Graeme Clark Collection
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ItemElectrode discrimination by early-deafened subjects using the Cochlear Limited multiple electrode cochlear implant( 2000)Objective: The aims of this study were to determine whether electrode discrimination by early-deafened subjects using the Cochlear Limited prosthesis varied at different locations on the electrode array, was influenced by the effects of auditory deprivation and experience with electric stimulation, and was related to speech perception. Design: Difference limens for electrode discrimination were measured in 16 early-deafened subjects at three positions on the array: electrodes 18 (apical), 14 (mid), and 8 (basal). Electrodes were stimulated using random variations in current level to minimize the influence of loudness cues. Assessed were correlations between the difference limens, subject variables related to auditory deprivation (age at onset of deafness, duration of deafness, and age at implantation) and auditory experience (duration of implant use and the total time period of auditory experience), and speech perception scores from two closed-set and two open-set tests. Results: The average difference limens across the three positions were less than two electrodes for 75%, of subjects, with average limens between 2 and 6.5 electrodes for the remaining 25% of subjects. Significant differences across the three positions were found for 69% of subjects. The average limens and those at the basal position positively correlated with variables related to auditory deprivation, with larger limens for subjects implanted at a later age and with a longer duration of deafness. The average limens and those at the apical position negatively correlated with closed-set speech perception scores, with lower scores for subjects with larger limens, but not with open-set scores. Speech scores also negatively correlated with variables related to auditory deprivation. Conclusions: These findings showed that early-deafened subjects were generally successful in electrode discrimination although performance varied across the array for over half the subjects. Discrimination performance was influenced by the effects of auditory deprivation, and both electrode discrimination and variables related to auditory deprivation influenced closed-set speech perception.
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ItemPitch estimation by early-deafened subjects using a multiple-electrode cochlear implant( 2000)Abstract not available due to copyright.
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ItemShort-term auditory memory in children using cochlear implants and its relevance to receptive language( 2002)The aim of this study was to assess auditory sequential, short-term memory (SSTM) performance in young children using cochlear implants (CI group) and to examine the relationship of this performance to receptive language performance. Twenty-four children, 5 to 11 years old, using the Nucleus 22-electrode cochlear implant, were tested on a number of auditory and visual tasks of SSTM. The auditory memory tasks were designed to minimize the effect of auditory discrimination ability. Stimuli were chosen that children with cochlear implants could accurately identify with a reaction time similar to that of a control group of children with normal hearing (NH group). All children were also assessed on a receptive language test and on a nonverbal intelligence scale. As expected, children using cochlear implants demonstrated poorer auditory and visual SSTM skills than their hearing peers when the stimuli were verbal or were pictures that could be readily labelled. They did not differ from their peers with normal hearing on tasks where the stimuli were less likely to be verbally encoded. An important finding was that the CI group did not appear to have a sequential memory deficit specific to the auditory modality. The difference scores (auditory minus visual memory performance) for the CI group were not significantly different from those for the NH group. SSTM performance accounted for significant variance in the receptive language performance of the CI group. However, a forward stepwise regression analysis revealed that visual spatial memory (one of the subtests of the nonverbal IQ test) was the main predictor of variance in the language scores of the children using cochlear implants.
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ItemElectrode discrimination and speech perception in young children using cochlear implants( 2000)Objective: The aim was to determine the efficacy of a child-appropriate procedure to assess electrode discrimination ability in young children using cochlear implants and to investigate the relationship of electrode discrimination ability and speech perception performance in children implanted at a young age. Design: An adaptation of the play audiometry procedure was used to assess electrode discrimination in seventeen 4- to 10-yr-old children. The children were required to respond with a game-like motor response when a repeating stimulation on a reference electrode “changed” to a different electrode. They were also assessed on a speech feature discrimination test, a closed-set word recognition test and a nonverbal intelligence task. Results: Sixty-five percent of subjects demonstrated ability to discriminate adjacent electrodes in mid and apical regions of the cochlea, whilst the remaining subjects needed electrode separations of between two and nine electrodes for successful discrimination. In a forward stepwise regression analysis electrode discrimination ability was found to be the strongest factor in accounting for variance in the speech perception scores. Subject variables such as duration of deafness, nonverbal intelligence and implant experience did not significantly account for further variance in the speech perception scores for this group of children. Conclusions: Electrode discrimination ability was the strongest factor in predicting performance on speech perception measures in a group of children using cochlear implants.
