Binaural Processing Research Articles

Improved binaural speech reception thresholds through small symmetrical separation of speech and noise.

Speech perception in noise is challenging and is improved by binaural hearing. Since signal processing of assistive hearing devices often modifies or masks the peripheral binaural head-shadow or better-ear effects, central binaural processing should be measured separately. In a prospective study, 10 listeners with normal hearing were tested with the German matrix sentence test in a set-up with two loudspeakers located at opposite angles in the horizontal plane with respect to S0N0. The speech reception threshold (SRT) was investigated depending on the separation angle between speech and noise. The lowest (best) SRT was obtained for a separation of target and interfering source from S0N0 at an angle of about S±60°N∓60°. The derived normative curve was comparable to SRTs predicted by the binaural-speech-intelligibility-model. The systematic separation of signal and noise showed a significant improvement in speech intelligibility for normal-hearing people even for small separation angles. This experimental setting was verified. This study aimed to assess the effect of small sound source separation on binaural hearing and speech perception.

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.

Binaural Interaction in Tinnitus Patients

The auditory brainstem response (ABR) is a commonly used objective clinical measure for hearing evaluation. It can be also used to draw conclusions about the functioning of distinct stages of the auditory pathway including the binaural processing stages using the binaural interaction component (BIC) of the ABR. Objective: To study binaural processing in normal hearing subjects complaining of tinnitus. Methods: Sixty cases with bilateral normal peripheral hearing were included in this work, divided into 2 groups, i.e., group 1 (comprised of 30 healthy subjects representing the control group) and group 2 (comprised of 30 subjects with tinnitus representing the study group). All of the subjects were submitted to a basic audiological evaluation (including pure tone audiometry, speech audiometry, and immittancemetry) and ABR audiometry recorded in monaural and then binaural conditions. Results: In monaural recording, the tinnitus group showed significantly delayed latencies of waves I, III, and V in addition to significantly reduced wave I and III amplitudes when compared with the controls. Similar significant findings were found when binaural ABR responses were compared between both groups. Comparing BIC between both groups showed significant earlier BIC for latencies of waves I and V in the control group, while the BIC for amplitudes showed similar results in both groups. Conclusions: These finding suggest the presence of binaural processing deficits in tinnitus patients at different levels along the ascending auditory pathway.

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.

Event related potentials in cases of amblyaudia

<p class="abstract"><strong>Background:</strong> Amblyaudia is a weakness in the listener’s binaural processing of auditory information. Subjects with amblyaudia also demonstrate binaural integration deficits and may display similar patterns in their evoked responses in terms of latency and amplitude of these responses. The purpose of this study was to identify the presence of amblyaudia in a population of young children subjects and to measure mismatch negativity (MMN), P300 and cortical auditory evoked potentials (CAEPs) for those individuals.</p><p class="abstract"><strong>Methods:</strong> Subjects included in this study were divided into 2 groups control group that consisted of 20 normal hearing subjects with normal developmental milestones and normal speech development. The study group (GII) consisted of 50 subjects with central auditory processing disorders (CAPDs) diagnosed by central auditory screening tests. </p><p class="abstract"><strong>Results:</strong> With using dichotic tests including dichotic digits test (DDT) and competing sentence test (CST), we could classify these cases into normal, dichotic dysaudia, amblyaudia, and amblyaudia plus with percentages (40%, 14%, 38%, 8% respectively). Using event related potentials, we found that P300 and MMN are more specific in detecting neurocognitive dysfunction related to allocation of attentional resources and immediate memory in these cases.</p><p class="abstract"><strong>Conclusions:</strong> The presence of amblyaudia in cases of central auditory processing disorders (CAPDs) and event related potentials is an objective tool for diagnosis, prognosis and follow up after rehabilitation.</p>

Binaural interaction component in auditory evoked potentials: characteristics and potential applications in audiology

Background and Aim: Since the first report of recording the binaural interaction component (BIC) in 1970, many studies have been con­ducted on BIC but none of them make its way to clinical application yet. The present paper aims at reviewing the characteristics and potential applications of BIC in audiology. Recent Findings: BIC may be a potentially sensitive objective tool in identifying subjects with auditory processing disorders and moni­toring auditory training effects. It can also help effective electrode insertion in bilateral cochlear implantation. Besides, BIC has shed light on the binaural processing maturation in infants. BIC recoding faces some difficulties as it is sensitive to noise and presentation rate, and has low amp­litude, especially in brainstem level. These iss­ues might contribute to its limited clinical app­lications. Conclusion: Although BIC has not been int­roduced as an objective tool for testing binaural processing, it has the potential to be a reliable test. Furthermore, BIC may be used in situations where no behavioral test can be conducted. Such circumstances are during cochlear implan­tation or testing uncooperative pre-school chil­dren for auditory processing or the lack of standard behavioral tests for them. Further res­earch on BIC is highly recommended before it can gain any clinical application. Keywords: Binaural interaction; cochlear implant; spatial processing; auditory processing

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

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. 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. 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. 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.

