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Central Auditory Processing Disorder (CAPD) refers to various dysfunctions that occur in the central auditory nervous system during the processing of auditory information even though the person has normal hearing thresholds. Dysfunctions, perception of temporal aspects of sound in general; occurs during the tasks of decoding the frequency and intensity of sounds, processing information from both ears, separating speech from background noise, capturing temporal sequence in verbal information flow, and coping with temporal masking effects. These difficulties in processing sound in the central auditory system lead to inability to answer questions appropriately, following conversation and directions, poor auditory memory, poor reading and writing skills, inability to organize events in the mind, and communicative-psychosocial problems. The diagnosis of CAPD remains a difficult and controversial issue, as it has common symptoms with other developmental or learning-related disorders and the assessment methods are generally subjective. However, in recent years, the number of studies that emphasize more on the treatment/therapy approaches recommended for CAPD and show the positive effects of the applied approaches with both objective and subjective test methods has been increasing. The aim of this study is to review the literature on individual therapy interventions in which "methods to improve auditory skills or auditory training", which is one of the recommended approaches for the treatment and management of CAPD. Formal therapy studies recommended for the improvement of auditory skills, including children who were reported to have been diagnosed with CAPD, regardless of the criteria used for diagnosis in the literature regarding the diagnosis of CAPD, are included in the scope of this review. As a result, it is thought that spreading the use of "auditory training" approaches in clinics by establishing standards is important in the intervention of patients with CAPD. [ABSTRACT FROM AUTHOR]

Albert (Al) S. Feng (1944 − 1921) was a pioneer in the area of neuroethology of auditory systems. This special issue of the Journal of Comparative Physiology A commemorates his life and work by presenting 15 articles written by friends, students, and colleagues, many of whom have become leading experts themselves in this field. Their contributions not only provide a comprehensive overview of bioacoustics in amphibians and mammals (including bats), but also are intended to inspire a new generation of scientists to advance our understanding of brain mechanisms of acoustic perception. [ABSTRACT FROM AUTHOR]

The primary objective of this experiment was to measure the temporal and spatial processing capabilities of older individuals and use statistical models to identify the individual contributions of these temporal and spatial processing capabilities to spatial release from masking (SRM). Repeated measures Twenty-five older listeners with varying degrees of hearing loss participated in this experiment. SRM using the coordinate response measure, gap detection thresholds and localisation acuity for 1/3-octave-wide Gaussian noise bands centred at 500 and 4000 Hz were measured for all the listeners. Older listeners had better speech recognition thresholds when target and maskers were spatially separated as compared to when they were co-located. In addition, hearing loss and localisation acuity at 500 Hz were significant predictors in a multiple regression model predicting SRM. However, gap detection thresholds did not significantly contribute to the multiple regression model predicting SRM. Based on our data, we conclude that SRM at 30° spatial separation between the target and symmetric maskers is driven by the ability of the individuals to use interaural time difference cues. [ABSTRACT FROM AUTHOR]

Humans make use of small differences in the timing of sounds at the two ears—interaural time differences (ITDs)—to locate their sources. Despite extensive investigation, however, the neural representation of ITDs in the human brain is contentious, particularly the range of ITDs explicitly represented by dedicated neural detectors. Here, using magneto- and electro-encephalography (MEG and EEG), we demonstrate evidence of a sparse neural representation of ITDs in the human cortex. The magnitude of cortical activity to sounds presented via insert earphones oscillated as a function of increasing ITD—within and beyond auditory cortical regions—and listeners rated the perceptual quality of these sounds according to the same oscillating pattern. This pattern was accurately described by a population of model neurons with preferred ITDs constrained to the narrow, sound-frequency-dependent range evident in other mammalian species. When scaled for head size, the distribution of ITD detectors in the human cortex is remarkably like that recorded in vivo from the cortex of rhesus monkeys, another large primate that uses ITDs for source localization. The data solve a long-standing issue concerning the neural representation of ITDs in humans and suggest a representation that scales for head size and sound frequency in an optimal manner. • Neural representation of ITD in human cortex is sparse and sound-frequency dependent • Cortical activation to ITD is correlated with spatial perceptual qualities • Scaled for head size, humans and macaques show a common cortical representation of ITD • Our findings suggest a common representation of ITDs across mammalian cortex The neural representation of interaural time differences (ITDs) in humans is contentious. Undurraga et al. show that cortical and behavioral measures of ITD are best explained by a sparse representation of neural detectors. Humans and macaques show a similar cortical pattern of activity, suggesting a common representation of ITDs in primates. [ABSTRACT FROM AUTHOR]

