Graeme Clark Collection
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ItemPlace coding of vowel formants for cochlear implant patients( 1990)Abstract not available due to copyright.
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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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ItemSpeech recognition for 40 patients receiving multichannel cochlear implants( 1986)We collected data on 40 patients who received the Nucleus multichannel cochlear implant. Results were reviewed to determine if the coding strategy is effective in transmitting the intended speech features and to assess patient benefit in terms of communication skills. All patients demonstrated significant improvement over preoperative results with a hearing aid for both lipreading enhancement and speech recognition without lipreading. Of the patients, 50% demonstrated ability to understand connected discourse with auditory input only. For the 23 patients who were tested 12 months postoperatively, there was substantial improvement in open-set speech recognition.
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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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ItemElectrical stimulation of the auditory nerve: the influence of electrode position on neural excitation(Kugler & Ghendini, 1990)Improved speech recognition among cochlear implant patients would appear to be dependent on a number of factors including improved speech processing strategies and an improvement in the effectiveness of electrically stimulating residual auditory nerve fibers (i.e. lower thresholds, wider dynamic ranges and more localized current spread). Previous human temporal bone studies have shown that free fit scala tympani electrode arrays generally lay along the outer wall of the scala tympani. Therefore, there is a relatively large distance between the electrode array and the residual neural elements within Rosenthal's canal. In the present study, we systematically varied the location of the electrode within the scala tympani to examine the influence of electrode position on neural excitation.
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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