Robust Data-Driven Auditory Profiling Towards Precision Audiology.

The sources and consequences of a sensorineural hearing loss are diverse. While several approaches have aimed at disentangling the physiological and perceptual consequences of different etiologies, hearing deficit characterization and rehabilitation have been dominated by the results from pure-tone audiometry. Here, we present a novel approach based on data-driven profiling of perceptual auditory deficits that attempts to represent auditory phenomena that are usually hidden by, or entangled with, audibility loss. We hypothesize that the hearing deficits of a given listener, both at hearing threshold and at suprathreshold sound levels, result from two independent types of “auditory distortions.” In this two-dimensional space, four distinct “auditory profiles” can be identified. To test this hypothesis, we gathered a data set consisting of a heterogeneous group of listeners that were evaluated using measures of speech intelligibility, loudness perception, binaural processing abilities, and spectrotemporal resolution. The subsequent analysis revealed that distortion type-I was associated with elevated hearing thresholds at high frequencies and reduced temporal masking release and was significantly correlated with elevated speech reception thresholds in noise. Distortion type-II was associated with low-frequency hearing loss and abnormally steep loudness functions. The auditory profiles represent four robust subpopulations of hearing-impaired listeners that exhibit different degrees of perceptual distortions. The four auditory profiles may provide a valuable basis for improved hearing rehabilitation, for example, through profile-based hearing-aid fitting.

The Binaural Interaction Component of the Auditory Brainstem Response Under Precedence Effect Conditions.

The purpose of this study was to measure the binaural interaction component (BIC) derived from click-evoked auditory brainstem responses (ABRs) using stimuli configured to elicit the Precedence Effect. The hypothesis was that the contribution of binaural processing to echo suppression can be evidenced by a diminished or absent BIC associated with the echo. Ten normal-hearing young adults provided ABRs generated by sequences of click pairs. Results showed that BICs elicited by diotic clicks in isolation were obliterated when those diotic clicks were preceded by a click pair having an interaural time difference of 400 µs and where the interclick interval was 8.4 ms. The presence of the leading click pair increased the latency of the ABR generated by the lagging diotic click pair but did not decrease its amplitude. The results were interpreted as indicating a contribution of binaural processing at the level of the brainstem to echo suppression, at least for the conditions tested here.

Binaural interaction component of the auditory brainstem response in children with autism spectrum disorder

IntroductionThere is ample evidence that auditory dysfunction is a common feature of autism spectrum disorder (ASD). Binaural interaction component (BIC) manifests binaural interaction and is valid and proven response which reflects ongoing binaural processing. ObjectivesTo investigate the differences in binaural interaction component of auditory brainstem response (ABR-BIC) between children with autism spectrum disorder (ASD) and normal peers and to correlate between ABR-BIC amplitudes and the acquired communication skills in ASD children. MethodsASD was diagnosed according to the criteria of 5th edition of diagnostic and statistical manual of mental disorders (DSM-V) and all children with ASD underwent test of acquired communication skills (TACS). Click evoked ABRs were elicited by left monaural, right monaural and binaural stimulation at intensity of 65 dBnHL in all participants. ABR-BIC was then calculated as the difference between the binaurally evoked ABR waveform and a predicted binaural waveform created by algebraically summing the left and right monaurally evoked ABRs. The difference in amplitudes that gives rise to ABR-BIC is at IV-VI waves. ResultsABR-BIC amplitudes were demonstrated to be significantly reduced in the ASD group compared to the control group. There was significant positive correlation between ABR-BIC amplitude and the language and social scores in TACS. ConclusionThis study provided an objective evidence of binaural processing disorder in children with ASD.

