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.

Objectives: The ability to localize sound sources is crucial for everyday listening, as it contributes to spatial awareness and the detection of warning signs. Individuals with hearing impairment have poorer localization abilities, which further deteriorate when they are fitted with a hearing aid. Although numerous studies have addressed this phenomenon, there is a lack of systematic evidence. The aim of the current systematic review is to address the following research question, \"Do behavioural measures of spatial hearing ability improve with bilateral hearing aid fitting compared to the unaided hearing condition?\"Design: A comprehensive search was conducted by two independent authors utilizing electronic databases, using various electronic databases, covering the period of 1965 to 2022. The inclusion and exclusion criteria were formulated using the Population, Intervention, Compression, Outcome, and Study design (PICOS) format, and the certainty of evidence was determined using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) guidelines.Results: The comprehensive search resulted in 2199 studies, 17 studies for qualitative synthesis and 15 studies for quantitative synthesis. The collected data was divided into two groups, namely vertical and horizontal localization. The results of the quantitative analysis indicate that the localization performance was significantly better in the unaided condition for both vertical and horizontal planes. The certainty of our evidence was judged to be moderate, meaning that \"we are moderately confident in the effect estimate. The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different\".Conclusion: The review findings demonstrate that the bilateral fitting of the hearing aid did not effectively preserve spatial cues, which resulted in poorer localization performance irrespective of the plane of assessment.Review Registration: Prospective Register of Systematic Reviews (PROSPERO); CRD42022358164.
Hearing aids are a widely used rehabilitative method to compensate for the loss of audibility in individuals with hearing impairment. The current review highlights that, even though hearing aids can enhance audibility, they often fail to preserve spatial cues.This review paper provides a comprehensive summary of the existing literature, focusing on the preservation of spatial cues by hearing aids and the technologies that can enhance localization performance to a certain degree.The findings of the current study encourage both researchers and hearing aid manufacturers to advance their research methods pertaining to the preservation of spatial cues. This advancement has the potential to improve spatial awareness and possibly improve speech perception in the presence of noise in hearing aid users.

Identify and evaluate the effectiveness of methods for improving postoperative cochlear implant (CI) hearing performance in subjects with single-sided deafness (SSD) and asymmetric hearing loss (AHL).
Embase, PubMed, Scopus.
Systematic review and narrative synthesis. English language studies of adult CI recipients with SSD and AHL reporting a postoperative intervention and comparative audiometric data pertaining to speech in noise, speech in quiet and sound localization were included.
32 studies met criteria for full text review and 6 (n = 81) met final inclusion criteria. Interventions were categorized as: formal auditory training, programming techniques, or hardware optimization. Formal auditory training (n = 10) found no objective improvement in hearing outcomes. Experimental CI maps did not improve audiologic outcomes (n = 9). Programed CI signal delays to improve synchronization demonstrated improved sound localization (n = 12). Hardware optimization, including multidirectional (n = 29) and remote (n = 11) microphones, improved sound localization and speech in noise, respectively.
Few studies meeting inclusion criteria and small sample sizes highlight the need for further study. Formal auditory training did not appear to improve hearing outcomes. Programming techniques, such as CI signal delay, and hardware optimization, such as multidirectional and remote microphones, show promise to improve outcomes for SSD and AHL CI users.

Bimodal provision of patients with asymmetric hearing loss with a hearing aid ipsilaterally and a cochlear implant (CI) contralaterally is probably the most complicated type of CI provision due to a variety of inherent variables. This review article presents all the systematic interaural mismatches between electric and acoustic stimulation that can occur in bimodal listeners. One of these mismatches is the interaural latency offset, i.e., the time difference of activation of the auditory nerve by acoustic and electric stimulation. Methods for quantifying this offset are presented by registering electrically and acoustically evoked potentials and measuring processing delays in the devices. Technical compensation of the interaural latency offset and its positive effect on sound localization ability in bimodal listeners is also described. Finally, most recent findings are discussed which may explain why compensation of the interaural latency offset does not improve speech understanding in noise in bimodal listeners.
UNASSIGNED: Die bimodale Versorgung von Patienten mit Hörgerät (HG) ipsilateral und Cochleaimplantat (CI) kontralateral bei asymmetrischem Hörverlust ist aufgrund vieler inhärenter Variablen die komplizierteste Versorgungsart im Kontext der Versorgung mit CI. Im vorliegenden Übersichtsartikel werden alle systematischen interauralen Unterschiede zwischen elektrischer und akustischer Stimulation dargestellt, die bei dieser Versorgungsart auftreten können. Darüber hinaus werden Methoden zur Quantifizierung des interauralen Latenzoffsets, also des Zeitunterschieds zwischen der akustischen und elektrischen Stimulation des Hörnervs, mittels Registrierung auditorisch evozierter Potenziale – erzeugt durch akustische bzw. elektrische Stimulation – und Messungen an den Sprachprozessoren und Hörgeräten vorgestellt. Die technische Kompensation des interauralen Latenzoffsets und ihre positive Auswirkung auf die Schalllokalisationsfähigkeit bimodal mit CI und HG versorgter Patienten wird ebenfalls beschrieben. Zuletzt werden neueste Erkenntnisse diskutiert, die Gründe dafür aufzeigen, warum die Kompensation des interauralen Latenzoffsets das Sprachverstehen im Störgeräusch bei bimodal versorgten CI-/HG-Trägern nicht verbessert.

