Graeme Clark Collection
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ItemShort-term auditory memory in children using cochlear implants and its relevance to receptive language [Abstract]( 2000)Current work indicates that many children using cochlear implants are able to hear fine differences between speech sounds but are not progressing as wel1 as expected in receptive language ability. There is anecdotal evidence from teachers that some children using cochlear implants have poor short-term auditory memory ability, which may be impeding their language development. Temporal ordering and short-term memory storage capacity involve higher order processing. Severe auditory deprivation prior to implantation may have caused auditory processing deficits at a cortical level. This study aims to assess short-term, sequential, auditory memory ability in children using cochlear implants and to determine the relationship between this ability and receptive language ability. Short-term auditory memory ability has not been previously investigated in profoundly deaf children using hearing aids and/or cochlear implants. Twenty-four children using the 22-electrode cochlear implant were tested on five short-term sequential memory tasks, three with auditory stimuli and two with visual stimuli. There were 8 children in each of the age groups; 5-6 years, 7-8 years, and 9-11 years. Twenty-four age-matched, normally hearing children served as a control group. Al1 children were also assessed on the receptive subtests of the CELF (Clinical Evaluation of Language Fundamentals) and on the nonverbal scale of the Kaufman Assessment Battery for Children (K-ABC) which measures nonverbal intelligence. This study assessed short-term auditory memory with tasks that required minimal language ability. Prior to the memory tasks, the child had to demonstrate accurate identification of the stimuli with a similar reaction time to the normally hearing controls. As expected there is a significant effect of age on memory performance for the 24 normally hearing children, with older children performing better than the younger children. The memory performance of the children using cochlear implants is therefore described in terms of its deviation from expected performance for a given chronological age. Preliminary results suggest that it is unlikely that auditory deprivation causes a memory deficit specific to the auditory modality. Performance on visual memory tasks is very similar to performance on analogous auditory memory tasks for a group of implant users. The performance of children using cochlear implants on a variety of memory tasks does not appear to be significantly different to that of normally hearing children who are of similar age and nonverbal intel1igence. In contrast their receptive language scores are substantially inferior.
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ItemSpeech perception in implanted children: influence of preoperative residual hearing on outcomes [Abstract]( 1998)Since the first child was implanted with the Nucleus 22-channel prosthesis in Melbourne in 1985, several thousand children world-wide have now benefitted from this technology. More effective paediatric assessment and management procedures have now been developed, allowing cochlear implants to be offered to children under the age of 2 years. Improvements in speech processing strategy have also been implemented in the Nucleus implant system, resulting in increased mean speech perception benefits for implanted adults. Although a range of performance on formal measures of hearing, speech or language has been reported for children using implants, results from the first decade of implant experience consistently show that significant benefits are available to children receiving their implant at an early age. Reported speech perception results for implanted children show that a considerable proportion (60%) of paediatric patients in the Melbourne and Sydney clinics are able to understand some open-set speech using electrical stimulation alone. These results, and the upward trend of mean speech perception benefits shown for postlinguistically deafened adults have raised questions as to whether severely, or severely-to-profoundly deaf children currently using hearing aids would in fact benefit more from a cochlear implant. To investigate the potential influence of the degree of preoperative residual hearing on postoperative speech perception, results for all implanted children in the Melbourne and Sydney cochlear implant programs were analysed. Results showed that as a group, children with higher levels of preoperative residual hearing were consistently more likely to achieve open-set speech perception benefits. Potential factors in this finding could be higher levels of ganglion cell survival or greater patterning of the auditory pathways using conventional hearing aids prior to implantation. Conversely, children with the least preoperative residual hearing were less predictable, with some children achieving open-set perception, and others showing more limited closed-set benefits to perception. For these children, it is likely that preoperative residual hearing is of less significance than other factors in outcomes.
