Graeme Clark Collection

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Author: COHEN, LAWRENCE × End date: 1999 × Start date: 1991 × Subject: otolaryngology × Subject: safety studies ×

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    Steady state evoked potentials: a new tool for the accurate assessment of hearing in cochlear implant candidates
    Rance, G. ; Rickards, F. W. ; Cohen, L. T. ; Burton, M. J. ; Clark, Graeme M. ( 1993)
    Precise determination of residual hearing in prospective cochlear implant candidates is essential. As the minimum age of implantation for young children has reduced, the use of objective measures of hearing has become more important. At the University of Melbourne Cochlear Implant Clinic, steady state evoked potential (SSEP) assessments are routinely carried out on all candidates under the age of 5 years using a microcomputer and custom-designed hardware in the manner described by Cohen et al. [1].
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    Development of safe and effective electrodes: a risk management approach [Abstract]
    Clark, Graeme M. ; COWAN, ROBERT ; Saunders, Elaine ; TYKOCINSKI, MICHAEL ; Cohen, Lawrence ; Treaba, Claudiu ; Briggs, Robert S. ; GIBSON, PETER ( 1999)
    Results from studies on experimental animals, computer modelling and preliminary psychophysical studies with three patients, have confirmed the potential for subjective improvement with electrode arrays which lie closer to the modiolus than does the Nucleus straight array. Results of psychophysical studies with three cochlear implant patients, using developmental pre-curved arrays, confirm the feasibility of improving patients' performance through improvements in electrode design. In particular, it was found in psychophysical tests, with patients using a developmental pre-curved electrode array, that both maximum comfortable level and threshold reduced with decreasing distance of a stimulated electrode from the modiolus, and that the dynamic range increased. More intense neural excitation patterns were obtained with the closer electrodes. From this it is inferred that the development of more sophisticated electrode arrays, positioned closer to the modiolus than is currently the case with the Nucleus standard array, will enable the development of improved speech processing strategies. There are technical constraints in the design of a peri-modiolar array, and currently a number of approaches to this problem have been investigated. Whilst the goal of the design is that it be effective for sophisticated and variable manners of stimulus delivery, a primary constraint is safety.
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    Benefits of pre-curved electrode arrays for the Nucleus multichannel cochlear implant [Abstract]
    Pyman, B. ; Clark, Graeme M. ; Saunders, Elaine ; Cohen, Lawrence T. ; Cowan, Robert S. C. ; Treaba, C. ; Dahm, M. ; Tykocinski, M. ( 1998)
    The purpose of the study was to evaluate whether placement of an electrode closer to the modiolus would provide a more efficient interface with the auditory nerve. A pre-curved, banded 22-electrode array has been developed. Following comprehensive safety studies, the array was inserted in three adult patients. Detailed x-ray analyses have been conducted to specify the positions of the electrode bands. Psychophysical studies have been conducted, within each subject, using electrodes which lie at differing distances from the modiolus. These studies have shown that as the distance from the modiolus decreased, electrode threshold currents decreased and dynamic ranges increased. Thresholds were lower than in a comparison group of standard array users. Forward masking studies showed current spread to be more focused at the electrodes lying closer to the modiolus. Electrode discrimination was also better at electrodes closer to the modiolus. JND for loudness, expressed as a function of dynamic range also decreased in this condition. Thus, a preliminary profile of the parameters of interest, for an improved implant design, suggest that an array which lies closer to the modiolus can result in lower current requirements and a more localised pattern of neural excitation.
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    Steady state evoked potentials: an objective measure of residual hearing in young cochlear implant candidates [Abstract]
    Rance, G. ; Rickards, F. W. ; Cohen, L. T. ; Marsh, M. ; Cousins, V. ; Clark, Graeme M. ( 1993)
    Precise determination of hearing thresholds in prospective cochlear implant candidates is essential. As the minimum age of implantation for youl1g children has been reduced, the use of objective measures of hearing has become an important part of their pre-operative evaluation. Steady-state evoked potentials are scalp potentials elicited in response to sinusoidally amplitude and/or frequency modulated tones. A system has been developed at The University of Melbourne which allows the presence: of such a response to be detected automatically thus permitting an objective. frequency specific estimate of hearing to be made in sleeping or awake subjects. This paper investigates the use of SSEPs in determining hearing thresholds in young profoundly deaf children. Responses in such patients are compared with those: obtained in neonates, and a group of sleeping adult subjects with varying degrees of sensori-neural hearing loss. Results indicate that the SSE? procedure is well suited as a measure assessing residual hearing in profoundly deaf children suitable for a cochlear implant in that it can provide an accurate estimate of auditory thresholds using frequency specific stimuli presented at high levels.