Unilateral Hearing Loss: Understanding Speech Recognition and Localization Variability-Implications for Cochlear Implant Candidacy

Investigating the Utility of a Compact Loudspeaker Array for Audiometric Testing

PURPOSE

This project addressed the uses of a loudspeaker array for audiometric measurements. It sought to evaluate a prototype compact array in terms of the reliability of test results across sound booths.

METHOD

A seven-loudspeaker array was developed to deliver sounds from -60° to +60° on an arc with a radius of 0.5 m. The system was equipped with a head position sensing system to maintain the listener's head near the optimal test position. Three array systems were distributed to each of the two test sites for within-subject assessments of booth equivalence on tests of sound localization, speech reception in noise, and threshold detection. A total of 36 subjects participated, 18 at each test site.

RESULTS

Results showed excellent interbooth consistency on tests of sound localization using speech and noise signals, including conditions in which one or both ears were covered with a muff. Booth consistency was also excellent on sound field threshold measurements for detecting quasi-diffuse noise bands. Nonequivalence was observed in some cases of speech-in-noise tests, particularly with a small one-person booth. Acoustic analyses of in situ loudspeaker responses indicated that some of the nonequivalent comparisons on speech-in-noise tests could be traced to the effects of reflections.

CONCLUSIONS

Overall, the results demonstrate the utility and reliability of a compact array for the assessment of localization ability, speech reception in noise, and sound field thresholds. However, the results indicate that researchers and clinicians should be aware of the reflection effects that can influence the results of sound field tests in which signal and noise levels from separate loudspeakers are critical.

Asymmetry in Cortical Thickness of the Heschl's Gyrus in Unilateral Ear Canal Atresia

HYPOTHESIS

Unilateral congenital conductive hearing impairment in ear canal atresia leads to atrophy of the gray matter of the contralateral primary auditory cortex or changes in asymmetry pattern if left untreated in childhood.

BACKGROUND

Unilateral ear canal atresia with associated severe conductive hearing loss results in deteriorated sound localization and difficulties in understanding of speech in a noisy environment. Cortical atrophy in the Heschl's gyrus has been reported in acquired sensorineural hearing loss but has not been studied in unilateral conductive hearing loss.

METHODS

We obtained T1w and T2w FLAIR MRI data from 17 subjects with unilateral congenital ear canal atresia and 17 matched controls. Gray matter volume and thickness were measured in the Heschl's gyrus using Freesurfer.

RESULTS

In unilateral congenital ear canal atresia, Heschl's gyrus exhibited cortical thickness asymmetry (right thicker than left, corrected p = 0.0012, mean difference 0.25 mm), while controls had symmetric findings. Gray matter volume and total thickness did not differ from controls with normal hearing.

CONCLUSION

We observed cortical thickness asymmetry in congenital unilateral ear canal atresia but no evidence of contralateral cortex atrophy. Further research is needed to understand the implications of this asymmetry on central auditory processing deficits.

Functional to structural plasticity in unilateral sudden sensorineural hearing loss: neuroimaging evidence

A cortical plasticity after long-duration single side deafness (SSD) is advocated with neuroimaging evidence while little is known about the short-duration SSDs. In this case-cohort study, we recruited unilateral sudden sensorineural hearing loss (SSNHL) patients and age-, gender-matched health controls (HC), followed by comprehensive neuroimaging analyses. The primary outcome measures were temporal alterations of varied dynamic functional network connectivity (dFNC) states, neurovascular coupling (NVC) and brain region volume at different stages of SSNHL. The secondary outcome measures were pure-tone audiograms of SSNHL patients before and after treatment. A total of 38 SSNHL patients (21 [55%] male; mean [standard deviation] age, 45.05 [15.83] years) and 44 HC (28 [64%] male; mean [standard deviation] age, 43.55 [12.80] years) were enrolled. SSNHL patients were categorized into subgroups based on the time from disease onset to the initial magnetic resonance imaging scan: early- (n = 16; 1-6 days), intermediate- (n = 9; 7-13 days), and late- stage (n = 13; 14-30 days) groups. We first identified slow state transitions between varied dFNC states at early-stage SSNHL, then revealed the decreased NVC restricted to the auditory cortex at the intermediate- and late-stage SSNHL. Finally, a significantly decreased volume of the left medial superior frontal gyrus (SFGmed) was observed only in the late-stage SSNHL cohort. Furthermore, the volume of the left SFGmed is robustly correlated with both disease duration and patient prognosis. Our study offered neuroimaging evidence for the evolvement from functional to structural brain alterations of SSNHL patients with disease duration less than 1 month, which may explain, from a neuroimaging perspective, why early-stage SSNHL patients have better therapeutic responses and hearing recovery.

A Five-Decade Text Mining Analysis of Cochlear Implant Research: Where We Started and Where We Are Heading

Background and Objectives: Since its invention in the 1970s, the cochlear implant (CI) has been substantially developed. We aimed to assess the trends in the published literature to characterize CI. Materials and Methods: We queried PubMed for all CI-related entries published during 1970-2022. The following data were extracted: year of publication, publishing journal, title, keywords, and abstract text. Search terms belonged to the patient's age group, etiology for hearing loss, indications for CI, and surgical methodological advancement. Annual trends of publications were plotted. The slopes of publication trends were calculated by fitting regression lines to the yearly number of publications. Results: Overall, 19,428 CIs articles were identified. Pediatric-related CI was the most dominant sub-population among the age groups, with the highest rate and slope during the years (slope 5.2 ± 0.3, p < 0.001), while elderly-related CIs had significantly fewer publications. Entries concerning hearing preservation showed the sharpest rise among the methods, from no entries in 1980 to 46 entries in 2021 (slope 1.7 ± 0.2, p < 0.001). Entries concerning robotic surgery emerged in 2000, with a sharp increase in recent years (slope 0.5 ± 0.1, p < 0.001). Drug-eluting electrodes and CI under local-anesthesia have been reported only in the past five years, with a gradual rise. Conclusions: Publications regarding CI among pediatrics outnumbered all other indications, supporting the rising, pivotal role of CI in the rehabilitation of children with sensorineural hearing loss. Hearing-preservation publications have recently rapidly risen, identified as the primary trend of the current era, followed by a sharp rise of robotic surgery that is evolving and could define the next revolution.

Feasibility of Virtual Reality-Based Auditory Localization Training With Binaurally Recorded Auditory Stimuli for Patients With Single-Sided Deafness

OBJECTIVES

To train participants to localize sound using virtual reality (VR) technology, appropriate auditory stimuli that contain accurate spatial cues are essential. The generic head-related transfer function that grounds the programmed spatial audio in VR does not reflect individual variation in monaural spatial cues, which is critical for auditory spatial perception in patients with single-sided deafness (SSD). As binaural difference cues are unavailable, auditory spatial perception is a typical problem in the SSD population and warrants intervention. This study assessed the applicability of binaurally recorded auditory stimuli in VR-based training for sound localization in SSD patients.

METHODS

Sixteen subjects with SSD and 38 normal-hearing (NH) controls underwent VR-based training for sound localization and were assessed 3 weeks after completing training. The VR program incorporated prerecorded auditory stimuli created individually in the SSD group and over an anthropometric model in the NH group.

RESULTS

Sound localization performance revealed significant improvements in both groups after training, with retained benefits lasting for an additional 3 weeks. Subjective improvements in spatial hearing were confirmed in the SSD group.

CONCLUSION

By examining individuals with SSD and NH, VR-based training for sound localization that used binaurally recorded stimuli, measured individually, was found to be effective and beneficial. Furthermore, VR-based training does not require sophisticated instruments or setups. These.

RESULTS

suggest that this technique represents a new therapeutic treatment for impaired sound localization.

Long-Term Binaural Hearing Improvements for Cochlear Implant Users with Asymmetric Hearing Loss

OBJECTIVE

To assess long-term binaural hearing abilities for cochlear implant (CI) users with unilateral hearing loss (UHL) or asymmetric hearing loss (AHL).

METHODS

A prospective, longitudinal, repeated measures study was completed at a tertiary referral center evaluating adults with UHL or AHL undergoing cochlear implantation. Binaural hearing abilities were assessed with masked speech recognition tasks using AzBio sentences in a 10-talker masker. Performance was evaluated as the ability to benefit from spatial release from masking (SRM). SRM was calculated as the difference in scores when the masker was presented toward the CI-ear (SRMci ) or the contralateral ear (SRMcontra ) relative to the co-located condition (0°). Assessments were completed pre-operatively and at annual intervals out to 5 years post-activation.

RESULTS

Twenty UHL and 19 AHL participants were included in the study. Linear Mixed Models showed significant main effects of interval and group for SRMcontra . There was a significant interaction between interval and group, with UHL participants reaching asymptotic performance early and AHL participants demonstrating continued growth in binaural abilities to 5 years post-activation. The improvement in SRM showed a significant positive correlation with contralateral unaided hearing thresholds (p = 0.050) as well as age at implantation (p = 0.031).

CONCLUSIONS

CI recipients with UHL and AHL showed improved SRM with long-term device use. The time course of improvement varied by cohort, with the UHL cohort reaching asymptotic performance early and the AHL cohort continuing to improve beyond 1 year. Differences between cohorts could be driven by differences in age at implantation as well as contralateral unaided hearing thresholds.

