Das Ziel der vorliegenden Arbeit war die Untersuchung einer Kohorte erwachsener Patienten mit einseitiger Taubheit (single-sided deafness SSD), die ein Cochlea-Implantat erhalten haben. Es sollten Faktoren ermittelt werden, die es ermöglichen, eine Voraussage über die spätere Hörleistung mit Cochlea Implantat treffen zu können. Der Beobachtungszeitraum umfasste die Jahre 2009 - 2016. Das Patientenkollektiv bestand aus 55 einseitig ertaubten Erwachsenen. Die Sprachverständlichkeit wurde mit dem Freiburger Zahlentest bei 65 dB SPL, dem Freiburger Einsilbertest bei 65 dB SPL und 80 dB SPL, sowie dem HSM-Satztest ohne Störgeräusch bei 65 dB SPL getestet. Es hat sich gezeigt, dass mit steigender Hörerfahrung mit einer Verbesserung der Hörkompetenz zu rechnen ist. Im untersuchten Patientenkollektiv schnitten Patienten mit der Kombination aus einer langen Ertaubungsdauer und einer entzündlichen Ätiologie signifikant schlechter ab als die Vergleichsgruppe. / The present study investigated a cohort of adult patients with single-sided deafness (SSD) who received a cochlear implant. The aim was to identify various factors that are predictive for the subsequent hearing performance with cochlear implant. The observation period covered the years 2009 - 2016 and the patient population consisted of 55 adults suffering from single-sided deafness. Speech intelligibility was tested using the Freiburg number test at 65 dB SPL, the Freiburg monosyllabic test at 65 dB SPL and 80 dB SPL, and the Hochmair-Schulz-Moser (HSM) sentence test without noise at 65 dB SPL. It has been shown that with increased hearing experience, an improvement in hearing competence can be expected. The analysis of the data revealed that patients with the combination of a long duration of deafness and an inflammatory etiology performed significantly worse than the comparison group.

Cochlear implants (CIs) are prosthetic devices used to partially restore hearing for profound and severely deaf individuals. CIs convert sounds into electrical pulses which stimulate the auditory nerve fibers. An accurate model of auditory nerve fibers (ANFs) would help in improving the functionality of CIs. Previous studies have shown that the original Hodgkin-Huxley (1952) model (with kinetics adjusted for mammalian body temperature) may be better at describing nodes of Ranvier in ANFs than models for other mammalian axon types. However, the Hodgkin-Huxley model is still unable to explain a number of phenomena observed in auditory nerve responses to CI stimulation, such as short-term and long-term adaptation, the time-course of relative refractoriness, and stimulus-dependent random fluctuations in membrane threshold. Recent physiological investigations of spiral ganglion cells have shown the presence of a number of ion channel types not considered in the previous modelling studies, including low-threshold potassium (𝐼^KLT) channels and hyperpolarization-activated cation (𝐼^h) channels. In this thesis, inclusion of these ion channel types in a stochastic Hodgkin-Huxley model is investigated. Four versions of the model are formed and compared: that is, the standard Hodgkin-Huxley model, the standard model with /h only added, the standard model with 𝐼^KLT only added, and finally, the standard model with both h and 𝐼^KLT added. Two group of responses are explored: i) single-pulse responses and ii) pules-train responses. For the single pulse responses, a charge-balanced biphasic stimulus pulse is used. The effect of varying the pulse-width and the interphase gap is investigated for both leading phase polarities. Results are compared to responses for single monophasic stimulus pulses in some cases. Pulse-train responses are investigated for charge-balanced depolarizing-phase leading biphasic pulses at rates of 200, 800, and 2000 pulse/s. Results from single-pulse responses show an increase in spike threshold when one or both of these channel types are included. The addition of 𝐼^KLT increases random threshold fluctuations in the stochastic model, particularly for longer pulse widths. For pulse-train responses, rapid adaptation in spike rate may be resulting from 𝐼^KLT whereas 𝐼^h produces slower "short-term" adaptation. Thus, the simulation results suggest that including 𝐼^KLT and/or 𝐼^h in a Hodgkin-Huxley model improves the accuracy of the model in describing auditory nerve fiber responses during cochlear implant stimulation. / Thesis / Master of Applied Science (MASc)

