Graeme Clark Collection
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ItemPredicting speech perception outcomes for children using multichannel cochlear implants [Abstract]( 2002)The ability to predict outcomes for children who are cochlear implant candidates is most helpful in counselling families and making clinical recommendations. Open-set speech perception results have been collected for all children implanted with the Nucleus device in Melbourne. Speech perception as assessed at six month intervals following implantation. Information wascollected for each child regarding type of hearing loss, duration and age at onset of profound hearing loss, age at implantation, pre and post-implant communication mode, developmental delay, speech coding scheme and implant experience.
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ItemLatest results for adults & children using cochlear implants & future implications( 2000)The overall success of a cochlear implant procedure is most often quantified by assessing how well implantees can understand speech. This is because a primary aim of the application of cochlear implants is to improve communication, and it is relatively straightforward to obtain accurate measures of speech recognition. The quality of cochlear implant hearing is not well described by measuring an audiogram, as the detection of sound is similar across all implantees if the device is functioning correctly. A commonly used measure of speech understanding is the CID everyday sentence test where the number of correctly identified words within sentences is assessed. In the early days of cochlear implants, subjects could only recognize a few words without lipreading but the most recent results show average scores of 80% without lipreading for this sentence test, after 6 months of experience with the device.
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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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ItemFactors influencing gap detection in children using cochlear implants [Abstract]( 1998)Two studies on gap detection were conducted with children implanted with the Cochlear Limited multiple-electrode prosthesis. In the first study, gap thresholds were measured at three pulse rates (200, 500, and 1000 pulses/s) and two stimulus durations (500 and 1000 ms) in 15 subjects. Average gap thresholds ranged from 1.8 to 32.1 ms. There was, essentially, no effect of pulse rate and in all but two subjects, no effect of stimulus duration. For these two subjects, thresholds were higher for the 1000 ms stimulus duration. In the second study, the relationships between gap thresholds and subject characteristics, and between gap thresholds and speech perception scores were examined using data from 27 subjects. A significant negative correlation between age at onset of deafness and gap thresholds was found, indicating that subjects with an earlier onset of deafness had larger gap thresholds, and most of the variability in gap thresholds was found for the congenitally deaf subjects. Gap thresholds did not correlate with other subject variables, such as duration of deafness and duration of implant use. Significant negative correlations were found between gap thresholds and word scores for open-set BKB sentences in the auditory-visual condition and the lipreading enhancement scores for the same test, indicating that subjects with poorer gap thresholds had lower speech scores. Gap thresholds did not correlate with word scores for BKB sentences in the audition alone condition, and scores for closed-set monosyllabic word tests.
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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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ItemPrediction of variance in neural response to cochlear implant stimulation and its implications for perception [Abstract]( 1997)Cochlear implant patients' perception of sound is derived via electrical pulses arising from an electrode array. Chosen aspects of the acoustic spectrum are coded via a stimulation pattern designed according to some sound coding algorithm. Thus, a patients' ability to discriminate between sounds, and in turn their understanding, is directly related to their ability to differentiate between the patterns of electrical stimulation which code various sounds.
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ItemCurrent speech perception benefits for adults using the speak strategy with the nucleus 22-channel cochlear implant( 1997)Present day recipients of the Nucleus 22-channel cochlear implant make use of the SPEAK speech processing strategy in the Spectra 22 speech processor. Introduced in 1994, the SPEAK strategy is based upon research conducted at the University of Melbourne and the Bionic Ear Institute. This paper compares the pre-and post-operative speech perception abilities of adults who have used the SPEAK speech processing strategy since the 'start-up' of their cochlear implant system. Data was analysed from open-set sentence and word tests administered pre-operatively and at regular intervals postoperatively. Patients showed significant improvement in their ability to recognise speech, when listening with the cochlear implant without lipreading, within the first two weeks. Mean scores for open-set sentences were 15% preoperatively and 64% two weeks after initial programming.
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ItemSpeech cues for cochlear implantees: spectral discrimination [Abstract]( 1997)The ability of cochlear implantees to understand speech varies over a wide range. While some implantees achieve scores close to 100 % open set word tests, other require visual cues to achieve a significant score on these tests. The focus of this research is to investigate reasons for the wide range of ability and therefore to improve the speech processors used by individual implantees. This study first investigated whether the relative importance of various frequency regions of the speech spectrum differs for implantees of different performance levels, and for implantee groups compared to normally hearing subjects.
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ItemSpeech perception of hearing aid users versus cochlear implantees [Abstract]( 1997)Recent improvements in speech recognition for profoundly deaf, cochlear implant patients have suggested that some people with a severe hearing impairment would be more successful with a cochlear implant than a hearing aid. Unfortunately, no studies have investigated the speech perception of the severely hearing impaired in order compare their speech perception abilities with those of cochlear implant users. To investigate this area further, a detailed investigation of the hearing aid performance of people with a severe hearing loss is being conducted in the Department of Otolaryngology at The University of Melbourne. The range of hearing losses for this study was defined as a pure tone average of greater than 6OdBHL, but no worse than 100dBSPL in the better ear. At present thirty-five (n=35) participants have been involved in this study. Each participant took part in a series of speech perception tests which included 24 consonant recognition, 11 vowel recognition, CNC words, CUNY sentences, and the connected speech test.
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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.