O implante coclear tem sido indicado para a reabilitação de crianças com Espectro da Neuropatia Auditiva, com ampla variação no desempenho na percepção de fala. Caso o desenvolvimento das estruturas auditivas centrais não ocorra normalmente, pode-se presumir que as habilidades perceptuais que são a base para a percepção e produção da fala também não se desenvolverão normalmente. Nesse contexto, é possível questionar se a maneira como o sistema auditivo dessas crianças responde à estimulação elétrica após o período de privação sensorial poderia ser uma das justificativas para a variabilidade no resultado obtido com o implante coclear. O objetivo deste estudo foi caracterizar o componente P1 dos potenciais evocados auditivos de longa latência em indivíduos com Espectro da Neuropatia Auditiva usuários de implante coclear e correlacioná-los com o desempenho na percepção de fala e secundariamente a outras variáveis relacionadas ao implante coclear. Participaram do estudo 14 crianças com Espectro da Neuropatia Auditiva, usuárias de implante coclear, de ambos os sexos, na faixa etária de 4 a 11 anos. Foi realizada a pesquisa dos potenciais evocados auditivos de longa latência com estimulação acústica, utilizando estímulo de fala /da/ apresentado em campo livre, e a avaliação da percepção de fala por meio do protocolo GASP (BEVILACQUA; TECH, 1996). Como resultado, foi constatado que foi possível registrar o componente P1 em 85,7% desta população, sendo que o valor da latência do componente P1 apresentou correlação significante com o tempo de privação sensorial demonstrando que quanto maior o tempo de privação sensorial, maior a latência do componente P1. Não foi observada correlação significante entre o componente P1 e o tempo de uso do implante coclear. Foi observado que quando separados os indivíduos em grupos de acordo com o desempenho na percepção de fala, aqueles que apresentaram um melhor desempenho possuíam a latência do componente P1 estatisticamente menor, comparados ao de pior desempenho. Com os resultados obtidos neste estudo foi possível caracterizar o componente P1 dos potenciais evocados auditivos de longa latência em crianças com Espectro da Neuropatia Auditiva usuárias de implante coclear e demonstrar a correlação com o desempenho de percepção de fala e tempo de privação sensorial. Em crianças com Espectro da Neuropatia Auditiva, o componente P1 pode servir como um preditor do desempenho da criança usuária de implante coclear para a percepção de fala. / The cochlear implant has been recommended for the rehabilitation of children with Auditory Neuropathy Spectrum, with wide variation in performance in speech perception. If the development of central auditory structures does not occur normally, one can assume that the perceptual abilities that are the basis for the perception and speech production will not develop normally either. In this context one might question if the way the auditory system of these children respond to electrical stimulation after a period of sensory deprivation could be one of the reasons for this variability in the results obtained with the cochlear implant. The aim of this study was to characterize the P1 component of long-latency auditory evoked potentials in cochlear implanted individuals with Auditory Neuropathy Spectrum and correlate it with performance in speech perception and secondarily to other variables related to cochlear implant. The study included 14 cochlear implanted children with Auditory Neuropathy Spectrum, of both sexes, aged from four to eleven years. We studied the long-latency auditory evoked potential with acoustic stimulation, using speech stimuli presented in open field, and assessment of speech perception by means of GASP test (BEVILACQUA; TECH, 1996). As a result, we found that it was possible to register the P1 component in 85.7% of this population, and the P1 component latency value showed a significant correlation with the duration of sensory deprivation showing that the longer the duration of sensory deprivation, the greater the latency of the P1 component. There was no significant correlation between the P1 component and the time of cochlear implant use. It was observed that when the individuals were separated into groups according to performance on speech perception, those who performed better had the P1 component latency statistically lower when compared to the worst performers. With the results obtained from this study it was possible to characterize the P1 component of long-latency auditory evoked potentials in cochlear implanted children with Auditory Neuropathy Spectrum and demonstrate a correlation with the performance of speech perception. In children with Auditory Neuropathy Spectrum, the P1 component may serve as a predictor of the performance of a cochlear implanted child for speech perception.

