Frequency Fitting Optimization Using Evolutionary Algorithm in Cochlear Implant Users with Bimodal Binaural Hearing.

Alexis Saadoun,Ludwig Serge Aho Glélé,Alexis Bozorg Grayeli,Vincent Péan,Antoine Schein,Pierrick Legrand

doi:10.3390/brainsci12020253

Abstract

Optimizing hearing in patients with a unilateral cochlear implant (CI) and contralateral acoustic hearing is a challenge. Evolutionary algorithms (EA) can explore a large set of potential solutions in a stochastic manner to approach the optimum of a minimization problem. The objective of this study was to develop and evaluate an EA-based protocol to modify the default frequency settings of a MAP (fMAP) of the CI in patients with bimodal hearing. Methods: This monocentric prospective study included 27 adult CI users (with post-lingual deafness and contralateral functional hearing). A fitting program based on EA was developed to approach the best fMAP. Generated fMAPs were tested by speech recognition (word recognition score, WRS) in noise and free-field-like conditions. By combining these first fMAPs and adding some random changes, a total of 13 fMAPs over 3 generations were produced. Participants were evaluated before and 45 to 60 days after the fitting by WRS in noise and questionnaires on global sound quality and music perception in bimodal binaural conditions. Results: WRS in noise improved with the EA-based fitting in comparison to the default fMAP (41.67 ± 9.70% versus 64.63 ± 16.34%, respectively, p = 0.0001, signed-rank test). The global sound quality and music perception were also improved, as judged by ratings on questionnaires and scales. Finally, most patients chose to keep the new fitting definitively. Conclusions: By modifying the default fMAPs, the EA improved the speech discrimination in noise and the sound quality in bimodal binaural conditions.

Highlights

Introduction published maps and institutional affilStereophony is based on combining information in the brain from the two ears
With binaural hearing, the head-shadow increases the signal-to-noise ratio at the farthest ear from the noise, while this ratio decreases at the nearest ear to the noise source
For subject 6 (Oticon Medical), the 3 most apical electrodes were deactivated during the first postoperative months because of unpleasant sounds

Summary

Introduction

Stereophony is based on combining information in the brain from the two ears. The brain makes use of many different cues to determine the 3D characteristics of an auditory landscape [1]. Their complete combination is required for stereophony to be achieved, but access to only some bilateral cues may still generate substantial benefits. Advantages of binaural stimulation, as opposed to monaural hearing, are (1) redundancy (summation effect) which enhances the signal detection; (2) localization of the sound-source (in the horizontal plane) based on inter-aural time differences (ITD) and level differences (ILD); and (3) improved speech discrimination in noise when signal and noise are spatially separated (squelch effect).

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