Many users of bilateral cochlear implants (BiCIs) localize sound sources less accurately than do people with normal hearing. This may be partly due to using two independently functioning CIs with fixed compression, which distorts and/or reduces interaural level differences (ILDs). Here, we investigate the potential benefits of using binaurally coupled, dynamic compression inspired by the medial olivocochlear reflex; an approach termed "the MOC strategy" (Lopez-Poveda et al., 2016, Ear Hear 37:e138-e148). Twelve BiCI users were asked to localize wideband (125–6000 Hz) noise tokens in a virtual horizontal plane. Stimuli were processed through a standard (STD) sound processing strategy (i.e., involving two independently functioning sound processors with fixed compression) and three different implementations of the MOC strategy: one with fast (MOC1) and two with slower contralateral control of compression (MOC2 and MOC3). The MOC1 and MOC2 strategies had effectively greater inhibition in the higher than in the lower frequency channels, while the MOC3 strategy had slightly greater inhibition in the lower than in the higher frequency channels. Localization was most accurate with the MOC1 strategy, presumably because it provided the largest and less ambiguous ILDs. The angle error improved slightly from 25.3° with the STD strategy to 22.7° with the MOC1 strategy. The improvement in localization ability over the STD strategy disappeared when the contralateral control of compression was made slower, presumably because stimuli were too short (200 ms) for the slower contralateral inhibition to enhance ILDs. Results suggest that some MOC implementations hold promise for improving not only speech-in-noise intelligibility, as shown elsewhere, but also sound source lateralization. • Sound lateralization for bilateral cochlear-implant users was tested using virtual acoustics. • Binaural sound coding inspired by the medial olivocochlear reflex can enhance inter-aural level differences. • The use of binaurally coupled compression can improve sound lateralization. [ABSTRACT FROM AUTHOR]

Abstract: The auditory processing atypicalities experienced by many individuals on the autism spectrum disorder might be understood in terms of difficulties parsing the sound energy arriving at the ears into discrete auditory ‘objects’. Here, we asked whether autistic adults are able to make use of two important spatial cues to auditory object formation – the relative timing and amplitude of sound energy at the left and right ears. Using electroencephalography, we measured the brain responses of 15 autistic adults and 15 age‐ and verbal‐IQ‐matched control participants as they listened to dichotic pitch stimuli – white noise stimuli in which interaural timing or amplitude differences applied to a narrow frequency band of noise typically lead to the perception of a pitch sound that is spatially segregated from the noise. Responses were contrasted with those to stimuli in which timing and amplitude cues were removed. Consistent with our previous studies, autistic adults failed to show a significant object‐related negativity (ORN) for timing‐based pitch, although their ORN was not significantly smaller than that of the control group. Autistic participants did show an ORN to amplitude cues, indicating that they do not experience a general impairment in auditory object formation. However, their P400 response – thought to indicate the later attention‐dependent aspects of auditory object formation – was missing. These findings provide further evidence of atypical auditory object processing in autism with potential implications for understanding the perceptual and communication difficulties associated with the condition. [ABSTRACT FROM AUTHOR]

Auditory research has a rich history of combining experimental evidence with computational simulations of auditory processing in order to deepen our theoretical understanding of how sound is processed in the ears and in the brain. Despite significant progress in the amount of detail and breadth covered by auditory models, for many components of the auditory pathway there are still different model approaches that are often not equivalent but rather in conflict with each other. Similarly, some experimental studies yield conflicting results which has led to controversies. This can be best resolved by a systematic comparison of multiple experimental data sets and model approaches. Binaural processing is a prominent example of how the development of quantitative theories can advance our understanding of the phenomena, but there remain several unresolved questions for which competing model approaches exist. This article discusses a number of current unresolved or disputed issues in binaural modelling, as well as some of the significant challenges in comparing binaural models with each other and with the experimental data. We introduce an auditory model framework, which we believe can become a useful infrastructure for resolving some of the current controversies. It operates models over the same paradigms that are used experimentally. The core of the proposed framework is an interface that connects three components irrespective of their underlying programming language: The experiment software, an auditory pathway model, and task-dependent decision stages called artificial observers that provide the same output format as the test subject. [ABSTRACT FROM AUTHOR]

The inferior colliculus (IC) is the common target of separate pathways that transmit different types of auditory information. Beyond tonotopy, little is known about the organization of response properties within the 3-dimensional layout of the auditory midbrain in most species. Through study of interaural time difference (ITD) processing, the functional properties of neurons can be readily characterized and related to specific pathways. To characterize the representation of ITDs relative to the frequency and hodological organization of the IC, the properties of neurons were recorded and the sites recovered histologically. Subdivisions of the IC were identified based on cytochrome oxidase (CO) histochemistry. The results were plotted within a framework formed by an MRI atlas of the gerbil brain. The central nucleus was composed of two parts, and lateral and dorsal cortical areas were identified. The lateral part of the central nucleus had the highest CO activity in the IC and a high proportion of neurons sensitive to ITDs. The medial portion had lower CO activity and fewer ITD-sensitive neurons. A common tonotopy with a dorsolateral to ventromedial gradient of low to high frequencies spanned the two regions. The distribution of physiological responses was in close agreement with known patterns of ascending inputs. An understanding of the 3-dimensional organization of the IC is needed to specify how the single tonotopic representation in the IC central nucleus leads to the multiple tonotopic representations in core areas of the auditory cortex. [ABSTRACT FROM AUTHOR]

