Graeme Clark Collection
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ItemManikin and cochlear implant patient test results with a portable adaptive beamforming processor to suppress the effects of noise( 1995)A simple adaptive beamformer (ABF) was implemented in a real-time portable speech processor and tested with four cochlear implant patients. The ABF algorithm used signals from only two microphones - one behind each ear - to attenuate sounds not arriving from the direction directly in front of the patient, and was compared with a strategy in which the two microphone signals were simply added together (two-microphone broadside strategy). Tests with the four patients were conducted in quiet and in noise. Results at a 0 dB signal-to-noise ratio showed large improvements in speech intelligibility for all patients, when compared to the two-microphone broadside strategy. Physical measurement of the directional characteristics of the ABF processor were made with a Kemar manikin. The effects of reverberation were explored by placing the manikin in different acoustic environments and observing the attenuation of the noise alone at various angles. A near-anechoic environment allowed the noise to be attenuated by as much as 21 dB, whereas in a highly reverberant concrete stairwell, the ABF processor was unable to provide any directional gain beyond about 3 dB.
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ItemEvaluation of a portable two-microphone adaptive beamforming speech processor with cochlear implant patients( 1995)Abstract not available due to copyright.
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ItemCombined electrical and acoustical stimulation using a bimodal prosthesis( 1993)A new device incorporating a cochlear implant speech processor and a speech-processing hearing aid for the un-implanted ear has been designed and tested with four severely hearing-impaired patients. The aim of the device is to provide a more acceptable and effective combination of electrical and acoustic signals to the two ears. When used monaurally, and binaurally in conjunction with the cochlear implant, the speech-processing hearing aid mean scores for open-set sentences, words, and consonants were as good as or better than the mean scores for the patients' own conventional hearing aids. Some patients improved much more than did others. Although not conclusive, these results are encouraging, especially as they were achieved with a laboratory prototype that did not allow the patients to become accustomed to the processor in everyday situations.
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ItemThe development of the nucleus multiple-channel cochlear implant( 1993)Physiology, biology, psychophysics and speech research studies led to the development of the inaugural cue-extraction speech processing strategy used in the Nucleus multiple-channel cochlear implant. This resulted in postlinguistically deaf adults obtaining open-set word scores for electrical stimulation alone, as well as significant improvements in understanding running speech when electrical stimulation was combined with lip-reading. Further speech processing research has resulted in progressive improvements in speech perception for postlinguistically deaf adults. The improvements have principally involved presenting more spectral information on a place coding basis, but additional temporal information has also improved its performance. The cue-extraction or speech-feature strategies used with the multiple-channel implant have also been shown to provide postlinguistically and prelinguistically deaf children (two to 17 years of age) with significant help in communication. In the children, open-set speech scores are most frequently obtained in the youngest age groups, and with longer periods of auditory training.
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ItemParameter selection and programming recommendations for the ACE and CIS speech processing strategies [Abstract]( 1999)The Nucleus 24 Cochlear Implant system with the SPrint processor provides access to multiple speech processing strategies and a wide range of programming parameters. Strategy comparison studies have suggested that the optimal parameter set and coding strategy varies from individual to individual. It is necessary, however, to establish some default programming parameters and fitting guidelines. Therefore we have investigated the effect of stimulation rate and the number of channels or maxima in the ACE or CIS strategies, as well as the optimal programming strategy for subjects with a limited number of available electrodes. Speech perception was tested using monosyllabic words and sentences in noise, with the evaluation protocol designed to take into account learning effects. Take-home experience was provided with all programs, and subjects were asked to complete a comparative performance questionnaire regarding program preference. Six or eight subjects were enrolled in each study.
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ItemAn improved speech processor for a 22-electrode cochelar implant [Abstract]( 1992)A spectral maxima speech processing strategy ( SMSP) has been developed as a result of research to improve the speech perception performance of a multiple-channel cochlear implant. With this speech processing strategy. the six spectral maxima from the outputs of 16 band pass filters are used to stimulate the cochlea on a place basis at a constant rate. This SMSP strategy has been compared with the MSP-MULTIPEAK strategy, the present speech processor provided by Cochlear Pty. Limited, on four postlinguistically deaf adults. The study showed that the SMSP strategy was significantly better than the MSP-MULTJPEAK for the recognition of closed-set vowels and consonants, and open-set monosyllable words and sentences in background noise.
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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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ItemDevelopment of an advanced electrotactile speech processor [Abstract]( 1992)Initial studies with a multiple channel electrotactile speech processor ('Tickle Talker') showed that profoundly hearing-impaired adults and children could achieve significant improvements on speech perception tests through use of tactual-encoded estimates of fundamental frequency, second formant frequency and amplitude envelope. Results showed that the device provided tactual cues which could be used to discriminate speech features such as vowel length and place, and consonant manner and voicing. However, discrimination of initial consonant voicing was not as consistent as for other features. Accurate discrimination of consonant voicing and manner (particularly high frequency information) is critical, since this Information is generally inaudible through hearing aids, and difficult to lipread.