Single-Sided Deafness Cochlear Implant Sound-Localization Behavior With Multiple Concurrent Sources.

OBJECTIVES: For listeners with one deaf ear and the other ear with normal/near-normal hearing (single-sided deafness [SSD]) or moderate hearing loss (asymmetric hearing loss), cochlear implants (CIs) can improve speech understanding in noise and sound-source localization. Previous SSD-CI localization studies have used a single source with artificial sounds such as clicks or random noise. While this approach provides insights regarding the auditory cues that facilitate localization, it does not capture the complex nature of localization behavior in real-world environments. This study examined SSD-CI sound localization in a complex scenario where a target sound was added to or removed from a mixture of other environmental sounds, while tracking head movements to assess behavioral strategy. DESIGN: Eleven CI users with normal hearing or moderate hearing loss in the contralateral ear completed a sound-localization task in monaural (CI-OFF) and bilateral (CI-ON) configurations. Ten of the listeners were also tested before CI activation to examine longitudinal effects. Two-second environmental sound samples, looped to create 4- or 10-sec trials, were presented in a spherical array of 26 loudspeakers encompassing ±144° azimuth and ±30° elevation at a 1-m radius. The target sound was presented alone (localize task) or concurrently with one or three additional sources presented to different loudspeakers, with the target cued by being added to (Add) or removed from (Rem) the mixture after 6 sec. A head-mounted tracker recorded movements in six dimensions (three for location, three for orientation). Mixed-model regression was used to examine target sound-identification accuracy, localization accuracy, and head movement. Angular and translational head movements were analyzed both before and after the target was switched on or off. RESULTS: Listeners showed improved localization accuracy in the CI-ON configuration, but there was no interaction with test condition and no effect of the CI on sound-identification performance. Although high-frequency hearing loss in the unimplanted ear reduced localization accuracy and sound-identification performance, the magnitude of the CI localization benefit was independent of hearing loss. The CI reduced the magnitude of gross head movements used during the task in the azimuthal rotation and translational dimensions, both while the target sound was present (in all conditions) and during the anticipatory period before the target was switched on (in the Add condition). There was no change in pre- versus post-activation CI-OFF performance. CONCLUSIONS: These results extend previous findings, demonstrating a CI localization benefit in a complex listening scenario that includes environmental and behavioral elements encountered in everyday listening conditions. The CI also reduced the magnitude of gross head movements used to perform the task. This was the case even before the target sound was added to the mixture. This suggests that a CI can reduce the need for physical movement both in anticipation of an upcoming sound event and while actively localizing the target sound. Overall, these results show that for SSD listeners, a CI can improve localization in a complex sound environment and reduce the amount of physical movement used.

Interaural Time-Difference Discrimination as a Measure of Place of Stimulation for Cochlear-Implant Users With Single-Sided Deafness.

Current clinical practice in programming a cochlear implant (CI) for individuals with single-sided deafness (SSD) is to maximize the transmission of speech information via the implant, with the implicit assumption that this will also result in improved spatial-hearing abilities. However, binaural sensitivity is reduced by interaural place-of-stimulation mismatch, a likely occurrence with a standard CI frequency-to-electrode allocation table (FAT). As a step toward reducing interaural mismatch, this study investigated whether a test of interaural-time-difference (ITD) discrimination could be used to estimate the acoustic frequency yielding the best place match for a given CI electrode. ITD-discrimination performance was measured by presenting 300-ms bursts of 100-pulses-per-second electrical pulse trains to a single CI electrode and band-limited pulse trains with variable carrier frequencies to the acoustic ear. Listeners discriminated between two reference intervals (four bursts each with constant ITD) and a moving target interval (four bursts with variable ITD). For 17 out of the 26 electrodes tested across eight listeners, the function describing the relationship between ITD-discrimination performance and carrier frequency had a discernable peak where listeners achieved 70% to 100% performance. On average, this peak occurred 1.15 octaves above the CI manufacturer's default FAT. ITD discrimination shows promise as a method of estimating the cochlear place of stimulation for a given electrode, thereby providing information to optimize the FAT for SSD-CI listeners.

Head Shadow and Binaural Squelch for Unilaterally Deaf Cochlear Implantees.

BACKGROUND: Cochlear implants (CIs) can improve speech-in-noise performance for listeners with unilateral sensorineural deafness. But these benefits are modest and in most cases are limited to head-shadow advantages, with little evidence of binaural squelch. HYPOTHESIS: The goal of the investigation was to determine whether CI listeners with normal hearing or moderate hearing loss in the contralateral ear would receive a larger head-shadow benefit for target speech and noise originating from opposite sides of the head, and whether listeners would experience binaural squelch in the free field in a test involving interfering talkers. METHODS: Eleven CI listeners performed a speech-identification task in the presence of interfering noise or speech. Six listeners had single-sided deafness (normal or near-normal audiometric thresholds in the acoustic ear) and five had asymmetric hearing loss (hearing loss in the acoustic ear treated with a hearing aid). Listeners were tested with the acoustic ear only and bilaterally with the CI turned on. One set of conditions examined head-shadow effects with target speech and masking noise presented from azimuths of 0 or ±108 degrees. A second set of conditions examined binaural squelch, with target speech presented from the front and interfering talkers symmetrically placed on both sides. RESULTS: On average, the largest head-shadow benefit (5 dB) occurred when the target and masking noise were presented on opposite sides of the head. Listeners also showed an average of 2 dB of squelch, but only when the target speech was masked by interfering talkers of the same sex as the target. CONCLUSIONS: CIs provide listeners with unilateral deafness important benefits for speech perception in complex spatial environments, including a larger head-shadow benefit when speech and noise originate on opposite sides of the head, and an improved ability to perceptually organize an auditory scene with multiple competing voices.The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or US Government.

