Graeme Clark Collection
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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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ItemAuditory processing abilities in children using cochlear implants: their relevance to speech perception [Abstract]( 1999)This study aimed to investigate the relationships between some basic auditory processing skills, subject variables and speech perception ability in young children using cochlear implants. A modification of the play audiometry procedure was used to measure electrode discrimination and "rate-of-processing" ability in seventeen 4-10 year old children. In the electrode discrimination task, children responded with a game-like motor response when a repeating stimulation on a reference electrode "changed" to a different electrode. In the "rate-of processing" task, children had to respond to the "change" to a different electrode, when the duration of the stimuli and the time interval between the stimuli were decreased. Normally hearing children were assessed on this task with acoustic stimulation. Nonverbal intelligence, speech feature discrimination and closed-set word recognition were also measured in the children using implants.
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ItemThe use of click-ABR and steady state evoked potentials for hearing assessment in young cochlear implant candidates [Abstract]( 1997)The accurate assessment of hearing thresholds in prospective cochlear implant candidates is essential. As the minimum age of implantation has reduced, audiologists have been faced with the complicated task of obtaining precise audiometric information in children whose immaturity may severely restrict the assessment process. Clearly for these young candidates, there is a place for a reliable, objective measure of residual hearing in the pre-operative test battery. This paper examines the degree of accuracy with which the click-ABR and the steady-state evoked potential (SSEP) techniques can provide estimates of hearing level in subjects with several profound hearing loss.
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ItemTowards a SSEP hearing screening test for neonates [Abstracts]( 1997)Newborn hearing screening tests utilizing evoked otoacoustic emissions (EOAEs) and/or the auditory brainstem response (ABR) recording have been recommended by the NIH(1993). The University of Melbourne experience with steady-state evoked potentials (SSEPs) in newborns suggests that they too, have potential as a screening tool (Rickards et al, 1984). In the present study, SSEPs were recorded from neonates in a pilot study of how the technology may be applied to newborn hearing screening. Eighty-eight neonates were tested using transient-and distortion product EOAEs, ABRs and SSEPs. Only those infants who had TEOAEs, DPOAEs, and ABRs that met a rigid and objective "pass" criteria were included in the study. SSEPs were evoked by amplitude modulated tones using carrier frequencies at 500, 1000, 2000, and 4000 HZ, and modulation frequencies between 75 and 95 Hz presented at levels between 40 and 80 dB SPL. Out of 324 individual SSEP tests, 12% were no-stimulus control trials. Phase-coherence statistics were used to determine when a significant or "passing" result had been obtained. Preliminary results show that a 94% pass rate is achieved for a CF of 2 KHZ, presented at 60 dB SPL, but that pass rates are lower (79% to 89%) for 500, 1KHz and 4KHZ CF's at the same stimulus levels. For lower stimulus levels, pass rates do not exceed 80% for any carrier frequency. Phase-coherence estimates were made for 32, 64, ahd 96 samples at each carrier and modulation frequency combination. We will report the phase coherence estimates for each CF, MF and level combination as a function of sample size, in order to suggest a protocol that may be efficient in newborn hearing screening applications.
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ItemExpandable leadwires for a paediatric cochlear implant [Abstract]( 1993)Anatomic studies of skull growth have shown an increase (about 20 mm) in the distance between the round window and the asterion where the receiver-stimulator is usually located. In order to accommodate the skull growth of young patients, an expandable leadwire connecting the receiver-stimulator and the electrode array is necessary. Several expandable leadwires were evaluated in experimental animals, including helical leadwires protected by Silastic tubes and leadwires, with "V" or "W"-shaped levels in a single phase, and protected by thin Silastic or Teflon bags. The leadwires together with their controls were implanted on young animal's scapulae, temporal and parietal bones and in subcutaneous tissue. The in vivo expansion of the leadwire was monitored by periodic x-ray examination and the force to expand the leadwire was measured at the completion of implantation. The results showed that helical leadwires weresurrounded by fibrous tissue and a large force was required to expand them. The V or W-shaped leadwires were able to expand up to 20 mm in vivo and only a moderate force was required to expand them. For most of the cases, there was none or little fibrous tissue in Silastic or Teflon bags. The results indicated that for a paediatric cochlear implant, leadwires with V or W-shaped levels could, expand and biocompatible envelopes could effectively protect the leadwires from being bound by fibrous tissue.
