Graeme Clark Collection
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ItemSignal processing for multichannel cochlear implants: past, present and future [Abstract]( 1994)Since the late 1970's, many groups have worked on developing effective signal processing for multichannel cochlear implants. The main aim of such schemes has been to provide the best possible speech perception for those using the device. Secondary aims of providing awareness and discrimination of environmental sounds and appreciation of music have also been considered. Early designs included some that attempted to simulate the normal cochlea. The application of such complex processing schemes was limited by the technology of the times. In some cases, researchers reverted to the use of single channel systems which could be controlled reliably with the existing technology. In other cases, as with the Australian implant, a simple multichannel processing scheme was devised that allowed a reliable implementation with available electronics. Over the next 15 years, largely due to the improvements in integrated circuit technology, the signal processors have slowly become more complex. Further psychophysical research has shown how additional information can be transferred effectively to implant users via electrical stimulation of the cochlea. This has lead to rapid improvement in the speech perception abilities of adults using cochlear implants. Some of the main developments in signal processing over the last 15 years will be discussed along with the latest speech perception results obtained with the new SPEAK processing scheme for the Australian 22-channel cochlear implant. Initial results for SPEAK show mean scores of 70% (equivalent to 85-90% phoneme scores) for open set monosyllabic word testing for experienced adult users. Although there remains a large range of performance for all users of cochlear implants, average speech perception scores for all implanted adults have also improved significantly with the developments in signal processing. It appears likely that multichannel cochlear implants will be a viable alternative for the treatment of severe hearing loss in the future.
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ItemSpeech processing for cochlear implants(JAI Press Ltd, 1992)The cochlear implant is a hearing prosthesis designed to replace the function of the ear. The operation of the prosthesis can be described as a sequence of four functions: the processing of the acoustic signal received by a microphone; the transfer of the processed signal through the skin; the creation of neural activity in the auditory nerve; and the integration of the experience of this neural activity into the perceptual and cognitive processing of the implantee.
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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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ItemSpeech perception using a two-formant 22-electrode cochlear prosthesis in quiet and in noise( 1987)A new speech-processing strategy has been developed for the Cochlear Pty. Ltd. 22-electrode cochlear prosthesis which codes an estimate of the first formant frequency in addition to the amplitude. voice pitch and second formant frequencies. Two groups of cochlear implant patients were tested 3 months after implant surgery, one group (n= 13) having used the old (F0F2) processing strategy and the other (n=9) having used the new (F0FIF2) strategy. All patients underwent similar postoperative training programs. Results indicated significantly improved speech recognition for the F0FIF2 group particularly on open set tests with audition alone. Additional testing with a smaller group of patients was carried out with competing noise (speech babble). Results for a closed set spondee test showed that patient performance was significantly degraded at a signal-to-noise ratio of 10 dB when using the F0F2 strategy, but was not significantly affected with the F0FIF2 strategy.
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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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ItemSpeech recognition performance with a two-formant coding strategy for a multi-channel cochlear prosthesis [Abstract]( 1986)Over the last two years, a new speech coding strategy (F0F1F2) has been developed for the Nucleus multi-channel cochlear prosthesis designed to provide information about the first formant, in addition to the second formant and voicing frequency information provided by the “standard” speech processing strategy (F0F2). This strategy uses quasi-simultaneous stimulation of two electrode pairs within the cochlea at the voice pitch rate. The positions of the two sites of stimulation vary independently according to the frequencies of the first and second formants. The amplitude at each site is determined from the first and second formant amplitudes. Seven patients were changed to this strategy and an initial study showed significant improvements in recognition of open set sentence material (from a mean of 30.4% for F0F2 to 62.9% for F0F1F2) and for speech tracking without lipreading (from 11.8 wpm to 30.5 wpm). Phoneme recognition investigations indicated that: 1) vowel identification was improved due to the addition of first formant frequency information in the new strategy, 2) consonant identification was also improved, due to the extra information provided by the independent variation of the amplitude components. These encouraging results led to the use of the F0F1F2 strategy for all new patients from April 1985. Results for recorded speech testing (MAC battery) three months after surgery have been compared for 13 patients who used the F0F1F2 strategy. Significant improvements were observed for the F0F1F2 group on most of the tests. Mean scores for open set testing were as follows: a) spondee recognition: 13.6% for F0F2 and 26.0% for F0F1F2, b) CID sentences: 15.9% for F0F2 and 37.8% for F0F1F2, c) monosyllabic words: 4.9% for F0F2 and 12.4% for F0F1F2, d) phoneme recognition: 23.1% for F0F2 and 33.4% for F0F1F2.