Having Two Ears Facilitates the Perceptual Separation of Concurrent Talkers for Bilateral and Single-Sided Deaf Cochlear Implantees.

OBJECTIVES: Listening to speech with multiple competing talkers requires the perceptual separation of the target voice from the interfering background. Normal-hearing listeners are able to take advantage of perceived differences in the spatial locations of competing sound sources to facilitate this process. Previous research suggests that bilateral (BI) cochlear-implant (CI) listeners cannot do so, and it is unknown whether single-sided deaf (SSD) CI users (one acoustic and one CI ear) have this ability. This study investigated whether providing a second ear via cochlear implantation can facilitate the perceptual separation of targets and interferers in a listening situation involving multiple competing talkers. DESIGN: BI-CI and SSD-CI listeners were required to identify speech from a target talker mixed with one or two interfering talkers. In the baseline monaural condition, the target speech and the interferers were presented to one of the CIs (for the BI-CI listeners) or to the acoustic ear (for the SSD-CI listeners). In the bilateral condition, the target was still presented to the first ear but the interferers were presented to both the target ear and the listener's second ear (always a CI), thereby testing whether CI listeners could use information about the interferer obtained from a second ear to facilitate perceptual separation of the target and interferer. RESULTS: Presenting a copy of the interfering signals to the second ear improved performance, up to 4 to 5 dB (12 to 18 percentage points), but the amount of improvement depended on the type of interferer. For BI-CI listeners, the improvement occurred mainly in conditions involving one interfering talker, regardless of gender. For SSD-CI listeners, the improvement occurred in conditions involving one or two interfering talkers of the same gender as the target. This interaction is consistent with the idea that the SSD-CI listeners had access to pitch cues in their normal-hearing ear to separate the opposite-gender target and interferers, while the BI-CI listeners did not. CONCLUSIONS: These results suggest that a second auditory input via a CI can facilitate the perceptual separation of competing talkers in situations where monaural cues are insufficient to do so, thus partially restoring a key advantage of having two ears that was previously thought to be inaccessible to CI users.

Cochlear implantation leading to successful stapedectomy in the contralateral only-hearing ear.

Cochlear implants have recently begun to be offered to patients with single-sided deafness (SSD). Implantation in these patients has led to good results in suppressing ipsilateral tinnitus and in providing audiologic benefits in terms of speech perception in noise and localization. One previously unreported benefit of cochlear implantation in patients with SSD is the restoration of functional hearing in the previously deaf ear, which may allow for surgical opportunities in the contralateral hearing ear. We report a case in which cochlear implantation in the deaf left ear of a 50-year-old man allowed for surgical intervention in the previously only-hearing right ear, which in turn led to the restoration of normal middle ear function. Further studies may be warranted to consider the surgical candidacy of the contralateral only-hearing ear as another potential indication for cochlear implantation in patients with SSD.

An initial experience of cochlear implantation for patients with single-sided deafness after prior osseointegrated hearing device.

OBJECTIVE: To compare preoperative and postoperative sound localization and surgical outcomes in patients with a history of osseointegrated hearing device (OHD) placement who underwent cochlear implantation for severe to profound sensorineural hearing loss in one ear and normal cochlear function in the contralateral ear (single-sided deafness [SSD]). STUDY DESIGN: Case series. STUDY SETTING: Tertiary care center, cochlear implant (CI) program. PATIENTS: Five patients with a previously placed OHD, implanted at our institution between late 2012 and late 2013, who were undergoing cochlear implantation to address SSD. Causes of their initial SSD included iatrogenic sudden sensorineural hearing loss, and perilymphatic fistula. Indications for cochlear implantation included a desire for binaural hearing, surgical treatment for tinnitus, and staging for treatment of contralateral conductive hearing loss. INTERVENTIONS: Cochlear implantation; intraoperative and postoperative antibiotics. MAIN OUTCOME MEASURES: Accuracy of sound localization for environmental sounds presented in a mixture for three device conditions: monaurally with the acoustic hearing ear only, OHD in addition to the acoustic hearing ear, and CI in addition to the acoustic hearing ear. Complications. Continued use of CI. RESULTS: Modestly improved sound localization with CI compared with monaural listening or listening with an OHD (p < 0.0001). Wound dehiscence and infection with our first two patients; none with the use of perioperative and postoperative antibiotics (three patients). Four patients continued to use their CI for at least 4 months after activation (mean, 13 mo) and expressed satisfaction with the device; one was lost to follow-up. CONCLUSION: Cochlear implantation for this population of patients produced modestly improved localization accuracy, and most patients expressed satisfaction with this intervention. In this series of cochlear implantation after OHD, our first two patients had wound infection and dehiscence. We recommend perioperative and postoperative antibiotics to prevent this complication.