Graeme Clark Collection
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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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ItemElectrical stimulation of the auditory nerve in deaf kittens: effects on cochlear nuclei [Abstract]( 1990)Acoustic experience plays an important role in the development of the auditory system. Neonatal sound deprivation will result in significant reduction of both the cell soma area and total volume of the ventral cochlear nuclei (VCN) in adult animals (Webster, 1988). The present study has been undertaken to investigate this phenomenon by examining the effects of electrical stimulation of the auditory nerve of the kitten, on the morphology of the cochlear nucleus in animals deprived of sound following the administration of ototoxic drugs.
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ItemExcitation and inhibition in responses of cochlear nucleus single units to electrical stimulation of the auditory nerve [Abstract]( 1990)We have investigated the extracellular response of cochlear nucleus single units to electrical pulse train stimulation of the auditory nerve via an electrode array implanted into the feline scala tympani. The findings of these studies provide the physiological basis for the future design of the implanted electrode array and electronics and external speech processor of a cochlear implant prosthesis system.
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ItemRapid and permanent hearing loss in cats following co-administration of kanamycin and ethacrynic acid [Abstract]( 1990)A safe, simple and effective technique for producing profound-totally deaf animal models in both young and adult cats is required for auditory prosthesis related research. Exposure to loud noises can result in a partial hearing loss, the degree of which varies significantly among animals. Long-term systemic injection of an aminoglycoside ototoxic drug frequently results in renal dysfunction and can show significant variation in response among animals (Shepherd & Clark, 1985). Finally, direct infusion of ototoxic drugs produces extensive and highly variable cochlear pathology, unsuitable for auditory prosthesis research.
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ItemThe effect of position of the scala tympani electrode array on auditory nerve excitation [Abstract]( 1990)Multiple-channel auditory prostheses provide both temporal and formant information to profoundly-totally deaf patients. This is achieved via direct electrical stimulation of selective regions of the residual auditory nerve using an electrode array located in the scala tympani. Histological evidence has shown that these electrode arrays lie along the outer wall of the scala tympani, some distance from the residual nerve elements. In the present study we systematically varied the position of the electrode array within the cat scala tympani in order to investigate the influence of electrode position on neural excitation. Such knowledge may contribute to the development of improved electrode arrays for auditory prostheses.
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ItemClinical results for profoundly deaf patients using the 22-elctrode cochlear prosthesis [Abstract]( 1987)The 22-electrode cochlear prosthesis developed in Australia by the University of Melbourne and Cochlear Pty. Limited has been in clinical use in Melbourne for five years. Results for 40 postlingually deaf adults have shown significant communication benefit for 90% of patients. Twenty patients (50%) have demonstrated the ability to understand conversational speech without lipreading or visual cues. No electronic or mechanical failures have been observed in any of the implanted devices. There have been no serious medical complications, but psychological disturbance has occurred in two cases. Experience with prelingually deaf adults has indicated that initial hearing responses for this group are not as good as for the postlingually deaf patients. However, improvement over time has been evident with consistent use of the device. Long-term benefit for these patients will depend to a large extent on motivational and social factors. Results for a small number of young deaf children have been encouraging. The age at onset of profound deafness, intelligence, educational management and family support are all important factors affecting the potential benefit of a cochlear implant for a child.
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ItemResults for the Nucleus multiple-electrode cochlear implant in two children [Abstract]( 1988)Two males, 9 years 10 months (CHILD 1) and 5 years 5 months (CHILD 2) at time of surgery, were implanted with the Nucleus multiple-electrode cochlear implant. Both patients were deafened as a result of meningitis in their third year. Assessments of speech perception, speech production and language skills were undertaken at regular intervals, pre and post operatively. For both patients in the audition alone condition, some speech perception post operative scores were significantly higher than pre operative scores and progressive improvements in scores over successive post operative data collection times were seen. Significant differences between the visual alone and auditory-visual condition scores were also observed for CHILD 1 post operatively. Speech production post operative scores were significantly higher than pre operative scores for both patients. The receptive vocabulary scores for both patients improved at a higher rate than that of age-matched normal children. The acquisition of expressive and receptive language skills for CHILD 2 was at a higher rate than that of age-matched children. Differences in the results between the two patients were seen, and this may be related to age and duration of deafness.
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ItemVentral cochlear nucleus and auditory nerve fibre responses to electrical stimulation of the cat cochlea [Abstract]( 1987)Discharge patterns of cat auditory nerve fibres and ventral cochlear nucleus neurones to constant-current biphasic pulses have been recorded. The study was carried out to determine the input-output characteristics of the neurones, for variations in the rate and intensity of electrical stimulation. Neural discharges were highly synchronized with the current pulses at suprathreshold stimulus intensities, and saturation discharge rates usually equalled stimulus pulse rates up to 800 pulses/s. The electrically-driven discharge patterns of ventral cochlear nucleus neurones exhibiting "primary-like" responses were similar to those recorded from electrically-stimulated auditory nerve fibres. Comparison of the neural responses to electrical and acoustic stimulation may help in the design of improved speech processors for cochlear implants. Field potential responses were depressed at high stimulus rates and charge densities, suggesting stimulus-induced reduction in neural excitability. The effects of stimulus parameter variations on field potentials may help in determining safety limits of the electrical stimulus.
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ItemElectrical stimulation of the auditory nerve: effects of high stimulus rates [Abstract](Australian Physiological and Pharmacological Society, 1986)We have previously described non-damaging stimulus levels for chronic intracochlear electrical stimulation (Shepherd et al, 1983). However, maximum safe stimulus levels have yet to be clearly defined. Moreover, the importance of various stimulus parameters and their effects on the auditory nerve is not well understood. In the present study we have examined the effects of stimulus repetition rate on the auditory nerve by monitoring the Electrically-evoked Auditory Brainstem Response (EABR). Such information is necessary if speech processing strategies incorporating high pulse rates (i.e. > 300 pps) are to be made available to cochlear implant patients.
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ItemTraining and assessment of children using a multi-electrode cochlear implant [Abstract]( 1986)A training and assessment protocol has been developed for a research study on deaf children using multi-electrode cochlear implants. The areas of assessment and training include speech perception and production, language and communication skills. Material which is appropriate for language-and developmental-age is selected from a large battery of: tests to ensure that the individual abilities of children are addressed. A single-subject, time-series design has been adopted for regular assessment of the child's performance. The participating child receives a minimum of six months' pre-operative training and assessment using high gain hearing aids or a tactile device. Also included are audiological and medical evaluations to determine the child's suitability for inclusion in the study. Approximately two months are allocated for pre-operative, operative and postoperative surgical management as well as fitting and setting the external speech processor. Post-operatively, the same training and assessment procedures continue for a number of years. Extensive psychophysical studies are also undertaken to measure the child's abilities to discriminate simple stimuli which differ in electrical stimulus parameter values.