We have recently proposed a binaural cochlear implant (CI) sound processing strategy inspired by the contralateral medial olivocochlear reflex (the MOC strategy) and shown that it improves intelligibility in steady-state noise (Lopez-Poveda et al., 2016, Ear Hear 37:e138-e148). The aim here was to evaluate possible speech-reception benefits of the MOC strategy for speech maskers, a more natural type of interferer. Speech reception thresholds (SRTs) were measured in six bilateral and two single-sided deaf CI users with the MOC strategy and with a standard (STD) strategy. SRTs were measured in unilateral and bilateral listening conditions, and for target and masker stimuli located at azimuthal angles of (0°, 0°), (−15°, +15°), and (−90°, +90°). Mean SRTs were 2–5 dB better with the MOC than with the STD strategy for spatially separated target and masker sources. For bilateral CI users, the MOC strategy (1) facilitated the intelligibility of speech in competition with spatially separated speech maskers in both unilateral and bilateral listening conditions; and (2) led to an overall improvement in spatial release from masking in the two listening conditions. Insofar as speech is a more natural type of interferer than steady-state noise, the present results suggest that the MOC strategy holds potential for promising outcomes for CI users. [ABSTRACT FROM AUTHOR]

Objectives: To explore the possible effects of recurrent otitis media (ROM) in early childhood on binaural processing and verbal memory in school-aged children. Methods: Two hundred eleven children, including 31 children with and 180 children without a history of ROM, were examined. A dichotic digit test (DDT) and a forward and backward digit memory span test (DMST) were administered. Results: A significant difference was observed between age groups among ROM-free children. The ROM-positive group earned significantly poorer results than the ROM-free group in all measurements, except for the right DDT (rDDT) score. Furthermore, a significant correlation was found between the DDT and EA scores with both DMST scores in the ROM-free group. The correlation between the rDDT and forward DMST scores was not significant in the ROM-positive group, and no significant correlation was observed between the EA score and either DMST score. Conclusions: Our findings support that a history of OM in early childhood based on a parental survey of children is associated with differences in DDT and DMST outcomes. [ABSTRACT FROM AUTHOR]

This paper proposes a method for binaural reconstruction of a sound scene captured with a portable-sized array consisting of several microphones. The proposed processing is separating the scene into a sum of small number of sources, and the spectrogram of each of them is in turn represented as a small number of latent components. The direction of arrival (DOA) of each source is estimated, which is followed by binaural rendering of each source at its estimated direction. For representing the sources, the proposed method uses low-rank complex-valued non-negative matrix factorization combined with DOA-based spatial covariance matrix model. The binaural reconstruction is achieved by applying the binaural cues (head-related transfer function) associated with the estimated source DOA to the separated source signals. The binaural rendering quality of the proposed method was evaluated using a speech intelligibility test. The test results indicated that the proposed binaural rendering was able to improve the intelligibility of speech over stereo recordings and separation by minimum variance distortionless response beamformer with the same binaural synthesis in a three-speaker scenario. An additional listening test evaluating the subjective quality of the rendered output indicates no added processing artifacts by the proposed method in comparison to unprocessed stereo recording. [ABSTRACT FROM AUTHOR]

Recently, with the use of an amplitude-modulated binaural beat (AMBB), in which sound amplitude and interaural-phase difference (IPD) were modulated with a fixed mutual relationship (Dietz et al. 2013b), we demonstrated that the human auditory system uses interaural timing differences in the temporal fine structure of modulated sounds only during the rising portion of each modulation cycle. However, the degree to which peripheral or central mechanisms contribute to the observed strong dominance of the rising slope remains to be determined. Here, by recording responses of single neurons in the medial superior olive (MSO) of anesthetized gerbils and in the inferior colliculus (IC) of anesthetized guinea pigs to AMBBs, we report a correlation between the position within the amplitude-modulation (AM) cycle generating the maximum response rate and the position at which the instantaneous IPD dominates the total neural response. The IPD during the rising segment dominates the total response in 78% of MSO neurons and 69% of IC neurons, with responses of the remaining neurons predominantly coding the IPD around the modulation maximum. The observed diversity of dominance regions within the AM cycle, especially in the IC, and its comparison with the human behavioral data suggest that only the subpopulation of neurons with rising slope dominance codes the sound-source location in complex listening conditions. A comparison of two models to account for the data suggests that emphasis on IPDs during the rising slope of the AM cycle depends on adaptation processes occurring before binaural interaction. [ABSTRACT FROM AUTHOR]

The ability to locate the direction of a target sound in a background of competing sources is critical to the survival of many species and important for human communication. Nevertheless, brain mechanisms that provide for such accurate localization abilities remain poorly understood. In particular, it remains unclear how the auditory brain is able to extract reliable spatial information directly from the source when competing sounds and reflections dominate all but the earliest moments of the sound wave reaching each ear. We developed a stimulus mimicking the mutual relationship of sound amplitude and binaural cues, characteristic to reverberant speech. This stimulus, named amplitude modulated binaural beat, allows for a parametric and isolated change of modulation frequency and phase relations. Employing magnetoencephalography and psychoacoustics it is demonstrated that the auditory brain uses binaural information in the stimulus fine structure only during the rising portion of each modulation cycle, rendering spatial information recoverable in an otherwise unlocalizable sound. The data suggest that amplitude modulation provides a means of "glimpsing" low-frequency spatial cues in a manner that benefits listening in noisy or reverberant environments. [ABSTRACT FROM AUTHOR]

