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Normal-hearing (NH) listeners rely on two binaural cues, the interaural time (ITD) and level difference (ILD), for azimuthal sound localization. Cochlear-implant (CI) listeners, however, rely almost entirely on ILDs. One reason is that present-day clinical CI stimulation strategies do not convey salient ITD cues. But even when presenting ITDs under optimal conditions using a research interface, ITD sensitivity is lower in CI compared to NH listeners. Since it has recently been shown that NH listeners change their ITD/ILD weighting when only one of the cues is consistent with visual information, such reweighting might add to CI listeners’ low perceptual contribution of ITDs, given their daily exposure to reliable ILDs but unreliable ITDs. Six bilateral CI listeners completed a multi-day lateralization training visually reinforcing ITDs, flanked by a pre- and post-measurement of ITD/ILD weights without visual reinforcement. Using direct electric stimulation, we presented 100- and 300-pps pulse trains at a single interaurally place-matched electrode pair, conveying ITDs and ILDs in various spatially consistent and inconsistent combinations. The listeners’ task was to lateralize the stimuli in a virtual environment. Additionally, ITD and ILD thresholds were measured before and after training. For 100-pps stimuli, the lateralization training increased the contribution of ITDs slightly, but significantly. Thresholds were neither affected by the training nor correlated with weights. For 300-pps stimuli, ITD weights were lower and ITD thresholds larger, but there was no effect of training. On average across test sessions, adding azimuth-dependent ITDs to stimuli containing ILDs increased the extent of lateralization for both 100- and 300-pps stimuli. The results suggest that low-rate ITD cues, robustly encoded with future CI systems, may be better exploitable for sound localization after increasing their perceptual weight via training.

Purpose The purpose of this study was to characterize spatial hearing abilities of children with longstanding unilateral hearing loss (UHL). UHL was expected to negatively impact children's sound source localization and masked speech recognition, particularly when the target and masker were separated in space. Spatial release from masking (SRM) in the presence of a two-talker speech masker was expected to predict functional auditory performance as assessed by parent report. Method Participants were 5- to 14-year-olds with sensorineural or mixed UHL, age-matched children with normal hearing (NH), and adults with NH. Sound source localization was assessed on the horizontal plane (−90° to 90°), with noise that was either all-pass, low-pass, high-pass, or an unpredictable mixture. Speech recognition thresholds were measured in the sound field for sentences presented in two-talker speech or speech-shaped noise. Target speech was always presented from 0°; the masker was either colocated with the target or spatially separated at ±90°. Parents of children with UHL rated their children's functional auditory performance in everyday environments via questionnaire. Results Sound source localization was poorer for children with UHL than those with NH. Children with UHL also derived less SRM than those with NH, with increased masking for some conditions. Effects of UHL were larger in the two-talker than the noise masker, and SRM in two-talker speech increased with age for both groups of children. Children with UHL whose parents reported greater functional difficulties achieved less SRM when either masker was on the side of the better-hearing ear. Conclusions Children with UHL are clearly at a disadvantage compared with children with NH for both sound source localization and masked speech recognition with spatial separation. Parents' report of their children's real-world communication abilities suggests that spatial hearing plays an important role in outcomes for children with UHL.

Bilateral cochlear implants (BI-CIs) or a CI for single-sided deafness (SSD-CI; one normally functioning acoustic ear) can partially restore spatial-hearing abilities, including sound localization and speech understanding in noise. For these populations, however, interaural place-of-stimulation mismatch can occur and thus diminish binaural sensitivity that relies on interaurally frequency-matched neurons. This study examined whether plasticity—reorganization of central neural pathways over time—can compensate for peripheral interaural place mismatch. We hypothesized differential plasticity across two systems: none for binaural processing but adaptation for pitch perception toward frequencies delivered by the specific electrodes. Interaural place mismatch was evaluated in 19 BI-CI and 23 SSD-CI human subjects (both sexes) using binaural processing (interaural-time-difference discrimination with simultaneous bilateral stimulation), pitch perception (pitch ranking for single electrodes or acoustic tones with sequential bilateral stimulation), and physical electrode-location estimates from computed-tomography (CT) scans. On average, CT scans revealed relatively little BI-CI interaural place mismatch (26° insertion-angle mismatch) but a relatively large SSD-CI mismatch, particularly at low frequencies (166° for an electrode tuned to 300 Hz, decreasing to 14° at 7000 Hz). For BI-CI subjects, the three metrics were in agreement because there was little mismatch. For SSD-CI subjects, binaural and CT measurements were in agreement, suggesting little binaural-system plasticity induced by mismatch. The pitch measurements disagreed with binaural and CT measurements, suggesting place-pitch plasticity or a procedural bias. These results suggest that reducing interaural place mismatch and potentially improving binaural processing by reprogramming the CI frequency allocation would be better done using CT-scan than pitch information.SIGNIFICANCE STATEMENTElectrode-array placement for cochlear implants (bionic prostheses that partially restore hearing) does not explicitly align neural representations of frequency information. The resulting interaural place-of-stimulation mismatch can diminish spatial-hearing abilities. In this study, adults with two cochlear implants showed reasonable interaural alignment, whereas those with one cochlear implant but normal hearing in the other ear often showed mismatch. In cases of mismatch, binaural sensitivity was best when the same cochlear locations were stimulated in both ears, suggesting that binaural brainstem pathways do not experience plasticity to compensate for mismatch. In contrast, interaurally pitch-matched electrodes deviated from cochlear-location estimates and did not optimize binaural sensitivity. Clinical correction of interaural place mismatch using binaural or computed-tomography (but not pitch) information may improve spatial-hearing benefits.

