Graeme Clark Collection
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ItemThe spectral maxima sound processor: recent findings in speech perception and psychophysics(Wien, 1994)The Spectral Maxima Sound Processor (SMSP) was developed at the University of Melbourne for use with the Mini System 22 implant manufactured by Cochlear Pty Ltd. The SMSP has been shown in recent studies to provide improved speech perception to implantees when compared to the currently commercially available processor for this implant (the MSP (MULTIPEAK) processor). In the first of three experiments, the effect on speech perception of increasing the rate of stimulation of the SMSP and of increasing the number of electrodes activated in each stimulation cycle was studied. It was found that these parameter changes made little difference to speech perception in quiet but both changes were advantageous for some subjects when listening in noise. The second and third experiments investigated psychophysically the effects of two aspects of the SMSP strategy which differ from previous processors for this implant. In the second experiment, it was found that concurrent stimulation of two adjacent or nearby electrodes evoked a pitch which was intermediate to that of either electrode. This may explain, in part, the better discrimination of vowel formants by users of the SMSP. In the third experiment, it was found that a pitch related to the modulation frequency was evoked by amplitude-modulating a constant rate stimulus, provided that the rate of stimulation was sufficiently high (four times the modulation frequency) or a multiple of the modulation frequency. This result may explain the equal ability of SMSP and MSP users to perceive speaker differences and intonation patterns, even though the rate of stimulation is constant In the SMSP.
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ItemHabilitation issues in the management of children using the cochlear multiple-channel cochlear prosthesis(Wien, 1994)Since 1985, a significant proportion of patients seen in the Melbourne cochlear implant clinic have been children. The children represent a diverse population, with both congenital and acquired hearing-impairments, a wide-range of hearing levels pre-implant, and an age range from 2 years to 18 years. The habilitation programme developed for the overall group must be flexible enough to be tailored to the individual needs of each child, and to adapt to the changing needs of children as they progress. Long-term data shows that children are continuing to show improvements after 5-7 years of device use, particularly in their perception of open-set words and sentences. Habilitation programs must therefore be geared to the long-term needs of children and their families. Both speech perception and speech production need to be addressed in the specific content of the habilitation program for any individual child. In addition, for young children, the benefits of improved speech perception should have an impact on development of speech and language, and the focus of the programme for this age child will reflect this difference in emphasis. Specific materials and approaches will vary for very young children, school-age and teenage children. In addition, educational setting will have a bearing on the integration of listening and device use into the classroom environment.
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ItemCochlear implants: historical perspectives(Whurr, 1995)These historical perspectives are seen from a personal point of view, and date back to the author's first involvement with cochlear implant research at the beginning of 1967. The perspectives are aimed at presenting the questions asked, the difficulties faced and the solutions achieved in the development of our multichannel cochlear prosthesis. Work in other centres is discussed when relevant, to set our research in context. Space does not permit a detailed presentation of our research or the contributions of others. It is hoped, however, that by presenting personal perspectives on the cut and thrust of human endeavour, and its interface with technology, a contribution will be made to the overall goal of understanding the origins of cochlear implants.
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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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ItemComparison of current speech coding strategies( 1993)This paper reports on two studies carried out at the University of Melbourne jointly with Cochlear Pty Ltd. The studies demonstrated substantial speech perception improvements over the current Multipeak strategy in background noise.
