Graeme Clark Collection
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ItemRehabilitation for multiple-channel cochlear prosthesis patients(Raven Press, 1985)The postoperative program for multiple-channel cochlear prosthesis patients can be divided into four main areas: 1) Psychophysical evaluation is carried out to optimize the patient's speech processor for their individual needs, Measurements required include threshold, dynamic range and pitch ranking for each of the implanted electrodes. 2) Counselling is very important to ensure patients are able to effectively operate their speech processor and that they are aware of factors in the environment which may affect performance (e.g., noise). 3) Auditory training and training in conjunction with lipreading for tasks grading from simple (e.g., discrimination of word length) to more difficult (e.g. consonant discrimination) is of benefit in making patients aware of their capabilities with the prosthesis and helping them to improve communication skills. However, highly specific training (e.g., closed set vocabulary) does not seem to be of general benefit to patients. Speech tracking provides a training procedure relevant to normal communication but has some limitations due to the degree of familiarity reached with a particular speaker. 4) Assessment of patients is carried out at this stage in great detail as it is necessary to collect data about the effectiveness of cochlear implants and also to provide information about possible improvements to speech processing strategies and external hardware. The amount of assessment required will decline as the procedure becomes established, but some investigation will continue to be necessary.
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ItemPsychophysics of multiple-channel stimulation(Raven Press, 1985)Eight patients implanted with multiple-channel cochlear prostheses have displayed good discrimination of sound sensations elicited at different sites within the cochlea. All patients rank the sensations from "sharp" to "dull" in an order which corresponds with basal to apical position in the cochlea. Detailed psychophysical studies have been carried out on two patients. These showed that discrimination of rate of (pulsatile) stimulation is good for frequencies up to 300 Hz and falls off sharply for frequencies above this. Electrode transitions (changes in position along the cochlea) are well discriminated for fast changes (25 msec), whereas rate transitions are not well discriminated for changes faster than 100 msec. From these results a speech processing strategy was formulated where second formant information is mapped to position in the cochlea and fundamental frequency mapped to rate of stimulation. Vowel and consonant confusion studies show consistent results for all patients using this processing strategy. A study involving two electrode stimuli demonstrated the possibility of presenting first formant information in addition to the second formant and fundamental frequency.
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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.