Graeme Clark Collection
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ItemSpeech perception in implanted children: effects of preoperative residual hearing and speech processing strategy [Abstract]( 1997)Since the first child was implanted with the Nucleus 22-channel cochlear prosthesis in Melbourne in 1985, the number of implanted children world-wide has rapidly expanded. Over this period, more effective paediatric assessment and management procedures have developed, allowing cochlear implants to be offered to children under the age of 2 years. In addition, a succession of improved speech processing strategies have been implemented in the Nucleus implant system, resulting in increased mean speech perception benefits for implanted adults. Research in the Melbourne and Sydney Cochlear Implant Clinics has also demonstrated that young children can adapt to and benefit from improved speech processing strategies such as the Speak strategy. 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 speech perception benefits to improve over time with advances in speech processing. 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 effect of the level 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 8 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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ItemFuture developments in speech processing for multichannel cochlear implants in children [Abstract]( 1992)The average speech perception score for adult implant patients is now about 60% on an open-set sentence test without lipreading. This is higher than the scores obtained by many profound and severe-to-profoundly impaired hearing aid users. This suggests that some hearing aid users, particularly those who use a hearing aid in one ear only, could benefit from a cochlear implant. As neither the implant nor the hearing aid will provide perfect speech recognition it is to be expected that this group should obtain maximum benefit by using the hearing aid in one ear together with the implant in the other ear. However, experience with this group of patients has shown that many people find the use of two independent devices unacceptable. Furthermore, perceptual interaction of the acoustic and electrical signals makes it desirable to be able to control the two outputs in a more co-ordinated way than is possible with two independent devices. Consequently, a "bimodal" speech processor has been developed with both acoustic and electrical outputs controlled from the same speech processing unit. Feature coding aspects of the implant processing have been applied to the acoustic signal in such a way as to enhance speech perception with the hearing aid and improve compatibility with the implant. Initial testing with the bimodal aid shows promise to help severely-to-profoundly impaired individuals. The device has also been useful as a research tool to investigate the complex interactions of simultaneous acoustic and electrical stimulation. The Spectral Maxima Sound Processor (SMSP) has also been developed at the University of Melbourne for use with the Nucleus cochlear implant. Studies with adult subjects have shown improved perception of vowels, consonants, words and sentences in quiet and sentences in background noise with the SMSP as compared with the MSP(MULTIPEAK) which is currently supplied for use with this implant. Results for four subjects showed mean scores for open set sentences at a 10 dB signal-to-noise ratio of 78.7% for the SMSP and 50.0% for the MSP. Mean scores for the same group on open set monosyllabic words in quiet were 57.4% for SMSP and 39.9% for MSP. These results suggest that future improvements in speech perception will be possible for children using the Nucleus cochlear implant.
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ItemFactors affecting speech perceptual performance for children using the 22-electrode cochlear prosthesis [Abstract]( 1992)Speech perception results for all 40 children and adolescents implanted with the. Nucleus 22 electrode cochlear prosthesis in Melbourne (as of February 1, 1992) were used to categorize performance for each child into one of six hierarchical groups: 1: detection of speech including high frequencies 2: discrimination of suprasegmental features of speech in addition to 1,3: discrimination and recognition of .vowel sounds in addition to 1 and 2,.4: discrimination arid recognition of consonant sounds in addition to 1, 2 and 3,5: open set speech. recognition with scores less than 20% for unfamiliar material in addition to 1 to 4,6: open set speech recognition with scores greater than 20% for unfamiliar material in addition to 1 to 5, above.All children demonstrated discrimination of suprasegmentals (level 2) and 58% demonstrated some openset speech recognition (levels 5 and 6). The pattern of results suggested that children who can discriminate segmental features of speech tend to achieve open set speech perception after adequate experience with the prosthesis. The performance level, described above, was used as the dependent variable in a multiple regression analysis to assess the effect of various factors on speech perception performance. The duration of profound hearing impairment and the amount of experience with the prosthesis were shown to contribute significantly to the variance, in performance level. A weaker trend was evident (or recently implanted children which may suggest that those' in oral/aural educational settings progress more rapidly, in terms of speech perception, than those in total communication settings. Age at implantation, cause of deafness, hearing levels prior to implantation, and number of electrodes in use, did not contribute significantly. to the variance in speech perception performance for these children. The results showed that all children with less than seven years of profound hearing impairment and with over one year of experience with the prosthesis have achieved some open-set speech recognition. This is an encouraging result as the trend in clinical application of cochlear prostheses has been towards implanting younger children in recent years. If this sample of hearing-impaired children in Melbourne is representative of the general population, we may expect that most implanted young children will ,develop reasonable speech perception skills after adequate experience and training.
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ItemClinical results for children using the 22-channel cochlear prosthesis [Abstract]( 1991)Twenty five profoundly/totally hearing-impaired children aged between 2 and 18 years have been implanted with the 22-channel cochlear prosthesis (Cochlear Pty. Ltd.) at The University of Melbourne over the last five years. Speech perception, speech production and language development have been monitored for these children both pre- and postoperatively. Results have shown improvements for all children in speech perception, postoperatively. The younger children (< 12 years) and those with an acquired (postlinguistic) profound hearing loss, have demonstrated some open-set speech recognition without visual clues. In general, older children with a prelinguistic profound hearing loss have not attained this level of performance. Improvements in speech production and language have also been demonstrated and tend to occur faster in younger children. Importantly, a number of congenitally deaf young children have shown significant improvements in speech perception, production and language. Important factors in the success of cochlear implants in children appear to be: educational environment - it is vital to have a strong auditory component (i.e. non-signing); careful attention to correct programming and maintenance of the prosthesis; support of family and other professionals.