LEVEL OF EVIDENCE

3 Laryngoscope, 133:1480-1485, 2023.

The effect of noise on the cortical activity patterns of speech processing in adults with single-sided deafness

The most common complaint in people with single-sided deafness (SSD) is difficulty in understanding speech in a noisy environment. Moreover, the neural mechanism of speech-in-noise (SiN) perception in SSD individuals is still poorly understood. In this study, we measured the cortical activity in SSD participants during a SiN task to compare with a speech-in-quiet (SiQ) task. Dipole source analysis revealed left hemispheric dominance in both left- and right-sided SSD group. Contrary to SiN listening, this hemispheric difference was not found during SiQ listening in either group. In addition, cortical activation in the right-sided SSD individuals was independent of the location of sound whereas activation sites in the left-sided SSD group were altered by the sound location. Examining the neural-behavioral relationship revealed that N1 activation is associated with the duration of deafness and the SiN perception ability of individuals with SSD. Our findings indicate that SiN listening is processed differently in the brains of left and right SSD individuals.

Attentional modulation of auditory cortical activity in individuals with single-sided deafness

Persons with single-sided deafness (SSD) typically complain about the impaired ability to locate sounds and to understand speech within background noise. However, the findings from previous studies suggest that paying attention to sounds could mitigate the degraded spatial and speech-in-noise perception. In the present study, we characterize the pattern of cortical activation depending on the side of deafness, and attentional modulation of neural responses to determine if it can assist better sound processing in people with SSD. For the active listening condition, adult subjects with SSD performed sound localization tasks. On the other hand, they watched movies without attending to speech stimuli during passive listening. The sensor-level global field power of N1 and source-level N1 activation were computed to compare the active- and passive-listening conditions and left- and right-sided deafness. The results show that attentional modulation differs depending on the side of deafness: active listening increased the cortical activity in individuals with left-sided deafness but not in those with right-sided deafness. At the source level, the attentional gain was more apparent in left-sided deafness in that paying attention enhanced brain activation in both hemispheres. In addition, SSD participants with larger cortical activities in the right primary auditory cortex had shorter durations of deafness. Our results indicate that the side of deafness can change top-down attentional processing in the auditory cortical pathway in SSD patients.

Sound localization in patients with idiopathic sudden hearing loss

BACKGROUND

Patients with unilateral hearing loss have difficulty localizing sound. Severe-to-profound unilateral hearing loss is most commonly caused by idiopathic sudden sensorineural hearing loss (SSNHL).

AIMS/OBJECTIVES

To assess the sound localization ability of patients with idiopathic unilateral SSNHL and examine the factors affecting the results.

MATERIAL AND METHODS

We retrospectively enrolled 141 patients with idiopathic unilateral SSNHL. The assessment stimuli were speech-shaped noise from one of the nine loudspeakers in a 180° arc. Multiple regression analysis was used to examine the factors that affected sound localization ability.

RESULTS

There was a strong correlation between the hearing level on the affected side post-treatment and the deviation score as the index of sound localization ability. The results of the multiple regression analysis suggested that sound localization may be partially affected by hearing level on the unaffected side and age.

CONCLUSIONS AND SIGNIFICANCE

The results showed that sound localization ability decreased in idiopathic SSNHL patients with severe-to-profound hearing loss post-treatment. This study provides important data for future interventions for unilateral hearing loss, including cochlear implants.

The Effect of Sound Localization on Auditory-Only and Audiovisual Speech Recognition in a Simulated Multitalker Environment

Information regarding sound-source spatial location provides several speech-perception benefits, including auditory spatial cues for perceptual talker separation and localization cues to face the talker to obtain visual speech information. These benefits have typically been examined separately. A real-time processing algorithm for sound-localization degradation (LocDeg) was used to investigate how spatial-hearing benefits interact in a multitalker environment. Normal-hearing adults performed auditory-only and auditory-visual sentence recognition with target speech and maskers presented from loudspeakers at -90°, -36°, 36°, or 90° azimuths. For auditory-visual conditions, one target and three masking talker videos (always spatially separated) were rendered virtually in rectangular windows at these locations on a head-mounted display. Auditory-only conditions presented blank windows at these locations. Auditory target speech (always spatially aligned with the target video) was presented in co-located speech-shaped noise (experiment 1) or with three co-located or spatially separated auditory interfering talkers corresponding to the masker videos (experiment 2). In the co-located conditions, the LocDeg algorithm did not affect auditory-only performance but reduced target orientation accuracy, reducing auditory-visual benefit. In the multitalker environment, two spatial-hearing benefits were observed: perceptually separating competing speech based on auditory spatial differences and orienting to the target talker to obtain visual speech cues. These two benefits were additive, and both were diminished by the LocDeg algorithm. Although visual cues always improved performance when the target was accurately localized, there was no strong evidence that they provided additional assistance in perceptually separating co-located competing speech. These results highlight the importance of sound localization in everyday communication.

Disease Related Morbidity and Quality of Life Impairment in Patients with Single Sided Deafness

Patients with single sided-deafness (SSD) have hearing deficits amounting to a handicap to their everyday quality of life and are likely to suffer serious social challenges. There is a significant gap in the "disability" aspect of SSD in literature. The study was undertaken to compare the quality of life of SSD patients in various domains with normal hearing individuals. 51 patients of SSD with pure sensorineural hearing loss with impaired ear having a pure tone average of more than or equal to 70 dB was compared with 50 subjects with normal hearing sensitivity. Pure tone audiometric testing and the english version of Speech, Spatial and Qualities of Hearing Scale (SSQ) were used to enumerate subjective advantage. Total average SSQ score across domains in patients (6.6 ± 1.2) was significantly poorer in comparison to the control group (8.4 ± 0.9). Based on SSQ, patients with SSD experience hearing disability in comparison to the control group (p < 0.01). The ratings of all the items in the SSQ subdomains were higher in the reference group than in the patient group. Individuals with single sided-deafness experience significant auditory disability in all the three domains of speech, spatial & qualities of hearing. Therefore, these patients should be strongly counselled for currently available treatment options.

Cochlear implantation for paediatric and adult cases of unilateral and asymmetric hearing loss

PURPOSE OF REVIEW

Children and adults with unilateral or asymmetric hearing loss (UHL/AHL) have poorer spatial hearing (e.g. speech understanding in complex maskers and localization) and quality of life compared with peers with normal hearing bilaterally. Patients with UHL/AHL experience limited benefits with contralateral-routing technologies (e.g. bone conduction, CROS hearing aid systems). Cochlear implantation allows for stimulation of the auditory pathway for the poorer hearing ear. The present study reviews the recent literature on outcomes of cochlear implant use for recipients with UHL/AHL.

RECENT FINDINGS

Recent research corroborates previous investigations of the significant benefits on measures of spatial hearing, tinnitus severity and quality of life for adult cochlear implant recipients. These benefits are also observed in pediatric cochlear implant recipients, with an association of better outcomes with younger ages at implantation for congenital cases and shorter durations of UHL/AHL for acquired cases. In addition, randomized trials demonstrate better outcomes with cochlear implant use versus contralateral-routing technologies.

SUMMARY

Cochlear implantation supports better spatial hearing and quality of life in children and adults with UHL/AHL as compared to alternative listening conditions. Current research supports the expansion of candidacy criteria and insurance coverage for cochlear implantation for patients with UHL/AHL to improve their binaural hearing.

American Cochlear Implant Alliance Task Force Guidelines for Clinical Assessment and Management of Adult Cochlear Implantation for Single-Sided Deafness

The indications for cochlear implantation have expanded to include individuals with profound sensorineural hearing loss in the impaired ear and normal hearing (NH) in the contralateral ear, known as single-sided deafness (SSD). There are additional considerations for the clinical assessment and management of adult cochlear implant candidates and recipients with SSD as compared to conventional cochlear implant candidates with bilateral moderate to profound sensorineural hearing loss. The present report reviews the current evidence relevant to the assessment and management of adults with SSD. A systematic review was also conducted on published studies that investigated outcomes of cochlear implant use on measures of speech recognition in quiet and noise, sound source localization, tinnitus perception, and quality of life for this patient population. Expert consensus and systematic review of the current literature were combined to provide guidance for the clinical assessment and management of adults with SSD.

Masked Speech Recognition as a Function of Masker Location for Cochlear Implant Users With Single-Sided Deafness

PURPOSE

Cochlear implant (CI) recipients with normal or near normal hearing (NH) in the contralateral ear, referred to as single-sided deafness (SSD), experience significantly better speech recognition in noise with their CI than without it, although reported outcomes vary. One possible explanation for differences in outcomes across studies could be differences in the spatial configurations used to assess performance. This study compared speech recognition for different spatial configurations of the target and masker, with test materials used clinically.

METHOD

Sixteen CI users with SSD completed tasks of masked speech recognition presented in five spatial configurations. The target speech was presented from the front speaker (0° azimuth). The masker was located either 90° or 45° toward the CI-ear or NH-ear or colocated with the target. Materials were the AzBio sentences in a 10-talker masker and the Bamford-Kowal-Bench Speech-in-Noise test (BKB-SIN; four-talker masker). Spatial release from masking (SRM) was computed as the benefit associated with spatial separation relative to the colocated condition.

RESULTS

Performance was significantly better when the masker was separated toward the CI-ear as compared to colocated. No benefit was observed for spatial separations toward the NH-ear. The magnitude of SRM for spatial separations toward the CI-ear was similar for 45° and 90° when tested with the AzBio sentences, but a larger benefit was observed for 90° as compared to 45° for the BKB-SIN.

