Binaural Hearing System Research Articles

Cochlear Implantation: Concept, Results Outcomes and Quality of Life.

Cochlear implant today are an essential method of auditory rehabilitation in patients with severe to profound hearing loss. Due to the rapid development of implant technology the results have been markedly improved. Today about 80 % of patients can use the telephone and children achieve near to normal hearing and speech development. In consequence, more patients are candidates for a cochlear implant today including those with high frequency deafness and single sided deafness. However, today only 60,000 out of 1 Million CI-candidates in Germany have been implanted so far. In future multi modal universal auditory implants will provide combined electric-mechanical stimulation to make best use of the residual auditory hearing and the electrical stimulation of the auditory nerve. They allow a continuous adaptation of the stimulation strategy onto the given functional status of haircells and auditory nerve fibers especially in cases of progressive hearing loss. Brain computer interfaces will allow the automated fitting and adaptation to the acoustic scene by optimizing the signal processing for best possible auditory performance. Binaural hearing systems will improve directional hearing and speech perception in noise. Advanced implants are composed of individualized electrodes by additive manufacturing which can be inserted atraumaticly by a computer and robot assisted surgery. After insertion they automatically adept to the anatomy of the individual cochlear. These advanced implants are composed with additional integrated biological components for the preservation of residual hearing and regeneration of neural elements to improve the electrode nerve interface. This will allow to increase the number of electrical contacts as a major step towards the bionic ear. This will allow overcoming the principal limits of today's cochlear implant technology. Advanced care models will allow an easy way for the patient towards hearing preservation cochlear implantation under local anesthesia using minimal invasive high precision cochlear implant surgery. These implant systems will become a personal communicator with improved connectivity. Remote care and self-fitting will empower the patient to optimize his own hearing.

Exploiting Deep Neural Networks and Head Movements for Robust Binaural Localization of Multiple Sources in Reverberant Environments

This paper presents a novel machine-hearing system that exploits deep neural networks (DNNs) and head movements for robust binaural localisation of multiple sources in reverberant environments. DNNs are used to learn the relationship between the source azimuth and binaural cues, consisting of the complete cross-correlation function (CCF) and interaural level differences (ILDs). In contrast to many previous binaural hearing systems, the proposed approach is not restricted to localisation of sound sources in the frontal hemifield. Due to the similarity of binaural cues in the frontal and rear hemifields, front-back confusions often occur. To address this, a head movement strategy is incorporated in the localisation model to help reduce the front-back errors. The proposed DNN system is compared to a Gaussian mixture model (GMM) based system that employs interaural time differences (ITDs) and ILDs as localisation features. Our experiments show that the DNN is able to exploit information in the CCF that is not available in the ITD cue, which together with head movements substantially improves localisation accuracies under challenging acoustic scenarios in which multiple talkers and room reverberation are present.

Design, construction, and evaluation of a binaural dummy head

Binaural-dummy-heads are often used as standard measurement devices where modeling of the human binaural hearing system is desired. The binaural-dummy-head imitates a human head (and torso) which is used in binaural recording as well as research areas such as hearing aids, sound localization, noise measurements, etc. Commercially available binaural heads are not economically efficient for some purposes. This paper outlines a less expensive binaural dummy head built using ANSI/ASA S3.36-2012 standard as a reference as part of an independent coursework. A hard plastic mannequin was used as head and torso, and the two ears were real human ear replicas casted out of water-based alginate gel. The complex Head-Related Transfer Functions (HRTF) of our dummy head were measured in an anechoic chamber to evaluate its spectral and directional properties and were compared to the same properties of the standard commercial dummy head.

The relation between the information delivered by head-related transfer function and human spatial hearing

The human auditory system is capable of performing various tasks related to spatial hearing including sound localization and source segregation. The performance of these tasks depends on many factors, including the complexity of the sound field; the way in which the information from the sound field is transferred to the ears; and the ability of the binaural hearing system to extract the required information. This study focuses on the role of the transfer system represented by the HRTFs that relate the sound field to the signals at the ears. Previously, a measure for the information delivered by the HRTFs was proposed, and the role of HRTFs in human sound localization in the horizontal and median planes was investigated. In the current study, the role of HRTFs in human sound localization is further investigated by analyzing localization in the entire three-dimensional space. Then, the proposed measure is used to investigate the role of HRTFs in source segregation as part of a spatial-release from masking task. The results show that the information delivered by the HRTFs can account for the increase in intelligibility as a function of the spatial separation between the desired source and the masker reported in the literature. However, the decrease in intelligibility with increasing number of spatially separated maskers seems to be related to the binaural hearing system, and cannot be explained by the information in the HRTFs.

