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Evaluating Enhanced Auditory Perception Augmentation Via Stochastic Resonance
This research thesis explores improving auditory perception through the use of stochastic resonance (SR), a phenomenon in which the throughput of non-linear signals is enhanced using additive noise. While SR has been successfully explored in a variety of perceptual channels (visual, tactile, vestibular), past psychoacoustic experiments have yielded conflicting results. This study aims to understand how SR can be observed in the auditory system accounting for individual differences. Two studies were carried out to investigate SR within the auditory system. Both studies observed how white noise magnitude influences perception of pure tone stimuli across the frequency spectrum. The Threshold Optimization Study aimed to correlate SR enhancement with a subject’s audiometric threshold, predicting that noise levels equal to the subject’s threshold at a specific frequency tone would yield the highest SR benefit. Ten subjects completed pure tone audiometry with and without noise. Observing auditory thresholds with subthreshold, at-threshold, and suprathreshold additive noise yielded insignificant results. The noise levels tested did not improve or worsen audiometric performance across the board, which led to changes in the experimental methodology, specifically the noise levels that were presented and signal administration. Using those changes a second Protocol Development Study was conducted to replicate the results found in past psychoacoustic studies.The additional study also aimed to observe SR, but expanded the noise spectrum to also find the masking that was not discovered in the first study. Four lab members completed pure tone audiometry with and without the presence of noise over a broad range of noise levels. A qualitative analysis suggests masking existed for frequencies with low thresholds given the noise levels that were tested. For some subjects, SR benefits may have been observed, but for others they did not appear to be present. With these small subject numbers, this study did not yield conclusive results. A discussion of the results, as well as, further improvements into the experimental methods is given. Applying these lessons learned, more accurate perceptual threshold testing can be conducted within the lab, allowing greater reporting confidence for future studies. The additional study also aimed to observe SR, but expanded the noise spectrum to also find the masking that was not discovered in the first study. Four lab members completed pure tone audiometry with and without the presence of noise over a broad range of noise levels. A qualitative analysis suggests masking existed for frequencies with low thresholds given the noise levels that were tested. For some subjects, SR benefits may have been observed, but for others they did not appear to be present. With these small subject numbers, this study did not yield conclusive results. A discussion of the results, as well as, further improvements into the experimental methods is given. Applying these lessons learned, more accurate perceptual threshold testing can be conducted within the lab, allowing greater reporting confidence for future studies
非線形振動を励起させることによる回転するタイヤ内でのエナジーハーべスティング
学位の種別: 課程博士審査委員会委員 : (主査)東京大学准教授 中野 公彦, 東京大学教授 須田 義大, 東京大学准教授 大石 岳史, 東京大学教授 割澤 伸一, 東京大学教授 金 範埈University of Tokyo(東京大学
The Effects of Intracortical Microstimulation Parameters on Neural Responses
RÉSUMÉ Les microstimulations de tissues nerveux du cerveau sont utilisés dans un grand nombre de prothèses sensorielles, de thérapies cliniques et autres activités de recherche se servant de la stimulation électrique. Actuellement, les paramètres de stimulation sont adaptés à chaque application via des tests itératifs. Les méthodes d'optimisation cherchent à améliorer les stimuli développés pour des objectifs spécifiques de stimulation, mais la compréhension fondamentale de la façon dont les paramètres de stimulation influencent les circuits neuronaux qu’ils activent reste largement incomplète. Ce déficit retarde l'optimisation de protocoles existants et rend le développement de nouvelles applications de stimulation difficile. À ce jour, un certain nombre de dispositifs prothétiques validés dès les années 1970 restent en développement, principalement en raison de l'incapacité de ces dispositifs à communiquer efficacement avec le cerveau. Pour utiliser la stimulation électrique afin de transmettre des messages au système nerveux central, une meilleure conception du patron du signal de stimulation est nécessaire. Dans cette thèse, nous étudions l'influence que chaque paramètre du signal (un courant constant, symétrique carré biphasique) exerce sur les réponses qu'il évoquées au travers des microstimulations de la zone intracorticale caudale du membre antérieur dans le cortex moteur chez le rat. Les paramètres de ce signal sont l'amplitude du courant, la fréquence et la durée d'impulsion, l’intervalle d'interphase et la durée du train. Leurs effets ont été évalués par un examen des réponses électromyographiques évoquées dans les muscles des membres antérieurs du rat en réponse à chaque stimulus. Les principaux résultats décrivent comment chaque paramètre de stimulation influence l'amplitude, la latence d’apparition et la durée de la réponse. Une composante jusque-là inexplorée du signal de la réponse (que nous appelons 'activation résiduelle') est aussi analysée pour la première fois. Les théories quant à l'origine et le mécanisme neuronal sous-jacent de ce phénomène sont proposés et les paramètres de stimulation touchant son apparition, la prévalence et la durée sont décrits. La fiabilité des signaux de stimulation pour évoquer des réponses cohérentes est également évaluée par rapport aux variations de paramètres. Une méthodologie pour la conception optimisée des signaux de stimulation est proposée en utilisant un modèle de calcul simple, représentant les relations d'entrée-sortie entre les paramètres de stimulation et les réponses qu'ils évoquent. Ce modèle utilise une approche de réseau neuronal artificiel et peut être utilisé pour prédire les propriétés de la réponse lorsque les paramètres du stimulus sont connus. Compte tenu de la prévalence de la stimulation cérébrale dans les applications cliniques, de recherche et thérapeutiques, les procédures méthodologiques et de modélisation proposées ont des implications importantes dans l'optimisation des paradigmes de stimulation actuels et le développement de protocoles de stimulation pour de nouvelles applications.
----------ABSTRACT Microstimulation of brain tissue plays a key role in a variety of sensory prosthetics, clinical therapies and research applications. At present, stimulus parameters are tailored to each application via iterative testing. Computational optimization methods seek to improve tried and tested waveforms developed for specific purposes, however the fundamental understanding of how stimulation parameters influence the neural circuits they activate remains widely unknown. This deficit hinders both the optimization of existing protocols and the development of new stimulation applications. To date, a number of prosthetic devices validated as early as the 1970’s linger in the development stages largely due to the inability to effectively interface these devices with the brain. In order to use electrical stimulation to convey messages to the central nervous system, a better understanding of stimulus signal design is required. In this thesis, I investigate the influence that each parameter of the constant-current, symmetric, biphasic square waveform exerts on the responses it evokes through intracortical microstimulation of the caudal forelimb area of the rat motor cortex. The parameters under investigation include the current amplitude, pulse frequency, pulse duration, interphase interval and train duration of the stimulus and effects were assessed by examining the electromyographic responses evoked in the rat forelimb muscles in response to each stimulus. The major findings describe how each parameter of the stimulus signal influences the magnitude, onset latency, and duration of the response. A previously unexplored component of the response signal (which we called ‘residual activation’) is analyzed for the first time. Hypotheses as to the origin and underlying neural mechanism of this phenomenon are proposed and the stimulus parameters affecting its occurrence, prevalence and duration are described. The reliability of stimulation signals for evoking consistent responses is also assessed with respect to parameter variations. A methodology for the informed design of stimulation signals is proposed and aided by the development of a simple computational model representing the input-output relationships between stimulation parameters and the responses they evoke. This model uses an artificial neural network approach and can be used to predict the properties of the response when the parameters of the stimulus are known. Given the prevalence of brain stimulation in clinical, research and therapeutic applications the proposed methodological and modeling procedures have important implications in the optimization of current stimulation paradigms and the development of stimulation protocols for new applications