Graeme Clark Collection
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ItemImplantation of the new CI-24M Cochlear Limited receiver-stimulator and its electrode array(Monduzzi Editore, 1997)Cochlear Limited has released the new CI-24M model Nucleus 24 electrode cochlear implant system encompassing a series of new features. It offers the potential for improvements in hearing and cosmesis, as well as telemetry.
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ItemAn extension of the Multipeak speech processing strategy for the MSP/MINI 22 cochlear implant system( 1992)The speech perception of three post-linguistically deaf adults using the Nucleus MSP/Mini System 22 cochlear implant system programmed with a new speech processing strategy, MPEAK+AO. was evaluated. The MPEAK+AO strategy retains all the information of the standard Multipeak speech processing strategy and additionally presents acoustic components below 400Hz to the most-apical electrode. This extra spectral Information may help implantees understand speech, particularly in noise. Since the estimated fundamental frequency is presented as the rate of stimulation at a fixed intracochlear site and is thereby potentially perceived more easily. and the amplitude of the stimulation on the apical electrode, associated with the voice fundamental, Is directly determined from the estimated energy in the relevant spectral region. these coding factors may provide a better representation ot the prosodic information in speech and a more complete auditory feedback signal. The comparison between Multipeak and MPEAK+AO included tests of vowel, consonant and CNC word recognition. Speech materials were presented with both a male and female speaker. Sentence material. presented with background masking noise (four-speaker babble) was also used. The results showed that the new strategy significantly improved the ability of these MSP users to recognise words in open-set sentences in noisy conditions.
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ItemA new algorithm for voicing detection and voice pitch estimation based on the neocognitron( 1992)Over the last decade cochlear implants have been used increasingly to restore hearing to the profoundly deaf. One of the more widely used implants is the Nucleus multi-electrode implant, developed by the University of Melbourne and Cochlear Pty. Ltd. The speech processor used with this implant is the MSP, programmed with the multipeak strategy. This device incorporates circuits to estimate the fundamental frequency (FO) of speech signals, and to decide whether voicing is present. This paper describes a new FO estimator and voicing detection algorithm based on the neocognitron; a neural network modelled on the retina and early visual system. Performance was compared with that of three other FO estimation algorithms: linear predictive coding (LPC), cepstral analysis and the algorithm used in the Multipeak-MSP processor. For the speech samples tested, the neocognitron performed more reliably than the other three systems. On the basis of these results, this work may be able to provide benefits to existing and future cochlear implant users.
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ItemTwo speech processing schemes for the University of Melbourne multi-channel cochlear implant prosthesis( 1989)A series of speech perceptual studies was conducted on normally hearing subjects using synthesized acoustic signals based on two speech processing schemes: zero-crossing and filter bank. The filter bank scheme was shown to provide more speech information than the zero-crossing scheme. These schemes were implanted in a laboratory-based speech processor, which is described. A low-power switched capacitor speech spectrum analyzer embodying several novel design methodologies is also described. This spectrum analyzer can be used to implement the filter bank scheme in a wearable speech processor.
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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.