METHOD FOR OPERATING A BINAURAL HEARING SYSTEM AS WELL AS A BINAURAL HEARING SYSTEM

A hearing system and a method for operating a binaural hearing system are disclosed that comprises at least two hearing devices (1, 2) to be at least partly inserted into or to be worn behind the left and right ear of a user. Each hearing device (1, 2) comprises at least one microphone (2a, 2b) to generate an electrical signal corresponding to an acoustic signal. The inventive method comprises the step of : - determining contra-lateral information (CLD) based on an acoustic signal recorded by a microphone (2a, 2b) of the contra-lateral hearing device (1, 2), - determining ipsi-lateral information (ILD) based on an acoustic signal recorded by a microphone (2b, 2a) of the ipsi-lateral hearing device (2, 1), - providing a coordination level, the coordination level being indicative of a degree of synchronization of the two hearing devices (1, 2), and - adjusting processes in the ipsi-lateral hearing device (2, 1) in accordance with the coordination level, wherein the coordination level either being determined from the contra-lateral information and/or from the ipsi-lateral information, or being obtained from an external device (8). The inventive hearing system has the advantage that the hearing devices (1, 2) can be operated at different coordination levels resulting in improved hearing ability and inconspicuousness for the user.

Application of binaural hearing system for assessment of environmental noise impact

In the present work an experimental system is presented that allows one to investigate physical principles of binaural hearing and identication of sound sources. It is checked that at low frequencies interaural time difference (whereas at high frequencies n the interaural level difference) cue is preferable for recognizing location of sound sources. At intermediate frequencies human auditory system uses both processes for binaural hearing. Also the effect of trafc noise on binaural hearing is investigated. It is shown that environmental noises consist mainly of low frequency spectral components. Therefore noise is considered to have inuence on binaural cues which human auditory system uses for spatial sound localization at low frequencies, i. e. the interaural time difference.

"Polyaural" array processing for robust automatic speech recognition in noisy and reverberant environments

It is well known that human binaural processing is very useful for separating incoming sound sources as well as for improving the intelligibility of speech in reverberant environments. In this paper we present a new method of signal processing for robust speech recognition using multiple microphones. The method, loosely based on the human binaural hearing system, consists of passing the speech signals detected by multiple microphones through bandpass filtering and nonlinear halfwave rectification operations, and then cross‐correlating the outputs from each channel within each frequency band. These operations provide rejection of off‐axis interfering signals. These operations are repeated (in a non‐physiological fashion) for the negative of the signal, and an estimate of the desired signal is obtained by combining the positive and negative outputs. We demonstrate that the use of this approach provides substantially better recognition accuracy than delay‐and‐sum beamforming using the same sensors for target signals in the presence of additive broadband and speech maskers, and it provides substantial improvements in specific reverberant environments as well. [Supported by NSF and DARPA]

Synchronized binaural hearing system

The invention relates to a binaural hearing system comprising a first and a second hearing prosthesis adapted for wireless bi-directional communication of digital data signals. A first clock generator of the first hearing prosthesis operates as a master clock circuit for both hearing prostheses of the binaural hearing system to ensure synchronous sampling of the respective microphone input signals. The invention also relates to a wireless synchronised hearing aid system comprising a first and a second hearing prosthesis. The hearing prostheses are operated in a time-synchronised manner so as to provide a DSP-based hearing aid system with matched signal delay through the hearing prostheses.

電話両耳聴システムの臨床的効果

電話両耳聴システムの臨床的効果

Method and apparatus for reducing background noise in communication systems and for enhancing binaural hearing systems for the hearing impaired

Directional hearing in noisy environments is enhanced using small conventional microphones. In one embodiment a conventional first order bidirectional gradient microphone is employed in connection with a barrier to produce sound shadow at the rearward end of the microphone. In other embodiments such as hearing assistive devices worn on a person's head or body, the head or body of that person serves as the barrier. The result is a significant reduction in gain for all frequencies of acoustic energy emanating from generally rearward of the microphone. The sound shadow creates an apparent change of direction of arrival for rearwardly arriving acoustic energy, thereby making it appear to the microphone that the sound is approaching from the high attenuation 90° direction. Two spaced bidirectional microphones worn on a person's body may be positioned to take advantage of this effect while simulating binaural hearing in an assistive listening device. A similar directional result is obtained with two conventional cardioid microphones mounted on a common casing to face in opposite directions. Electronic circuitry subtracts the output signal of the rearward facing microphone from the output signal of the forward facing microphone to render the combination highly directional. Case noise and other mechanical vibrations modulating the two output signals are nulled out in the subtraction process.

Experiments in binaural hearing: Masking, speech intelligibility, and binaural hearing aids

The late J. Donald Harris had a great interest in binaural hearing and binaural amplification systems for the hearing impaired. This paper is dedicated to his memory. Research on binaural release from masking has been substantial. A similar but smaller research effort has focused on binaural improvements in intelligibility and related issues involving binaural hearing aids. There have been few attempts, however, to integrate the two areas of research. Methods for predicting binaural improvements in intelligibility from models of binaural release from masking will be reviewed. Data from an experimental evaluation of one such method will be presented and the implications for the design of binaural amplification systems for the hearing impaired will be discussed.

