Comparison of Speech Understanding Between a Tonotopy-based Bimodal Fitting and a Default Bimodal Fitting in Newly Cochlear-implanted Patients: a Double-blind Randomized Crossover Study.

Introduction:

Cochlear implantation allows the rehabilitation of profound bilateral deafness, restoring speech perception and verbal communication when the traditional hearing aid no longer provides satisfactory hearing gain. A cochlear implant includes an electrode array and its functioning is based on the principle of cochlear tonotopy: Each electrode encodes a frequency spectrum according to its position in the cochlea (high frequencies are assigned to the basal electrodes and low frequencies to the apical electrodes). The cochlear implant thus breaks down the frequency spectrum into a number of frequency bands via bandpass filters corresponding to the number of electrodes in the implant. During the fitting these bands can be modified by the audiologist.

Bimodal hearing refers to the use of a CI in one ear with a HA on the contralateral side. This association allows for adults and children a better perception of speech in quiet and in noise, a better perception of music, hearing comfort, better sound quality, better localization of sound and, consequently, a better quality of life compared to unilateral CI alone. However, there is great variability in the integration process; while some bimodal users show substantial benefits, others receive little or no benefit.

This variability could be due to the mismatch of frequencies (tonotopic shift) between the CI and the contralateral HA.

Recently MED-EL has developed an "anatomy-based fitting" (ABF) strategy based on the tonotopy that allows, from a postoperative scanner, to calculate the theoretical characteristic frequency of neurons stimulated by each electrode contact and to transmit this information to the fitting software of the CI.