Graeme Clark Collection
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ItemCritical bands following the selective destruction of cochlear inner and outer hair cells( 1979)Critical bandwidths and absolute intensity thresholds were measured in cats before and after kanamycin treatment which induced selective inner and outer hair cell losses. Hair cell losses were measured from cochleograms constructed from surface preparations of the organ of Corti. Results suggested that, for the test frequencies and stimulus intensities employed, critical bandwidths were not affected for frequencies tonotopically located in cochlear regions where only outer hair cells were lost. Critical bands were widened or not measurable only when inner hair cell losses exceeding 40% were also associated with complete loss of outer hair cells. The experiment suggests that cochlear frequency selectivity can be mediated by inner hair cells alone.
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ItemElectrical network properties and distribution of potentials in the cat cochlea [Abstract](Australian Physiological and Pharmacological Society, 1978)The-patterns of electrical resistance and capacitance in the cochlea formed by the anatomical organisation of the tissue structures and fluids are important in determining the distribution of electrical potentials which arise during normal acoustic stimulation (von Bekesy,1951). Cochlear potential distributions have in the past been measured by recording from the scalar fluids both the spread of cochlear microphonics and also potentials due to electrical stimulation. However, similar distributions in the hair cell-nerve ending region of the organ of Corti may not necessarily occur because of current shunting effects due to the electrical network patterns. To examine these current shunting effects, a three dimensional mathematical model of the electrical properties of the cat cochlea was constructed. This was formed from a two dimensional cochlear cross-section model similar to that proposed by Johnstone et al., (1966) for the guinea pig. Sixteen such sections were resistively coupled to form the three dimensional model. Results derived from this model predict that during electrical stimulation of the cochlea, the current in the organ of Corti region attenuates quite differently to the scalar voltage by a degree which depends on the stimulus electrode configuration.
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ItemFrequency discrimination and critical bands following the selective destruction of cochlear inner and outer hair cells( 1977)The role of the inner and outer hair cells of the cochlea in frequency discrimination and critical band measurements is not clearly understood. There is, however, evidence for an interaction between the hair cells in threshold determinations (1) and frequency selectivity (2). Furthermore, although there is increasing evidence that a place theory is more importance than a periodicity theory in frequency coding the situation is still not clear, and the role of the inner and outer hair cells in frequency discrimination and critical band measurements should provide additional evidence to help clarify the situation.
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ItemProsthetic devices for the management of patients with severe sensorineural deafness( 1977)It is estimated that 5-10% of patients with significant hearing loss do not get satisfactory help with a hearing aid. This means that in Australia there are about 5,000-10,000 people who need further treatment. Furthermore, a large number of these patients are born deaf and their proper management is critical if they are going to develop adequate speech and language. If these patients are going 10 perceive speech, the speech must be broken down into signals that can be used 10 stimulate the residual hearing, excite the auditory nerve fibres by electrical stimulation or stimulate another sensory system such as vision or the skin senses. These alternatives offer real hope for the patient with severe sensori-neural deafness as there is a great deal of redundancy in the speech signal. This is illustrated in Fig. 1 which shows the raw signal obtained on a cathode ray oscilloscope for the word "ear". It can be seen that there is an overall waveform envelope which is now thought to be quite important in speech perception. Inside the speech waveform there are waves of many shapes and sizes. Far too many for your eye to detect at a glance, and indeed too many for your ear to perceive. In fact, when you hear phonemes and words your brain only picks up key signals.
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ItemA multiple electrode cochlear implant(Cambridge University Press, 1977)It is generally agreed that if a cochlear implant hearing prosthesis is to enable a patient to understand speech, it must be a multiple-electrode system. In addition, stimulation of the auditory nervous system should approximate the patterns of neural excitation occurring in people with normal hearing, and this is especially important when a patient has previously experienced hearing. For this reason the correct application of electrophysiological principles to the design of a hearing prosthesis is desirable, and is discussed in this paper with special reference to a device developed in the Departments of Otolaryngology and Electrical Engineering at the University of Melbourne (UMDOLEE).
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ItemThe clinical assessment of cochlear implant patients(Cambridge University Press, 1977)This paper is a discussion of the clinical assessment routine adopted following experience gained over the last three years from evaluating 27 patients with severe sensori-neural deafness to determine whether they are suitable for the cochlear implantation of a multiple-electrode receiving and stimulating device developed jointly in the Departments of Otolaryngology and Electrical Engineering at the University of Melbourne.
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ItemA multiple-electrode array for a cochlear implant(Cambridge University Press, 1976)It is becoming increasingly evident from experimental work on animals and humans that if cochlear implants are going to help patients understand speech, they must be designed to stimulate a number of different groups of auditory nerve fibres.
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ItemHistopathological findings in cochlear implants in cats(Cambridge University Press, 1975)If cochlear implants are to be used on patients, it is important that experimental studies should be carried out on animals so that tissue tolerance and other long term effects of electrode implantations can be assessed. Consequently, an experimental study by Simmons (1967) is of interest, as it has shown that a stainless steel electrode inserted into the basal turn of the cochlea through the round window can be tolerated, and not lead to permanent damage unless infection supervenes. Furthermore, in a study by Axelsson and Hallen (1973) it has been demonstrated that drilling an opening in the cochlea will usually only lead to localized damage of the cochlear structures, and that the opening in the bone normally heals.
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ItemA cochlear implant electrode(Cambridge University Press, 1975)If patients with severe sensorineural deafness are going to perceive speech by electrical stimulation of the terminal auditory nerve fibres, it must be carried out on the basis of the place theory of pitch perception, as experimental studies have shown that electrical stimulation with single electrodes on the basis of the volley theory is not satisfactory (Clark, 1969; Kiang and Moxon, 1972; Simmons and Glattke, 1972). For this reason, it will be necessary to develop an array of electrodes that will enable a number of different auditory nerve fibres to be stimulated separately.
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ItemA surgical approach for a cochlear implant: an anatomical study(Cambridge University Press, 1975)There is now increased interest in the possibility of restoring brain and nerve function by applying recent developments in electronics and current knowledge of neurophysiology. This is evident from the research being undertaken to see whether a visual cortical implant can help blind patients, and whether electrical stimulation of the auditory pathways can help patients with severe loss of hearing.