Graeme Clark Collection
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ItemA clinical report on receptive vocabulary skills in cochlear implant users( 1995)Objective: The aim was to measure the rate of vocabulary acquisition for cochlear implant users and compare the pre- and postoperative rates with published data for other groups with normal or impaired hearing. The hypothesis was that the postoperative rate would be greater than the preoperative rate. Design: The Peabody Picture Vocabulary Test (PPVT) was administered to 32 children, adolescents, and prelinguistically deafened adults implanted with the 22-electrode cochlear implant. Age at implantation ranged from 2 y r 6 mo to 20 yr and implant use ranged from 6 mo to 7 yr 8 mo. Results: The group mean postoperative performance at various postoperative intervals was significantly higher than mean preoperative performance. Single-subject data indicated statistically significant gains over time on this test for 13 of the subjects. The mean postoperative rate of vocabulary acquisition of 1.06 times the rate for normally hearing children was significantly greater than the mean preoperative rate of 0.43. Conclusions: These rates of improvement were in accord with previous reports on smaller numbers of implant users, but could not be attributed unambiguously to use of the implant because no control group was used for this clinical work. Variables such as age at implantation, duration of profound deafness, communication mode, and speech perception skill failed to significantly predict rate of improvement on the PPVT.
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ItemA clinical report on speech production of cochlear implant users( 1995)Objective: The aim was to assess articulation and speech intelligibility over time in a group of cochlear implant users implanted at 8 yr or over. The hypothesis was that the postoperative speech production performance would be greater than the preoperative performance. Design: A test of intelligibility using sentences and an articulation test measuring non-imitative elicited speech were administered to 11 and 10 subjects, respectively, who were implanted with the 22-electrode cochlear implant. Nine subjects received both tests. Age at implantation ranged from 8 yr to 20 yr and implant use ranged from 1 yr to 4 yr 5 mo. Results: For both the intelligibility and articulation tests roughly half of the subjects showed significant improvements over time and group mean postoperative performance significantly exceeded preoperative performance. Improvements occurred for front, middle, and back consonants; for stops, fricatives, and glides and for voiceless and voiced consonants. Conclusions: Despite being deprived of acoustic speech information for many childhood years, roughly half of the patients assessed showed significant gains in speech intelligibility and articulation postimplantation. The lack of a control group of non-implanted patients means that we cannot separate out the influence of the implant on speech production from other influences such as training and tactile-kinaesthetic feedback.
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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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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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ItemPitch matching of electric and acoustic stimuli( 1995)In the electric coding of speech for multiple-electrode cochlear implants, acoustic frequency ranges are mapped onto electrodes. The question arises as to whether the pitches of the electrically evoked hearing sensations are similar to those evoked by the corresponding acoustic stimuli in normal-hearing listeners. Obviously, the sensations are similar enough for many postlingually deaf implant users to understand speech with a minimum of retraining, but it is unlikely that the electric signals sound identical to the acoustic ones. There will also be differences between implant users arising from the variable insertion depth of the electrode array, the number of electrodes in use, and the frequency-to-electrode mapping. The most direct method of determining pitch is to ask implant users to compare electric and acoustic stimuli, but studies of this sort have been hampered by the fact that very few implant users have usable hearing for acoustic signals. In 1978, Eddington et al 1 reported pitch-matching results for one unilaterally deaf volunteer. They concluded that pitch matching was "roughly consistent with electrode position and tonotopic maps of the cochlea derived from basilar membrane motion and hearing loss measurements." Several other studies 2-6 have investigated the relative pitch of electric signals using identification, scaling, and discrimination paradigms. These studies have established that electrode placement, electrode configuration, and rate of stimulation all affect the perceived pitch, and that the pitch increases tonotopically from apical to basal electrode positions. They have not determined the pitch of electric stimuli in an absolute fashion that can be compared with acoustic stimuli, however. A knowledge of the absolute pitch of electric stimuli for individuals, or as a function of position in the cochlea, would be very useful in optimizing the frequency mapping for cochlear implants. The present study directly compared the pitch of acoustic pure tones in one ear with electric signals in the other ear of implant users with some residual hearing in the nonimplanted ear. The main questions addressed were whether the pulse rate of a matched electric stimulus would be equal to the frequency of the acoustic tone, and whether the electrode used in the matched stimulus would correspond in position to the place of maximum basilar membrane motion produced by the acoustic tone in a normal cochlea.
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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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ItemHabilitation issues in the management of children using the cochlear multiple-channel cochlear prosthesis(Wien, 1994)Since 1985, a significant proportion of patients seen in the Melbourne cochlear implant clinic have been children. The children represent a diverse population, with both congenital and acquired hearing-impairments, a wide-range of hearing levels pre-implant, and an age range from 2 years to 18 years. The habilitation programme developed for the overall group must be flexible enough to be tailored to the individual needs of each child, and to adapt to the changing needs of children as they progress. Long-term data shows that children are continuing to show improvements after 5-7 years of device use, particularly in their perception of open-set words and sentences. Habilitation programs must therefore be geared to the long-term needs of children and their families. Both speech perception and speech production need to be addressed in the specific content of the habilitation program for any individual child. In addition, for young children, the benefits of improved speech perception should have an impact on development of speech and language, and the focus of the programme for this age child will reflect this difference in emphasis. Specific materials and approaches will vary for very young children, school-age and teenage children. In addition, educational setting will have a bearing on the integration of listening and device use into the classroom environment.
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ItemCochlear implants for congenitally deaf adolescents: is open-set speech perception a realistic expectation?( 1994)The prognosis for benefit from use of cochlear implants in congenitally deaf adolescents, who have a long duration of profound deafness prior to implantation, has typically been low. Speech perception results for two congenitally deaf patients implanted as adolescents at the University of Melbourne/Royal Victorian Eye and Ear Hospital Clinic show that, after 12 months of experience, both patients had significant open-set speech discrimination scores without lipreading. These results suggest that although benefits may in general be low for congenitally deaf adolescents, individuals may attain significant benefits to speech perception after a short period of experience. Prospective patients from this group should therefore be considered on an individual basis with regard to prognosis for benefit from cochlear implantation.
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ItemComparison of current speech coding strategies( 1993)This paper reports on two studies carried out at the University of Melbourne jointly with Cochlear Pty Ltd. The studies demonstrated substantial speech perception improvements over the current Multipeak strategy in background noise.