Graeme Clark Collection

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    Evaluation of a new Spectral Peak coding strategy for the Nucleus 22 channel cochlear implant system
    Skinner, Margaret W. ; Clark, Graeme M. ; Whitford, Lesley A. ; Seligman, Peter M. ; Staller, Steven J. ; Shipp, David B. ; Shallop, Jon K. ; Everingham, Colleen ; Menapace, Christine M. ; Arndt, Patti L. ; Antogenelli, Trisha ; Brimacombe, Judith A. ; Pijl, Sipke ; Daniels, Paulette ; George, Catherine R. ; McDermott, Hugh J. ; Beiter, Anne L. ( 1994)
    Sixty-three postlinguistically deaf adults from four English-speaking countries participated in a 17-week field study of performance with a new speech coding strategy, Spectral Peak (SPEAK), and the most widely used strategy, Multipeak (MPEAK), both of which are implemented on wearable speech processors of the Nucleus 22 Channel Cochlear Implant System; MPEAK is a feature-extraction strategy, whereas SPEAK is a filterbank strategy. Subjects' performance was evaluated with an experimental design in which use of each strategy was reversed and replicated (ABAB). Average scores for speech tests presented sound-only at 70 dB SPL were higher with the SPEAK strategy than with the MPEAK strategy. For tests in quiet, mean scores for medial vowels were 74.8 percent versus 70.1 percent; for medial consonants, 68.6 percent versus 56.6 percent; for monosyllabic words, 33.8 percent versus 24.6 percent; and for sentences, 77.5 percent versus 67.4 percent. For tests in noise, mean scores for Four-Choice Spondees at +10 and +5 dB signal-to-noise ratio (S/N) were 88.5 percent versus 73.6 percent and 80.1 percent versus 62.3 percent, respectively; and for sentences at +15 dB, +10, and +5 dB S/N, 66.5 percent versus 43.4 percent, 61.5 percent versus 37.1 percent, and 60.4 percent versus 31.7 percent, respectively. Subjects showed marked improvement in recognition of sentences in noise with the new SPEAK filterbank strategy. These results agree closely with subjects' responses to a questionnaire on which approximately 80 percent reported they heard best with the SPEAK strategy for everyday listening situations.
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    Pitch ranking with nonsimultaneous dual-electrode electrical stimulation of the cochlea
    McDermott, Hugh J. ; McKay, Colette M. ( 1994)
    Abstract not available due to copyright.
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    Speech processing for multichannel cochlear implants: variations of the Spectral Maxima Sound Processor strategy
    McKay, Colette M. ; Vandali, Andrew E. ; McDermott, Hugh J. ; Clark, Graeme M. ( 1994)
    The Spectral Maxima Sound Processor (SMSP) incorporates a bank of 16 band-pass filters which are assigned to 16 intracochlear electrodes. In each stimulation period 6 electrodes are activated, based on the outputs of the filters with the largest amplitudes. The SMSP has previously been compared with the present MSP (MULTIPEAK) processor and found to improve speech comprehension results. The SMSP speech processing scheme has recently been implemented successfully in a new speech processor, also developed at the University of Melbourne, which utilises digital signal processing techniques. The programming flexibility of this processor has facilitated the investigation of variations of the SMSP strategy which might provide further enhancement of speech perception. Three variations have been investigated: firstly, increasing the constant pulse rate from the usual 250 Hz to 400 Hz; secondly, changing the number of electrodes selected in each stimulation period from 6 to numbers between 4 and 8; thirdly, sharpening the spectral peaks prior to selection of the active electrodes. The results of these studies showed that all three variations had minimal effect on speech perception in quiet, but that increasing the number of electrodes selected for stimulation to 8, or increasing the rate of stimulation, was advantageous for some subjects when listening in background noise.
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    Pitch percepts associated with amplitude-modulated current pulse trains in cochlear implantees
    McKay, Colette M. ; McDermott, Hugh J. ; Clark, Graeme M. ( 1994)
    Abstract not available due to copyright.