The dorsal nucleus of the lateral lemniscus (DNLL) is an auditory brain stem structure that generates a long-lasting GABAergic output, which is important for binaural processing. Despite its importance in binaural processing, little is known about the cellular physiology and the synaptic input kinetics of DNLL neurons. To assess the relevant physiological parameters of DNLL neurons, their late postnatal developmental profile was analyzed in acute brain slices of 9- to 26-day-old Mongolian gerbils. The observed developmental changes in passive membrane and action potential (AP) properties all point toward an improvement of fast and precise signal integration in these neurons. Accordingly, synaptic glutamatergic and GABAergic current kinetics accelerate with age. The changes in intrinsic and synaptic properties contribute nearly equally to reduce the latency and jitter in AP generation and thus enhance the temporal precision of DNLL neurons. Furthermore, the size of the synaptic NMDA current is developmentally downregulated. Despite this developmental reduction, DNLL neurons display an NMDA-dependent postsynaptic amplification of AP generation, known to support high firing rates, throughout this developmental period. Taken together, our findings indicate that during late postnatal development DNLL neurons are optimized for high firing rates with high temporal precision. [ABSTRACT FROM AUTHOR]

Abstract: Humans show a very robust ability to localize sounds in adverse conditions. Computational models of binaural sound localization and technical approaches of direction-of-arrival (DOA) estimation also show good performance, however, both their binaural feature extraction and the strategies for further analysis partly differ from what is currently known about the human auditory system. This study investigates auditory model based DOA estimation emphasizing known features and limitations of the auditory binaural processing such as (i) high temporal resolution, (ii) restricted frequency range to exploit temporal fine-structure, (iii) use of temporal envelope disparities, and (iv) a limited range to compensate for interaural time delay. DOA estimation performance was investigated for up to five concurrent speakers in free field and for up to three speakers in the presence of noise. The DOA errors in these conditions were always smaller than 5°. A condition with moving speakers was also tested and up to three moving speakers could be tracked simultaneously. Analysis of DOA performance as a function of the binaural temporal resolution showed that short time constants of about 5ms employed by the auditory model were crucial for robustness against concurrent sources. [Copyright &y& Elsevier]

Background: Binaural hearing improves our ability to understand speech and to localize sounds. Hearing loss can interfere with binaural cues, and despite the success of amplification, ~25% of people with bilateral hearing loss fit with two hearing aids choose to wear only one (e.g., Brooks and Bulmer, 1981). One explanation is reduced binaural processing, which occurs when the signal presented to one ear interferes with the perception of the signal presented to the other ear (e.g., Jerger et al, 1993). Typical clinical measures, however, are insensitive to binaural processing deficits. Purpose: The purpose of this study was to determine the extent to which behavioral measures of binaural performance were related to electrophysiological measures of binaural processing in subjects with symmetrical pure-tone sensitivity. Research Design: The relationship between middle latency responses (MLRs) and behavioral performance on binaural listening tasks was assessed by Spearman's rho correlation analyses. Separate repeated measures analyses of variance (RMANOVAs) were performed for MLR latency and MLR amplitude. Study Sample: Nineteen subjects were recruited for the present study based on a clinical presentation of symmetrical pure-tone sensitivity with asymmetrical performance on a word-recognition in noise test. This subpopulation of patients included both subjects with and subjects without hearing loss. Data Collection and Analysis: Monaural and binaural auditory processing was measured behaviorally and electrophysiologically in right-handed subjects. The behavioral tests included the Words-in-Noise test (WIN), the dichotic digits test (DDT), and the 500 Hz masking level difference (MLD). Electrophysiologic responses were measured by the binaural interaction component (BIC) of the MLR. The electrophysiological responses were analyzed to examine the effects of peak (Na, Pa, and Nb) and condition (monaural left, monaural right, binaural, and BIC) on MLR amplitude and latency. Results: Significant correlations were found among electrophysiological measures of binaural hearing and behavioral tests of binaural hearing. A strong correlation between the MLD and the binaural Na-Pa amplitude was found (r5.816). Conclusions: The behavioral and electrophysiological measures used in the present study clearly showed evidence of reduced binaural processing in ~10 of the subjects in the present study who had symmetrical pure-tone sensitivity. These results underscore the importance of understanding binaural auditory processing and how these measures may or may not identify functional auditory problems. [ABSTRACT FROM AUTHOR]

