Graeme Clark Collection
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ItemBiophysical design considerations of the cochlear prosthesis [Abstract]( 1980)In order for the cochlear prosthesis to transfer sufficient information to primary auditory nerve fibres for recognition of speech-like sounds, it is necessary to electrically excite discrete fibre populations at several points along the cochlear spiral (Tong et al., 1979). In addition, because of the large number of stimulus electrodes and the small volume of the scala tympani in which the electrodes are usually implanted, current transfer must derive from "passive" electrochemical processes in order to preserve the normal biochemical environment of the nerve fibres. From measurements made in the human cochlea during implantation of the cochlear prosthesis, it has been shown that the longitudinal ground current distribution arising from a multielectrode system incorporating a common intracochlear ground electrode is accurately replicated by measurements made in a saline-filled uniform tube of diameter 3-5 rom. Further measurements in such tubes are described which investigate the possibility of improved current localisation by reduction of the ground electrode impedance and the possibility of producing greater electrochemical "passivity" by the use of voltage sourcing in preference to current sourcing.
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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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ItemResults of a preliminary clinical trial on a multiple channel cochlear prosthesis( 1985)Speech discrimination testing was carried out under clinical trial conditions for eight profoundly postlingually deaf adults to assess the efficacy of a newly developed 22-channel cochlear prosthesis and speech processor. Three months postoperatively, these patients showed significantly better results with the cochlear prosthesis than for preoperative testing with a conventional hearing aid or vibrotactile aid (following a 6-month trial with the aid) on each of a series of tests from the Minimal Auditory Capabilities battery. Assessment of lipreading enhancement using standard speech tests, consonant recognition studies, and speech tracking showed significant improvements for each patient when using the cochlear prosthesis. Six patients showed a significant amount of open set speech discrimination without lipreading at levels which have not been reported for single electrode cochlear prostheses. The two patients who performed poorly on these tests both had restricted multiple channel systems due to their disease, one patient being restricted to virtually a single channel system and the other to only ten of the 22 electrodes. These results indicate that this multiple channel cochlear prosthesis has potential as a treatment for profound postlingual deafness over a wide range of etiologies and ages.
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ItemClinical results using a multiple-channel cochlear prosthesis( 1984)A total of eight profoundly deaf patients have been implanted with the Nucleus Limited multiple-channel cochlear prosthesis at the University of Melbourne since it became available in late 1982. All patients are everyday users of the device. Speech testing using the device alone has shown consistently high scores for a variety of closed set tests and significant levels of open set speech understanding in most of the patients. Lipreading assessment with phoneme, word, sentence and speech tracking material shows significant improvement when using the prosthesis for all patients tested. Other benefits reported are recognition of environmental sounds, decrease in tinnitus. increased confidence in social and vocational situations and improved voice control. One patient is able to cope with interactive conversations over the telephone and three others are able to use the telephone in a limited way without special codes.
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ItemA multi-channel hearing prosthesis for profound-to-total hearing loss( 1984)A multi-channel cochlear implant hearing prosthesis providing 22 separate channels of stimulation has been developed. The electronics for the implantable receiver-stimulator have been incorporated on a single chip, using digital circuits and employing CMOS technology. The chip is enclosed in a titanium capsule with platinum/ceramic electrode feed-throughs. A pocket-sized speech processor and directional microphone extract the following speech parameters: signal amplitude, fundamental frequency and formant frequency. The fundamental frequency is coded as electric pulse rate, and formant frequency by electrode position. The speech processor has been realized using hybrid circuits and CMOS gate arrays. The multi-channel prosthesis has undergone a clinical trial on four postlingually deaf patients with profound-total hearing losses. The speech perception results indicate that they were able to obtain open-set speech recognition scores for phonetically balanced words, CID sentences and spondees. In all cases the tests showed significant improvements when using the cochlear prosthesis combined with lipreading compared to lipreading alone.
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ItemA multi-channel cochlear prosthesis for profound-to-total hearing loss( 1984)A multi-channel cochlear prosthesis for profound-total hearing loss has been developed by the University of Melbourne and Nucleus Limited. Clinical trials have shown that the prosthesis provides significant help for postlingually deaf adult patients (lost hearing after normal language patterns have been established). The prosthesis helps the patients understand running speech when combined with lipreading, and a proportion obtain significant open-set speech scores for electrical stimulation alone. The patients with these open-set score can use the device in situations where lipreading is not possible, for example, to converse over the telephone. The prosthesis consists of an externally worn, pocket-sized speech-processor, a headset and an implanted receiver/stimulator and electrode array. The headset contains an .ear-level directional microphone that picks up the speech signal. The speech processor encodes the speech as a series of electrical pulses on the electrode array. The data describing these pulses and the power required to produce them, are sent to the receiver/stimulator from .a radio-frequency coil mounted on the headset. The receiver/stimulator decodes the data and delivers the speech signal as a series of biphasic electrical pulses to the 22 electrodes which have been gently passed along the scala tympani during implantation.
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ItemCochlear implant round window sealing procedures in the cat: an investigation of autograft and heterograft materials( 1984)In this series of experiments it was shown that a round window seal produced with a muscle autograft or a Teflon felt disc glued to the electrode prevented a Staphylococcus aureus infection in the bulla extending to the cochlea. The seal following a fascial autograft also prevented β-haemolytic streptococci type A spreading to the basal turn of the cochlea. On the other hand Dacron® velour is contra-indicated as it was associated with a strong inflammatory response and a high incidence of infection. The studies also indicated that infection can extend to the cochlea before the round window membrane has healed. The junctional area between the graft and the margin of the round window niche is a potentially vulnerable site.
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ItemClinical trial of a multi-channel cochlear prosthesis: results on 10 postlingually deaf patients( 1984)The clinical trial of a multi-channel cochlear prosthesis has been carried out on 10 profoundly-totally deaf adult patients. Speech perception tests have shown that all the patients received significant benefit from the device. They obtained improvements in understanding running speech from 47% to 550% when using the device in conjunction with lipreading compared to lipreading alone. With an open-set CID sentence test, three patients obtained scores showing an ability to understand speech without the need to lipread, and a further three patients had scores indicating they could also receive useful information without lipreading. In two patients, very limited open-set scores for electrical stimulation alone were obtained. This was most probably due to the fact that only a few channels of stimulation were possible due to cochlear disease and they were therefore receiving information more like a single-channel device. The prosthesis has also been found to provide considerable help in hearing and recognizing everyday sounds.
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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.