Association of Tonotopic Mismatch With the Speech Recognition of Cochlear Implant Users With Unilateral Hearing Loss.

Objective: Review the relationship of tonotopic mismatch with the speech recognition of cochlear implant (CI) users with unilateral hearing loss (UHL; also known as single-sided deafness).

Patients: Twenty-seven adults (≥18 yr of age) with late-onset UHL.

Intervention: Cochlear implantation.

Main outcome measures: Speech recognition was assessed at 6 months post-activation with consonant-nucleus-consonant (CNC) words in the CI alone condition (contralateral ear masked). In the combined condition (CI plus the normal-hearing ear), masked speech recognition was assessed using AzBio sentences in a 10-talker masker (0-dB signal-to-noise ratio) in three target-to-masker configurations. Tonotopic mismatch was calculated as the semitone deviation between the center filter frequency and the cochlear place frequency of the most apical electrode contact.

Results: There was a significant, negative association between tonotopic mismatch and CNC scores ( r27 = -0.43, p = 0.013) and masked speech recognition when the target was from the front and the masker was presented toward the normal-hearing ear ( r27 = -0.36, p = 0.033).

Conclusions: The speech recognition of adult CI users with UHL in the CI alone and bilateral listening conditions may be significantly influenced by tonotopic mismatches. These findings support the need for prospective investigation of methods to reduce or eliminate tonotopic mismatches (e.g., implantation of electrode arrays that approximate cochlear place and/or individualized mapping of filter frequencies) for CI users with UHL.