CONCLUSIONS

Masked speech recognition in CI users with SSD varies as a function of the spatial configuration of the target and masker. Results supported an expansion of the clinical test battery at the study site to assess binaural hearing abilities for CI candidates and recipients with SSD. The revised test battery presents the target from the front speaker and the masker colocated with the target, 90° toward the CI-ear, or 90° toward the NH-ear.

Altered topological properties of the intrinsic functional brain network in patients with right-sided unilateral hearing loss caused by acoustic neuroma

Neuroimaging studies have identified alterations in functional connectivity between specific brain regions in patients with unilateral hearing loss (UHL) and different influence of the side of UHL on neural plasticity. However, little is known about changes of whole-brain functional networks in patients with UHL and whether differences exist in topological organization between right-sided UHL (RUHL) and left-sided UHL (LUHL). To address this issue, we employed resting-state fMRI (rs-fMRI) and graph-theoretical approaches to investigate the topological alterations of brain functional connectomes in patients with RUHL and LUHL. Data from 44 patients with UHL (including 22 RUHL patients and 22 LUHL patients) and 37 healthy control subjects (HCs) were collected. Functional brain networks were constructed for each participant, following by graph-theoretical network analyses at connectional and global (e.g., small-worldness) levels. The correlations between brain network topologies and clinical variables were further studied. Using network-based analysis, we found a subnetwork in the visual cortex which had significantly lower connectivity strength in patients with RUHL as compared to HCs. At global level, all participants showed small-world architecture in functional brain networks, however, significantly lower normalized clustering coefficient and small-worldness were observed in patients with RUHL than in HCs. Moreover, these abnormal network metrics were demonstrated to be correlated with the clinical variables and cognitive performance of patients with RUHL. Notably, no significant alterations in the functional brain networks were found in patients with LUHL. Our findings demonstrate that RUHL (rather than LUHL) is accompanied with aberrant topological organization of the functional brain connectome, indicating different pathophysiological mechanisms between RUHL and LUHL from a viewpoint of network topology.

Sound Localization in Single-Sided Deaf Participants Provided With a Cochlear Implant

Spatial hearing is crucial in real life but deteriorates in participants with severe sensorineural hearing loss or single-sided deafness. This ability can potentially be improved with a unilateral cochlear implant (CI). The present study investigated measures of sound localization in participants with single-sided deafness provided with a CI. Sound localization was measured separately at eight loudspeaker positions (4°, 30°, 60°, and 90°) on the CI side and on the normal-hearing side. Low- and high-frequency noise bursts were used in the tests to investigate possible differences in the processing of interaural time and level differences. Data were compared to normal-hearing adults aged between 20 and 83. In addition, the benefit of the CI in speech understanding in noise was compared to the localization ability. Fifteen out of 18 participants were able to localize signals on the CI side and on the normal-hearing side, although performance was highly variable across participants. Three participants always pointed to the normal-hearing side, irrespective of the location of the signal. The comparison with control data showed that participants had particular difficulties localizing sounds at frontal locations and on the CI side. In contrast to most previous results, participants were able to localize low-frequency signals, although they localized high-frequency signals more accurately. Speech understanding in noise was better with the CI compared to testing without CI, but only at a position where the CI also improved sound localization. Our data suggest that a CI can, to a large extent, restore localization in participants with single-sided deafness. Difficulties may remain at frontal locations and on the CI side. However, speech understanding in noise improves when wearing the CI. The treatment with a CI in these participants might provide real-world benefits, such as improved orientation in traffic and speech understanding in difficult listening situations.

Proficiency in Using Level Cue for Sound Localization Is Related to the Auditory Cortical Structure in Patients With Single-Sided Deafness

Spatial hearing, which largely relies on binaural time/level cues, is a challenge for patients with asymmetric hearing. The degree of the deficit is largely variable, and better sound localization performance is frequently reported. Studies on the compensatory mechanism revealed that monaural level cues and monoaural spectral cues contribute to variable behavior in those patients who lack binaural spatial cues. However, changes in the monaural level cues have not yet been separately investigated. In this study, the use of the level cue in sound localization was measured using stimuli of 1 kHz at a fixed level in patients with single-sided deafness (SSD), the most severe form of asymmetric hearing. The mean absolute error (MAE) was calculated and related to the duration/age onset of SSD. To elucidate the biological correlate of this variable behavior, sound localization ability was compared with the cortical volume of the parcellated auditory cortex. In both SSD patients (n = 26) and normal controls with one ear acutely plugged (n = 23), localization performance was best on the intact ear side; otherwise, there was wide interindividual variability. In the SSD group, the MAE on the intact ear side was worse than that of the acutely plugged controls, and it deteriorated with longer duration/younger age at SSD onset. On the impaired ear side, MAE improved with longer duration/younger age at SSD onset. Performance asymmetry across lateral hemifields decreased in the SSD group, and the maximum decrease was observed with the most extended duration/youngest age at SSD onset. The decreased functional asymmetry in patients with right SSD was related to greater cortical volumes in the right posterior superior temporal gyrus and the left planum temporale, which are typically involved in auditory spatial processing. The study results suggest that structural plasticity in the auditory cortex is related to behavioral changes in sound localization when utilizing monaural level cues in patients with SSD.

Ear-Specific Hemispheric Asymmetry in Unilateral Deafness Revealed by Auditory Cortical Activity

Profound unilateral deafness reduces the ability to localize sounds achieved via binaural hearing. Furthermore, unilateral deafness promotes a substantial change in cortical processing to binaural stimulation, thereby leading to reorganization over the whole brain. Although distinct patterns in the hemispheric laterality depending on the side and duration of deafness have been suggested, the neurological mechanisms underlying the difference in relation to behavioral performance when detecting spatially varied cues remain unknown. To elucidate the mechanism, we compared N1/P2 auditory cortical activities and the pattern of hemispheric asymmetry of normal hearing, unilaterally deaf (UD), and simulated acute unilateral hearing loss groups while passively listening to speech sounds delivered from different locations under open free field condition. The behavioral performances of the participants concerning sound localization were measured by detecting sound sources in the azimuth plane. The results reveal a delayed reaction time in the right-sided UD (RUD) group for the sound localization task and prolonged P2 latency compared to the left-sided UD (LUD) group. Moreover, the RUD group showed adaptive cortical reorganization evidenced by increased responses in the hemisphere ipsilateral to the intact ear for individuals with better sound localization whereas left-sided unilateral deafness caused contralateral dominance in activity from the hearing ear. The brain dynamics of right-sided unilateral deafness indicate greater capability of adaptive change to compensate for impairment in spatial hearing. In addition, cortical N1 responses to spatially varied speech sounds in unilateral deaf people were inversely related to the duration of deafness in the area encompassing the right auditory cortex, indicating that early intervention would be needed to protect from maladaptation of the central auditory system following unilateral deafness.

Effects of Head Movements on Sound-Source Localization in Single-Sided Deaf Patients With Their Cochlear Implant On Versus Off

OBJECTIVES

We investigated the ability of single-sided deaf listeners implanted with a cochlear implant (SSD-CI) to (1) determine the front-back and left-right location of sound sources presented from loudspeakers surrounding the listener and (2) use small head rotations to further improve their localization performance. The resulting behavioral data were used for further analyses investigating the value of so-called "monaural" spectral shape cues for front-back sound source localization.

DESIGN

Eight SSD-CI patients were tested with their cochlear implant (CI) on and off. Eight normal-hearing (NH) listeners, with one ear plugged during the experiment, and another group of eight NH listeners, with neither ear plugged, were also tested. Gaussian noises of 3-sec duration were band-pass filtered to 2-8 kHz and presented from 1 of 6 loudspeakers surrounding the listener, spaced 60° apart. Perceived sound source localization was tested under conditions where the patients faced forward with the head stationary, and under conditions where they rotated their heads between (Equation is included in full-text article.).

RESULTS

(1) Under stationary listener conditions, unilaterally-plugged NH listeners and SSD-CI listeners (with their CIs both on and off) were nearly at chance in determining the front-back location of high-frequency sound sources. (2) Allowing rotational head movements improved performance in both the front-back and left-right dimensions for all listeners. (3) For SSD-CI patients with their CI turned off, head rotations substantially reduced front-back reversals, and the combination of turning on the CI with head rotations led to near-perfect resolution of front-back sound source location. (4) Turning on the CI also improved left-right localization performance. (5) As expected, NH listeners with both ears unplugged localized to the correct front-back and left-right hemifields both with and without head movements.

CONCLUSIONS

Although SSD-CI listeners demonstrate a relatively poor ability to distinguish the front-back location of sound sources when their head is stationary, their performance is substantially improved with head movements. Most of this improvement occurs when the CI is off, suggesting that the NH ear does most of the "work" in this regard, though some additional gain is introduced with turning the CI on. During head turns, these listeners appear to primarily rely on comparing changes in head position to changes in monaural level cues produced by the direction-dependent attenuation of high-frequency sounds that result from acoustic head shadowing. In this way, SSD-CI listeners overcome limitations to the reliability of monaural spectral and level cues under stationary conditions. SSD-CI listeners may have learned, through chronic monaural experience before CI implantation, or with the relatively impoverished spatial cues provided by their CI-implanted ear, to exploit the monaural level cue. Unilaterally-plugged NH listeners were also able to use this cue during the experiment to realize approximately the same magnitude of benefit from head turns just minutes after plugging, though their performance was less accurate than that of the SSD-CI listeners, both with and without their CI turned on.

