Graeme Clark Collection
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ItemElectrophonically driven single unit responses of the anteroventral cochlear nucleus in cat [Abstract]( 1996)Electrical stimulation of the cochlea results in both direct and electrophonic excitation of auditory nerve fibres. It has been proposed that electrophonic stimulation results from the creation of a mechanical disturbance on the basilar membrane which has properties similar those resulting from acoustic stimuli. Auditory nerve compound action potential (CAP) forward masking studies1 show the level of frequency specific electrophonic stimulation is highly correlated with the spectral energy of the electrical stimulus waveform. The level of spectral energy in pulsatile biphasic electrical stimuli decreases toward low frequencies suggesting the level of electrophonic stimulation will be diminished in the low frequency region of the cochlea.
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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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ItemThe use of click-ABR and steady state evoked potentials for hearing assessment in young cochlear implant candidates [Abstract]( 1997)The accurate assessment of hearing thresholds in prospective cochlear implant candidates is essential. As the minimum age of implantation has reduced, audiologists have been faced with the complicated task of obtaining precise audiometric information in children whose immaturity may severely restrict the assessment process. Clearly for these young candidates, there is a place for a reliable, objective measure of residual hearing in the pre-operative test battery. This paper examines the degree of accuracy with which the click-ABR and the steady-state evoked potential (SSEP) techniques can provide estimates of hearing level in subjects with several profound hearing loss.
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ItemImplantation of the new nucleus C1-3 receiver stimulator and electrode array [Abstract]( 1997)There is an important need to fix the cochlear implant electrode array 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 sites have been in the region of the posterior root of the zygoma and the floor of the antrum. Fixation has been by Dacron mesh ties platinum wire ties, or clips inserted with-special instruments. Biological cements have previously been tried but found to be toxic. The most ideal site is in the region of the cochleostomy.
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ItemAetiology of hearing loss in children presenting for cochlear implantation and outcomes [Abstract]( 1997)The aetiology of hearing loss has a significant bearing on the likely outcome of cochlear implantation and therefore is an important consideration in patient selection and workup. Disease processes which result in sensorineural hearing loss may be associated with other structural or functional neurological disorders, in addition to 'damage to the cochlea and auditory pathways.
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ItemThe histological and physiological effects of the auditory brainstem prosthesis of the auditory pathway [Abstract]( 1997)The cochlear implant can successfully rehabilitate the majority of profoundly deaf patients. However, some of them cannot benefit from the cochlear implant due to bilateral interruption of the auditory nerve, particularly from neurofibromatosis II. These patients can be stimulated directly with an auditory brainstem prosthesis on the cochlear nucleus. To examine the safety and the efficacy of this prosthesis, the cochlear nuclei of guinea pigs were implanted unilaterally with bipolar surface electrodes, and stimulated acutely using charge-balanced, biphasic current pulses at rates of 250, SOO or 1000 Hz and charge intensities of 1.8, 2.8, 3.5 or 7.1?C/phase/cm2.
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ItemCurrent speech perception benefits for adults using the speak strategy with the nucleus 22-channel cochlear implant( 1997)Present day recipients of the Nucleus 22-channel cochlear implant make use of the SPEAK speech processing strategy in the Spectra 22 speech processor. Introduced in 1994, the SPEAK strategy is based upon research conducted at the University of Melbourne and the Bionic Ear Institute. This paper compares the pre-and post-operative speech perception abilities of adults who have used the SPEAK speech processing strategy since the 'start-up' of their cochlear implant system. Data was analysed from open-set sentence and word tests administered pre-operatively and at regular intervals postoperatively. Patients showed significant improvement in their ability to recognise speech, when listening with the cochlear implant without lipreading, within the first two weeks. Mean scores for open-set sentences were 15% preoperatively and 64% two weeks after initial programming.
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ItemSpeech cues for cochlear implantees: spectral discrimination [Abstract]( 1997)The ability of cochlear implantees to understand speech varies over a wide range. While some implantees achieve scores close to 100 % open set word tests, other require visual cues to achieve a significant score on these tests. The focus of this research is to investigate reasons for the wide range of ability and therefore to improve the speech processors used by individual implantees. This study first investigated whether the relative importance of various frequency regions of the speech spectrum differs for implantees of different performance levels, and for implantee groups compared to normally hearing subjects.
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ItemSpeech perception of hearing aid users versus cochlear implantees [Abstract]( 1997)Recent improvements in speech recognition for profoundly deaf, cochlear implant patients have suggested that some people with a severe hearing impairment would be more successful with a cochlear implant than a hearing aid. Unfortunately, no studies have investigated the speech perception of the severely hearing impaired in order compare their speech perception abilities with those of cochlear implant users. To investigate this area further, a detailed investigation of the hearing aid performance of people with a severe hearing loss is being conducted in the Department of Otolaryngology at The University of Melbourne. The range of hearing losses for this study was defined as a pure tone average of greater than 6OdBHL, but no worse than 100dBSPL in the better ear. At present thirty-five (n=35) participants have been involved in this study. Each participant took part in a series of speech perception tests which included 24 consonant recognition, 11 vowel recognition, CNC words, CUNY sentences, and the connected speech test.
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ItemThe biosafety of hyaluronate (healon) for cochlear implantation [Abstract](Monduzzi Editore, 1997)Insertion of the electrode array of multiple channel cochlear implants may be aided using Hyalurate. It is felt that this substance acts as a lubricant allowing the array to be inserted more deeply and less traumatically. This has potential advantages of improving pitch perception in cochlear implant patients. To investigate the biosafety of Hyaluronate an animal study was undertaken. Dummy electrodes were inserted into the cochleae of six normal hearing cats. Hyaluronate was used as a lubricant in one ear and the other ear served as a control. Measurement of hearing thresholds before and after surgery did not reveal hearing loss attributable to the Hyaluronate. The temporal bones from these cats were sectioned and the histological sections analysed for evidence of spiral ganglion cell or hair cell loss. Initial results have not demonstrated poorer spiral ganglion cell survival or greater hair cell loss in the group in which Hyaluronate was used.