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ItemPaediatric cochlear implant surgery [Abstract]( 1992)The operation in children is similar to that in adults, but special care needs to be taken with the skin flap, the anchoring of the electrode array and the sealing of .the cochleostomy. Research into the effects of head growth and otitis media in an implanted ear indicates that these should not be a problem. Surgical complications are also similar to those in adults, with the most common being related to the skin flap. The major complication rate at 4 % is slightly less than that in adults and most of these get effective implant function.
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ItemPaediatric cochlear implantation: radiological and histopathological studies of skull growth in the monkey( 1993)The human skull undergoes significant growth within the first two years of life (Dahm et aI, 1992). Therefore, before children under two can be considered candidates for cochlear implantation, the effects of the surgical procedure on subsequent skull growth must be well understood. To evaluate the effects of implantation on skull growth four macaque monkeys were implanted with dummy cochlear implants at six months of age. To model the procedure in the very young child, the bed for the receiver-stimulator was drilled across a calvarial suture down to the underlying dura and an electrode array inserted into the scala tympani via a mastoidectomy and posterior,tympanotomy. Plain skull radiographs were perioqical1y taken to monitor skull growth for periods of up to three years following implantation. Their longitudinal measurements revealed no evidence of asymmetrical skull growth when compared with unimplanted control animals. Computer tomographic scans taken at post-mortem confirmed these findings. Finally, subsequent histopathological evaluation of the receiver-stimulator package bed indicated that it becomes obliterated by hard tissue, resulting in a localized flattening of the vault under the receiver-stimulator. However, this tissue exhibited histological evidence of sutures, indicating that the surgical procedure should not lead to premature sutural closure. In conclusion, the present experimental results suggest that long-term cochlear implantation in very young children will not lead to any significant skull deformity.
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ItemThe effect of inflammation on blood vessel area as a cause of variation in ganglion cell density measurements in the cat cochlea [Abstract]( 1992)The success of a cochlear implant depends on an adequate number of surviving spiral ganglion cells. Further loss of ganglion cells may arise from the biology of cochlear implantation itself. The quantitative analysis of ganglion cells is, therefore, an important consideration when assessing the biological safety of a cochlear implant.
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ItemSpeech perception benefits for children using the 22-channel Melbourne/cochlear hearing prosthesis [Abstract]( 1993)In 1985; the first child was implanted with the Cochlear 22-channel cochlear prosthesis at the University of Melbourne Royal Victorian Eye & Ear Hospital Cochlear Implant Clinic. There are now 42 children who have received the device in Melbourne. Analysis of patient details for these children show a very heterogeneous group, with a wide range in age, hearing thresholds, duration of deafness and aetiology. The major aetiologies found were either a congenital profound deafness.; or a hearing loss due to meningitis. In all but 3 cases, the children are using 15 or more electrodes in the array. Speech perception benefits have been analyzed according to a six-level hierarchical classification scheme. All of-the children achieved a minimum benefit of discrimination of suprasegmental information (Category 2), and 59% of the children achieved open-set understanding of unfamiliar speech material without the aid of lip-reading (Categories 5 & 6). Detailed analysis suggests that the majority of children achieving open-set speech perception benefits had more than one year of experience with their implant. and less than seven years of profound deafness prior to implantation.
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ItemFactors associated with open-set speech perception in children using the Cochlear multiple-channel prosthesis [Abstract]( 1993)Since 1985, nearly 100 children have received the 22-channel cochlear prosthesis from the Melbourne and Sydney cochlear implant clinics. These two clinics account for the bulk of casesin Australia, and have similar management philosophies and selection criteria. The patient population represents a variety of etiologies, and ranges in age from 2 - 18 years of age. Bothcongenital and postlinguistic hearing losses are included. In order to assess benefit to speech perception in such a diverse group, the children's results have been tabulated according to a six level hierarchical scale of speech perception achievement. The scale ranges from category I,detection of sound only, to category 6, which includes significant perception scores for open-setwords and sentences. Analysis of the results shows that the majority of the children are achieving open-set speech perception benefits, and that results continue to improve with additional experience with their devices. There are a number of contributing factors to these open-set speech� perception results which have impact both on selection issues and on habilitation with different age ranges �of patients.