Effects of Simulated and Profound Unilateral Sensorineural Hearing Loss on Recognition of Speech in Competing Speech

OBJECTIVES

Unilateral hearing loss (UHL) is a condition as common as bilateral hearing loss in adults. Because of the unilaterally reduced audibility associated with UHL, binaural processing of sounds may be disrupted. As a consequence, daily tasks such as listening to speech in a background of spatially distinct competing sounds may be challenging. A growing body of subjective and objective data suggests that spatial hearing is negatively affected by UHL. However, the type and degree of UHL vary considerably in previous studies. The aim here was to determine the effect of a profound sensorineural UHL, and of a simulated UHL, on recognition of speech in competing speech, and the binaural and monaural contributions to spatial release from masking, in a demanding multisource listening environment.

DESIGN

Nine subjects (25 to 61 years) with profound sensorineural UHL [mean pure-tone average (PTA) across 0.5, 1, 2, and 4 kHz = 105 dB HL] and normal contralateral hearing (mean PTA = 7.2 dB HL) were included based on the criterion that the target and competing speech were inaudible in the ear with hearing loss. Thirteen subjects with normal hearing (19 to 60 years; mean left PTA = 4.1 dB HL; mean right PTA = 5.5 dB HL) contributed data in normal and simulated "mild-to-moderate" UHL conditions (PTA = 38.6 dB HL). The main outcome measure was the threshold for 40% correct speech recognition in colocated (0°) and spatially and symmetrically separated (±30° and ±150°) competing speech conditions. Spatial release from masking was quantified as the threshold difference between colocated and separated conditions.

RESULTS

Thresholds in profound UHL were higher (worse) than normal hearing in separated and colocated conditions, and comparable to simulated UHL. Monaural spatial release from masking, that is, the spatial release achieved by subjects with profound UHL, was significantly different from zero and 49% of the magnitude of the spatial release from masking achieved by subjects with normal hearing. There were subjects with profound UHL who showed negative spatial release, whereas subjects with normal hearing consistently showed positive spatial release from masking in the normal condition. The simulated UHL had a larger effect on the speech recognition threshold for separated than for colocated conditions, resulting in decreased spatial release from masking. The difference in spatial release between normal-hearing and simulated UHL conditions increased with age.

CONCLUSIONS

The results demonstrate that while recognition of speech in colocated and separated competing speech is impaired for profound sensorineural UHL, spatial release from masking may be possible when competing speech is symmetrically distributed around the listener. A "mild-to-moderate" simulated UHL decreases spatial release from masking compared with normal-hearing conditions and interacts with age, indicating that small amounts of residual hearing in the UHL ear may be more beneficial for separated than for colocated interferer conditions for young listeners.

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.

Acoustic Hearing Can Interfere With Single-Sided Deafness Cochlear-Implant Speech Perception

OBJECTIVES

Cochlear implants (CIs) restore some spatial advantages for speech understanding in noise to individuals with single-sided deafness (SSD). In addition to a head-shadow advantage when the CI ear has a better signal-to-noise ratio, a CI can also provide a binaural advantage in certain situations, facilitating the perceptual separation of spatially separated concurrent voices. While some bilateral-CI listeners show a similar binaural advantage, bilateral-CI listeners with relatively large asymmetries in monaural speech understanding can instead experience contralateral speech interference. Based on the interference previously observed for asymmetric bilateral-CI listeners, this study tested the hypothesis that in a multiple-talker situation, the acoustic ear would interfere with rather than improve CI speech understanding for SSD-CI listeners.

DESIGN

Experiment 1 measured CI-ear speech understanding in the presence of competing speech or noise for 13 SSD-CI listeners. Target speech from the closed-set coordinate response-measure corpus was presented to the CI ear along with one same-gender competing talker or stationary noise at target-to-masker ratios between -8 and 20 dB. The acoustic ear was presented with silence (monaural condition) or with a copy of the competing speech or noise (bilateral condition). Experiment 2 tested a subset of 6 listeners in the reverse configuration for which SSD-CI listeners have previously shown a binaural benefit (target and competing speech presented to the acoustic ear; silence or competing speech presented to the CI ear). Experiment 3 examined the possible influence of a methodological difference between experiments 1 and 2: whether the competing talker spoke keywords that were inside or outside the response set. For each experiment, the data were analyzed using repeated-measures logistic regression. For experiment 1, a correlation analysis compared the difference between bilateral and monaural speech-understanding scores to several listener-specific factors: speech understanding in the CI ear, preimplantation duration of deafness, duration of CI experience, ear of deafness (left/right), acoustic-ear audiometric thresholds, and listener age.

RESULTS

In experiment 1, presenting a copy of the competing speech to the acoustic ear reduced CI speech-understanding scores for target-to-masker ratios ≥4 dB. This interference effect was limited to competing-speech conditions and was not observed for a noise masker. There was dramatic intersubject variability in the magnitude of the interference (range: 1 to 43 rationalized arcsine units), which was found to be significantly correlated with listener age. The interference effect contrasted sharply with the reverse configuration (experiment 2), whereby presenting a copy of the competing speech to the contralateral CI ear significantly improved performance relative to monaural acoustic-ear performance. Keyword condition (experiment 3) did not influence the observed pattern of interference.

CONCLUSIONS

Most SSD-CI listeners experienced interference when they attended to the CI ear and competing speech was added to the acoustic ear, although there was a large amount of intersubject variability in the magnitude of the effect, with older listeners particularly susceptible to interference. While further research is needed to investigate these effects under free-field listening conditions, these results suggest that for certain spatial configurations in a multiple-talker situation, contralateral speech interference could reduce the benefit that an SSD-CI otherwise provides.

Adults with unilateral congenital ear canal atresia - sound localization ability and recognition of speech in competing speech in unaided condition

BACKGROUND

Individuals with unilateral hearing loss show poor spatial hearing, but individual variability is high.

AIMS/OBJECTIVES

To investigate if the degree of hearing loss in unilateral ear canal atresia affects horizontal sound localization and speech recognition.

MATERIALS AND METHODS

Twelve subjects with unilateral ear canal atresia without childhood hearing intervention. Previously published data from eight normal-hearing subjects in normal binaural as well as experimentally induced unilateral hearing loss served as a reference. Horizontal sound localization and recognition of speech in spatially separate competing speech were assessed.

RESULTS

Linear regression analysis demonstrated a relationship between sound localization accuracy (SLA) and the air conduction pure tone average of the atretic ear (r = 0.85, p=.007). The large proportion of variability in SLA (72%) explained by the degree of hearing loss of the atretic ear indicates that binaural processing is possible. SLA was worse than for normal hearing individuals (p<.0001), and comparable to moderate simulated unilateral hearing loss (p=.13). Speech discrimination was significantly worse than normal (p<.0001) and not dependent on degree of hearing loss of the atretic ear.

CONCLUSIONS AND SIGNIFICANCE

Individuals with congenital unilateral ear canal atresia show impaired horizontal SLA and recognition of speech in competing speech.

Cochlear Implantation in Adults With Single-sided Deafness: Outcomes and Device Use

OBJECTIVE

To describe our experience with adults undergoing cochlear implantation (CI) for treatment of single-sided deafness (SSD).

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

Fifty-three adults with SSD.

INTERVENTIONS

Unilateral CI.

MAIN OUTCOME MEASURES

Speech perception testing in quiet and noise, tinnitus suppression, and device usage from datalogs.

RESULTS

The mean age at CI was 53.2 years (SD 11.9). The mean duration of deafness was 4.0 years (SD 7.8). The most common etiology was idiopathic sudden SNHL (50%). Word recognition improved from 8.7% (SD 15) preoperatively to 61.8% (SD 20) at a mean follow-up of 3.3 years (SD 1.8) (p < 0.0001). Adaptive speech recognition testing in the "binaural with CI" condition (speech directed toward the front and noise toward the normal hearing ear) revealed a significant improvement by 2.6-dB SNR compared to the preoperative unaided condition (p = 0.0002) and by 3.6-dB SNR compared to when a device to route sound to the contralateral side was used (p < 0.0001). Tinnitus suppression was reported to be complete in 23 patients (43%) and improved in 20 patients (38%) while the device was on. The addition of the CI did not lead to a decrement in hearing performance in any spatial configuration. Device usage averaged 8.7 (SD 3.7) hours/day.

CONCLUSIONS

Cochlear implantation in adult SSD patients can suppress tinnitus and achieve speech perception outcomes comparable with CI in conventional candidates. Modest improvements in spatial hearing were also observed and primarily attributable to the head shadow effect. Careful patient selection and counseling regarding potential benefits are important to optimize outcomes.

