Graeme Clark Collection
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ItemContributing factors to improved speech perception in children using the nucleus 22-channel cochlear prosthesis( 1997)It has been established that use of multiple-channel intracochlear implants can significantly improve speech perception for postlinguistically deafened adults. In the development of the Nucleus 22-channel cochlear implant, there have been significant developments in speech processing strategies, providing additional benefits to speech perception for users. This has recently culminated in the release of the Speak speech processing strategy, developed from research at the University of Melbourne. The Speak strategy employs 20 programmable bandpass filters which are scanned at an adaptive rate, with the largest outputs of these filters presented to up to ten stimulation channels along the electrode array. Comparative studies of the Speak processing strategy (in the Nucleus Spectra-22 speech processor), with the previously-used Multipeak (Multipeak) speech processing strategy (in the Minisystem-22 speech processor), with profoundly deaf adult cochlear implant users have shown that the Speak processing strategy provides a significant benefit to adult users both in quiet situations and particularly in the presence of background noise. Since the first implantation of the Nucleus device in a profoundly hearing-impaired child in Melbourne in 1985, there has been a rapid growth in the number of children using this device. Studies of cochlear implant benefits for children using the Nucleus 22-channel cochlear implant have also shown that children can obtain significant benefits to speech perception, speech production and language, including open-set understanding of words and sentences using the cochlear implant alone. In evaluating contributing factors to speech perception benefits available for children, four specific factors are important to investigate: (1) earlier implantation -resulting from earlier detection of deafness; (2) improved hardware and surgical techniques -allowing implantation in infants; (3) improved speech processing, and (4) improved habilitation techniques. Results reported previously have been recorded primarily for children using the Multipeak strategy implemented in the MSP speech processor. While it is important to evaluate the factors which might contribute to improvements in speech perception benefits, an important question is the effect of improved speech processing strategy, since this will determine what is perceived through the device. Given that adult patients changing to the Spectra speech processor had also shown improved perception in noisy situations, and the fact that children are in general in noisy environments in the classroom setting for a large proportion of their day, it was of obvious interest to evaluate the potential for benefit in poor signal-to-noise ratios from use of the Speak processing strategy and from specific training in the ability to perceive in background noise. The study was aimed at evaluating whether children who were experienced in use of the Multipeak speech processing strategy would be able to changeover to the new Speak processing strategy, which provides a subjectively different output. Secondly, the study aimed to evaluate the benefits which might accrue to children from use of controlled habilitation in background noise.
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ItemIs age at cochlear implantation in children important? A 2-deoxyglucose study in cats.( 1997)Should one implant prelinguistically deaf children at the earliest possible age or is it better to wait a couple of years? In normally hearing kittens functional auditory development is completed, up to the level of the inferior colliculus (IC), by 30 days after birth (DAB) [1]. However, in deaf kittens stimulation with a cochlear implant can alter the IC map even at ages up to 120 DAB [2]. In normally hearing children the auditory brainstem response approximates the adult form by the age of 2 years. Studies of deaf children with cochlear implants have indicated that implantation by the age of 5-6 yields a high success rate. We implanted neonatally deafened kittens at different ages, stimulated them for long periods, then looked at the spread of 2-deoxyglucose (2-DG) in the IC. If age is a factor in plasticity in deaf cats, then the distribution of 2-DG uptake should vary with age at implantation.
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ItemTraining place pitch perception in cochlear implant users [Abstract]( 1997)The study has aimed at determining whether the ability to use place coded vowel formant information could be enhanced with analytical vowel training in a group of -congenitally deafened patients, who showed limited speech perception skills after cochlear implant experience ranging from 1y8m to 6y11m. It has investigated whether improvements in vowel perception after training can carry over to word recognition. A further objective was to see whether poorer vowel perception was associated with poorer electrode position difference limens. Three children, one adolescent and one young adult were assessed with synthesized versions of the words /hid, head, had, hud, hod, hood/ and a natural version of these words as well as with a closed-set monosyllabic word task. The change in performance after 10 training sessions was compared to the change in performance during a non-training period. Four of the five patients showed a significant gain in synthetic vowel perception post-training on at least one assessment, but only two patients showed gains across a number of tests post-training. For one of these 2 children improvements in vowel perception generalized to word perception. Patients’ electrode limens ranged from 1 to 3 electrodes except for 1 adolescent whose minimal progress post-training could be partly explained by poorer apical electrode discrimination. The findings are discussed with reference to a number of factors, including the notion of a "critical period" for neural plasticity.
