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Objective Snoring can be excited in different locations within the upper airways during sleep. It was hypothesised that the excitation locations are correlated with distinct acoustic characteristics of the snoring noise. To verify this hypothesis, a database of snore sounds is developed, labelled with the location of sound excitation. Methods Video and audio recordings taken during drug induced sleep endoscopy (DISE) examinations from three medical centres have been semi-automatically screened for snore events, which subsequently have been classified by ENT experts into four classes based on the VOTE classification. The resulting dataset containing 828 snore events from 219 subjects has been split into Train, Development, and Test sets. An SVM classifier has been trained using low level descriptors (LLDs) related to energy, spectral features, mel frequency cepstral coefficients (MFCC), formants, voicing, harmonic-to-noise ratio (HNR), spectral harmonicity, pitch, and microprosodic features. Results An unweighted average recall (UAR) of 55.8% could be achieved using the full set of LLDs including formants. Best performing subset is the MFCC-related set of LLDs. A strong difference in performance could be observed between the permutations of train, development, and test partition, which may be caused by the relatively low number of subjects included in the smaller classes of the strongly unbalanced data set. Conclusion A database of snoring sounds is presented which are classified according to their sound excitation location based on objective criteria and verifiable video material. With the database, it could be demonstrated that machine classifiers can distinguish different excitation location of snoring sounds in the upper airway based on acoustic parameters.

Objective- The distinction of snoring and loud breathing is often subjective and lies in the ear of the beholder. The aim of this study is to identify and assess acoustic features with a high suitability to distinguish these two classes of sound, in order to facilitate an objective definition of snoring based on acoustic parameters. Methods- A corpus of snore and breath sounds from 23 subjects has been used that were classified by 25 human raters. Using the openSMILE feature extractor, 6 373 acoustic features have been evaluated for their selectivity comparing SVM classification, logistic regression, and the recall of each single feature. Results- Most selective single features were several statistical functionals of the first and second mel frequency spectrum-generated perceptual linear predictive (PLP) cepstral coefficient with an unweighted average recall (UAR) of up to 93.8%. The best performing feature sets were low level descriptors (LLDs), derivatives and statistical functionals based on fast Fourier transformation (FFT), with a UAR of 93.0%, and on the summed mel frequency spectrum-generated PLP cepstral coefficients, with a UAR of 92.2% using SVM classification. Compared to SVM classification, logistic regression did not show considerable differences in classification performance. Conclusion- It could be shown that snoring and loud breathing can be distinguished by robust acoustic features. The findings might serve as a guidance to find a consensus for an objective definition of snoring compared to loud breathing.

Computational human head models have been used in electrophysiological studies, and they have been able to provide useful information that is unable or difficult to acquire from experimental or imaging studies. However, most of these models are purely volume conductor models that overlooked the electric excitability of axons in the white matter of the brain. This study combined a finite element (FE) model of electroconvulsive therapy (ECT) with a whole-brain tractography analysis as well as the cable theory of neuronal excitation. We have reconstructed a whole-brain tractogram with 500 neural fibres from the diffusion-weighted magnetic resonance scans, and extracted the information on electrical potential from the FE ECT model of the same head. We then calculated the first and second spatial derivatives of the electrical potential, which describes the activating function for homogenous axons and investigated sensitive regions of white matter activation.

Three-dimensional (3D) computational models of the inner ear have been utilised to assist in investigating the factors that influence cochlear implant (CI) outcomes. A volume conductor cochlear model with an implanted electrode array was reconstructed from X-ray microtomography $(\mu$ CT) scans of a cadaveric human temporal bone. To mimic an in-vivo setting, the cochlea was embedded in a head model. The finite element (FE) method was used to analyse the electrical potential $\varphi$ in the cochlear nerve as a result of CI stimulation. In order to study the influence of electrode array placement on the current spread within the cochlea and the modiolus, computer simulations with six electrode array placements were conducted. $\varphi$ was evaluated at the tip of nerve fibres reconstructed within the cochlear nerve so as to predict the stimulation of a neuron population. It was found in most cases that a medial electrode array placement produced a narrower $\varphi$ peak at the fibre tip than a lateral one, although the differences were small.

In cochlear implants, severe limitations arise from electrical crosstalk between channels. Therefore, the current trend in cochlear implants is to increase stimulation rates to encode signals with higher temporal precision. However, the fundamental question: "What is the limit of temporal precision due to inherent neuronal dynamics of the stimulated neurons?" has not yet been resolved. In this study we have developed a double-pulse method and, for the first time, reversed stimulus polarity systematically between consecutive pulses to elucidate subthreshold-induced temporal interaction effects. This method allowed us to determine the time-course of subthreshold temporal interaction in human subjects which identifies the limits of encoded temporal precision. Our results show significant temporal interaction up to 600 μs inter-pulse interval. In all the cases tested we saw a facilitation effect on threshold. Interaction effects at a 20% below threshold pre-conditioning stimulation showed up to 38% ± 6% threshold reduction. These results imply that there is significant temporal interaction between two subsequent pulses. This interaction diminishes the precision of amplitude coding. We predict interaction effects on temporal precision and channel interaction. For (interleaved) stimulation with short inter-pulse intervals it is interesting to consider our interaction results; and it may become important to consider them for future coding strategies where high temporal precision is required. In an increasing group of binaural implanted patients this will be the case when interaural time differences are encoded with μs precision.

Objective: Obstructive sleep apnea (OSA) is a serious chronic disease and a risk factor for cardiovascular diseases. Snoring is a typical symptom of OSA patients. Knowledge of the origin of obstruction and vibration within the upper airways is essential for a targeted surgical approach. Aim of this paper is to systematically compare different acoustic features, and classifiers for their performance in the classification of the excitation location of snore sounds. Methods: Snore sounds from 40 male patients have been recorded during drug-induced sleep endoscopy, and categorized by Ear, Nose & Throat (ENT) experts. Crest Factor, fundamental frequency, spectral frequency features, subband energy ratio, mel-scale frequency cepstral coefficients, empirical mode decomposition-based features, and wavelet energy features have been extracted and fed into several classifiers. Using the ReliefF algorithm, features have been ranked and the selected feature subsets have been tested with the same classifiers. Results: A fusion of all features after a ReliefF feature selection step in combination with a random forests classifier showed the best classification results of 78% unweighted average recall by subject independent validation. Conclusion: Multifeature analysis is a promising means to help identify the anatomical mechanisms of snore sound generation in individual subjects. Significance: This paper describes a novel approach for the machine-based multifeature classification of the excitation location of snore sounds in the upper airway.