A Psychoacoustic and Electrophysiological Study

von Wedel H, von Wedel U—Ch, Streppel M. Monaural and binaural time resolution ability in the aged; A psychoacoustic and electrophysiological study. Acta Otolaryngol (Stockh) 1991; Suppl. 476: 161—166.Time resolution ability is an important factor of auditory processing, especially in binaural hearing. In psychoacoustical and electrophysiological studies the time resolution of brief modulations of signal amplitude and frequency in monaural hearing, including gap detection ability, was analysed. To reveal the time resolution ability of the binaural hearing system, brief interaural modulations of signal amplitude, short changes of interaural time delay or noise coherence in broadband noise bursts were generated. The sensation levels of these short—lasting changes in the noise structure and the cortical evoked potentials were investigated in young normal hearing subjects and in the elderly. Thus age—dependent changes in monaural and binaural time resolution ability could be detected. For the monaural experiments, lengthened time constants of between 2—20 ms, depending on the degree of intensity or frequency modulation could be derived for older subjects. The binaural experiments were characterized by prolongation between 4—26 ms for short interaural signal delay changes. For both groups the time constants derived from the electrophysiological investigations were more prolonged, which might be explained by masking effects or habituation. Further electrophysiological investigations will be required to differentiate between time resolution processes of brief signal changes within the peripheral and central parts of the auditory system.

Tonal masking and frequency selectivity for the monaural and binaural hearing systems

A series of masking experiments was performed with the aim of comparing frequency selectivity for the monaural and binaural systems. The masking stimulus used in this study combined a sinusoid, which was gated simultaneously with the signal, with a continuous broadband noise. Signal frequency was fixed at 500 Hz. In one condition, the tonal masker and noise were interaurally in phase and the signal was phase reversed. In a second condition, noise, tonal masker, and signal were presented to one ear alone. Signal thresholds were obtained as a function of masker frequency for these two conditions. After making an appropriate selection of noise levels, masking functions for the monaural and binaural system conditions were found to agree closely except for a region about their tips where the binaural condition was more detectable. Two possible interpretations of these results are discussed. Either the monaural and binaural systems contain filters each which have similarly shaped skirts, or the frequency selectivity observed under both diotic and dichotic conditions (for large frequency separations of masker and signal) reflect the operation of a common peripheral filter.

Comparison of frequency selectivity for the monaural and binaural hearing systems: Evidence from a probe-frequency procedure

Frequency selectivity was measured for one monaural system condition (NOSO) and two binaural system conditions (NOSπ and NOSM) using the probe-frequency method originated by Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 (1968)]. Subjects were first trained to detect a 500-Hz tone in noise for each condition of the experiment. Following training, the usual detection paradigm was altered such that on 25% of the trials a second signal of a different frequency was substituted for the 500-Hz signal. Performance at each of these secondary or probe-frequencies was transformed into equivalent decibels of attenuation by means of psychometric functions obtained at 500 Hz. A correction was then applied to these data which compensated for the relationship between frequency and the size of the MLD. The transformed and corrected data were interpreted as describing attenuation characteristics of an internal auditory filter. No systematic difference was found between attenuation characteristics for the two binaural system conditions. However, the attenuation characteristics for the binaural system conditions were approximately twice as wide as those for the NOSO condition.

A comparison of forward masking for the monoaural and binaural hearing systems

Forward masking functions were obtained using a 500‐Hz tonal musket of 100‐ms duration, followed by a 20‐ms sinusoidal test probe at the same frequency. A continuous, broadband noise was also present during the experiment. Noise levels were chosen so that for long ISI's, masking functions for both the monaural and binaural system conditions would asymptote at a common level of signal detectability. In the monaural system condition, the masker, signal, and noise were all presented to one ear alone, while for the binaural system conditions, the signal was antiphasic, the noise homophasic, and the tonal masker was either homophasic or antiphasic. Results showed the mortaural system condition to exhibit the fastest recovery from masking. For the binaural system conditions, the homophasic tonal masker was more effective than the antiphasic masker when masker and signal were temporally nonoverlapping, but the reverse was found for simultaneous presentation of signal and masker. These data are interpreted as demonstrating that the binaural system has a longer integration time than does the monaural system. [Work supported by the Neurobehavioral Sciences Program, University of Iowa.]

Frequency selectivity in the binaural and monaural hearing systems: Evidence from a modified two-tone masking procedure

A series of masking experiments was performed with the aim of comparing frequency selectivity of the binaural and monaural hearing systems. In these experiments, the masking stimulus contained both a sinusold, which was gated simultaneously with a 100-ms signal, and a continuous broad-band noise musket. The frequency of the tonal masker was varied while that of the signal was fixed at 500 Hz. Signal thresholds were obtained in a 3 ITFC paradigm with an updown adaptive procedure. In the first part of the experiment, the tonal musket was omitted and noise levels were selected so that signals in N0Sπ and NmSm conditions were equally detectable. When a tonal musket which was intense relative to the noise was subsequently introduced a comparison of masking functions obtained for N0M0Sπ, N0MπSπ, and NmMmSm, conditions (here “M” denotes the tonal masker) suggests that the binaural and monaural systems possess identical internal filters. However, a replication of the N0MπSπ and NmMmSm conditions with a low masker-to-noise ratio leads to a different conclusion: that the binaural system is less frequency selective than the monaural system. The implications of these results are discussed. [Work supported by the Neurobehavioral Sciences Program, University of Iowa.]