Graeme Clark Collection
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ItemThe development of a tympanic membrane sensor for a totally implantable cochlear implant or hearing aid(Monduzzi Editore, 1997)We present the design and development of a tympanic membrane sensor for a totally implantable cochlear implant or hearing aid system. The sensor employs a fiber-optic lever which is hermetically sealed in a biocompatible cartridge and implanted in the middle ear cavity. The sensor prototype has been designed, constructed and tested in cats. In addition, the implantation procedure of the device has also been studied using human temporal bones.
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ItemPreliminary results on spectral shape perception and discrimination of musical sounds by normal hearing subjects and cochlear implantees( 1997)This paper presents an overview of an ongoing research project investigating the perception of musical timbre by people with normal hearing, impaired hearing, and cochlear implants. The investigation of musical timbre has been limited to the perception of steady-state frequency spectra from 10 different sources, including sampled acoustic instruments, sung vowels, and synthetic waveforms. Subjects were tested in three different tasks: I) the discrimination of spectra when presented in all possible pairs; 2) the measurement of the internally-perceived frequency spectra using a forward-masking paradigm; and 3) the identification of the spectra by name with the restricted set of sound sources from which they were sampled. Preliminary results from the normally hearing subjects show the spectra to be 99.8% distinguishable, and that significant detail is evident in the internal spectral envelopes from different sounds. There was around 50%-correct identification of stimuli by name with the original sound sources from which they were sampled. The experimental work with hearing impaired and cochlear implant subjects has commenced.
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ItemPeri-modiolar electrode arrays: a comparison of electrode position n the human temporal bone(Monduzzi Editore, 1997)This paper describes a radiologic evaluation of three types of peri-modiolar arrays, comparing their trajectory within the scala tympani with a standard Mini-22 electrode. All peri-modiolar arrays were found to lie closer to the modiolus for much of their insertion length compared with the standard array. While one design showed evidence for the potential of increased insertion trauma, two designs produced satisfactory results. Although further electrode development, temporal bone and histopathologic studies arE required, it would appear that the benefits of peri-modiolar electrode arrays will be realised clinically.
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ItemEvoked potential assessment of children with severe/profound hearing loss: a comparison of steady-state evoked potential (SSEP) and behavioural hearing threshold levels in subjects with absent click evoked auditory brainstem responses (ABR)(Monduzzi Editore, 1997)Steady-state evoked potential testing offers a means of obtaining accurate, frequency specific estimates of hearing threshold in subjects with even severe to total hearing losses. As such, the technique can play an important role in the preoperative evaluation of young cochlear implant candidates.
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ItemSiting the receiver-stimulator of the CI-24M model of the Cochlear Limited multiple-channel cochlear implant and fixation of its electrode array(Monduzzi Editore, 1997)The correct siting of the cochlear implant receiver-stimulator package is important. The package should not obtrude significantly above the surface of bone, and should be so that blows to the head do not in damage to the package, skull or brain. The cochlear implant electrode array must be fixed at a site close to the cochlea, so that the electrode will not slide out, or be subject to differential movement with growth changes. Fixation, with Dacron® mesh, platinum-iridium ties, or clips, has been in the region of the posterior root of the zygoma and the floor of the antrum. Our research studies demonstrate that a specially-designed collar around the array can be placed through the cochleostomy and provide the necessary locking to prevent retraction of the array. It has a ceramic surround to encourage union with neighbouring bone, and stress relief to reduce wire fracture at the point where the array leaves the cochlea.
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ItemDevelopment of silicon microelectrodes for cochlear implant technology(Piscataway, 1997)Silicon fabrication technology is being explored as a possible solution to the manufacturing of advanced cochlear implant electrode arrays. Silicon probes have been produced with thickness of 5?m and coated in Parylene� polymer to provide strength. To enable handling they are given a backing of silicone rubber before surgical use. This paper presents some techniques used to produce such silicon microelectrodes.
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ItemThe effect of pulsatile intracochlear electrical stimulation on intracellularly recorded cochlear nucleus neurons(Monduzzi Editore, 1997)The anterior division of the ventral cochlear nucleus (AVCN) is the first relay station of the auditory pathway. We examined responses of neurons in the A VCN to intracochlear electrical stimulation using in vivo intracellular recordings. Twin pulse stimulation results indicated that these neurones evoke action potentials which are able to follow pulsatile stimulation at high rates. This ability to respond to each pulse along the stimulus train diminished when stimulus duration was increased to 50 ms. At rates 400 Hz and below in all neurones tested a deterministic response was seen to this longer duration pulsatile stimulation. With increasing rate of stimulation the response become more stochastic with apparent loss of encoding ability. These results have in1pIications in the clinical application of cochlear implants operating at high stimulus rates.
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ItemThe relationship between aetiology of hearing loss and outcome following cochlear implantation in a paediatric population(Monduzzi Editore, 1997)Eighty-eight children who underwent cochlear implantation at the University of Melbourne Cochlear Implant Clinic are reviewed. The aetiology of the hearing loss is classified and is compared to their best level of speech perception performance. The group whose hearing loss was not congenital in origin performed better than those who were congenital in origin. Of those whose hearing loss was congenital in nature those with rubella appeared to perform best.
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ItemThe interactions between the cytokine LIF and the neurotrophins on spiral ganglion cells(Monduzzi Editore, 1997)The survival of auditory neurones depends on the continued supply of trophic factors. Early post-natal spiral ganglion cells (SGC) in a dissociated cell culture were used as a model of auditory innervation to test the trophic factors leukaemia inhibitory factor (LIF) and neurotrophin-3 (NT-3) for their ability, individually or in combination, to promote neuronal survival.
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ItemThe histological and physiological effects of the auditory brainstem prosthesis of the auditory pathway(Monduzzi Editore, 1997)To rehabilitate profoundly deaf patients who cannot benefit from the cochlear implant due to bilateral interruption of the auditory nerve, particularly from neurofibromatosis II, the histological and physiological effects of an auditory brainstem prosthesis on the cochlear nuclei of guinea pigs were examined in order to establish the safety and the efficacy of this prosthesis.
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