In certain conditions, especially with diotic headphone presentation, hearing sensations are located inside the head. Dichotic headphone presentation can result in lateralization: delaying one of the headphone input signals or reducing its amplitude typically pushes the hearing sensation inside the head towards the contralateral ear. Systematic connections between physical stimulus parameters and hearing-sensation positions provide insight into auditory-localization mechanisms and are helpful in designing and evaluating models. However, typical paradigms of addressing lateral displacement, magnitude estimation or pointing, may suffer from response biases. This study aims at evaluating the suitability of a two-alternative forced choice paradigm: eight normal-hearing subjects were asked to indicate, by pushing one of two buttons, whether the hearing sensation associated with a pure interaural phase or intensity difference occurred “left or right”, without any reference or further instructions. Posing a notably simple task without internal mapping, this procedure appears advantageous regarding response biases. The results indicate a high intra-individual reproducibility and plausible inter-individual agreement. None of the participants encountered or reported difficulties using the inherently assumed “internal center” in their decision process. The data suggests the existence of an inter-individually similar decision criterion. Descriptively speaking, the results support the existence of a similar lateralization midpoint.In certain conditions, especially with diotic headphone presentation, hearing sensations are located inside the head. Dichotic headphone presentation can result in lateralization: delaying one of the headphone input signals or reducing its amplitude typically pushes the hearing sensation inside the head towards the contralateral ear. Systematic connections between physical stimulus parameters and hearing-sensation positions provide insight into auditory-localization mechanisms and are helpful in designing and evaluating models. However, typical paradigms of addressing lateral displacement, magnitude estimation or pointing, may suffer from response biases. This study aims at evaluating the suitability of a two-alternative forced choice paradigm: eight normal-hearing subjects were asked to indicate, by pushing one of two buttons, whether the hearing sensation associated with a pure interaural phase or intensity difference occurred “left or right”, without any reference or further instructions. Posing a nota...

Globular bushy cells (GBCs) located in the ventral cochlear nucleus are an essential part of the sound localization pathway in the mammalian auditory system. They receive inputs directly from the auditory nerve and are particularly sensitive to temporal cues due to their synaptic and membrane specializations. GBCs act as coincidence detectors for incoming spikes through large synapses—endbulbs of Held—which connect to their soma. Since endbulbs of Held are an integral part of the auditory information conveying and processing pathway, they were extensively studied. Virtually all in vitro studies showed large synaptic depression, but on the other hand a few in vivo studies showed relatively small depression. It is also still not well understood how synaptic properties functionally influence firing properties of GBCs. Here we show how different levels of synaptic depression shape firing properties of GBCs in in vivo-like conditions using computer simulations. We analyzed how an interplay of synaptic depression (0–70%) and the number of auditory nerve fiber inputs (10–70) contributes to the variability of the experimental data from previous studies. We predict that the majority of synapses of GBCs with high characteristic frequencies (CF > 500 Hz) have a rate dependent depression of less than 20%. GBCs with lower CF (

This review evaluates the potential of optogenetic methods for the stimulation of the auditory nerve and assesses the feasability of optogenetic cochlear implants (CIs). It provides an overview of all critical steps like opsin targeting strategies, how opsins work, how their function can be modeled and included in neuronal models and the properties of light sources available for optical stimulation. From these foundations, quantitative estimates for the number of independent stimulation channels and the temporal precision of optogenetic stimulation of the auditory nerve are derived and compared with state-of-the-art electrical CIs. We conclude that optogenetic CIs have the potential to increase the number of independent stimulation channels by up to one order of magnitude to about 100, but only if light sources are able to deliver confined illumination patterns independently and parallelly. Already now, opsin variants like ChETA and Chronos enable driving of the auditory nerve up to rates of 200 spikes/s, close to the physiological value of their maximum sustained firing rate. Apart from requiring 10 times more energy than electrical stimulation, optical CIs still face major hurdles concerning the safety of gene transfection and optrode array implantation, for example, before becoming an option to replace electrical CIs.

The present study evaluated whether the poorer baseline performance of cochlear implant (CI) users or the technical and/or physiological properties of CI stimulation are responsible for the absence of masking release.This study measured speech reception thresholds (SRTs) in continuous and modulated noise as a function of signal to noise ratio (SNR).A total of 24 subjects participated: 12 normal-hearing (NH) listeners and 12 subjects provided with recent MED-EL CI systems.The mean SRT of CI users in continuous noise was -3.0 ± 1.5 dB SNR (mean ± SEM), while the normal-hearing group reached -5.9 ± 0.8 dB SNR. In modulated noise, the difference across groups increased considerably. For CI users, the mean SRT worsened to -1.4 ± 2.3 dB SNR, while it improved for normal-hearing listeners to -18.9 ± 3.8 dB SNR.The detrimental effect of fluctuating maskers on SRTs in CI users shown by prior studies was confirmed by the current study. Concluding, the absence of masking release is mainly caused by the technical and/or physiological properties of CI stimulation, not just the poorer baseline performance of many CI users compared to normal-hearing subjects. Speech understanding in modulated noise was more robust in CI users who had a relatively large electrical dynamic range.

