Localization training results in individuals with unilateral severe to profound hearing loss

Review of Binaural Processing With Asymmetrical Hearing Outcomes in Patients With Bilateral Cochlear Implants

Bilateral cochlear implants (BiCIs) result in several benefits, including improvements in speech understanding in noise and sound source localization. However, the benefit bilateral implants provide among recipients varies considerably across individuals. Here we consider one of the reasons for this variability: difference in hearing function between the two ears, that is, interaural asymmetry. Thus far, investigations of interaural asymmetry have been highly specialized within various research areas. The goal of this review is to integrate these studies in one place, motivating future research in the area of interaural asymmetry. We first consider bottom-up processing, where binaural cues are represented using excitation-inhibition of signals from the left ear and right ear, varying with the location of the sound in space, and represented by the lateral superior olive in the auditory brainstem. We then consider top-down processing via predictive coding, which assumes that perception stems from expectations based on context and prior sensory experience, represented by cascading series of cortical circuits. An internal, perceptual model is maintained and updated in light of incoming sensory input. Together, we hope that this amalgamation of physiological, behavioral, and modeling studies will help bridge gaps in the field of binaural hearing and promote a clearer understanding of the implications of interaural asymmetry for future research on optimal patient interventions.

A Review of Virtual Reality for Individuals with Hearing Impairments

Virtual Reality (VR) technologies have the potential to be applied in a clinical context to improve training and rehabilitation for individuals with hearing impairment. The introduction of such technologies in clinical audiology is in its infancy and requires devices that can be taken out of laboratory settings as well as a solid collaboration between researchers and clinicians. In this paper, we discuss the state of the art of VR in audiology with applications to measurement and monitoring of hearing loss, rehabilitation, and training, as well as the development of assistive technologies. We review papers that utilize VR delivered through a head-mounted display (HMD) and used individuals with hearing impairment as test subjects, or presented solutions targeted at individuals with hearing impairments, discussing their goals and results, and analyzing how VR can be a useful tool in hearing research. The review shows the potential of VR in testing and training individuals with hearing impairment, as well as the need for more research and applications in this domain.

Auditory cortical plasticity after cochlear implantation in asymmetric hearing loss is related to spatial hearing: a PET H215O study

In asymmetric hearing loss (AHL), the normal pattern of contralateral hemispheric dominance for monaural stimulation is modified, with a shift towards the hemisphere ipsilateral to the better ear. The extent of this shift has been shown to relate to sound localization deficits. In this study, we examined whether cochlear implantation to treat postlingual AHL can restore the normal functional pattern of auditory cortical activity and whether this relates to improved sound localization. The auditory cortical activity was found to be lower in the AHL cochlear implanted (AHL-CI) participants. A cortical asymmetry index was calculated and showed that a normal contralateral dominance was restored in the AHL-CI patients for the nonimplanted ear, but not for the ear with the cochlear implant. It was found that the contralateral dominance for the nonimplanted ear strongly correlated with sound localization performance (rho = 0.8, P < 0.05). We conclude that the reorganization of binaural mechanisms in AHL-CI subjects reverses the abnormal lateralization pattern induced by the deafness, and that this leads to improved spatial hearing. Our results suggest that cochlear implantation enables the reconstruction of the cortical mechanisms of spatial selectivity needed for sound localization.

Intensive Training of Spatial Hearing Promotes Auditory Abilities of Bilateral Cochlear Implant Adults: A Pilot Study

OBJECTIVE

The aim of this study was to evaluate the feasibility of a virtual reality-based spatial hearing training protocol in bilateral cochlear implant (CI) users and to provide pilot data on the impact of this training on different qualities of hearing.

DESIGN

Twelve bilateral CI adults aged between 19 and 69 followed an intensive 10-week rehabilitation program comprised eight virtual reality training sessions (two per week) interspersed with several evaluation sessions (2 weeks before training started, after four and eight training sessions, and 1 month after the end of training). During each 45-minute training session, participants localized a sound source whose position varied in azimuth and/or in elevation. At the start of each trial, CI users received no information about sound location, but after each response, feedback was given to enable error correction. Participants were divided into two groups: a multisensory feedback group (audiovisual spatial cue) and an unisensory group (visual spatial cue) who only received feedback in a wholly intact sensory modality. Training benefits were measured at each evaluation point using three tests: 3D sound localization in virtual reality, the French Matrix test, and the Speech, Spatial and other Qualities of Hearing questionnaire.

RESULTS

The training was well accepted and all participants attended the whole rehabilitation program. Four training sessions spread across 2 weeks were insufficient to induce significant performance changes, whereas performance on all three tests improved after eight training sessions. Front-back confusions decreased from 32% to 14.1% ( p = 0.017); speech recognition threshold score from 1.5 dB to -0.7 dB signal-to-noise ratio ( p = 0.029) and eight CI users successfully achieved a negative signal-to-noise ratio. One month after the end of structured training, these performance improvements were still present, and quality of life was significantly improved for both self-reports of sound localization (from 5.3 to 6.7, p = 0.015) and speech understanding (from 5.2 to 5.9, p = 0.048).