This study describes data on auditory-visual integration and visually-guided adaptation of auditory distance perception using the ventriloquism effect (VE) and ventriloquism aftereffect (VAE). In an experiment, participants judged egocentric distance of interleaved auditory or auditory-visual stimuli with the auditory component located from 0.7 to 2.04 m in front of listeners in a real reverberant environment. The visual component of auditory-visual stimuli was displaced 30% closer (V-closer), 30% farther (V-farther), or aligned (V-aligned) with respect to the auditory component. The VE and VAE were measured in auditory and auditory-visual trials, respectively. Both effects were approximately independent of target distance when expressed in logarithmic units. The VE strength, defined as a difference of V-misaligned and V-aligned response bias, was approximately 72% of the auditory-visual disparity regardless of the visual-displacement direction, while the VAE was stronger in the V-farther (44%) than the V-closer (31%) condition. The VAE persisted to post-adaptation auditory-only blocks of trials, although it was diminished. The rates of build-up/break-down of the VAE were asymmetrical, with slower adaptation in the V-closer condition. These results suggest that auditory-visual distance integration is independent of the direction of induced shift, while the re-calibration is stronger and faster when evoked by more distant visual stimuli.

INTRODUCTION A new external, adhesive, no-pressure bone-conduction device provides rehabilitation for conductive hearing loss and single-sided deafness (SSD). The purpose of the study is to evaluate speech recognition performance with the bone-conduction contralateral routing of signal (aBC-CROS) and compare it to an air-conduction CROS (AC-CROS) used by subjects for at least 1 year. METHODS Ten SSD patients underwent speech understanding in noise tests with their AC-CROS, the aBC-CROS, and unaided. The 1st test session took place the day the aBC-CROS was fitted, with the second session after 2 weeks of aBC-CROS use. Two configurations were used: speech presented on the deaf side and noise on the normal side and the reverse. RESULTS The speech recognition threshold (SRT) improved with both devices when speech was presented to the deaf side. Nine patients showed significant improvement (p

A new non-invasive adhesive bone conduction hearing device (ABCD) has been proposed as an alternative solution for reversible bilateral conductive hearing loss in recurrent or long-lasting forms of otitis media with effusion (OME) in children that cannot undergo surgical treatment. Our aim was to assess the effectiveness of ABCD in children with OME. Twelve normal-hearing Italian-speaking volunteers, in whom a conductive hearing loss was simulated, participated in the study. The free-field average hearing threshold was determined and, to evaluate binaural hearing skills, loudness summation and the squelch effect were assessed. Five conditions were tested: (1) unaided without earplugs, (2) unaided with bilateral earplugs, (3) aided right ear with bilateral earplugs, (4) aided left ear with bilateral earplugs, and (5) bilateral aid with bilateral earplugs. Post-hoc analysis showed a significant statistical difference between plugged, unplugged, and each aided condition. The main results were a better loudness summation and a substantial improvement of the squelch effect in the bilaterally aided. Our results suggest that ABCD is a valid treatment for patients with conductive hearing loss that cannot undergo bone conduction implant surgery. It is also important to consider bilateral aids in order to deal with situations in which binaural hearing is fundamental.

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.

Directionality is the only hearing aid technology — in addition to amplification — proven to help hearing aid users hear better in noise. Hearing aid directionality has been documented to improve speech intelligibility in multiple laboratory studies. In contrast, real-world studies have shown a disconnect between the potential of the technology and what hearing aid users experience in their daily life. This article describes the real-world studies that inspired ReSound to take a different approach to applying directional microphone technology. This approach is based on the idea that hearing aid directionality can leverage natural binaural hearing and inherent listening strategies. The directional strategy includes three listening modes that will be explained. These are the Spatial Cue Preservation mode, the Binaural Listening mode, and the Speech Intelligibility mode. The strategy and the advantages it provides in terms of sound quality, spatial hearing, and improved signal-to-noise ratio with maintained awareness of surroundings are explained.

