Graeme Clark Collection
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ItemThe effects of electrode position and stimulus period on the hearing sensations in a multiple-channel cochlear implant patient [Abstract]( 1981)Abstract not available due to copyright.
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ItemPerceptual dissimilarity and discrimination studies using two-electrode stimulation with a multiple-channel cochlear implant patient [Abstract]( 1981)Abstract not available due to copyright.
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ItemPitch and loudness studies on a multiple-channel cochlear implant patient [Abstract]( 1981)Abstract not available due to copyright.
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ItemMeningitis after cochlear implantation: the risk is low, and preventive measures can reduce this further( 2007)Since the 1980s, more than 80 000 people have received cochlear implants worldwide. These implants are designed to enable people who are severely or profoundly deaf to experience sound and speech. Since 1990, implantation has become standard treatment for people who cannot communicate effectively despite well fitted hearing aids. Children who are deaf when they are born can perceive sound and learn to speak if they receive cochlear implants at a young age (ideally under 18 months). The use of cochlear implants has been thought to be safe. But since 2002 the number of patients with meningitis related to cochlear implantation has increased worldwide. Mortality and neurological complications after meningitis are high. We need to investigate the reasons for this and look at measures to reduce them.
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ItemStiffness properties for nucleus standard straight and contour electrode arrays( 2004)Trauma and damage during insertion of electrode arrays into the human cochlea are strongly related to the stiffness of the array. The stiffness properties of electrode arrays, which were determined by three-point flexural bending and buckling tests, are reported in this paper. To date there has been limited publication on mechanical properties of these electrode arrays. Previous studies mainly focused on characterizing the stiffness of the tip of the Nucleus straight array with little emphasis on characterizing the stiffness of its whole length. In this study, stiffnesses of the Nucleus straight and contour electrode arrays have been determined along their length. Young’s modulus of elasticity of the Nucleus straight array has been found to increase from the tip (182 MPa) to the rear end (491 MPa), whereas the stiffness of the contour array is greatest near the tip (480 MPa) and is fairly uniform in the middle and rear sections of the electrode array (380-400 MPa). Buckling experiments have shown that the contour array has much higher critical buckling load (about four times) than the Nucleus straight array. The results from three-point flexural bending and buckling experiments provide significant data for the development of electrode arrays, from which new array designs with improved flexibility can be developed. The results of stiffness properties are also important input for use in finite element models to predict the trajectories during insertion and to help evaluate the effects of different electrode array designs on damage sustained during insertion.
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ItemBionic ears: their development and future advances using neurotrophins and inherently conducting polymers( 2004)The development of the multiple-channel bionic ear for hearing and speech understanding in profoundly deaf people is the result of integrating biological and physical sciences with engineering. It is the first clinically successful restoration of sensory and brain function, and brings electronic technology into a direct functional relationship with human consciousness. It presently transmits essential place and coarse temporal information for the coding of frequency, but the fine temporal and place excitation of groups of nerve fibres is inadequate for high-fidelity sound. This is required for adequate musical appreciation and hearing in noise. Research has demonstrated that nerve growth factors preserve the peripheral processes of the auditory nerves so that an electrode array placed close to these fibres could produce this fine temporal and spatial coding. The nerve growth factors can be incorporated into inherently conducting polymers that are part of the array so the peripheral processes can be preserved at the same time as they arc electrically stimulated.
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ItemThe effect of language ability and residual hearing on speech perception outcomes for older children using multichannel cochlear implants [Abstract]( 2002)Early-deafened teenagers or young adults have shown somewhat disappointing performance with cochlear implants in the past, however, in recent years a proportion of older children have demonstrated excellent speech perception performance. There is a great deal of variability in speech perception performance within this group. It is important to investigate the factors influencing performance so that adolescents and their families can make informed decisions regarding cochlear implant surgery. This study considered a number of possible predictive factors in a group of 25 children implanted in Melbourne between the ages of 8 and 18 years. Subjects completed open set speech perception testing using BKB sentences both pre-and postoperatively, and pre-operative language testing using the Peabody Picture Vocabulary Test. Data were collected regarding the type of hearing loss, age at implant, age at hearing aid fitting, audiometric details, and the pre-and post-operative communication mode. Multivariate analysis suggested that three factors were associated with postoperative speech perception performance. Results were improved for subjects with better pre-operative speech perception, better pre-operative language ability, and when the duration of profound hearing loss was shorter. These three factors accounted for 66% of the variance in this group. The results of this study suggest that children who have useful pre-implant speech perception, and higher age-equivalent scores on language measures, would be expected to do well with a cochlear implant. A shorter duration of profound hearing loss is also advantageous. Mean speech perception scores for the older group were not significantly different from younger children.
