Evaluating and Improving Cochlear Length Measurements on Clinical Computed Tomography Images

Cochlear implants provide the sensation of sound to deaf individuals. An accurate estimate of cochlear duct length (CDL) is required for pre-operative implant electrode selection and can be obtained from clinical computed tomography (CT) by measuring the “A-value”. The objectives of this work were to estimate the accuracy and variability in manual A-value measurements, and to automate measurements. Four specialists repeatedly measured the A-value on clinical CT images from which the inter- and intra-observer variability were calculated. Accuracy was assessed by comparison to measurements on higher resolution micro-CT images. Motivated by this study, software was developed to automate the A-value measurement by registering an annotated atlas to unlabelled images. There was significant variability in manual A-value measurements made using either standard clinical or multi-planar reformatted views with the latter exhibiting higher variability but better accuracy. The automated approach eliminated variability and improved accuracy, enabling the correct selection of electrode length

Auf einem menschlichen Gehörmodell basierende Elektrodenstimulationsstrategie für Cochleaimplantate

Cochleaimplantate (CI), verbunden mit einer professionellen Rehabilitation, haben mehreren hunderttausenden Hörgeschädigten die verbale Kommunikation wieder ermöglicht. Betrachtet man jedoch die Rehabilitationserfolge, so haben CI-Systeme inzwischen ihre Grenzen erreicht. Die Tatsache, dass die meisten CI-Träger nicht in der Lage sind, Musik zu genießen oder einer Konversation in geräuschvoller Umgebung zu folgen, zeigt, dass es noch Raum für Verbesserungen gibt.Diese Dissertation stellt die neue CI-Signalverarbeitungsstrategie Stimulation based on Auditory Modeling (SAM) vor, die vollständig auf einem Computermodell des menschlichen peripheren Hörsystems beruht.Im Rahmen der vorliegenden Arbeit wurde die SAM Strategie dreifach evaluiert: mit vereinfachten Wahrnehmungsmodellen von CI-Nutzern, mit fünf CI-Nutzern, und mit 27 Normalhörenden mittels eines akustischen Modells der CI-Wahrnehmung. Die Evaluationsergebnisse wurden stets mit Ergebnissen, die durch die Verwendung der Advanced Combination Encoder (ACE) Strategie ermittelt wurden, verglichen. ACE stellt die zurzeit verbreitetste Strategie dar. Erste Simulationen zeigten, dass die Sprachverständlichkeit mit SAM genauso gut wie mit ACE ist. Weiterhin lieferte SAM genauere binaurale Merkmale, was potentiell zu einer Verbesserung der Schallquellenlokalisierungfähigkeit führen kann. Die Simulationen zeigten ebenfalls einen erhöhten Anteil an zeitlichen Pitchinformationen, welche von SAM bereitgestellt wurden. Die Ergebnisse der nachfolgenden Pilotstudie mit fünf CI-Nutzern zeigten mehrere Vorteile von SAM auf. Erstens war eine signifikante Verbesserung der Tonhöhenunterscheidung bei Sinustönen und gesungenen Vokalen zu erkennen. Zweitens bestätigten CI-Nutzer, die kontralateral mit einem Hörgerät versorgt waren, eine natürlicheren Klangeindruck. Als ein sehr bedeutender Vorteil stellte sich drittens heraus, dass sich alle Testpersonen in sehr kurzer Zeit (ca. 10 bis 30 Minuten) an SAM gewöhnen konnten. Dies ist besonders wichtig, da typischerweise Wochen oder Monate nötig sind. Tests mit Normalhörenden lieferten weitere Nachweise für die verbesserte Tonhöhenunterscheidung mit SAM.Obwohl SAM noch keine marktreife Alternative ist, versucht sie den Weg für zukünftige Strategien, die auf Gehörmodellen beruhen, zu ebnen und ist somit ein erfolgversprechender Kandidat für weitere Forschungsarbeiten.Cochlear implants (CIs) combined with professional rehabilitation have enabled several hundreds of thousands of hearing-impaired individuals to re-enter the world of verbal communication. Though very successful, current CI systems seem to have reached their peak potential. The fact that most recipients claim not to enjoy listening to music and are not capable of carrying on a conversation in noisy or reverberative environments shows that there is still room for improvement.This dissertation presents a new cochlear implant signal processing strategy called Stimulation based on Auditory Modeling (SAM), which is completely based on a computational model of the human peripheral auditory system.SAM has been evaluated through simplified models of CI listeners, with five cochlear implant users, and with 27 normal-hearing subjects using an acoustic model of CI perception. Results have always been compared to those acquired using Advanced Combination Encoder (ACE), which is today’s most prevalent CI strategy. First simulations showed that speech intelligibility of CI users fitted with SAM should be just as good as that of CI listeners fitted with ACE. Furthermore, it has been shown that SAM provides more accurate binaural cues, which can potentially enhance the sound source localization ability of bilaterally fitted implantees. Simulations have also revealed an increased amount of temporal pitch information provided by SAM. The subsequent pilot study, which ran smoothly, revealed several benefits of using SAM. First, there was a significant improvement in pitch discrimination of pure tones and sung vowels. Second, CI users fitted with a contralateral hearing aid reported a more natural sound of both speech and music. Third, all subjects were accustomed to SAM in a very short period of time (in the order of 10 to 30 minutes), which is particularly important given that a successful CI strategy change typically takes weeks to months. An additional test with 27 normal-hearing listeners using an acoustic model of CI perception delivered further evidence for improved pitch discrimination ability with SAM as compared to ACE.Although SAM is not yet a market-ready alternative, it strives to pave the way for future strategies based on auditory models and it is a promising candidate for further research and investigation