CONCLUSIONS

This pilot study shows the feasibility and potential clinical relevance of this type of intervention involving a sensorial immersive environment and could pave the way for more systematic rehabilitation programs after cochlear implantation.

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.

Intrinsic brain activity reorganization contributes to long-term compensation of higher-order hearing abilities in single-sided deafness

Single-sided deafness (SSD) is an extreme case of partial hearing deprivation and results in a significant decline in higher-order hearing abilities, including sound localization and speech-in-noise recognition. Clinical studies have reported that patients with SSD recover from these higher-order hearing abilities to some extent over time. Neuroimaging studies have observed extensive brain functional plasticity in patients with SSD. However, studies investigating the role of plasticity in functional compensation, particularly those investigating the relationship between intrinsic brain activity alterations and higher-order hearing abilities, are still limited. In this study, we used resting-state functional MRI to investigate intrinsic brain activity, measured by the amplitude of low-frequency fluctuation (ALFF), in 19 patients with left SSD, 17 patients with right SSD, and 21 normal hearing controls (NHs). All patients with SSD had durations of deafness longer than 2 years. Decreased ALFF values in the bilateral precuneus (PCUN), lingual gyrus, and left middle frontal gyrus were observed in patients with SSD compared with the values of NHs. Longer durations of deafness were correlated with better hearing abilities, as well as higher ALFF values in the left inferior parietal lobule, the angular gyrus, the middle occipital gyrus, the bilateral PCUN, and the posterior cingulate gyrus. Moreover, we observed a generally consistent trend of correlation between ALFF values and higher-order hearing abilities in specific brain areas in patients with SSD. That is, better abilities were correlated with lower ALFF values in the frontal regions and higher ALFF values in the PCUN and surrounding parietal-occipital areas. Furthermore, mediation analysis revealed that the ALFF values in the PCUN were a significant mediator of the relationship between the duration of deafness and higher-order hearing abilities. Our study reveals significant plasticity of intrinsic brain activity in patients with SSD and suggests that reorganization of intrinsic brain activity may be one of the compensatory mechanisms that facilitate improvement in higher-order hearing abilities in these patients over time.

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.

The Effect of Hearing Aids on Sound Localization in Mild Unilateral Conductive Hearing Loss

BACKGROUND

 Binaural hearing is of utmost importance for communicating in noisy surroundings and localizing the direction of sound. Unilateral hearing loss (UHL) affects the quality of life in both childhood and adulthood, speech development, and academic achievements. Sound amplification using air-conducting hearing aids (HAs) is a common option for hearing rehabilitation of UHL. The processing time of digital HAs can significantly delay the acoustic stimulation in 3 to 10 milliseconds, which is far longer than the maximal natural interaural time difference (ITD) of 750 microseconds. This can further impair spatial localization in these patients.

PURPOSE

 We sought to assess whether HA effects on ITD and interaural level difference (ILD) impair localization among subjects with unilateral conductive hearing loss (UCHL).

RESEARCH DESIGN

 "Normal"-hearing participants underwent localization testing in different free field settings.

STUDY SAMPLE

 Ten volunteers with "normal"-hearing thresholds participated.

INTERVENTION

 Repeated assessments were compared between "normal" (binaural) hearing, UCHL induced by insertion of an inactivated HA to the ear canal (conductive HL), and amplification with a HA.

RESULTS

 In UCHL mode, with HA switched-off, localization was significantly impaired compared to "normal" hearing (NH; η2 = 0.151). Localization error was more pronounced when sound was presented from the front and from the side of the occluded ear. When switched-on, amplification with HAs significantly improved localization for all participants compared to UCHL. Better localization with HAs was seen in high frequencies compared to low frequencies (η2 = 0.08, 0.03). Even with HAs, localization did not reach that of NH (η2 = 0.034).

CONCLUSION

 Mild UCHL caused localization to deteriorate. HAs significantly improved sound localization, albeit the delay caused by the device processing time. Most of the improvements were seen in high-frequency sounds, representing a beneficial effect of amplification on ILD. Our results have potential clinical value in situations of mild CHL, for instance, otitis media with effusion.