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    A comparison of speech perception of cochlear implantees using the Spectral Maxima Sound Processor (SMSP) and the MSP (Multipeak) processor
    McKay, Colette M. ; McDermott, Hugh J. ; Vandali, Andrew E. ; Clark, Graeme M. ( 1992)
    The Spectral Maxima Sound Processor (SMSP) is a portable speech processor which has recently been developed at the University of Melbourne for use with multiple-electrode cochlear implants. In this processor, the six largest outputs (maxima) of 16 bandpass filters are used to stimulate the cochlea on a place basis at a constant rate. This speech processing strategy has been compared with the MSP(MULTIPEAK) strategy, in which four electrodes are selected for stimulation in every glottal pulse period. The study was undertaken on four postlinguistically deaf adults. The results show that, for this group of subjects, the performance of the SMSP processor was significantly better than that of the MSP(MUL TIPEAK) processor for the recognition of closed-set vowels and consonants, open-set monosyllabic words, and open-set sentences in noise, when using electrical stimulation alone. The SMSP mean scores were: vowels 91.3%, consonants 74.9%, words 57.4%, and sentences in noise 78.7%. The MSP(MULTIPEAK) mean scores were: vowels 76.3%, consonants 59.4%, words 39.9%, and sentences in noise 50.0%.
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    Perceptual performance of subjects with cochlear implants using the spectral maxima sound processor (SMSP) and the mini speech processor (MSP)
    McKay, Colette M. ; McDermott, H. J. ( 1993)
    A portable sound processor has been developed at the University of Melbourne for use with the 22-ectrode cochlear implant manufactured by Cochlear Pty Limited. In this report, the performance of the Spectral Maxima Sound Processor (SMSP) is compared with the Mini Speech Processor (MSP) presently used clinically with this implant. Results of tests with 5 subjects demonstrate that the performance of the SMSP significantly exceeds that of the MSP for recognizing vowels and consonants in closed-set confusion studies and open-set monosyllabic word tests, although recognition of speaker identity and intonation patterns is similar for both processors. Information transmission analysis of phoneme features confirms that most features, such as vowel formant frequencies and consonant manner and place of articulation, are better conveyed with the SMSP. Possible reasons for its improved performance are discussed.
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    A portable programmable digital sound processor for cochlear implant research
    McDermott, Hugh J. ; Vandali, Andrew E. ; van Hoesel, Richard J. M. ; McKay, Colette M ; HARRISON, MARK ; Cohen, Lawrence T. ( 1993)
    A programmable sound processor which utilizes digital signal processing has been developed for hearing prosthesis research. It incorporates a Motorola DSP56001 integrated circuit, 32K words of memory, a 12 b analog-to-digital converter, and a data formatter and transmitter which conveys control codes to the receiver-stimulator of a cochlear implant. The processor is pocket-sized and battery powered. It has been programmed to emulate the Spectral Maxima Sound Processor for the University of Melbourne/Nucleus 22 electrode implant, and is currently being used by several implantees. In continuing research, speech processing programs are being improved, and other applications, including signal processing for binaural implants and advanced hearing aids, are being developed.
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    A new portable sound processor for the University of Melbourne/ Nucleus Limited multielectrode cochlear implant
    McDermott, Hugh J. ; McKay, Colette M. ; Vandali, Andrew E. ( 1992)
    Abstract not available due to copyright.
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    Preliminary results with a six spectral maxima speech processor for The University of Melbourne/Nucleus multiple electrode cochlear implant
    McKay, Colette M. ; McDermott, Hugh J. ; VANDALI, ANDREW ; Clark, Graeme M. ( 1991)
    An improved sound processor for a multiple-channel cochlear implant hearing prosthesis has been developed. The spectral maxima sound processor (SMSP) extracts the six largest frequency components of speech and presents stimuli at a rate of 250 Hz to electrodes at positions selected on the basis of the spectral frequencies. It was designed for use initially with the advanced cochlear implant recently developed at the University of Melbourne, which is capable of high rate and quasi-simultaneous stimulation. The present study, however, was carried out with two subjects who have the more widely used 22-electrode implant produced commercially by Cochlear Pty Limited (formerly Nucleus Limited). Preliminary results comparing the performance of the SMSP with that of previous speech processing techniques (F0/F1/F2 strategy) are presented. The results indicate that the SMSP is capable of providing implanters with significantly greater information about speech.