Graeme Clark Collection
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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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ItemBiological safety(Singular Publishing, 1997)Biological safety has been extensively studied at the Department of Otolaryngology, The University of Melbourne, for cochlear implantation in adults, and subsequently for specific issues in infants and young children. Many of the studies have general applicability to cochlear implantation, but some have specific relevance to the Nucleus (Cochlear Limited) multiple-channel cochlear implant systems, and have been fundamental to their approval by the U.S. Food and Drug Administration (FDA). The Nucleus system was first approved by the FDA as safe and effective for postlinguistically deaf adults in October 1985, and 5 years later, on 27 June 1990, was approved for use in children from 2 years of age and older. The general research questions studied for adults are directly relevant for children and infants, but there are also specific questions that need to be answered when operating on children under 2 years of age.
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ItemResults for children and adolescents using the multichannel cochlear prosthesis [Abstract]( 1992)The first adolescent to use the 22-electrode cochlear prosthesis was Implanted In Melbourne in 1985 and the first child (less than 10 years), the following year. Since then, over 100 children have received the cochlear prosthesis in Australia and over 1200 worldwide. Detailed assessment of 200 children in the U.S.A., Australia and Germany lead to the market approval of the prosthesis by the U.S. Food and Drug Administration in July 1990. The analysis of results for these children has proven to be difficult due to the use of different tests in different places, the lack of appropriate assessment tools for young children, the wide range of performance, and the problems of cooperation for young children. Despite these problems, some trends are beginning to emerge in the speech perception results for implanted children. Children with a greater amount of auditory experience before becoming profoundly deaf tend to perform better, as do children with more experience with the cochlear prosthesis. Those with a greater number of electrodes in use also perform better, a result supported by adult studies. Although older prelinguistically deafened children do not perform as well as postlinguistically deafened adults, there appears to be little difference between results for pre-and post-linguistically deafened young children. These trends In speech perception results will be discussed in more detail.
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ItemCochlear implantation for children: an update [Abstract]( 1992)The performance of the Nucleus 22 channel cochlear implant has been assessed on 142 English speaking children who have worn their device for at least 12 months. The safety of the device has been evaluated on 309 children. A significant improvement for prosody was observed in 66%, for closed-set words in 63% and open-set words in 46%, using electrical stimulation alone. Performance over time increased, especially for open-set speech tests. Prelinguistically deaf children had similar scores to postlinguistically deaf children from prosody and closed-set word tests, but scores were not as good for open-set word tests. Lipreading enhancement was assessed using the CID sentence test, and the mean lipreading-alone score of 51% increased significantly to 71% when lipreading was combined with electrical stimulation. Speech intelligibility was determined with McGarr material and 63% were significantly more intelligible after 12 months' implant experience. There were 6-8% medical/surgical complications compared to 12% for a comparable group of adults. In 2.6% surgical intervention was required and this was primarily for infection or necrosis of the flap.
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ItemThe development of the Melbourne/Cochlear multiple-channel cochlear implant for profoundly deaf children( 1992)In 1978-79, a speech processing strategy which extracted the voicing (FO) and second formant (F2) frequencies and presented these as rate and place of stimulation respectively to residual auditory nerve fibres was developed for the University of Melbourne's prototype multiple-channel receiver-stimulator (Clark et aI1977, Clark et a11978, Tong et aI1980). This speech processing strategy was shown to provide post linguistically deaf adults with some open-set speech comprehension using electrical stimulation alone, and considerable help when used in combination with lipreading (Clark et al 1981).
