Graeme Clark Collection
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ItemA "Combionic Aid": Combined speech processing for a cochlear implant in one ear and speech processing hearing aid in the other ear [Abstract]( 1993)Independent use of a cochlear implant in one ear and a hearing aid in the other is not acceptable for many implant users with some residual hearing. Psychophysical evidence suggests that there are substantial interactions between acoustic and electrical signals including masking and loudness summation. These effects may contribute to the difficulty in using two independent devices and it is desirable to control the parameters of the electrical and acoustical signals far more accurately than is possible with two independent devices with separate microphones. In order to achieve this control we have developed a Combionic aid incorporating an implant and an 'in1planlcompatible' hearing aid controlled from the same speech processor. The new processor is particularly flexible and can implement a wide variety of speech processing strategies for combined acoustic and electrical stimulation. A benchtop prototype has been tested with five patients using a range of different speech tests. In general, patients do better when they use acoustic and electrical information simultaneously than they do with either alone. Some patients on some tests perform significantly better with the bimodal aid than they do with independent hearing aids and implant processors worn together. Wearable devices have now been built and evaluations of these devices are continuing.
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ItemPre- & post-operative factors affecting speech perception in adult cochlear implant users( 1997)A common feature of published studies of cochlear implantation is a very wide range of performance levels within a group of patients. It is well-established that preoperative factors including duration of deafness, age at implantation, duration of implant use and etiology can have statistically significant effects on speech perception with a cochlear implant, but they do not account for a very high proportion of the variance within groups of implant users. The biological basis for these effects is not well established. For example, it is unclear whether the effect of duration of deafness is due to a decrease in the number of surviving ganglion cells in the cochlea, to the detailed distribution of functional neurons within the cochlea, to degeneration of nerve function at higher auditory centers, to plastic neural effects during deafness, or to a combination of all of these mechanisms. Data for other factors may cast some light on these possibilities.
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ItemThe auditory cortex and auditory deprivation: experience with cochlear implants in the congenitally deaf [Abstract]( 1995)The primary auditory cortex (AI) exhibits a topographic representation of the organ of Corti in normal hearing animals. Plasticity studies have shown that this orderly representation of frequency can be modified following a restricted hearing loss or by behavioural trainingl,2. Little is known, however, of the effects of a profound hearing loss on AI, although a number of early studies have suggested an enhancement of activity from other modalities3. Knowledge of the functional status of the central auditory pathway in the profoundly deaf, and the ability of these structures to undergo reorganization particularly following long periods of auditory deprivation - are important issues for the clinical management of cochlear implant patients. In this paper we review our recent clinical and experimental experience with cochlear implants in the congenitally deaf.
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ItemThe effect of language knowledge on speech perception: what are we really assessing? [Abstract]( 1996)It is a common finding that many hearing-impaired children have poorer language skills than their normally-hearing peers of the same age. It is also logical to assume that the measurement of open-set speech perception in children with cochlear implants could be affected by limited receptive vocabulary and syntactic knowledge. Therefore, we may be significantly underestimating the speech perception abilities of some hearing-impaired children.
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ItemClinical comparison of open-set speech perception with MSP and WSPIII speech processors and preliminary results for the new SPEAK processor [Abstracts]( 1993)There are several studies which compare the WSP III (FOIF11F2) and MSP (Multipeak) speech processors for the Nucleus multiple-channel cochlear implant in small, controlled groups of patients. In the present study we were interested in the benefits of open set speech perception provided by the MSP over the prior WSP III speech processor in a large, unselected clinical population.
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ItemFuture directions in the clinical application of multichannel cochlear prostheses [Abstract]( 1992)Three main areas of work at the University of Melbourne relating to the clinical application of multichannel cochlear prostheses will be discussed. Speech perception results for 40 children and adolescents implanted with the Nucleus multichannel device will be presented with an analysis of potentially predictive clinical factors. Overall results have shown that 60% of the children have developed useful open-set speech recognition ability without visual cues. Due to the improved speech perception for postlinguistically deafened adult cochlear implant patients, the multichannel implant has become a viable alternative for patients with some useful residual hearing. A "bimodal" speech processor which provides acoustic output for the residual hearing ear and electrical output for the cochlear implant will also be discussed. This device provides a flexible, programmable acoustic processor which can make use of feature coding aspects of the implant processing. The "bimodal" device has also addressed problems of incompatibility of the implant signal with the acoustic signal from conventional hearing aids. Results for the new "Spectral Maxima Speech Processor" (SMSP) will also be presented. The SMSP has shown improved speech perception performance in quiet and in noise when compared with the MSP (MULTIPEAK) system, currently in use with the Nucleus device. Results for four subjects with the SMSP showed mean scores of 57.4% for open-set monosyllabic words in quiet, and 78.7% for open-set sentences in a 10 dB signal-to-noise ratio
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ItemFuture developments in speech processing for multichannel cochlear implants in children [Abstract]( 1992)The average speech perception score for adult implant patients is now about 60% on an open-set sentence test without lipreading. This is higher than the scores obtained by many profound and severe-to-profoundly impaired hearing aid users. This suggests that some hearing aid users, particularly those who use a hearing aid in one ear only, could benefit from a cochlear implant. As neither the implant nor the hearing aid will provide perfect speech recognition it is to be expected that this group should obtain maximum benefit by using the hearing aid in one ear together with the implant in the other ear. However, experience with this group of patients has shown that many people find the use of two independent devices unacceptable. Furthermore, perceptual interaction of the acoustic and electrical signals makes it desirable to be able to control the two outputs in a more co-ordinated way than is possible with two independent devices. Consequently, a "bimodal" speech processor has been developed with both acoustic and electrical outputs controlled from the same speech processing unit. Feature coding aspects of the implant processing have been applied to the acoustic signal in such a way as to enhance speech perception with the hearing aid and improve compatibility with the implant. Initial testing with the bimodal aid shows promise to help severely-to-profoundly impaired individuals. The device has also been useful as a research tool to investigate the complex interactions of simultaneous acoustic and electrical stimulation. The Spectral Maxima Sound Processor (SMSP) has also been developed at the University of Melbourne for use with the Nucleus cochlear implant. Studies with adult subjects have shown improved perception of vowels, consonants, words and sentences in quiet and sentences in background noise with the SMSP as compared with the MSP(MULTIPEAK) which is currently supplied for use with this implant. Results for four subjects showed mean scores for open set sentences at a 10 dB signal-to-noise ratio of 78.7% for the SMSP and 50.0% for the MSP. Mean scores for the same group on open set monosyllabic words in quiet were 57.4% for SMSP and 39.9% for MSP. These results suggest that future improvements in speech perception will be possible for children using the Nucleus cochlear implant.
