Modelling of the mammalian auditory system is valuable in understanding perception processes and has benefits in the design of signal processing systems and human prosthetic implants. However, as models increase in complexity, traditional methods of modelling using general purpose computers become very slow. One method of overcoming this is to use electronic implementations of these models. This thesis looks into the feasibility of auditory system implementations in digital technology, through the implementation of the Four-Stage Pitch System for pitch detection in hearing proposed by Hewitt and Meddis.

Using a Kalman filter that contains a forward-predictive model of a relevant system, to predict the states of that system by means of an analysis-by-synthesis implementation in order to evade significant time delays incurred by feedback mechanisms was previously applied to the coordinated movement of limbs by means of the cerebellum. In this dissertation, the same concept was applied to the auditory system in order to investigate if such a concept is a universal neurophysiological method for correctly estimating a state in a quick and reliable way. To test this assumption an auditory system model and Kalman estimator were designed, where the Kalman filter contained a stochastically equivalent forward-predictive model of the complete auditory system model. The Kalman filter was used to estimate the power found in a particular band of the frequency spectrum and its performance in the mean-squared error sense was compared to that of a simple postsynaptic current decoding filter under various types of neural channel noise. It was shown that the Kalman filter, containing a biologically plausible internal model could estimate the power better than a postsynaptic current decoding filter, proposed in the literature. When the just-noticeable difference in intensity discrimination, as reported in the literature, was compared to model-predictions, it was shown that a smaller mean-squared error results in the case of the designed auditory system model and Kalman estimator. This suggests that the application of the Kalman filter concept is important as it provides a bridge between measured data and the auditory system model. It was concluded that a Kalman filter model containing a biologically plausible internal model can explain some characteristics of the signal processing of the auditory system. The research suggests that the principle of an estimator that contains an internal model could be a universal neurophysiological method for the correct estimation of a desired state. / Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

A new approach to study angiotensin receptor distribution in the brain has been taken by developing antibodies to partial sequence of the angiotensin II (AII) type-1 receptor subtype (AT1) and demonstrating the presence of receptors with immunohistochemical staining. The antibody to a portion of the 3rd cytoplasmic loop of the AT1 receptor revealed distinctive punctate immunoreactive staining on cell bodies. The cell bodies were distributed in the forebrain in paraventricular and supraoptic nuclei, the organum vasculosum lamina terminalis, median preoptic area and subfornical organ. In the brainstem, the entire locus coeruleus was stained, together with the adjacent mesencephalic and motor nuclei of the trigeminal nerve. The auditory system including the cochlear nucleus and superior olivary nuclei were stained. In the medulla, all the structures involved in blood pressure control were stained including the nucleus of the solitary tract, the 12th nerve nuclei, the rostroventral lateral area and the nucleus ambiguous. Sites where AT2 receptors are located were not stained or staining was limited to specific area such as the medial accessory nucleus of the inferior olive. Immunocytochemical staining of AT1 receptors provides a new and more precise approach to the cellular localization of AII receptors.

The mature central nervous system (CNS) has the capacity to reorganise when there is a change in sensory input. However, studies using the N1 cortical auditory evoked potential, or its magnetic homolog N1m, have not consistently demonstrated evidence of plasticity in adults with late onset unilateral deafness. In addition, little is known about the time course of experience-related plasticity in adults with unilateral deafness. The aim of the studies described in this thesis was to investigate plasticity in adults with unilateral deafness, using N1 auditory evoked potentials. Deafness occurred as a result of surgery for the removal of an acoustic neuroma. The stimuli were 500-Hz and 4-kHz tones presented monaurally to the intact ear, and the data were analysed using global field power and dipole source analysis. In the first study (Chapter 3), hemispheric asymmetries in the N1 response were measured in a group of 24 normally hearing adults at presentation levels of 40, 60 and 80 dB sensation level (SL). The results revealed that the mean hemispheric asymmetry was greater for the 4-kHz stimulus but there was no significant effect of presentation level. In addition, the results revealed that the magnitude of hemispheric asymmetry depended on the ear of stimulation; a trend for larger asymmetries was observed following stimulation of the left ear. The results of the study provide confidence that the methodology is suitable for measuring hemispheric asymmetries in individuals with unilateral deafness. The effect of stimulus level is important since this will vary in plasticity studies involving individuals with late onset unilateral deafness due to their pure tone sensitivity thresholds. Clarifying the effect of stimulus frequency in normally hearing adults is important since the effect of stimulus frequency on plasticity following unilateral deafness has not been reported previously.In the second study (Chapter 4), N1 responses were measured in 19 adults with unilateral deafness (10 and 9 right- and left-sided deafness respectively). Stimuli were typically presented at 60 dB SL. The results revealed that there was significantly greater mean activity and a shift towards reduced hemispheric asymmetries compared with 19 audiogram-matched controls. Similar changes were apparent after both right- and left-sided deafness, and for both 500-Hz and 4-kHz stimuli. Therefore the results reveal evidence of experience-related plasticity that mirrors the findings reported in animal models. The reduced hemispheric asymmetries were reflected in the dipole source model used in this thesis by changes in dipole strength, location and orientation. These findings may explain the inconsistencies reported in previous studies that have used N1 or N1m, where dipole location and orientation have not always been taken into adequate consideration.In the third study (Chapter 5), longitudinal measurements were made in six adults just prior to the onset of complete unilateral deafness, and at 1-, 3- and 6-months after the onset (4 right-sided and 2 left-sided deafness respectively). The results from the second study were further analysed by splitting the data into two groups: nine participants with <2 years deafness and 10 with ≥2 year's deafness. The results from the longitudinal data revealed that there was a significant difference in mean activity across the four conditions. For both stimulus types an increase in mean activity occurred after the onset of deafness, and hemispheric asymmetries were reduced. The biggest changes occurred within 1-month, although further increases were noted in some individuals with ≥2 year's duration of deafness. Changes that continue over this period of time suggest different physiological mechanisms for plasticity within the human central auditory system.