Many studies provide detailed behavioural and neurophysiological information on the ability of crickets to localize a sound source under ideal acoustic conditions, but very little is known about how they perform in real habitats. We investigated directional hearing of crickets in the field using a neurophysiological approach, by recording the activity of the two prominent, bilaterally homologous AN1 neurons simultaneously in a cricket’s habitat. The discharge and latency differences of the pair of neurons in response to conspecific chirps presented at different distances and directions were taken as a measure of directional information. The maximum hearing distance differed between individuals and weather conditions from 1 to 15 m (mean 9.2 m). Although the AN1 activity generally decreased with increasing distance, large fluctuations in the magnitude of responses occurred with distance, indicating that the intensity gradient over distance is often irregular. The directional information provided in the discharge differences of the two neurons also varied with distance. Again, there was no simple directional gradient on the transmission channel; rather, with decreasing distance to the source there were receiver locations providing suprathreshold responses, but no directional information. The consequences for the ability of field crickets to communicate acoustically close to the ground are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Unilateral hearing loss causes difficulty hearing in noise (the “cocktail party effect”) due to absence of redundancy, head-shadow, and binaural squelch. This study explores the emergence of the head-shadow and binaural squelch effects in children with unilateral congenital aural atresia undergoing surgery to correct their hearing deficit. Adding patients and data from a similar study previously published, we also evaluate covariates such as the age of the patient, surgical outcome, and complexity of the task that might predict the extent of binaural benefit – patients’ ability to “use” their new ear – when understanding speech in noise. Methods: Patients with unilateral congenital aural atresia were tested for their ability to understand speech in noise before and again 1 month after surgery to repair their atresia. In a sound-attenuating booth participants faced a speaker that produced speech signals with noise 90 degrees to the side of the normal (non-atretic) ear and again to the side of the atretic ear. The Hearing in Noise Test (HINT for adults or HINT-C for children) was used to estimate the patients’ speech reception thresholds. The speech-in-noise test (SPIN) or the Pediatric Speech Intelligibility (PSI) Test was used in the previous study. Results: There was consistent improvement, averaging 5dB regardless of age, in the ability to take advantage of head-shadow in understanding speech with noise to the side of the non-atretic (normal) ear. There was, in contrast, a strong negative linear effect of age (r 2 =.78, selecting patients over 8 years) in the emergence of binaural squelch to understand speech with noise to the side of the atretic ear. In patients over 8 years, this trend replicated over different studies and different tests. Children less than 8 years, however, showed less improvement in the HINT-C than in the PSI after surgery with noise toward their atretic ear (effect size=3). No binaural result was correlated with degree of hearing improvement after surgery. Conclusions: All patients are able to take advantage of a favorable signal-to-noise ratio in their newly opened ear; that is with noise toward the side of the normal ear (but this physical, bilateral, head-shadow effect need not involve true central binaural processing). With noise toward the atretic ear, the emergence of binaural squelch replicates between two studies for all but the youngest patients. Approximately 2dB of binaural gain is lost for each decade that surgery is delayed, and zero (or poorer) binaural benefit is predicted after 38 years of age. Older adults do more poorly, possibly secondary to their long period of auditory deprivation. At the youngest ages, however, binaural results are different in open- and closed-set speech tests; the more complex hearing tasks may involve a greater cognitive load. Other cognitive abilities (late evoked potentials, grey matter in auditory cortex, and multitasking) show similar effects of age, peaking at the same late-teen/young-adult period. Longer follow-up is likely critical for the understanding of these data. Getting a new ear may be – like multitasking – challenging for the youngest and oldest subjects. [Copyright &y& Elsevier]

Abstract: A model of the effective processing of interaural timing disparities in the human auditory system is presented which provides modifications and extensions to existing models motivated by recent physiological findings. In particular, an established model of excitatory–inhibitory (EI) neuronal connectivity is complemented by a model that is based on a rate code derived from the interaural phase difference (IPD). The IPD model is shown to successfully simulate literature data on fine structure and envelope-based binaural detection and lateralization experiments. In order to investigate the processing of temporal fluctuations of interaural timing disparities, detection thresholds of broadband binaural-beat stimuli were measured in six normal-hearing listeners and were compared with model simulations. In a first experiment, the highest detectable beat frequency was found to be 96 Hz for a noise bandwidth of 550 Hz and 219 Hz for a bandwidth of 1100 Hz. Both models predicted lower thresholds, but performed increasingly better when the integration time constants of the binaural processors were reduced. In a second experiment, the signal-to-noise ratio at the detection threshold of binaural-beat stimuli mixed with interaurally uncorrelated noise was measured as a function of the beat frequency. The threshold increased about 1.7 dB per octave which was simulated similarly by both models. The results indicate that the primary temporal resolution of the binaural system for detecting interaural timing disparities is much higher than the temporal resolution found in higher auditory processes as supposedly involved in, e.g., masking. [Copyright &y& Elsevier]