Introdução: O implante coclear (IC) amplamente aceito como forma de intervenção e (re) habilitação nas perdas auditivas severas e profundas nas diversas faixas etárias. Contudo observa-se no usuário do IC unilateral queixas como localização e compreensão sonora em meio ao ruído, gerado pelo padrão anormal de estimulação sensorial. A fim de fornecer os benefícios da audição binaural, é preconizado a estimulação bilateral, seja por meio do IC bilateral ou com a adaptação de um aparelho de amplificação sonora individual (AASI) contralateralmente ao IC. Esta última condição é referida como estimulação bimodal, quando temos, concomitantemente dois modos de estimulação: Elétrica (IC) e acústica (AASI). Não há dados suficientes na literatura voltados à população infantil que esclareça ou demonstre o desenvolvimento do córtex auditivo na audição bimodal. Ressalta-se que não foram encontrados estudos em crianças. Objetivo: Caracterizar o PEAC complexo P1, N1 P2 em usuários da estimulação bimodal e verificar se há correlação com testes de percepção de fala. Metodologia: Estudo descritivo de séries de casos, com a realização do PEAC em cinco crianças usuárias da estimulação bimodal, a partir da metodologia proposta por Ventura (2008) utilizando o sistema Smart EP USB Jr da Intelligent Hearing Systems. Foi utilizado o som de fala /da/, apresentado em campo livre. O exame será realizado em três situações: Somente IC, IC e AASI e somente AASI. A análise dos dados dos potenciais corticais foi realizada após a marcação da presença ou ausência dos componentes do complexo P1-N1-P2 por dois juízes com experiência em potenciais evocados. Resultados: Foi obtida a captação do PEAC em todas as crianças em todas as situações de teste, além do que foi possível observar a correlação destes com os testes de percepção auditiva da fala. Foi possível verificar que o registro dos PEAC é um procedimento viável para a avaliação da criança com estimulação bimodal, porém, ainda não há dados suficientes quanto a utilização deste para a avaliação e indicação do IC bilateral. / Introduction: The cochlear implant (CI) is already accepted in the area, as an intervention (re)habilitation in severe and profound hearing loss in different age groups. However, it is observed in the unilateral CI users have complaints such as sound localization and understanding speech in noise. Recent studies with Cortical Auditory Evoked Potential (CAEP) demonstrated the fact that the CI cannot favors the ipsilateral development of the auditory pathway as expected. Therefore, unilateral CI users have an abnormal pattern of sensory stimulation. In this sense, the patient is advised and encouraged as to the fitting of hearing aids (HA) in no-implanted ear, especially in the presence of residual acoustic hearing in order to provide the benefits of binaural hearing. This condition is referred to bimodal hearing, when combining electric stimulation from the CI with acoustic stimulation from the contralateral ear provides to HA. Not enough data in the literature has focused on the child population to clarify or demonstrate the development of the auditory cortex in the bimodal hearing. Objective: To characterize the CAEP complex P1-N1-P2 users of bimodal stimulation and check for correlation with performance on tests of speech perception. Methods: A cross-sectional observational study, with the completion of the CAEP in six children using the Bimodal stimulation, the CAEP recording will be based in the methodology proposed by VENTURA (2008) using the system Smart EP USB Jr Intelligent Hearing Systems. The speech sound / of /, presented in free field, will be used. The potential will be recorded in three situations: monaural hearing (only CI); Bimodal hearing (IC and HA) and monoaural hearing (only HA). The examination will be held in three situations: monaural hearing (only IC); Bimodal hearing (IC and hearing aids) and hearing monaural (only the hearing aid). Data analysis of the cortical potential was performed after the marking of the presence or absence of the components of the N1-P1-P2 complex by two judges experienced in evoked potentials. It was verified that the record of the ECCP is a viable procedure for the assessment of children with bimodal stimulation and can assist in bilateral IC nomination process or the maintenance of bimodal stimulation.