Instant improvement in monaural spatial hearing abilities through cognitive feedback

Several studies report that sound localization performance of acute and chronic monauralized normal-hearing listeners can improve through training. Typically, training sessions are administered daily for several days or weeks. While this intensive training is effective, it may also be that monaural localization abilities improve instantly after providing explicit top-down information about the direction dependent change in timbre and level. The aim of the present study was to investigate whether cognitive feedback (i.e., top-down information) could instantly improve sound localization in naive acutely monauralized listeners. Forty-three normal-hearing listeners (experimental group), divided over five different centers, were tested. Two control groups, consisting of, respectively, nine and eleven normal-hearing listeners, were tested in one center. Broadband sounds (0.5-20 kHz) were presented from visible loudspeakers, positioned in azimuth (- 90° to 90°). Participants in the experimental group received explicit information about the noticeable difference in timbre and the poor localization in the monauralized listening condition, resulting in an instant improvement in sound localization abilities. With subsequent roving of stimulus level (20 dB), sound localization performance deteriorated immediately. The reported improvement is related to the context of the localization test. The results provide important implications for studies investigating sound localization in a clinical setting, especially during closed-set testing, and indicate the importance of top-down information.

Sound source localization patterns and bilateral cochlear implants: Age at onset of deafness effects

The ability to determine a sound’s location is critical in everyday life. However, sound source localization is severely compromised for patients with hearing loss who receive bilateral cochlear implants (BiCIs). Several patient factors relate to poorer performance in listeners with BiCIs, associated with auditory deprivation, experience, and age. Critically, characteristic errors are made by patients with BiCIs (e.g., medial responses at lateral target locations), and the relationship between patient factors and the type of errors made by patients has seldom been investigated across individuals. In the present study, several different types of analysis were used to understand localization errors and their relationship with patient-dependent factors (selected based on their robustness of prediction). Binaural hearing experience is required for developing accurate localization skills, auditory deprivation is associated with degradation of the auditory periphery, and aging leads to poorer temporal resolution. Therefore, it was hypothesized that earlier onsets of deafness would be associated with poorer localization acuity and longer periods without BiCI stimulation or older age would lead to greater amounts of variability in localization responses. A novel machine learning approach was introduced to characterize the types of errors made by listeners with BiCIs, making them simple to interpret and generalizable to everyday experience. Sound localization performance was measured in 48 listeners with BiCIs using pink noise trains presented in free-field. Our results suggest that older age at testing and earlier onset of deafness are associated with greater average error, particularly for sound sources near the center of the head, consistent with previous research. The machine learning analysis revealed that variability of localization responses tended to be greater for individuals with earlier compared to later onsets of deafness. These results suggest that early bilateral hearing is essential for best sound source localization outcomes in listeners with BiCIs.

Involving Children and Teenagers With Bilateral Cochlear Implants in the Design of the BEARS (Both EARS) Virtual Reality Training Suite Improves Personalization

Older children and teenagers with bilateral cochlear implants often have poor spatial hearing because they cannot fuse sounds from the two ears. This deficit jeopardizes speech and language development, education, and social well-being. The lack of protocols for fitting bilateral cochlear implants and resources for spatial-hearing training contribute to these difficulties. Spatial hearing develops with bilateral experience. A large body of research demonstrates that sound localisation can improve with training, underpinned by plasticity-driven changes in the auditory pathways. Generalizing training to non-trained auditory skills is best achieved by using a multi-modal (audio-visual) implementation and multi-domain training tasks (localisation, speech-in-noise, and spatial music). The goal of this work was to develop a package of virtual-reality games (BEARS, Both EARS) to train spatial hearing in young people (8–16 years) with bilateral cochlear implants using an action-research protocol. The action research protocol used formalized cycles for participants to trial aspects of the BEARS suite, reflect on their experiences, and in turn inform changes in the game implementations. This participatory design used the stakeholder participants as co-creators. The cycles for each of the three domains (localisation, spatial speech-in-noise, and spatial music) were customized to focus on the elements that the stakeholder participants considered important. The participants agreed that the final games were appropriate and ready to be used by patients. The main areas of modification were: the variety of immersive scenarios to cover age range and interests, the number of levels of complexity to ensure small improvements were measurable, feedback, and reward schemes to ensure positive reinforcement, and an additional implementation on an iPad for those who had difficulties with the headsets due to age or balance issues. The effectiveness of the BEARS training suite will be evaluated in a large-scale clinical trial to determine if using the games lead to improvements in speech-in-noise, quality of life, perceived benefit, and cost utility. Such interventions allow patients to take control of their own management reducing the reliance on outpatient-based rehabilitation. For young people, a virtual-reality implementation is more engaging than traditional rehabilitation methods, and the participatory design used here has ensured that the BEARS games are relevant.

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.