Abstract: Individuals with developmental dyslexia are often impaired in their ability to process certain linguistic and even basic non-linguistic auditory signals. Recent investigations report conflicting findings regarding impaired low-level binaural detection mechanisms associated with dyslexia. Binaural impairment has been hypothesized to stem from a general low-level processing disorder for temporally fine sensory stimuli. Here we use a new behavioral paradigm to address this issue. We compared the response times of dyslexic listeners and their matched controls in a tone-in-noise detection task. The tonal signals were either Huggins Pitch (HP), a stimulus requiring binaural processing to elicit a pitch percept, or a pure tone—perceptually similar but physically very different signals. The results showed no difference between the two groups specific to the processing of HP and thus no evidence for a binaural impairment in dyslexia. However, dyslexic subjects exhibited a general difficulty in extracting tonal objects from background noise, manifested by a globally delayed detection speed. [Copyright &y& Elsevier]

The precedence effect describes the phenomenon whereby echoes are spatially fused to the location of an initial sound by selectively suppressing the directional information of lagging sounds (echo suppression). Echo suppression is a prerequisite for faithful sound localization in natural environments but can break down depending on the behavioral context. To date, the neural mechanisms that suppress echo directional information without suppressing the perception of echoes themselves are not understood. We performed in vivo recordings in Mongolian gerbils of neurons of the dorsal nucleus of the lateral lemniscus (DNLL), a GABAergic brainstem nucleus that targets the auditory midbrain, and show that these DNLL neurons exhibit inhibition that persists tens of milliseconds beyond the stimulus offset, so-called persistent inhibition (PI). Using in vitro recordings, we demonstrate that PI stems from GABAergic projections from the opposite DNLL. Furthermore, these recordings show that PI is attributable to intrinsic features of this GABAergic innervation. Implementation of these physiological findings into a neuronal model of the auditory brainstem demonstrates that, on a circuit level, PI creates an enhancement of responsiveness to lagging sounds in auditory midbrain cells. Moreover, the model revealed that such response enhancement is a sufficient cue for an ideal observer to identify echoes and to exhibit echo suppression, which agrees closely with the percepts of human subjects. [ABSTRACT FROM AUTHOR]

Abstract: A time-varying Wiener filter specifies the ratio of a target signal and a noisy mixture in a local time-frequency unit. We estimate this ratio using a binaural processor and derive a ratio time-frequency mask. This mask is used to extract the speech signal, which is then fed to a conventional speech recognizer operating in the cepstral domain. We compare the performance of this system with a missing-data recognizer that operates in the spectral domain using the time-frequency units that are dominated by speech. To apply the missing-data recognizer, the same binaural processor is used to estimate an ideal binary time-frequency mask, which selects a local time-frequency unit if the speech signal within the unit is stronger than the interference. We find that the performance of the missing data recognizer is better on a small vocabulary recognition task but the performance of the conventional recognizer is substantially better when the vocabulary size is increased. [Copyright &y& Elsevier]

We review new recognition and localization skills in patients using one or two cochlear implant(s). We observed one unilateral patient who showed localization performance above chance. We also provide evidence for binaural processing in bilateral cochlear implant patients, even when tested with speech from the front without noise. We unsuccessfully attempted to find correlations between localization and squelch, between these variables and pre-implant threshold differences, or these variables and post-implant recognition differences. We strongly believe that new tests are needed to examine the potential benefit of two implants. We describe three tests that we use to show a binaural advantage: cued recognition, movement direction, and recognition with multiple jammers. [ABSTRACT FROM AUTHOR]

We explored whether transferring signals between two hearing aids could improve speech intelligibility in noise. This was evaluated using a simulated conversation in a car; speech was presented to the right ear and car noise was presented either to the right or both ears. In three cross-aid communication conditions, the noise in the right ear was scaled and subtracted from the noise in the left ear. Speech intelligibility was determined for a group of normally hearing listeners and a group with bilateral hearing loss. The hearing-impaired group had relatively higher intelligibility scores when the car noise was diotic, whereas the normal-hearing group had relatively higher intelligibility scores in the binaural (dichotic) conditions. The cross-aid conditions led to improved intelligibility compared to the reference conditions. The results indicate that the transfer of signals between hearing aids may be of benefit when listening to speech in a car. Sumario Exploramos si la transferencia de señales entre dos auxiliares auditivos podría mejorar la inteligibilidad del lenguaje en ruido. Esto fue evaluado simulando una conversación en un auto; se presentó una señal de lenguaje al oído izquierdo y un ruido de automóvil en el oído derecho o en ambos. En tres condiciones de comunicación inter-audífono, el ruido en el oído derecho fue graduado y sustraído del ruido en el oído izquierdo. Se determinó la inteligibilidad del lenguaje en un grupo de sujetos normo-oyentes y en un grupo con hipoacusia bilateral. El grupo de hipoacúsicos obtuvo puntuaciones de inteligibilidad del lenguaje relativamente mayores cuando el ruido del automóvil fue diótico, mientras que el grupo de normo-oyentes obtuvo puntuaciones de inteligibilidad relativamente mayores en las condiciones binaurales (dicóticas). Las condiciones inter-audífono llevaron a una inteligibilidad mejorada, comparada con las condiciones de referencia. Los resultados indican que la transferencia de señales entre auxiliares auditivos puede ser de beneficio cuando se escucha lenguaje dentro de un auto. [ABSTRACT FROM AUTHOR]

