Graeme Clark Collection

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Start date: 2000 × End date: 2009 × Subject: otology × Type: Conference Item ×

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    Improved sound processing for cochlear implants
    James, C.J. ; Just, Y. ; Knight, M.R. ; Martin, L.F.A. ; McKay, C.M. ; Plant, K.L. ; Tari, S. ; Vandali, A.E. ; Clark, Graeme M. ; Cowan, R.S.C. ; McDermott, H. J. ; Blamey, P. J. ; Dawson, P. ; Fearn, R. A. ; Grayden, D. B. ; Henshall, K. R. ( 2002)
    Four signal processing schemes currently under development aim to improve the perception of sounds/ especially speech, for children and adults using the Nucleus cochlear implant system. The schemes are (1) fast-acting input-signal compression, (2) Adaptive Dynamic Range Optimisation (ADRO), (3) TESM, a scheme that emphasises transients in signals, and (4) DRSP, a strategy that applies different stimulation rates to selected sets of electrodes.
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    Brainstem encoding of short voice onset times in natural speech
    Clarey, J. C. ; Paolini, A. G. ; Clark, Graeme M. ( 2001)
    An auditory nerve study has shown that short voice onset times (VOTs) in synthetic consonant-vowel syllables are not accurately encoded by the fibres' discharge rate. We have re-examined this issue within the ventral Cochlear nucleus (VCN), using natural speech and a fine-grain analysis of single unit responses. We recorded extracellularly from 93 VCN neurons in rats anaesthetised with urethane (2.5 g/kg ip). After identifying a cell's response type and best frequency (BF), 3 syllables spoken by a male were presented at double rate and 3 intensities (/bεt/, /dεt/, and /gεt/, at 45, 65, and 75 dB SPL). These three syllables differ in their VOTs (the interval between consonant release and the onset of glottal pulses associated with voicing) due to the different points of articulation of the three initial stop consonants. In many neurons (particularly onset cells), these syllables evoked a clear response to consonant release, followed by an interval of inactivity or reduced activity before the periodic response to the vowel's voicing frequency commenced. This interval of reduced or no activity corresponded to a given syllable's VOT. The responses of all cells (BFs: 0.9-19 kHz) to the 9 different syllable-SPL combinations were plotted as Grand Average post-stimulus time histograms. In 8/9 combinations, syllable onset was associated with a statistically significant peak in activity and the next significant peak in discharge rate occurred at the time of voice onset (± I ms). These results indicate that the prominent responses to consonant release and voice onset, produced by the synchronous firing of neurons with a wide range of BFs, accurately encode short VOTs.
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    How much residual hearing is too much?
    Cowan, R. S. C. ; Dowell, R. C. ; Psarros, C. ; Dettman, S. J. ; Rance, G. ; Clark, Graeme M. ( 2000)
    The value of cochlear implants as an established clinical option for profoundly hearing-impaired adults and children has been supported by significant research results over a number of years (U.S. National Institutes of Health Consensus Statement 1995). As a direct consequence of the level of benefits shown for cochlear implant users on measures of speech perception, research has focused on investigating whether severely hearing impaired adults and children would be suitable candidates for cochlear implantation. I n considering the candidature of any individual, both medical and audiological suitability are investigated. The primary concern is to establish to what degree the patient would benefit from use of the cochlear implant.