Otoacoustic emissions (OAEs) have been under investigation since their discovery 30 years ago (Kemp, 1978). Otoacoustic emissions are quiet sounds generated within the cochlea that can be detected with a sensitive microphone placed within the ear canal. They are used clinically as a hearing screening tool but have the potential for diagnostic and monitoring purposes. For this dissertation, high-resolution instrumentation was developed for improving the acquisition of OAEs. It was shown that a high bit-depth device is required in order to simultaneously characterize the ear canal and the cochlear responses. This led to a reduction in the stimulus artifact that revealed early latency, high-frequency otoacoustic emissions. Next, a swept-tone technique originally developed for use in acoustical systems was formally developed for use in the human ear. The swept-tone technique allows for the simultaneous acquisition of a system's impulse response and its distortion components. The swept-tone was first used in this study to characterize the ear canal transfer properties. From that transfer function, a compensation routine was developed which equalized the magnitude and phase distortions of the ear canal. As a result, an improved acoustical click could be presented to the ear, which allowed for further reduction of the stimulus artifact, revealing early latency emissions. Spectral flatness and effective duration measurements of the compensated click showed an improvement over traditional click stimuli. Furthermore, wavelet analysis and time-frequency latency computations showed that higher frequency otoacoustic emissions were recoverable when using a compensated click stimulus. The swept-tone technique was then utilized for the direct acquisition of otoacoustic emissions. The swept-tone response was compressed to an impulse response and compared to a standard click response. It was found that several similarities exist between the two response types. The divergences, primarily in the low-frequencies, have implications in the generation mechanisms involved in a click-evoked otoacoustic emission. The swept-tone response provided some clinical benefits, namely in an improved signal-to-noise ratio, and in the removal of obstructive synchronized spontaneous OAEs when compared to a standard click response. Current methods are restricted by noise contamination, and the use of a swept-tone technique can reduce the acquisition time by up to a factor of four, compared to standard click methods. These implications and future potential studies are discussed.

The medial olivocochlear reflex (MOCR) is a brainstem-mediated reflex that reduces cochlear amplifier gain when elicited by sound. The MOCR may provide benefits such as protection from acoustic trauma and improved hearing in background noise. Measurement of MOCR effects may also have clinical applications. MOCR effects can be measured using transient-evoked otoacoustic emissions (TEOAEs), as amplitudes of TEOAEs are typically reduced during MOCR activation. The primary purpose of the current study was to quantify the repeatability of MOCR effects on TEOAEs because high repeatability in a healthy population is a necessary (but not sufficient) component of a clinically-useful test. A secondary purpose was to assess the relationship between MOCR strength and speech perception in noise. Twenty-one normal hearing subjects ages 18-30 participated. TEOAEs were elicited using 35 dB sensation level (SL) clicks. The MOCR was elicited using contralateral acoustic stimulation (CAS) consisting of 35 dB SL broadband noise. Sixteen measurements were made across a 5-week period (4 visits × 4 measurements per visit). TEOAEs were bandpass filtered in 1/6-octaves from 1-2 kHz. An individualized time-frequency analysis was used to select the largest TEOAE envelope peak within a restricted time analysis window. Responses were characterized as the complex ratio of TEOAEs obtained with versus without CAS. The statistical significance of effects was assessed. Results revealed generally high levels of stability across time, as assessed by the interquartile ranges of all results and as assessed by Cronbach's alpha. Four MOCR measurements appeared to be adequate to obtain a reliable baseline measurement. Individualized time-frequency analyses were also important for obtaining reliable measurements. However, several subjects showed stable baseline measurements but unusual patterns of variability at subsequent sessions. These changes did not appear to be the result of changes in auditory status, methodological issues, or equipment issues. No significant relationship was found between MOCR strength and speech perception in noise. Results suggest that MOCR measurements are stable in most subjects when using careful measurement and analysis methods, but that further work is needed to better characterize changes in MOCR and to validate the current methodology in a larger number of subjects.

