Graeme Clark Collection

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Author: Seligman, Peter × End date: 1999 × Start date: 1990 × Type: Conference Item × Subject: cochlear implants ×

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    Electrical stimulus induced changes in excitability of the auditory nerve
    Huang, C. O. ; Shepherd, Robert K. ; Seligman, P. M. ; Clark, Graeme M. ( 1997)
    High rate electrical stimulation of the auditory nerve using stimulus intensities well above the clinical limits can induce a significant reduction in the excitability of the auditory nerve as measured by a decrement in the amplitude of the electrically evoked auditory brainstem response (EABR). Two potential mechanisms may be associated with this stimulus induced reduction in activity: 1) stimulus induced prolonged neuronal hyperactivity; and 2) the generation of adverse electrochemical productions from the electrode surface. The purpose of the present study was to assess the extent to which adverse electrochemical damage contributes to the stimulus induced reduction in auditory nerve excitability. Twenty-six adult guinea pigs anaesthetized with ketamine (40 mg/kg i.p.) and xylazine (4 mglkg i.p.), were bilaterally implanted and unilaterally stimulated for two hours using a stimulus intensity of two or four times EABR threshold. Stimulus rates of 200, 400, or 1000 pulses/s (pps) were delivered via a standard platinum scala tympani electrode or large surface area ("high Q") platinum electrode.
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    Cochlear implants: high rate stimulation studies and the effect of electrode position [Abstract]
    Shepherd, R. K. ; Huang, C. Q. ; Xu, J. ; Tykocinski, M. ; Seligman, P. M. ; Clark, Graeme M. ( 1996)
    This paper summarizes our recent findings investigating the safety of high rate electrical stimulation, and reviews the effects of electrode position on auditory excitability. These studies used charge balanced biphasic pulses and electrode shorting between stimuli to minimize any residual charge or direct current. High rate (400-1000 pulses/s) electrical stimulation of the auditory nerve can result in significant stimulus induced reductions in auditory nerve excitability at stimulus levels well above those used clinically (1). The extent of this reduction was dependent on stimulus rate, intensity and duty cycle, implying that such changes were related to the degree of evoked activity.
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    Latest results and future directions in speech processing for the Nucleus multichannel cochlear prosthesis [Abstract]
    Dowell, R. ; Whitford, L. ; Seligman, P. ; Vandali, A. ; Hollow, R. ; Clark, Graeme M. ( 1995)
    The past two years has seen the introduction of the Speak speech encoding scheme for most patients using the Nucleus 22-channel cochlear prosthesis. This scheme, based on the Spectral Maxima Speech Processor (SMSP) developed at the University of Melbourne, uses a bank of 20 band-pass filters to present detailed spectral information to the intracochlear electrode array. Clinical trials of this speech processor have shown highly significant improvements over the previous Multipeak scheme in English, German, French and Japanese speaking patients. The largest improvements were evident for open-set testing in background noise, which represents a more realistic measure of everyday benefit than testing in quiet. The latest results for adults who have changed from Multipeak to Speak will be presented, along with results over time for newly-implanted patients using the Speak scheme. New research aimed at improving the speech processing in both the spectral and temporal domains will also be discussed.