same strategy without apical stimulation. Secondary objectives: * Evaluate differential frequency thresholds and correlation with qualitative perceptions of music. * Evaluate the effect of the stimulation of the apical zones on the results of speech audiometry with the FineHearing strategy. * Evaluate the effect of the stimulation of the apical zones on the subjective quality of sounds by questionnaire with the FineHearing strategy. Plan of study: it is a Single-center, randomized, double-blind, cross-over study