Biophysically detailed representations of neural network models provide substantial insight to underlying neural processing mechanisms in the auditory systems of the brain. For simple biological systems the behavior can be represented by simple equations or flow charts. But for complex systems, more detailed descriptions of individual neurons and their synaptic connectivity are typically required. Creating extensive network models allows us to test hypotheses, apply specific manipulations that cannot be done experimentally and provide supporting evidence for experimental results. Several studies have been made on establishing realistic models of the cochlear nucleus (Manis and Campagnola, 2018; Eager et al., 2004), the part of the brainstem where sound signals enter the brain, both on individual neuron and networked structure levels. These models are based on both in vitro and in vivo physiological data, and they successfully demonstrate certain aspects of the neural processing of sound signals. Even though these models have been tested with tone bursts and isolated phonemes, the representation of speech in the cochlear nucleus and how it may support robust speech intelligibility remains to be explored with these detailed biophysical models. In this study, the basis of creating a biophysically detailed model of microcircuits in the cochlear nucleus is formed following the approach of Manis and Campagnola (2018). The focus of this thesis is more on bushy cell microcircuits. We have updated Manis and Campagnola (2018) model to take inputs from the new phenomenological auditory periphery model of Bruce et al. (2018). Different cell types in the cochlear nucleus are modelled by detailed cell models of Rothman and Manis (2003c) and updated Manis and Campagnola (2018) cell models. Networked structures are built out of them according to published anatomical and physiological data. The outputs of these networked structures are used to create post-stimulus-time-histograms (PSTH) and response maps to investigate the representation of tone bursts and average localized synchronized rate (ALSR) of phoneme 'e' and are compared to published physiological data (Blackburn and Sachs, 1990). / Thesis / Master of Applied Science (MASc)

This research details the creation and characterization of a new biomimetic artificial inner hair cell sensor in an artificial cochlear environment. Designed to mimic the fluid flows around the inner hair cells of the human cochlea, the artificial cochlear environment produces controlled, linear sinusoidal fluid flows with frequencies between 25 and 400 Hz. The lipid bilayer-based artificial inner hair cell generates current through changes in the bilayer's capacitance. This capacitance change occurs as the sensor's artificial stereocilium transfers the force in the fluid flow to the bilayer. Frequency tuning tests are performed to characterize the artificial inner hair cell's response to a linear chirp signal from 1 to 400 Hz. The artificial inner hair cell's response peaks at a resonant frequency of approximately 83 Hz throughout most of the tests. Modelling the artificial stereocilium as a pinned free beam with a rotational spring at the pinned end yields a rotational spring stiffness of 177*10^-6 Nm/rad. Results with 0 mV potential applied across the bilayer indicate that current generation at 0 mV likely comes from other sources besides the bilayer. Increasing the voltage potential increases the broadband power output of the system, with an approximately linear relationship. A final test keeps the fluid flow frequency constant and varies the fluid velocity and applied voltage potential. Manipulation of the applied voltage potential results in a fluid velocity to RMS current relationship reminiscent of the variable sensitivity of the human cochlea. / Master of Science

Postlingually deafened cochlear implant (CI) adults have large variability in speech perception abilities. While CIs are one of the most successful neural prosthetic devices, they are not able to adequately provide fine structure cues which results in a degraded signal for the listener to interpret. While behavioral measures remain the gold standard for determining speech perception abilities, an objective measure is needed for patients who are unable to provide reliable behavioral responses. Behavioral, cognitive, and neural measures were collected in this study to identify potential neural biomarkers that correlate with speech perception performance. Behavioral experiments evaluated participants' abilities to identify, discriminate, and recognize words as well as sentences in quiet and in noise. Cognitive measures were assessed to determine the roles of attention, impulse control, memory, and cognitive flexibility on speech recognition. Auditory event-related potentials (ERP) were obtained with a double oddball paradigm to produce the mismatch negativity (MMN) response, which has been shown to have associations with phonetic categorical perception at the group level. The results indicated that executive function is highly predictive of speech performance and that the MMN is associated with categorical perception at the individual level. These findings are clinically relevant to determining appropriate follow-up care post-implantation.

