Graeme Clark Collection
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ItemRehabilitation strategies for adult cochlear implant users(Monduzzi Editore, 1997)This paper summarizes open-set speech perception results using audition alone for a large group of adult Nucleus cochlear implant users in Melbourne. The results show wide variation in performance but significant improvement over the years from 1982 to 1995. Analysis of these results shows that speech processor developments have made the major contribution to this improvement over this time. Recent results for patients using the SPECTRA-SPEAK processor show !hat most subjects obtain good speech perception within six months of implantation and the need for intensive auditory training is minimal for many of these patients. Postoperative care should encourage consistent device use by providing opportunities for success and providing long term technical support for implant users. In some cases, including elderly patients, those with long term profound deafness, and those with special needs, there will still be a need for additional rehabilitation and auditory training support.
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ItemFactors affecting outcomes in children with cochlear implants(Monduzzi Editore, 1997)Open-set speech perception tests were completed for a group of 52 children and adolescents who were long-term users of the Nucleus multiple channel cochlear prosthesis. Results showed mean scores for the group of 32.4% for open-set BKE sentences and 48.1% for phonemes in open-set monosyllabic words. Over 80% of the group performed significantly on these tas1cs. Age at implantation was identified as a significant factor affecting speech perception performance with improved scores for children implanted early. This factor was evident in the results at least down to the age of three years. Duration.. of profound hearing loss, progressive hearing loss, educational program and preoperative residual hearing were also identified as significant factors that may affect speech perception performance.
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ItemSpeech perception, production and language results in a group of children using the 22-electrode cochlear implant( 1989)Paper presented at the 118th Meeting of the Acoustical Society of America
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ItemSignal processing in quiet and noise( 1987)It has been shown that many profoundly deaf patients using multichannel cochlear implants are able to understand significant amounts of conversational speech using the prosthesis without the aid of lipreading. These results are usually obtained under ideal acoustic conditions but, unfortunately, the environments in which the prostheses are most often used are rarely perfect. Some form of competing signal is always present in the urban setting, from other conversations, radio and television, appliances, traffic noise and so on. As might be expected, implant users in general find background noise to be the largest detrimental factor in their understanding of speech, both with and without the aid of lipreading. Recently, some assessment of implant patient performance with competing noise has been attempted using a four-alternative forced-choice spondee test (1) at Iowa University. Similar testing has been carried out at the University of Melbourne with a group of patients using the Nucleus multichannel cochlear prosthesis. This study formed part of an assessment of a two formant (F0/FI/F2) speech coding strategy (2). Results suggested that the new scheme provided improved speech recognition both in quiet and with competing noise. This paper reports on some more detailed investigations into the effects of background noise on speech recognition for multichannel cochlear implant users.
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ItemA formant-estimating speech processor for cochlear implant patients(Speech Science and Technology Conference, 1986)A simple formant-estimating speech processor has been developed to make use of the "hearing" produced by electrical stimulation of the auditory nerve with a multiple-channel cochlear implant. Thirteen implant patients were trained and evaluated with a processor that presented the second formant frequency, fundamental frequency, and amplitude envelope of the speech. Nine patients were trained and evaluated with a processor that presented the first formant frequency and amplitude as well. The second group performed significantly better in discrimination tasks and word and sentence recognition through hearing alone. The second group also showed a significantly greater improvement when hearing and lipreading was compared with lipreading alone in a speech tracking task.
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ItemPsychophysics of multiple-channel stimulation(Raven Press, 1985)Eight patients implanted with multiple-channel cochlear prostheses have displayed good discrimination of sound sensations elicited at different sites within the cochlea. All patients rank the sensations from "sharp" to "dull" in an order which corresponds with basal to apical position in the cochlea. Detailed psychophysical studies have been carried out on two patients. These showed that discrimination of rate of (pulsatile) stimulation is good for frequencies up to 300 Hz and falls off sharply for frequencies above this. Electrode transitions (changes in position along the cochlea) are well discriminated for fast changes (25 msec), whereas rate transitions are not well discriminated for changes faster than 100 msec. From these results a speech processing strategy was formulated where second formant information is mapped to position in the cochlea and fundamental frequency mapped to rate of stimulation. Vowel and consonant confusion studies show consistent results for all patients using this processing strategy. A study involving two electrode stimuli demonstrated the possibility of presenting first formant information in addition to the second formant and fundamental frequency.