Graeme Clark Collection
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ItemImproved sound processing for cochlear implants( 2002)Four signal processing schemes currently under development aim to improve the perception of sounds/ especially speech, for children and adults using the Nucleus cochlear implant system. The schemes are (1) fast-acting input-signal compression, (2) Adaptive Dynamic Range Optimisation (ADRO), (3) TESM, a scheme that emphasises transients in signals, and (4) DRSP, a strategy that applies different stimulation rates to selected sets of electrodes.
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ItemSpeech perception in implanted children: effects of preoperative residual hearing and speech processing strategy [Abstract]( 1997)Since the first child was implanted with the Nucleus 22-channel cochlear prosthesis in Melbourne in 1985, the number of implanted children world-wide has rapidly expanded. Over this period, more effective paediatric assessment and management procedures have developed, allowing cochlear implants to be offered to children under the age of 2 years. In addition, a succession of improved speech processing strategies have been implemented in the Nucleus implant system, resulting in increased mean speech perception benefits for implanted adults. Research in the Melbourne and Sydney Cochlear Implant Clinics has also demonstrated that young children can adapt to and benefit from improved speech processing strategies such as the Speak strategy. Reported speech perception results for implanted children show that a considerable proportion (60%) of paediatric patients in the Melbourne and Sydney clinics are able to understand some open set speech using electrical stimulation alone. These results, and the upward trend of speech perception benefits to improve over time with advances in speech processing. have raised questions as to whether severely, or severely-to-profoundly deaf children currently using hearing aids would in fact benefit more from a cochlear implant. To investigate the potential effect of the level of preoperative residual hearing on postoperative speech perception. results for all implanted children in the Melbourne and Sydney cochlear implant programs were analysed. Results showed that as 8 group, children with higher levels of preoperative residual hearing were consistently more likely to achieve open-set speech perception benefits. Potential factors in this finding could be higher levels of ganglion cell survival or greater patterning of the auditory pathways using conventional hearing aids prior to implantation. Conversely, children with the least preoperative residual hearing were less predictable, with some children achieving open-set perception, and others showing more limited closed-set benefits to perception. For these children, it is likely that preoperative residual hearing is of less significance than other factors in outcomes.
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ItemA stimulation of spatio-temporal firing across auditory nerve fibres( 1997)Present cochlear implant speech processing strategies give recipients a perception of sound inferior to that of the normal hearing population. Since it is beyond current technology to achieve an electrically evoked auditory-nerve output identical to that of normal hearing, stimulation strategies are limited to approximating certain features of the neural firing patterns. The importance of the spatio-temporal firing patterns of an ensemble of auditory nerve fibres to speech perception has been stated in previous studies (1,2). This paper utilises a composite model of the cochlea and hair-cell/auditory nerve transduction using artificial and speech signals as input to produce a spatio-temporal excitation pattern which represents the fluctuating firing probability of the auditory neurons. A model of electrical stimulation of the auditory nerve is then used to show how stimulation strategies currently used produce neural firing patterns qualitatively different to those produced by normal hearing. Our investigations indicate that it is possible to generate electrical stimulation parameters that cause the spatio-temporal responses of the neural population to better approximate normal hearing. These responses enable us to identify stimulation parameters required to obtain the chosen neural firing patterns. A number of examples illustrate the utility of this method, revealing the spatio-temporal responses for varying numbers of neurons and electrode displacements.