Graeme Clark Collection

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    A multiple-channel cochlear implant: an evaluation using open-set CID sentences
    Clark, Graeme M. ; Tong, Yit Chow ; Martin, Lois F. A. ( 1981)
    A multiple-channel cochlear implant and speech processor have been used in two postlingually deaf adult patients with a total hearing loss, to enable them to perceive varying degrees of running speech. The results have been confirmed with open-set CID everyday sentence tests. Using the implant alone, the patients obtained 8% and 14% scores with pre-recorded material, and 34% and 36% scores for "live" presentations. This was equivalent to the perception of 35% of connected discourse. When the implant was used in conjunction with lipreading, improvements of 188% and 386% were obtained over lipreading alone, and the scores were 68% and 98% which were equivalent to the perception of 60% and 95% of connected discourse.
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    Speech processing for a multiple-electrode cochlear implant hearing prosthesis
    Tong, Y. C. ; Clark, Graeme M. ; Seligman, P. M. ; Patrick, J. F. ( 1980)
    Abstract not available due to copyright.
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    Design criteria of a multiple-electrode cochlear implant hearing prosthesis
    Clark, Graeme M. ; Black, R. C. ; Forster, I. C. ; Patrick, J. F. ; Tong, Y. C. ( 1978)
    Abstract not available due to copyright.
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    Research advances for cochlear implants
    Clark, Graeme M. ( 1998)
    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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    Continuing improvements in speech processing for adult cochlear implant patients
    Hollow, R. D. ; Dowell, R. C. ; Cowan, R. S. C. ; Skok, M. C. ; Pyman, B. C. ; Clark, Graeme M. ( 1995)
    The Cochlear 22-channel cochlear implant has employed a succession of improved speech-processing strategies since its first use in an adult patient in Melbourne in 1982. 1 The first patients received the F0F2 coding strategy developed by the University of Melbourne, in the Wearable Speech Processor (WSP). The F0F2 coding scheme presented the implant user with three acoustic features of speech. These were 1) the amplitude of the waveform, presented as the amount of current charge, 2) fundamental frequency (F0) or voice pitch, presented as rate of biphasic pulsatile stimulation, and 3) the spectral range of the second formant frequency (F2), which was represented by varying the site of stimulation along the electrode array.
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    Implant designs for future coding strategies
    Patrick, J. F. ; Evans, A. R. ( 1995)
    This paper briefly describes the history of speech processing developments leading to the presently available Speak processing strategy. The similarities and differences of the Speak and Continuous Interleaved Sampling (CIS) strategies are then discussed and some recent key experimental observations are examined as a guide to potential future coding strategies. Key issues for future coding strategies and implant designs are the number of electrodes and stimulation rates in use. Consideration of these issues has led to development of a prototype implant to be used for advanced speech-processing research.
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    Evaluation of the Nucleus Spectra 22 Processor and New Speech Processing Strategy (SPEAK) in postlinguistically deafened adults
    Whitford, Lesley A. ; Seligman, Peter M. ; Everingham, Colleen E. ; Antognelli, Trisha ; Skok, Marisa C. ; Hollow, Rodney D. ; Plant, Kerrie L. ; Gerin, Elvira S. ; Staller, Steve J. ; McDermott, Hugh J. ; Gibson, William R. ; Clark, Graeme M. ( 1995)
    A new speech processing strategy (SPEAK) has been compared with the previous Multipeak (MPEAK) strategy in a study with 24 postlinguistically deafened adults. The results show that performance with the SPEAK coding strategy was significantly better for 58.3% of subjects on closed-set consonant identification, for 33.3% of subjects on closed-set vowel identification and open-set monosyllabic word recognition, and for 81.8% of subjects on open-set sentence recognition in quiet and in competing noise (+ 10 dB signal-to-noise ratio). By far the largest improvement observed was for sentence recognition in noise, with the mean score across subjects for the SPEAK strategy twice that obtained with MPEAK.
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    Comparison of the SPEAK (Spectral Maxima) and multipeak speech processing strategies and improved speech perception in background noise
    Clark, Graeme M. ; Whitford, L. ; Van Hoesel, R. ; McKay, C. M. ; McDermott, H. D. ; Seligman, P. ; Vandali, A. ; Pyman, B. C. ; Cowan, R. C. ( 1995)
    As more is known about speech processing for Cochlear Implant patients, results should continue to improve. It now appears possible that Cochlear Implant patients may, in some instances, reach performance levels that are better than those obtained by most severely deaf people who use hearing aids.
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    Multichannel cochlear implant speech processing: further variations of the spectral maxima sound processor strategy
    Vandali, A. E. ; Harrison, J. M. ; Huigen, J. M. ; Plant, K. ; Clark, Graeme M. ( 1995)
    The spectral maxima sound processor (SMSP) was first developed at the University of Melbourne in 1989. A full description of the SMSP has been given by McDermott et al.1 In short, the SMSP utilizes an ear-level microphone to measure acoustic sound pressure. A 16-channel band-pass filter bank is used to analyze the sound spectrum at discrete time intervals. Each of the 16 filters is assigned to one of the 16 intracochlear electrodes according to frequency. Within each time interval the six channels with the largest band-pass filter amplitudes are selected and used to stimulate six corresponding electrodes in quick succession. The current implementation of the SMSP2 differs from the original in that a digital signal processor is used in place of the analog filter bank and the microprocessor. The filter bank has been implemented with a discrete Fourier transform. Also, the input dynamic range has been improved by increasing the resolution of the analog-to-digital converter from 8 to 12 bits.