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ItemThe importance of different frequency bands to the speech perception of cochlear implantees [Abstract]( 1996)It is well known that cochlear implantees exhibit a wide range of speech perception ability. Understanding the reason for this variability may lead to improved speech processors. This study investigates whether implantees rely on different areas of the speech spectrum for speech cues, compared to normally hearing listeners, and whether poor performers rely on different spectral areas than better performers. Six subjects with the Mini System 22 implant and using the SPEAK strategy participated in this experiment. Scores for monosyllabic words were obtained using the full speech spectrum and with selected frequency bands removed from the subjects’ speech processor maps. The Articulation Index (AI) is a measure of the proportion of speech information available to a listener, and the relative contribution to AI from different frequency bands is termed the Importance Function. The five frequency bands studied in this experiment were determined to be of equal importance to normally hearing listeners for the speech material used. The scores for each implantee were transformed into AI values, and hence the relative importance of the bands was determined. This relative importance was compared between the implantee group and normally hearing listeners to determine the way in which speech perception by electrical stimulation varies from that by acoustical stimulation. Comparisons were also made between individual implantees to determine whether correlations exist between their speech perception ability and their use of cues in different parts of the spectrum. Further research will determine whether the differences among implantees are correlated with their ability to perceive changes in stimulation place or temporal characteristics.
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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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ItemPreoperative residual hearing as a predictor of postoperative speech scores for adult cochlear implant users [Abstract]( 1994)The development of multiple channel cochlear implants has been a significant advance in the rehabilitation of profound hearing loss. Speech perception benefits have been particularly evident for postlinguistically deafened adults, who as a group have shown not only supplementation of lipreading scores but also significant comprehension of words and sentences using an implant alone, without the aid of lipreading. In many cases, patients are able to use their implant for telephone conversation. Speech perception benefits for adult users have increased with advances in speech processing and improved means of habilitation. These improvements in open-set speech benefits for adult users have resulted in a steady increase in group mean scores and a reevaluation of selection criteria for cochlear implantation. In the initial development of cochlear implants, only those with little or no residual hearing were considered as candidates. Current selection criteria now include those with substantial residual hearing, who may score up to 40% in the best-aided condition on word and sentence speech perception tests. In order to provide realistic expectations for prospective cochlear implant patients, it is important to establish the relationship of many preimplant factors to postimplant speech perception benefits. For severely hearing impaired adults, the relationship between preoperative residual hearing, as measured by aided word and sentence speech perception test scores, and postoperative speech perception benefits is of significant interest. Analysis of data collected over a 15 year period for adult patients is presented. The rationale for conducting full speech perception assessments for all potential cochlear implant patients is stressed.
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ItemA clinical report on vocabulary skills in cochlear implant users [Abstract]( 1994)Receptive vocabulary results are reported for 32 children, adolescents and prelinguistically deafened adults implanted with the 22-electrode cochlear implant at the Melbourne Cochlear Implant Clinic. Age at implantation ranged from 2 years, 6 months to 20 years and implant use ranged from 1 year to 7 years, 8 months. There were significant gains from pre- to postoperative assessments on the Peabody Picture Vocabulary Test (PPVT) for the majority of subjects. Rates of improvement found are compatible with previous reports on smaller numbers of implant users, but cannot be attributable unambiguously to use of the implant. The group postoperative performance was significantly higher than mean preoperative performance (n =25). The relationship of variables such as duration of implant use, duration of profound deafness and speech perception ability to improvement on the PPVT is discussed. Expressive vocabulary results on the Renfrew Word Finding Vocabulary Scale are reported for 11 of the subjects. Less substantial gains were made on this measure.
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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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ItemThe Tickle Talker: a speech perception aid for profoundly hearing impaired children [Abstract]( 1990)Fifteen prelingually profoundly hearing-impaired children participated in speech perception training and evaluation, to assess potential benefits from use of the Tickle Talker. This device, a multichannel electrotactile speech processor, developed by Cochlear Pty. Ltd. and the University of Melbourne, presents speech as a pattern of electrical sensations felt on the fingers. The eight small electrodes are located over the digital nerve bundles, on both sides of the four fingers of the non-dominant hand. Speech processing hardware is similar to that used in the 22-channel cochlear implant. In the encoding strategy, second formant frequency (F2) is presented as electrode position, speech waveform amplitude as stimulus strength, and fundamental frequency (FO) as rate of stimulation. Each child participated in an ongoing training program involving clinicians, teachers and parents. The evaluation program included measures of sound and speech detection thresholds, and discrimination of speech features, words and open-set sentences. Both individual and mean scores for all the children demonstrate significant improvements in speech perception scores when input from the Tickle Talker is combined with either aided-residual hearing, or aided residual hearing and lipreading. These results are consistent with those previously reported for profoundly hearing-impaired adults using the Tickle Talker, and indicate that children are able to integrate speech information provided through the tactual modality with information from vision or residual hearing.
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ItemSpeech feature recognition by profoundly deaf children using the University of Melbourne multichannel electrotactile aid [Abstract]( 1989)Abstract not available due to copyright.