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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    A protocol for the prevention of infection in cochlear implant surgery
    Clark, Graeme M. ; Pyman, Brian C. ; Pavillard, Robin E. (Cambridge University Press, 1980)
    The reduction of infection to an absolute minimum is a very desirable goal in any form of surgery. It is especially important with a cochlear implant operation as infection in the labyrinth can lead to degeneration of the auditory nerve fibres it is hoped to stimulate electrically (Clark et al, 1975). Furthermore, as the implantation of foreign materials increases the risk of infection, as the operation can last 6-7 hours (Altemeier et al., 1976), and as the operators are in very close proximity to the implant site, more stringent measures for the prevention of infection need to be adopted than with other forms of otological surgery. For these reasons a protocol has been developed for preventing infection in our cochlear implant surgery. This is an overall approach to the prevention of infection and involves pre-operative measures, an operating theatre routine, the use of horizontal laminar flow filter units, correct surgical technique and the use of systemic and local antibiotics.
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    Temporal coding of speech information for cochlear implant patients
    Millar, J. B. ; Martin, L. F. A. ; Tong, Y. C. ; Clark, Graeme M. ( 1987)
    A modified speech-processing strategy incorporating the temporal coding of information strongly correlated with the first formant of speech was evaluated in a long-term clinical experiment with a single patient. The aim was to assess whether the patient could learn to extract information from the time domain in addition to the time domain cues for voice excitation frequency already received from the initial strategy. It was found that the patient gained no significant advantage from the modified strategy, but there was no disadvantage either, and the patient expressed a preference for the modified strategy for everyday use.
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    Responses of cat auditory nerve fibers to biphasic electrical current pulses
    Javel, E. ; Tong, Y. C. ; Shepherd, R. K. ; Clark, Graeme M. ( 1987)
    Discharge patterns of single auditory nerve fibers were recorded from normal-hearing cats implanted with a I2-band intracochlear electrode array. Stimuli were biphasic current pulses of specifiable width, amplitude, and rate. Acoustic tuning curves were obtained to determine the cochlear positions of the fibers. Response latencies to electrical stimuli formed two groups. Short latency (0.3 to 0.7 ms) responses were attributed to direct activation of spiral ganglion neurons. At high stirnulus intensities, these often exhibited abrupt shifts toward even shorter latencies. Long latency (> 1.5 ms) responses were probably caused by electrophonic activation of functional hair cells. Response thresholds to electrical stimuli depended on a fiber's proximity to the stimulating electrodes, and they did not depend on a fiber's acoustic response threshold or spontaneous discharge rate. High intensity (> 1.5 mA) stimuli could excite fibers over a wide range of characteristic frequencies, even for the narrowest (0.45 mm) electrode separations. Response threshold was an exponentially decreasing function of pulse width for widths up to 300µs/phase. Fiber discharges were highly phase-locked at all suprathreshold intensities, and saturation discharge rates usually equaled stimulus pulse rates for rates up to at least 800 pulses/s. Dynamic ranges were small (I to 6 dB), increased with pulse rate, and were uncorrelated with electrical response threshold. Within the dynamic range, shapes of poststimulus time and interspike interval histograms resembled those obtained in response to acoustic stimuli. Depolarization block caused fiber activity to cease in 2 to 5 seconds for sustained stimuli presented at high (> 600 pulses/s) pulse rates and intensities.
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    Recent developments with the Nucleus 22-electrode cochlear implant: a new two formant speech coding strategy and its performance in background noise
    Franz, Burkhard K-H. G. ; Dowell, Richard C. ; Clark, Graeme M. ; Seligman, Peter M. ; Patrick, James F. ( 1987)
    A clinical evaluation of speech processing strategies for the Nucleus 22-electrode cochlear implant showed improvements in understanding speech using the new F0F1F2 speech coding strategy instead of the F0F2 strategy. Significant improvement in closed-set speech recognition in the presence of background noise was an additional advantage of the new speech processing strategy.
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    Surgical anatomy of the round window with special reference to cochlear implantation
    Franz, Burkhard K. H. ; Clark, Graeme M. ; Bloom, David M. (Cambridge University Press, 1987)
    When the multi-channel cochlear implant electrode is inserted into the scala tympani through the round window the operation is best performed via a posterior tympanotomy. The view of the round window membrane, however, is incomplete because of its orientation and the fact that it has a conical shape. Nevertheless, a good view along the basal turn is obtained after the antero-inferior overhang of the round window niche and the crista fenestrae have been removed. It might be damaging to drill away the postero-superior overhang as the osseous spiral lamina lies extremely close to the round window membrane.
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    Effect of experimentally induced otitis media on cochlear implants
    Franz, Burkhard K-H. ; Clark, Graeme M. ; Bloom, David M. ( 1987)
    Cat cochleas implanted with scala tympani prostheses were investigated histologically after inoculating the bullae with a suspension of group A streptococci. The prosthesis was passed through the round window membrane in one ear. In the other the prosthesis bypassed the round window via an opening anteroinferior to the round window niche. Before death, horseradish peroxidase was administered as a tracer for possible pathways of infection. Results showed that group A streptococci were pathogenic to the cat and caused inflammation in the bulla. The unimplanted round window membrane and the seals around the electrode entry points prevented infection from entering the cochlea. The seals around electrodes inserted either through the round window membrane or an opening drilled anteroinferior to the niche were equally effective. The horseradish peroxidase tracer studies showed, however, that a gap existed between the electrode and membranous seal, and this could be a potentially vulnerable site under certain conditions. Drilling an anteroinferior opening into the cochlea resulted in bony sequestra entering the cochlea. This can be avoided by blue-lining the opening and removing bone with picks before making an opening through the endosteum.
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    Refined surgical technique for insertion of banded electrode array
    Franz, B. K-H. G. ; Clark, Graeme M. ( 1987)
    A refined electrode insertion technique is presented for the multichannel cochlear implant. It comprises two basic steps. The first step is the removal of the anteroinferior overhang of the round window and crista fenestrae, or alternatively an opening drilled into the scala tympani anteroinferior to the round window. The second is rotation of the electrode during insertion, counterclockwise in the right ear and clockwise in the left ear.
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    Evaluation of a two-formant speech-processing strategy for a multichannel cochlear prosthesis
    Dowell, R. C. ; Seligman, P. M. ; Blamey, P. J. ; Clark, Graeme M. ( 1987)
    Initial results with the two-formant speech-processing strategy (F0FIF2) confirm the advantage of a multichannel cochlear prosthesis capable of stimulating at different sites within the cochlea. The successful presentation of two spectral components by varying the place of stimulation leads to the possibility of presenting further spectral information in this manner. Because virtually all multichannel implant patients demonstrate good "place" (electrode site) discrimination, these more refined coding strategies should lead to benefits for the majority of implantees. Already, with the F0FIF2 strategy, we have a system that appears to provide some effective auditory-alone communication ability for the average patient.
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    Middle ear infection postimplantation: response of the round window membrane to Streptococcus pyogenes
    Cranswick, N. E. ; Franz, B. K-H. ; Clark, Graeme M. ; Shepherd, R. K. ; Bloom, D. M. ( 1987)
    The seal of the implanted round window membrane to resist Streptococcus pyogenes invasion from the middle ear was investigated in 12 cats. Results showed that the implanted round window membrane is able to form a barrier for S pyogenes starting 1 week postimplantation. Under normal conditions S pyogenes did not pass through the round window membrane, nor through the gap that existed between the membrane and the prosthesis. Mechanical disruption of the round window seal, however, and severe inflammatory response to S pyogenes caused the infection to extend into the inner ear.