A combined bilateral and binaural active noise control algorithm for closed-back headphones

Commercial noise-cancelation headphones are based on active noise control (ANC) algorithm. However, all existing ANC headphones are based on bilateral ANC approach, where two independent monaural ANC systems are used respectively for the left and the right ear cups. The performance of bilateral ANC approach strictly depends on the number of noise sources, direction of noise sources and noise types. Its performance decreases when the number of noise sources increases. Human’s hearing system is binaural in nature and noise control can take advantage of binaural processing to further enhance noise reduction compared to conventional bilateral ANC headphones. In this paper, we first propose a binaural ANC algorithm to evaluate its performance over the bilateral ANC algorithm and subsequently, modify into a combined bilateral-binaural ANC (CBBANC) algorithm for headphones in order to improve noise reduction performance for different cases when there are more than one noise sources and all noise sources are situated at different locations and for diffuse field noise. Experimentation results show that the combined binaural-bilateral ANC has better performance in all our tests compared to the conventional bilateral ANC headphones.

Effects of rate and age in processing interaural time and level differences in normal-hearing and bilateral cochlear-implant listeners.

Bilateral cochlear implants (BICIs) provide improved sound localization and speech understanding in noise compared to unilateral CIs. However, normal-hearing (NH) listeners demonstrate superior binaural processing abilities compared to BICI listeners. This investigation sought to understand differences between NH and BICI listeners' processing of interaural time differences (ITDs) and interaural level differences (ILDs) as a function of fine-structure and envelope rate using an intracranial lateralization task. The NH listeners were presented band-limited acoustical pulse trains and sinusoidally amplitude-modulated tones using headphones, and the BICI listeners were presented single-electrode electrical pulse trains using direct stimulation. Lateralization range increased as fine-structure rate increased for ILDs in BICI listeners. Lateralization range decreased for rates above 100 Hz for fine-structure ITDs, but decreased for rates lower or higher than 100 Hz for envelope ITDs in both groups. Lateralization ranges for ITDs were smaller for BICI listeners on average. After controlling for age, older listeners showed smaller lateralization ranges and BICI listeners had a more rapid decline for ITD sensitivity at 300 pulses per second. This work suggests that age confounds comparisons between NH and BICI listeners in temporal processing tasks and that some NH-BICI binaural processing differences persist even when age differences are adequately addressed.

Human Frequency Following Response Correlates of Spatial Release From Masking.

Purpose Speech recognition in complex listening environments is enhanced by the extent of spatial separation between the speech source and background competing sources, an effect known as spatial release from masking (SRM). The aim of this study was to investigate whether the phase-locked neural activity in the central auditory pathways, reflected in the frequency following response (FFR), exhibits SRM. Method Eighteen normal-hearing adults (8 men and 10 women, ranging in age from 20 to 42 years) with no known neurological disorders participated in this study. FFRs were recorded from the participants in response to a target vowel /u/ presented with spatially colocated and separated competing talkers at 3 ranges of signal-to-noise ratios (SNRs), with median SNRs of -5.4, 0.5, and 6.8 dB and for different attentional conditions (attention and no attention). Results Amplitude of the FFR at the fundamental frequency was significantly larger in the spatially separated condition as compared to the colocated condition for only the lowest (< -2.4 dB SNR) of the 3 SNR ranges tested. A significant effect of attention was found when subjects were actively focusing on the target stimuli. No significant interaction effects were found between spatial separation and attention. Conclusions The enhanced representation of the target stimulus in the separated condition suggests that the temporal pattern of phase-locked brainstem neural activity generating the FFR may contain information relevant to the binaural processes underlying SRM but only in challenging listening environments. Attention may modulate FFR fundamental frequency amplitude but does not seem to modulate spatial processing at the level of generating the FFR. Supplemental Material https://doi.org/10.23641/asha.9992597.

Binaural processing and phonological awareness in Australian Indigenous children from the Northern Territory: A community based study