Cortical Regions Activated by Spectrally Degraded Speech in Adults With Single Sided Deafness or Bilateral Normal Hearing

Those with profound sensorineural hearing loss from single sided deafness (SSD) generally experience greater cognitive effort and fatigue in adverse sound environments. We studied cases with right ear, SSD compared to normal hearing (NH) individuals. SSD cases were significantly less correct in naming last words in spectrally degraded 8- and 16-band vocoded sentences, despite high semantic predictability. Group differences were not significant for less intelligible 4-band sentences, irrespective of predictability. SSD also had diminished BOLD percent signal changes to these same sentences in left hemisphere (LH) cortical regions of early auditory, association auditory, inferior frontal, premotor, inferior parietal, dorsolateral prefrontal, posterior cingulate, temporal-parietal-occipital junction, and posterior opercular. Cortical regions with lower amplitude responses in SSD than NH were mostly components of a LH language network, previously noted as concerned with speech recognition. Recorded BOLD signal magnitudes were averages from all vertices within predefined parcels from these cortex regions. Parcels from different regions in SSD showed significantly larger signal magnitudes to sentences of greater intelligibility (e.g., 8- or 16- vs. 4-band) in all except early auditory and posterior cingulate cortex. Significantly lower response magnitudes occurred in SSD than NH in regions prior studies found responsible for phonetics and phonology of speech, cognitive extraction of meaning, controlled retrieval of word meaning, and semantics. The findings suggested reduced activation of a LH fronto-temporo-parietal network in SSD contributed to difficulty processing speech for word meaning and sentence semantics. Effortful listening experienced by SSD might reflect diminished activation to degraded speech in the affected LH language network parcels. SSD showed no compensatory activity in matched right hemisphere parcels.

Action planning and affective states within the auditory peripersonal space in normal hearing and cochlear-implanted listeners

Fast reaction to approaching stimuli is vital for survival. When sounds enter the auditory peripersonal space (PPS), sounds perceived as being nearer elicit higher motor cortex activation. There is a close relationship between motor preparation and the perceptual components of sounds, particularly of highly arousing sounds. Here we compared the ability to recognize, evaluate, and react to affective stimuli entering the PPS between 20 normal-hearing (NH, 7 women) and 10 cochlear-implanted (CI, 3 women) subjects. The subjects were asked to quickly flex their arm in reaction to positive (P), negative (N), and neutral (Nu) affective sounds ending virtually at five distances from their body. Pre-motor reaction time (pm-RT) was detected via electromyography from the postural muscles to measure action anticipation at the sound-stopping distance; the sounds were also evaluated for their perceived level of valence and arousal. While both groups were able to localize sound distance, only the NH group modulated their pm-RT based on the perceived sound distance. Furthermore, when the sound carried no affective components, the pm-RT to the Nu sounds was shorter compared to the P and the N sounds for both groups. Only the NH group perceived the closer sounds as more arousing than the distant sounds, whereas both groups perceived sound valence similarly. Our findings underline the role of emotional states in action preparation and describe the perceptual components essential for prompt reaction to sounds approaching the peripersonal space.

Bone-anchored hearing system, contralateral routing of signals hearing aid or cochlear implant: what is best in single-sided deafness?

PURPOSE

The aim of the study was to compare long-term results after 1 year in patients with single-sided deafness (SSD) who were fitted with different hearing aids. The participants tested contralateral routing of signals (CROS) hearing aids and bone-anchored hearing systems (BAHS). They were also informed about the possibility of a cochlear implant (CI) and chose one of the three devices. We also investigated which factors influenced the choice of device.

METHODS

Prospective study with 89 SSD participants who were divided into three groups by choosing BAHS, CROS, or CI. All participants received test batteries with both objective hearing tests (speech perception in noise and sound localisation) and subjective questionnaires.

RESULTS

16 participants opted for BAHS-, 13 for CROS- and 30 for CI-treatment. The greater the subjective impairment caused by SSD, the more likely patients were to opt for surgical treatment (BAHS or CI). The best results in terms of speech perception in noise (especially when sound reaches the deaf ear and noise the hearing ear), sound localization, and subjective results were achieved with CI.

CONCLUSION

The best results regarding the therapy of SSD are achieved with a CI, followed by BAHS. This was evident both in objective tests and in the subjective questionnaires. Nevertheless, an individual decision is required in each case as to which SSD therapy option is best for the patient. Above all, the patient's subjective impairment and expectations should be included in the decision-making process.

Hearing examinations in Southern Denmark (HESD) database: a valuable tool for hearing-related epidemiological research

OBJECTIVE

To introduce and document the recently established HESD (Hearing Examinations in Southern Denmark) database, including the necessary data preprocessing steps, and to describe the hearing loss (HL) characteristics of the study sample.

DESIGN

Clinical auditory information has been collected for approximately 20 years in the state-funded clinics of the Region of Southern Denmark. We reviewed these data and conducted extensive preprocessing through data selection, integration, cleaning, transformation, and classification. HL profiling was then assessed in terms of severity, asymmetry, configuration, site of lesion, and audiogram shape.

STUDY SAMPLE

The final number of complete audiograms available in the HESD database was 271,556, corresponding to detailed hearing information for 143,793 adults.

RESULTS

The distribution of HL characteristics differed significantly (p < 0.001) between men and women for all categories analysed. Clear differences were observed for asymmetry and audiogram configuration. However, both men and women had higher prevalence of unilateral, moderate, and sensorineural HL.

CONCLUSIONS

This work highlights the potential of the HESD database as a source of audiology-related epidemiological data. It can be used to evaluate the distribution of HL characteristics and also to investigate risk factors for HL and the associations between HL and other health outcomes.

Sound localization latency in normal hearing and simulated unilateral hearing loss

Directing gaze towards auditory events is a natural behavior. In addition to the well-known accuracy of auditory elicited gaze responses for normal binaural listening, their latency is a measure of possible clinical interest and methodological importance. The aim was to develop a clinically feasible method to assess sound localization latency (SLL), and to study SLL as a function of simulated unilateral hearing loss (SUHL) and the relationship with accuracy. Eight healthy and normal-hearing adults (18-40 years) participated in this study. Horizontal gaze responses, recorded by non-invasive corneal reflection eye-tracking, were obtained during azimuthal shifts (24 trials) of a 3-min continuous auditory stimulus. In each trial, a sigmoid function was fitted to gaze samples. Latency was estimated by the abscissa corresponding to 50% of the arctangent amplitude. SLL was defined as the mean latency across trials. SLL was measured in normal-hearing and simulated SUHL conditions (SUHL₃₀ and SUHL₄₃: mean threshold of 30 dB HL and 43 dB HL across 0.5, 1, 2, and 4 kHz). In the normal-hearing condition, the mean ± SD SLL was 280 ± 40 ms (n = 8) with a test-retest SD = 20 ms. A linear mixed model showed a statistically significant effect of listening condition on SLL. The SUHL₃₀ and SUHL₄₃ conditions revealed a mean SLL of 370 ± 49 ms and 540 ± 120 ms, respectively. Repeated measures correlation analysis showed a clear relationship between SLL and the average sound localization accuracy (R² = 0.94). The rapid and reliable method to obtain SLL may be an important clinical tool for evaluation of binaural processing. Future studies in clinical cohorts are needed to assess whether SLL may reveal information about binaural processing abilities beyond that afforded by sound localization accuracy.

Cochlear Implantation in Cases of Asymmetric Hearing Loss: Subjective Benefit, Word Recognition, and Spatial Hearing

A prospective clinical trial evaluated the effectiveness of cochlear implantation in adults with asymmetric hearing loss (AHL). Twenty subjects with mild-to-moderate hearing loss in the better ear and moderate-to-profound hearing loss in the poorer ear underwent cochlear implantation of the poorer hearing ear. Subjects were evaluated preoperatively and at 1, 3, 6, 9, and 12 months post-activation. Preoperative performance was evaluated unaided, with traditional hearing aids (HAs) or with a bone-conduction HA. Post-activation performance was evaluated with the cochlear implant (CI) alone or in combination with a contralateral HA (bimodal). Test measures included subjective benefit, word recognition, and spatial hearing (i.e., localization and masked sentence recognition). Significant subjective benefit was reported as early as the 1-month interval, indicating better performance with the CI compared with the preferred preoperative condition. Aided word recognition with the CI alone was significantly improved at the 1-month interval compared with preoperative performance with an HA and continued to improve through the 12-month interval. Subjects demonstrated early, significant improvements in the bimodal condition on the spatial hearing tasks compared with baseline preoperative performance tested unaided. The magnitude of the benefit was reduced for subjects with AHL when compared with published data on CI users with normal hearing in the contralateral ear; this finding may reflect significant differences in age at implantation and hearing sensitivity across cohorts.

Brain Functional Alterations in Long-term Unilateral Hearing Impairment

BACKGROUND

The rate of patients with unilateral hearing impairments (UHI) increase with age and are characterized by asymmetric auditory afferents in which auditory information is asymmetrically transmitted to the brain. Long-term bilateral hearing imbalance can cause abnormal functional changes in the cerebral cortex. However, the relationship between functional alterations in the brain and the severity of the hearing impairment remains unclear.

METHODS

This study included 33 patients with UHI (left-sided impairment in 17 and right-sided impairment in 16) and 32 healthy patients. All participants underwent resting-state, blood oxygen level dependent functional magnetic resonance imaging. Fractional amplitude of low frequency fluctuation (fALFF) values were calculated after data preprocessing and compared among the left-sided and right-sided impairment groups and the control group. Pure tone audiometry was used to evaluate patients' hearing impairment level. The correlation between fALFF values of abnormal brain regions and the duration and severity of hearing impairment was analyzed.

RESULTS

Results provide evidence for altered resting-state functional activities in the brain of patients with left or right long-term UHI, with significantly increased fALFF values in the Heschl's gyrus, superior temporal gyrus, and insula were observed. Moreover, complicated networks reorganization involved in the visual, cognitive, sensorimotor and information transmission functions except for the auditory function and some brain regions exhibited functional changes only in the one-sided impairment group. In addition, the severity of hearing impairment is related with the functional activities in the bilateral Heschl's gyrus, bilateral insula, right superior temporal gyrus, and left middle frontal gyrus.