Biomedical optics express 9(11), 5330 - 5339 (2018). doi:10.1364/BOE.9.005330, Propagation-based phase-contrast computed tomography has become a valuable tool for visualization of three-dimensional biological samples, due to its high contrast between materials with similar attenuation properties. However, one of the most-widely used phase-retrieval algorithms imposes a homogeneity assumption onto the sample, which leads to artifacts for numerous applications where this assumption is violated. Prominent examples are biological samples with highly-absorbing implants. Using synchrotron radiation, we demonstrate by the example of a guinea pig inner ear with a cochlear implant electrode, how a recently developed model-based iterative algorithm for propagation-based phase-contrast computed tomography yields distinct benefits for such a task. We find that the model-based approach improves the overall image quality, removes the detrimental influence of the implant and accurately visualizes the cochlea., Published by OSA, Washington, DC

In certain conditions, especially with diotic headphone presentation, hearing sensations are located inside the head. Dichotic headphone presentation can result in lateralization: delaying one of the headphone input signals or reducing its amplitude typically pushes the hearing sensation inside the head towards the contralateral ear. Systematic connections between physical stimulus parameters and hearing-sensation properties provide insight into auditory-localization mechanisms and are helpful in designing and evaluating models thereof. While various studies on the lateral displacement of hearing sensations exist, fewer data is available on the respective shape or spatial extent. Based on observations from a pure-tone lateralization experiment, this study aims at taking a first step towards quantifying the typical shape of the corresponding hearing sensations: in two separate experiments, twelve normal-hearing subjects reported a) the overall spatial extent of the hearing sensation or, if applicable, of all simultaneously occurring sensations and b) the number of simultaneously occurring, spatially separated hearing sensations. The data suggests, in line with earlier studies, considerable differences between the results for pure interaural phase and amplitude differences, respectively. Based on the results, an initial empirical description of the stimulus-dependent hearing sensations in pure-tone lateralization summarizes the observations, especially regarding location and spatial shape.In certain conditions, especially with diotic headphone presentation, hearing sensations are located inside the head. Dichotic headphone presentation can result in lateralization: delaying one of the headphone input signals or reducing its amplitude typically pushes the hearing sensation inside the head towards the contralateral ear. Systematic connections between physical stimulus parameters and hearing-sensation properties provide insight into auditory-localization mechanisms and are helpful in designing and evaluating models thereof. While various studies on the lateral displacement of hearing sensations exist, fewer data is available on the respective shape or spatial extent. Based on observations from a pure-tone lateralization experiment, this study aims at taking a first step towards quantifying the typical shape of the corresponding hearing sensations: in two separate experiments, twelve normal-hearing subjects reported a) the overall spatial extent of the hearing sensation or, if applicable, of a...

The auditory system of humans and other mammals is able to use interaural time and intensity differences as well as spectral cues to localize sound sources. One important cue for localizing low-frequency sound sources in the horizontal plane are interaural time differences (ITDs), which are first analyzed in the medial superior olive (MSO) in the brainstem. Results from electrophysiological and psychoacoustic studies suggest ITD encoding in the relative activities of neuronal populations in the two brain hemispheres. This contribution first explores the neuronal encoding of fine-structure ITDs using a physiologically motivated spiking neuronal-network model of the mammalian MSO. Results from this model confirm robust ITD encoding in the relative activity of the MSOs in both hemispheres. Based on the neuronal-network simulations, a simple probabilistic model of subsequent ITD processing is proposed. This simplified model connects the neuronal responses of the two hemispheres with different hearing sensatio...

Videomicroscopy with subpixel analysis is an excellent system for quantification of outer hair cell (OHC) movements. The resolution of a few nanometers is accurate enough to show induced differences of electromotility.Electromotility of OHCs is a voltage-dependent process resulting from a membrane protein named prestin. Voltage sensitivity is conferred to prestin by intracellular anions. Reduction of these anions reduces electromotility. Videomicroscopy and subpixel tracking combine video-based analysis with a resolution of few nanometers. The aim of this study was to show the feasibility of a system for quantification of OHC movements.Electromotility was investigated under normal and reduced intracellular chloride conditions. Cells were stimulated by the patch-clamp technique. Voltage steps were 500 ms long, ranging from -170 to +30 mV in 10 mV steps.As in previous studies our results show the following. The direction of OHC movement depends on the polarity of voltage steps, length changes are not equal for symmetrical voltage steps of opposite polarity, average shortening for a depolarizing step (-70 mV to +30 mV) is about 13 nm/mV. Hyperpolarization (-70 mV to -170 mV) on average evokes elongations of about 3 nm/mV. Half maximal chloride concentration reduces motility by 14%; half maximal electromotility is reached by a 94% reduction of chloride.

Several possibilities exist for quantifying speech intelligibility in noise, for example tests with single words or sentences. In the clinical routine, usually a single sentence test is used repeatedly, so that its vocabulary is often known to the patients. Thus, not only speech intelligibility but also long-term memory is tested. New speech material is then required to explicitly address intelligibility. With the aim of providing new and optimized material, in this pilot study, semantically, syntactically, and phonetically balanced words were taken from German sentence tests, based on databases for written and spoken German words. The resulting vocabulary consists of 54 words (nouns, adjectives, verbs, and numbers), for which word-reception thresholds were determined for ten normal-hearing subjects. With these thresholds, five-word lists of equal semantic context, equal word intelligibility, and with balanced phonetic cues were built. Non-acoustic advantages of an intelligibility test constructed this wa...

Our notion of how speech is processed is still very much dominated by von Helmholtz's theory of hearing. He deduced that the human inner ear decomposes the spectrum of sound signals. However, physiological recordings of auditory nerve fibers (ANF) showed that the rate-place code, which is thought to transmit spectral information to the brain, is at least complemented by a temporal code. In our paper we challenge the rate-place code using a complex but realistic scenario: speech in noise. We used a detailed model of human auditory processing that closely replicates key aspects of auditory nerve spike trains. We performed quantitative evaluations of coding strategies using standard automatic speech recognition (ASR) tools. Our test data was spoken letters of the whole English alphabet from a variety of speakers, with and without background noise. We evaluated a purely rate-place-based encoding strategy, a temporal strategy based on interspike intervals, and a combination thereof. The results suggest that as few as 4% of the total number of ANFs would be sufficient to code speech information in a rate-place fashion. Rate-place coding performed its best for speech in clean conditions at normal sound level, but broke down at higher-than-normal levels, and failed dramatically in noise at high levels. Low-spontaneous rate fibers improved the rate-place code, mainly for vowels and at higher-than-normal levels. At high speech levels, and in particular in the presence of background noise, combining rate-place coding with the temporal coding strategy greatly improved recognition accuracy. We therefore conclude that the human auditory system does not rely on a rate-place code alone but requires the abundance of fibers for precise temporal coding.

