Graeme Clark Collection
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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.
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ItemDecrement in auditory nerve function following acute high rate stimulation using various stimulus paradigms in guinea pigs [Abstract]( 1996)Previous experimental studies have shown that chronic electrical stimulation of the auditory nerve using charge balanced biphasic current pulses at rates of up to 500 pulses per second (pps) do not adversely affect the adjacent spiral ganglion population. More recently psychophysical trials have indicated that speech processing strategies based on high pulse rates (1000 pps or more) can improve speech perception in cochlea implant patients. In this paper we summarize the results following acute high rate stimulation using different stimulus paradigms.
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ItemCochlear implants: high rate stimulation studies and the effect of electrode position [Abstract]( 1996)This paper summarizes our recent findings investigating the safety of high rate electrical stimulation, and reviews the effects of electrode position on auditory excitability. These studies used charge balanced biphasic pulses and electrode shorting between stimuli to minimize any residual charge or direct current. High rate (400-1000 pulses/s) electrical stimulation of the auditory nerve can result in significant stimulus induced reductions in auditory nerve excitability at stimulus levels well above those used clinically (1). The extent of this reduction was dependent on stimulus rate, intensity and duty cycle, implying that such changes were related to the degree of evoked activity.
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ItemIs age at cochlear implantation in children important? A 2-deoxyglucose study in cats [Abstracts]( 1996)Cochlear implants are one treatment for children who are born deaf or become deaf before acquiring language. The question of optimum age for implantation arises. Is it better to implant a child as early as possible, or is it sufficient to do the implantation during the pre-school years? Using an animal model, we have studied the response of the auditory brainstem to implantation at various ages. Although the auditory brainstem of hearing cats matures within the first month of life, a study by Snyder et al. (1990) implied that in neonatally deafened cats the capability for "maturation" or plasticity extended at least up to 120 days.
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ItemNeural responses after direct stimulation of the auditory brainstem in guinea pigs: a safety study [Abstract]( 1996)Bilateral loss of function of the auditory nerve results is a profound hearing loss that cannot be restored by hearing aids or cochlear implants. A central auditory prosthesis has been developed to deliver electrical pulses directly to the terminals of these nerves within the brainstem at the cochlear nucleus (CN). To determine the safety of this stimulation, neuronal excitability was monitored by recording electrica1ly evoked auditory brainstem responses (EABR) and neural activation was determined by uptake of the radioactive glucose analogue. C142-deoxyglucose (2-DG).
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ItemDoes age at implantation affect the plastic changes? A 2-DG study in cat inferior colliculus [Abstract]( 1996)Cochlear implants are one treatment for children who are born deaf or become deaf before acquiring language. Using the animal model, we have studied the optimum age for implantation in such cases. Cats were deafened at 10 days after birth with kanamycin and ethacrynic acid. All were implanted with a 4-electrode array in the left cochlea at age from 100 to over 180 days.
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ItemMechanisms of temporal pitch coding and their implication for cochlear implants [Abstract]( 1996)Mounting evidence suggest that the mammalian auditory system is able to extract pitch percepts from the temporal components of phase-locked neural responses and also from the rate-place components of neural response. Exactly how these two methods of frequency estimation are combined within the auditory system is still an open question, and will depend on the exact properties of each.
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ItemSpeech perception results for implanted children with different levels of preoperative residual hearing [Abstract]( 1996)Many reports have established that hearing-impaired children using the Nucleus 22-channel cochlear implant may show both significant benefits to lipreading, and significant scores on open-set words and sentences using electrical stimulation only. These findings have raised suggestions that severely or severely-to-profoundly deaf children might benefit more from a cochlear implant than conventional amplification.
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ItemSpeech perception results for the nucleus multiple channel cochlear implant in children and adults with residual hearing [Abstract]( 1996)Speech perception results for profoundly deaf children and adults using advanced speech processing strategies for the Nucleus multiple-channel cochlear implant have continued to improve, and are now better than those reported in research with severely-to-profoundly hearing-impaired people using aided residual hearing.