Graeme Clark Collection
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ItemIssues in the development of multichannel tactile devices for hearing-impaired children and adults( 1995)Levitt, Pickett and Houde (1980), in their landmark monograph, noted that the history of tactile aid development has been characterized by periodic bursts of enthusiasm and research, often culminating in identification of new avenues to be explored for improving tactile perception of speech. While several research groups have maintained long-term interest in tactile research (Boothroyd, 1985; Oller, Payne, & Gavin, 1980; Saunders, 1985), there was a marked increase in reports of new multichannel tactile devices during the 1980s (reviewed in McGarr, 1989). This upsurge may have been spurred in part by the rapid increase world-wide in the number of hearing-impaired children and adults using cochlear implants as everyday communication devices, and the perceived need for a non-surgical approach to assisting hearing-impaired children. Despite this increase in tactile research, no tactile device has yet achieved widespread commercial use by the hearing-impaired community. It is, therefore, of interest to question why cochlear implants have been more widely accepted than tactile devices.
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ItemAcute effects of high-rate stimulation on auditory nerve function in guinea pigs( 1995)Cochlear implants have been shown to successfully provide profoundly deaf patients with auditory cues for speech discrimination. Furthermore, a number of safety studies using the Melbourne/Cochlear electrode array indicated that chronic electrical stimulation using charge-balanced biphasic current pulses and stimulus rates between 100 and 500 pulses per second (pps) do not result in additional spiral ganglion loss or general cochlear pathology.1-3 However, safe maximum levels for stimulus parameters (stimulus rate, charge per phase, charge density) have not yet been adequately defined.
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ItemCochlear implants: future research directions( 1995)The future of cochlear implants for profoundly deaf people now seems assured, and further research should improve its benefits. The present benefits of cochlear implants have now been clearly demonstrated. The results have shown that many postlingually deaf adults get significant open-set speech recognition using electrical stimulation alone, and that profoundly deaf children with a cochlear implant get better speech perception than similar children who use hearing aids or tactile vocoders.
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ItemPotential and limitations of cochlear implants in children( 1995)Multiple-channel cochlear implants have been in use with children and adolescents for 8 years. The speech perception, speech production, and language of many of these children has been investigated in some detail.l-4 There have been many predictions about factors that may affect the performance of children with implants. For instance, it has been suggested that children with a congenital loss of hearing would not have the same potential to benefit from a cochlear implant as those with an acquired loss. Similarly, it has been suggested that younger children are likely to gain more benefit from a cochlear implant because of the effect of various critical ages for language learning.5 As more results have become available, it has been our observation that the performance of any particular child with a cochlear implant does not appear to follow well-defined rules, and that generalizations about the potential of certain groups of children are likely to encounter many exceptions. We now have a large quantity of results for children using cochlear implants, and it may be possible to determine some of the factors that have a significant effect on performance. This paper will attempt to identify some of these factors by reviewing speech perception results for 100 children implanted with the Nucleus 22-channel cochlear prosthesis in Australia and speech perception results for adult patients. This analysis will use an "information processing" model of a child using a cochlear implant. That is, we will assume that a child will benefit from a cochlear implant in terms of speech perception, production, and language development, if he or she receives a maximal amount of auditory information from the environment, and is able to process this information successfully. This model divides potential limiting or predictive factors into those that affect the information presented to the auditory system (eg, implant technology, surviving auditory neurons) and those that affect the processing of this information (eg, development of central auditory pathways, amount and consistency of auditory input).
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ItemControl strategies for nerves modeled by self-exciting point processes( 1995)Cochlear implants electrically stimulate the auditory nerve with the aim of generating a perception of sound via an evoked neural response pattern. An electrically stimulated auditory nerve responds differently to an acoustically stimulated auditory nerve, and the surviving nerves of patients with a hearing loss may exhibit characteristics different from those of normal-hearing people. Thus, the cochlear implant evoked response pattern differs greatly from that of the normal hearing situation. One method of understanding such response patterns is to employ a mathematic model. If possible, the model should permit the determination of neural response differences between closely related sounds, and facilitate the design of stimuli that evoke desired neural response patterns. How should such a model be chosen?
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ItemSignal processing for multichannel cochlear implants: past, present and future [Abstract]( 1994)Since the late 1970's, many groups have worked on developing effective signal processing for multichannel cochlear implants. The main aim of such schemes has been to provide the best possible speech perception for those using the device. Secondary aims of providing awareness and discrimination of environmental sounds and appreciation of music have also been considered. Early designs included some that attempted to simulate the normal cochlea. The application of such complex processing schemes was limited by the technology of the times. In some cases, researchers reverted to the use of single channel systems which could be controlled reliably with the existing technology. In other cases, as with the Australian implant, a simple multichannel processing scheme was devised that allowed a reliable implementation with available electronics. Over the next 15 years, largely due to the improvements in integrated circuit technology, the signal processors have slowly become more complex. Further psychophysical research has shown how additional information can be transferred effectively to implant users via electrical stimulation of the cochlea. This has lead to rapid improvement in the speech perception abilities of adults using cochlear implants. Some of the main developments in signal processing over the last 15 years will be discussed along with the latest speech perception results obtained with the new SPEAK processing scheme for the Australian 22-channel cochlear implant. Initial results for SPEAK show mean scores of 70% (equivalent to 85-90% phoneme scores) for open set monosyllabic word testing for experienced adult users. Although there remains a large range of performance for all users of cochlear implants, average speech perception scores for all implanted adults have also improved significantly with the developments in signal processing. It appears likely that multichannel cochlear implants will be a viable alternative for the treatment of severe hearing loss in the future.
