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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ItemA multiple-channel cochlear implant: an evaluation using nonsense syllables( 1981)A study using nonsense syllables has shown that a multiple-channel cochlear implant with speech processor is effective in providing information about, voicing and manner and to a lesser extent place distinctions. These distinctions supplement lipreading cues. Furthermore, the average percentage improvements in overall identification scores for multiple-channel electrical stimulation and lipreading compared to lipreading alone were 71% for a laboratory-based speech processor and 122 % for a wearable unit.
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ItemA multiple-channel cochlear implant: an evaluation using an open-set word test( 1981)Multiple-channel electrical stimulation of the hearing nerve in conjunction with speech reading has helped two post-lingually deaf patients with total hearing losses understand running speech in every day situations. This has been confirmed using open-set phonetically balanced word tests, where the patients achieved 60% and 40% scores with isolated-words and 80% and 73% for phonemes-in-isolated words. The tests also showed that the cochlear implant improved word recognition by a factor of four in one patient and two in another compared with speechreading alone. The speech processor used extracted the voicing frequency and energy and the frequency and energy of the dominant spectral peak in the mid-frequency range. The parameters for voicing determined the rate of stimulation for all electrodes, and the parameters for the dominant spectral peak in the midfrequency range determined the site of electrode stimulation and current level.
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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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ItemModulation detection interference in cochlear implant subjects( 1998)Abstract not available due to copyright.
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ItemStudies of prosody perception by cochlear implant patients( 1998)Prosodic information is conveyed to normally-hearing listeners by variations in acoustic fundamental frequency, amplitude envelope, and duration of speech segments. This study measured cochlear implant patients' sensitivity to these parameters in electrically coded speech. The psychophysical discrimination of electric parameters used to code prosodic information, were examined, together with prosody perception using speech processing strategies which modified the contributions of these parameters. Patients were implanted with the Cochlear Limited prosthesis and used the MPEAK speech processing strategy. In the psychophysical studies, difference limens were measured for steady-state and time-varying stimuli, of different pulse rates and pulse durations, over a series of different stimulus durations. These limens were obtained using an adaptive procedure which converged on the 50 per cent correct point. In the prosody perception studies, performance was measured for the MPEAK strategy and for strategies which modified the contributions of pulse rate and pulse duration. Data were collected for five tests of prosodic contrasts. Difference limens for steady-state pulse rates were larger at higher rates (17 per cent at 400 pulses/s) than at lower rates (6 per cent at 100 pulses/s). For some patients, limens for the time-varying pulse rates were larger than those for the steady-state pulse rates while for the other patients, the limens were similar. Difference limens for pulse duration were 0.3 dB, corresponding to 4 per cent of the dynamic range, for steady-state stimuli and doubled in size for the time-varying stimuli. Prosody perception performance was generally poorer for the modified strategies than for the MPEAK strategy, suggesting that the removal of information coded by pulse rate and pulse duration reduced the perception of prosodic contrasts.
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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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ItemFormant frequency values of vowels produced by preadolescent boys and girls( 1995)Abstract not available due to copyright.
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ItemPitch perception for different modes of stimulation using the Cochlear multiple-electrode prosthesis( 1994)Abstract not available due to copyright.