Graeme Clark Collection
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ItemAssessment of intracochlear ossification by three-dimensional reconstruction of computerised scans( 1995)The aim of the study was to investigate whether the three-dimensional (3-D) images from computed tomography (CT) scans of the ears could adequately define the site and extent of new bone in the cochlea, and how these images compared with those created by magnetic resonance imaging (MRI). The patients whose investigations were used in the study were being assessed for a cochlear implant and were selected on the basis of their history and the appearance of their two-dimensional (2-D) CT scans. Four patients had progressive mixed deafness, a family history of deafness, and stapedectomies. They were considered to be deaf from otosclerosis and needed further assessment because their scans showed either obstructed cochleas from new bone, or demineralized otic capsules to the point that we could not determine whether new bone was present or not. The fifth patient was being assessed within 3 months of suffering deafness from meningitis. In one ear he had extensive ossification, and in the other the degree of opacification shown in axial and coronal cuts of the basal turn was inconsistent. Essentially the problem is that at the magnification used in examination of the inner ear, the resolution of 2-D CT scans gives indistinct borders between bone and water. Magnetic resonance imaging has commonly been used in these cases. The study showed that it is now possible to confirm whether or not there is new bone and to demonstrate the site and extent of new bone with both 3-D and MRI images. It is not possible to give a degree of sensitivity and specificity for this observation because of the small group of subjects in the study. It should be worth applying the reconstruction software to scans from helical scanners with a view to assessing whether the resolution of the 3-D images can be improved further.
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ItemExperimental animal model of intracochlear ossification in relation to cochlear implantation( 1995)Histopathologic examinations of the temporal bones of implanted human patients and experimental animals have demonstrated various degrees of abnormal fibrous tissue or new bone formation within the cochlea; in some cases, extensive new bone formation was reported. The presence of new bone following cochlear implantation is undesirable, since it may adversely affect current distributions in the electrically stimulated cochlea. The pathogenesis of intracochlear osteoneogenesis as a direct result of cochlear implantation is unclear. The aim of this study is to use an experimental animal model to investigate some of the factors underlying the formation of new bone and fibrous tissue within the implanted cochlea, especially the role of insertion trauma and bone chips, and also a possible way of inhibiting such a process using an anticalcific agent of the diphosphonate family, disodium ethane-1-hydroxy-1, 1-diphosphonate(EHDP). The local release of EHDP from a polydimethylsiloxane (Silastic silicone rubber, Dow Corning Corp) controlled delivery system has been shown effective in the context of bioprosthetic heart valve. Its application within the cochlea has not been documented, to our knowledge.
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ItemImplant designs for future coding strategies( 1995)This paper briefly describes the history of speech processing developments leading to the presently available Speak processing strategy. The similarities and differences of the Speak and Continuous Interleaved Sampling (CIS) strategies are then discussed and some recent key experimental observations are examined as a guide to potential future coding strategies. Key issues for future coding strategies and implant designs are the number of electrodes and stimulation rates in use. Consideration of these issues has led to development of a prototype implant to be used for advanced speech-processing research.
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ItemDischarge rate-level functions from dorsal cochlear nucleus single units in response to acoustic and electrical stimulation of the auditory nerve( 1995)Discharge rate-level (I/O) functions possessed by dorsal cochlear nucleus (DCN) units were examined, in response to bipolar electrical stimulation of the cochlea of the barbiturate-anesthetized cat. Spontaneously active units usually possessed nonmonotonic functions with a minimum, and spontaneously inactive units usually possessed monotonic functions or nonmonotonic functions with a maximum (NM+). In response to acoustic high-pass filtered noise, the function relating discharge rate and cut off frequency resembled the same unit's I/O function to electrical stimulation. The I/O functions to acoustic characteristic tones were usually monotonic or NM+. These results suggest that in the DCN, a prerequisite for the generation of acoustic-like responses with an electrical stimulus may be the matching of the cochlear place and spatial extent activated by each stimulus.