To investigate cochlear implant (CI) performance, geometric computational models of the cochlea have been used to assess and optimise electrode insertion strategies and to investigate current flow through the cochlear volume as a result of intra-cochlear stimulation. Most of these models are derived low-resolution computed tomography (CT) and radiographic scans of humans or high-resolution histological sections of cochleae that are not viable for in vivo studies. Often these models lack a significant set of detail, still use a generic shape of the inner structures of the cochlea or obscured structures and are not clinically translatable. A method for the predication of obscured landmarks from reference landmarks is needed to generate user-specific computational models of the cochlea if the data source is of low quality. A standard set of prediction polynomial functions derived from high-resolution μCT scans needs to be developed and applied to clinically available CT images of the cochlea. Although histological sections of the human cochlea provide the best resolution of the cochlear structures, midmodialar sequential sectioning of the cochlea is not possible. μCT scans provide a solution, as the images are still of high quality and allow for detailed measurement of cochlear parameters on midmodiolar sections. Secondly, the more recent construction of a knowledge-based automated landmark computational model needs to be refined. The search fields that the automated models template uses to place a landmark need to be standardised and should have the ability to morph the cochlear shape together with the inner bony structures. Such models are of great clinical importance, as they can be generated much more quickly to inform CI surgeons on the individual cochlear anatomy of a CI patient and maintenance of CI. Lastly, the effect that taxonomic class has on the functional implications of an implanted electrode array has yet to be determined. The cochlear geometry that best predicts the location of the electrode array is important, as it has a significant implication for hearing outcomes. This thesis assesses the anatomical geometric factors that affect inter-person variations at the peripheral-electrode interface by developing a pre-operative approach to person-specific model design for implant candidates. This approach aims to increase the accuracy and details of geometric parameters that are available for model construction and integrate the image data into three-dimensional (3D) computational volume conduction models. The study used a landmark-based approach to measure the cochlear parameters that contribute to cochlear variation, as well as the development of algorithms to derive obscured landmarks from consistently available cochlear landmarks. A workflow in the form of a custom script UPCochlea.m that describes the technical aspects of landmark analysis was created to describe each cochlea algorithmically and to extract spiral trajectories that describe cochlear anatomy. Polynomial algorithms for the description of each spiral were created for use as standard for determining each cochlear class and the prediction of obscured spirals on clinically available data. This is the first study of its kind to describe all eight spirals that constitute the cochlea and spiral lamina. Automatic generation of user-specific landmark-based 3D computational models is a rapid process that can easily be translated into a clinical tool that may inform surgeons, manufacturers of CI’s and bio-engineers on the maintenance of such models. By refining the search fields for the template that landmark-based automated cochlear computational models search for a landmark to be placed, more accurate automated computational models could be generated. Psychometric data from CI users are correlated with the anatomical dimensions, their taxonomic classification and electrode locations derived from postoperative patient scans to determine the factors, if any, that may affect electrode array locations and thus the functional outcomes of CI users. The factors that contribute to speech and hearing outcomes may be used to optimise the parameter settings for CI user device programming / Thesis (PhD (Biosystems))--University of Pretoria, 2019. / Electrical, Electronic and Computer Engineering / PhD (Biosystems) / Restricted

No description available.

京都大学 / 新制・論文博士 / 博士(医学) / 乙第13632号 / 論医博第2323号 / 新制||医||1074(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 辻川 明孝, 教授 滝田 順子, 教授 森田 智視 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

