Graeme Clark Collection
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ItemA multiple-channel cochlear implant: an evaluation using open-set CID sentences( 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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ItemSpeech processor design for a multiple-channel cochlear implant( 1980)This paper outlines the strategy adopted for a laboratory-based speech processor used to provide speech information to patients with a multiple-channel cochlear implant It also presents the results of vowel and consonant recognition studies and speech test using open sets of words and sentences.
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ItemTwo-component hearing sensations produced by two-electrode stimulation in the cochlear of a deaf patient( 1983)http://www.sciencemag.org/cgi/content/abstract/219/4587/993?ijkey=v6jEOhdpzPCxw&keytype=ref&siteid=sci
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ItemA speech processing strategy for multiple-electrode cochlear implant prostheses(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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ItemPsychophysical studies evaluating the feasibility of a speech processing strategy for a multiple-channel cochlear implant( 1983)Abstract not available due to copyright.
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ItemThe histopathological effects of chronic electrical stimulation of the cat cochlea(Cambridge University Press, 1983)The success of a cochlear implant depends on stimulating an adequate number of viable spiral ganglion cells. The effect of chronic electrical stimulation on ganglion cells is therefore an important consideration when assessing the effectiveness and safety of such a device. The histopathological assessment of chronic unstimulated intracochlear electrodes is now well documented (Simmons, 1967; Clark, 1973; Clark et al, 1975; Schindler and Merzenich, 1974; Schindler, 1976; Schindler et al, 1977; Sutton et al, 1980). These experimental studies have used a variety of electrode designs, materials and surgical techniques. However, all have shown that chronic implantation has little effect on the peripheral nerves and the spiral ganglion cells adjacent to an implant, provided the insertion procedure is free of trauma and infection.
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ItemChronic electrical stimulation of the auditory nerve in cats: physiological and histopathological results( 1983)The ability of spiral ganglion cells to survive long-term electrical stimulation is a precondition for the success of cochlear prostheses. In this study 10 cats were implanted bilaterally with bipolar scala tympani electrodes and stimulated for periods of up to 2029 hours using charge balanced biphasic current pulses. The status of the auditory nerve was monitored periodically by recording electrically evoked auditory brainstem responses. At the conclusion of the stimulation program, spiral ganglion cell survival was assessed for stimulated and control cochleas; comparison of the two groups showed no statistically significant difference. The results of this study indicate that long-term intracochlear electrical stimulation using carefully controlled biphasic pulses does not adversely affect the spiral ganglion cell population.
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ItemThe clinical trial of a multi-channel cochlear prosthesis( 1983)The results of a multiple-electrode cochlear implant carried out on 1st August, 1978 on a totally deaf patient (post-lingual hearing loss) showed that he could perceive sounds of different pitches depending on the electrode stimulated, and this finding was consistent with the place theory of frequency coding. Furthermore, stimulating individual electrodes produced percepts which the patient described as vowel-like in quality. The patient could also perceive different pitches which varied with the rate of stimulation up to 200 pulses/second, but at higher rates he had difficulties perceiving pitch changes (Clark et al. 1978; Tong et al, 1979). As a result of the psychophysical studies a speech processor was developed. The speech processor extracted: firstly, the voicing frequency to help the patient hear the rhythm of speech and know whether a speech sound was voiced or unvoiced (e.g., /b/ versus /p/); and, secondly, the second formant to enable the patient to recognize vowels and consonants and so hear words. In order to maximize speech intelligibility, the second formant stimulated an appropriate electrode, and the rate of stimulation on that electrode was related to the voicing frequency.
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ItemCurrent distributions of intracochlear electrodes in cats [Abstract](Monash University Press, 1983)A non-invasive technique, "two electrode mapping" has been developed to measure the current distribution of a multichannel electrode array within the feline scala tympani. An electrode’s current distribution is an important determinant of its ability to excite discrete neural groups. The electrode array, a “banded electrode” is a series of platinum rings, supported by a cylinder of silastic which fits freely into the scala tympani. All cats had normal hearing pre-operatively and were implanted through the round window. Hearing was normal within 10 dB after implantation, necessitating the presentation of 30-40 dB white noise to the implanted ear throughout experimentation to mask the electrophonic component (Black et al., 1983).
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ItemSelection of speech processing for cochlear implant prostheses(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.