Neuroscientific and clinical studies on auditory perception often use headphones to limit sound interference. In these conditions, sounds are perceived as internalized because they lack the sound-attributes that normally occur with a sound produced from a point in space around the listener. Without the spatial attention mechanisms that occur with localized sounds, auditory functional assessments could thus be underestimated. We hypothesize that adding virtually externalization and localization cues to sounds through headphones enhance sound discrimination in both healthy participants and patients with a disorder of consciousness (DOC). Hd-EEG was analyzed in 14 healthy participants and 18 patients while they listened to self-relevant and irrelevant stimuli in two forms: diotic (classic sound presentation with an “internalized” feeling) and convolved with a binaural room impulse response (to create an “externalized” feeling). Convolution enhanced the brains’ discriminative response as well as the processing of irrelevant sounds itself, in both healthy participants and DOC patients. For the healthy participants, these effects could be associated with enhanced activation of both the dorsal (where/how) and ventral (what) auditory streams, suggesting that spatial attributes support speech discrimination. Thus, virtually spatialized sounds might “call attention to the outside world” and improve the sensitivity of assessment of brain function in DOC patients.

We simulated the effect of several automatic gain control (AGC) and AGC-like systems and head movement on the output levels, and resulting interaural level differences (ILDs) produced by bilateral cochlear-implant (CI) processors. The simulated AGC systems included unlinked AGCs with a range of parameter settings, linked AGCs, and two proprietary multi-channel systems used in contemporary CIs. The results show that over the range of values used clinically, the parameters that most strongly affect dynamic ILDs are the release time and compression ratio. Linking AGCs preserves ILDs at the expense of monaural level changes and, possibly, comfortable listening level. Multichannel AGCs can whiten output spectra, and/or distort the dynamic changes in ILD that occur during and after head movement. We propose that an unlinked compressor with a ratio of approximately 3:1 and a release time of 300-500 ms can preserve the shape of dynamic ILDs, without causing large spectral distortions or sacrificing listening comfort.

Objectives to develop a safe and effective way of qualifying children for a second device cochlear implantation. Material and methods. There were 50 children from two to twelve years old after unilateral cochlear implantation under our observation. During qualification, the following criteria were taken into account: audiometry results, use of the hearing aid in the non-implanted ear and benefit of the device, speech and hearing development after the first cochlear implantation. Results. According to our findings the second cochlear implantation was recommended for 12 (24%) patients; in 16 (32%) cases the second cochlear implantation was refused; in 22 (44%) cases it was recommended to postpone implantation of the second device. Conclusion. Our results demonstrate that the safe and effective way of qualifying for a second cochlear implant can restore binaural hearing that is crucial for the child's speech and hearing development and enhance integration into a world of peers.

The neurons of the medial superior olive (MSO) of mammals extract azimuthal information from the delays between sounds reaching the two ears [interaural time differences (ITDs)]. Traditionally, all models of sound localization have assumed that MSO neurons represent a single population of cells with specialized and homogeneous intrinsic and synaptic properties that enable the detection of synaptic coincidence on a timescale of tens to hundreds of microseconds. Here, using patch-clamp recordings from large populations of anatomically labeled neurons in brainstem slices from male and female Mongolian gerbils (Meriones unguiculatus), we show that MSO neurons are far more physiologically diverse than previously appreciated, with properties that depend regionally on cell position along the topographic map of frequency. Despite exhibiting a similar morphology, neurons in the MSO exhibit subthreshold oscillations of differing magnitudes that drive action potentials at rates between 100 and 800 Hz. These oscillations are driven primarily by voltage-gated sodium channels and are distinct from resonant properties derived from other active membrane properties. We show that graded differences in these and other physiological properties across the MSO neuron population enable the MSO to duplex the encoding of ITD information in both fast, submillisecond time-varying signals as well as in slower envelopes. SIGNIFICANCE STATEMENT Neurons in the medial superior olive (MSO) encode sound localization cues by detecting microsecond differences in the arrival times of inputs from the left and right ears, and it has been assumed that this computation is made possible by highly stereotyped structural and physiological specializations. Here we report using a large (>400) sample size in which MSO neurons show a strikingly large continuum of functional properties despite exhibiting similar morphologies. We demonstrate that subthreshold oscillations mediated by voltage-gated Na(+) channels play a key role in conferring graded differences in firing properties. This functional diversity likely confers capabilities of processing both fast, submillisecond-scale synaptic activity (acoustic “fine structure”), and slow-rising envelope information that is found in amplitude-modulated sounds and speech patterns.

When vision is unavailable, auditory level and reverberation cues provide important spatial information regarding the environment, such as the size of a room. We investigated how room-size estimates were affected by stimulus type, level, and reverberation. In Experiment 1, 15 blindfolded participants estimated room size after performing a distance bisection task in virtual rooms that were either anechoic (with level cues only) or reverberant (with level and reverberation cues) with a relatively short reverberation time of T60 = 400 milliseconds. Speech, noise, or clicks were presented at distances between 1.9 and 7.1 m. The reverberant room was judged to be significantly larger than the anechoic room ( p < .05) for all stimuli. In Experiment 2, only the reverberant room was used and the overall level of all sounds was equalized, so only reverberation cues were available. Ten blindfolded participants took part. Room-size estimates were significantly larger for speech than for clicks or noise. The results show that when level and reverberation cues are present, reverberation increases judged room size. Even relatively weak reverberation cues provide room-size information, which could potentially be used by blind or visually impaired individuals encountering novel rooms.