CONCLUSION

In conclusion, alterations in functional activity are observed in the brains of patients with long-term hearing impairments and multiple brain regions within different functional networks are involved in the brain functional remodeling. The brain reintegration mechanism appears to be asymmetrical and the lateralization pattern in the contralateral brain hemisphere for auditory information processing related with the severity of hearing impairment.

Updating spatial hearing abilities through multisensory and motor cues

Spatial hearing relies on a series of mechanisms for associating auditory cues with positions in space. When auditory cues are altered, humans, as well as other animals, can update the way they exploit auditory cues and partially compensate for their spatial hearing difficulties. In two experiments, we simulated monaural listening in hearing adults by temporarily plugging and muffing one ear, to assess the effects of active or passive training conditions. During active training, participants moved an audio-bracelet attached to their wrist, while continuously attending to the position of the sounds it produced. During passive training, participants received identical acoustic stimulation and performed exactly the same task, but the audio-bracelet was moved by the experimenter. Before and after training, we measured adaptation to monaural listening in three auditory tasks: single sound localization, minimum audible angle (MAA), spatial and temporal bisection. We also performed the tests twice in an untrained group, which completed the same auditory tasks but received no training. Results showed that participants significantly improved in single sound localization, across 3 consecutive days, but more in the active compared to the passive training group. This reveals that benefits of kinesthetic cues are additive with respect to those of paying attention to the position of sounds and/or seeing their positions when updating spatial hearing. The observed adaptation did not generalize to other auditory spatial tasks (space bisection and MAA), suggesting that partial updating of sound-space correspondences does not extend to all aspects of spatial hearing.

Mechanisms of Localization and Speech Perception with Colocated and Spatially Separated Noise and Speech Maskers Under Single-Sided Deafness with a Cochlear Implant

OBJECTIVES

This study tested listeners with a cochlear implant (CI) in one ear and acoustic hearing in the other ear, to assess their ability to localize sound and to understand speech in collocated or spatially separated noise or speech maskers.

DESIGN

Eight CI listeners with contralateral acoustic hearing ranging from normal hearing to moderate sensorineural hearing loss were tested. Localization accuracy was measured in five of the listeners using stimuli that emphasized the separate contributions of interaural level differences (ILDs) and interaural time differences (ITD) in the temporal envelope and/or fine structure. Sentence recognition was tested in all eight CI listeners, using collocated and spatially separated speech-shaped Gaussian noise and two-talker babble. Performance was compared with that of age-matched normal-hearing listeners via loudspeakers or via headphones with vocoder simulations of CI processing.

RESULTS

Localization improved with the CI but only when high-frequency ILDs were available. Listeners experienced no additional benefit via ITDs in the stimulus envelope or fine structure using real or vocoder-simulated CIs. Speech recognition in two-talker babble improved with a CI in seven of the eight listeners when the target was located at the front and the babble was presented on the side of the acoustic-hearing ear, but otherwise showed little or no benefit of a CI.

CONCLUSION

Sound localization can be improved with a CI in cases of significant residual hearing in the contralateral ear, but only for sounds with high-frequency content, and only based on ILDs. In speech understanding, the CI contributed most when it was in the ear with the better signal to noise ratio with a speech masker.

Dynamic Changes in Synaptic Plasticity Genes in Ipsilateral and Contralateral Inferior Colliculus Following Unilateral Noise-induced Hearing Loss

Unilateral noise-induced hearing loss reduces the input to the central auditory pathway disrupting the excitatory and inhibitory inputs to the inferior colliculus (IC), an important binaural processing center. Little is known about the compensatory synaptic changes that occur in the IC as a consequence of unilateral noise-induced hearing loss. To address this issue, Sprague-Dawley rats underwent unilateral noise exposure resulting in severe unilateral hearing loss. IC tissues from the contralateral and ipsilateral IC were evaluated for acute (2-d) and chronic (28-d) changes in the expression of 84 synaptic plasticity genes on a PCR array. Arc and Egr1 genes were further visualized by in situ hybridization to validate the PCR results. None of the genes were upregulated, but many were downregulated post-exposure. At 2-d post-exposure, more than 75% of the genes were significantly downregulated in the contralateral IC, while only two were downregulated in the ipsilateral IC. Many of the downregulated genes were related to long-term depression, long-term potentiation, cell adhesion, immediate early genes, neural receptors and postsynaptic density. At 28-d post-exposure, the gene expression pattern was reversed with more than 85% of genes in the ipsilateral IC now downregulated. Most genes previously downregulated in the contralateral IC 2-d post-exposure had recovered; less than 15% remained downregulated. These time-dependent, asymmetric changes in synaptic plasticity gene expression could shed new light on the perceptual deficits associated with unilateral hearing loss and the dynamic structural and functional changes that occur in the IC days and months following unilateral noise-induced hearing loss.

Speech-in-Noise and Quality-of-Life Measures in School-Aged Children With Normal Hearing and With Unilateral Hearing Loss

OBJECTIVES

(1) Measure sentence recognition in co-located and spatially separated target and masker configurations in school-aged children with unilateral hearing loss (UHL) and with normal hearing (NH). (2) Compare self-reported hearing-related quality-of-life (QoL) scores in school-aged children with UHL and NH.

DESIGN

Listeners were school-aged children (6 to 12 yrs) with permanent UHL (n = 41) or NH (n = 35) and adults with NH (n = 23). Sentence reception thresholds (SRTs) were measured using Hearing In Noise Test-Children sentences in quiet and in the presence of 2-talker child babble or a speech-shaped noise masker in target/masker spatial configurations: 0/0, 0/-60, 0/+60, or 0/±60 degrees azimuth. Maskers were presented at a fixed level of 55 dBA, while the level of the target sentences varied adaptively to estimate the SRT. Hearing-related QoL was measured using the Hearing Environments and Reflection on Quality of Life (HEAR-QL-26) questionnaire for child subjects.

RESULTS

As a group, subjects with unaided UHL had higher (poorer) SRTs than age-matched peers with NH in all listening conditions. Effects of age, masker type, and spatial configuration of target and masker signals were found. Spatial release from masking was significantly reduced in conditions where the masker was directed toward UHL subjects' normal-hearing ear. Hearing-related QoL scores were significantly poorer in subjects with UHL compared to those with NH. Degree of UHL, as measured by four-frequency pure-tone average, was significantly correlated with SRTs only in the two conditions where the masker was directed towards subjects' normal-hearing ear, although the unaided Speech Intelligibility Index at 65 dB SPL was significantly correlated with SRTs in four conditions, some of which directed the masker to the impaired ear or both ears. Neither pure-tone average nor unaided Speech Intelligibility Index was correlated with QoL scores.

CONCLUSIONS

As a group, school-aged children with UHL showed substantial reductions in masked speech perception and hearing-related QoL, irrespective of sex, laterality of hearing loss, and degree of hearing loss. While some children demonstrated normal or near-normal performance in certain listening conditions, a disproportionate number of thresholds fell in the poorest decile of the NH data. These findings add to the growing literature challenging the past assumption that one ear is "good enough."

Effect of Audibility and Suprathreshold Deficits on Speech Recognition for Listeners With Unilateral Hearing Loss

Objectives:

We examined the influence of impaired processing (audibility and suprathreshold processes) on speech recognition in cases of sensorineural hearing loss. The influence of differences in central, or top-down, processing was reduced by comparing the performance of both ears in participants with a unilateral hearing loss (UHL). We examined the influence of reduced audibility and suprathreshold deficits on speech recognition in quiet and in noise.

Design:

We measured speech recognition in quiet and stationary speech-shaped noise with consonant–vowel–consonant words and digital triplets in groups of adults with UHL (n = 19), normal hearing (n = 15), and bilateral hearing loss (n = 9). By comparing the scores of the unaffected ear (UHL+) and the affected ear (UHL−) in the UHL group, we were able to isolate the influence of peripheral hearing loss from individual top-down factors such as cognition, linguistic skills, age, and sex.

Results:

Audibility is a very strong predictor for speech recognition in quiet. Audibility has a less pronounced influence on speech recognition in noise. We found that, for the current sample of listeners, more speech information is required for UHL− than for UHL+ to achieve the same performance. For digit triplets at 80 dBA, the speech recognition threshold in noise (SRT) for UHL− is on average 5.2 dB signal to noise ratio (SNR) poorer than UHL+. Analysis using the speech intelligibility index (SII) indicates that on average 2.1 dB SNR of this decrease can be attributed to suprathreshold deficits and 3.1 dB SNR to audibility. Furthermore, scores for speech recognition in quiet and in noise for UHL+ are comparable to those of normal-hearing listeners.

Conclusions:

Our data showed that suprathreshold deficits in addition to audibility play a considerable role in speech recognition in noise even at intensities well above hearing threshold.

Evaluation of a New Algorithm to Optimize Audibility in Cochlear Implant Recipients

OBJECTIVES

A positive relation between audibility and speech understanding has been established for cochlear implant (CI) recipients. Sound field thresholds of 20 dB HL across the frequency range provide CI users the opportunity to understand soft and very soft speech. However, programming the sound processor to attain good audibility can be time-consuming and difficult for some patients. To address these issues, Advanced Bionics (AB) developed the SoftVoice algorithm designed to remove system noise and thereby improve audibility of soft speech. The present study aimed to evaluate the efficacy of SoftVoice in optimizing AB CI recipients' soft-speech perception.