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ItemChanges in synthetic and natural vowel perception after specific training for congenitally deafened patients using a multichannel cochlear implant( 1997)Objective: The aim was to determine whether the ability to use place-coded vowel formant information could be improved after training in a group of congenitally deafened patients, who showed limited speech perception ability after cochlear implant use ranging from 1 yr 8 mo to 6 yr 11 mo. A further aim was to investigate the relationship between electrode position difference limens and vowel recognition. Design: Three children, one adolescent, and one young adult were assessed with synthesized versions of the words /hid, head, had, hud, hod, hood/ containing three formants and with a natural version of these words as well as with a 12-alternative, closed-set task containing monosyllabic words. The change in performance during a nontraining period was compared to the change in performance after 10 training sessions. Results: After training, two children showed significant gains on a number of tests and improvements were consistent with their electrode discrimination ability. Difference limens ranged from one to three electrodes for these patients as well as for two other patients who showed minimal to no improvements. The minimal gains shown by the final patient could be partly explained by poorer apical electrode position difference limen. Conclusions: Significant gains in vowel perception occurred post-training on several assessments for two of the children. This suggests the need for children to continue to have aural rehabilitation for a substantial period after implantation. Minimal improvements, however, occurred for the remaining patients. With the exception of one patient, their poorer performance was not associated with poorer electrode discrimination.
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ItemSpeech perception results for children with implants with different levels of preoperative residual hearing( 1997)Objective: Many reports have established that hearing-impaired children using the Nucleus 22 channel cochlear implant may show both significant benefits to lipreading and significant scores on open-set words and sentences using electrical stimulation only. These findings have raised questions about whether severely or severely-to-profoundly deaf children should be candidates for cochlear implants. To study this question, postoperative results for implanted children with different levels of preoperative residual hearing were evaluated in terms of speech perception benefits. Study Design/Setting: A retrospective study of the first 117 children, sequentially, to undergo implantation in the Melbourne and Sydney Cochlear Implant Clinics was undertaken. All children had been assessed by and received their implants in a tertiary referral centre. Main Outcome Measures: To assess aided residual hearing, the children were grouped into four categories of hearing on the basis of their aided residual hearing thresholds measured preoperatively. To assess benefits, the scores of children on standard speech perception tests were reviewed. As different tests were used for children with different ages and language skills, children were grouped into categories according to the level of postoperative speech perception benefit. Results: The results showed that children in the higher categories of aided preoperative residual hearing showed significant scores on open-set word and sentence perception tests using the implant alone. For children in lower categories of aided residual hearing, results were variable within the groups. More than 90% of children with implants with aided residual hearing thresholds in the speech range above I kHz achieved open-set understanding of words and sentences. Conclusion: While the results of this preliminary study confirm previous findings of differential outcomes for children with different levels of preoperative residual hearing, they suggest that children with severe to profound hearing impairments should be considered for cochlear implantation.
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ItemSurgery(Singular Publishing, 1997)Cochlear implant surgery should be undertaken only after the cochlear implant team has established that the child is not achieving useful communication with a hearing aid. This can be difficult because of poor language development in deaf children in this age group or because the child is at a preverbal stage and too young for the use of formal assessment tests. The child's unaided and aided thresholds, however, are important for assessment, as are his or her communication skills. These need to be evaluated by an experienced paediatric audiologist.
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ItemPreoperative medical evaluation(Singular Publishing, 1997)The aim of the medical assessment of infants and children is to determine the cause, severity and duration of any hearing loss as well as the presence of any medical conditions that may influence their management with a cochlear implant. There should also be an initial assessment of the child's communication skills and the parental expectations for his or her education.
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ItemIntroduction(Singular Publishing, 1997)From the time single-channel cochlear implants were first implanted in children in the early 1980s in Los Angeles (Laxford et al 1987) closely followed in 1985 by the multiple-channel cochlear implant in Melbourne (Clark et al 1987a, 1987b) there has been a considerable expansion in the work to apply the multiple-channel cochlear implant to infants and young children.
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ItemCochlear implants in adults and children: comment( 1997)This is a well-written review of the NIH Consensus report on cochlear implants for adults and children.
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ItemPitch and loudness estimation for single and multiple pulse per period electric pulse rates by cochlear implant patients( 1997)Abstract not available due to copyright.