Graeme Clark Collection
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ItemA review of the biological, psychophysical, and speech processing principles used to design the tickle talker( 1992)The Tickle Talker is a wearable electrotactile speech processor, designed to be used by profoundly hearing-impaired children and adults in conjunction with lipreading and residual hearing. The effectiveness of such a device is affected by an interaction between biological, human engineering, psychophysical, and speech processing considerations. The requirements, the design principles, and the performance of the Tickle Talker in each of these areas will be discussed. Electrical stimulation of the nerve bundles lying along the sides of the fingers was chosen to provide safe, comfortable, energy-efficient stimulation of a well-organised and sensitive part of the tactile sensory system. This is achieved at a small cost to the appearance and mobility of one hand when using the Tickle Talker. The biphasic pulse waveform used to stimulate the nerve bundles has been chosen to ensure a biologically safe stimulus. The electrical parameters (pulse duration, pulse rate, and electrode position) that are used to encode speech information are varied within ranges that are matched to the characteristics of the tactile sense. The usable ranges and information-carrying potential of each of these parameters have been assessed in psychophysical experiments. A comparison of these results with similar experimental data for cochlear implant and hearing aid users is instructive in assessing the possible limitations of tactile and auditory speech processors. The results discussed will include the discrimination and identification of stimuli differing in intensity, duration and pulse rate; the identification of different spatial patterns of stimulation, and the detection of gaps in stimuli. In most respects, the tactile results are similar to the corresponding auditory measures. The resolution of temporal differences such as pulse rate discrimination or gap detection are generally not as good as in the auditory case, but may be as good or better than the corresponding results for some profoundly hearing-impaired individuals. The speech processor used in the Tickle Talker is a "feature extraction" device that explicitly estimates the second formant frequency, amplitude envelope, and fundamental frequency of the voice and encodes them in terms of electrode position, pulse width and pulse rate of the electrical stimulation pattern. Consideration of the psychophysical results and the speech information available from these parameters allows optimization of the Tickle Talker's operation and a broad estimation of its potential performance in speech discrimination. The perception of duration and place of articulation (front/back) of vowels, and the manner and voicing of consonants are expected to be improved by the Tickle Talker. Prosodic variations conveyed by pulse rate are expected to be perceived by some users, but not all. High frequency consonants such as: /s/,/z/./?/, and /t?/ are encoded in a particularly salient manner by the Tickle Talker.
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ItemSpeech processing for cochlear implants(JAI Press Ltd, 1992)The cochlear implant is a hearing prosthesis designed to replace the function of the ear. The operation of the prosthesis can be described as a sequence of four functions: the processing of the acoustic signal received by a microphone; the transfer of the processed signal through the skin; the creation of neural activity in the auditory nerve; and the integration of the experience of this neural activity into the perceptual and cognitive processing of the implantee.
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ItemCochlear implants in children, adolescents, and prelinguistically deafened adults: speech perception( 1992)A group of 10 children, adolescents, and prelinguistically deafened adults were implanted with the 22-electrode cochlear implant (Cochlear Pty Ltd) at the University of Melbourne Cochlear Implant Clinic and have used the prosthesis for periods from 12 to 65 months. Postoperative performance on the majority of closed-set speech perception tests was significantly greater than chance, and significantly better than preoperative performance for all of the patients. Five of the children have achieved substantial scores on open-set speech tests using hearing without lipreading. Phoneme scores in monosyllabic words ranged from 30% to 72%; word scores in sentences ranged from 26% to 74%. Four of these 5 children were implanted during preadolescence (aged 5:5 to 10:2 years) and the fifth, who had a progressive loss, was implanted during adolescence (aged 14:8 years). The duration of profound deafness before implantation varied from 2 to 8 years. Improvements were also noted over postoperative data collection times for the younger children. The remaining 5 patients who did not demonstrate open-set recognition were implanted after a longer duration of profound deafness (aged 13:11 to 20:1 years). The results are discussed with reference to variables that may affect implant performance, such as age at onset of loss, duration of profound loss, age at implantation, and duration of implantation. They are compared with results for similar groups of children using hearing aids and cochlear implants.