Sound Localization and Lateralization by Bilateral Bone Conduction Devices, Middle Ear Implants, and Cartilage Conduction Hearing Aids

Sound localization in daily life is one of the important functions of binaural hearing. Bilateral bone conduction devices (BCDs), middle ear implants, and cartilage conduction hearing aids have been often applied for patients with conductive hearing loss (CHL) or mixed hearing loss, for example, resulting from bilateral microtia and aural atresia. In this review, factors affecting the accuracy of sound localization with bilateral BCDs, middle ear implants, and cartilage conduction hearing aids were classified into four categories: (1) types of device, (2) experimental conditions, (3) participants, and (4) pathways from the stimulus sound to both cochleae. Recent studies within the past 10 years on sound localization and lateralization by BCDs, middle ear implants, and cartilage conduction hearing aids were discussed. Most studies showed benefits for sound localization or lateralization with bilateral devices. However, the judgment accuracy was generally lower than that for normal hearing, and the localization errors tended to be larger than for normal hearing. Moreover, it should be noted that the degree of accuracy in sound localization by bilateral BCDs varied considerably among patients. Further research on sound localization is necessary to analyze the complicated mechanism of bone conduction, including suprathreshold air conduction with bilateral devices.

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.

Improving Sensitivity of the Digits-In-Noise Test Using Antiphasic Stimuli

Supplemental Digital Content is available in the text.

Objectives:

The digits-in-noise test (DIN) has become increasingly popular as a consumer-based method to screen for hearing loss. Current versions of all DINs either test ears monaurally or present identical stimuli binaurally (i.e., diotic noise and speech, N_oS_o). Unfortunately, presentation of identical stimuli to each ear inhibits detection of unilateral sensorineural hearing loss (SNHL), and neither diotic nor monaural presentation sensitively detects conductive hearing loss (CHL). After an earlier finding of enhanced sensitivity in normally hearing listeners, this study tested the hypothesis that interaural antiphasic digit presentation (N_oS_π) would improve sensitivity to hearing loss caused by unilateral or asymmetric SNHL, symmetric SNHL, or CHL.

Design:

This cross-sectional study recruited adults (18 to 84 years) with various levels of hearing based on a 4-frequency pure-tone average (PTA) at 0.5, 1, 2, and 4 kHz. The study sample was comprised of listeners with normal hearing (n = 41; PTA ≤ 25 dB HL in both ears), symmetric SNHL (n = 57; PTA > 25 dB HL), unilateral or asymmetric SNHL (n = 24; PTA > 25 dB HL in the poorer ear), and CHL (n = 23; PTA > 25 dB HL and PTA air-bone gap ≥ 20 dB HL in the poorer ear). Antiphasic and diotic speech reception thresholds (SRTs) were compared using a repeated-measures design.

Results:

Antiphasic DIN was significantly more sensitive to all three forms of hearing loss than the diotic DIN. SRT test–retest reliability was high for all tests (intraclass correlation coefficient r > 0.89). Area under the receiver operating characteristics curve for detection of hearing loss (>25 dB HL) was higher for antiphasic DIN (0.94) than for diotic DIN (0.77) presentation. After correcting for age, PTA of listeners with normal hearing or symmetric SNHL was more strongly correlated with antiphasic (r_partial[96] = 0.69) than diotic (r_partial = 0.54) SRTs. Slope of fitted regression lines predicting SRT from PTA was significantly steeper for antiphasic than diotic DIN. For listeners with normal hearing or CHL, antiphasic SRTs were more strongly correlated with PTA (r_partial[62] = 0.92) than diotic SRTs (r_partial[62] = 0.64). Slope of the regression line with PTA was also significantly steeper for antiphasic than diotic DIN. The severity of asymmetric hearing loss (poorer ear PTA) was unrelated to SRT. No effect of self-reported English competence on either antiphasic or diotic DIN among the mixed first-language participants was observed.

Conclusions:

Antiphasic digit presentation markedly improved the sensitivity of the DIN test to detect SNHL, either symmetric or asymmetric, while keeping test duration to a minimum by testing binaurally. In addition, the antiphasic DIN was able to detect CHL, a shortcoming of previous monaural or binaurally diotic DIN versions. The antiphasic DIN is thus a powerful tool for population-based screening. This enhanced functionality combined with smartphone delivery could make the antiphasic DIN suitable as a primary screen that is accessible to a large global audience.

Cochlear Implant Use Remains Consistent Over Time in Children With Single-Sided Deafness

OBJECTIVES

To measure the acceptance of a cochlear implant by children with single-sided deafness (SSD) using datalogging technology in the cochlear implant processor.

DESIGN

Datalogs from follow-up clinical audiology appointments for 23 children with SSD were extracted from their cochlear implant processors ranging from 1 to 8 visits (M = 3.74, SD = 1.79). The number of hours the cochlear implant was in use per day, the number of times the coil disconnected from the internal device, and the percentage of daily cochlear implant use in different auditory environments were collected from the datalogs. Linear mixed-effects regressions were used to analyze the relationship between age, hearing experience, cochlear implant use, and coil-offs per day. Nonlinear regressions were conducted to evaluate cochlear implant use in different environments.