Processing of basic auditory features, one of the earliest stages of auditory perception, has been the focus of considerable investigations in schizophrenia. Although numerous studies have shown abnormalities in pitch perception in schizophrenia, other basic auditory features such as intensity, duration, and sound localization have been less explored. Additionally, the relationship between basic auditory features and symptom severity shows inconsistent results, preventing concrete conclusions. Our aim was to present a comprehensive overview of basic auditory processing in schizophrenia and its relationship with symptoms. We conducted a systematic review according to the PRISMA guidelines. PubMed, Embase, and PsycINFO databases were searched for studies exploring auditory perception in schizophrenia compared to controls, with at least one behavioral task investigating basic auditory processing using pure tones. Forty-one studies were included. The majority investigated pitch processing while the others investigated intensity, duration and sound localization. The results revealed that patients have a significant deficit in the processing of all basic auditory features. Although the search for a relationship with symptoms was limited, auditory hallucinations experience appears to have an impact on basic auditory processing. Further research may examine correlations with clinical symptoms to explore the performance of patient subgroups and possibly implement remediation strategies.

To assess spatial hearing, tinnitus, and quality-of-life outcomes in adults with single-sided deafness (SSD) who underwent cochlear implantation.
PubMed, MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Web of Science, and Scopus databases were searched from January 2008 to September 2021 following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.
Studies reporting spatial hearing, tinnitus, and quality-of-life outcomes in adult cochlear implant (CI) recipients (≥18 yr old) with SSD were evaluated. Study characteristics, demographic data, spatial hearing (speech recognition in noise, sound source localization), tinnitus (severity, loudness), and quality-of-life outcomes were collected.
From an initial search of 1,147 articles, 36 studies that evaluated CI use in 796 unique adults with SSD (51.3 ± 12.4 yr of age at time of implantation) were included. The mean duration of deafness was 6.2 ± 9.6 years. There was evidence of improvement for speech recognition in noise using different target-to-masker spatial configurations, with the largest benefit observed for target-to-masker configurations assessing head shadow (mean, 1.87-6.2 dB signal-to-noise ratio). Sound source localization, quantified as root-mean-squared error, improved with CI use (mean difference [MD], -25.3 degrees; 95% confidence interval [95% CI], -35.9 to -14.6 degrees; p < 0.001). Also, CI users reported a significant reduction in tinnitus severity as measured with the Tinnitus Handicap Inventory (MD, -29.97; 95% CI, -43.9 to -16.1; p < 0.001) and an improvement in spatial hearing abilities as measured with the Spatial, Speech, and Qualities of Hearing questionnaire (MD, 2.3; 95% CI, 1.7 to 2.8; p < 0.001).
Cochlear implantation and CI use consistently offer improvements in speech recognition in noise, sound source localization, tinnitus, and perceived quality of life in adults with SSD.

Patients with single-sided deafness can experience an ipsilateral disabling tinnitus that has a major impact on individuals\' social communication and quality of life. Cochlear implants appear to be superior to conventional treatments to alleviate tinnitus in single-sided deafness. We conducted a systematic review to evaluate the effectiveness of cochlear implants in single-sided deafness with disabling tinnitus when conventional treatments fail to alleviate tinnitus (PROSPERO ID: CRD42022353292). All published studies in PubMed/MEDLINE and SCOPUS databases until December 2021 were included. A total of 474 records were retrieved, 31 studies were included and were divided into two categories according to whether tinnitus was assessed as a primary complaint or not. In all studies, cochlear implantation, evaluated using subjective validated tools, succeeded in reducing tinnitus significantly. Objective evaluation tools were less likely to be used but showed similar results. A short-(3 months) and long-(up to 72 months) term tinnitus suppression was reported. When the cochlear implant is disactivated, complete residual tinnitus inhibition was reported to persist up to 24 h. The results followed a similar pattern in studies where tinnitus was assesed as a primary complaint or not. In conclusion, the present review confirmed the effectiveness of cochlear implantation in sustainably reducing disabling tinnitus in single-sided deafness patients.

OBJECTIVE: This review article reviews the contemporary studies of localization ability for different populations in different listening environments and provides possible future research directions.
CONCLUSIONS: The ability to accurately localize a sound source relying on three cues (interaural time difference, interaural level difference, and spectral cues) is important for communication, learning, and safety. Confounding effects including noise and reverberation, which exist in common listening environments, mask or alter localization cues and negatively affect localization performance. Hearing loss, a common public health issue, also affects localization accuracy. Although hearing devices have been developed to provide excellent audibility of speech signals, less attention has been paid to preserving and replicating crucial localization cues. Unique challenges are faced by users of various hearing devices, including hearing aids, bone-anchored hearing instruments, and cochlear implants. Hearing aids have failed to consistently improve localization performance and, in some cases, significantly impair sound localization. Bone-conduction hearing instruments show little to no benefit for sound localization performance in most cases, although some improvement is seen in binaural users. Although cochlear implants provide great hearing benefit to individuals with severe-to-profound sensorineural hearing loss, cochlear implant users have significant difficulty localizing sound, even with two implants. However, technologies in each of these areas are advancing to reduce interference with desired sound signals and preserve localization cues to help users achieve better hearing and sound localization in real-life environments.

