Graeme Clark Collection
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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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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.
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ItemSignal processing in quiet and noise( 1987)It has been shown that many profoundly deaf patients using multichannel cochlear implants are able to understand significant amounts of conversational speech using the prosthesis without the aid of lipreading. These results are usually obtained under ideal acoustic conditions but, unfortunately, the environments in which the prostheses are most often used are rarely perfect. Some form of competing signal is always present in the urban setting, from other conversations, radio and television, appliances, traffic noise and so on. As might be expected, implant users in general find background noise to be the largest detrimental factor in their understanding of speech, both with and without the aid of lipreading. Recently, some assessment of implant patient performance with competing noise has been attempted using a four-alternative forced-choice spondee test (1) at Iowa University. Similar testing has been carried out at the University of Melbourne with a group of patients using the Nucleus multichannel cochlear prosthesis. This study formed part of an assessment of a two formant (F0/FI/F2) speech coding strategy (2). Results suggested that the new scheme provided improved speech recognition both in quiet and with competing noise. This paper reports on some more detailed investigations into the effects of background noise on speech recognition for multichannel cochlear implant users.
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ItemSpeech recognition abilities in profoundly deafened adults using the Nucleus 22 Channel Cochlear Implant System( 1987)Research in the area of cochlear prostheses to restore a level of hearing sensation to the profoundly deaf has been ongoing at a number of centers throughout the world since the 1960's. 3, 4, 7, 8,. Work on a multichannel cochlear implant that utilizes a speech feature extraction coding strategy and multi-sited, sequential, bipolar stimulation to enhance pitch perception began at the University of Melbourne under the direction of Professor Graeme Clark in the 1970's. Collaboration with Nucleus Limited, a multi-national biomedical corporation from Australia, led to the development of the current version of the prosthesis. The Nucleus 22 Channel Cochlear Implant System has been described in detail elsewhere. 1, 5
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ItemSpeech processing for electrical stimulation of the auditory nerve( 1986)The development of cochlear prostheses which provide hearing .sensation to those previously totally deaf by means of electro-neural stimulation has brought new hope for normal communication to a portion of the deaf community that had previously been beyond help by conventional hearing aids. A cochlear prosthesis provide hearing sensation by exciting nerve fibres in the auditory nerve using small electrical current passed through one or more electrode placed in or around the cochlea. Once this artificial link in the auditory information pathway has been established there still remain considerable challenge in the selection of appropriate coding of information to be transmitted along it. In this paper we consider the design of signal processing necessary for an effective speech perception, prosthesis via the electrical stimulation of the auditory nerve.
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ItemA formant-estimating speech processor for cochlear implant patients(Speech Science and Technology Conference, 1986)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. Nine patients were trained and evaluated with a processor that presented the first formant frequency and amplitude as well. The second group performed significantly better in discrimination tasks and word and sentence recognition through hearing alone. The second group also showed a significantly greater improvement when hearing and lipreading was compared with lipreading alone in a speech tracking task.
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ItemPatient results for a multiple-channel cochlear prosthesis(Raven Press, 1985)Six patients implanted with multiple-channel cochlear prostheses and using take-home, wearable speech processors, were assessed three months postoperatively using the Minimal Auditory Capabilities (MAC) battery. Results showed statistically significant improvement on virtually all tests over their preoperative performance with a hearing aid. Four patients showed significant results for open set speech testing. Lipreading tests, using word and sentence material, showed significant improvement for all patients when the cochlear prosthesis was used with lipreading compared to lipreading alone. All the above tests were carried out without training with recorded material of an unfamiliar speaker. Improvements in communication speed of 55% to 126% over lipreading alone were obtained for the six patients as assessed by the speech tracking procedure. These results are for scores averaged over eight sessions of tracking with the two conditions (with and without cochlear prosthesis). The order of conditions was alternated at each session to control practice effects. The wearable speech processor is used all day every day by five patients, and four hours a day by one patient. Reported benefit is not only for communication but also for the recognition of environmental sounds. Four patients have attempted using the telephone with some success in a restricted context situation. One patient uses the telephone routinely without using any special coding strategies. Reported problems with the cochlear prosthesis are primarily related to background noise. Results for these six patients are consistent with those obtained for two patients implanted with a prototype multiple-channel prosthesis in 1978-1979.