This study investigated the incidence of peripheral hearing loss in sickle cell anemia and the possibility of central auditory nervous system involvement. Nine Black subjects with sickle cell disease and nine with normal hemoglobin were administered an auditory test battery. There appeared to be no correlation between number of crisis episodes, duration of symptoms, severity of symptoms, and audiologic manifestations. Acoustic reflex testing suggested the possibility of "aired neural function in the sickle cell group. Whether impaired function was due to peripheral VIIIth nerve or to central brain stem involvement could not be determined. Results of the central auditory test battery suggested the possibility of impaired or reduced central auditory function in subjects with sickle cell anemia.

Corujas se destacam por suas habilidades visuais e auditivas. Pouco é conhecido sobre a neuroanatomia do seu telencéfalo. Assim, caracterizamos através de técnicas histo/imunoistoquímicas o telencéfalo da coruja-da-igreja. Os núcleos da base foram delineados através da sua intensa imunomarcação para DARPP-32 e tirosina hidroxilase. Áreas sensoriais primárias tálamorrecipientes, como o entopálio (E), L2 do Field L auditório e o núcleo basorostral palial, foram caracterizadas pela quase ausência de DARPP-32 e alta atividade da citocromo oxidase (CO). As pseudo-camadas do Wulst visual foram delineadas com uma combinação de métodos, incluindo a ativação da CO, e imunomarcação para DARPP-32. O Wulst visual e o Field L se destacaram como regiões enormes, enquanto o E se revelou menor. Os dados sugerem que a morfologia de muitas regiões telencefálicas da coruja-da-igreja é semelhante àquela em outras aves. Contudo, o Wulst e o Field L se destacaram por seu tamanho e grau de organização, refletindo a importância do sistema visual e auditivo no comportamento de corujas. / Owls possess exceptional visual and auditory capacities. There is only limited information about the neuroanatomy of their forebrain. Thus, we characterized by histo/immunohistochemical techniques the forebrain of the barn owl. The basal ganglia were delineated by their intense immunostaining for DARPP-32 and tyrosine hydroxylase. Primary thalamorecipient sensory areas, such as the entopallium (E), L2 of the auditory Field L and the basorostral palial nucleus were characterized by the almost absence of DARPP-32 and their high citocrome oxidase (CO) activity. The pseudo layers of the visual Wulst were delineated by a combination of methods, including CO activity and immunostaining for DARPP-32.The Wulst and Field L were outlined by their huge size, whereas the E was small. These data suggest that the morphology of many telencephalic regions of the barn owl is similar to that in other birds. However, the Wulst and Field L were highlighted by their size and degree of organization, reflecting the importance of the visual and auditory system for the behavior of owls.

The diploma thesis deals with noise measurement. The theoretical part contains the knowledge gained by studying literature. I have described acoustics, sound and noise, noise and health and legislative contexts as well as noise reduction methods. The practical part contains information about the company and individual machinery, the results of measurements and their evaluation according to valid legislation. I have suggested appropriate measures to reduce the noise burden on operators.

When a baby is born deaf, a cochlear implant is often recommended as a medical habilitation tool to the parents. A cochlear implant is designed to bypass a damaged cochlea and stimulates auditory nerve directly, from where signals are sent all the way to the auditory cortex where sounds are perceived. We expect that a deaf child can detect and discriminate speech sounds with this device. With continuous auditory experiences, we hope that the auditory cortex of the deaf child can be developed as children with normal hearing do. Can a cochlear implant facilitate the development of the auditory brain? This study attempts to answer this question, exploring developmental effects on evoked potentials measured at the cortical level. Early-implanted, pre-lingually deafened cochlear implant users showed similar developmental patterns of cortical auditory evoked potentials to those of normal hearing listeners. However, the responses, related to sound discrimination, were affected by noise more in cochlear implant users. This may be related to perceptual abilities of cochlear implant users in harder listening conditions. The findings indicate that cortical auditory evoked potentials, related to both detection and discrimination, can be used to document the long developmental trajectory of the central auditory system in both normal hearing listeners and cochlear implant users. This study suggests that these responses can be used as a tool for estimating behavioral performance in cochlear implant users.