For abruptly gated sound, interaural time difference (ITD) cues at onset carry greater perceptual weight than those following. This research explored how envelope shape influences such carrier ITD weighting. Experiment 1 assessed the perceived lateralization of a tonal binaural beat that transitioned through ITD (diotic envelope, mean carrier frequency of 500 Hz). Listeners' left/right lateralization judgments were compared to those for static-ITD tones. For an 8 Hz sinusoidally amplitude-modulated envelope, ITD cues 24 ms after onset well-predicted reported sidedness. For an equivalent-duration "abrupt" envelope, which was unmodulated besides 20-ms onset/offset ramps, reported sidedness corresponded to ITDs near onset (e.g., 6 ms). However, unlike for sinusoidal amplitude modulation, ITDs toward offset seemingly also influenced perceived sidedness. Experiment 2 adjusted the duration of the offset ramp (25-75 ms) and found evidence for such offset weighting only for the most abrupt ramp tested. In experiment 3, an ITD was imposed on a brief segment of otherwise diotic filtered noise. Listeners discriminated right- from left-leading ITDs. In sinusoidal amplitude modulation, thresholds were lowest when the ITD segment occurred during rising amplitude. For the abrupt envelope, the lowest thresholds were observed when the segment occurred at either onset or offset. These experiments demonstrate the influence of envelope profile on carrier ITD sensitivity.

Bilateral cochlear-implant (CI) users struggle to understand speech in noisy environments despite receiving some spatial-hearing benefits. One potential solution is to provide acoustic beamforming. A headphone-based experiment was conducted to compare speech understanding under natural CI listening conditions and for two non-adaptive beamformers, one single beam and one binaural, called “triple beam,” which provides an improved signal-to-noise ratio (beamforming benefit) and usable spatial cues by reintroducing interaural level differences. Speech reception thresholds (SRTs) for speech-on-speech masking were measured with target speech presented in front and two maskers in co-located or narrow/wide separations. Numerosity judgments and sound-localization performance also were measured. Natural spatial cues, single-beam, and triple-beam conditions were compared. For CI listeners, there was a negligible change in SRTs when comparing co-located to separated maskers for natural listening conditions. In contrast, there were 4.9- and 16.9-dB improvements in SRTs for the beamformer and 3.5- and 12.3-dB improvements for triple beam (narrow and wide separations). Similar results were found for normal-hearing listeners presented with vocoded stimuli. Single beam improved speech-on-speech masking performance but yielded poor sound localization. Triple beam improved speech-on-speech masking performance, albeit less than the single beam, and sound localization. Thus, triple beam was the most versatile across multiple spatial-hearing domains.

Purposes: To evaluate the instant auditory benefit of an adhesive bone conduction hearing aid (ADHEAR) on children with bilateral congenital microtia, especially the sound localization ability under unilateral and bilateral fitting. Methods: Twelve patients with bilateral congenital microtia aged from 6 to 17 were included in this study. Pure tone threshold under sound field, speech recognition threshold in quiet and sound localization abilities were tested and compared before and after wearing the device. The pure tone threshold test was additionally repeated for two different wearing method – adhesive or fixed with softband; the sound localization test was repeated for both unilateral and bilateral fitting. Correlation analysis was then conducted to find the influencing factors of sound localization improvement. Results: Significant auditory improvement were found: the average pure tone threshold (PTA) reduced by 24.8 (adhesive) and 27.3 dB HL (softband), with no significant difference between the two wearing methods. The speech recognition threshold also improved by 29.0 dB. As for sound localization abilities, no significant improvement was found under unilateral fitting; but half (6 of 12) of the patients were notably benefited from bilateral fitting. The improvement was found to be strong correlated with the patients’ unaided sound localization ability – those with poorer localization abilities tends to benefit more. Moreover, it was found that the sound localization improvement was also negatively related with the malformation degrees of the patients’ head. Summary: ADHEAR affords significant auditory benefits for children with bilateral congenital microtia, in terms of sound and speech perception. The sound localization abilities could be partly improved instantly by bilateral fitting, and the improvement is related with factors such as adaption and skull malformations.

To perform adaptive behaviours, animals have to establish a representation of the physical “outside” world. How these representations are created by sensory systems is a central issue in sensory physiology. This review addresses the history of experimental approaches toward ideas about sensory coding, using the relatively simple auditory system of acoustic insects. I will discuss the empirical evidence in support of Barlow’s “efficient coding hypothesis”, which argues that the coding properties of neurons undergo specific adaptations that allow insects to detect biologically important acoustic stimuli. This hypothesis opposes the view that the sensory systems of receivers are biased as a result of their phylogeny, which finally determine whether a sound stimulus elicits a behavioural response. Acoustic signals are often transmitted over considerable distances in complex physical environments with high noise levels, resulting in degradation of the temporal pattern of stimuli, unpredictable attenuation, reduced signal-to-noise levels, and degradation of cues used for sound localisation. Thus, a more naturalistic view of sensory coding must be taken, since the signals as broadcast by signallers are rarely equivalent to the effective stimuli encoded by the sensory system of receivers. The consequences of the environmental conditions for sensory coding are discussed.