The mel-frequency cepstral coefficient (MFCC) or perceptual linear prediction (PLP) feature extraction typically used for automatic speech recognition (ASR) employ several principles which have known counterparts in the cochlea and auditory nerve: frequency decomposition, mel- or bark-warping of the frequency axis, and compression of amplitudes. It seems natural to ask if one can profitably employ a counterpart of the next physiological processing step, synaptic adaptation. We, therefore, incorporated a simplified model of short-term adaptation into MFCC feature extraction. We evaluated the resulting ASR performance on the AURORA 2 and AURORA 3 tasks, in comparison to ordinary MFCCs, MFCCs processed by RASTA, and MFCCs processed by cepstral mean subtraction (CMS), and both in comparison to and in combination with Wiener filtering. The results suggest that our approach offers a simple, causal robustness strategy which is competitive with RASTA, CMS, and Wiener filtering and performs well in combination with Wiener filtering. Compared to the structurally related RASTA, our adaptation model provides superior performance on AURORA 2 and, if Wiener filtering is used prior to both approaches, on AURORA 3 as well.

In this paper, we investigate computing air damping in a comb-drive resonator by numerically solving the three-dimensional (3-D) Stokes equation for the entire resonator using the FastStokes Solver. In addition, we used a recently developed computer microvision system to directly measure resonator frequency response. By comparing the measured results to those generated by one dimensional analytic models and by numerical solution of the 3-D Stokes' equation, we demonstrate that numerically solving the Stokes' equation is fast and also generates a model that matches quality the factor to within 10%. We also show that results based on one-dimensional (1-D) models mispredict quality factor by more than a factor of two. In addition, the detailed drag force distribution generated by the FastStokes solver is used to identify sources of errors in the 1-D models.

Dynamic material properties of the tectorial membrane (TM) have been measured at audio frequencies in TMs excised from the apical portions of mouse cochleae. We review, integrate, and interpret recent findings. The mechanical point impedance of the TM in the radial, longitudinal, and transverse directions is viscoelastic and has a frequency dependence of the form 1/(K(j2pif)(alpha)) for 10or=for=4000 Hz, where f is frequency, K is a constant, j=-1, and alpha approximately 0.66. Comparison with other connective tissues shows that the TM is a relatively lossy viscoelastic material. The median magnitudes of the point impedance at 10 Hz in the radial, longitudinal, and transverse directions are 4.6 x 10(-3) N.s/m, 1.8 x 10(-3) N.s/m, and 2.7 x 10(-3) N.s/m. Consistent with osmotic responses (Freeman et al., 2003), the TM point impedance is anisotropic - the TM is stiffer in the radial than in the longitudinal and transverse directions. The mechanical space constant of the TM is approximately 20 microm. Comparisons reveal that in the apical region of the mouse cochlea, the TM dynamic stiffness at 10 Hz is 10 times larger than the static stiffness of the aggregate hair cells in a mechanical space constant and roughly comparable to the stiffness of the basilar membrane. We conclude that the TM provides a mechanical load on the basilar membrane and that the lability of the TM to changes in endolymph composition may well be reflected in changes in basilar membrane motion.

Models are valuable tools to assess how deeply we understand complex systems: only if we are able to replicate the output of a system based on the function of its subcomponents can we assume that we have probably grasped its principles of operation. On the other hand, discrepancies between model results and measurements reveal gaps in our current knowledge, which can in turn be targeted by matched experiments. Models of the auditory periphery have improved greatly during the last decades, and account for many phenomena observed in experiments. While the cochlea is only partly accessible in experiments, models can extrapolate its behavior without gap from base to apex and with arbitrary input signals. With models we can for example evaluate speech coding with large speech databases, which is not possible experimentally, and models have been tuned to replicate features of the human hearing organ, for which practically no invasive electrophysiological measurements are available. Auditory models have become instrumental in evaluating models of neuronal sound processing in the auditory brainstem and even at higher levels, where they are used to provide realistic input, and finally, models can be used to illustrate how such a complicated system as the inner ear works by visualizing its responses. The big advantage there is that intermediate steps in various domains (mechanical, electrical, and chemical) are available, such that a consistent picture of the evolvement of its output can be drawn. However, it must be kept in mind that no model is able to replicate all physiological characteristics (yet) and therefore it is critical to choose the most appropriate model—or models—for every research question. To facilitate this task, this paper not only reviews three recent auditory models, it also introduces a framework that allows researchers to easily switch between models. It also provides uniform evaluation and visualization scripts, which allow for direct comparisons between models.

High-frequency resolution is one of the salient features of peripheral sound processing in the mammalian cochlea. The sensitivity originates in the active amplification of the travelling wave on the basilar membrane by the outer hair cells (OHCs), where electrically induced mechanical action of the OHC on a cycle-by-cycle basis is believed to be the crucial component. However, it is still unclear if this electromechanical action is sufficiently fast and can produce enough force to enhance mechanical tuning up to the highest frequencies perceived by mammals. Here we show that isolated OHCs in the microchamber configuration are able to overcome fluid forces with almost constant displacement amplitude and phase up to frequencies well above their place-frequency on the basilar membrane. The high-frequency limit of the electromotility, defined as the frequency at which the amplitude drops by 3 dB from its asymptotic low-frequency value, is inversely dependent on cell length. The frequency limit is at least 79 kHz. For frequencies up to 100 kHz, the electromotile response was specified by an overdamped ( Q = 0.42) second-order resonant system. This finding suggests that the limiting factor for frequencies up to 100 kHz is not the speed of the motor but damping and inertia. The isometric force produced by the OHC was constant at least up to 50 kHz, with amplitudes as high as 53 pN/mV being observed. We conclude that the electromechanical transduction process of OHCs possesses the necessary high-frequency properties to enable amplification of the travelling wave over the entire hearing range.

