Graeme Clark Collection
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ItemThe engineering of future cochlear implants(Croom Helm, 1985)Speech is a complex acoustic signal, and information is transmitted to the brain at a rapid rate. For example during a conversation ten phonemes are uttered per second. Furthermore, these complex speech sounds are coded into patterns of neural discharges that enable the subject to understand speech. In order, therefore, to bring speech signals directly to residual auditory nerve fibres, considerable processing of the speech signal is required before the central nervous system will recognise and comprehend it. The magnitude of the task can be further appreciated when one considers that there are an average of 31,400 nerve fibres in the human auditory nerve and a large proportion of these convey information to the brain about the speech frequencies. Research studies are showing, however, that the perception of ongoing speech with cochlear implants may be achieved 'With speech processing strategies which can be achieved by current electronic technology.
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ItemTelephone use by a multi-channel cochlear implant patient: an evaluation using open-set CID sentences(Cambridge University Press, 1985)A totally deaf person with a multiple-channel cochlear prosthesis obtained open-set speech discrimination using the telephone. CID Everyday Sentences were presented by telephone to the patient, who repeated an average of 21 per cent of key words correctly on the first presentation, and 47 per cent when a repeat of the sentences was permitted. This result is consistent with the patient's reports of telephone usage.
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ItemA comparison of three speech coding strategies using an acoustic model of a cochlear implant( 1985)Abstract not available due to copyright.
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ItemCochlear implant and otitis media: a pilot study to assess the feasibility of pseudomonas aeruginosa and streptococcus pneumoniae infection in the cat( 1984/85)An experimental model for the induction of otitis media in cats is described using pseudomonas aeruginosa and streptococcus pneumoniae. Until now the cat has been regarded as being resistant to streptococcus pneumoniae infections, whereas pseudomonas aeruginosa is known to cause a most virulent otitis media in this animal. A successful inoculation using streptococcus pneumoniae, however, can be achieved by direct inoculation of a highly concentrated suspension of microorganisms in the bulla, retention of the organisms by Gelfoam®, and enhancement of virulence by intrapertioneal inoculation in mice. The model promises to be an important contribution in studying the effects of pneumococcal otitis media in Cochlear Implants.
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ItemComparison of two cochlear implant speech-processing strategies( 1984)Speech processors extracting either the fundamental frequency (F0) alone, or the fundamental frequency combined with second formant information (F0-F2), have been evaluated on a totally deaf patient using a multiple-channel cochlear implant. A closed set test using 16 spondees and a modified rhyme test showed that for electrical stimulation alone the F0-F2 speech processor was significantly better than the F0 processor. The open set tests using phonetically balanced words and Central Institute for the Deaf everyday sentences showed that for electrical stimulation alone and electrical stimulation combined with lipreading, the results with the F0-F2 speech processor were all significantly better than with the F0 processor. Information transmission for consonant speech features was also better when using the F0-F2 processor.
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ItemSurgery for an improved multiple-channel cochlear implant( 1984)An improved multiple-channel cochlear implant has been developed. The titanium container with enclosed electronics, the receiver coil and the connector are embedded in medical-grade Silastic. The upper half of the implant has a diameter of 35 mm and a height of 4.5 mm. and the lower half a diameter of 23 mm and a height of.5 mm. The electrode array has also been designed to reduce the possibility of breakage due to repeated movements over many years. The surgery involves drilling a bed in the mastoid bone for the receiver-stimulator, and fixing the proximal electrode under the mastoid cortex. Gentle insertion of the electrode array through the round window and along the seala tympani is achieved with a specially designed microclaw.
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ItemAn acoustic model of a multiple-channel cochlear implant( 1984)Abstract not available due to copyright.
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ItemSpeech processing studies using an acoustic model of a multiple-channel cochlear implant( 1984)Abstract not available due to copyright.
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ItemAmplitude and pulse rate difference limens for electrical stimulation of the cochlea following graded degeneration of the auditory nerve( 1983)Experimentally deafened cats with differing populations of residual spiral ganglion cells were implanted with cochlear electrodes and were electrically stimulated. They were conditioned to respond to changes in electrical pulse rate amplitude, and both electrical pulse rate and amplitude difference limens were determined. It was found that although there were some variations in difference limens between animals, these showed no correlation with residual cell populations over the range 8-44%.
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ItemSelection of patients for multiple-channel cochlear implantation(Raven Press, 1985)Only profoundly, bilaterally deaf adults are considered for evaluation. It is necessary to determine that the patient's communication ability cannot be improved to any significant degree with conventional hearing aids currently available. Initial assessment consists of audiometry, hearing aid evaluation(s), otological and medical examination, and for patients with no recent experience with hearing aids, a hearing aid trial. Polytome x-rays of temporal bones is carried out to ensure that cochlea structures are not grossly abnormal. Electrical stimulation of the promontory is used to confirm the presence of residual auditory nerve fibers. Where there is an audiometric difference between ears, the poorer ear is chosen for implantation provided there are no other contraindications. Intensive counselling is carried out to enable patients to make a fully informed decision about implantation. Patients undergo a battery of speech discrimination and lipreading tests with their hearing aid after their hearing aid trial. This is to provide a baseline for comparison with postoperative results and to assess the benefit obtained from the hearing aid. Any significant improvement in test results when using a hearing aid over lipreading alone would be a contraindication for implantation. Medical assessment is carried out as for any major surgery, including pathology, respiratory function tests and cardiovascular assessment. Particular emphasis is placed on infection prevention immediately preoperatively and during surgery.