The Listening in Spatialized Noise test (LISN®) produces a three-dimensional auditory environment under headphones, using only a PC and an audiometer, and was designed to provide an ecologically valid assessment of auditory figure-ground skills in children. The listener is required to indicate the intelligibility level of a story presented at 0° azimuth, in the presence of distracter sentences simultaneously presented at either 0° or ±90° azimuth. Various measures assess the extent to which either spatial, vocal, or spatial and vocal cues combined, increase a listener's ability to comprehend the story, without being affected by differences between participants in variables such as linguistic skills. There was a trend of improved performance with increasing age for 48 normally hearing seven-, eight-, and nine-year-olds, and sixteen adults. Whereas some significant differences were found between adults and children, there were no significant differences in performance between the seven-, eight-, and nine-year-olds on any measure, and no significant gender or practice effects were observed. Future studies on children with suspected auditory processing disorder were considered warranted. Sumario La prueba de audición en ruido espacializado (LISN®) produce un ambiente auditivo tridimensional con audífonos, por medio de una PC y un audiómetro. Se diseñó para proporcionar una evaluación ecológicamente válida de las habilidades figura/fondo en niños. Se le pide al sujeto que escucha que indique el nivel de inteligibilidad de una historia presentada a 0° azimut en presencia de oraciones simultáneas como distractor ya sea a 0° o a ±90° azimut. Hay varias mediciones que evalúan el grado en que las claves vocales, espaciales o vocales y espaciales combinadas, aumentan la habilidad del sujeto para comprender la historia, sin que se vean afectadas por las diferencias entre participantes, tales como las habilidades lingüísticas. Hubo una tendencia a mejorar el desempeño con el incremento de la edad en 48 sujetos normoyentes de 7,8 y 9 años y en 16 adultos. Mientras que algunas diferencias significativas se encontraron entre niños y adultos, no hubo diferencias significativas en el desempeño entre los niños de 7,8 y 9 años en ninguna medición, ni tampoco se observó ninguna diferencia entre géneros o por efecto de la práctica. Se consideran necesarios más estudios en niños con sospecha de alteraciones en el procesamiento auditivo. [ABSTRACT FROM AUTHOR]

Abstract: In an effort to examine the rules by which information of bilaterally applied bone-conducted signals arising from interaural time differences (ITD) and interaural intensity differences (IID) is combined, data were measured for continuous 500 Hz narrow band noise at 65–70 dB HL in 11 patients with bilateral congenital aural atresia. Time–intensity trading functions were obtained by shifting the sound image towards one side using ITD, and shifting back to a centered sound image by varying the IID in the same ear (auditory midline task). ITD values were varied from −600 to +600 μs at 200 μs steps, where negative values indicate delays to the right ear. The results indicate that time–intensity trading is present in patients with bilateral aural atresia. The gross response properties of time–intensity trading in response to bone-conducted signals were comparable in patients with bilateral aural atresia and normal-hearing subjects, though there was a larger inter-subject variability and higher discrimination thresholds across IIDs in the atresia group. These results suggest that the mature auditory brainstem has a potential to employ binaural cues later in life, although to a restricted degree. A binaural fitting of a bone-conducted hearing aid might optimize binaural hearing and improve sound lateralization, and we recommend now systematically bilateral fitting in aural atresia patients. [Copyright &y& Elsevier]

Deficits in temporal resolution and/or the precedence effect may underlie part of the speech understanding difficulties experienced by older listeners in degraded acoustic environments. In a previous investigation, R. Roberts and J. Lister (2004) identified a positive correlation between measures of temporal resolution and the precedence effect, specifically across-channel gap detection (as measured dichotically) and fusion. Across-channel gap detection may also be measured using frequency-disparate markers. Thus, the present investigation was designed to determine if the relation is specific to dichotic gap detection or may generalize to all types of across-channel gap detection. Gap-detection thresholds (GDTs) for fixed-frequency and frequency-disparate markers and lag-burst thresholds (LBTs) were measured for 3 groups of listeners: young with normal hearing sensitivity (YNH), older with normal hearing sensitivity (ONH), and older with sensorineural hearing loss (OIH). Also included were conditions of diotic and dichotic GDT. Largest GDTs were measured for the frequency-disparate markers, whereas largest LBTs were measured for the fixed-frequency markers. ONH and OIH listeners exhibited larger frequency-disparate and dichotic GDTs than YNH listeners. Listener age and hearing loss appeared to influence temporal resolution for frequency-disparate and dichotic stimuli, which is potentially important for the resolution of timing cues in speech. Age and hearing loss did not significantly influence fusion as measured by LBTs. Within each participant group, most GDTs and LBTs were positively, but not significantly, correlated. For all participants combined, across-channel GDTs and LBTs were positively and significantly correlated. This suggests that the 2 tasks may rely on a common across-channel temporal mechanism. [ABSTRACT FROM AUTHOR]

