Graeme Clark Collection
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ItemSpeech perception, production and language results in a group of children using the 22-electrode cochlear implant( 1989)Paper presented at the 118th Meeting of the Acoustical Society of America
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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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ItemMultichannel cochlear implantation in Usher's Syndrome(Kelleher & Associates, 1990)Four patients with Usher's syndrome have been implanted with the multichannel cochlear prosthesis developed by the University of Melbourne and Cochlear Pty. Ltd. All four patients have made good progress with the implant and use the device during most waking hours. One subject, an adult who developed speech and language before developing profound deafness, has learned to use the cochlear implant for auditory alone communication. Her results on speech perception testing compare favourably with other implanted adults. The other subjects were adolescents or young adults when implanted and had congenital profound or total hearing losses. These subjects retained adequate vision for lipreading but had lost hearing before the development of speech and language. Results for these subjects have indicated that the cochlear implant significantly aids lipreading and improves the detection and recognition of environmental sounds. However, they have not, as yet, been able to use the device for communication in the auditory alone condition. The ability to use the device in this condition would become important should vision deteriorate further. These preliminary results suggest that for patients with Usher's syndrome where deafness is progressive and speech and language have developed normally, the multichannel cochlear implant can provide an alternative auditory communication system when vision is no longer functional. When Usher's syndrome has caused a congenital profound deafness, it maybe necessary for the cochlear implant to be integrated into the child's normal speech and language development from an early age to obtain optimal results.
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ItemResults of multiple-electrode cochlear implants in children( 1987)Children in Australia and United States of America are now being implanted with the Nucleus 22 electrode intracochlear prosthesis utilizing the F0/F1F2 coding strategy. A total of 32 adolescents (10-17 years) and 24 preadolescents (2-9 years) have been implanted as of 31 August, 1987. No significant postoperative complications were recorded, the speech processors were successfully programmed, and all are users of the device. For the 56 children, the average length of postoperative stimulation time is 2.8 months. Because the majority of children have such short experience with the device we report herein two children from the University of Melbourne (A) and two children from the United States (U) who have been using the Nucleus system for 12 months or more. Child 1A has only 10 electrodes in the cochlea; therefore, the number of channels programmed for the children is 10, 17, 18 and 18, respectively. Child Al and A2 were deafened by meningitis at 3-3 and 3 years of age, respectively. Child U3 became profoundly deafened from a progressive sensorineural loss at age 11 and Child U4 was deafened by recurrent cochlear hydrops at age 13 years.
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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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ItemRehabilitation for multiple-channel cochlear prosthesis patients(Raven Press, 1985)The postoperative program for multiple-channel cochlear prosthesis patients can be divided into four main areas: 1) Psychophysical evaluation is carried out to optimize the patient's speech processor for their individual needs, Measurements required include threshold, dynamic range and pitch ranking for each of the implanted electrodes. 2) Counselling is very important to ensure patients are able to effectively operate their speech processor and that they are aware of factors in the environment which may affect performance (e.g., noise). 3) Auditory training and training in conjunction with lipreading for tasks grading from simple (e.g., discrimination of word length) to more difficult (e.g. consonant discrimination) is of benefit in making patients aware of their capabilities with the prosthesis and helping them to improve communication skills. However, highly specific training (e.g., closed set vocabulary) does not seem to be of general benefit to patients. Speech tracking provides a training procedure relevant to normal communication but has some limitations due to the degree of familiarity reached with a particular speaker. 4) Assessment of patients is carried out at this stage in great detail as it is necessary to collect data about the effectiveness of cochlear implants and also to provide information about possible improvements to speech processing strategies and external hardware. The amount of assessment required will decline as the procedure becomes established, but some investigation will continue to be necessary.
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ItemPsychophysics of multiple-channel stimulation(Raven Press, 1985)Eight patients implanted with multiple-channel cochlear prostheses have displayed good discrimination of sound sensations elicited at different sites within the cochlea. All patients rank the sensations from "sharp" to "dull" in an order which corresponds with basal to apical position in the cochlea. Detailed psychophysical studies have been carried out on two patients. These showed that discrimination of rate of (pulsatile) stimulation is good for frequencies up to 300 Hz and falls off sharply for frequencies above this. Electrode transitions (changes in position along the cochlea) are well discriminated for fast changes (25 msec), whereas rate transitions are not well discriminated for changes faster than 100 msec. From these results a speech processing strategy was formulated where second formant information is mapped to position in the cochlea and fundamental frequency mapped to rate of stimulation. Vowel and consonant confusion studies show consistent results for all patients using this processing strategy. A study involving two electrode stimuli demonstrated the possibility of presenting first formant information in addition to the second formant and fundamental frequency.