Graeme Clark Collection
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ItemNo Preview AvailablePersonal reflections on the multichannel cochlear implant and a view of the future(JOURNAL REHAB RES & DEV, 2008)The multichannel cochlear implant is the first neural prosthesis to effectively and safely bring electronic technology into a direct physiological relation with the central nervous system and human consciousness. It is also the first cochlear implant to give speech understanding to tens of thousands of persons with profound deafness and spoken language to children born deaf in more than 80 countries. In so doing, it is the first major advance in research and technology to help deaf children communicate since Sign Language of the Deaf was developed at the Paris deaf school (L'Institut National de Jeunes Sourds de Paris) >200 years ago. Furthermore, biomedical research has been fundamental for ensuring that the multielectrode implant is safe as well as effective. More recent research has also shown that bilateral implants confer the benefits of binaural hearing. Future research using nanotechnology should see high-fidelity sound received, which would help deaf persons communicate in noise and enjoy music. Research should also lead to implants in ears with useful hearing.
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ItemComponents of a rehabilitation programme for young children using the multichannel cochlear implant(Whurr, 1996)Rehabilitation with young hearing-impaired children may be defined as a teaching; learning process where the role of the clinician is to facilitate acquisition of listening, speech and language in a normal developmental order. This is often referred to as habilitation. It differs from rehabilitation for adults, which is the process by which lost communication skills are reacquired. It is worth discussing the role of the cochlear implant as a tool in this process. For the adult with acquired hearing loss, the cochlear implant might be expected, in part, to facilitate rehabilitation by restoring the auditory sense. The aim is to facilitate speech reception and provide the adult with a speech feedback loop. For a child receiving the cochlear implant, the aims are more complex. The device needs to provide speech perception abilities to facilitate the development of the entire linguistic system, to develop a range of speech sounds, to enable speech monitoring via auditory feedback and to access shared knowledge of the world. (From Introduction)
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ItemReduction in excitability of the auditory nerve following electrical stimulation at high stimulus rates( 1995)While recent studies have suggested that electrical stimulation of the auditory nerve at high stimulus rates (e.g., 1000 pulses/s) may lead to an improved detection of the fine temporal components in speech among cochlear implant patients, neurophysiological studies have indicated that such stimulation could place metabolic stress on the auditory nerve, which may lead to neural degeneration. To examine this issue we recorded the electrically evoked auditory brainstem response (EABR) of guinea pigs following acute bipolar intracochlear electrical stimulation using charge-balanced biphasic current pulses at stimulus rates varying from 100 to 1000 pulses/s and stimulus intensities ranging from 0.16 to 1.0 µC/phase. Charge density was held constant (~ 75 µC cm^-2 geom/phase) in those experiments. To monitor the recovery in excitability of the auditory nerve following this acute stimulation, EABR thresholds, wave I and III amplitudes and their latencies were determined for periods of up to 12 h following the acute stimulation. Higher stimulus rates and, to a lesser extent, higher intensities led to greater decrements in the post-stimulus EABR amplitude and prolonged the recovery period. While continuous stimulation at 100 pulses/s induced no decrement in the EABR, stimulation at 200 and 400 pulses/s produced an increasingly significant post-stimulus reduction of the EABR amplitude, which showed only partial recovery during the monitoring period. No EABR response could be evoked immediately following stimulation at 1000 pulses/s, using a probe intensity 16-19 dB below the stimulus intensity. However, partial EABR recovery was observed for wave III following stimulation at the lowest stimulus intensity (0.16 µC/phase). These stimulus-induced reductions in the EABR amplitude were also reflected in increased thresholds and latencies. Providing stimulus rate and intensity were held constant, stimulation at different charge densities (37.7, 75.5 and 150.7 µC cm^-2 geom/phase) had no influence on the post-stimulus EABR recovery. Significantly, the introduction of a 50% duty cycle into the stimulus pulse train resulted in a more rapid and complete post-stimulus recovery of the EABR compared to continuous stimulation. These data suggest that stimulus rate is a major contributor to the observed reduction in excitability of the electrically stimulated auditory nerve. This reduction may be a result of an activity-induced depletion of neural energy resources required to maintain homeostasis. The present findings have implications for the design of safe speech-processing strategies for use in multichannel cochlear implants.
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ItemSurgical and safety considerations of multi-channel cochlear implants in children( 1991)Multi-channel cochlear implants have become a viable surgical treatment for profoundly deaf individuals. With the Food and Drug Administration’s (FDA’s) June 1990 approval for the release of the 22-channel implant for children aged 2 to 17, more hearing impaired young people than ever before will be able to benefit from the auditory sensations provided by the device. The surgical procedure, the complications experienced, and safety issues are somewhat different for children than they are for adults. This report describes the modifications required in the surgical procedure and discusses the complications associated with cochlear implants in children. It then addresses issues related to the safety of the device, such as the prevention of middle ear infection. Finally, it summarizes new research conducted at the University of Melbourne and supported by the National Institutes of Health concerning skull growth, explantation/reimplantation, and sealing the electrode entry point into the cochlea.
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ItemForward masking patterns produced by intracochlear electrical stimulation of one and two electrode pairs in the human cochlea( 1989)Abstract not available due to copyright.
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ItemPerceptual independence of pulse rates used in speech coding schemes for a multichannel cochlear implant [Abstract]( 1989)Abstract not available due to copyright.
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ItemRevised selection criteria for the multiple-channel cochlear implant( 1991)The criteria of suitability for a cochlear implant have been extended from total deafness to include some individuals with residual hearing. The aim of the initial hearing evaluation is to define whether the speech discrimination is good enough to justify perseverance with a hearing aid. In adults, usually the pure tone audiogram and speech audiometry are accurate and consistent. In children, however, to achieve accuracy, free field testing must be complemented by repeated aided conditioned responses and objective evoked response audiometry. When a child has residual hearing it is more difficult to assess the potential for habilitation using an aid. For both adults and children, it is necessary to make a selection from a battery of tests on the basis of the subjects experience. This development highlights the need for otologists and audiologists to become familiar with the battery of tests used in evaluating severe deafness (Plant 1984) and to review decisions made about the management of people with severe to total deafness. In suitable people, the aim of treatment with the Cochlear multichannel implant and its multipeak speech processor is a significant score for open set speech discrimination tests using hearing alone. This cannot always be achieved but as long as the evaluation protocol has been used to warn patients before the operation, they will be satisfied with a result where the implant complements lip reading resulting in discrimination of running speech and detection of environmental sounds.