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No. of bitstreams: 1 KayoLNP_DISSERT.pdf: 11309924 bytes, checksum: 44b1f1effa046fdff7b794c0b4f4f371 (MD5) Previous issue date: 2016-07-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Telemedicine has enabled a closer relationship between the health professional and the patient, the use of smartphones as a tool for data exchange has allowed monitoring the distance of both the patient’s situation daily, as performing medical procedures. A problem that requires great attention and that telemedicine can be applied as a possible solution is the pre-diagnosis of hearing loss. When not diagnosed in time, in neonates, it can cause a number of complications, such as behavioral maladjustment, oral and written language disorders, poor school performance of the newborn, among others. But if previously diagnosed and treated, the child may also develop itself like a non-defective, such diagnosis can be given through the Otoacoustic Emissions test. Considering the importance of the audiological analysis, the Brazilian Congress approved Law No. 12.303, of August 2, 2010, which made mandatory the completion of the Otoacoustic Emissions test across the primary care network in the country. However the equipment responsible for performing the test has a high cost, leading to non-realization of most of the population, in its great majority poor, because the few devices distributed in the hospital network of public health. Observing this need, this paper makes use of a smartphone connected to a prototyping board Arduino Mega ADK to develop a tool that helps the realization of the Transient Evoked Otoacoustic Emissions (TEOAE) test in neonates. Using Arduino board to generate the signal and the smartphone to perform recording through a probe positioned in the patient’s ear were performed 3 noise floor recordings, 5 stimulus signal recording and 7 recordings tests in the patient’s ear. The recordings occurred continuously, starting and ending simultaneously with the stimulus. Subsequently held a spectral analysis via Matlab seeking to identify the existence of TEOAE, despite the identification of ear responses in the recordings, we still can not confirm that such responses are really TEOAE / A telemedicina tem possibilitado uma maior aproximação entre o profissional de saúde e o paciente, a utilização de smartphones como ferramenta para troca de dados tem permitido um acompanhamento a distância, tanto da situação do paciente diariamente, como da realização de procedimentos médicos. Um problema que requer muita atenção em que a telemedicina pode ser aplicada como possível solução é o pré-diagnóstico da deficiência auditiva. Quando não diagnosticada, em tempo, em recém-nascidos, a mesma pode acarretar uma série de complicações, como desajustes de comportamento, distúrbios da linguagem oral e escrita, baixo rendimento escolar do neonato, entre outros. Porém, se previamente diagnosticado e tratado, a criança pode desenvolver-se igualmente a uma não deficiente, tal diagnóstico pode ser dado através do teste de Emissões Otoacústicas. Diante da importância da análise audiológica, o Congresso Nacional Brasileiro aprovou a Lei No 12.303, de 2 de agosto de 2010, que tornou obrigatória a realização do teste de Emissões Otoacústicas em toda a rede básica de saúde no país. No entanto, o equipamento responsável por realizar o teste possui um alto custo, ocasionando a não realização em grande parte da população, em sua grande maioria carente, devido aos poucos aparelhos distribuídos na rede hospitalar de saúde pública. Observando essa necessidade, este trabalho utiliza-se de um smartphone conectado a uma placa de prototipação Arduino Mega ADK para desenvolver uma ferramenta que auxilia a realização do teste de Emissões Otoacústicas Evocadas Transientes (TEOAE) em neonatos. Utilizando a placa Arduino para gerar o sinal e o smartphone para realizar a gravação, através de uma sonda posicionada no ouvido do paciente foram realizadas 3 gravações do noise floor, 5 gravações do sinal de estímulo e 7 gravações dos testes no ouvido do paciente. As gravações ocorreram de forma contínua, iniciando e finalizando simultaneamente ao estímulo. Posteriormente realizou-se uma análise espectral através do Matlab buscando identificar a existência de TEOAE, apesar da identificação de respostas do ouvido nas gravações, ainda não foi possível confirmar que tais respostas são realmente TEOAE / 2017-04-12

Past studies have shown that the effects of selective auditory attention are evident in medial olivocochlear (MOC) activity, manifested as the contralateral suppression (CS) of transient evoked otoacoustic emissions (TEOAEs). This finding suggests the use of TEOAEs in the design of an auditory-based access technology as a potential access solution for children with severe disabilities. Thirteen participants with normal hearing threshold and normal middle ear function completed this study. The participants were instrumented with a TEOAE ear probe and presented with a contralateral acoustic stimulus. They were instructed to alternate auditory attention conditions as visually cued by symbols on an LCD display. Attentive and non-attentive conditions were detected with an overall accuracy of 70.17 +/- 12.54% at 2.44 +/- 0.3 bits per minute in a participant-specific classifier, and 65.92 +/- 13.91% in a participant-independent classifier. Detection of auditory attention exceeded random chance levels for 11 of 13 participants.