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ItemThe effects of post-implant habilitation on long-term outcomes for children using multichannel cochlear implants [Abstract]( 2002)Those working in the cochlear implant field advocate a regular habilitation program for young children receiving implants. Developing auditory skills and the incorporating these into general language development are considered to be key areas for such programs. Investigations of speech perception and language outcomes have demonstrated that the emphasis of spoken language development appears to enhance the results for implanted children. It remains difficult, however, to demonstrate the effect of habilitation as a separate factor and to determine how much individual attention is desirable for each child. This preliminary study considered the long term speech perception and language outcomes for two groups of children who received Nucleus cochlear implants in Melbourne. The first group (n = 17) was identified as receiving regular habilitation from the Melbourne Cochlear Implant Clinic over a four year post-operative period. A second group (n = 11) was identified as receiving very little regular habilitation over the post-operative period. Language and speech perception results for these two groups showed significant differences in performance on a wide range of measures. The group who received regular, formal habilitation demonstrated better performance on all measures. These groups included only congenitally, profoundly hearing- impaired children and did not differ significantly on mean age at implant or experience at the time of assessment. A more comprehensive study is needed to clarify these results on a larger group of children, and to control for additional confounding variables. Nonetheless, these results provide support for the incorporation of regular long-term habilitation into cochlear implant programs for children.
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ItemPredicting speech perception results for children using multichannel cochlear implants [Abstract]( 2002)It is most helpful in counselling families considering cochlear implantation to have some ability to predict outcomes for individual hearing-impaired children. Speech perception results for open-set words and sentences have been collected for all children implanted with the Nucleus device in Melbourne. Assessments are available at approximately six month intervals following implantation, Data was collected for each child regarding type of hearing loss, duration and age at onset of profound hearing loss, age at implantation, pre and post-implant communication mode, developmental delay, speech coding scheme and implant experience. These data were used as predictor variables in step-wise multiple linear regression analyses with the speech perception scores as the dependent variables. Shorter duration of profound hearing loss, later onset of profound hearing loss, exclusively oral communication mode following implantation, and longer implant experience were associated with significantly (p < 0.00 I) improved open-set speech perception. The use of the SPEAK signal coding scheme was shown to provide significantly better speech perception performance for children (p < 0.00 I). Developmental delay was associated with poorer speech perception outcomes (p < 0.0 I). Over 50% of the variance in speech perception scores was accounted for by these variables. The study suggests that younger implantation for congenitally deaf children leads to improved speech perception results. On the other hand, the development of auditory language skills in implanted children may be as important as age at implantation in enhancing long term outcomes. Regression equations derived from these results can be used to predict outcomes for cochlear implant candidates with a reasonable accuracy.
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ItemCochlear implants: a personal scientific journey [Abstract]( 2002)Electrical stimulation of the auditory system to reproduce hearing commenced through academic curiosity, and the hope of helping deaf people. It received direction from neurophysiology, and later psychophysics and speech science. In the 1960s and 1970s there were many questions requiring answers before cochlear implants could become a practical reality. Key concerns were: (1) the cochlea was too complex for electrical stimulation to reproduce the coding of sound; (2) multiple electrodes inserted into the cochlea for the place coding of frequency could damage the auditory nerves to be stimulated; (3) speech was too complex to be reproduced by electrical stimulation; and (4) children born deaf would not develop the appropriate neural connectivity for speech understanding. The first questions were addressed on the experimental animal. Speech research on patients was only possible with the advent of silicon chip technology allowing the development of an implantable receiver-stimulator package. Initial research established proof of principle that connected discourse was possible with multiple electrode stimulation of the auditory nerve in severely and profoundly deaf people. The research has been developed industrially for the benefits to be provided on a widespread basis through clinics worldwide. Further research has resulted in continuing improvements so that the average profoundly deaf person can hear as well as someone with severe hearing loss using a hearing aid. There is still much research required to achieve high fidelity sound, hearing in noise, and totally implantable devices.