Graeme Clark Collection
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ItemA clinical report on receptive vocabulary skills in cochlear implant users( 1995)Objective: The aim was to measure the rate of vocabulary acquisition for cochlear implant users and compare the pre- and postoperative rates with published data for other groups with normal or impaired hearing. The hypothesis was that the postoperative rate would be greater than the preoperative rate. Design: The Peabody Picture Vocabulary Test (PPVT) was administered to 32 children, adolescents, and prelinguistically deafened adults implanted with the 22-electrode cochlear implant. Age at implantation ranged from 2 y r 6 mo to 20 yr and implant use ranged from 6 mo to 7 yr 8 mo. Results: The group mean postoperative performance at various postoperative intervals was significantly higher than mean preoperative performance. Single-subject data indicated statistically significant gains over time on this test for 13 of the subjects. The mean postoperative rate of vocabulary acquisition of 1.06 times the rate for normally hearing children was significantly greater than the mean preoperative rate of 0.43. Conclusions: These rates of improvement were in accord with previous reports on smaller numbers of implant users, but could not be attributed unambiguously to use of the implant because no control group was used for this clinical work. Variables such as age at implantation, duration of profound deafness, communication mode, and speech perception skill failed to significantly predict rate of improvement on the PPVT.
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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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ItemPitch matching of electric and acoustic stimuli( 1995)In the electric coding of speech for multiple-electrode cochlear implants, acoustic frequency ranges are mapped onto electrodes. The question arises as to whether the pitches of the electrically evoked hearing sensations are similar to those evoked by the corresponding acoustic stimuli in normal-hearing listeners. Obviously, the sensations are similar enough for many postlingually deaf implant users to understand speech with a minimum of retraining, but it is unlikely that the electric signals sound identical to the acoustic ones. There will also be differences between implant users arising from the variable insertion depth of the electrode array, the number of electrodes in use, and the frequency-to-electrode mapping. The most direct method of determining pitch is to ask implant users to compare electric and acoustic stimuli, but studies of this sort have been hampered by the fact that very few implant users have usable hearing for acoustic signals. In 1978, Eddington et al 1 reported pitch-matching results for one unilaterally deaf volunteer. They concluded that pitch matching was "roughly consistent with electrode position and tonotopic maps of the cochlea derived from basilar membrane motion and hearing loss measurements." Several other studies 2-6 have investigated the relative pitch of electric signals using identification, scaling, and discrimination paradigms. These studies have established that electrode placement, electrode configuration, and rate of stimulation all affect the perceived pitch, and that the pitch increases tonotopically from apical to basal electrode positions. They have not determined the pitch of electric stimuli in an absolute fashion that can be compared with acoustic stimuli, however. A knowledge of the absolute pitch of electric stimuli for individuals, or as a function of position in the cochlea, would be very useful in optimizing the frequency mapping for cochlear implants. The present study directly compared the pitch of acoustic pure tones in one ear with electric signals in the other ear of implant users with some residual hearing in the nonimplanted ear. The main questions addressed were whether the pulse rate of a matched electric stimulus would be equal to the frequency of the acoustic tone, and whether the electrode used in the matched stimulus would correspond in position to the place of maximum basilar membrane motion produced by the acoustic tone in a normal cochlea.
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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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ItemRole of a multichannel electrotactile speech processor in a cochlear implant program for profoundly hearing-impaired adults( 1991)Four profoundly hearing-impaired adults who did not meet current selection criteria for implantation at the University of Melbourne were each fitted with a wearable multichannel electrotactile speech processor (Tickle Talker). The subjects were evaluated with a test battery of speech discrimination tests subsequent to training in use of the device. Thresholds for detection of pure tones were lower for the Tickle Talker than for hearing aids across the frequency range 250 to 4000 Hz. Mean speech detection thresholds for the Ling 5-sound test showed that all sounds were detected by users of the electrotactile device at normal conversational speech intensity levels. Mean speech discrimination scores were significantly higher (p < 0.05) in the tactually aided condition as compared with the tactually unaided for identification of vowels and consonants, on open-set words, open-set sentences, and on connected discourse tracking. Mean scores increased by 20% for vowels, 19% for consonants, 30% for openset words, and 25% for open-set sentences when the Tickle Talker was used in a multimodal combination with lipreading or lipreading and hearing aids. Speechtracking rates for three subjects showed increases of from 18 to 28 wpm when the tactile device was used. Comparison of tactually aided versus unaided tracking rates for two subjects with long-term experience shows continuing improvement with additional experience with the device. These results demonstrate that hearing impaired adults not meeting selection criteria for cochlear implantation may benefit from use of an electrotactile speech processor, and highlight the potential benefits from integration of such devices into cochlear implant programs for profoundly hearing-impaired patients.