To prevent intensive noise exposure in advance and be safely controlled during such exposure, hearing protection devices (HPDs) have been widely used by workers. The present study evaluates the effectiveness of these HPDs, partitioned into three different outcomes, such as sound attenuation, sound localization, and speech perception. Seven electronic journal databases were used to search for published articles from 2000 to 2021. Based on inclusion criteria, 20 articles were chosen and then analyzed. For a systematic review and meta-analysis, standardized mean differences (SMDs) and effect size were calculated using a random-effect model. The funnel plot and Egger\'s regression analysis were conducted to assess the risk of bias. From the overall results of the included 20 articles, we found that the HPD function performed significantly well for their users (SMDs: 0.457, 95% confidence interval (CI): 0.034-0.881, p < 0.05). Specifically, a subgroup analysis showed a meaningful difference in sound attenuation (SMDs: 1.080, 95% CI: 0.167-1.993, p < 0.05) when to wear and not to wear HPDs, but indicated no significance between the groups for sound localization (SMDs: 0.177, 95% CI: 0.540-0.894, p = 0.628) and speech perception (SMDs: 0.366, 95% CI: -0.100-1.086, p = 0.103). The HPDs work well for their originally designated purposes without interfering to find the location of the sound sources and for talking between the workers. Taking into account various factors, such as the characteristics of the users, selection of appropriate types, and fitting methods for wearing in different circumstances, seems to be necessary for a reliable systematic analysis in terms of offering the most useful information to the workers.

In 2019, the US Food and Drug Administration approved cochlear implantation for children with single-sided deafness (SSD). The absence of robust clinical data specific to pediatric patients to guide shared decision-making and to identify potential advantages is a challenge in family counseling.
To evaluate the audiological and patient-reported outcomes in children who underwent cochlear implantation for SSD and to assess the association between time of implantation, subjective outcomes, and cochlear implant device use rates.
MEDLINE, Embase, Scopus, Cochrane, and PubMed were searched for English-language articles that were published in a peer-reviewed journal from database inception to February 18, 2020.
Inclusion criteria were designed to capture studies that evaluated pediatric patients (1) younger than 18 years, (2) with a diagnosis of SSD for which they underwent a cochlear implantation, and (3) with at least 1 outcome of interest measured numerically: speech perception, sound localization, device use, and patient-reported outcomes. Of the 526 articles reviewed, 12 (2.3%) met the selection criteria.
The Meta-analyses Of Observational Studies in Epidemiology (MOOSE) reporting guidelines were followed. Data were pooled using fixed-effect and random-effect models. The following information was obtained from each article: study characteristics, patient characteristics, hearing loss and intervention characteristics, and outcomes.
Outcomes were (1) postoperative changes in speech perception (in quiet was measured as a proportion of correct responses, and in noise was measured as decibel signal to noise ratio for speech reception threshold) and sound localization (measured in degree of localization error), (2) patient-reported audiological outcomes (measured by the speech, spatial, and qualities of hearing scale), and (3) device use rates among children who received cochlear implantation for SSD.
Twelve observational studies that evaluated 119 children (mean [SD] age, 6.6 [4.0] years) with SSD who received a cochlear implant were included. Most children showed clinically meaningful improvement in speech perception in noise (39 of 49 children [79.6%]) and in quiet (34 of 42 children [81.0%]). Long duration of deafness (>4 years in congenital SSD and >7 years in perilingual SSD) was the most commonly proposed reason for lack of improvement. Sound localization as measured by degrees of error from true location (mean difference [MD], -24.78°; 95% CI, -34.16° to -15.40°; I2 = 10%) improved statistically significantly after cochlear implantation. Patients with acquired SSD and shorter duration of deafness compared with those with congenital SSD reported greater improvements in speech (MD, 2.27; 95% CI, 1.89-2.65 vs 1.58; 95% CI, 1.00-2.16) and spatial (MD, 2.95; 95% CI, 2.66-3.24 vs 1.68; 95% CI, 0.96-2.39) hearing qualities. The duration of deafness among device nonusers was statistically significantly longer than the duration of deafness among regular device users (median difference, 6.84; 95% CI, 4.02-9.58).
This systematic review and meta-analysis found that cochlear implantation for children with SSD was associated with clinically meaningful improvements in audiological and patient-reported outcomes; shorter duration of deafness may lead to better outcomes. These findings can guide future research efforts, refine cochlear implantation candidacy criteria, and aid in family counseling and shared decision-making.