Graeme Clark Collection
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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 analysis of high rate speech processing strategies using the Nucleus 24 cochlear implant [Abstract]( 1998)The effects of varying the stimulation rate on speech perception was evaluated in five postlinguistically deaf adult users of the Nucleus 24 Cochlear Implant System. Three different rates of electrical stimulation, 250, 807, and 1615 pulses per second per channel were employed. For the high stimulus rate the analysis frequency was the same as for the medium rate condition. The study investigated the effect of varying rate of stimulation when using the electrode selection technique of the SPEAK strategy. The study used a repeated ABC experimental design, in order to account for learning effects and to minimize ordering effects. Speech perception was evaluated using both monosyllabic words (open-sets of CNC words in quiet) and sentence materials (open-sets of CUNY sentences at signal-to-noise ratios from +20 to 0dB). In addition, the subjects' perception of closed-sets of 19 vowels and 24 consonants, presented in the H/VID and A/C/A context, were also investigated. The recognition and perception of distinctive features were assessed across strategies and patients. Preliminary speech perception results have shown no statistically significant difference in performance between the low and medium stimulation rates. However, significantly poorer results were observed for the high rate condition for some tests with some individuals. Individual differences may be explained by the effects of rate of stimulation on speech features.
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ItemAn analysis of high rate speech processing strategies using the Nucleus 24 cochlear implant [Abstract]( 1998)Speech comprehension for a group of five users of the Nucleus 24 Cochlear Implant system was explored at three rates of electrical stimulation, 250, 807, and 1615 pulses per second per channel. For the high stimulus rate the analysis frequency was the same as for the medium rate condition. The study investigated the effect of varying rate of stimulation when using the electrode selection technique of the SPEAK strategy. This has been undertaken using a repeated ABC experimental design to account for learning and minimize ordering effects. Speech perception was assessed using open-sets of CNC words in quiet and open-sets of CLTNY sentences at signal-to-noise ratios from +20 to 0dB. Closed-sets of 19 vowels and 24 consonants were also presented, in the H/V/D and A/C/A context. The recognition and perception of distinctive features were assessed across strategies and patients. Preliminary speech perception results have shown no statistically significant difference in performance between the low and medium stimulation rates. However, significantly poorer results were observed for the high rate condition for some tests. Individual differences may be explained by the effects of rate of stimulation on speech features.
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ItemTemporal coding in auditory neurons to electrical stimulation [Abstract]( 1997)The temporal response of the auditory pathway following intracochlear electrical stimulation will reflect the level of encoded temporal information, which is important for the further developmentof cochlear implant speech processing strategies, and in tum lead to a better understanding of temporal coding of acoustic stimuli Temporal coding of sound frequencies is based on the phase or time locked neural response seen to low frequency acoustic stimuli. The ability of neurons to respond in a time locked manner may determine the degree of encoded temporal frequency information. Electrophysiological studies have shown that the degree of response synchrony to charge balanced biphasic electrical stimuli is far greater than that seen to acoustic stimuli. We have investigated the temporal response properties of single units in the anteroventral cochlear nucleus (AVCN) in the cat to rates of electrical stimulation up to 800 pulses/s.
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ItemPreliminary speech perception results for children with the 22-electrode Melbourne / cochlear hearing prosthesis( 1992)The Cochlear 22-electrode cochlear prosthesis was first implanted in a child at the Cochlear Implant Clinic at the University of. Melbourne and Royal Victorian Eye & Ear Hospital in 1985. Since that time 42 children have received the device in Melbourne. Analysis of patient details shows that the majority of these children have a congenital as opposed to on acquired aetiology of hearing loss. In all but 3 cases, the children use 15 or more electrodes. In order to assist with evaluation of, benefits to speech perception across the very heterogeneous group of children, a six level hierarchical classification scheme for speech perception performance levels was created. All of the children achieved a minimum of Category 2 (discrimination of suprasegmental information). In total, 59 % of the children achieved Category 5 or 6 (open set recognition for unfamiliar materials). Analysis showed that the majority of these children had more than one year of experience. In contrast, the majority of children in Category 2 are those with less than one year of experience with the device.
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ItemImprovements in speech processing for the nucleus cochlear implant [Abstract]( 1992)The Nucleus Cochlear implant allows ~ variety of multiple channel speech processing strategies to be developed and trialled. The initial strategy first developed by the University of Melbourne presented the second formant frequency as place and voicing as rate of stimulation. The strategy was subsequently improved by presenting the first format on a place basis as well. Since that time the addition of more spectral information coded as place of stimulation and temporal information presented as variations in amplitude have resulted in better open-set CNC word and sentence scores for electrical stimulation alone. One of the improved strategies selects four pairs of electrodes from the 22 electrode array each glottal pulse to present the first and second formants as well as the output from two high Frequency band pass filters. The other strategy stimulates six of the 22 electrodes representing the six maximal outputs from 16 bandpass filters. The clinical results have shown that both the above strategies results in better open-set speech perception for electrical stimulation in quiet and in noise. 80 % scores have been obtained for open-sets of CNC words and 90 % for open-sets of words in sentences for some of the patients using the latter strategy.