A complete battery of audiometric methods is required for the differential diagnosis of different hearing disabilities (including puretone audiometry, impedance, stapes reflex, speech audiometry, brainstam evoked response audiometry, otoacoustic emissions, etc.). In many cases, a comprehensive diagnosis is not possible. Here we describe a new technique based on a laser-Doppler vibrometer that has the potential for non-invasive diagnosis not only middle ear disease but also cochlear pathologies. Disturbance of cochlear function can be ascertained because the input impedance of the cochlea acts as a mechanical load on the middle ear and therefore influences motion of the umbo. In the present study vibration of the umbo and eardrum were measured with a commercially available laser-Doppler vibrometer coupled directly into a standard surgical microscope. The use of the microscope allowed non-invasive measurements of vibrations without having to introduce reflecting material onto the tympanic membrane. Sound pressure was measured with a calibrated probe microphone placed near the tympanic membrane. The displacement response and the specific acoustic impedance of the umbo were calculated from the velocity and sound pressure measured. For normal hearing subjects, the amplitude of the umbo's displacement for frequencies from 0.1 kHz to 1 kHz was 1 nm at 60 dB SPL and decreased with a slope of 6 dB/octave for frequencies between 1 and 5 kHz. A strong correlation was found between the specific acoustic impedance of the umbo and hearing thresholds for hearing-impaired subjects (having otosclerosis or sensorineural hearing losses). The frequency response of the umbo proved to be a means for evaluating the function of both the middle ear and the cochlea under pathological conditions. The measurement technique described is also suitable for intraoperative investigation of the frequency response of the opened middle ear, as well as for the in situ frequency response of partial and total ossicular replacement prostheses.

In this paper a new similarity index for neurograms is proposed. This index is inspired by the Needleman-Wunsch algorithm which determines the minimum number of operations to transform a vector into another in terms of insertions, deletions and substitutions. The Needleman-Wunsch algorithm can be extended to the two dimensional case and the number of transformations required to change a matrix into another is used to define a measure of similarity. This similarity measure is applied to neurograms and optimized to perform prediction of speech intelligibility in noise. Word recognition scores for for speech samples in noise are evaluated using the proposed similarity index, showing a clear improvement in speech intelligibility estimation with respect to other neurogram similarity metrics in the literature. The proposed similarity index is not restricted to a certain time resolution and could serve to evaluate neurogram similarity with respect to temporal fine structure in future.

This chapter describes a model framework for evaluating the precision of as to which interaural time differences, ITD, are represented in the left- and right-ear auditory-nerve responses. This approach is very versatile, as it allows not only for the evaluation of spiking neuronal responses from models of intact inner ears but also of responses of the deaf ears of cochlear implantees. The model framework delivers quantitative data and, therefore, enables comparisons between different cochlear-implant coding strategies. As the model of electric excitation of the auditory nerve also includes effects such as channel crosstalk, neuronal adaptation and mismatch of electrode positions between left and right ears, its predictive power is much higher than an analysis of the electrical impulses delivered to the electrodes. Evaluation of a novel fine-structure-coding strategy as used by a major implant manufacturer, revealed that, in a best case scenario, sophisticated strategies should be able to provide ITD cues with sufficient precision for sound localization. However, whether these cues can actually be exploited by cochlear implant users has yet to be determined by listening tests. Nevertheless, the model framework introduced here is a valuable tool for the development and pre-evaluation of bilateral cochlear implant coding strategies.

To test the hypothesis that the tip-links of hair-cell stereocilia are essential for mechanoelectrical transduction, tip-links of isolated outer hair cells (OHCs) of the guinea-pig cochlea were eliminated with a proteolytic enzyme, elastase, and the influence on the receptor potential measured with the whole-cell patch-clamp technique. Within 45 s of immersion of the hair bundle in 20 IU/ml elastase, the receptor potential in response to direct deflection of the hair bundle was irreversibly abolished. The electrical input impedance of the cell remained unchanged, implying that the channels of the basolateral membrane were not affected by elastase. The effect of elastase on the receptor potential was comparable to changes seen after mechanically induced hair-bundle damage. As a further control, a putative transduction-channel blocker, dihydrostreptomycin (68 microM), which does not affect tip-links, was applied to the hair bundle. Although the receptor potential was also blocked by dihydrostreptomycin, the effect was reversible. The results suggest that tip-links are required for mechanoelectrical transduction of mammalian OHCs.

Several possibilities exist for quantifying speech intelligibility in noise, for example tests with single words or sentences. In the clinical routine, usually a single sentence test is used repeatedly, so that its vocabulary is often known to the patients. Thus, not only speech intelligibility but also long term memory is tested. New speech material is then required to explicitly address intelligibility. With the aim of providing new and optimized material, in this study, semantically, syntactically, and phonetically balanced words were taken from German sentence tests, based on databases for written and spoken German words. The resulting vocabulary consists of 54 words (nouns, adjectives, verbs, and numbers), for which word-reception thresholds were determined for ten normal-hearing subjects. With these thresholds, five-word lists of equal semantic context, equal word intelligibility, and with balanced phonetic cues were built. Non-acoustic advantages of an intelligibility test constructed this way are ...