Past studies have shown that the effects of selective auditory attention are evident in medial olivocochlear (MOC) activity, manifested as the contralateral suppression (CS) of transient evoked otoacoustic emissions (TEOAEs). This finding suggests the use of TEOAEs in the design of an auditory-based access technology as a potential access solution for children with severe disabilities. Thirteen participants with normal hearing threshold and normal middle ear function completed this study. The participants were instrumented with a TEOAE ear probe and presented with a contralateral acoustic stimulus. They were instructed to alternate auditory attention conditions as visually cued by symbols on an LCD display. Attentive and non-attentive conditions were detected with an overall accuracy of 70.17 +/- 12.54% at 2.44 +/- 0.3 bits per minute in a participant-specific classifier, and 65.92 +/- 13.91% in a participant-independent classifier. Detection of auditory attention exceeded random chance levels for 11 of 13 participants.

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Noise exposure is one of the most prevalent causes of irreversible occupational disease in Sweden and in many other countries. In hearing conservation programs, aimed at preventing noise-induced hearing loss, audiometry is an important instrument to highlight the risks and to assess the effectiveness of the program. A hazardous working environment and persons affected by it can be identified by monitoring the hearing thresholds of individual employees or groups of employees over time. However, in order to evaluate the prevalence of occupational noise-induced hearing loss, relevant reference data of unexposed subjects is needed. The first part of this dissertation concerns the changes in hearing thresholds over three decades in two occupational environments with high noise levels in the province of Östergötland, Sweden: the mechanical and the wood processing industries. The results show a positive trend, with improving median hearing thresholds from the 1970s into the 1990s. However, the hearing loss present also in the best period, during the 1990s, was probably greater than if the occupational noise exposure had not occurred. This study made clear the need for a valid reference data base, representing the statistical distribution of hearing threshold levels in a population not exposed to occupational noise but otherwise comparable to the group under study. In the second part of the dissertation, reference data for hearing threshold levels in women and men aged from 20 to 79 years are presented, based on measurements of 603 randomly selected individuals in Östergötland. A mathematical model is introduced, based on the hyperbolic tangent function, describing the hearing threshold levels as functions of age. The results show an age-related gender difference, with poorer hearing for men in age groups above 50 years. The prevalence of different degree of hearing loss and tinnitus is described for the same population in the third part of the dissertation. The overall prevalence of mild, moderate, severe or profound hearing loss was 20.9% collectively for women and 25.0% collectively for men. Tinnitus was reported by 8.9% of the women and 17.6% of the men. Approximately 2.4% of the subjects under study had been provided with hearing aids. However, about 7.7% were estimated to potentially benefit from hearing aids as estimated from their degree of hearing loss. Noise-induced hearing loss primarily causes damage to the outer hair cells of the inner ear. The fourth and last part of the dissertation evaluates the outer hair cell function, using otoacoustic emission measurements (OAE). Prevalence results from three different measuring techniques are presented: spontaneous otoacoustic emissions (SOAE), transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE). Gender and age effects on the recorded emission levels were also investigated. Women showed higher emission levels compared to men and for both women and men the emission levels decreased with increasing age. The results from the OAE recordings were shown to be somewhat affected by the state of the middle ear. The study included tympanometry, and the relation of the outcome ofthis test to the otoacoustic emissions is described, where high middle ear compliance resulted in low emission level. Reference data for the tympanometric measurements are also presented. The results of this project form an essential part of the important work against noiseinduced hearing loss, which needs continuous monitoring. The reference data presented here will provide a valid and reliable data base for the future assessment of hearing tests performed by occupational health centres in Sweden. This data base will in turn prove useful for comparison studies for Sweden as a responsible fellow EU member country setting high standards for work force safety. The statistical distribution of hearing threshold levels as a function of age for men and women in tabulated form is available on the Swedish Work Environment Authority (Arbetsmiljöverket) web site: http://www.av.se/publikationer/bocker/fysiskt/h293.shtm.