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ItemPitch and loudness estimation for single and multiple pulse per period electric pulse rates by cochlear implant patients( 1997)Abstract not available due to copyright.
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ItemGap detection by early-deafened cochlear-implant subjects( 1999)Abstract not available due to copyright.
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ItemA clinical report on speech production of cochlear implant users( 1995)Objective: The aim was to assess articulation and speech intelligibility over time in a group of cochlear implant users implanted at 8 yr or over. The hypothesis was that the postoperative speech production performance would be greater than the preoperative performance. Design: A test of intelligibility using sentences and an articulation test measuring non-imitative elicited speech were administered to 11 and 10 subjects, respectively, who were implanted with the 22-electrode cochlear implant. Nine subjects received both tests. Age at implantation ranged from 8 yr to 20 yr and implant use ranged from 1 yr to 4 yr 5 mo. Results: For both the intelligibility and articulation tests roughly half of the subjects showed significant improvements over time and group mean postoperative performance significantly exceeded preoperative performance. Improvements occurred for front, middle, and back consonants; for stops, fricatives, and glides and for voiceless and voiced consonants. Conclusions: Despite being deprived of acoustic speech information for many childhood years, roughly half of the patients assessed showed significant gains in speech intelligibility and articulation postimplantation. The lack of a control group of non-implanted patients means that we cannot separate out the influence of the implant on speech production from other influences such as training and tactile-kinaesthetic feedback.
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ItemThe effects of auditory feedback from the nucleus cochlear implant on the vowel formant frequencies produced by children and adults( 1993)Cochlear implants provide an auditory signal with which profoundly deaf users may monitor their own speech production. The vowel production of two adults and three children who used the Nucleus multiple-electrode cochlear implant was examined to assess the effect of altered auditory feedback. Productions of words were recorded under conditions where the talkers received auditory feedback (speech processor turned on) and where no auditory feedback was provided (speech processor turned off). Data were collected over 3 days at weekly intervals. First and second formant frequencies were measured and the data were analysed to assess significant differences between auditory feedback conditions, vowel context, and data collection points. Overall, the results varied across talkers, across the data collection days, and depended on the consonant environment of the vowel. However, two effects of auditory feedback were noted. First, there was a generalized shift in first formant frequencies between the processor on and processor off conditions across three of the five subjects, but the shift differed in direction for each subject. Second, for three of the five talkers, the two front vowels /ε/ and /I/ were more neutralised in the absence of auditory feedback. However, this effect was less pronounced than that noted by previous studies.
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ItemElectrode position, repetition rate, and speech perception by early-and-late-deafened cochlear implant patients( 1993)Psychophysical and speech perception studies were conducted on eight patients using the 22electrode cochlear implant manufactured by Cochlear Pty. Ltd. Four early-deafened patients became deafened at 1-3 years of age and were implanted at 5-14 years of age. Four late-deafened (postlingual adult) patients became deafened at 38-47 years of age and were implanted at 42-68 years of age. Psychophysical studies measured the discrimination of trajectories with time-varying electrode positions and repetition rates. Speech perception studies measured performance using two speech coding strategies: a multi-electrode strategy which coded the first and second formant frequencies, the amplitudes of the two formants, and the fundamental frequency; and a single-electrode strategy which coded the amplitudes of the first and second formants, and the fundamental frequency. In general, the four late-deafened patients and one early-deafened patient were more successful than the other three early-deafened patients in the discrimination of electrode position trajectories and in speech perception using the multi-electrode strategy. Three of the four late-deafened patients were more successful than the early-deafened patients in the discrimination of repetition rate trajectories. Speech perception performance in the single-electrode strategy was closely related to performance in repetition rate discrimination. The improvement in speech perception performance from the single-electrode to multi-electrode strategy was consistent with successful performance in electrode discrimination.
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ItemResults for two children using a multiple-electrode intracochlear implant( 1989)Abstract not available due to copyright.