Graeme Clark Collection
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ItemA speech processing strategy for multiple-electrode cochlear implant prostheses(Monash University Press, 1983)Speech studies in a number of research centres have shown that useful speech information could be presented to deaf patients using single or multiple electrode cochlear implant prostheses (Parking & Anderson, 1983). In our laboratory, speech processing strategies were formulated on the basis of psychophysical results. This paper examines the psychophysical characteristics of the hearing sensations produced by electrical stimulation using scala tympani electrodes in postlingually deaf patients; a speech processing strategy is then discussed on the basis of these characteristics.
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ItemPhysiological and histopathological effects of chronic intracochlear electrical stimulation(Monash University Press, 1983)Direct and r.f. currents are known to result in destruction of neural tissue. However, it is now apparent that non-destructive electrical stimulation can be achieved by the use of biphasic pulsatile stimuli (Lilly, 1960; Mortimer et al., 1970; Hughes et al., 1980). Although maximum biologically safe stimulation regimes have yet to be clearly defined, the evidence of a number of investigators suggests that charge density per phase and charge injection per phase are important parameters when establishing biologically safe levels of electrical stimulation (Pudenz et al., 1975; Pudenz et al., 1977; Brown et al., 1977; Babb et al., 1977). Furthermore, considerable attention has been given to ensure that the stimulus is not producing adverse electrochemical reactions that could result in physical or toxic injury to the biological environment. Brummer et al. (1977) have defined the upper limit of electrochemically safe electrical stimulation for platinum electrodes as charge balanced biphasic pulses at a maximum charge density of 300 ?C/cm2 geom./phase.
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ItemSelection of speech processing for cochlear implant prostheses(Monash University Press, 1983)In this paper we consider a framework against which to discuss strategies for the design of speech processors for cochlear implant prostheses. We hope to encourage discussion of the bases for such a framework even though it may seem a distant objective owing to the large gaps in our understanding of several component parts of cochlear implant systems. The existence of such a framework would provide a background against which to view the current diverse cochlear implant systems and to evaluate their performance.
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ItemThe implanted round window membrane in the cat [Abstract](Monash University Press, 1983)In cochlear implants the round window is convenient for the electrode insertion into the scala tympani because the surgical approach is reasonably easy and the inserted electrode lies close to systematically organised nerve fibres in the spiral lamina. However, complications might occur when a poor seal, extensive tissue damage or surgical asepsis are present that lead to a reduction in the nerve fibre population which is needed for electrical stimulation. Published articles available do not describe the role of the window membrane in cochlear implants. Probably this can be referred to the finidng of abundant scar tissue in the window niche and around the electrode giving the impression of a safely implanted electrode. This study performed on seven cats over 5 months was concerned with morphological properties of the implanted window membrane at different stages after implantation. In addition, horseradishperoxydase was used as a tracersubstance to give data concerning the sealing properties of the implanted round window membrane.
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ItemInitial results for six patients with a multiple-channel cochlear prosthesis(Monash University Press, 1983)A total of eight patients have been assessed with the multi-channel cochlear prosthesis at the University of Melbourne. The first two patients were implanted with a prototype device in 1978 and 1979, and their results with various speech evaluation procedures have been reported and summarized in detail elsewhere (Clark & Tong, 1982). Briefly, these results indicated that some very significant benefit could be obtained for these patients when using the cochlear prosthesis with external speech processing, particularly when using the device in conjunction with lipreading. It was also shown that some significant understanding of speech was possible without lipreading (open-set) for both patients, although this was fairly limited.
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ItemThe auditory brainstem response in hearing and deaf cats evoked by intracochlear electrical stimulation(Monash University Press, 1983)This study was performed to investigate in detail the auditory brainstem response (ABR) for intracochlear electrical stimulation. Brainstem response audiometry is a simple, noninvasive procedure with the responses under many stimulus conditions being readily understood in terms of single auditory nerve discharge properties. The amplitude and latency behaviour of the Nl brainstem response correlates well with that recorded directly from the auditory nerve (Huang & Buchwald, 1978). In addition, the brainstem response can be divided into frequency-specific components corresponding to tonotopical locations in the cochlea, as exhibited in the method of derived responses (e.g. Parker &Thornton, 1978). It is therefore well suited to both physiological and clinical investigation of auditory function and therefore should be useful in evaluating auditory function under conditions of electrical stimulation of the cochlea.
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ItemElectrical stimulation of the human cochlea: psychophysical and speech studies(Plenum Publishing Corporation, 1981)This report describes psychophysical and speech studies conducted on two of our post-lingually deaf patients implanted with the nature of the hearing sensations produced by the individual electrodes, and to investigate the feasibility of the transmission of speech information to higher centres by means of cadences of stimulation using on electrode at a time. Two totally deaf patients (MC1 and MC2) participated in these studies.
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ItemSpeech perception, production and language results in a group of children using the 22-electrode cochlear implant( 1989)Paper presented at the 118th Meeting of the Acoustical Society of America
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ItemA digital computer model of electrical stimulation in the human cochlea for auditory prosthesis research( 1990)A three-dimensional model of electrical stimulation in the human cochlea has been developed and implemented on a digital computer. The model was used to estimate the distributions of electric potential and current density in the human cochlea in response to electrical stimulation using scala tympani electrodes. The computed distributions were used to investigate the relative merits of two scala tympani electrode designs. The results showed that the electrode design consisting of a medial electrode pair in the scala tympani is a more viable alternative than a lateral electrode pair for patients suffering from profound-to-total hearing impairment.
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ItemPreliminary results with a miniature speech processor for the 22-electrode Melbourne/Cochlear hearing prosthesis(Kugler & Ghedini, 1990)The 22-electrode cochlear prosthesis developed by the University of Melbourne in conjunction with Cochlear Pty Ltd has been used successfully by profoundly deaf patients since 1982 and is now a part of everyday life for some 2000 people in many countries around the world. The implanted part of the prosthesis has remained relatively unchanged in this time except for the alteration of the design in 1986 to incorporate an implanted magnet and reduce the overall thickness of the device. The implanted magnet eliminated the need for wire headsets which were difficult to fit and in some cases did not maintain the position of the external transmitter coil adequately. This was felt to be essential before the prosthesis could be used in young children.