Sound localization abilities of unilateral hybrid cochlear implant users with bilateral low-frequency hearing

OBJECTIVE: To assess the sound localization abilities of subjects unilaterally implanted with a hybrid cochlear implant in different sound localization conditions.

STUDY DESIGN: A prospective, single-subject repeated measures design was performed to assess the sound localization abilities in 5 different listening conditions: combined (hybrid cochlear implant and contralateral acoustic hearing), bimodal, bilateral acoustic, ipsilateral acoustic, and contralateral acoustic.

SETTING: Tertiary referral center.

PATIENTS: Eighteen subjects with bilateral low-frequency residual hearing, implanted with a hybrid cochlear implant, were enrolled in this study.

MAIN OUTCOME MEASURES: Postoperative sound localization in 5 different listening conditions.

RESULTS: Average group results showed a significant improvement in sound localization for all binaural hearing conditions (combined, bimodal, and bilateral acoustic) over monaural conditions (ipsilateral acoustic and contralateral acoustic). Subjects performed significantly better in the combined condition compared with the bimodal and bilateral acoustic conditions when sound was presented from the front and the side of their cochlear implant.

CONCLUSION: Best results, for most subjects, were obtained with the routinely used combined fitting. The additional acoustic stimulation of the implanted ear did not significantly improve sound localization. However, a marked improvement has been found by the addition of electrical stimulation, for especially the azimuths ipsilateral and to the front of the cochlear implant, implying the importance of the cochlear implant in sound localization.