Sound-induced displacement responses in the plane of the organ of Corti were studied in the apical turn in the isolated temporal-bone preparation of the guinea-pig cochlea. Swept sinusoidal sound stimuli (100-500 Hz) were delivered closed-field to the external auditory meatus. The surface of the organ of Corti was continuously monitored using a CCD video camera. Displacement responses in the plane of the organ of Corti were determined by analyzing the change of the location of the cells (pixel-by-pixel) within the visual field of the microscope. Displacement responses followed the stimulus amplitude and were observable at Hensen's cells, three rows of outer hair cells and inner hair cells. The most prominent displacement responses were over the outer hair cells; the maximum amplitude was 0.6-1.7 microns at 100 dB SPL. Tuned displacement responses were found; the Q10 dB was 1.3 +/- 0.6. The best frequency was tonotopically organized, decreasing toward the apex with a space constant of 0.4-0.9 mm/oct. The motion was directed either strial-apically or strial-basally in a frequency dependent manner. With the aid of laser interferometric measurements of the transverse displacement, it was concluded that sound stimulation does not induce slow DC motion in the organ of Corti for the isolated temporal-bone preparation.

Outer hair cells (OHC) were isolated from the apical two turns of the guinea-pig cochlea and their hair-bundle stimulated mechanically by a glass probe. In accordance with in vivo data (Dallos, 1985), the resting membrane potential was typically -64 mV (N = 200). The maximum amplitudes of the receptor potentials were between 0.4 and 5.2 mV peak-to-peak, with mean of 1.5 mV +/- 0.9 mV (N = 81). The sensitivity was 0.015 mV/nm or 2 mV/deg. The frequency response of the receptor potential followed a first order low-pass filter characteristic with a corner frequency of about 63 Hz. For frequencies up to at least 1.6 kHz, the frequency response of mechanoelectrical transduction was dominated by the electrical input impedance of the cell. The presence of a single time constant in the voltage response to stereociliary deflection implies that the frequency response of mechanoelectrical transduction far exceeds that of the electrical input impedance of the cell; its time constant must be faster than 100 microseconds. Under in vivo conditions, OHC should be capable of providing a sufficiently large receptor potential to supply enough energy for electromechanical feedback.

Auditory nerve fibers (ANF) convey information about sound to the central nervous system. For both normal hearing subjects and cochlear implant patients the most drastic step of sound coding for neuronal processing is when the analog signal is converted into discrete nerve-action potentials. As any information lost during this process is no longer available for neural processing, it is important to understand the underlying principles of sound coding in the intact auditory system and the limitations in the case of direct electrical stimulation of the auditory nerve. Here we focus on a model of spiral ganglion type I neurons with Hodgkin-Huxley type ion channels, which are also found in cochlear nucleus neurons. Depending on the task, we model the neurons at different levels of detail. Our results show that for acoustic stimuli, the model provides realistic refractoriness and generates more realistic spike trains compared to a spike generator with absolute and exponentially decaying refractoriness added. Not surprisingly, speech discrimination in electrical hearing is lower than in acoustic hearing. On the other hand, the analysis of transmitted information shows that the temporal precision of coding seems to be very high because at levels well above threshold, action potentials are elicited quasi-deterministic by the electrical stimuli. We argue that CIS strategies a) waste as much as 50

In the inner ear sounds are converted into action potentials and propagated to the central nervous system. The cochlear nucleus in the auditory brainstem is the first station that receives synaptic inputs from auditory nerve fibers (ANF) and consists of several neuron types. Here we focus on globular bushy cells (GBC) that are part of the sound localization pathway. One of the main properties of GBC is their excellent temporal firing precision in response to sounds.Our model of GBCs is a point neuron with Hodgkin-Huxley type ion channels (HPAC, Kht, Klt). It receives several excitatory inputs from an inner ear model simulating responses of ANFs. ANF activity drives endbulb of Held synapses located directly on the GBC soma. We modeled two types of synapses: with short-term depression as measured in many in-vitro studies (Yang and Xu-Friedman 2009) and without depression as reported by recent in-vivo studies (Borst 2010).The model is able to reproduce standard experiments involving pure tone stimulation. In particular the PSTH displays proper levels of spontaneous and driven rates as well as characteristic primary-like with notch shapes. Additionally, stimulation with low frequency tones shows improvement in synchronization that can be characterized as high-sync (SI > 0.9) according to Joris et al. (1994). Interestingly high entrainment levels where achieved only by the model without synaptic depression.In summary, our model is able to reproduce the key features of GBC responses. Our results suggest that depression in-vivo is much lower compared to in-vitro conditions. In the future, the model will allow us to study the response of GBCs to complex natural stimuli like speech.

The auditory pathway is an excellent system to study temporal aspects of neuronal processing. Unlike other sensory systems, temporal cues cover an extremely wide range of information: for sound localization, interaural time differences with a precision of tens of microseconds are extracted. Phase-locking of auditory nerve responses, which is related to the coding of the temporal fine structure, occurs from the lowest audible frequencies probably up to 3 kHz in humans. Amplitude modulations in speech signals are processed in the ms to tens of ms range. And finally, the energy of spoken speech itself is modulated with a frequency of about 4 Hz, corresponding to a syllable frequency in the order of few hundreds of ms. To extract temporal cues at all timescales, it is important to understand how temporal information is coded. We investigate temporal coding of speech signals using the methods of information theory and a model of the human inner ear. The model is based on a traveling-wave model, a nonlinear compression stage which mimics the function of the "cochlear amplifier", a model of the sensory cells, the afferent synapse and spike generation (Sumner ) which we extended to replicate "offset adaptation" (Zhang). We used the action potentials of the auditory nerve to drive Hodgkin-Huxley-type point models of various neurons in the cochlear nucleus. In this investigation we only report data from onset neurons, which exhibit extraordinary fast membrane time-constants below 1 ms. Onset neurons are known for their precise temporal processing. They achieve precisely timed action potentials by coincidence detection: they fire only if at least 10% of the auditory nerve fibers which innervate them fire synchronously. With information theory, we analyzed the transmitted information rate coded in neural spike trains of modeled neurons in the cochlear nucleus for vowels. We found that onset neurons are able to code temporal information with sub-millisecond precision (