O objetivo deste estudo foi realizar e determinar a validade de um protocolo de teste de verificação eletroacústica para Sistemas de Frequência Modulada (FM) acoplados a diferentes processadores de fala de implantes cocleares. Participaram deste estudo 40 crianças, com idades entre 5 e 18 anos incompletos, usuários de quatro modelos diferentes de processadores de fala. A verificação eletroacústica foi realizada por meio do uso do equipamento Audioscan Verifit (VF-1) com acoplador HA-1, além do uso do dispositivo de verificação de escuta correspondente a cada modelo de processador de fala do implante coclear. Nos casos em que a transparência não foi atingida, foi realizada alteração no ajuste do ganho do Sistema FM e avaliação da percepção auditiva da fala no ruído por meio da aplicação da versão brasileira do teste Phrases in Noise Test (PINT). Houve transparência entre o Sistema FM e o implante coclear em 85% dos dispositivos avaliados. Após o ajuste do ganho FM nos outros casos, os dispositivos apresentaram-se transparentes quando o teste de verificação eletroacústica foi repetido. Também foi observado que os participantes submetidos ao teste de percepção de fala no ruído apresentaram melhor desempenho após o novo ajuste, de modo que, nestes casos, a transparência eletroacústica ocasionou em transparência comportamental. Concluiuse que o protocolo de verificação eletroacústica utilizado mostrou-se efetivo para a avaliação da transparência entre o Sistema FM e o implante coclear. A realização prévia do ajuste do processador de fala e do ganho do Sistema FM mostrou-se essencial para que a transparência fosse atingida. / The purpose of this study was perform and determine the validity of an electroacoustic verification test for FM Systems coupled to different cochlear implant speech processors. The sample included 40 participants between 5-18 years users of four different models of speech processors. For the electroacoustic evaluation, we used the Audioscan Verifit device with the HA-1 coupler and the listening check devices corresponding to each speech processor model. In cases where the transparency was not achieved, was made a modification in the FM gain adjustment and used the Brazilian version of the \"Phrases in Noise Test\" (PINT) to evaluate the speech perception in competitive noise. It was observed that there was transparency between the FM System and the cochlear implant in 85% of the participants evaluated. After adjusting the gain of the FM receiver in the other participants, the devices showed transparency when the electroacoustic verification test was repeated. It was also observed that they presented better performance in speech perception in noise after a new adjustment, that is, in these cases, the electroacoustic transparency caused behavioral transparency. It was concluded that the electroacoustic evaluation protocol suggested was effective to evaluate transparency between the FM System and the cochlear implant. Performing the adjustment of the speech processor and the FM System gain are essential when fitting this device.

A resolução temporal tem sido estudada em usuários de implante coclear (IC) de acordo com os novos algoritmos implementados nas estratégias de codificação da fala. O objetivo deste estudo foi determinar o perfil de desempenho de crianças usuárias de IC multicanal nas tarefas de detecção de seqüência temporal em dois testes comportamentais, Teste de Padrões de Freqüência (TPF) e Teste de Padrões de Duração (TPD). Avaliou-se 43 crianças usuárias de IC com idade entre 7 e 11 anos e 5 meses, regularmente matriculadas e acompanhadas no Centro de Pesquisas Audiológicas do Hospital de Reabilitação de Anomalias Craniofaciais da Universidade de São Paulo. Destas 26 eram usuárias do IC Combi®40+ com a estratégia de codificação da fala Continuous Interleaved Sampler, cinco do IC Nucleus®24K e 12 do Nucleus®24M com a estratégia Advanced Combination Encoder, sendo 28 do gênero feminino e 15 do masculino. O tempo médio de surdez foi de 3 anos e o tempo médio de uso do IC de 4 anos e 9 meses. Ambos os testes foram aplicados em campo livre a 60 dBNA. As crianças foram solicitadas a responder por meio de respostas não verbal (NV) e verbal (V). O TPF constou da apresentação de uma seqüência de 3 tons com duração de 500 ms que diferiam na freqüência, 1430 Hz (alto) ou 880 Hz (baixo), perfazendo um total de 6 padrões distintos. O TPD constou da apresentação de uma seqüência de 3 tons de 1000 Hz que diferiam na duração, 500 ms (longo) ou 250 ms (curto), constituído também de 6 padrões de seqüências distintos. Foram apresentadas 10 repetições dos 6 padrões no total de 60 estímulos para TPD e TPF, em cada criança. Aplicou-se o mesmo protocolo de testes em 43 crianças, balanceadas em gênero e faixa etária, sem alterações de linguagem, fala, audição e/ou aprendizagem (grupo controle). Realizou-se análise estatística multivariada com o teste da razão de verossimilhança no modelo logístico ajustado e com testes de correlação. As análises evidenciaram que o desempenho no TPF com resposta NV foi significativamente superior à resposta V para todos os sujeitos, por outro lado observou-se diferença de desempenho entre as respostas NV e V apenas nas crianças entre 7 e 9 anos do grupo experimental. Constatou-se melhora significativa do desempenho com a idade para o TPDNV e TPDV (grupo experimental) e para o TPFV, TPDNV e TPDV (grupo controle). Todos os usuários do IC Combi®40+ apresentaram desempenho superior aos usuários do IC Nucleus®24K e Nucleus®24M em todas as condições avaliadas. Não houve correlações entre o desempenho e o tempo de uso do IC, tempo de surdez e teste de percepção da fala. Os sujeitos do gênero masculino apresentaram