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ItemIssues in long-term management of children with cochlear implants and tactile devices [Abstract]( 1994)For many children with severe and profound hearing losses, conventional hearing aids are unable to provide sufficient amplification to ensure good oral communication and/or in the case of very young children, development of speech and language. Traditionally a number of these children have opted for the use of sign language alone or in Total Communication approaches as a primary means of communication. The advent of multiple channel cochlear implants for children and the continuing development of multiple channel speech processing tactile devices provide auditory approaches to resolving communication difficulties for these children. The successful use of such devices depends on a number of factors including the information provided through the aid; the ease of use, convenience and reliability of the aid; the individual communication needs of the child; and the habilitation and management program used with the device. Long-term data has shown that children continue to show increased speech perception benefits from improvements in speech processing and from further experience with these devices. Habilitation and management programs must therefore be geared to meet the changing needs of children as they progress and of families as children mature and face new challenges. Habilitation must address specific individual needs in speech perception and in speech production. For very young children, benefits of improved speech perception should have an impact on the development of speech and language, and habilitation and management must emphasise the need for language growth.
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ItemCochlear implants in children: unlimited potential? [Abstract]( 1994)Multichannel cochlear implants have been in use for adolescents for 8 years and for children for 6 years. Due to the substantial benefits obtained by postlinguistically deafened adults using multichannel implants, there was a degree of optimism about the potential benefits for profoundly hearing impaired children using these devices. It was speculated that children may adapt more quickly and learn to use information from implants more effectively than adults. On the other hand, there were cautionary predictions that there may be a "critical age", particularly for congenitally or early deafened children, that, once passed, would preclude effective use of auditory information from implants. This age was variously predicted to be anywhere from 2 to 12 years, based on neurophysiological, developmental or psychological arguments. With some years of experience with implanted children, it can now be said that neither the optimistic nor the more cautionary "critical age" predictions have been supported. As with many areas of clinical science, the situation appears to be far more complex than first thought. This paper will discuss the results obtained for 100 children using the multichannel cochlear implant in Sydney and Melbourne in terms of predictive factors, and the potential for the future application of multichannel cochlear implants in children. The results suggest that experience with implant, the number of years of auditory deprivation, the amount of preoperative residual hearing, and the postoperative educational environment may have a significant effect on speech perceptual abilities in implanted children. In addition, approximately 60% of all implanted children show significant open-set speech perception ability with auditory input alone. It is now possible for multichannel cochlear implants to provide auditory skills sufficient for young children to develop functionally normal speech and language through audition, provided consistent, long term habilitation is available.
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ItemSpeech perception for adults using cochlear implants(Whurr, 1994)A mere 16 years ago, the title of this chapter would have created considerable consternation in audiological circles. A high proportion of otologists and audiologists would have wondered, with good reason, about the potential content of such a chapter. In 1977, there were certainly cochlear implants in use with reported benefits, but reliable documentation of any useful speech perception under controlled conditions was difficult to find. The rapid development of cochlear prostheses since that time has led to thousands of profoundly hearing-impaired adults obtaining benefits for speech perception, and there is now no doubt regarding the efficacy of such devices. This chapter will provide a brief overview of this rapid improvement in the speech perception of adult cochlear implant users, consider some of the reasons for this improvement, and discuss some of the factors that may influence speech perception performance for the individual user. (From Introduction)
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ItemThe perception of electrodes by cochlear implant patients who became deaf early in life [Abstract]( 1994)Two separate studies measuring the perception of differences in site of electrode stimulation were conducted with cochlear implant patients who became deaf early in life. The multiple-electrode prosthesis manufactured by Cochlear Pty. Limited was used. Two of the possible mechanisms for the discrimination of different electrodes are pitch and loudness. The first study measured the discrimination of different electrodes using two procedures which minimised the influences of loudness cues on performance. In the first procedure, the stimulation patterns were symmetric sweeps across electrodes. The reference stimuli were apical-basal trajectories and the comparison stimuli were basal-apical trajectories. The electric stimulation levels were the same in the reference and comparison stimuli because the same electrodes were used in the trajectories. In the second procedure, the stimulation patterns used randomised variations in electric stimulation levels on the different electrodes. By randomly varying the loudness of the stimuli in a discrimination task, the patient is required to listen for more salient cues such as pitch. Both procedures gave comparable results. The second study was concerned with the estimation of order in percepts for stimulation on the different electrodes along the array which was related to the tonotopic order of the cochlea. Approximately half of the early-deafened patients tested revealed a tonotopic order in percepts which was comparable to that obtained from postlinguistically deafened adults.