Graeme Clark Collection

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1981 - 1989 13 1990 - 1994 7
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End date: 1994 × Type: Conference Paper × Subject: cochlear implant ×

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    A speech processing strategy for multiple-electrode cochlear implant prostheses
    Tong, Y. C. ; Clark, Graeme M. (Monash University Press, 1983)
    Speech studies in a number of research centres have shown that useful speech information could be presented to deaf patients using single or multiple electrode cochlear implant prostheses (Parking & Anderson, 1983). In our laboratory, speech processing strategies were formulated on the basis of psychophysical results. This paper examines the psychophysical characteristics of the hearing sensations produced by electrical stimulation using scala tympani electrodes in postlingually deaf patients; a speech processing strategy is then discussed on the basis of these characteristics.
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    Selection of speech processing for cochlear implant prostheses
    Millar, J. B. ; Tong, Y. C. ; Clark, Graeme M. (Monash University Press, 1983)
    In this paper we consider a framework against which to discuss strategies for the design of speech processors for cochlear implant prostheses. We hope to encourage discussion of the bases for such a framework even though it may seem a distant objective owing to the large gaps in our understanding of several component parts of cochlear implant systems. The existence of such a framework would provide a background against which to view the current diverse cochlear implant systems and to evaluate their performance.
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    The implanted round window membrane in the cat [Abstract]
    Franz, B. ; Clark, Graeme M. ; Ng, J. ; Bloom, D. (Monash University Press, 1983)
    In cochlear implants the round window is convenient for the electrode insertion into the scala tympani because the surgical approach is reasonably easy and the inserted electrode lies close to systematically organised nerve fibres in the spiral lamina. However, complications might occur when a poor seal, extensive tissue damage or surgical asepsis are present that lead to a reduction in the nerve fibre population which is needed for electrical stimulation. Published articles available do not describe the role of the window membrane in cochlear implants. Probably this can be referred to the finidng of abundant scar tissue in the window niche and around the electrode giving the impression of a safely implanted electrode. This study performed on seven cats over 5 months was concerned with morphological properties of the implanted window membrane at different stages after implantation. In addition, horseradishperoxydase was used as a tracersubstance to give data concerning the sealing properties of the implanted round window membrane.
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    Initial results for six patients with a multiple-channel cochlear prosthesis
    Dowell, R. C. ; Brown, A. M. ; Seligman, P. M. ; Clark, Graeme M. (Monash University Press, 1983)
    A total of eight patients have been assessed with the multi-channel cochlear prosthesis at the University of Melbourne. The first two patients were implanted with a prototype device in 1978 and 1979, and their results with various speech evaluation procedures have been reported and summarized in detail elsewhere (Clark & Tong, 1982). Briefly, these results indicated that some very significant benefit could be obtained for these patients when using the cochlear prosthesis with external speech processing, particularly when using the device in conjunction with lipreading. It was also shown that some significant understanding of speech was possible without lipreading (open-set) for both patients, although this was fairly limited.
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    The auditory brainstem response in hearing and deaf cats evoked by intracochlear electrical stimulation
    Black, R. C. ; Clark, Graeme M. ; O'Leary, S. J. ; Walters, C. (Monash University Press, 1983)
    This study was performed to investigate in detail the auditory brainstem response (ABR) for intracochlear electrical stimulation. Brainstem response audiometry is a simple, noninvasive procedure with the responses under many stimulus conditions being readily understood in terms of single auditory nerve discharge properties. The amplitude and latency behaviour of the Nl brainstem response correlates well with that recorded directly from the auditory nerve (Huang & Buchwald, 1978). In addition, the brainstem response can be divided into frequency-specific components corresponding to tonotopical locations in the cochlea, as exhibited in the method of derived responses (e.g. Parker &Thornton, 1978). It is therefore well suited to both physiological and clinical investigation of auditory function and therefore should be useful in evaluating auditory function under conditions of electrical stimulation of the cochlea.
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    Electrical stimulation of the human cochlea: psychophysical and speech studies
    Clark, Graeme M. (Plenum Publishing Corporation, 1981)
    This report describes psychophysical and speech studies conducted on two of our post-lingually deaf patients implanted with the nature of the hearing sensations produced by the individual electrodes, and to investigate the feasibility of the transmission of speech information to higher centres by means of cadences of stimulation using on electrode at a time. Two totally deaf patients (MC1 and MC2) participated in these studies.
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    Pitch and vowel perception in cochlear implant users
    Blamey, Peter J. ; Parisi, Elvira S. ( 1994)
    Two methods of determining the pitch or timbre of electrical stimuli in comparison with acoustic stimuli are described. In the first experiment, the pitch of pure tones and electrical stimuli were compared directly by implant users who have residual hearing in the non-implanted ear. This resulted in a relationship between frequency in the non-implanted ear and position of the best-matched electrode in the implanted ear. In the second experiment, one- and two-formant synthetic vowels, with formant frequencies covering the range from 200 to 4000 Hz, were presented to the same implant users through their implant or through their hearing aid. The listeners categorised each stimulus according to the closest vowel from a set of eleven possibilities, and a vowel centre was calculated for each response category for each ear. Assuming that stimuli at the vowel centres in each ear sound alike, a second relationship between frequency and electrode position was derived. Both experiments showed that electrically-evoked pitch is much lower than that produced by pure tones at the corresponding cochlear location in normally-hearing listeners. This helps to explain why cochlear implants with electrode arrays that rarely extend beyond the basal turn of the cochlea have achieved high levels of speech recognition in postlinguistically deafened adults without major retraining or adaptation by the users. The techniques described also have potential for optimising speech recognition for individual implant users.
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    Using an automatic word-tagger to analyse the spoken language of children with impaired hearing
    Blamey, P. J. ; Grogan, M. L. ; Shields, M. B. ( 1994)
    The grammatical analysis and description of spoken language of children with impaired hearing is time-consuming, but has important implications for their habilitation and educational management. Word-tagging programs have achieved high levels of accuracy with text and adult spoken language. This paper investigates the accuracy of one automatic word tagger (AUTASYS 3.0 developed for the International Corpus of English project, ICE) on a small corpus of spoken language samples from children using a cochlear implant. The accuracy of the tagging and the usefulness of the results in comparison with more conventional analyses are discussed.
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    Combination and comparison of electric stimulation and residual hearing
    BLAMEY, PETER ; Dooley, Gary ; Parisi, Elvira ( 1994)
    Speech processing for cochlear implant users has now reached a level where some severely hearing-impaired hearing aid users may be better aided by a cochlear implant, or a hearing aid and implant together. This paper reviews studies comparing the loudness, pitch, and vowel perception in opposite ears of adults using cochlear implants and hearing aids. A study of nine subjects showed narrow dynamic ranges and steep loudness growth in both ears. Mismatches in aided thresholds and dynamic ranges at different frequencies resulted in highly variable loudness differences between the ears for some subjects. A comparison using pure tones showed that the electric pitch depended on both rate and electrode site. Pitch of electrodes was lower than expected from the characteristic frequency distribution in a normal cochlea. Synthetic vowels were used to show that signals presented via the implant and hearing aid may be perceived as different vowels in the two ears.
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