The Addition of a Contralateral Microphone for Unilateral Cochlear Implant Users

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Abstract
This study aimed to investigate whether unilateral cochlear implant (CI) users benefit from the addition of a contralateral microphone (CI-CROS) for spatial speech recognition. Tertiary referral otology and cochlear implant center. The digits-in-noise test was used to measure speech in noise recognition abilities. Evaluations were made in 3 conditions: speech and noise presented from the front of the listener (S0N0) and with spatial separation of speech and noise (S90N-90 and S-90N90). The performance of CI patients using CI-CROS was compared with their unilateral CI condition (n = 10), normal-hearing subjects (n = 12), and bilateral CI users (n = 5). The presence and extent of several binaural phenomena (binaural summation, binaural squelch, and the better-ear effect) were evaluated. CI-CROS only provided a benefit in the listening situation wherein speech originates from the side of the CROS microphone; however, this benefit was repealed by disadvantages in other listening conditions. With CI-CROS, the hearing of patient is essentially monaural, albeit with bilateral input; therefore, patients were not able to benefit from the same binaural advantages as normal-hearing subjects and bilateral CI users. Moreover, patients using CI-CROS lost the ability to choose the optimal listening condition to perform as well as unilateral CI users. We conclude that CI-CROS is not advisable for unilateral CI users. Bilateral cochlear implantation would be a better alternative for the rehabilitation of patients with unaidable hearing on the contralateral side.

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