Intelligibility in Children with Cochlear Implants: The /t/ vs. /k/ Contrast

Previous research has found that the speech of children with cochlear implants (CI) is less intelligible than the speech of peers with normal hearing (NH). This claim has been supported by research showing that children with CIs have difficulty with the late-acquired spectral contrast of /s/ vs. /ʃ/: correctly produced words containing these initial-consonants are less intelligible when produced by children with CIs relative to children with NH. The current study examined whether a similar result is observed with the early-acquired spectral contrast of /t/ vs. /k/. Crowd-sourced data were used to evaluate intelligibility of /t/- and /k/-initial words correctly produced by children with CIs and children with NH embedded in multi-talker babble. Results indicated that whole-word productions of children with CIs were less intelligible than productions of children with NH for words beginning with this early-acquired contrast. However, results also indicated this difference in intelligibility was not dependent on the intelligibility of the initial consonant alone

Exploring Quality Management Strategies to Mitigate Culture Shock Among Cochlear Implant Users

AbstractAfter the cochlear implant (CI) activation period and therapy, adult CI users who travel overseas encounter culture shock factors that paralyze their coping capability, which need normalization through management strategies during the post-cochlear-implantation process (PCIP). In the structure of the conceptual framework, a plan is presented for addressing the management strategy. An integrated system of product-process-service-care portrays the product as an active implant within an individual bearer fostering a CI user’s physical, physiological, and psychological traits. The problematic aspects alter the end users’ coping capability in an unfamiliar host environment abroad. The qualitative research approach used was a single case study with five embedded units. The bounding of the study was to the United States and English-speaking regions of Canada, from which CI users may travel into host countries abroad. Participants are adult PCIP program managers. NVivo tools allow coding managerial opinions before analysis. The study results shed light on ways for innovation managers to (a) prevent inconsistencies producing a loss of quality during culture shock crisis, (b) positively integrate adult CI users for social change by locally or remotely mitigating culture shock factors through the social exchange, and (c) manage expectations. The management strategies needed to mitigate culture shock among adult CI users in crisis consists of (a) predicting the quality of the process, (b) executing mitigation strategy drivers, and (c) overcoming both standing disability and environmental factors. Total quality management aims at reducing the cost of quality and thus the PCIP system cost for raising the quality of a positive social exchange of adult CI users in a culture shock crisis

