Graeme Clark Collection
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ItemSpeech processor design for a multiple-channel cochlear implant( 1980)This paper outlines the strategy adopted for a laboratory-based speech processor used to provide speech information to patients with a multiple-channel cochlear implant It also presents the results of vowel and consonant recognition studies and speech test using open sets of words and sentences.
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ItemA "Combionic Aid": Combined speech processing for a cochlear implant in one ear and speech processing hearing aid in the other ear [Abstract]( 1993)Independent use of a cochlear implant in one ear and a hearing aid in the other is not acceptable for many implant users with some residual hearing. Psychophysical evidence suggests that there are substantial interactions between acoustic and electrical signals including masking and loudness summation. These effects may contribute to the difficulty in using two independent devices and it is desirable to control the parameters of the electrical and acoustical signals far more accurately than is possible with two independent devices with separate microphones. In order to achieve this control we have developed a Combionic aid incorporating an implant and an 'in1planlcompatible' hearing aid controlled from the same speech processor. The new processor is particularly flexible and can implement a wide variety of speech processing strategies for combined acoustic and electrical stimulation. A benchtop prototype has been tested with five patients using a range of different speech tests. In general, patients do better when they use acoustic and electrical information simultaneously than they do with either alone. Some patients on some tests perform significantly better with the bimodal aid than they do with independent hearing aids and implant processors worn together. Wearable devices have now been built and evaluations of these devices are continuing.
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ItemPsychophysical matching of sensations produced by acoustic and electrical stimulation of the auditory nerve [Abstract](Monash University Press, 1983)The aim of this study was to establish an acoustic model of a multiple-channel cochlear implant that could be used in the development of speech coding strategies. Identical psychophysical tests were carried out with electrical stimuli for two cochlear implant patients and with acoustic stimuli for three normally hearing listeners. Each electrical stimulus was a train of biphasic pulses at a constant rate between 50 and 100 pps directed to one of the 10 electrodes spaced at 1.5mm intervals around the basal turn of the cochlea (Clark et al. 1977). The corresponding acoustic stimulus was a train of noise bursts at a rate equal to the electrical pulse rate. The noise bursts were passed through one of 8 bandpass filters with centre frequencies equally spaced on a logarithmic scale from 1140 to 10880 Hz representing 8 different electrodes.
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Item"Cochlear View" and its application in cochlear implant patients [Abstract]( 1994)Recent advances in multichannel intracochlear implantation have generated interests in correlating individual stimulating electrodes to pitch perception. An appropriate radiographic technique is required to precisely document the location of the implanted intracochlear electrode array. Anatomical studies, including the measurements of the temporal bone using high-resolution CT films and 3D reconstruction from the petrous bone sections, were conducted to define the spatial position of cochlea in the skull. Thus, a "Cochlear View" was designed and introduced for postoperative radiological evaluation of multichannel intracochlear implantation. In this paper, a detailed radiographic method and radiological interpretation of the "Cochlear View" are described. A plain radiograph of the "Cochlear View" was taken of 120 patients who had received the Nucleus multichannel implant. Studies have shown that a plain radiograph of the "Cochlear View" provides sufficient information to correctly evaluate the results of implantation, including the insertion depth and position of individual electrodes. It plays an important role in guiding the management of frequency mapping and acts as a useful reference for further research purposes.
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ItemSpeech perception benefits for children using an advanced cochlear implant speech processing strategy in quiet and in noise [Abstract]( 1994)A new speech processing strategy (SPEAK) has been developed by the University of Melbourne and Cochlear Pty Ltd for use with the Nucleus 22-channel electrode array. In this strategy, 20 programmable filters are repetitively scanned at an average rate of 250Hz and the largest spectral components or maxima are selected from the incoming speech signal. This new speech processing strategy has been shown to provide significantly improved benefits in adult implant patients, particularly in the presence of background noise. This report presents data of a preliminary paediatric clinical trial of the new SPEAK speech processing strategy.