DESIGN

Two studies were conducted. Study 1 had two phases, 1A and 1B. Sixteen adult, AB CI recipients participated in Study 1A. Acute testing was performed in the unilateral CI condition using a Harmony processor programmed with participants' everyday-use program (Everyday) and that same program but with SoftVoice implemented. Speech recognition measures were administered at several presentation levels in quiet (35 to 60 dB SPL) and in noise (60 dB SPL). In Study 1B, 10 of the participants compared Everyday and SoftVoice at home to obtain feedback regarding the use of SoftVoice in various environments. During Study 2, soft-speech perception was acutely measured with Everyday and SoftVoice for 10 participants using the Naida CI Q70 processor. Results with the Harmony (Study 1A) and Naida processors were compared. Additionally, Study 2 evaluated programming options for setting electrode threshold levels (T-levels or Ts) to improve the usability of SoftVoice in daily life.

RESULTS

Study 1A showed significantly higher scores with SoftVoice than Everyday at soft presentation levels (35, 40, 45, and 50 dB SPL) and no significant differences between programs at a conversational level (60 dB SPL) in quiet or in noise. After take-home experience with SoftVoice and Everyday (Study 1B), 5 of 10 participants reported preferring SoftVoice over Everyday; however, 6 reported bothersome environmental sound when listening with SoftVoice at home. Results of Study 2 indicated similar soft-speech perception between Harmony and Naida processors. Additionally, implementing SoftVoice with Ts at the manufacturer's default setting of 10% of Ms reduced reports of bothersome environmental sound during take-home experience; however, soft-speech perception was best with SoftVoice when Ts were behaviorally set above 10% of Ms.

CONCLUSIONS

Results indicate that SoftVoice may be a potential tool for optimizing AB users' audibility and, in turn, soft-speech perception. To achieve optimal performance at soft levels and comfortable use in daily environments, setting Ts must be considered with SoftVoice. Future research should examine program parameters that may benefit soft-speech perception when used in combination with SoftVoice (e.g., increased input dynamic range).

Counting or discriminating the number of voices to assess binaural fusion with single-sided vocoders

For single-sided deafness cochlear-implant (SSD-CI) listeners, different peripheral representations for electric versus acoustic stimulation, combined with interaural frequency mismatch, might limit the ability to perceive bilaterally presented speech as a single voice. The assessment of binaural fusion often relies on subjective report, which requires listeners to have some understanding of the perceptual phenomenon of object formation. Two experiments explored whether binaural fusion could instead be assessed using judgments of the number of voices in a mixture. In an SSD-CI simulation, normal-hearing listeners were presented with one or two "diotic" voices (i.e., unprocessed in one ear and noise-vocoded in the other) in a mixture with additional monaural voices. In experiment 1, listeners reported how many voices they heard. Listeners generally counted the diotic speech as two separate voices, regardless of interaural frequency mismatch. In experiment 2, listeners identified which of two mixtures contained diotic speech. Listeners performed significantly better with interaurally frequency-matched than with frequency-mismatched stimuli. These contrasting results suggest that listeners experienced partial fusion: not enough to count the diotic speech as one voice, but enough to detect its presence. The diotic-speech detection task (experiment 2) might provide a tool to evaluate fusion and optimize frequency mapping for SSD-CI patients.

Quality of life in persons with hearing loss: a study of patients referred to an audiological service

Objective: To investigate the relationship between hearing loss (HL) and general quality of life (QoL) in adults seeking hearing aids (HAs). Design: The patients completed the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire's general part and a questionnaire measuring self-assessed communication ability (Abbreviated Profile of hearing Aid Benefit-APHAB). These responses were compared with EORTC scores from a general population and patients with former head and neck cancer. Study sample: One-hundred and fifty-eight adults with HL were recruited prior to hearing aid (HA) fitting with one half seeking renewal of their HA. Results: General QoL scores among patients with HL were similar to those in the general population, but higher than in many chronic serious diseases. Patients with unilateral HL reported slightly worse social function and more fatigue than patients with bilateral HL. Self-assessed communication ability correlated with general QoL scores. Also, we found that best ear pure tone average (PTA), cognitive and physical QoL function predicted APHAB scores. Conclusion: In the investigated HL group, general QoL scores seem to be relatively close to those seen in the general population.

The impact of permanent early-onset unilateral hearing impairment in children - A systematic review

BACKGROUND

Decision-making on treatment and (re)habilitation needs to be based on clinical expertise and scientific evidence. Research evidence for the impact of permanent unilateral hearing impairment (UHI) on children's development has been mixed and, in some of the reports, based on fairly small, heterogeneous samples. Additionally, treatment provided has been highly variable, ranging from no action taken or watchful waiting up to single-sided cochlear implantation. Published information about the effects of treatment has also been heterogeneous. Moreover, earlier reviews and meta-analyses published on the impact of UHI on children's development have generally focused on select areas of development.

OBJECTIVES

This systematic review aimed to summarize the impact of children's congenital or early onset unilateral hearing impairment on listening and auditory skills, communication, speech and language development, cognitive development, educational achievements, psycho-social development, and quality of life.

METHODS

Literature searches were performed to identify reports published from inception to February 16th, 2018 with the main electronic bibliographic databases in medicine, psychology, education, and speech and hearing sciences as the data sources. PubMed, CINALH, ERIC, LLBA, PsychINFO, and ISI Web of Science were searched for unilateral hearing impairment with its synonyms and consequences of congenital or early onset unilateral hearing impairment. Eligible were articles written in English, German, or Swedish on permanent unilateral hearing impairments that are congenital or with onset before three years of age. Hearing impairment had to be of at least a moderate degree with PTA ≥40 dB averaged over frequencies 0.5 to 2 or 0.5-4 kHz, hearing in the contralateral ear had to have PTA_{0.5-2 kHz} or PTA_{0.5-4 kHz} ≤ 20 dB, and consequences of unilateral hearing impairment needed to be reported in an unanimously defined population in at least one of the areas the review focused on. Four researchers independently screened 1618 abstracts and 566 full-text articles for evaluation of study eligibility. Eligible full-text articles were then reviewed to summarize the results and assess the quality of evidence. Additionally, data from 13 eligible case and multi-case studies, each having less than 10 participants, were extracted to summarize their results. Quality assessment of evidence was made adapting the Grades of Recommendations, Assessment, Development, and Evaluation (GRADE) process, and reporting of the results adheres to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards.

RESULTS

Three articles with the quality of evidence graded as very-low to low, fulfilled the eligibility criteria set. Due to the heterogeneity of the articles, only a descriptive summary could be generated from the results. Unilateral hearing impairment was reported to have a negative impact on preverbal vocalization of infants and on sound localization and speech perception both in quiet and in noise.

CONCLUSIONS

No high-quality studies of consequences of early-onset UHI in children were found. Inconsistency in assessing and reporting outcomes, the relatively small number of participants, low directness of evidence, and the potential risk of confounding factors in the reviewed studies prevented any definite conclusions. Further well-designed prospective research using larger samples is warranted on this topic.

Effect of Tinnitus and Duration of Deafness on Sound Localization and Speech Recognition in Noise in Patients With Single-Sided Deafness

Patients with single-sided deafness (SSD) often experience poor sound localization, reduced speech understanding in noise, reduced quality of life, and tinnitus. The present study aims to evaluate effects of tinnitus and duration of deafness on sound localization and speech recognition in noise by SSD subjects. Sound localization and speech recognition in noise were measured in 26 SSD and 10 normal-hearing (NH) subjects. Speech was always presented directly in front of the listener. Noise was presented to the deaf ear, in front of the listener, or to the better hearing ear. Tinnitus severity was measured using visual analog scale and Tinnitus Handicap Inventory. Relative to NH subjects, SSD subjects had significant deficits in sound localization and speech recognition in all listening conditions (p < .001). For SSD subjects, speech recognition in noise was correlated with mean hearing thresholds in the better hearing ear (p < .001) but not in the deaf ear. SSD subjects with tinnitus performed poorer in sound localization and speech recognition in noise than those without tinnitus. Shorter duration of deafness was associated with greater tinnitus and sound localization difficulty. Tinnitus visual analog scale and Tinnitus Handicap Inventory were highly correlated; the degree of tinnitus was negatively correlated with sound localization and speech recognition in noise. Those experiencing noticeable tinnitus may benefit more from cochlear implantation than those without; subjective tinnitus reduction may be correlated with improved sound localization and speech recognition in noise. Subjects with longer duration of deafness demonstrated better sound localization, suggesting long-term compensation for loss of binaural cues.