desempenhos superiores ao feminino para a maioria dos testes. O desempenho no TPF foi superior ao TPD. Neste estudo, as diferenças existentes em relação ao processamento do sinal nos IC devem ter interferido no desempenho das habilidades de ordenação temporal. Novas pesquisas são necessárias para complementação destes achados. / Temporal resolution has been studied in cochlear implant (CI) users, according to new algorithms implemented for speech coding strategies. The present study was aimed at determining the performance profile of multi-channel CI users in temporal-sequence detection tasks using pair of behavioral tests: frequency patterns test (FPT) and duration patterns test (DPT). Forty-three cochlear implanted children, age ranging from 7 to 11 yrs and 5 months, regularly enrolled and followed at the Audiological Research Center, the Craniofacial Anomalies Rehabilitation Hospital of the University of São Paulo, were evaluated. Twenty-six children were users of CI Combi®40+ with the Continuous Interleaved Sampler speech coding strategy; five of CI Nucleus®24K and twelve were users of Nucleus®24M with the Advanced Combination Encoder strategy; 28 were females, and 15 males. The mean auditory deprivation time was 3 years, and the mean CI use duration was 4 years and 9 months. Both tests were applied at 60 dBNA on free-field. Children were instructed to deliver answers through nonverbal (NV) and verbal (V) responses. FPT comprises the presentation of a three-tone sequence with a 500 ms duration which differed in the frequency: 1430 Hz (high) or 880 Hz (low), consisting of six distinct patterns. While DPT comprised the presentation of a three-tone sequence of 1000 Hz, which differed in the duration, either with 500 ms (long) or 250 ms (short), giving six distinct sequence patterns. Ten repetitions of six patterns totaling 60 stimuli for DPT and FPT were presented to each child. The same test protocol was applied to 43 children, balanced according to gender and age range, with no language, speech, hearing and/or learning alterations (control). Multivariate statistical analysis was used, with the likelihood ratio test to the adjusted logistic model, and correlation analysis. The analyses showed that the performance on FPT with a NV response was significantly superior to that of V response for all subjects. On the other hand, performance difference in between NV and V responses was observed only in the 7-9 year-old experimental group. Significant performance improvements with age were observed in NVDPT and VDPT for experimental group, as well as in VFPT, NVDPT and VDPT for control group. All users of CI Combi®40+ showed better performance compared to Nucleus®24K or Nucleus®24M users, for all assessed conditions. No correlations were found between performance and the use duration of CI, sensory deprivation time, and speech perception test result. Male subjects had a superior performance than females, for most of the tests. The performance on FPT was superior to that on DPT. In this study, the observed differences related to CI signal processing strategies must have interfered in the performance of temporal ordering abilities. Further research, to complement these findings, is necessary.

Introdução: A estimulação elétrica gerada pelo Implante Coclear (IC) pode ser capaz de melhorar a sincronia neural e contribuir para o desenvolvimento das habilidades auditivas de sujeitos portadores de Neuropatia Auditiva/Dessincronia Auditiva (NA/DA). Objetivo: Esta pesquisa teve como objetivo avaliar o desempenho auditivo e as características do Potencial de Ação Composto Eletricamente Evocado no Nervo Auditivo Evocado Eletricamente (ECAP) em um grupo de 18 crianças portadoras de NA/DA e usuárias de IC, comparando os resultados obtidos com um grupo controle de crianças usuárias de IC portadoras de deficiência auditiva neurossensorial (DANS). Método: A avaliação da percepção auditiva foi composta pela determinação dos limiares tonais em campo livre e a realização de testes de percepção de fala. Para a avaliação das características do ECAP, foram realizadas as medidas de limiar e amplitude da resposta neural, bem como a curva de crescimento da amplitude e a função de recuperação do nervo auditivo na freqüência de estimulação de 80Hz. Para os sujeitos pertencentes ao grupo da NA/DA, os valores de limiar e amplitude da resposta neural foram também registrados na freqüência de estimulação de 35Hz. Resultados: Diferenças estatisticamente significantes não foram encontradas no desenvolvimento das habilidades auditivas entre o grupo de crianças portadoras de NA/DA e o grupo controle. As características do registro do ECAP não apresentaram diferenças estatisticamente significantes nos dois diferentes grupos e não foram observadas modificações estatisticamente significantes nas características do potencial com a utilização da freqüência de estimulação de 35Hz no grupo de sujeitos portadores de NA/DA. Conclusões: O IC caracterizou-se como um efetivo recurso para o desenvolvimento das habilidades auditivas em 94% dos sujeitos portadores de NA/DA avaliados ao longo do estudo. Os benefícios na percepção auditiva observados, bem como a possibilidade do registro do ECAP demonstraram que a estimulação elétrica foi capaz de compensar a alteração da sincronia neural decorrente da NA/DA Diante da heterogeneidade existente, uma conduta clínica comum a todos os sujeitos portadores de NA/DA ainda não pode ser definida e adotada. A avaliação criteriosa de cada caso de maneira específica deve ser realizada no momento anterior à indicação cirúrgica. / Introduction: The electrical stimulation generated by the Cochlear Implant (CI) may improve the neural synchrony and hence contribute to