Objectives Many individuals with noise-related hearing loss continue working in environments where they are periodically exposed to high levels of noise, which increases their risk for further hearing loss. These individuals often must remove their hearing aids in operational environments because of incompatibility with the mandated personal protective equipment, thus reducing situational awareness. Extended-wear hearing aids might provide a solution for these individuals because they can be worn for weeks or months at a time, protect users from high-level noise exposures, and are compatible with communication headsets, earmuffs, and other types of personal protective equipment. The purpose of this study was to evaluate localization ability and speech understanding, feasibility of fitting and use, and acceptability in terms of comfort in a population of noise-exposed, active duty Service members. Design Participants in the study were active duty Service members who were experienced hearing aid users and were currently using standard hearing aids bilaterally. Participants were fitted with extended-wear hearing aids for up to 14 weeks. Laboratory measures included functional gain, sound localization, and speech recognition (in quiet and in noise). Performance was compared between unaided, standard hearing aids, extended-wear hearing aids, and extended-wear hearing aids combined with a tactical communication device (3M Peltor ComTac). In addition, self-perceived benefit between extended-wear hearing aids and standard hearing aids was compared. Results The extended-wear hearing aids provided more attenuation of external sound when turned off compared to standard hearing aids. Speech understanding in quiet and in noise was comparable between extended-wear hearing aids and standard hearing aids and was better when a tactical communication device was worn in addition to extended-wear hearing aids. Localization with extended-wear hearing aids was the worst, intermediate with the standard hearing aids, and the best when the ears were unaided. The extended-wear hearing aids and standard hearing aids provided similar self-perceived communication benefits relative to unaided ears. Device failure and issues with extended-wear hearing aids fit and comfort contributed to a high participant withdrawal rate. Conclusions Overall, the hearing benefits of extended-wear hearing aids for Service members with hearing loss were comparable to those obtained with standard hearing aids, except for sound localization, which was poorer with extended-wear hearing aids. Extended-wear hearing aids provide the additional benefits of protecting the ears from high-level impulsive noise and being compatible with tactical communication and protection systems and other existing personal protective equipment and communication gear. The withdrawal rate in this study, however, suggests that extended-wear hearing aids may not be suitable for active duty Service members in locations where properly trained hearing professionals are not available to replace or re-insert extended-wear hearing aids when needed due to discomfort or device failure.

The cochlear implant (CI) as a treatment option for single-sided deafness (SSD) started with a clinical study looking in to the influence of cochlear implantation with a MED-EL device on incapacitating unilateral tinnitus in SSD. The study began in 2003 and was conducted by P. Van de Heyning and his team in Antwerp, Belgium. The first CI in SSD without tinnitus in Germany was implanted by J. Mueller and R. Jacob in Koblenz in 2005. Translational research activities took place since then to evaluate the CI as a treatment option for SSD not only in adults but also in children. They assessed the hearing performance of SSD patients implanted with CI, importance of long electrode arrays in SSD patients, degree of acceptance of CI by SSD children, importance of early CI implantation in SSD children in developing language skills, music enjoyment by hearing with two ears and evidence on spiral ganglion cell body distribution. In 2013, MED-EL was the first CI manufacturer to receive the CE mark for the indication of SSD and asymmetric hearing loss (AHL) in adults and children. In 2019, MED-EL was the first CI manufacturer to get its CI device approved for patients over the age of five with SSD and AHL, by the FDA in the USA. This article covers the milestones of translational research from the first concept to the widespread clinical use of CI in SSD.

Background This prospective study evaluated sound localization and brain responses to monaural and binaural stimulation via bone conduction devices in 3 individuals with bilateral conductive hearing loss (1 acquired and 2 congenital). Aims and objectives To determine the (1) Cortical areas that are activated with pure tones. (2) Potential benefits of bilateral devices. Materials and methods A new audiological test is described (real-life lateralization test) and applied. NeuroSPECT studies were done using pure tones delivered via bone conduction devices (Baha Attract) stimulating monaurally and binaurally. The tests were performed 2–4 months after the placement of the second device. Results The use of unilateral devices as well as bilateral devices under our testing conditions did not improve sound localization. There was improvement in lateralization with bilateral devices. In the three subjects, cortical activation with binaural auditory stimulation with the Baha Attract occurred in the same auditory areas compared with monaural stimulation. However, while in the individual with acquired loss, the degree of activation was less intense in binaural compared to monaural stimulation; in the congenital cases, binaural stimulation resulted in summation of stimuli. Conclusion In congenital bilateral conductive hearing losses that have not been stimulated early, there are central auditory areas that are deprived. Even if these are only two cases, this is suggestive of the importance of bilateral early auditory stimulation in cases of congenital conductive hearing losses and supportive of the use of bilateral rather than unilateral devices. How to cite this article Goycoolea MV, Neubauer S, Levy R, et al. Evaluation of Brain Activation (NeuroSPECT) by Uni- and Bilateral Auditory Stimulation in Patients with Conductive Hearing Loss and Bilateral Bone Conduction Devices. Int J Head Neck Surg 2021;12(1):22–30.