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ItemSpeech perception, production and language results in a group of children using the 22-electrode cochlear implant( 1992)Five children out of a group of nine (aged 5.5 to 19.9 years) implanted with the 22-electrode cochlear implant (Cochlear Ply. Ltd.) have achieved substantial scores on open-set speech tests using hearing without lipreading. Phoneme scores for monosyllabic words ranged from 40% to 72%. Word scores in sentences ranged from 26% to 74%. Four of these five children were implanted during preadolescence. The fifth child, who had a progressive loss and was implanted during adolescence after a short period of very profound deafness, scored highest on all speech perception tests. The remaining four children who did not demonstrate open-set recognition were implanted during adolescence after a long duration of profound deafness. Post-operative performance on closed-set speech perception tests was better than pre-operative performance for all children. Improvements in speech and language assessments were also noted. These improvements tended to be greater for the younger children. The results are discussed with reference to variables which may contribute to successful implant use: such as age at onset, duration of profound hearing loss, age at implantation, aetiology, educational program, and the type of training provided.
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ItemEvaluation of expandable leadwires for paediatric cochlear implants( 1993)The development of cochlear implants for use in very young children (1-2 years old) will require techniques designed to accommodate temporal bone growth. Previous anatomic studies have shown that the leadwire of a cochlear implant must be capable of expanding up to 20 mm between the round window and the implanted receiver-stimulator in response to skull growth. In the present study morphologic and biomechanical evaluation of five expandable leadwire designs was conducted following their implantation in young cats. Two helical shaped leadwire designs frequently exhibited extensive fibrous tissue adhesions and broke during long-term implantation. In contrast, thin, flexible Silastic envelopes were effective in minimizing tissue adhesions. Residual V- and Z-shaped leadwires, placed in these envelopes, showed little evidence of fibrous tissue adhesions following implantation periods of up to 2 years. Moreover, these leadwires readily expanded both during the growth of the animal and when biomechanical expansion studies performed at the completion of the implant period. These expandable leadwire designs appear to be appropriate candidates for use in pediatric cochlear implants.
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ItemPaediatric cochlear implantation: radiologic observations of skull growth( 1993)We investigated the effects of long-term implantation of auditory prostheses on skull growth in young animals. Four monkeys were implanted with dummy cochlear implants at 6 months of age. To simulate implantation in children, the bed for the receiver-stimulator or interconnecting plug was drilled across a calvarial suture down to the underlying dura. Plain skull oentgenograms were periodically taken to monitor head growth for up to 3 years after implantation. These longitudinal measurements revealed no significant asymmetric skull growth. Postmortem measurements using computed tomographic scans confirmed these results and showed no significant difference in the intracranial volumes between the implanted and control sides of each animal or between experimental and nonimplanted control monkeys. These results suggest that long-term cochlear implantation in very young children will not cause any significant deformity of the skull.
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ItemThe postnatal growth of the temporal bone and its implications for cochlear implantation in children( 1993)The postnatal growth of the human temporal bone was examined by direct anatomical measurements on 60 cadaver specimens of all ages. The bones were dissected as one would perform cochlear implant surgery using a posterior tympanotomy approach. Nineteen anatomical /surgical landmarks with implications for cochlear implant surgery were identified on each bone and the distance between these points measured. The temporal hone was found to be a complex structure, phylogenetically, anatomically and functionally consisting of four different parts with independent postnatal development. The inner and middle cars were adult size at birth. The external auditory canal and most parts of the temporal hone were subject to significant lateral growth. The size of the pneumatised mastoid increased in all directions. In the facial recess, however, no postnatal growth was observed. Between birth and adulthood an average of 12 mm (SD 5 mm) of growth was seen directly between the sino-dural angle and the round window, the landmarks approximating the Implantation site for the receiver-stimulator and the electrode entry point into the inner car. However, if an electrode leadwire is fixed at a cortical fixation site such as the posterosuperior point of Macewen's triangle, the leadwire would be subject to approximately 20 mm of growth. These results indicate that a paediatric cochlear implant design incorporating an expandable leadwire to accommodate this growth should allow up to 25 mm of leadwire lengthening. The fossa incudis showed no growth relative to the round window and was found to be a convenient fixation site for the electrode array close to the cochlea. From an anatomical and surgical point of view, cochlear implantation in very young children is feasible, provided the electrode array is secured and the design accommodates for controlled leadwire lengthening.