Cochlear implants are extremely successful devices, they provide open speech understanding for most patients, despite their limited spectral- and temporal resolution. The largest detriments in performance are in noisy conditions, the appreciation of music, perception of tonal languages and spatial hearing. As for these tasks temporal information is thought to play a crucial role, we analyzed the precision of coding by neurons in the auditory brainstem using the framework of information theory. We used our model of peripheral sound processing, which codes sound into realistic spike trains of the auditory nerve followed by Hodgkin-Huxley type neurons in the first neural processing stage, the auditory brainstem. Stellate neurons, which integrate approximately five supra-threshold inputs from auditory nerve fibers, code the spectral energy of sound. In contrast, the so-called octopus neurons, which exhibit strong onset characteristics, achieve exquisite temporal precision by coincidence detection of their innervating auditory nerve fibers. They are able to code information with a precision in the 20 μs range, which is required for spatial hearing, where octopus neurons are believed to play a key role. For both neuron types, the major portion of information is coded with a temporal precision ranging from 0.2 to 4 ms. Our results motivate novel coding strategies for cochlear implants which code temporal information with much higher fidelity. Only temporal precision in the μs-range will allow children with bilateral implants to develop the neuronal circuitry required for spatial localization based on temporal cues.

Our study focuses on biophysical modeling of the auditory periphery and initial stages of neural processing. We examined in detail synaptic excitation between inner hair cells and spiral ganglion type I neurons. Spiral ganglion neurons encode and convey information about sound to the central nervous system in the form of action potentials. For the purpose of our study we utilized a biophysical model of the auditory periphery proposed by Sumner (2002). It consists of outer/middle ear filters, a basilar membrane filter bank, an inner hair cell model coupled with complex vesicle pool dynamics at the presynaptic membrane. Finally, fusion of vesicles, modelled with a probabilistic function, releases neurotransmitter into the synaptic cleft. Response of auditory nerve fibers is modeled with a spike generator. The absolute refractory period is set to 0.75 ms and the relative refractory period is modelled with an exponentially decaying function. In our approach we substituted the artificial spike generation and refraction model with a more realistic spiral ganglion neuron model with Hodgkin-Huxley type ion channels proposed by Negm and Bruce (2008). The model included several channels also found in cochlear nucleus neurons (K_A, K_ht, K_lt). Our model consisted of the postsynaptic bouton (1.5x1.7µm) from high-spontaneous rate fibers. We coupled the model of the synapse with the spiral ganglion neuron using a synaptic excitation model fitted to results from Glowatzki and Fuchs' (2002) experiments, who conducted patch clamp measurements at the afferent postsynapse. We verified our hybrid model against various experiments, mostly pure tone stimulation. Rate intensity functions fitted experimental data well, rates varied from about 40 spikes/s to a maximum of 260 spikes/s. Adaptation properties were investigated with peri-stimulus time histograms (PSTH). As adaptation is mainly governed by vesicle pool dynamics, only small changes occurred compared with the statistical spike generation model and adaptation was consistent with experiments. Interestingly, Hodgkin-Huxley models of spiral ganglion neurons exhibited a notch visible in the PSTH after rapid adaptation that could also be observed in experiments. This was not revealed by the statistical spike generator. The fiber's refractory period was investigated using inter-spike interval histograms. The refractory period varied with simulus intensity from 1ms (spontaneous activity) to 0.7ms (84dB_SPL). We also analyzed phase locking with the synchronization index. It was slightly lower compared to the statistical spike generator. By varying the density of K_lt and K_A channels, we could replicate heterogenity of auditory nerve fibers as shown by Adamson et al. (2002). In summary, replacing the statistical spike generation model with a more realistic model of the postsynaptic membrane obsoletes the introduction of non-physiologic parameters for absolute and relative refraction. It improves the refractory behaviour and provides more realistic spike trains of the auditory nerve. Acknowledgments: Supported by within the Munich Bernstein Center for Computational Neuroscience by the German Federal Ministry of Education and Research (reference numbers 01GQ0441 and 01GQ0443).

A critical step in encoding sound for neuronal processing occurs when the analog pressure wave is coded into discrete nerve-action potentials. Recent pool models of the inner hair cell synapse do not reproduce the dead time period after an intense stimulus, so we used visual inspection and automatic speech recognition (ASR) to investigate an offset adaptation (OA) model proposed by Zhang et al. [1]. OA improved phase locking in the auditory nerve (AN) and raised ASR accuracy for features derived from AN fibers (ANFs). We also found that OA is crucial for auditory processing by onset neurons (ONs) in the next neuronal stage, the auditory brainstem. Multi-layer perceptrons (MLPs) performed much better than standard Gaussian mixture models (GMMs) for both our ANF-based and ON-based auditory features. Similar results were previously obtained with MSG (Modulation-filtered SpectroGram) auditory features[2]. Thus we believe researchers working with novel features should consider trying MLPs.

In this paper we use information theory to quantify the information in the output spike trains of modeled cochlear nucleus onset neurons. Onset neurons are known for their precise temporal processing, and they code the periodicity of voiced speech with high fidelity. We conclude that the maximum information transmission rate for a single neuron is close to 1000 bits/s, which corresponds to 3.26 bits/spike. For quasi-periodic signals like voiced speech, the transmitted information saturates with word duration, with 90% of the information being transmitted within 73 ms. Information theory also shows that the maximum temporal resolution of onset neurons is approximately 0.1 ms

A major difference between the human auditory system and automatic speech recognition (ASR) lies in their representation of sound signals: whereas ASR uses a smoothed low-dimensional temporal and spectral representation of sound signals, our hearing system relies on extremely high-dimensional but temporally sparse spike trains. A strength of the latter representation is in the inherent coding of time, which is exploited by neuronal networks along the auditory pathway. We demonstrate ASR results using features purely derived from simulated spike trains of auditory nerve fibers (ANF) and a layer of octopus neurons. Octopus neurons located in the cochlear nucleus are known for their distinct temporal processing: they not only reject steady-state excitation and fire on signal onsets but also enhance the amplitude modulations of voiced speech. With multi-condition training we do not reach the performance of conventional mel-frequency cepstral coefficients (MFCC) features. With clean training however, our spike-based features performed similarly to MFCCs. Further, recognition scores in noise were improved when features derived from ANFs, which mainly represent spectral characteristics of speech signals, were combined with features derived from spike trains of octopus neurons. This result is promising given the relatively small number of neurons we used and the limitations in how the auditory model was interfaced to the ASR back end.