Localization ability, using six different listening conditions, was studied on four adult bilateral implant listeners to better understand the frequency and electrode contributions to localization. Results suggest that localization is best when the full spectrum is presented to all frequencies and that localization is severely impaired if the spectrum is split between ears. Localization is better when the high-frequency only spectrum is presented compared to when the low-frequency only spectrum is presented. However, localization is still possible with only low-frequency information. In addition, some localization is possible when stimulating only one electrode. Even the best localization performance in any conditions did not approach that of listeners with normal hearing. [Copyright &y& Elsevier]

l Binaural processing of envelope (ENV) and temporal fine structure (TFS) information was examined by frequency-following responses (FFRs) in rat ICC. l Binaural FFR ENV received a predominant contribution from contralateral inputs while inhibited by ipsilateral inputs, showing a binaural inhibition property. l Binaural FFR TFS was excited by the inputs from both sides, showing a binaural summation property. l Results suggested distinct binaural integration mechanisms for ENV and TFS information. Complex broadband sounds are decomposed by peripheral auditory filters into a series of relatively narrowband signals, each with a slowly varying envelope (ENV) and a rapidly fluctuating temporal fine structure (TFS). ENV and TFS information at the bilateral ears contribute differentially to auditory perception. However, whether the difference could attribute to mechanisms of binaural integration remains an open question. As a potential neural correlate, subsets of neurons in the central nucleus of the inferior colliculus (ICC) are known to integrate binaural information with binaural inhibition or binaural summation. Therefore, we recorded the frequency-following responses (FFRs) to the ENV and TFS components of narrowband noises in the ICC of anesthetized rats and examined changes in FFR amplitude and stimulus-response coherence under various sound-delivery settings. We showed that binaural FFR ENV was predominantly elicited by contralateral inputs and inhibited by ipsilateral inputs, exhibiting a "binaural-inhibition" like property. On the other hand, binaural FFR TFS received a balanced contribution from both sides, echoing the "binaural-summation" mechanism. What is more, binaural FFR ENV was significantly correlated with contralateral-evoked but not ipsilateral-evoked FFR ENV , while binaural FFR TFS correlated with both contralateral- and ipsilateral-evoked FFR TFS. Overall, these results suggest distinct binaural processing of ENV and TFS information at the midbrain level. [ABSTRACT FROM AUTHOR]

AbstractNeurons in the avian nucleus laminaris (NL) are the first to receive binaural information and are presumed to play a role in encoding interaural time differences (ITD). NL not only receives excitatory projections from the ipsi‐and contralateral nucleus magnocellularis, but also receives inhibitory (GABAergic) input. This study investigates how GABA (γ‐aminobutyric acid) influences ITD coding in NL. Intracellular responses of chick NL neurons were studied in a brain slice preparation. Both excitatory inputs to NL were electrically activated and the delay between trains of bilateral stimuli (simulated‐interaural time difference [s‐ITD]) was varied. The resulting s‐ITD functions were recorded in the presence of 0–75 μm GABA. The discharge rate of NL neurons varied with s‐ITD. Cells responded maximally using s‐ITDs at which the peak of the ipsi‐ and contralateral excitatory postsynaptic potentials occurred simultaneously (favourable s‐ITD). At unfavourable s‐ITDs, the discharge rates usually fell below unilateral levels. GABA had contrary effects on the s‐ITD functions depending on the drug concentration. A low GABA dose enhanced excitability at favourable s‐ITD, but not at unfavourable s‐ITDs. In contrast, higher GABA concentrations diminished excitability. Moderate GABA concentrations had no consistent effect. These results suggest that the GABAergic input to NL will either increase or decrease the excitability of the NL neuron depending on the degree to which this GABAergic input is activated. A gain control hypothesis is presented in which the GABAergic input makes ITD processing in NL independent of the stimulus intensity by adjusting the excitability of NL neurons. [ABSTRACT FROM AUTHOR]

Within the cochlea, broadband sounds like speech and music are filtered into a series of narrowband signals, each with a relatively slowly varying envelope (ENV) imposed on a rapidly oscillating carrier (the temporal fine structure, TFS). Information about ENV is conveyed by the timing and short-term rate of action potentials in the auditory nerve while information about TFS is conveyed by synchronization of action potentials to a specific phase of the waveform in the cochlea (phase locking). This paper describes the effects of age and hearing loss on the binaural processing of ENV and TFS information, i.e. on the processing of differences in ENV and TFS at the two ears. The binaural processing of TFS information is adversely affected by both hearing loss and increasing age. The binaural processing of ENV information deteriorates somewhat with increasing age but is only slightly affected by hearing loss. The reduced TFS processing abilities found for older/hearing-impaired subjects may partially account for the difficulties that such subjects experience in complex listening situations when the target speech and interfering sounds come from different directions in space. • The binaural processing of envelope (ENV) and temporal fine structure (TFS) is reviewed. • Hearing loss and greater age adversely affect the processing of interaural time differences in TFS. • Hearing loss and greater age only slightly affect the processing of interaural time differences in ENV. • Hearing loss and greater age are associated with reduced masking level differences. • Hearing loss and greater age are associated with reduced spatial release from masking. [ABSTRACT FROM AUTHOR]