Graeme Clark Collection
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ItemChanges in synthetic and natural vowel perception after specific training for congenitally deafened patients using a multichannel cochlear implant( 1997)Objective: The aim was to determine whether the ability to use place-coded vowel formant information could be improved after training in a group of congenitally deafened patients, who showed limited speech perception ability after cochlear implant use ranging from 1 yr 8 mo to 6 yr 11 mo. A further aim was to investigate the relationship between electrode position difference limens and vowel recognition. Design: Three children, one adolescent, and one young adult were assessed with synthesized versions of the words /hid, head, had, hud, hod, hood/ containing three formants and with a natural version of these words as well as with a 12-alternative, closed-set task containing monosyllabic words. The change in performance during a nontraining period was compared to the change in performance after 10 training sessions. Results: After training, two children showed significant gains on a number of tests and improvements were consistent with their electrode discrimination ability. Difference limens ranged from one to three electrodes for these patients as well as for two other patients who showed minimal to no improvements. The minimal gains shown by the final patient could be partly explained by poorer apical electrode position difference limen. Conclusions: Significant gains in vowel perception occurred post-training on several assessments for two of the children. This suggests the need for children to continue to have aural rehabilitation for a substantial period after implantation. Minimal improvements, however, occurred for the remaining patients. With the exception of one patient, their poorer performance was not associated with poorer electrode discrimination.
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ItemSpeech perception results for children with implants with different levels of preoperative residual hearing( 1997)Objective: Many reports have established that hearing-impaired children using the Nucleus 22 channel cochlear implant may show both significant benefits to lipreading and significant scores on open-set words and sentences using electrical stimulation only. These findings have raised questions about whether severely or severely-to-profoundly deaf children should be candidates for cochlear implants. To study this question, postoperative results for implanted children with different levels of preoperative residual hearing were evaluated in terms of speech perception benefits. Study Design/Setting: A retrospective study of the first 117 children, sequentially, to undergo implantation in the Melbourne and Sydney Cochlear Implant Clinics was undertaken. All children had been assessed by and received their implants in a tertiary referral centre. Main Outcome Measures: To assess aided residual hearing, the children were grouped into four categories of hearing on the basis of their aided residual hearing thresholds measured preoperatively. To assess benefits, the scores of children on standard speech perception tests were reviewed. As different tests were used for children with different ages and language skills, children were grouped into categories according to the level of postoperative speech perception benefit. Results: The results showed that children in the higher categories of aided preoperative residual hearing showed significant scores on open-set word and sentence perception tests using the implant alone. For children in lower categories of aided residual hearing, results were variable within the groups. More than 90% of children with implants with aided residual hearing thresholds in the speech range above I kHz achieved open-set understanding of words and sentences. Conclusion: While the results of this preliminary study confirm previous findings of differential outcomes for children with different levels of preoperative residual hearing, they suggest that children with severe to profound hearing impairments should be considered for cochlear implantation.
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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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ItemCochlear implants in the third millennium( 1999)This article discusses the specific challenges facing cochlear implantation in the Third Millennium.
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ItemGap detection by early-deafened cochlear-implant subjects( 1999)Abstract not available due to copyright.
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ItemChronic electrical stimulation of the auditory nerve using non-charge-balanced stimuli( 1999)This study was designed to evaluate the pathophysiological response of the cochlea following long-term intracochlear electrical stimulation using a poorly charge-balanced stimulus regime, leading to direct current (DC) levels >0.1 µA. Four normal-hearing adult cats were bilaterally implanted with scala tympani electrode arrays and unilaterally stimulated for periods up to 2200 h. Stimuli consisted of 50 µs monophasic current pulses presented at 2000 pulses per second (pps) per channel, and resulted in DC levels of 0.4-2.8 µA. Both acoustic and electrical (EABR) evoked potentials were periodically recorded during the stimulation program. Frequency-specific stimuli indicated that an extensive and widespread hearing loss occurred over the 4-24 KHz region in all stimulated cochleae, although the 2 KHz region exhibited thresholds close to normal in some animals, despite long-term implantation and chronic stimulation. Longitudinal EABRs showed a statistically significant increase in threshold for three of the four animals. Histopathological evaluation of the cochleae revealed a highly significant reduction in ganglion cell density in stimulated cochleae compared with their controls. Spiral ganglion cell loss was significantly correlated with the degree of inflammation, duration of electrical stimulation, and the level of DC. In conclusion, the present study highlights the potential for neural damage following stimulation using poorly charge-balanced stimuli.
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ItemAided speech recognition abilities of adults with a severe or severe-to-profound hearing loss( 1998)Adults with severe or severe-to-profound hearing losses constitute between 11% and 13.5% of the hearing impaired population. A detailed investigation of the speech recognition of adults with severe (n = 20) or severe-to-profound (n = 14) hearing loss was conducted at The University of Melbourne. Each participant took part in a series of speech recognition tasks while wearing his or her currently fitted hearing aid(s). The assessments included closed-set tests of consonant recognition and vowel recognition, combined with open-set tests of nonosyllabic word recognition and sentence recognition. Sentences were presented in quiet listening conditions. Although the results demonstrated wide variability in performance, some general trends were observed. As expected vowels were generally well perceived compared with consonants. Monosyllabic word recognition scores for both the adults with a severe hearing impairment (M = 67.2%) and the adults with a severe-to profound hearing impairment (M = 38.6%) could be predicted from the segmental tests, with an allowance for lexical effects. Scores for sentences presented in quiet showed additional linguistic effects and a significant decrease in performance with the addition of background noise (from 82.9% to 74.1% for adults with a severe hearing loss and from 55.8% to 34.2% for adults with a severe-to-profound hearing loss). Comparisons were made between the participants and a group of adults using a multiple-channel cochlear implant. This comparison indicated that some adults with a severe or severe-to-profound hearing loss may benefit from the use of a cochlear implant. The results of this study support the contention that cochlear implant candidacy should not rely solely on audiometric thresholds.
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ItemThe perceptual dimensions of single-electrode and nonsimultaneous dual-electrode stimuli in cochlear implantees( 1996)Abstract not available due to copyright.
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ItemControl strategies for neurons modeled by self-exciting point processes( 1996)Abstract not available due to copyright.