Differences in Intrinsic Brain Abnormalities Between Patients With Left- and Right-Sided Long-Term Hearing Impairment

Unilateral hearing impairment is characterized by asymmetric hearing input, which causes bilateral unbalanced auditory afferents and tinnitus of varying degrees. Long-term hearing imbalance can cause functional reorganization in the brain. However, differences between intrinsic functional changes in the brains of patients with left- and those with right-sided long-term hearing impairments are incompletely understood. This study included 67 patients with unilateral hearing impairments (left-sided, 33 patients; right-sided, 34 patients) and 32 healthy controls. All study participants underwent blood oxygenation level dependent resting-state functional magnetic resonance imaging and T1-weighted imaging with three-dimensional fast spoiled gradient-echo sequences. After data preprocessing, fractional amplitude of low frequency (fALFF) and functional connectivity (FC) analyses were used to evaluate differences between patients and healthy controls. When compared with the right-sided hearing impairment group, the left-sided hearing impairment group showed significantly higher fALFF values in the left superior parietal gyrus, right inferior parietal lobule, and right superior frontal gyrus, whereas it showed significantly lower fALFF values in the left Heschl’s gyrus, right supramarginal gyrus, and left superior frontal gyrus. In the left-sided hearing impairment group, paired brain regions with enhanced FC were the left Heschl’s gyrus and right supramarginal gyrus, left Heschl’s gyrus and left superior parietal gyrus, left superior parietal gyrus and right inferior parietal lobule, right inferior parietal lobule and right superior frontal gyrus, and left and right superior frontal gyri. In the left-sided hearing impairment group, the FC of the paired brain regions correlated negatively with the duration and pure tone audiometry were in the left Heschl’s gyrus and right supramarginal gyrus. In the right-sided hearing impairment group, the FC of the paired brain regions correlated negatively with the duration was in the left Heschl’s gyrus and superior parietal gyrus, and with pure tone audiometry was right inferior parietal lobule and superior frontal gyrus. The intrinsic reintegration mechanisms of the brain appeared to differ between patients with left-sided hearing impairment and those with right-sided hearing impairment, and the severity of hearing impairment was associated with differences in functional integration in certain brain regions.

Results in Adult Cochlear Implant Recipients With Varied Asymmetric Hearing: A Prospective Longitudinal Study of Speech Recognition, Localization, and Participant Report

OBJECTIVES

Asymmetric hearing with severe to profound hearing loss (SPHL) in one ear and better hearing in the other requires increased listening effort and is detrimental for understanding speech in noise and sound localization. Although a cochlear implant (CI) is the only treatment that can restore hearing to an ear with SPHL, current candidacy criteria often disallows this option for patients with asymmetric hearing. The present study aimed to evaluate longitudinal performance outcomes in a relatively large group of adults with asymmetric hearing who received a CI in the poor ear.

DESIGN

Forty-seven adults with postlingual hearing loss participated. Test materials included objective and subjective measures meant to elucidate communication challenges encountered by those with asymmetric hearing. Test intervals included preimplant and 6 and 12 months postimplant. Preimplant testing was completed in participants' everyday listening condition: bilateral hearing aids (HAs) n = 9, better ear HA n = 29, and no HA n = 9; postimplant, each ear was tested separately and in the bimodal condition.

RESULTS

Group mean longitudinal results in the bimodal condition postimplant compared with the preimplant everyday listening condition indicated significantly improved sentence scores at soft levels and in noise, improved localization, and higher ratings of communication function by 6 months postimplant. Group mean, 6-month postimplant results were significantly better in the bimodal condition compared with either ear alone. Audibility and speech recognition for the poor ear alone improved significantly with a CI compared with preimplant. Most participants had clinically meaningful benefit on most measures. Contributory factors reported for traditional CI candidates also impacted results for this population. In general, older participants had poorer bimodal speech recognition in noise and localization abilities than younger participants. Participants with early SPHL onset had better bimodal localization than those with later SPHL onset, and participants with longer SPHL duration had poorer CI alone speech understanding in noise but not in quiet. Better ear pure-tone average (PTA) correlated with all speech recognition measures in the bimodal condition. To understand the impact of better ear hearing on bimodal performance, participants were grouped by better ear PTA: group 1 PTA ≤40 dB HL (n = 19), group 2 PTA = 41 to 55 dB HL (n = 14), and group 3 PTA = 56 to 70 dB HL (n = 14). All groups showed bimodal benefit on speech recognition measures in quiet and in noise; however, only group 3 obtained benefit when noise was toward the CI ear. All groups showed improved localization and ratings of perceived communication.

CONCLUSIONS

Receiving a CI for the poor ear was an effective treatment for this population. Improved audibility and speech recognition were evident by 6 months postimplant. Improvements in sound localization and self-reports of communication benefit were significant and not related to better ear hearing. Participants with more hearing in the better ear (group 1) showed less bimodal benefit but greater bimodal performance for speech recognition than groups 2 and 3. Test batteries for this population should include quality of life measures, sound localization, and adaptive speech recognition measures with spatially separated noise to capture the hearing loss deficits and treatment benefits reported by this patient population.

Effects of Cochlear Implantation on Binaural Hearing in Adults With Unilateral Hearing Loss

A FDA clinical trial was carried out to evaluate the potential benefit of cochlear implant (CI) use for adults with unilateral moderate-to-profound sensorineural hearing loss. Subjects were 20 adults with moderate-to-profound unilateral sensorineural hearing loss and normal or near-normal hearing on the other side. A MED-EL standard electrode was implanted in the impaired ear. Outcome measures included: (a) sound localization on the horizontal plane (11 positions, -90° to 90°), (b) word recognition in quiet with the CI alone, and (c) masked sentence recognition with the target at 0° and the masker at -90°, 0°, or 90°. This battery was completed preoperatively and at 1, 3, 6, 9, and 12 months after CI activation. Normative data were also collected for 20 age-matched control subjects with normal or near-normal hearing bilaterally. The CI improved localization accuracy and reduced side bias. Word recognition with the CI alone was similar to performance of traditional CI recipients. The CI improved masked sentence recognition when the masker was presented from the front or from the side of normal or near-normal hearing. The binaural benefits observed with the CI increased between the 1- and 3-month intervals but appeared stable thereafter. In contrast to previous reports on localization and speech perception in patients with unilateral sensorineural hearing loss, CI benefits were consistently observed across individual subjects, and performance was at asymptote by the 3-month test interval. Cochlear implant settings, consistent CI use, and short duration of deafness could play a role in this result.

Cochlear implantation as a treatment for single-sided deafness and asymmetric hearing loss: a randomized controlled evaluation of cost-utility

Background

Single-sided deafness (SSD) and asymmetric hearing loss (AHL) have recently been proposed as a new indication for cochlear implantation. There is still no recommended treatment for these hearing deficits, and most options considered rely on the transfer of sound from the poor ear to the better ear, using Contralateral Routing of the Signal (CROS) hearing aids or bone conduction (BC) devices. In contrast, cochlear implantation allows the poor ear to be stimulated and binaural hearing abilities to be partially restored. Indeed, most recently published studies have reported an improvement in the spatial localisation of an incoming sound and better speech recognition in noisy environments after cochlear implantation in SSD/AHL subjects. It also provides consistent relief of tinnitus when associated. These encouraging hearing outcomes raise the question of the cost-utility of this expensive treatment in an extended indication.

Methods

The final endpoint of this national multicentre study is to determine the incremental cost-utility ratio (ICUR) of cochlear implantation in comparison to the current standard of care in France through simple observation, using a randomised controlled trial. Firstly, the study comprises a prospective and descriptive part, where 150 SSD/AHL subjects try CROS hearing aids and a BC device for three weeks each. Secondly, the choice is made between CROS hearing aids, BC implanted device and cochlear implantation. Hearing outcomes and quality of life measurements are described after 6 months for the subjects who chose CROS, BC or declined any option. The subjects who opt for cochlear implantation are randomised between one group where the cochlear implant is inserted without delay and one group of simple initial observation. Hearing outcomes and quality of life measurements are compared after 6 months.

Discussion

The present study was designed to assess the efficiency of cochlear implantation in SSD/AHL. A favourable cost-utility ratio in this extended indication would strengthen the promising clinical results and justify a reimbursement by the health insurance. The efficiency of other options (CROS, BC) will also be described.

Trial registration

This research has been registered in ClinicalTrials.gov (http://www.clinicaltrials.gov/), the 29th July 2014 under the n°NCT02204618.

A review of the effects of unilateral hearing loss on spatial hearing

The capacity of the auditory system to extract spatial information relies principally on the detection and interpretation of binaural cues, i.e., differences in the time of arrival or level of the sound between the two ears. In this review, we consider the effects of unilateral or asymmetric hearing loss on spatial hearing, with a focus on the adaptive changes in the brain that may help to compensate for an imbalance in input between the ears. Unilateral hearing loss during development weakens the brain's representation of the deprived ear, and this may outlast the restoration of function in that ear and therefore impair performance on tasks such as sound localization and spatial release from masking that rely on binaural processing. However, loss of hearing in one ear also triggers a reweighting of the cues used for sound localization, resulting in increased dependence on the spectral cues provided by the other ear for localization in azimuth, as well as adjustments in binaural sensitivity that help to offset the imbalance in inputs between the two ears. These adaptive strategies enable the developing auditory system to compensate to a large degree for asymmetric hearing loss, thereby maintaining accurate sound localization. They can also be leveraged by training following hearing loss in adulthood. Although further research is needed to determine whether this plasticity can generalize to more realistic listening conditions and to other tasks, such as spatial unmasking, the capacity of the auditory system to undergo these adaptive changes has important implications for rehabilitation strategies in the hearing impaired.

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Unilateral hearing loss in infancy can disrupt spatial hearing, even after binaural inputs are restored.

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Plasticity in the developing brain enables substantial recovery in sound localization accuracy.

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Adaptation to unilateral hearing loss is based on reweighting of monaural spectral cues and binaural plasticity.

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Training on auditory tasks can partially compensate for unilateral hearing loss, highlighting potential therapies.