Graeme Clark Collection
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ItemThe histopathology of the human temporal bone and auditory central nervous system following cochlear implantation in a patient: correlation with psychophysics and speech perception results( 1988)Cochlear implantation has become a recognised surgical procedure for the management of a profound-total hearing loss, especially in patients who have previously had hearing before going deaf (postlingual deafness). Nevertheless, it is important for progress in the field that patients who have had a cochlear implant, bequeath their temporal bones for research. This will then make it possible to further assess the safety of the procedure, and the factors that are important for its effectiveness. Biological safety has been assessed in a number of studies on animals, in particular, the biocompatibility of the materials used (1,2), the histopathological effects of long-term implantation on the cochlea (3, 4, 5, 6, 7, 8), and the effects of chronic electrical stimulation on the viability of spiral ganglion cells (9, 10, 11, 12). In studying the temporal bones of deceased cochlear implant patients it is possible to help establish that the animal experimental results are applicable to Man. Surgical trauma has been most frequently evaluated by inserting electrodes into cadaver temporal bones. It is important, however, to examine bones that have been previously implanted surgically to ensure that the cadaver findings are applicable to operations on patients. The effectiveness of cochlear implantation can be studied by correlating the histopathological findings, the dendrite and spiral ganglion cell densities, in particular, with the psychophysical and speech perception results. Other benefits also accrue, for example, establishing the accuracy of preoperative X-rays and electrical stimulation of the promontory in predicting cochlear pathology and spiral ganglion cell numbers. For the above reasons it has been especially interesting to examine both the temporal bones and central nervous system from one of our patients (patient 13) who participated in the initial clinical trial of the Cochlear Proprietary Limited (a member of the Nucleus group) multiple-electrode cochlear prosthesis, and who died due to a myocardial infarction following coronary bypass surgery.
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ItemThe University of Melbourne/Nucleus cochlear prosthesis( 1988)This is a review of research to develop the University of Melbourne/Nucleus cochlear prosthesis for patients with a profound-total hearing loss. A more complete review can be obtained in Clark et al. A prototype receiver-stimulator and multiple-electrode array developed at the University of Melbourne was first implanted in a postlingually deaf adult patient with a profound-total hearing loss on 1 August 1978. A speech processing strategy which could help this patient understand running speech, especially when combined with lipreading was developed in 1978 following initial psychophysical studies. A prototype wearable speech processor was fabricated in 1979, that could provide significant help for the first two patients in understanding running speech when used in combination with lipreading compared with lipreading alone, and it also enabled them to understand some running speech when using electrical stimulation alone. An implantable receiver-stimulator and wearable speech processor embodying the principles of the prototype devices were then produced for clinical trial by the Australian biomedical firm, Nucleus Ltd, and its subsidiaries, Cochlear Pty Ltd and Cochlear Corporation. This cochlear implant was initially clinically trialled on six patients at The Royal Victorian Eye & Ear Hospital in 1982, and shown to give similar results to those obtained with the prototype device. In view of these findings a clinical trial was carried out for a Premarket Approval Application to the US Food and Drug Administration (FDA), and extended to a number of centres in the US, Canada, and West Germany. This clinical trial confirmed that patients could understand running speech when electrical stimulation was combined with lipreading, and that some patients could also understand running speech when using electrical stimulation alone. Today, more than 600 patients world-wide are using cochlear implants developed from the research described in this paper.
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ItemEvaluation of a two-formant speech-processing strategy for a multichannel cochlear prosthesis( 1987)Initial results with the two-formant speech-processing strategy (F0FIF2) confirm the advantage of a multichannel cochlear prosthesis capable of stimulating at different sites within the cochlea. The successful presentation of two spectral components by varying the place of stimulation leads to the possibility of presenting further spectral information in this manner. Because virtually all multichannel implant patients demonstrate good "place" (electrode site) discrimination, these more refined coding strategies should lead to benefits for the majority of implantees. Already, with the F0FIF2 strategy, we have a system that appears to provide some effective auditory-alone communication ability for the average patient.
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ItemA multiple-electrode intracochlear implant for children( 1987)A multiple-electrode intracochlear implant that provides 21 stimulus channels has been designed for use in young children. It is smaller than the adult version and has magnets to facilitate the attachment of the headset. It has been implanted in two children aged 5 and 10 years. The two children both lost hearing in their third year, when they were still learning language. Following implantation, it was possible to determine threshold and comfortable listening levels for each electrode pair. This was facilitated in the younger child by prior training in scaling visual and electrotactile stimuli. Both children are regular users of the implant, and a training and assessment program has been commenced.
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ItemAcoustic parameters measured by a formant-estimating speech processor for a multiple-channel cochlear implant( 1987)Abstract not available due to copyright.
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ItemVowel and consonant recognition of cochlear implant patients using formant-estimating speech processors( 1987)Abstract not available due to copyright.
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ItemA formant-estimating speech processor for cochlear implant patients( 1987)A simple formant-estimating speech processor has been developed to make use of the “hearing” produced by electrical stimulation of the auditory nerve with a multiple-channel cochlear implant. Thirteen implant patients were trained and evaluated with a processor that presented the second formant frequency, fundamental frequency, and amplitude envelope of the speech (F0F2). Nine patients were trained and evaluated with a processor that presented the first and second formant frequencies, fundamental frequency, and first and second formant amplitudes (F0F1F2). The most common use of the speech processor was in conjunction with lipreading, so the patients were trained in lipreading plus hearing, as well as hearing alone. The F0F1F2 group performed significantly better in discrimination tasks and word and sentence recognition through hearing alone. The F0F1F2 group also showed a significantly greater improvement when hearing and lipreading was compared with lipreading alone in a speech tracking task. A study of spondee recognition in noise with hearing alone indicated that the added first formant information produced an improvement that was equivalent to a 5 dB increase in the signal-to-noise ratio.
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ItemClinical results with a hearing aid and a single-channel vibrotactile device for profoundly deaf adults( 1985)The speech perception of a group of 19 adults with post-lingual profound to total hearing loss was tested with nine c1osedset speech tests without lipreading two open-set tests without lipreading and two open-set speech tests with lipreading. The subjects were all prospective cochlear implant patients participating in a clinical trial of the implant and the results reported here were obtained as part of the pre-operative assessment. They were divided into groups on the basis of their prior experience with the aid(s), their speech detection thresholds with the two aids and their personal preferences. Seven of the subjects used a hand-held single-channel vibrotactile device and the other 12 used a powerful conventional hearing aid. Subjects from each group scored significantly better than chance on the closed set tests without lipreading. Training or regular hearing aid use was correlated with good performance on the closed-set tests. No subject showed a significant improvement of the lipreading score when the aid was used as a supplement. The use of sophisticated wearable tactile devices and extensive training may allow a better result, but in this clinical program, neither a hearing aid nor a single channel vibrotactile device greatly benefited the postlingually profoundly deaf adults.
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ItemThe multi-channel cochlear implant( 1984/85)The multi-channel cochlear implant codes sounds on the bases of rate and place pitch. Experimental studies on animals and patients have shown it is difficult for electrical stimulation to code rate pitch above about 200-400 pulses/second. Therefore to convey as much information about speech as possible it is necessary to produce multi-channel stimulation or place pitch so that the important frequency cues in vowels and consonants can be perceived by the patient.
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ItemAn acoustic model of a multiple-channel cochlear implant( 1984)Abstract not available due to copyright.