Towards a better understanding of sensory substitution: the theory and practice of developing visual-to-auditory sensory substitution devices

Visual impairment is a global and potentially devastating affliction. Sensory substitution devices have the potential to lessen the impact of blindness by presenting vision via another modality. The chief motivation behind each of the chapters that follow is the production of more useful sensory substitution devices. The first empirical chapter (chapter two) demonstrates the use of interactive genetic algorithms to determine an optimal set of parameters for a sensory substitution device based on an auditory encoding of vision (“the vOICe”). In doing so, it introduces the first version of a novel sensory substitution device which is configurable at run-time. It also presents data from three interactive genetic algorithm based experiments that use this new sensory substitution device. Chapter three radically expands on this theme by introducing a general purpose, modular framework for developing visual-to-auditory sensory substitution devices (“Polyglot”). This framework is the fuller realisation of the Polyglot device introduced in the first chapter and is based on the principle of End-User Development (EUD). In chapter four, a novel method of evaluating sensory substitution devices using eye-tracking is introduced. The data shows both that the copresentation of visual stimuli assists localisation and that gaze predicted an auditory target location more reliably than the behavioural responses. Chapter five explores the relationship between sensory substitution devices and other tools that are used to acquire real-time sensory information (“sensory tools”). This taxonomy unites a range of technology from telescopes and cochlear implants to attempts to create a magnetic sense that can guide further research. Finally, in chapter six, the possibility of representing colour through sound is explored. The existence of a crossmodal correspondence between (equi-luminant) hue and pitch is documented that may reflect a relationship between pitch and the geometry of visible colour space

Investigating Lateralization of Mouse Auditory Cortex using Bilateral in vivo Widefield Calcium Imaging

The survival of most species relies on the ability for individuals to communicate effectively with one another; whether that be during courtship interactions, socialization, or offspring-parent exchanges. In humans, responses to speech are lateralized demonstrating left- hemisphere dominance. Prior studies suggest this lateralization in mice; however, these studies use group averages, which may obscure small differences within one animal that might be observable through examining an individual animal bilaterally. The present study utilizes a novel bilateral in vivo widefield calcium imaging microscope to simultaneously image both hemispheres of awake, head-fixed male and female GCaMP6s transgenic mice. We found that the relative location and topology of auditory cortical areas is highly symmetrical between the hemispheres within individual animals. Vocalizations activate A2, AAF, DM, and UF in both hemispheres. Division of activation between the cortical areas is similar between the hemispheres in response to all stimulus types. However, the left hemisphere shows significantly higher activation in A2 to ultrasonic tones and vocalizations than the right hemisphere. Furthermore, both naïve males and virgin females show a left hemisphere bias in A2 in response to ultrasonic tones and adult vocalizations; however, there is a specific bias in females to pup calls. In conclusion, while topology of auditory cortex is symmetrical across hemispheres, there is a strong left bias in A2 responsiveness to ultrasonic tones and vocalizations