RESULTS

Children with SSD wore their cochlear implants for 6.22 (SD = 2.81; range = 0.0004 to 14.74) hours per day on average. No significant change in cochlear implant use was seen as the children grew older or gained more hearing experience. As hearing experience increased, the number of coil-offs per day was reduced. Preschoolers spent more time in "music" and "speech" and less time in "noise" and "quiet" than older and younger children while older children spent more time in "speech-in-noise."

CONCLUSIONS

Children with SSD consistently wear their cochlear implants. However, the auditory environments to which they are exposed vary over time. Regular cochlear implant use by this population suggests that it does not detract from a normal-hearing ear and that children with SSD appreciate access to bilateral input.

A Graphical-User-Interface-Based Azimuth-Collection Method in Autonomous Auditory Localization of Real and Virtual Sound Sources

Auditory localization of spatial sound sources is an important life skill for human beings. For the practical application-oriented measurement of auditory localization ability, the preference is a compromise among (i) data accuracy, (ii) the maneuverability of collecting directions, and (iii) the cost of hardware and software. The graphical user interface (GUI)-based sound-localization experimental platform proposed here (i) is cheap, (ii) can be operated autonomously by the listener, (iii) can store results online, and (iv) supports real or virtual sound sources. To evaluate the accuracy of this method, by using 12 loudspeakers arranged in equal azimuthal intervals of 30° in the horizontal plane, three groups of azimuthal localization experiments are conducted in the horizontal plane with subjects with normal hearing. In these experiments, the azimuths are reported using (i) an assistant, (ii) a motion tracker, or (iii) the newly designed GUI-based method. All three groups of results show that the localization errors are mostly within 5-12°, which is consistent with previous results from different localization experiments. Finally, the stimulus of virtual sound sources is integrated into the GUI-based experimental platform. The results with the virtual sources suggest that using individualized head-related transfer functions can achieve better performance in spatial sound source localization, which is consistent with previous conclusions and further validates the reliability of this experimental platform.

Activities of the Right Temporo-Parieto-Occipital Junction Reflect Spatial Hearing Ability in Cochlear Implant Users

Spatial hearing is critical for us not only to orient ourselves in space, but also to follow a conversation with multiple speakers involved in a complex sound environment. The hearing ability of people who suffered from severe sensorineural hearing loss can be restored by cochlear implants (CIs), however, with a large outcome variability. Yet, the causes of the CI performance variability remain incompletely understood. Despite the CI-based restoration of the peripheral auditory input, central auditory processing might still not function fully. Here we developed a multi-modal repetition suppression (MMRS) paradigm that is capable of capturing stimulus property-specific processing, in order to identify the neural correlates of spatial hearing and potential central neural indexes useful for the rehabilitation of sound localization in CI users. To this end, 17 normal hearing and 13 CI participants underwent the MMRS task while their brain activity was recorded with a 256-channel electroencephalography (EEG). The participants were required to discriminate between the probe sound location coming from a horizontal array of loudspeakers. The EEG MMRS response following the probe sound was elicited at various brain regions and at different stages of processing. Interestingly, the more similar this differential MMRS response in the right temporo-parieto-occipital (TPO) junction in CI users was to the normal hearing group, the better was the spatial hearing performance in individual CI users. Based on this finding, we suggest that the differential MMRS response at the right TPO junction could serve as a central neural index for intact or impaired sound localization abilities.

Haptic sound-localisation for use in cochlear implant and hearing-aid users

Users of hearing-assistive devices often struggle to locate and segregate sounds, which can make listening in schools, cafes, and busy workplaces extremely challenging. A recent study in unilaterally implanted CI users showed that sound-localisation was improved when the audio received by behind-the-ear devices was converted to haptic stimulation on each wrist. We built on this work, using a new signal-processing approach to improve localisation accuracy and increase generalisability to a wide range of stimuli. We aimed to: (1) improve haptic sound-localisation accuracy using a varied stimulus set and (2) assess whether accuracy improved with prolonged training. Thirty-two adults with normal touch perception were randomly assigned to an experimental or control group. The experimental group completed a 5-h training regime and the control group were not trained. Without training, haptic sound-localisation was substantially better than in previous work on haptic sound-localisation. It was also markedly better than sound-localisation by either unilaterally or bilaterally implanted CI users. After training, accuracy improved, becoming better than for sound-localisation by bilateral hearing-aid users. These findings suggest that a wrist-worn haptic device could be effective for improving spatial hearing for a range of hearing-impaired listeners.

Sound-localisation performance in patients with congenital unilateral microtia and atresia fitted with an active middle ear implant

OBJECTIVE

This study assessed the safety and sound-localisation ability of the Vibrant Soundbridge (VSB) (Med-EL, Innsbruck, Austria) in patients with unilateral microtia and atresia (MA).