Existing music questionnaires have shown that postlingually deafened adult cochlear implant (CI) users generally find music to be less enjoyable following implantation. However, they did not investigate, in detail, which factors influence CI users’ music listening enjoyment, nor did they examine the approach a music training program should take. In order to obtain such information, a questionnaire, the University of Canterbury Music Listening Questionnaire (UCMLQ), was developed. The UCMLQ investigated: (i) the effect of implantation on CI users’ music listening enjoyment (determined by comparing the levels of enjoyment experienced post-implantation to prehearing loss, and just before implantation); (ii) the effect of a hearing aid in the unimplanted ear on CI users’ music perception and appreciation; (iii) the effect of timbre on music listening enjoyment whereby respondents will be asked to rate the pleasantness and naturalness of common instruments and voices, and also, give ratings on the instruments’ sound quality based on what they expect these instruments to sound to a person with normal hearing; (iv) whether respondents have a preference for a particular musical style (e.g. Country and Western, Jazz, Classical, etc); (v) whether respondents’ have a preference for, firstly, low-pitched versus high-pitched instruments/voices; secondly, music with instruments-only, voice-only, or both instruments and voice; and lastly, music with smaller number of performers versus greater number of performers; (vi) practical methods or ‘tips’ for enhancing everyday music listening enjoyment were collated; and finally, (vii) respondents were asked for their views and opinions on the content and logistics of a ‘take-home’ MTP for improving their music listening enjoyment. One-hundred postlingually deafened adult CI users, ranging in age from 18 to 88 years (mean = 62.1, SD = 17.1), completed the UCMLQ. All respondents used a Nucleus CI24 implant and the ACE speech processing strategy. Results showed that following implantation, respondents generally found music to be less enjoyable but they also preferred certain types of instruments and music: (i) low-frequency instruments over high-frequency instruments; (ii) certain instruments (e.g. the guitar) over others (e.g. brass instruments); (iii) smaller numbers of performers as opposed to larger numbers; (iv) Country and Western music as opposed to Pop/Rock, Jazz, Classical-small group, and Classical-orchestra; and (v) music with a slow rhythm/beat, and words. A comparison of the ratings given by CI and Hearing Aid (CI+HA) users and CI-only users also revealed that CI+HA users felt that they were significantly more able to follow the melody-line of musical styles, identify these styles, and they also rated musical styles to sound significantly ‘more normal’ than the CI-only users did. However, no statistically significant difference was found between the two groups’ (CI+HA users versus CI-only users) ratings for common instrumental sounds. In regards to respondents’ interest in partaking in a ‘take-home’ music training program (MTP), 54% of respondents stated that they would be interested in undertaking one. Respondents also indicated that the MTP should focus on improving their ability to recognise tunes, in particular, tunes known before implantation, and commonly-known tunes, and the MTP should offer a wide range of musical styles. In addition, training sessions should be of 30- minutes duration, 2 times per week, and the MTP should come in the form of a DVD with subtitles. Overall, this study collected information which not only helps us to better understand CI users’ appreciation of music but also could be used in the shaping and development of a future MTP.

No description available.

<p>Cochlear implants (CIs) are devices that restore some level of hearing to deaf individuals. Because of their design and the impaired nature of the deafened auditory system, CIs provide listeners with limited spectral and temporal information, resulting in speech recognition that degrades more rapidly for CI listeners than for normal hearing listeners in noisy and reverberant environments (Kokkinakis and Loizou, 2011). This research project aimed to mitigate the effects of reverberation by directly manipulating the CI pulse train. A reverberation detection algorithm was initially developed to control processing when switching between the mitigation algorithm and a standard signal processing algorithm used when no mitigation is needed. Next, the benefit of removing two separate effects of reverberation was studied. Finally, two reverberation mitigation algorithms were developed. Because the two algorithms resulted in comparable performance, the effect of one algorithm on speech recognition was assessed in normal hearing (NH) and CI listeners. </p><p>Reverberation detection, which has not been thoroughly investigated in the CI literature, would provide a method to control the initiation of a reverberation mitigation algorithm. Although a mitigation algorithm would ideally remove reverberation without affecting non-reverberant signals, most noise and reverberation mitigation algorithms make errors and should only be applied when necessary. Therefore, a reverberation detection algorithm was designed to control the reverberation mitigation algorithm and thereby reduce unnecessary processing. The detection algorithm was implemented by first developing features from the frequency-time matrices that result from the standard CI speech processing algorithm. Next, using these features, a maximum a posteriori classifier was shown to successfully discriminate speech in quiet, reverberation, speech shaped noise, and white Gaussian noise with 94% accuracy.</p><p>In order to develop the mitigation algorithm that would be controlled by the reverberation detection algorithm, a unique approach to reverberation mitigation was considered. This research project hypothesized that focusing mitigation on one effect of reverberation, either self-masking (masking within an individual phoneme) or overlap-masking (masking of one phoneme by a preceding phoneme) (Bolt and MacDonald, 1949), may allow for a reverberation mitigation strategy that operates in real-time. In order to determine the feasibility of this approach, the benefit of mitigating the two effects of reverberation was assessed by comparing speech recognition scores for speech in reverberation to reverberant speech after ideal self-masking mitigation and to reverberant speech after ideal overlap-masking mitigation. Testing was completed with normal hearing listeners via an acoustic model as well as with CI listeners using their devices. Mitigating either effect was found to improve CI speech recognition in reverberant environments. These results suggested that a new, causal approach could be taken to reverberation mitigation.</p><p>Based on the success of the feasibility study, two initial overlap-masking mitigation algorithms were implemented and applied once reverberation was detected in speech stimuli. One algorithm processed a pulse train signal after CI speech processing, while the second algorithm processed the acoustic signal. Performance of the two overlap-masking mitigation algorithms was evaluated in simulation by comparing pulses that were determined to be overlap-masking with the known truth. Using the features explored in this work, performance was comparable between the two methods. Therefore, only the post-CI speech processing reverberation mitigation algorithm was implemented in a CI speech processing strategy. </p><p>An initial experiment was conducted, using NH listeners and an acoustic model designed to present the frequency and temporal information that would be available to a CI listener. Listeners were presented with speech stimuli in the presence of both mitigated and unmitigated simulated reverberant conditions, and speech recognition was found to improve after reverberation mitigation. A subsequent experiment, also using NH listeners and an acoustic model, explored the effects of recorded room impulse responses (RIRs) and added noise (speech shaped noise and multi-talker babble) on the mitigation strategy. Because reverberation mitigation did not consistently improve speech recognition in these conditions, an analysis of the fundamental differences between simulated and recorded RIRs was conducted. Finally, CI listeners were presented with simulated reverberant speech, both with and without reverberation mitigation, and the effect of the mitigation strategy on speech recognition was studied. Because the reverberation mitigation strategy did not consistently improve speech recognition, future work is required to analyze the effects of algorithm-specific parameters for CI listeners.</p> / Dissertation