In this thesis I attempt to explain mechanisms of neuronal coding in the auditory system as a form of adaptation to statistics of natural stereo sounds. To this end I analyse recordings of real-world auditory environments and construct novel statistical models of these data. I further compare regularities present in natural stimuli with known, experimentally observed neuronal mechanisms of spatial hearing. In a more general perspective, I use binaural auditory system as a starting point to consider the notion of function implemented by sensory neurons. In particular I argue for two, closely-related tenets: 1. The function of sensory neurons can not be fully elucidated without understanding statistics of natural stimuli they process. 2. Function of sensory representations is determined by redundancies present in the natural sensory environment. I present the evidence in support of the first tenet by describing and analysing marginal statistics of natural binaural sound. I compare observed, empirical distributions with knowledge from reductionist experiments. Such comparison allows to argue that the complexity of the spatial hearing task in the natural environment is much higher than analytic, physics-based predictions. I discuss the possibility that early brain stem circuits such as LSO and MSO do not \"compute sound localization\" as is often being claimed in the experimental literature. I propose that instead they perform a signal transformation, which constitutes the first step of a complex inference process. To support the second tenet I develop a hierarchical statistical model, which learns a joint sparse representation of amplitude and phase information from natural stereo sounds. I demonstrate that learned higher order features reproduce properties of auditory cortical neurons, when probed with spatial sounds. Reproduced aspects were hypothesized to be a manifestation of a fine-tuned computation specific to the sound-localization task. Here it is demonstrated that they rather reflect redundancies present in the natural stimulus. Taken together, results presented in this thesis suggest that efficient coding is a strategy useful for discovering structures (redundancies) in the input data. Their meaning has to be determined by the organism via environmental feedback.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-04-26T20:08:35Z No. of bitstreams: 1 ThawannMalfattiBorges_DISSERT.pdf: 27333324 bytes, checksum: 7928d876effa4fd0184f0b246ecd1c34 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-04-29T20:35:41Z (GMT) No. of bitstreams: 1 ThawannMalfattiBorges_DISSERT.pdf: 27333324 bytes, checksum: 7928d876effa4fd0184f0b246ecd1c34 (MD5) / Made available in DSpace on 2016-04-29T20:35:41Z (GMT). No. of bitstreams: 1 ThawannMalfattiBorges_DISSERT.pdf: 27333324 bytes, checksum: 7928d876effa4fd0184f0b246ecd1c34 (MD5) Previous issue date: 2015-06-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Tinnitus is the perception of a sound in the absence of a corresponding physical stimulus. It is not clear yet what mechanisms are involved in tinnitus and how it starts and/or becomes chronic. Due to the relationship between tinnitus and somatosensory trauma/stimuli, the dorsal cochlear nucleus (DCN), a region known to integrate somatosensory and auditory pathways, has been identified as a potential key structure in the generation of phantom sound perception. Here, we target specific neuronal populations in the DCN to allow further investigation on how this region may contribute to the generation of tinnitus signals that spread to other auditory areas. We examined the expression of optogenetic proteins (Channelrhodopsin 2 - ChR2; and enhanced Archaerhodopsin 3.0 - eArch3.0), targeting neurons expressing Calmoduline Kinase II alpha (CaMKIIa) promoter in wild-type C57/Bl6 mice and neurons expressing nicotinic acetylcholine receptor subunit alpha-2 promoter (ChRNA2) in ChRNA2- Cre transgenic C57/Bl6 mice, using local virus injection, verified by fluorescence microscopy. Unit responses were differentiated based on their electrophysiological response to sound. We then investigated if firing of neurons expressing optogenetic tools can be controlled in vivo and if the same neurons also fire action potentials in response to precisely timed sound stimulation. Both in vivo and preliminary in vitro data shows that neurons expressing ChR2 do respond to sound, and that they furthermore also can respond to light stimulation with a stable and similar waveform. Moreover, in vivo data shows that neurons expressing eArch3.0, responding to sound, will decrease their firing rate when exposed to green light. Thereby showing that optogenetic tools can be used functionally in the DCN, it is possible to further test tinnitus theories by, for example, producing an increased firing rate in the DCN, trying to mimic tinnitus; or inhibiting increased spontaneous firing rate in the DCN of animals with noise-induced or salycilate-induced tinnitus.