Cochlear implant (CI) users with a prelingual onset of hearing loss show poor sensitivity to interaural time differences (ITDs), an important cue for sound localization and speech reception in noise. Similarly, neural ITD sensitivity in the inferior colliculus (IC) of neonatally-deafened animals is degraded compared with animals deafened as adults. Here, we show that chronic bilateral CI stimulation during development can partly reverse the effect of early-onset deafness on ITD sensitivity. The prevalence of ITD sensitive neurons was restored to the level of adult-deaf (AD) rabbits in the early-deaf rabbits of both sexes that received chronic stimulation and behavioral training with wearable bilateral sound processors during development. We also found a partial improvement in neural ITD sensitivity in the early-deaf and stimulated rabbits compared with unstimulated rabbits. In contrast, chronic CI stimulation did not improve temporal coding in early-deaf rabbits. The present study is the first report showing functional restoration of ITD sensitivity with CI stimulation in single neurons and highlights the importance of auditory experience during development on the maturation of binaural circuitry.SIGNIFICANCE STATEMENTAlthough cochlear implants (CI) are highly successful in providing speech reception in quiet for many profoundly deaf people, CI users still face difficulty in noisy everyday environment. This is partly because of their poor sensitivity to differences in the timing of sounds arriving at the two ears [interaural time differences (ITDs)], which help to identify where the sound is coming from. This problem is especially acute in those who lost hearing early in life. Here, we present the first report that sensitivity of auditory neurons to ITDs is restored by CI stimulation during development in an animal model of neonatal deafness. These findings highlight the importance of providing early binaural auditory experience with CIs in deaf children.

The configuration of lizard ears, where sound can reach both surfaces of the eardrums, produces a strongly directional ear, but the subsequent processing of sound direction by the auditory pathway is unknown. We report here on directional responses from the first stage, the auditory nerve. We used laser vibrometry to measure eardrum responses in Tokay geckos and in the same animals recorded 117 auditory nerve single fiber responses to free-field sound from radially distributed speakers. Responses from all fibers showed strongly lateralized activity at all frequencies, with an ovoidal directivity that resembled the eardrum directivity. Geckos are vocal and showed pronounced nerve fiber directionality to components of the call. To estimate the accuracy with which a gecko could discriminate between sound sources, we computed the Fisher information (FI) for each neuron. FI was highest just contralateral to the midline, front and back. Thus, the auditory nerve could provide a population code for sound source direction, and geckos should have a high capacity to differentiate between midline sound sources. In brain, binaural comparisons, for example, by IE (ipsilateral excitatory, contralateral inhibitory) neurons, should sharpen the lateralized responses and extend the dynamic range of directionality. NEW & NOTEWORTHY In mammals, the two ears are unconnected pressure receivers, and sound direction is computed from binaural interactions in the brain, but in lizards, the eardrums interact acoustically, producing a strongly directional response. We show strongly lateralized responses from gecko auditory nerve fibers to directional sound stimulation and high Fisher information on either side of the midline. Thus, already the auditory nerve provides a population code for sound source direction in the gecko.

The auditory system detects and encodes sound information with high precision to provide a high-fidelity representation of the environment and communication. In mammals, detection occurs in the peripheral sensory organ (the cochlea) containing specialized mechanosensory cells (hair cells) that initiate the conversion of sound-generated vibrations into action potentials in the auditory nerve. Neural activity in the auditory nerve encodes information regarding the intensity and frequency of sound stimuli, which is transmitted to the auditory cortex through the ascending neural pathways. Glial cells are critical for precise control of neural conduction and synaptic transmission throughout the pathway, allowing for the precise detection of the timing, frequency, and intensity of sound signals, including the sub-millisecond temporal fidelity is necessary for tasks such as sound localization, and in humans, for processing complex sounds including speech and music. In this review, we focus on glia and glia-like cells that interact with hair cells and neurons in the ascending auditory pathway and contribute to the development, maintenance, and modulation of neural circuits and transmission in the auditory system. We also discuss the molecular mechanisms of these interactions, their impact on hearing and on auditory dysfunction associated with pathologies of each cell type.

Objective This study explored the effects of hearing protection devices (HPDs) and head protection on the ability of normal-hearing individuals to localize reverse alarms in background noise. Background Among factors potentially contributing to accidents involving heavy vehicles, reverse alarms can be difficult to localize in space, leading to errors in identifying the source of danger. Previous studies have shown that traditional tonal alarms are more difficult to localize than broadband alarms. In addition, HPDs and safety helmets may further impair localization. Method Standing in the middle of an array of eight loudspeakers, participants with and without HPDs (passive and level-dependent) had to identify the loudspeaker emitting a single cycle of the alarm while performing a task on a tablet computer. Results The broadband alarm was easier to localize than the tonal alarm. Passive HPDs had a significant impact on sound localization (earmuffs generally more so than earplugs), particularly double hearing protection, and level-dependent HPDs did not fully restore sound localization abilities. The safety helmet had a much lesser impact on performance than HPDs. Conclusion Where good sound localization abilities are essential in noisy workplaces, the broadband alarm should be used, double hearing protection should be avoided, and earplug-style passive or level-dependent devices may be a better choice than earmuff-style devices. Construction safety helmets, however, seem to have only a minimal effect on sound localization. Application Results of this study will help stakeholders make decisions that are more informed in promoting safer workplaces.