TRPA1 channels are sensors for noxious stimuli in a subset of nociceptive neurons. TRPA1 channels are also expressed in cells of the mammalian inner ear, but their function in this tissue remains unknown given that Trpa1–/– mice exhibit normal hearing, balance and sensory mechanotransduction. Here we show that non-sensory (supporting) cells of the hearing organ in the cochlea detect tissue damage via the activation of TRPA1 channels and subsequently modulate cochlear amplification through active cellshape changes. We found that cochlear supporting cells of wild type but not Trpa1–/– mice generate inward currents and robust long-lasting Ca2+ responses after stimulation with TRPA1 agonists. These Ca2+ responses often propagated between different types of supporting cells and were accompanied by prominent tissue displacements. The most prominent shape changes were observed in pillar cells which here we show possess Ca2+-dependent contractile machinery. Increased oxidative stress following acoustic overstimulation leads to the generation of lipid peroxidation byproducts such as 4-hydroxynonenal (4-HNE) that could directly activate TRPA1. Therefore, we exposed mice to mild noise and found a longer-lasting inhibition of cochlear amplification in wild type than in Trpa1–/– mice. Our results suggest that TRPA1-dependent changes in pillar cell shape can alter the tissue geometry and affect cochlear amplification. We believe this novel mechanism of cochlear regulation may protect or fine-tune the organ of Corti after noise exposure or other cochlear injuries.

Thesis (M.Eng.(Bio-Engineering))--University of Pretoria, 2008. / Summaries in Afrikaans and English. Includes bibliographical references.

L'implant cochléaire représente le dispositif de référence pour réhabiliter l'audition des patients atteints de surdités sévère à profonde. Les indications se sont récemment étendues vers les patients avec une audition résiduelle avec de bons résultats. Il persiste cependant une grande hétérogénéité des résultats auditifs. Plusieurs facteurs ont été identifiés comme influençant les performances auditives: durée de la surdité, intelligibilité préopératoire et stratégie de codage. Dans cette thèse, l'anatomie de la cochlée et la position postopératoire du porte-électrodes ont été étudiés afin d'identifier les facteurs de variabilité de la discrimination vocale inter- et intra-individuelle. Les résultats de cette thèse ont montré un lien entre la position de l'électrode et les performances auditives à court terme, alors que la plasticité neuronale pourrait jouer un rôle important dans l'adaptation de l'implant cochléaire aux structures neurales à long terme. De plus, la préservation des structures cochléaires est maintenant recommandée pour tous les candidats à l'implantation, quelle que soit leur audition préopératoire. Une étude radio-histologique sur rochers avec une insertion motorisée du porte-électrodes a été réalisée afin d'identifier les paramètres des forces d'insertion qui pourraient prédire le traumatisme de l'oreille interne lié à l'insertion. Une corrélation entre les valeurs de forces d'insertion et le traumatisme cochléaire a été trouvée dans les os temporaux. Ces valeurs, serviront au développement d'outils d'insertion " intelligents " pour réduire les lésions liées à l'insertion et ainsi conduire à des conditions de rééducation auditive optimale. / The cochlear implantation represents the standard technique to restore the hearing in totallydeafened persons, and the indications during the last years are widening also to patients withresidual hearing or presenting single sided deafness. Despite the overall good to very goodresults after cochlear implantation reported in literature a wide heterogeneity of the hearingoutcomes emerges in the single studies and poor results both in unilateral and bilateralcochlear implantation are still reported. Several patients’ specific factors have been identifiedas affecting postimplant speech perception score, including duration of deafness, residualpreoperative speech recognition, and different speech coding strategy. In this thesis theanatomy of the cochlea and the position of the electrode array in implanted patients have beenstudied with the attempt to identify the affecting factors that contribute to the variability of theinter- and intra-individual speech discrimination scores both in bilaterally and unilaterallyimplanted patients. Moreover, following the expanding indication for cochlear implantation,the preservation of inner ear structures is becoming recommended for all cochlear implantcandidates, regardless of their preoperative hearing. A radio-histological temporal bone studywith a motorized insertion of the array was performed in order to identify the insertion forcesparameters that could predict the possible traumatism involving the inner ear. The results ofthis thesis showed a relationship between the intracochlear electrode position and hearingperformance in the short term follow up, whereas the neural plasticity would play animportant role in the adaptation of the cochlear implant to the neural structures in the longterm. A correlation between insertion forces and inner ear traumatism was found in temporalbones. Two different force profiles for traumatic and atraumatic insertion were obtained; thesevalues, if confirmed by further studies, could be useful for the development of future forcefeedback automated cochlear implant insertion tool in order to reduce the risk of insertionrelated damage and provide the best chance for an optimal hearing rehabilitation in cochlearimplanted candidates.

