Objective: This study aimed to evaluate the interaction of electric and acoustic cues in diotic condition in cochlear implantees.
Materials and methods: Five adult cochlear implantees with residual contralateral hearing were prospectively evaluated in hearing aid only (HA), cochlear implant only (CI), and HA + CI modes by audiometry (pure tone, dissyllabic words, and sentences), and sound quality questionnaires. CI electrodes corresponding to preserved frequencies in the contralateral ear (free-field aided thresholds, <50 dB) were then deactivated, and patients were retested after 20 to 30 days.
Results: Sentences in silence showed a benefit of CI and the additive effect of HA + CI. As expected, performances with CI alone decreased after apical electrode deactivation. In contrast, speech performances (Marginal Benefit from Acoustic Amplification sentences) in HA + CI mode were not altered by electrode deactivation in silence (90 ± 5.9% before versus 81 ± 10.1% after deactivation, not significant, 2-way analysis of variance) or in noise (78 ± 4.8% before versus 66 ± 11.9% after deactivation, not significant, 2-way analysis of variance). Performances for dissyllabic words confirmed these results. Questionnaires showed a significant compensation of partial electrode deactivation by the contralateral hearing. Moreover, the human voice was reported to be significantly less metallic.
Conclusion: These results suggested a significant complementarity of acoustic and electric diotic cues but also some redundancy affecting the sound quality.