METHODS

This was a single-centre retrospective research study. Twelve subjects with unilateral conductive hearing loss (UCHL) caused by ipsilateral MA were recruited, each of whom underwent VSB implantation and auricular reconstruction. The bone-conduction (BC) threshold was measured postoperatively, and the accuracy of sound localisation was evaluated at least 6 months after surgery. Horizontal sound-localisation performance was investigated with the VSB activated and inactivated, at varying sound stimuli levels (65, 70 and 75 dB SPL). Localisation benefit was analysed via the mean absolute error (MAE).

RESULTS

There was no statistical difference in mean BC threshold of impaired ears measured preoperatively and postoperatively. When compared with VSB-inactivated condition, the MAE increased significantly in unilateral MA patients in the VSB-activated condition. Besides, sound-localisation performance worsened remarkably when sound was presented at 70 dB SPL and 75 dB SPL. Regarding the side of signal location, the average MAE with the VSB device was much higher than that without the VSB when sound was from the normal-hearing ear. However, no significant difference was observed when sound was located from the impaired ear.

CONCLUSION

This study demonstrates that in patients with unilateral MA, the VSB device does not affect inner-ear function. Sound-localisation ability is not improved, but deteriorated at follow-up. Our results suggest that the VSB-aided localisation abilities may be related to the thresholds between the ears, plasticity of auditory system and duration of use of VSB.

Learning to find spatially reversed sounds

Adaptation to systematic visual distortions is well-documented but there is little evidence of similar adaptation to radical changes in audition. We use a pseudophone to transpose the sound streams arriving at the left and right ears, evaluating the perceptual effects it provokes and the possibility of learning to locate sounds in the reversed condition. Blindfolded participants remain seated at the center of a semicircular arrangement of 7 speakers and are asked to orient their head towards a sound source. We postulate that a key factor underlying adaptation is the self-generated activity that allows participants to learn new sensorimotor schemes. We investigate passive listening conditions (very short duration stimulus not permitting active exploration) and dynamic conditions (continuous stimulus allowing participants time to freely move their heads or remain still). We analyze head movement kinematics, localization errors, and qualitative reports. Results show movement-induced perceptual disruptions in the dynamic condition with static sound sources displaying apparent movement. This effect is reduced after a short training period and participants learn to find sounds in a left-right reversed field for all but the extreme lateral positions where motor patterns are more restricted. Strategies become less exploratory and more direct with training. Results support the hypothesis that self-generated movements underlie adaptation to radical sensorimotor distortions.

Unilateral hearing loss: benefit of amplification in sound localization, temporal ordering and resolution

PURPOSE

To assess the hearing abilities of temporal ordering, temporal resolution and sound localization before and after the fitting of a hearing aid (HA) in individuals with unilateral hearing loss (UHL).

METHODS

There were evaluated 22 subjects, aged 18 to 60 years, diagnosed with sensorineural or mixed UHL, from mild to severe degrees. The study was divided into two stages: the pre and post-adaptation of HA. In both phases, subjects performed an interview, application of Questionnaire for Disabilities Associated with Impaired Auditory Localization, auditory processing screening protocol (APSP) and Random Gap Detection Test (RGDT).

RESULTS

This study found no statistically significant difference in sound localization and memory evaluations for verbal sounds in sequence, in RGDT and Questionnaire for Disabilities Associated with Impaired Auditory Localization.

CONCLUSION

With the effective use of hearing aids, individuals with UHL showed improvement in the auditory abilities of sound localization, ordering and temporal resolution.

Silencing cortical activity during sound-localization training impairs auditory perceptual learning

The brain has a remarkable capacity to adapt to changes in sensory inputs and to learn from experience. However, the neural circuits responsible for this flexible processing remain poorly understood. Using optogenetic silencing of ArchT-expressing neurons in adult ferrets, we show that within-trial activity in primary auditory cortex (A1) is required for training-dependent recovery in sound-localization accuracy following monaural deprivation. Because localization accuracy under normal-hearing conditions was unaffected, this highlights a specific role for cortical activity in learning. A1-dependent plasticity appears to leave a memory trace that can be retrieved, facilitating adaptation during a second period of monaural deprivation. However, in ferrets in which learning was initially disrupted by perturbing A1 activity, subsequent optogenetic suppression during training no longer affected localization accuracy when one ear was occluded. After the initial learning phase, the reweighting of spatial cues that primarily underpins this plasticity may therefore occur in A1 target neurons.

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.

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.