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ItemExpandable leadwires for a paediatric cochlear implant [Abstract]( 1993)Anatomic studies of skull growth have shown an increase (about 20 mm) in the distance between the round window and the asterion where the receiver-stimulator is usually located. In order to accommodate the skull growth of young patients, an expandable leadwire connecting the receiver-stimulator and the electrode array is necessary. Several expandable leadwires were evaluated in experimental animals, including helical leadwires protected by Silastic tubes and leadwires, with "V" or "W"-shaped levels in a single phase, and protected by thin Silastic or Teflon bags. The leadwires together with their controls were implanted on young animal's scapulae, temporal and parietal bones and in subcutaneous tissue. The in vivo expansion of the leadwire was monitored by periodic x-ray examination and the force to expand the leadwire was measured at the completion of implantation. The results showed that helical leadwires weresurrounded by fibrous tissue and a large force was required to expand them. The V or W-shaped leadwires were able to expand up to 20 mm in vivo and only a moderate force was required to expand them. For most of the cases, there was none or little fibrous tissue in Silastic or Teflon bags. The results indicated that for a paediatric cochlear implant, leadwires with V or W-shaped levels could, expand and biocompatible envelopes could effectively protect the leadwires from being bound by fibrous tissue.
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ItemPaediatric cochlear implant surgery [Abstract]( 1992)The operation in children is similar to that in adults, but special care needs to be taken with the skin flap, the anchoring of the electrode array and the sealing of .the cochleostomy. Research into the effects of head growth and otitis media in an implanted ear indicates that these should not be a problem. Surgical complications are also similar to those in adults, with the most common being related to the skin flap. The major complication rate at 4 % is slightly less than that in adults and most of these get effective implant function.
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ItemPaediatric cochlear implantation: radiological and histopathological studies of skull growth in the monkey( 1993)The human skull undergoes significant growth within the first two years of life (Dahm et aI, 1992). Therefore, before children under two can be considered candidates for cochlear implantation, the effects of the surgical procedure on subsequent skull growth must be well understood. To evaluate the effects of implantation on skull growth four macaque monkeys were implanted with dummy cochlear implants at six months of age. To model the procedure in the very young child, the bed for the receiver-stimulator was drilled across a calvarial suture down to the underlying dura and an electrode array inserted into the scala tympani via a mastoidectomy and posterior,tympanotomy. Plain skull radiographs were perioqical1y taken to monitor skull growth for periods of up to three years following implantation. Their longitudinal measurements revealed no evidence of asymmetrical skull growth when compared with unimplanted control animals. Computer tomographic scans taken at post-mortem confirmed these findings. Finally, subsequent histopathological evaluation of the receiver-stimulator package bed indicated that it becomes obliterated by hard tissue, resulting in a localized flattening of the vault under the receiver-stimulator. However, this tissue exhibited histological evidence of sutures, indicating that the surgical procedure should not lead to premature sutural closure. In conclusion, the present experimental results suggest that long-term cochlear implantation in very young children will not lead to any significant skull deformity.
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ItemThe development of auditory comprehension in children after receiving a cochlear multiple-channel implant( 1992)Since late 1989, half the cochlear implant patients at the Royal Victorian Eye and Ear Hospital have been young children. There is a gradual improvement of auditory comprehension in most cases using the criteria of environmental sound detection, as well as, prosody, high frequency phoneme and word discrimination. The rate of improvement and final result depend on the duration of deafness, presence of residual hearing, and quality of auditory-oral habilitation. Younger children usually progress more quickly than older children. Some adolescents who use Total Communication and who have no residual hearing, achieve assistance with lipreading. Children with Usher's Syndrome should be actively encouraged to participate in auditory-oral habilitation should they become totally deaf or blind.
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ItemThe effect of inflammation on blood vessel area as a cause of variation in ganglion cell density measurements in the cat cochlea [Abstract]( 1992)The success of a cochlear implant depends on an adequate number of surviving spiral ganglion cells. Further loss of ganglion cells may arise from the biology of cochlear implantation itself. The quantitative analysis of ganglion cells is, therefore, an important consideration when assessing the biological safety of a cochlear implant.