Effect of Interaural Asymmetrical Electrode Deactivation on Sentence Recognition in Noise and Spatial Release from Masking in Simulated Bilateral Cochlear Implant Listening

Authors: Hasna Fathima1, Arivudai Nambi1, Jayashree Bhat S2

1Kasturba Medical College, Mangalore, Manipal Academy of Higher Education
2Nitte Institute of Speech and Hearing

Background: For individuals with bilateral severe-profound hearing loss, bilateral CIs offer improved spatial hearing and speech understanding in noise. Electrode deactivation (ED) is a common clinical practice to mitigate the effects of malfunctioning or migrated electrodes. However, the effects of asymmetrical ED in case of bilateral CI on binaural processing have not been understood well. The asymmetrical ED in bilateral CI with ‘n-of-m’ signal processing could potentially compromise the binaural coherence of temporal envelope and consequently the ITD encoding. This study investigated the impact of unilateral ED on speech recognition in noise (SRN), spatial release from masking (SRM) and binaural coherence in simulated bilateral CI with ‘n-of-m’ signal processing strategy.

Methods: Twenty normal-hearing young adults participated in study. The target sentences were spatially filtered to at 0° and the masker was spatially filtered at 0°, 15°, 37.5°, and 90° using the Oldenburg head-related transfer function database. A 22-channel sine wave vocoder based on ‘n-of-m’ processing was applied to the spatialized target-masker mixture, in each ear. ED conditions were simulated unilaterally at basal (BD), middle (MD), or apical (AD) positions. The no deactivation (ND) on both sides served as a baseline. The perceptual experiment involved a test of SRN under one co-located condition and three spatially separated conditions. The binaural coherence was objectively computed under the ED conditions.

Results and Discussion: The results of repeated measure analysis of variance revealed that the effect of ED on SRN was not statistically significant, whereas that of spatial separation and SNR were significant. The ED did not show an effect on SRM. The objective evaluation revealed that ED results in a reduced binaural coherence in comparison to ND.

Conclusion: Unilateral ED in ‘n-of-m’ processed bilateral CIs can maintain speech recognition performance and spatial benefits.