This study provides a detailed quantitative description of the acoustically evoked vibration responses in the low-frequency region of the in vitro guinea-pig cochlea. Responses of the basilar membrane, the reticular lamina and Hensen cells were measured with a laser Doppler vibrometer, without the need for introducing artificial light reflectors. The apex of the cochlea was opened, leaving the helicotrema intact. Two response components were detected: a ‘fast’ component, which was probably caused by the hole in the cochlea, and a ‘slow’ component, which shared the features of a classical travelling wave. The velocity response of the ‘slow’ component exhibited a relatively flat low-frequency slope (15 dB/oct) and a much steeper high-frequency roll-off (third turn: −47 dB/oct; fourth turn: −35 dB/oct). The group delay was dependent on the characteristic frequency. In the fourth turn, the sharpness of the velocity tuning curves ( Q 10 dB : 1.0) was similar to those of in vivo mechanical and neural recordings, whereas in the third turn the tuning ( Q 10 dB : 1.1) was much less than for in vivo recordings. The results indicate that cochlear amplification, which is responsible for the high sensitivity and sharp tuning in the basal part of the cochlea, is much less pronounced in the apical turn of the cochlea.

The capacity of different audiological methods to detect a high noise susceptibility was examined in 20 normally hearing and 26 especially noise-susceptible subjects. The latter were selected from 422 soldiers in field studies: they had shown a temporary threshold shift (TTS) in pure tone audiometry (PTA) after regular training with firearms. In laboratory experiments, the TTS-positive soldiers were re-examined using greatly reduced sound intensities, which caused no TTS in a control subject group. Before and after acoustic stimulation, different subjective (PTA, high frequency audiometry (HFA), upper limit of hearing (ULH)) and objective (transiently evoked otoacoustic emissions (TEOAE), distortion products (DPOAE)) audiological tests were performed. After exposure to low impact noise in the laboratory, in both PTA and HFA, a TTS was observed in 11.5% (N = 3) of the noise-susceptible group (compared to 0% in the control group). In the TTS-positive group, deterioration of the ULH occurred in 28% (N = 7) (compared to 15% (N = 3) in the control group). An ULH improvement occurred in only one subject (3.8%) (compared to 25% (N = 5) in the control group). Significant alterations of click-evoked OAE-amplitudes were found in 26.9% (N = 7) of the selected groups, whereas stable emissions were observed in all but one subject (5%) of the control group. However, DPOAE alterations were seen in 19.2% (N = 5) of the TTS-positive soldiers but also in 25% (N = 5) of the control group. These results suggest that TEOAE provides a more sensitive and more objective method of detecting a subtle noise-induced disturbance of cochlear function than do PTA or DPOAE.

The efficient and systematic development of a middle ear prosthesis necessitates the use of computer models for the prosthesis itself and the reconstructed middle ear. The structure and parameters of the computer model have to be verified by specific measurements of the implant and the reconstructed ear. To obtain a realistic model of a reconstructed ear, three steps of modeling and measurements have been carried out. To get a first approach of the coupling elements a mechanical test rig representing a simplified reconstructed middle ear was built. The velocity of the stapedial footplate was measured with a laser Doppler vibrometer. The corresponding computer model was formulated, and the respective parameters were determined using the measured dynamical transfer functions. In the second step, a prosthesis was implanted into a human temporal bone without inner ear. Exciting this system with noise, the velocity of the stapes footplate was measured with the laser Doppler vibrometer. Based on the multibody system approach, a mechanical computer model was generated to describe the spatial motions of the reconstructed ossicular chain. Varying some significant parameters, simulations have been carried out. To describe the dynamical behavior of the system consisting of middle and inner ear, the computer model used in the second step has been enlarged by adding a simplified structure of the inner ear. The results were compared with in situ measurements taken from living humans.

An interferometric video system for measuring microelectromechanical systems (MEMS) with nanometer resolution is demonstrated. Interferograms are generated by combining light reflected from the target with light reflected from a reference mirror. Motions are determined from sequences of stop-action interferograms obtained with stroboscopic illumination. The system was used to measure motions of a microfabricated accelerometer. In-plane motions were determined by analysis of brightfield images using gradient methods with subpixel resolution. Results are compared for brightfield images obtained by blocking light from the reference arm of the interferometer and for brightfield images reconstructed from interferograms. Out-of-plane motions are determined by analyzing interferograms obtained with different positions of the reference mirror. Results demonstrate nanometer resolution of in-plane motions and subnanometer resolution of out-of-plane motions.

The tectorial membrane has long been postulated as playing a role in the exquisite sensitivity of the cochlea. In particular, it has been proposed that the tectorial membrane provides a second resonant system, in addition to that of the basilar membrane, which contributes to the amplification of the motion of the cochlear partition. Until now, technical difficulties had prevented vibration measurements of the tectorial membrane and, therefore, precluded direct evidence of a mechanical resonance. In the study reported here, the vibration of the tectorial membrane was measured in two orthogonal directions by using a novel method of combining laser interferometry with a photodiode technique. It is shown experimentally that the motion of the tectorial membrane is resonant at a frequency of 0.5 octave (oct) below the resonant frequency of the basilar membrane and polarized parallel to the reticular lamina. It is concluded that the resonant motion of the tectorial membrane is due to a parallel resonance between the mass of the tectorial membrane and the compliance of the stereocilia of the outer hair cells. Moreover, in combination with the contractile force of outer hair cells, it is proposed that inertial motion of the tectorial membrane provides the necessary conditions to allow positive feedback of mechanical energy into the cochlear partition, thereby amplifying and tuning the cochlear response.