the development of auditory skills in patients with Auditory Neuropathy / Auditory Dys-synchrony (AN/AD). Goal: The goal of the research was to evaluate the auditory performance and the characteristics of the electrically evoked compound action potential (ECAP) in a group of 18 cochlear implants recipients with AN/AD. The results were compared with the control group composed of cochlear implants recipients with sensorial hearing loss. Method: The auditory perception was evaluated by sound field thresholds and speech perception tests. To evaluate ECAP\'s characteristics, the threshold and amplitude of neural response together with the amplitude growth and recovery functions were evaluated at 80Hz stimulation rate. For the patients with AN/AD, the threshold and amplitude of neural response were also evaluated at 35Hz stimulation rate. Results: No significant statistical variance for the development of auditory skills was found when comparing children with AN/AD and the control group. The ECAP\'s characteristics variance between the patients with AN/AD and the control group at 80Hz stimulation rate as well as at 35Hz stimulation rate were also not statistically significant. Conclusion: The CI was seen as an efficient resource to develop auditory skills in 94% of the AN/AD patients considered by the research. The auditory perception benefits as well as the possibility to\' measure the ECAP showed that the electrical stimulation could compensate the neural dys-synchrony caused by the AN/AD. However, a unique clinical procedure cannot be proposed at this point. Therefore, a careful and complete evaluation of each AN/AD patient before recommending the Cochlear Implant is advised.

Although unilateral cochlear implants generally provide good speech understanding under quiet conditions, patients with unilateral cochlear implants frequently report difficulty in understanding speech in the presence of background noise and difficulty in localizing the source of sound. Since these two listening functions require binaural hearing in normal hearing individuals, there has been a growing interest in bilateral cochlear implants as intervention type for people with severe-to-profound bilateral hearing loss. This study investigated the outcomes of bilateral cochlear implants in all the adult recipients of the Pretoria Cochlear Implant Program. All the subjects with BCIs were asked to choose a significant other person to participate in the study. All the subjects (i.e. subjects with BCIs and their significant other people) were asked to participate in a semi-structured interview and to fill out a researcher-generated questionnaire. The subjects with BCIs also underwent audiometric testing. The majority of the subjects with BCIs were found to demonstrate improved ability to understand speech in the presence of background noise and, to some extent, in their ability to localize sound sources. As both quantitative and qualitative methods were used to determine the outcomes, it could be demonstrated that the majority of adult bilateral cochlear implant recipients gain from the auditory benefits in everyday listening situations. The majority of subjects and their significant other people conferred that their improved auditory skills allow them to be more participative in social, cultural, and other activities, which add to the quality of their lives. / Dissertation (MCommunication Pathology)--University of Pretoria, 2009. / Speech-Language Pathology and Audiology / Unrestricted

A decline in temporal resolution, or the ability of the auditory system to track fast changes in incoming sounds, is one factor thought to contribute to difficulties in speech perception that accompany the aging process. Aging effects on gap detection abilities, using behavioral or isolated electrophysiologic measures, have been studied previously. However, peripheral and central electrophysiological, and behavioral measures of temporal resolution have not been examined in the same subjects. Also, the relationship between age-related changes in temporal resolution and speech perception is still unclear, as is their interaction with cognition. By revisiting this question in CI users, it was possible to study aging effects on temporal resolution without the potential confound of age-related hearing loss. In addition, the device allows for manipulations of the temporal properties of a signal without concomitant changes in its spectrum, and for auditory-nerve recordings. This study had two main goals: (1) to determine how aging affects temporal resolution at the auditory periphery, the cortex and perceptually; and (2) to explore the relationship between age-related changes in temporal resolution, general cognitive functioning and speech perception. Results showed that when the auditory system is stimulated with a cochlear implant, few effects of advancing age on temporal resolution are evident. It is possible that, by stimulating the auditory nerve with precise timing, cochlear implants can help users overcome temporal resolution deficits. Alternatively, and perhaps more likely, it is possible that previous studies that reported age effects on temporal resolution were largely influenced by differences in peripheral processing, which were minimized in this study by the use of a cochlear implant. Across the age groups, digit span was the only variable significantly correlated with speech perception in noise and perception of time-compressed speech. A longer memory span for digits was associated with better outcomes in both tests of speech perception. This finding is consistent with previous research, and underscores the notion that cognitive factors, not age, may be more important for speech perception.

