Graeme Clark Collection
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ItemHearing restoration with the multichannel auditory brainstem implant( 1997)Restoration of useful hearing is now possible in patients with bilateral acoustic neuromas by direct electrical stimulation of the cochlear nucleus. Our first experience with the Multichannel Auditory Brainstem Implant is reported. A forty four year old female with bilateral acoustic neuromas and a strong family history of Neurofibromatosis Type II presented with profound bilateral hearing impairment. Translabyrinthine removal of the right tumour was performed with placement of the Nucleus eight electrode Auditory Brainstem Implant. Intraoperative electrically evoked auditory brainstem response monitoring successfully confirmed placement over the cochlear nucleus. Postoperatively, auditory responses were obtained on stimulation of all electrodes with minimal non-auditory sensations. The patient now receives useful auditory sensations using the "SPEAK" speech processing strategy. Auditory brainstem Implantation should be considered for patients with Neurofibromatosis Type II in whom hearing preservation tumour removal is not possible.
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ItemPsychophysical studies with two binaural cochlear implant subjects( 1997)Abstract not available due to copyright.
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ItemEngineering(Singular Publishing, 1997)The last two decades have seen major advances in cochlear implants for profoundly deaf people. Implants are now used by severely to profoundly deaf adults and children in almost every phase of daily life. They have become an established treatment, and today's expectations for all aspects of the cochlear implant system are much greater than they were for the experimental devices of the early 1980s. Hardware designs have improved to meet clinical and research demands, technological developments have made the devices smaller and more reliable, and speech processing research has yielded a series of improvements in patient benefit.
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ItemThe Melbourne Cochlear Implant Clinic program(Singular Publishing, 1997)The Melbourne Cochlear Implant Clinic program involves a multidisciplinary clinical team, collaborating with those engaged in more fundamental research, and with the biomedical company Cochlear Limited. This chapter reflects the contributions of many professionals to managing children with cochlear implants.
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ItemElectrical stimulation of the auditory nerve with a cochlear implant and the temporal coding of sound frequencies: a brief review( 1997)There is considerable evidence that the brain translates (encodes) the frequency of a sound into both place of excitation (place encoding), and the pattern of intervals between action potentials (temporal encoding). Furthermore, temporal encoding is now thought to be due to a temporal as well as spatial pattern of action potentials in a small group of neurons. This pattern needs to be reproduced with a cochlear implant for improved speech processing. Our recent research has also demonstrated that the timing of excitatory postsynaptic potentials seen with intracellular recordings from brain cells, rather than extracellularly recorded action potentials, correlates better with the frequency of sound. These excitatory postsynaptic potentials are likely to be the link between the patterns of action potentials arriving at nerve cells and the biomolecular activity in the cell. This response also needs to be replicated with improved speech processing strategies.
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ItemCochlear implants in adults and children: comment( 1997)This is a well-written review of the NIH Consensus report on cochlear implants for adults and children.
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ItemPitch and loudness estimation for single and multiple pulse per period electric pulse rates by cochlear implant patients( 1997)Abstract not available due to copyright.
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ItemVariability of amplitude and area of the auditory nerve compound action potential( 1997)The strength of neural response to sensory stimuli is often estimated by measurement of the amplitude of gross neural potentials. These gross potentials reflect the summed activity of a population of neurons. The amplitude of these potentials is dependent upon the synchrony of the contributing neural responses. We compared the variability of the peak-to-peak amplitude of the auditory nerve compound-action potential (CAP) with that of the area under the peaks. The area under the peaks was significantly less variable than the amplitude for responses to low frequency stimuli. Responses to other stimuli showed differences in the same direction, but these were not significant. We conclude that the area under these peaks is a more precise measure of neural response than measurement of waveform amplitude, at least for responses to low frequency stimuli.
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ItemChronic electrical stimulation of the auditory nerve at high rates: I. Effect on residual hearing [Abstract]( 1996)In addition to direct excitation of auditory nerve fibres, cochlear implant patients with small amounts of residual hearing may receive important additional auditory cues via electrophonic activation of hair cells 1. Before incorporating electrophonic hearing into speech processing strategies, the extent of hair cell survival following cochlear implantation must first be determined. We have recently demonstrated widespread survival of hair cells apical to electrode arrays implanted for periods of up to three years, the present report describes the effects of chronic electrical stimulation on hair cell survival.
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ItemChronic electrical stimulation of the auditory nerve at high rates: II. Cochlear pathophysiology [Abstract]( 1996)A major factor in the improved performance of cochlear implant patients has been the use of high stimulus rate speech processing strategies. While these strategies show clear clinical advantage, we know little of their long-term safety. Indeed, recent studies have indicated that high stimulus rates at intensities above clinical limits, can result in neural damage as a result of prolonged neuronal hyperactivity. The present study was designed to evaluate the effects of chronic electrical stimulation of the auditory nerve at high rates, using intensities within clinical limits.