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ItemDesign fundamentals for a tactile speech processor: i) encoding of speech information, and ii) biomedical safety considerations [Abstract]( 1992)Approaches to providing speech information through the tactual modality have varied in: number and spatial location of transducers; method of interfacing with the skin's sensory apparatus; and content of speech information presented. Use of a multiple speech feature encoding approach to design of a tactile device was implemented in the wearable multichannel electrotactile speech processor or Tickle Talker developed at the University of Melbourne. Psychophysical studies established that subjects could discriminate salient electrical parameters in the tactual display, and that this information could be used to discriminate acoustic speech feature contrasts. Results with normally-hearing and hearing-impaired adults and children using an FOF2 encoding strategy showed improved discrimination scores for closed-set speech feature discrimination batteries, closed-set vowel and consonant identification tasks, as well as for open-set word and sentence comprehension. Based on analyses of tactual encoding of speech features, alternative speech processing strategies designed to increase the quality of speech information available were evaluated. Results for two hearing-impaired adults showed improved feature discrimination with the addition of a voicing signal to the FOF2 strategy. Biomedical safety investigations conducted concurrently have established that the electrical parameters of the stimulus waveform, electrode handset design, and electrical circuitry of the device are free from potential risks. Longer-term physiological assessments included measures of possible effects of electrical stimulation on tactual sensitivity, finger temperature, finger and hand blood flow, electrical thresholds and maximum comfortable levels, and on central nervous system, function as measured by EEG. Results of the kinesthetic, vascular and neurological assessments showed no significant contraindications which might limit application or long-term use of the device.
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ItemClinical experience with the University of Melbourne multichannel electrotactile speech processor (Tickle Talker)( 1992)The Tickle Talker is a multiple channel electrotactile speech processor, developed for use by profoundly hearing-impaired adults and children. The device is intended to be used in combination with lipreading and aided residual hearing, to assist the greatest potential range of users. Sound detection and speech reception threshold levels for a group of 14 congenitally hearing-impaired children were shown to be lower when using the Tickle Talker than for hearing aids across the speech frequency range. Tactile-alone feature contrast testing with adults demonstrated that both segmental and suprasegmental speech feature information was available from the tactual display presented by the Tickle Talker. Clinical results from an ongoing program involving fourteen hearing-impaired children demonstrate benefits in speech perception achieved through use of the Tickle Talker. The children have a range of degree of hearing impairment and educational setting. Results show improvements in discrimination scores for vowel and consonant speech features, and increased scores for recognition of closed-set words and for open-set words and sentences. In addition, anecdotal evidence indicates changes in speech production which may be attributed to perceptual input from the device (both from perception of other speakers, and from voice self-monitoring). Results from a group of 4 adult patients show that tactile input may be effectively combined with either aided residual hearing, or aided residual hearing and lipreading to improve speech discrimination across a similar range of closed and open-set word and sentence tests and on speech tracking. The results indicate that some specific tailoring of the speech information provided through the device for the needs of users with differing degrees of hearing-impairment may be required to optimize potential benefits to speech discrimination.
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ItemSafety studies with the University of Melbourne multichannel electrotactile speech processor( 1992)Results of safety investigations conducted as an integral part of the development of a multichannel electrotactile speech processor (Tickle Talker™) are reported. Electrical parameters of the stimulus waveform, design of the electrode handset and cabling, and the electrical circuitry of the speech processor/stimulator and programming interface have been analysed for potential risks. Constant current biphasic square pulses delivered to electrodes positioned on the skin surface over the digital nerve bundles were chosen to optimize the safety, comfort, and function of the electrotactile stimulus. The device was battery-powered, and the user circuit was isolated from earth-referenced sources. Each electrode was isolated by capacitive coupling, preventing DC leakage of current to the user circuit. Studies of finger temperature showed slight cooling of the skin on the fingers of both stimulated and unstimulated hands for individual subjects following electrotactile stimulation through the Tickle Talker. Subsequent analysis of finger and hand vascular circulation in five subjects showed slight reductions in hand blood flow in some individuals. The results did not demonstrate a significant mean decrease in hand or finger blood flow following electrotactile stimulation. No evidence of sympathetic involvement was found, nor were any changes in vascular structure of the hand such as those associated with Raynaud's disease found. Evidence suggests that the decrease in temperature found in the initial study may be due to a change in the ratio of blood flow between arteriovenous anastomoses and nutritive capillary beds. Studies of: 1) changes in mean threshold and comfortable pulse widths over time; and, 2) changes in tactual sensitivity as measured by hot/cold, sharp/dull, and two-point difference limen discrimination, did not detect any systematic change in peripheral nervous system function following electrotactile stimulation. Analysis of electroencephalogram (EEG) recordings taken during electrotactile stimulation, and after relatively long periods of experience with the device did not show any pathological changes which might be associated with epileptic foci. In summary, no contraindications to long-term use of the Tickle Talker were detected in the studies performed.