The impact of the diagnosis and the reality of being hearing impaired could trigger uncomfortable feelings at different times in the client's life. With the cochlear implant, these feelings will still be a reality, as the implant does not heal the hearing impairment. Psychological interventions could assist the client during this healing process. The process of cochlear implants could also bring other challenges into the client's life. Expectations of quick healing play a major role and should be addressed throughout the process of implantation and rehabilitation. This is another opportunity for the psychologist to intervene. This research shows that the role of the psychologist could be expanded not only to evaluate but also to bring about change. The treatment model gives a logical and workable explanation of how and where the psychologist may intervene in the process of cochlear implantation. This model was tested and adapted by the cochlear implant team at the University of Pretoria over a period of ten years. The model may be used as a template for new teams. Intervening as described in the model presents the opportunity to address various different needs as they occur. The qualitative research design proved to be a fitting method to explore the experiences of the participants from their own viewpoints. The qualitative research is also congruent with a systemic perspective and emphasises social context, multiple perspectives, complexity, recursion and holism. This study aims to develop a complementary psychological treatment programme and create awareness within professionals working with hearing impairment of the complexity of systems. The study shows that one can only understand the behaviour of any given system by tracking changes that occur within that system and its subsystems and by tracking changes between that system and the larger whole. In this study three different therapeutic interventions are used on three different case studies, two children from different age groups and an adult, to accommodate the multiple realities of the different systems. The aim of the study with cochlear implantees and their families is to stimulate new leads and avenues of enquiry that may be used as a basis for further research. / Psychology / Thesis (D.Litt. et Phil. (Psychology))

This thesis deals with the issue of speech therapy for children of early school age with the cochlear implant. General knowledge about hearing impairment and the possibility of compensation, different types of cochlear implants and especially about the specifics and methodology of following speech therapy are summarized in the theoretical part of the thesis. The practical part consists of research, realized through questionnaires. The research deals with the current situation of speech therapy for children of early school age with a cochlear implant, with a special focus on post-implantation rehabilitation and its complexity. The result of the research demonstrates the complexity of speech therapy only in some speech therapy workplaces. The result of the research also demonstrates that speech therapy is highly individual and depends completely on specific situation and personality and communication skills of each child with a cochlear implant. KEYWORDS Hearing impairment, cochlear implant, cochlear implantation, child with a cochlear implant, early school age, rehabilitation, hearing and speech developement, speech therapy.

The impact of the diagnosis and the reality of being hearing impaired could trigger uncomfortable feelings at different times in the client's life. With the cochlear implant, these feelings will still be a reality, as the implant does not heal the hearing impairment. Psychological interventions could assist the client during this healing process. The process of cochlear implants could also bring other challenges into the client's life. Expectations of quick healing play a major role and should be addressed throughout the process of implantation and rehabilitation. This is another opportunity for the psychologist to intervene. This research shows that the role of the psychologist could be expanded not only to evaluate but also to bring about change. The treatment model gives a logical and workable explanation of how and where the psychologist may intervene in the process of cochlear implantation. This model was tested and adapted by the cochlear implant team at the University of Pretoria over a period of ten years. The model may be used as a template for new teams. Intervening as described in the model presents the opportunity to address various different needs as they occur. The qualitative research design proved to be a fitting method to explore the experiences of the participants from their own viewpoints. The qualitative research is also congruent with a systemic perspective and emphasises social context, multiple perspectives, complexity, recursion and holism. This study aims to develop a complementary psychological treatment programme and create awareness within professionals working with hearing impairment of the complexity of systems. The study shows that one can only understand the behaviour of any given system by tracking changes that occur within that system and its subsystems and by tracking changes between that system and the larger whole. In this study three different therapeutic interventions are used on three different case studies, two children from different age groups and an adult, to accommodate the multiple realities of the different systems. The aim of the study with cochlear implantees and their families is to stimulate new leads and avenues of enquiry that may be used as a basis for further research. / Psychology / Thesis (D.Litt. et Phil. (Psychology))

The topic of the thesis is people with hearing impairment implanted in their adulthood and rehabilitation after cochlear implantation. The thesis is divided into four chapters, the first three chapters are concerning the theory and the fourth chapter is empirical. The first chapter highlights the problem of a person with hearing impairment. The next chapter discusses about cochlear implant as adaptive technology, who is a suitable candidate for cochlear implant and what possibilities has future user. The third chapter is devoted to the area after cochlear implantation, including rehabilitation and other services for adults with cochlear implant. The empirical chapter of thesis presents a qualitative design of the research focused on rehabilitation after cochlear implantation in adults with hearing impairment. The research was realized in adult's users of cochlear implant and then supplemented by a questionnaire survey among experts in their field. The main objective of this work was mapped to that extent is realized rehabilitation in adults before and after cochlear implantation. KEY WORDS Person with hearing impairment Cochlear implant in adulthood Cochlear implantation Rehabilitation after cochlear implantation Quality of life