ObjectiveResearch has found that otitis media (OM) is highly prevalent in Australian Indigenous children, and repeated bouts of OM is often associated with minimal-to-moderate hearing loss. However, what is not yet clear is the extent to which OM with hearing loss impacts auditory signal processing specifically, but also binaural listening, listening in noise, and the potential impact on phonological awareness (PA) – an important, emergent literacy skill. The goal of this study was to determine whether auditory abilities, especially binaural processing, were associated with PA in children from populations with a high incidence of OM, living in a remote Australian Indigenous community in the Northern Territory (NT). MethodsForty-seven 5-12-year-olds from a bilingual school participated in the study. All were tested to determine hearing sensitivity (pure tone audiometry and tympanometry), with PA measured on a test specifically developed in the first language of the children. OM often results in a hearing loss that can affect binaural processing: the Dichotic Digit difference Test (DDdT) was used to evaluate the children's dichotic listening and the Listening in Spatialized Noise-sentences test (LiSN-S) was used to evaluate their abilities to listen to speech-in-noise. ResultsSeventeen (36%) and 16 (34%) had compromised middle ear compliance (combined Type-B and –C) in the right and left ear respectively. Six children demonstrated a bilateral mild hearing loss, and another five children demonstrated a unilateral mild hearing loss. Thirty-one children were able to complete the DDdT listening task, whereas only 24 completed the speech in noise task (LiSN-S). Forty-four children (94%) were able to complete the letter identification subtask, comprising part of the PA task. The findings revealed that age was significantly correlated with all tasks such that the older children performed better across the board. Once hearing thresholds were controlled for, PA also correlated significantly with both binaural processing tasks of dichotic listening (r = 0.59, p < 0.001) and listening to speech in noise (r = −0.56, p = 0.005); indicating a potential association between early, emergent literacy and listening skills. ConclusionsThe significant correlations between phonological awareness and dichotic listening as well as phonological awareness with listening to speech-in-noise skills suggests auditory processing, rather than hearing thresholds per se, are associated to phonological awareness abilities of this cohort of children. This suggests that the ability to process the auditory signal is critical.

Dichotic listening processing in patients with multiple sclerosis

Background and Aim: Dichotic listening dis­orders occur secondary to interhemispheric tran­sfer dysfunction. Central processing tests such as staggered spondaic words (SSW) and dich­otic digits test (DDT) are recommended for the evaluation of dichotic listening in patients with multiple sclerosis (MS). The present study aim­ed to evaluate dichotic listening in subjects with MS by SSW and DDT. Methods: This cross-sectional study was con­ducted on 45 patients with MS, including 20 males (mean ± SD age: 35.95 ± 5.73 y) and 25 females (mean ± SD age: 37.40 ± 6.1 y) and their data were collected by the Persian version of SSW (P-SSW) and DDT. The results com­pared to 45 normal subjects age- and gender-matched as the control group. Results: In patients with MS, P-SSW quanti­tative and qualitative errors (except for Sm2 and reversals), errors were significantly more than the control group (p ≤ 0.001). Right and left ear scores in DDT for the patients with MS were significantly lower, and right ear advantage was significantly higher than that in the control group (p ≤ 0.001). The results also showed a significant correlation between the test of P-SSW and DDT in the left ear. Conclusion: The present study showed that patients with MS hav * Corresponding author: Department of Audiology, School of Rehabilitation, Tehran University of Medical Sciences, Piche-Shemiran, Enghelab Ave., Tehran, 1148965141, Iran. Tel: 009821-77530636, E-mail: s_farahani@tums.ac.ir e lower performance in dichotic listening and binaural processing than normal peers. Identification of binaural proce­ssing deficit in patients with MS may lead to early rehabilitation and improving their function by facilitating auditory processing.

Neural Mechanisms of Binaural Processing in the Auditory Brainstem.

Spatial hearing, and more specifically the ability to localize sounds in space, is one of the most studied and best understood aspects of hearing. Because there is no coding of acoustic space at the receptor organ, physiological sensitivity to spatial aspects of sounds first emerges in the central nervous system. Much progress has been made in the identification and characterization of the circuits in the auditory brainstem that create sensitivity to binaural and monaural cues toward acoustic space. We review the progress over the past third of a century, with a focus on the mammalian brainstem and on the anatomy and cellular physiology underlying the physiological tuning of monaural and binaural circuits to acoustic cues toward spatial hearing. In addition to examining the detailed mechanisms involved in the processing of the three main spatial cues, we also review the integration of these cues and their use toward behavior. © 2019 American Physiological Society. Compr Physiol 9:1503-1575, 2019.

The effect of envelope modulations on binaural processing

An experiment was performed with 10 young normal-hearing listeners that attempted to determine if envelope modulations affected binaural processing in bandlimited pulse trains. Listeners detected an interaurally out-of-phase carrier pulse train in the presence of different amplitude modulations. The peaks of the pulses were constant (called “flat” or F), followed envelope modulations from an interaurally correlated 50-Hz bandwidth noise (called CM), or followed modulations from an interaurally uncorrelated noise (called UM). The pulse rate was varied from 50 to 500 pulses per second (pps) and the center frequency (CF) was 4 or 8 kHz. It was hypothesized that CM would cause no change or an increase in performance compared to F; UM would cause a decrease because of the blurring of the binaural detection cue. There was a small but significant decrease from F to CM (inconsistent with the hypothesis) and a further decrease from CM to UM (consistent with the hypothesis). Critically, there was a significant envelope by rate interaction caused by a decrease from F to CM for the 200–300 pps rates. The data can be explained by a subject-based factor, where some listeners experienced interaural envelope decorrelation when the sound was encoded by the auditory system that reduced performance when the modulations were present. Since the decrease in performance between F and CM conditions was small, it seems that most young normal-hearing listeners have very similar encoding of modulated stimuli across the ears. This type of task, when further optimized, may be able to assess if hearing-impaired populations experience interaural decorrelation from encoding modulated stimuli and therefore could help better understand the limited spatial hearing in populations like cochlear-implant users.