Development of Questionnaire for Auditory Localization

OBJECTIVE

Localization plays an important role in identifying the source of the stimuli. Aural localization is based on the phase (period-related time), intensity level, and spectral differences between the sounds at each ear. Various behavioral measures are available to check the interaural level, time, and frequency differences, which provide information on an individual's ability to localize the sound source. This might vary depending on the audibility and amplification devices. Although these behavioral measures are available, the perceptual quality of localization cannot be obtained using these measures. This study aimed to develop a questionnaire for auditory localization.

MATERIALS AND METHODS

A questionnaire was prepared, the content validated, and administered on 120 individuals in the age range of 18-50 years who were divided into three different groups.

RESULTS

The results of the descriptive and item analysis revealed a significant difference between the groups, with group I showing better localization ability. No significant difference was observed between the groups II and III. The receiver operating curve and cut-off scores were obtained. Individuals with a score of <42.5 on the questionnaire have better or good localization ability. The area covered under the curve is 0.987; therefore, the sensitivity and specificity of the questionnaire is also high.

CONCLUSION

It can be concluded that this questionnaire is a simple, valid, and preliminary measure for the auditory localization ability of an individual.

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.

•

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

•

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

•

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

•

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

Sound-localization performance of patients with single-sided deafness is not improved when listening with a bone-conduction device

An increased number of treatment options has become available for patients with single sided deafness (SSD), who are seeking hearing rehabilitation. For example, bone-conduction devices that employ contralateral routing of sound (CROS), by transmitting acoustic bone vibrations from the deaf side to the cochlea of the hearing ear, are widely used. However, in some countries, cochlear implantation is becoming the standard treatment. The present study investigated whether CROS intervention, by means of a CROS bone-conduction device (C-BCD), affected sound-localization performance of patients with SSD. Several studies have reported unexpected moderate to good unilateral sound-localization abilities in unaided SSD listeners. Listening with a C-BCD might deteriorate these localization abilities because sounds are transmitted, through bone conduction to the contralateral normal hearing ear, and could thus interfere with monaural level cues (i.e. ambiguous monaural head-shadow cues), or with the subtle spectral localization cues, on which the listener has learned to rely on. The present study included nineteen SSD patients who were using their C-BCD for more than five months. To assess the use of the different localization cues, we investigated their localization abilities to broadband (BB, 0.5-20 kHz), low-pass (LP, 0.5-1.5 kHz), and high-pass filtered noises (HP, 3-20 kHz) of varying intensities. Experiments were performed in complete darkness, by measuring orienting head-movement responses under open-loop localization conditions. We demonstrate that a minority of listeners with SSD (5 out of 19) could localize BB and HP (but not LP) sounds in the horizontal plane in the unaided condition, and that a C-BCD did not deteriorate their localization abilities.

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

OBJECTIVES

At a minimum, unilateral hearing loss (UHL) impairs sound localization ability and understanding speech in noisy environments, particularly if the loss is severe to profound. Accompanying the numerous negative consequences of UHL is considerable unexplained individual variability in the magnitude of its effects. Identification of covariables that affect outcome and contribute to variability in UHLs could augment counseling, treatment options, and rehabilitation. Cochlear implantation as a treatment for UHL is on the rise yet little is known about factors that could impact performance or whether there is a group at risk for poor cochlear implant outcomes when hearing is near-normal in one ear. The overall goal of our research is to investigate the range and source of variability in speech recognition in noise and localization among individuals with severe to profound UHL and thereby help determine factors relevant to decisions regarding cochlear implantation in this population.

DESIGN

The present study evaluated adults with severe to profound UHL and adults with bilateral normal hearing. Measures included adaptive sentence understanding in diffuse restaurant noise, localization, roving-source speech recognition (words from 1 of 15 speakers in a 140° arc), and an adaptive speech-reception threshold psychoacoustic task with varied noise types and noise-source locations. There were three age-sex-matched groups: UHL (severe to profound hearing loss in one ear and normal hearing in the contralateral ear), normal hearing listening bilaterally, and normal hearing listening unilaterally.

RESULTS

Although the normal-hearing-bilateral group scored significantly better and had less performance variability than UHLs on all measures, some UHL participants scored within the range of the normal-hearing-bilateral group on all measures. The normal-hearing participants listening unilaterally had better monosyllabic word understanding than UHLs for words presented on the blocked/deaf side but not the open/hearing side. In contrast, UHLs localized better than the normal-hearing unilateral listeners for stimuli on the open/hearing side but not the blocked/deaf side. This suggests that UHLs had learned strategies for improved localization on the side of the intact ear. The UHL and unilateral normal-hearing participant groups were not significantly different for speech in noise measures. UHL participants with childhood rather than recent hearing loss onset localized significantly better; however, these two groups did not differ for speech recognition in noise. Age at onset in UHL adults appears to affect localization ability differently than understanding speech in noise. Hearing thresholds were significantly correlated with speech recognition for UHL participants but not the other two groups.