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ItemPreliminary speech perception results for children with the 22-electrode Melbourne/ cochlear hearing prosthesis( 1993)The 22-electroce cochlear prosthesis developed by the University of Melbourne and Cochlear Pty. Ltd. has been shown to provide significant speech perception benefits to profoundly deafened adults. More recently, use of an improved Multipeak encoding strategy has significantly improved speech perception performance both in quiet and in noise. Benefits to speech perception in children have not as yet been fully documented, in part due to the shorter history of implant use in children and the smaller overall number of children implanted as compared with adults. The first implantation of the 22-electrode cochlear prosthesis in a child was carried out in Melbourne in January of 1985. In Melbourne, a 5-year-old child was operated on in April 1986, and a first congenitally deaf child in April 1987. The age of implantation has been progressively reduced, with the first 2-year-old child implanted in Melbourne in 1990. As at January 1992, approximately 1,200 children (under 18 years of age inclusive) have been implanted worldwide with the 22-electrode cochlear prosthesis. Of this number, approximately 50% are under the age of 6 years. The age of the child, aetiology of the hearing loss, age at onset and duration of the hearing loss, education program attended both prior to and subsequent to implantation, and parental motivation to assist in habilitation are all factors which may affect an individual child's development and progress with the device. Evaluation of performance in children is complicated by a number of issues, including the effects of delayed speech and language development, and the ability of individual children to perform auditory tests. The measure of performance chosen for any evaluation will also reflect the interests of the particular clinician. For example, effects of device use on speech production may be of interest to the speech therapist, whereas educational progress will be of primary importance to the teacher of an implanted child. However, in choosing an appropriate evaluation test to measure progress woth the cochlear prosthesis, it is vital to realize that all measures such as effects of device use on speech production, educational progress, development of language, and effects on social and communication skills depend on the child being able to accurately perceive speech information through her/his device.
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ItemTemporal and spatial coding in auditory prostheses(Wiley-Liss, 1990)By direct electrical stimulation of residual auditory nerve fibres, auditory prostheses by-pass the normal electro-mechanical transduction properties of the cochlea in patients who have few -if any -surviving inner or outer hair cells. These devices interface directly with the auditory nerve via stimulating electrodes placed within the scala tympani of the cochlea. While the great majority of profoundly-totally deaf patients using multiple-channel auditory prostheses receive considerable benefit from their device (Brown et al., 1987), a greater understanding of the basic response properties of the auditory nerve to electrical stimulation should result in the development of improved electrical stimulation regimes and electrode array designs. It is the purpose of this chapter to review these basic neural response properties.
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ItemPsychophysical and speech perceptual studies on cochlear implant patients(Springer-Verlag, 1990)One of the most important findings in cochlear implant research has been the orderly variation in perceptual characteristics produced by intracochlear electrodes in accordance with the tonotopic organization of the cochlea. The electrical signal dimension of electrode position has therefore been used extensively for presenting speech information to cochlear implant patients. This paper describes further psychophysical and speech perceptual results on the perceptual characteristics produced by intracochlear electrodes.
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ItemSpeech tracking: verfahrensweise und ergebnisse(Springer-Verlag, 1987)Das Speech Tracking wurde im Jahre 1978 von De Filippo und Scott als Schulungs-und Untersuchungsverfahren fur Einzelpersonen eingefuhrt, die weitgehend oder vollstandig ertaubt waren. Bei diesem Verfahren werden dem Patienten Textpassagen von zwei bis zehn Wortern vorgelesen. Der Zuhorende, in diesem Fall der Cochlear Implant-Trager, versucht die betroffene Passage wortlich zu wiederholen. Versteht der Patient eines der Worter nicht, so wendet der Vorleser Verfahren an, die dem Zuhorenden weitere Informationen uber den Inhalt vermitteln. Nachdem jedes Wort korrekt wiederholt worden ist, wird eine weitere Passage vorgelesen, bis ein Prufungszeitraum von 10 Minuten abgeschlossen ist (Martin et al. 1981, 1985; Chouard et al. 1983; Tong et al. 1980; Mecklenburg et al. 1984; Rosen et al. 1980).
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ItemThe engineering of future cochlear implants(Croom Helm, 1985)Speech is a complex acoustic signal, and information is transmitted to the brain at a rapid rate. For example during a conversation ten phonemes are uttered per second. Furthermore, these complex speech sounds are coded into patterns of neural discharges that enable the subject to understand speech. In order, therefore, to bring speech signals directly to residual auditory nerve fibres, considerable processing of the speech signal is required before the central nervous system will recognise and comprehend it. The magnitude of the task can be further appreciated when one considers that there are an average of 31,400 nerve fibres in the human auditory nerve and a large proportion of these convey information to the brain about the speech frequencies. Research studies are showing, however, that the perception of ongoing speech with cochlear implants may be achieved 'With speech processing strategies which can be achieved by current electronic technology.