Graeme Clark Collection

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http://hdl.handle.net/11343/375

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End date: 1999 × Start date: 1990 × Subject: auditory nerve × Subject: cochlear implants × Subject: electrical stimulation ×

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Now showing 1 - 4 of 4
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    Research advances for cochlear implants
    Clark, Graeme M. ( 1998)
    Abstract not available due to copyright.
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    Control strategies for neurons modeled by self-exciting point processes
    Irlicht, L. S. ; Clark, Graeme M. ( 1996)
    Abstract not available due to copyright.
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    Electrical stimulation of the auditory nerve: the coding of frequency, the perception of pitch and the development of cochlear implant speech processing strategies for profoundly deaf people
    Clark, Graeme M. ( 1996)
    1. The development of speech processing strategies for multiple-channel cochlear implants has depended on encoding sound frequencies and intensities as temporal and spatial patterns of electrical stimulation of the auditory nerve fibres so that speech information of most importance for intelligibility could be transmitted. 2. Initial physiological studies showed that rate encoding of electrical stimulation above 200 pulses/s could not reproduce the normal response patterns in auditory neurons for acoustic stimulation in the speech frequency range above 200 Hz and suggested that place coding was appropriate for the higher frequencies. 3. Rate difference limens in the experimental animal were only similar to those for sound up to 200 Hz. 4. Rate difference limens in implant patients were similar to those obtained in the experimental animal. 5. Satisfactory rate discrimination could be made for durations of 50 and 100 ms, but not 25 ms. This made rate suitable for encoding longer duration suprasegmental speech information, but not segmental information, such as consonants. The rate of stimulation could also be perceived as pitch, discriminated at different electrode sites along the cochlea and discriminated for stimuli across electrodes. 6. Place pitch could be scaled according to the site of stimulation in the cochlea so that a frequency scale was preserved and it also had a different quality from rate pitch and was described as tonality. Place pitch could also be discriminated for the shorter durations (25 ms) required for identifying consonants. 8. As additional speech frequencies have been encoded as place of stimulation, the mean speech perception scores have continued to increase and are now better than the average scores that severely-profoundly deaf adults and children with some residual hearing obtain with a hearing aid.
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    Psychophysics of electrical stimulation of the auditory nerve: implications for coding of sound and speech processing for cochlear implants [Keynote address]
    Clark, Graeme M. ( 1994)
    Psychophysical studies on electrical stimulation of the auditory nerve have contributed to our understanding of the coding of sound and speech signals. Those studies have also helped establish speech processing strategies for multiple-electrode cochlear implant patients. The first studies were on temporal coding of frequency and pitch perception to help determine whether a single or multiple electrode implant would be preferable for the coding of speech frequencies. Temporal frequency coding was initially studied in the experimental animal by measuring difference limens for frequency of stimulus rate. The results showed that rate coding occurs for low frequencies up to 200 or even 600 pulses per second. It was concluded that higher speech frequencies cannot be conveyed by variations in stimulus rate but require multiple-electrode stimulation. These studies in experimental animals were essentially confirmed in the human.