CONCLUSIONS

Auditory abilities of UHLs varied widely and could be explained only in part by hearing threshold levels. Age at onset and length of hearing loss influenced performance on some, but not all measures. Results support the need for a revised and diverse set of clinical measures, including sound localization, understanding speech in varied environments, and careful consideration of functional abilities as individuals with severe to profound UHL are being considered potential cochlear implant candidates.

Horizontal Localization in Simulated Unilateral Hearing Loss

Background and Objectives

The ability to localize a sound source is one of the binaural hearing benefits in a horizontal plane based on interaural time difference and interaural intensity difference. Unilateral or bilateral asymmetric hearing loss will affect binaural hearing and lead to sound locating errors. In this cross sectional analytical descriptive study, the localization error was investigated when participants turned their heads to the sound source with closed eyes and after simulating unilateral hearing loss by placing earplugs inside the right ear canal.

Subjects and Methods

This cross sectional analytical descriptive study was carried out on 30 right-handed adults, 22 female and 8 male (average: 25 years, standard deviation: 3.16). They were selected with the available random access method. Horizontal localization was evaluated with five speakers located at 0, ±30, and ±60 degree azimuths at a 1-meter distance from the examinee. Narrow-band noise signals were delivered at 35 dB SL in two “without earplug” and “with earplug” situations and the results were compared. The study was performed between September and December 2016 in Tehran, Iran.

Results

Significant differences were observed in localization errors between the “with earplug” and “without earplug” situations. The localization differences were greater for left-side speakers (-30 and -60 degrees) compared with right-side speakers (+30 and +60 degrees). The differences were more apparent at 4,000 and 6,000 Hz, which confirmed the effect of unilateral simulated hearing loss on interaural latency differences.

Conclusions

Simulating hearing loss by using an earplug in one ear (right) increased localization errors at all frequencies. The errors increased at higher frequencies.

Speech-in-noise perception in unilateral hearing loss: Relation to pure-tone thresholds and brainstem plasticity

We investigated speech recognition in noise in subjects with mild to profound levels of unilateral hearing loss. Thirty-five adults were evaluated using an adaptive signal-to-noise ratio (SNR50) sentence recognition threshold test in three spatial configurations. The results revealed a significant correlation between pure-tone average audiometric thresholds in the poorer ear and SNR thresholds in the two conditions where speech and noise were spatially separated: dichotic - with speech presented to the poorer ear and reverse dichotic - with speech presented to the better ear. This first result suggested that standard pure-tone air-conduction thresholds can be a reliable predictor of speech recognition in noise for binaural conditions. However, a subgroup of 14 subjects was found to have poorer-than-expected speech recognition scores, especially in the reverse dichotic listening condition. In this subgroup 9 subjects had been diagnosed with vestibular schwannoma at stage III or IV likely affecting the lower brainstem function. These subjects showed SNR thresholds in the reverse dichotic condition on average 4dB poorer (higher) than for the other 21 normally-performing subjects. For the 7 of 9 subjects whose vestibular schwannoma was removed, the deficit was no longer apparent on average 5 months following the surgical procedure. These results suggest that following unilateral hearing loss the capacity to use monaural spectral information is supported by the lower brainstem.

Management of unilateral hearing loss

OBJECTIVE

A representative sample of literature regarding unilateral hearing loss (UHL) was reviewed to provide evidence of the effects of UHL and the intervention options available for children with UHL. Considerations during the assessment and management of children with UHL are illustrated using case illustrations.

METHOD

Research articles published from 2013 to 2015 were searched in the PubMed database using the keywords "unilateral hearing loss". Articles from 1950 to 2013 were included from a previous literature review on minimal hearing loss [1]. A retrospective review of charts of 14 children with UHL was also conducted.

RESULTS

The evidence indicates that children with UHL are more likely to have structural anomalies of the inner ear; may face challenges in six different domains, and have six intervention options available. Evidence also indicates that although some children appear to exhibit no delays or difficulties, others have significant challenges, some of which continue into adulthood.

CONCLUSIONS

Children with UHL have to be treated on a case-by-case basis. Parent education regarding UHL, its effects, and all available management options is critical so they can make informed decisions. Close monitoring and good communication between professionals in different domains is crucial in order to minimize the potential negative effects of UHL.

Sound localization in a changing world

In natural environments, neural systems must be continuously updated to reflect changes in sensory inputs and behavioral goals. Recent studies of sound localization have shown that adaptation and learning involve multiple mechanisms that operate at different timescales and stages of processing, with other sensory and motor-related inputs playing a key role. We are only just beginning to understand, however, how these processes interact with one another to produce adaptive changes at the level of neuronal populations and behavior. Because there is no explicit map of auditory space in the cortex, studies of sound localization may also provide much broader insight into the plasticity of complex neural representations that are not topographically organized.