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ItemSpeech perception, production and language results in a group of children using the 22-electrode cochlear implant( 1992)Five children out of a group of nine (aged 5.5 to 19.9 years) implanted with the 22-electrode cochlear implant (Cochlear Ply. Ltd.) have achieved substantial scores on open-set speech tests using hearing without lipreading. Phoneme scores for monosyllabic words ranged from 40% to 72%. Word scores in sentences ranged from 26% to 74%. Four of these five children were implanted during preadolescence. The fifth child, who had a progressive loss and was implanted during adolescence after a short period of very profound deafness, scored highest on all speech perception tests. The remaining four children who did not demonstrate open-set recognition were implanted during adolescence after a long duration of profound deafness. Post-operative performance on closed-set speech perception tests was better than pre-operative performance for all children. Improvements in speech and language assessments were also noted. These improvements tended to be greater for the younger children. The results are discussed with reference to variables which may contribute to successful implant use: such as age at onset, duration of profound hearing loss, age at implantation, aetiology, educational program, and the type of training provided.
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ItemCochlear implants in children, adolescents, and prelinguistically deafened adults: speech perception( 1992)A group of 10 children, adolescents, and prelinguistically deafened adults were implanted with the 22-electrode cochlear implant (Cochlear Ply Ltd) at the University of Melbourne Cochlear Implant Clinic and have used the prosthesis for periods from 12 to 65 months. Postoperative performance on the majority of closed-set speech perception tests was significantly greater than chance, and significantly better than preoperative performance for all of the patients. Five of the children have achieved substantial scores on open-set speech tests using hearing without lipreading. Phoneme scores in monosyllabic words ranged from 30% to 72%; word scores in sentences ranged from 26% to 74%. Four of these 5 children were implanted during preadolescence (aged 5:5 to 10:2 years) and the fifth, who had a progressive loss, was implanted during adolescence (aged 14:8 years). The duration of profound deafness before implantation varied from 2 to 8 years. Improvements were also noted over postoperative data collection times for the younger children. The remaining 5 patients who did not demonstrate open-set recognition were implanted after a longer duration of profound deafness (aged 13:11to 20:1 years). The results are discussed with reference to variables that may affect implant performance, such as age at onset of loss, duration of profound loss, age at implantation, and duration of implantation. They are compared with results for similar groups of children using hearing aids and cochlear implants.
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ItemUse of a multichannel electrotactile speech processor by profoundly hearing-impaired children in a total communication environment( 1991)As part of a larger subject group, four profoundly hearing-impaired children enrolled in a total communication educational program were fitted with the University of Melbourne's multichannel electrotactile speech processor (Tickle Talker). Sound detection thresholds for pure tones were at lower levels with the tactile device than with hearing aids, especially for high frequency sounds above 2 kHz. Two of the children also detected all speech sounds of the Ling five-sound test at normal conversational levels using only the Tickle Talker. The children were able to use tactile input to achieve higher scores on three speech feature subtests of the PLOTT test when using the Tickle Talker plus hearing aids as compared to hearing aids alone. Mean improvements were 22.4 percent on vowel length, 28 percent on vowel identification, and 35 percent on consonant manner. Improvements were also shown by individual children on the closed-set WIPI and open-set PBK word tests, and on the open-set BKB sentence test, when the Tickle Talker was combined with hearing aids, and with hearing aids and lipreading. Comparisons of these results with those of children using the Tickle Talker in other educational settings show that children in a total communication environment can potentially benefit to a similar degree from use of tactual input. Anecdotal reports from the children and school staff members indicated that daily use of the Tickle Talker did not interfere with the signing aspects of total communication.
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ItemSpeech perception results in children using the 22-electrode cochlear implant [Abstract]( 1990)Twenty-one profoundly hearing impaired children ranging in age from 3 to 20 years have been implanted with the 22-electrode cochlear implant (Cochlear Pty ltd) at the University of Melbourne Cochlear Implant Clinic. Five children (aged 6.0 to 14.8 years) have achieved substantial scores on open set speech tests using hearing without lipreading. Phoneme scores in monosyllabic words ranged from 30% to 72%. Word scores in sentences ranged from 26% to 74%. Four of these five children were implanted during preadolescence and the fifth who had a progressive loss, was implanted during adolescence. Eight children (aged 3.0 to 11 years), have either been implanted recently or are too young for detailed assessments. However some have shown using closed set speech perception tests or vowel imitation tasks, that they are beginning to use the auditory input provided by the implant. The remaining children (aged 13.11 to 20.1 years) have not demonstrated open set recognition but are all full time users of the device. This group was implanted during adolescence after a long duration of profound deafness. The results will be discussed with reference to a number of variables which may contribute to successful implant use; such as age of onset of deafness, duration of deafness. age of implantation, educational program and type of training.