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ItemFactors affecting speech perceptual performance for children using the 22-electrode cochlear prosthesis [Abstract]( 1992)Speech perception results for all 40 children and adolescents implanted with the. Nucleus 22 electrode cochlear prosthesis in Melbourne (as of February 1, 1992) were used to categorize performance for each child into one of six hierarchical groups: 1: detection of speech including high frequencies 2: discrimination of suprasegmental features of speech in addition to 1,3: discrimination and recognition of .vowel sounds in addition to 1 and 2,.4: discrimination arid recognition of consonant sounds in addition to 1, 2 and 3,5: open set speech. recognition with scores less than 20% for unfamiliar material in addition to 1 to 4,6: open set speech recognition with scores greater than 20% for unfamiliar material in addition to 1 to 5, above.All children demonstrated discrimination of suprasegmentals (level 2) and 58% demonstrated some openset speech recognition (levels 5 and 6). The pattern of results suggested that children who can discriminate segmental features of speech tend to achieve open set speech perception after adequate experience with the prosthesis. The performance level, described above, was used as the dependent variable in a multiple regression analysis to assess the effect of various factors on speech perception performance. The duration of profound hearing impairment and the amount of experience with the prosthesis were shown to contribute significantly to the variance, in performance level. A weaker trend was evident (or recently implanted children which may suggest that those' in oral/aural educational settings progress more rapidly, in terms of speech perception, than those in total communication settings. Age at implantation, cause of deafness, hearing levels prior to implantation, and number of electrodes in use, did not contribute significantly. to the variance in speech perception performance for these children. The results showed that all children with less than seven years of profound hearing impairment and with over one year of experience with the prosthesis have achieved some open-set speech recognition. This is an encouraging result as the trend in clinical application of cochlear prostheses has been towards implanting younger children in recent years. If this sample of hearing-impaired children in Melbourne is representative of the general population, we may expect that most implanted young children will ,develop reasonable speech perception skills after adequate experience and training.
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ItemComparative performance of children using the cochlear 22-channel implant and 8-channel 'Tickle Talker'( 1992)Direct comparison of "Tickle Talker" and Cochlear Implant users is problematic, due to difficulties in matching groups of children for hearing loss, age, duration of deafness, speech perception and language skills, and educational placement. However, two studies were undertaken to compare and contrast potential benefits available from these two devices. In the first study, a number of children from one educational setting were evaluated over a six month period. Half of the children used the multiple channel cochlear implant, while the other half used the multiple channel "Tickle Talker". The number of training sessions, clinicians involved, type of training provided, and overall management philosophy were identical for both devices. Comparison of progress of these two groups of children demonstrates that both devices are effective in improving' communication. However, differences were found with the tactile device being more limited in information provided and speech perception benefits. In the second study, two children who have used both devices were evaluated. These two children initially used the ''Tickle Talker" for periods up to two years, and subsequently had a multiple-channel cochlear implant. Similar habilitation was provided to these children with both devices, and measures of speech perception were taken at similar time periods. Results for one of the children, a prelinguistically deafened adolescent, already show similar benefits in terms of supplementation of lipreading for both devices. However, this patient has also shown some open-set word and sentence perception using the implant-alone. To date, this level of performance has not been achieved with the ''Tickle Talker". The results of these studies suggest a role for a multiple channel tactile device in a cochlear implant clinic as a training device for evaluating the ability of adults or children to integrate speech information presented through different sensory modalities. This could facilitate pre-implant evaluation of the potential for children to benefit from added speech information, which is often difficult to evaluate in congenitally deaf children.
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ItemDevelopment of an advanced electrotactile speech processor [Abstract]( 1992)Initial studies with a multiple channel electrotactile speech processor ('Tickle Talker') showed that profoundly hearing-impaired adults and children could achieve significant improvements on speech perception tests through use of tactual-encoded estimates of fundamental frequency, second formant frequency and amplitude envelope. Results showed that the device provided tactual cues which could be used to discriminate speech features such as vowel length and place, and consonant manner and voicing. However, discrimination of initial consonant voicing was not as consistent as for other features. Accurate discrimination of consonant voicing and manner (particularly high frequency information) is critical, since this Information is generally inaudible through hearing aids, and difficult to lipread.