Egocentric Computer Vision and Machine Learning for Simulated Prosthetic Vision

Las prótesis visuales actuales son capaces de proporcionar percepción visual a personas con cierta ceguera. Sin pasar por la parte dañada del camino visual, la estimulación eléctrica en la retina o en el sistema nervioso provoca percepciones puntuales conocidas como “fosfenos”. Debido a limitaciones fisiológicas y tecnológicas, la información que reciben los pacientes tiene una resolución muy baja y un campo de visión y rango dinámico reducido afectando seriamente la capacidad de la persona para reconocer y navegar en entornos desconocidos. En este contexto, la inclusión de nuevas técnicas de visión por computador es un tema clave activo y abierto. En esta tesis nos centramos especialmente en el problema de desarrollar técnicas para potenciar la información visual que recibe el paciente implantado y proponemos diferentes sistemas de visión protésica simulada para la experimentación.Primero, hemos combinado la salida de dos redes neuronales convolucionales para detectar bordes informativos estructurales y siluetas de objetos. Demostramos cómo se pueden reconocer rápidamente diferentes escenas y objetos incluso en las condiciones restringidas de la visión protésica. Nuestro método es muy adecuado para la comprensión de escenas de interiores comparado con los métodos tradicionales de procesamiento de imágenes utilizados en prótesis visuales.Segundo, presentamos un nuevo sistema de realidad virtual para entornos de visión protésica simulada más realistas usando escenas panorámicas, lo que nos permite estudiar sistemáticamente el rendimiento de la búsqueda y reconocimiento de objetos. Las escenas panorámicas permiten que los sujetos se sientan inmersos en la escena al percibir la escena completa (360 grados).En la tercera contribución demostramos cómo un sistema de navegación de realidad aumentada para visión protésica ayuda al rendimiento de la navegación al reducir el tiempo y la distancia para alcanzar los objetivos, incluso reduciendo significativamente el número de colisiones de obstáculos. Mediante el uso de un algoritmo de planificación de ruta, el sistema encamina al sujeto a través de una ruta más corta y sin obstáculos. Este trabajo está actualmente bajo revisión.En la cuarta contribución, evaluamos la agudeza visual midiendo la influencia del campo de visión con respecto a la resolución espacial en prótesis visuales a través de una pantalla montada en la cabeza. Para ello, usamos la visión protésica simulada en un entorno de realidad virtual para simular la experiencia de la vida real al usar una prótesis de retina. Este trabajo está actualmente bajo revisión.Finalmente, proponemos un modelo de Spiking Neural Network (SNN) que se basa en mecanismos biológicamente plausibles y utiliza un esquema de aprendizaje no supervisado para obtener mejores algoritmos computacionales y mejorar el rendimiento de las prótesis visuales actuales. El modelo SNN propuesto puede hacer uso de la señal de muestreo descendente de la unidad de procesamiento de información de las prótesis retinianas sin pasar por el análisis de imágenes retinianas, proporcionando información útil a los ciegos. Esté trabajo está actualmente en preparación.<br /

Doctor of Philosophy

dissertationBy enabling neuroprosthetic technologies, neural microelectrodes can greatly improve diagnostic and treatment options for millions of individuals living with limb loss, paralysis, and sensory and autonomic neural disorders. However, clinical use of these devices is restricted by the limited functional lifetimes of implanted electrodes, which are commonly less than a few years. One cause is the evolution of damage to dielectric encapsulation that insulates microelectrodes from the physiological environment. Fluid penetration and exposure to an aggressive immunological response over time may weaken encapsulating films and cause electrical shunting. This reduces electrode impedance, diverts electrical signal away from target tissue, and causes multi-channel crosstalk. To date, no neural microelectrode encapsulating material or design approach has reliably resolved this issue. We employ the parylene C-encapsulated Utah Electrode Array (UEA), a silicon-micromachined neural interface FDA-cleared for human use, to execute three aims that address this challenge through investigations of new materials, electrode designs, and testing methods. We first evaluate a novel bilayer encapsulating film comprised of atomic layer deposited Al2O3 and parylene C, testing this film using UEAs and devices with UEA-relevant topography. Contrasting with previous work employing simplified planar structures, the incorporation of neural electrode features on test structures revealed failure modes pointing to the dissolution of Al2O3 over time. Our results emphasize the need for dielectric coatings resistant to water degradation as well as test methods that take electrode features into account. In our second aim, we show through finite element modeling and aggressive in vitro testing that use of degenerately doped silicon as a conductive neural electrode material can mitigate the consequences of encapsulation damage, owing to the high electrochemical impedance of silicon. Our final aim compares oxidative in vitro aging to long-term in vivo material damages and finds clear evidence that such in vitro testbeds may help predict certain in vivo damage modes. By pairing this testing with absorption and emission spectroscopic characterization modalities, we identify contributors to material damage and future design solutions. Our results will inform future material and testing choices, to improve the resilience of neural electrode dielectric encapsulation and enhance the longevity of neuroprostheses