The application of adaptive micro-electro-mechanical systems (MEMS) device in biologically-inspired cochlear model (cochlear biomodel) has been seen as a preferable approach to mimic closely the human cochlear response. The thesis focuses on the design and fabrication of resonant gate transistor (RGT) device applied towards the development of RGT cochlear biomodel. An array of RGT devices can mimic the cochlea by filtering the sound input signals into multiple electrical outputs. The RGT device consists of two main components; a) the MEMS bridge gate structure that transduces the sound input into mechanical vibrations and b) the channel with source/drain regions underneath the bridge gate structure that transduce the mechanical vibrations into electrical signals. The created mathematical model for RGT calculates the electrical outputs that are suited for neural spike coding. The neuromorphic auditory system is proposed by integrating the RGT devices with the spike event interface circuits. The novelty of the system lies in the adaptive characteristics of the RGT devices that can self-tune the frequency and sensitivity using the feedback control signals from the neuromorphic circuits. The bridge gates have been designed to cover the audible frequency range signals of 20 Hz - 20 kHz. Aluminium and tantalum have been studied as the material for the bridge gate structure. The fabrication of a bridge gate requires a gentle etch release technique to release the structure from a sacrificial layer. The downstream etch release technique employing oxygen/nitrogen plasma has been introduced and characterised. In the first iteration, aluminium bridge gates have been fabricated. The presence of tensile stress within aluminium had caused the aluminium bridge gates of length >1mm to collapse. In order to address this issue, tantalum bridge gates have been fabricated in the second iteration. Straight tantalum bridge gates in tensile stress and buckled tantalum bridge gates in compressive stress have been characterised. The frequency range of 550 Hz - 29.4 kHz has been achieved from the fabricated tantalum bridge gates of length 0.57mm - 5.8mm. The channel and source/drain regions have been fabricated and integrated with the aluminium or tantalum bridge gate structures to create the RGTs. In this study, the n-channel and p-channel resonant gate transistor (n-RGT and p-RGT) have been considered. In n-RGT, phosphorus ions are implanted to form the source/drain regions. High subthreshold currents have been measured from the n-RGTs. Thus, p- RGTs have been employed with considerably small subthreshold current. In p-RGT, boron ions are implanted to form the source/drain regions. The threshold voltage, transconductance and subthreshold current for both n-channel and p-channel resonant gate transistor devices have been characterised. In this work, the channel conductance of the n-RGT and p-RGT devices has been modulated successfully and the sensitivity tuning within the audible frequency range has been achieved from the tantalum bridge gates of the p-RGT devices. The characterisation and optimisation of the resonant gate transistor provide the first step towards the development of the adaptive RGT cochlear biomodel for the neuromorphic auditory system application.

The purpose of this study is to determine if significant audio-metric characteristics exist in individuals having cochlear lesions who trace a Bekesy pattern characteristic of individuals with normal hearing or conductive losses.