Objective To explore the behavioural and functional performance of a group of children with conductive unilateral hearing loss (UHL) due to congenital aural atresia. Method Twelve children aged 7 to 16 years (Mage 10.0, SD 3.1 years) formed the UHL group and 15 age-matched children (Mage 9.5, SD 3.6 years) with normal hearing formed the control group. Auditory skills were assessed using tests of sound localisation, spatial speech perception in noise, and self-ratings of auditory abilities (Listening Inventory for Education; LIFE and Speech, Spatial and Qualities of Hearing scale; SSQ). Results When speech was directed to the good ear, performance was poorer than for normal hearing controls. Sound localisation abilities were impaired in children with UHL. Children with UHL reported higher levels of difficulties in classroom settings compared to children with normal hearing, particularly for activities involving listening in noise and focused listening activities. Older children self-report and parents report difficulties for their children across all SSQ scales. Conclusions Children with UHL showed a wide range of auditory difficulties. As expected, speech recognition in noise differed from controls. Sound localisation abilities were variable; greater variability was seen for right ear hearing losses suggesting that some of these children may have developed compensatory mechanisms. Younger children identified listening difficulties for school situations where focussed auditory attention was needed. Older children and parents reported greatest difficulty for activities requiring perception of the direction, distance, and movement of sound. Higher levels of effort and inability to ignore sounds were reported as major difficulties.

To assess any differences in spatial listening ability of cochlear implant recipients when using both or only one of two bilateral cochlear implants (BCIs) for stimuli originating from behind the subject.Twelve loudspeakers were placed in the rear horizontal plane of the subjects to test the sound localisation performance of BCI users and normal-hearing listeners (NHLs) with or without interfering noise. Stimuli were presented via two rear loudspeakers simultaneously during the speech recognition test. In the tone recognition test, another anechoic chamber was used with stimuli presenting from a loudspeaker behind the participants.Twenty-seven NHLs and eleven BCI users.Average root-mean-square (RMS) error for the bilateral condition was significantly lower than that for the right and left cochlear implant (CI) conditions with or without interfering noises (Sound localisation with BCIs was significantly more accurate than with either implant alone. Speech and tone recognition scores were not better with two compared to those of one activated implant. Given the small number of subjects, the results should be considered as preliminary.

Binaural hearing is the ability of the human auditory system to integrate information received from both ears simultaneously. Binaural hearing is fundamental in understanding speech in noisy backgrounds. Any disfunction in one or both ears could cause a disruption in the processing mechanism. Auditory evoked potentials (AEPs) are electrical potentials evoked by externally presented auditory stimuli from any part of the auditory system. A non-invasive technology, electroencephalography (EEG) is used for the monitoring of AEPs. The research aims to identify the best suited electrode positions through correlation analysis and analyse the AEP signals from the selected electrodes in order to detect binaural sensitivity of the human brain. The study evaluates the time-averaged EEG responses of normal hearing subjects to auditory stimuli. The stimuli used for the study are 500 Hz Blackman windowed pure tones, presented in either homophasic (the same phase in both ears) or antiphasic (180-degree phase difference between the two ears) conditions. The study focuses on understanding the effect of phase reversal of auditory stimuli, an under interaural time difference (ITD) cue, on the middle latency response (MLR) region of the AEPs. A correlation analysis was carried out between the eight different locations and as a result, Cz and Pz electrode positions were selected as the best suited positions for further analysis. The selected electrode signals were further processed in the time domain and frequency domain analysis. In the time domain analysis, it was found that Cz electrode for eight subjects out of nine and Pz electrode for seven subjects out of nine, had the larger area under signal curve obtained in the antiphasic condition than in the homophasic signals. Frequency domain analysis showed that the frequency bands 20 to 25Hz and 25 to 30Hz had the most energy when elicited by antiphasic stimuli than by homophasic stimuli. The findings of this study can be further utilised for the detection of binaural processing in a human brain.

The difference in binaural benefit between bilateral cochlear implant (CI) users and normal hearing (NH) listeners has typically been attributed to CI sound coding strategies not encoding the acoustic fine structure (FS) interaural time differences (ITD). The Temporal Limits Encoder (TLE) strategy is proposed as a potential way of improving binaural hearing benefits for CI users in noisy situations. TLE works by downward-transposition of mid-frequency band-limited channel information and can theoretically provide FS-ITD cues. In this work, the effect of choice of lower limit of the modulator in TLE was examined by measuring performance on a word recognition task and computing the magnitude of binaural benefit in bilateral CI users. Performance listening with the TLE strategy was compared with the commonly used Advanced Combinational Encoder (ACE) CI sound coding strategy. Results showed that setting the lower limit to $\geq$ 200 Hz maintained word recognition performance comparable to that of ACE. While most CI listeners exhibited a large binaural benefit ( $\geq$ 6 dB) in at least one of the conditions tested, there was no systematic relationship between the lower limit of the modulator and performance. These results indicate that the TLE strategy has potential to improve binaural hearing abilities in CI users but further work is needed to understand how binaural benefit can be maximized.