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ItemManikin and cochlear implant patient test results with a portable adaptive beamforming processor to suppress the effects of noise( 1995)A simple adaptive beamformer (ABF) was implemented in a real-time portable speech processor and tested with four cochlear implant patients. The ABF algorithm used signals from only two microphones - one behind each ear - to attenuate sounds not arriving from the direction directly in front of the patient, and was compared with a strategy in which the two microphone signals were simply added together (two-microphone broadside strategy). Tests with the four patients were conducted in quiet and in noise. Results at a 0 dB signal-to-noise ratio showed large improvements in speech intelligibility for all patients, when compared to the two-microphone broadside strategy. Physical measurement of the directional characteristics of the ABF processor were made with a Kemar manikin. The effects of reverberation were explored by placing the manikin in different acoustic environments and observing the attenuation of the noise alone at various angles. A near-anechoic environment allowed the noise to be attenuated by as much as 21 dB, whereas in a highly reverberant concrete stairwell, the ABF processor was unable to provide any directional gain beyond about 3 dB.
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ItemFusion and lateralization study with two binaural cochlear implant patients( 1995)Psychophysical studies have been completed with two binaural cochlear implant patients. Results from a fusion and lateralization experiment with both patients are described. As found in an earlier study with the first binaural patient in Australia, the second patient also showed good sensitivity to interaural amplitude differences but poor sensitivity to interaural time delays when compared with normal-hearing subjects. The implications of this result are discussed.
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ItemIntroduction: International Cochlear Implant, Speech and Hearing Symposium - Melbourne 1994( 1995)The International Cochlear Implant Speech and Hearing Symposium - Melbourne 1994 covered a wide range of presentations in a number of disciplines. The scientific program included 287 oral presentations and 40 posters, presented to a total of 456 delegates from 38 countries. This was a considerable expansion in the number and range of presentations from the first international conference held in Melbourne in 1985 (Ann Otol Rhinal Laryngal 1987;96[suppl 128]). This growth highlights the importance of the discipline and the advances being made in this area.
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ItemThe progress of children using the multichannel cochlear implant in Melbourne( 1995)Multi-channel cochlear implantation in children began in Australia in 1985 and there are now close to 4000 profoundly deaf children and adolescents using the Australian implant system around the world. The aim of the implant procedure is to provide adequate hearing for speech and language development through auditory input. This contrasts with the situation for adults with acquired deafness where the cochlear implant aims to restore hearing for someone with well-developed auditory processing and language skills. As with adults, results vary over a wide range for children using the Multi-channel implant. Many factors have been suggested that may contribute to differences in speech perception for implanted children. In an attempt to better understand these factors, the speech perception results for children implanted in Melbourne were reviewed and subjected to statistical analysis. This has indicated that the amount of experience with the implant and the length of sensory deprivation are strongly correlated with perceptual results. This means that younger children are likely to perform better with an implant and that a number of years of experience are required for children to reach their full potential. The results have also indicated that educational placement and management play a crucial role in children reaching their potential. Overall, 60% of the children and adolescents in the study have reached a level of open-set speech understanding using the cochlear implant without lipreading.
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ItemCochlear implants in children: the value of cochleostomy seals in the prevention of labyrinthitis following pneumococcal otitis media( 1995)Cochlea implantation at an early age is important in rehabilitating profoundly hearing impaired children. Given the incidence of pneumococcal otitis media in young children, there has been concern that cochlear implantation could increase the possibility of otitis media, leading to labyrinthitis in this age group. Clinical experience has not indicated an increase in the frequency of otitis media and labyrinthitis in implanted adults or children over two years. However, labyrinthitis has occurred in implanted animals with otitis media. In order to assess the impact of cochlear implants on the occurrence of labyrinthitis, pneumococcal otitis media was induced in 21 kittens. Thirty-two kitten cochleas were implanted, of which 9 had a fascial graft and 9 a Gelfoam® graft. Nine control cochleas were unimplanted. Labyrinthitis occurred in 44% of unimplanted controls. 50% of implanted ungrafted cochleas, and 6% of implanted grafted cochleas. There was no statistically significant difference between the incidence of labyrinthitis in the implanted cochleas and the unimplanted controls. However there was a statistically significant difference between the ungrafted and grafted cochleas, but not between the two types of graft.
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ItemThe University of Melbourne Department of Otolaryngology( 1995)The University of Melbourne Department of Otolaryngology runs a general ENT Clinic as well as a Cochlear Implant Clinic. It forms the core of a Multicentre research group for deafness research, is heavily involved in teaching and education, and includes a School of Audiology. This article presents an overview of the activities of the Department.