Cochlear implantation (CI) can benefit patients with single-sided deafness (SSD) in terms of sound localization, speech understanding in noise, tinnitus severity, and quality of life (QoL). In previous studies, CI outcomes have been largely reported for SSD patients with normal “unrestricted” hearing in the contralateral ear. However, SSD patients may often have some degree of hearing loss in the contralateral ear (“restricted” acoustic hearing). In this study, we report results from a French clinical trial for CI in in SSD patients (NCT02204618). Localization, speech reception thresholds (SRTs) in noise, tinnitus severity, and QoL were evaluated in 18 SSD patients 1 year after CI. Data were analyzed for 2 subject groups according to the pure-tone average thresholds in the non-implanted ear: unrestricted acoustic hearing (UNRES; ≤25 dB HL; n = 10) and restricted acoustic hearing (RES; > 25 dB HL; n = 8). Across all subjects, localization was significantly better with the CI on than off (p = 0.005); there was no significant difference between subject groups (p = 0.301). When speech and noise were co-located (S0N0), there was no significant difference in SRTs with the CI on or off (p = 0.480); SRTs were significantly better for the UNRES than for the RES group (p = 0.005). When speech and noise were spatially separated (S_CIN_NH), SRTs were significantly better with the CI on than off (p < 0.001). While SRTs were better for the UNRES than for the RES group (p = 0.024), the CI benefit was more than 50% greater for the RES group due to the restoration of high-frequency speech cues. Questionnaire data showed that tinnitus severity was significantly reduced (p = 0.045) and QoL was significantly improved after one year of experience with the CI (p < 0.001). Age at testing was significantly correlated with SRTs for the S0N0 condition; duration of deafness was correlated with SRTs for the S_CIN_NH condition. There were relatively few correlations between behavioral and subjective measures, suggesting that both were valuable when assessing CI benefits for SSD patients. The present data suggest that indications for CI should be expanded to include unilaterally deaf patients who have normal hearing or mild-to-moderate hearing loss in the non-implanted ear.

BackgroundAdults with single sided deafness (SSD) have lost binaural function, which limits sound source localization, speech understanding in noise, and quality of life. For SSD patients, restoration of bilateral auditory input is possible only with a cochlear implant (CI). In this study, cortical auditory evoked potentials (CAEPs) and behavioral performance were measured in left-implanted (SSD-CI-L) and right-implanted (SSD-CI-R) patients before and after cochlear implantation. We hypothesized that improvements in behavioral performance would be accompanied by changes in CAEPs after cochlear implantation.DesignProspective longitudinal study.SettingTertiary referral center.MethodNine right-handed adult SSD CI patients participated in the study. CAEPs were recorded before cochlear implantation and at 6 and 12 months post-implantation. CAEPs were elicited using speech stimuli (/ba/) delivered in sound field at 70 dBA. Global field power (GFP) latency and amplitude were calculated for P1, N1 and P2 peaks at each test session. CAEP were analyzed at frontocentral (Cz) and temporal (P7, P8, T7 and T8) and mastoid electrodes (M1 and M2) contralateral to the CI ear. Behavioral measures (sentence recognition in noise, with and without spatial cues) were collected at the same test sessions as for CAEPs. Speech performance and CAEPs were also measured in a control group of normal-hearing (NH) subjects.ResultsWhile increased N1 amplitude was observed in the scalp potential maps for GFP and Cz for SSD-CI-L patients after implantation, the changes were not statistically significant. Peak CAEP amplitude at electrodes to contralateral to the CI ear increased after cochlear implantation for all SSD-CI patients, but significant increases were observed only for mastoid sites. Peak latencies for some components at temporal and mastoid sites remained significantly longer than for the NH control group, even after cochlear implantation. For SSD-CI-R patients, P2 peak amplitude for baseline GFP and Cz was significantly lower than for the NH control group. A significant improvement for speech understanding in noise was observed at 12 months post-implantation when speech was presented to the CI ear and noise to the non-implanted ear.ConclusionAfter cochlear implantation, speech understanding significantly improved when speech and noise were spatially separated. The increased N1 amplitude for SSD-CI-L patients and the increased bilateral activation for all SSD-CI patients may reflect cortical reorganization and restoration of binaural function after one year of experience with the CI. However, because of the limited number of SSD patients, significant changes in cortical activity after cochlear implantation were often difficult to observe.

Background For patients with single-sided deafness (SSD), restoration of binaural function via cochlear implant (CI) has been shown to improve speech understanding in noise. The objective of this study was to investigate changes in behavioral performance and cortical auditory responses following cochlear implantation. Design Prospective longitudinal study. Setting Tertiary referral center. Methods Six adults with SSD were tested before and 12 months post-activation of the CI. Six normal hearing (NH) participants served as experimental controls. Speech understanding in noise was evaluated for various spatial conditions. Cortical auditory evoked potentials were recorded with /ba/ stimuli in quiet and in noise. Global field power and responses at Cz were analyzed. Results Speech understanding in noise significantly improved with the CI when speech was presented to the CI ear and noise to the normal ear (p<0.05), but remained poorer than that of NH controls (p<0.05). N1 peak amplitude measure in noise significantly increased after CI activation (p<0.05), but remained lower than that of NH controls (p<0.05) at 12 months. After 12 months of CI experience, cortical responses in noise became more comparable between groups.