Background and Objective: Binaural hearing serves as an advantage in daily communication by facilitating better localization of sounds and perception of speech in the presence of noise. BIC of ABR has been used to understand the binaural representation of different stimuli, such as transient clicks, and complex signals, such as speech. The present study aimed to investigate the test-retest reliability of the binaural interaction component for click and speech evoked ABR. Methods: 30 individuals with normal hearing served as participants for the present study. ABR for click and speech stimuli (/da/) were recorded from these participants in monaural and binaural conditions. BIC was calculated using the formula: BIC = (L + R)- BI where, L + R is the sum of the left and right evoked potentials obtained with monaural stimulation, and BI is the response acquired from binaural stimulation. To investigate reliability, all the participants underwent three recording sessions. Session 1 and session 2 (intra-session) were carried out on the same day, separately. Whereas, session 3 (inter-session) was carried out after a minimum gap of 3 - 5 days after the first session. Intraclass correlation was used to investigate the test-retest reliability of click and speech evoked BIC across the three sessions. Results: The test-retest reliability for BICclick was found to be excellent for latency measures and fair to good for amplitude measures. BICspeech was found to be fair to good, except for BIC-3. Conclusion: The results of the present study indicate that the reliability of BICclick is better than that of BICspeech. These results suggest that the clinical utility of BICspeech should be exerted with caution.

Objective This study assessed the effect of ipsilateral bone-conduction amplification on spatial hearing abilities in subjects with congenital unilateral aural atresia (CUAA). Patients Twelve patients with unilateral conductive hearing loss secondary to CUAA and normal hearing in the contralateral ear were tested. Most (75%) had limited experience with a bone-conduction hearing aid (BCHA). Intervention Performance was evaluated with and without a BCHA fitted acutely on a softband. Main outcome measures Spatial hearing abilities were evaluated in two paradigms. Spatial release from masking was evaluated by comparing masked sentence recognition with a target and two speech maskers either colocated at 0 degree or with the maskers separated at +90 degrees and -90 degrees. Sound source localization was evaluated in a 180 degrees arc of loudspeakers on the horizontal plane. Performance was evaluated at 50 and 75 dB SPL, and results were compared for patients tested with and without a BCHA. Results Group level results indicate similar spatial release from masking in the aided and unaided conditions at both presentation levels. Localization at 50 dB SPL was similar aided and unaided, but at 75 dB SPL the root mean square error was lower unaided than aided (17.2 degrees vs 41.3 degrees; p = 0.010). Conclusions Use of a BCHA in patients with CUAA may interfere with auditory cues required for sound source localization when the signal level is intense enough to overcome the patient's conductive hearing loss. These findings have potential clinical implications in fitting of BCHAs to support optimal spatial hearing in patients with CUAA.

ObjectiveBinaural hearing is facilitated by neural interactions in the auditory pathway. Ageing results in impairment of localisation and listening in noisy situations without any significant hearing loss. The present study focused on comparing the binaural encoding of a speech stimulus at the subcortical level in middle-aged versus younger adults, based on speech-evoked auditory brainstem responses.MethodsThirty participants (15 young adults and 15 middle-aged adults) with normal hearing sensitivity (less than 15 dB HL) participated in the study. The speech-evoked auditory brainstem response was recorded monaurally and binaurally with a 40-ms /da/ stimulus. Fast Fourier transform analysis was utilised.ResultsAn independent sample t-test revealed a significant difference between the two groups in fundamental frequency (F0) amplitude recorded with binaural stimulation.ConclusionThe present study suggested that ageing results in degradation of F0 encoding, which is essential for the perception of speech in noise.

Background Eighteen patients underwent simultaneous bilateral stapes surgery in 2003-2006. Objectives We evaluated the long-term outcomes in this patient group, and assessed their hearing in noise and binaural hearing. Material and Methods Fifteen patients returned questionnaires concerning their hearing, taste function, and balance. Thirteen patients underwent pure-tone and speech audiogram, Finnish matrix sentence test, video head impulse test, and clinical examination on average 13 years after surgery. Results We found no significant difference in air- and bone conduction pure-tone average, speech audiometry, and the air-bone gap between the 1-year and the late postoperative visits. One patient had bilaterally a partial loss of the vestibulo-ocular reflex of unknown cause. Conclusions and Significance The hearing results 13 years after simultaneous bilateral stapes surgery remained good without any significant delayed complications. Simultaneous bilateral stapes surgery is a viable treatment option in selected patients with otosclerosis.