Redundant Information Is Sometimes More Beneficial Than Spatial Information to Understand Speech in Noise.

To establish a framework to unambiguously define and relate the different spatial effects in speech understanding: head shadow, redundancy, squelch, spatial release from masking (SRM), and so on. Next, to investigate the contribution of interaural time and level differences to these spatial effects in speech understanding and how this is influenced by the type of masking noise. In our framework, SRM is uniquely characterized as a linear combination of head shadow, binaural redundancy, and binaural squelch. The latter two terms are combined into one binaural term, which we define as binaural contrast: a benefit of interaural differences. In this way, SRM is a simple sum of a monaural and a binaural term. We used the framework to quantify these spatial effects in 10 listeners with normal hearing. The participants performed speech intelligibility tasks in different spatial setups. We used head-related transfer functions to manipulate the presence of interaural time and level differences. We used three spectrally matched masker types: stationary speech-weighted noise, a competing talker, and speech-weighted noise that was modulated with the broadband temporal envelope of the competing talker. We found that (1) binaural contrast was increased by interaural time differences, but reduced by interaural level differences, irrespective of masker type, and (2) large redundancy (the benefit of having identical information in two ears) could reduce binaural contrast and thus also reduce SRM. Our framework yielded new insights in binaural processing in speech intelligibility. First, interaural level differences disturb speech intelligibility in realistic listening conditions. Therefore, to optimize speech intelligibility in hearing aids, it is more beneficial to improve monaural signal-to-noise ratios rather than to preserve interaural level differences. Second, although redundancy is mostly ignored when considering spatial hearing, it might explain reduced SRM in some cases.

The frequency-following response as an assessment of spatial processing

Objective: It is important to detect children with difficulties distinguishing speech-in-noise early. Prompt identification may be assisted by an evoked potential. The aims of the present study were: 1) to evaluate the frequency-following response (FFR) as a measure of binaural processing and spatial listening and, 2) to investigate the relationship between the FFR and a behavioural measure of binaural processing and spatial listening.Design: A single group, repeated measures design. The FFR was recorded in two different spatial conditions and amplitudes compared to spatial listening ability.Study Sample: Thirty-two children (aged 6.0 to 13.1 years) with a range of spatial processing abilities as measured behaviourally using the Listening in Spatialised Noise Sentences test (LiSN-S).Results: FFR waveforms were elicited using speech-like stimuli in co-located and separated conditions. A significant (p≤0.005) spatial advantage effect was observed with larger amplitudes in the separated condition. No correlations were observed between FFR amplitude and LiSN-S results.Conclusions: The FFR shows promise as a measure of binaural processing and spatial listening, but could be measuring different processes to those measured by the LiSN-S.

No more than “slight” hearing loss and degradations in binaural processing

Listeners having, at most, "slight" hearing loss may exhibit substantial deficits in binaural detection [Bernstein and Trahiotis. (2016). J. Acoust. Soc. Am. 140, 3540-3548; (2018). J. Acoust. Soc. Am. 144, 292-307]. This study assessed whether such listeners also exhibit deficits discriminating interaural temporal disparities (ITDs) or interaural intensitive disparities (IIDs) and whether any deficits observed in those discrimination tasks would be accounted for by the interaural cross-correlation based model that successfully accounts for binaural detection. Thresholds were measured for detection of tones masked by noise in the NoSπ configuration and discrimination of ITD or IID. Gaussian noises (100 Hz-wide), served as maskers in the detection task and as reference and target stimuli in the discrimination tasks. Stimuli were centered at 500 Hz or 4 kHz. The latter were transpositions of stimuli centered at 125 Hz. Results demonstrate that listeners having, at most, slight hearing loss and who exhibit deficits in binaural detection, also exhibit deficits in ITD- and IID-discrimination. Coupled with appropriate decision variables, the cross-correlation-based model that accounts for elevated binaural detection thresholds among such listeners also accounted for their elevated ITD- and IID-thresholds. The deficits in all three tasks appear to stem from increased levels of stimulus-dependent, additive internal noise.