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

Speech processing in the human cochlea introduces travelling waves on the basilar membrane. These travelling waves have largely been ignored in most processing strategies. This study implements a hydrodynamical model in a speech processing strategy in order to investigate the neural spike train patterns for a travelling wave processing strategy. In cochlear implants a trade-off remains between the simulation rate and the number of electrode channels. This trade-off was investigated in the proposed travelling wave strategy. Taking into consideration existing current spread and electrical stimulation models, predicted neural spike train responses have shown that stimulating fewer channels (six and four) at stimulation rates of 2 400 pps and 3 600 pps gives better approximations of predicted normal hearing responses for input frequencies of 200 Hz, 600 Hz and 1 kHz, compared to stimulating more channels at lower channel stimulation rates. The predicted neural spike train patterns suggest that these resulting neural patterns might contain both spatial and temporal information that could be extracted by the auditory system. For a frequency of 4 kHz the predicted neural patterns for a channel-number stimulation-rate configuration of 2 - 7 200 pps suggested that although there is no travelling wave delay information, the predicted neural patterns still contain temporal information. The predicted ISI histograms show peaks at the input tone period and multiples thereof, with clusters of spikes evident around the tone period in the predicted spatio-temporal neural spike train patterns. Similar peaks at the tone period were observed for calculated ISI histograms for predicted normal hearing neural patterns and measured neural responses. The predicted spatio-temporal neural patterns for the input frequency of 200 Hz show the travelling wave delay with clusters of spikes at the tone period. This travelling wave delay can also be seen from predicted normal hearing neural responses. The current spread, however, shows a significant distortion effect around the characteristic frequency place where the travelling wave delay increases rapidly. Spacing electrodes more closely results in an increase in this distortion, with the nerve fibre threshold decreasing in adjacent populations of nerve fibres, increasing the probability of firing. The current spread showed a more limited distortion effect on travelling wave delays when electrodes were spaced across the cochlea, at an electrode spacing of 6.08 mm. ISI histogram results also showed increased peaks around the tone period and multiples thereof. These predicted neural spike train patterns suggest that travelling waves in processing strategies, although mostly ignored, might provide the auditory system with both the spatial and temporal information needed for better pitch perception. / Dissertation (MEng)--University of Pretoria, 2012. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

Post-implantation facial nerve stimulation is a common side-effect of cochlear electrical stimulation. Facial nerve stimulation can often be resolved through adjustments in speech processor fitting but, in some instances, exhibit limited benefit or may have a detrimental effect on speech perception. In this study, the apical reference stimulation mode was investigated as a potential intervention to facial nerve stimulation. Firstly, a model refinement software tool was developed to improve the accuracy of models created by an automated workflow. Secondly, the refined model of the human cochlea, facial nerve and electrode array, coupled with a neural model, was used to predict excitations of auditory and facial nerve fibres. Finally, psychoacoustic tests were used to determine auditory comfort and threshold levels for the apical reference stimulation mode while simultaneously capturing electromyography data. The refinement tool illustrated an improved accuracy compared to measured data. Models predicted a desirable outcome for apical reference stimulation, as facial nerve fibre thresholds were higher and auditory thresholds were lower, in direct comparison to conventional monopolar stimulation. Psychoacoustic tests illustrated decreased auditory thresholds and increased dynamic range during apical reference stimulation. Furthermore, apical reference stimulation resulted in lower electromyography energy levels, compared to conventional monopolar stimulation, which suggests a reduction in facial nerve stimulation. Subjective feedback corroborated that apical reference stimulation alleviated facial nerve stimulation. This suggests that apical reference stimulation may be a viable strategy to alleviate facial nerve stimulation considering the improvements in dynamic range and auditory thresholds, complemented with a reduction in facial nerve stimulation / Dissertation (MEng (Bioengineering))--University of Pretoria, 2019. / NRF / Electrical, Electronic and Computer Engineering / MEng (Bioengineering) / Unrestricted