Graeme Clark Collection
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ItemThe effect of language ability and residual hearing on speech perception outcomes for older children using multichannel cochlear implants [Abstract]( 2002)Early-deafened teenagers or young adults have shown somewhat disappointing performance with cochlear implants in the past, however, in recent years a proportion of older children have demonstrated excellent speech perception performance. There is a great deal of variability in speech perception performance within this group. It is important to investigate the factors influencing performance so that adolescents and their families can make informed decisions regarding cochlear implant surgery. This study considered a number of possible predictive factors in a group of 25 children implanted in Melbourne between the ages of 8 and 18 years. Subjects completed open set speech perception testing using BKB sentences both pre-and postoperatively, and pre-operative language testing using the Peabody Picture Vocabulary Test. Data were collected regarding the type of hearing loss, age at implant, age at hearing aid fitting, audiometric details, and the pre-and post-operative communication mode. Multivariate analysis suggested that three factors were associated with postoperative speech perception performance. Results were improved for subjects with better pre-operative speech perception, better pre-operative language ability, and when the duration of profound hearing loss was shorter. These three factors accounted for 66% of the variance in this group. The results of this study suggest that children who have useful pre-implant speech perception, and higher age-equivalent scores on language measures, would be expected to do well with a cochlear implant. A shorter duration of profound hearing loss is also advantageous. Mean speech perception scores for the older group were not significantly different from younger children.
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ItemThe effects of post-implant habilitation on long-term outcomes for children using multichannel cochlear implants [Abstract]( 2002)Those working in the cochlear implant field advocate a regular habilitation program for young children receiving implants. Developing auditory skills and the incorporating these into general language development are considered to be key areas for such programs. Investigations of speech perception and language outcomes have demonstrated that the emphasis of spoken language development appears to enhance the results for implanted children. It remains difficult, however, to demonstrate the effect of habilitation as a separate factor and to determine how much individual attention is desirable for each child. This preliminary study considered the long term speech perception and language outcomes for two groups of children who received Nucleus cochlear implants in Melbourne. The first group (n = 17) was identified as receiving regular habilitation from the Melbourne Cochlear Implant Clinic over a four year post-operative period. A second group (n = 11) was identified as receiving very little regular habilitation over the post-operative period. Language and speech perception results for these two groups showed significant differences in performance on a wide range of measures. The group who received regular, formal habilitation demonstrated better performance on all measures. These groups included only congenitally, profoundly hearing- impaired children and did not differ significantly on mean age at implant or experience at the time of assessment. A more comprehensive study is needed to clarify these results on a larger group of children, and to control for additional confounding variables. Nonetheless, these results provide support for the incorporation of regular long-term habilitation into cochlear implant programs for children.
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ItemFluctuating sensorineural hearing loss in children with Mondini malformation of the cochlea: implications for audiological management [Abstract]( 1994)Long term audiological data is presented for three children, who experienced fluctuating sensorineural hearing loss. Two children were preschool age and the third was in primary school at the time of fluctuation. All were subsequently diagnosed as having fistulas in association with Mondini malformation of the cochlea. These results serve to highlight the need for vigilance in monitoring hearing loss stability in young children when other external factors may limit the extent of information which can be obtained in any one appointment.
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ItemSignal processing for multichannel cochlear implants: past, present and future [Abstract]( 1994)Since the late 1970's, many groups have worked on developing effective signal processing for multichannel cochlear implants. The main aim of such schemes has been to provide the best possible speech perception for those using the device. Secondary aims of providing awareness and discrimination of environmental sounds and appreciation of music have also been considered. Early designs included some that attempted to simulate the normal cochlea. The application of such complex processing schemes was limited by the technology of the times. In some cases, researchers reverted to the use of single channel systems which could be controlled reliably with the existing technology. In other cases, as with the Australian implant, a simple multichannel processing scheme was devised that allowed a reliable implementation with available electronics. Over the next 15 years, largely due to the improvements in integrated circuit technology, the signal processors have slowly become more complex. Further psychophysical research has shown how additional information can be transferred effectively to implant users via electrical stimulation of the cochlea. This has lead to rapid improvement in the speech perception abilities of adults using cochlear implants. Some of the main developments in signal processing over the last 15 years will be discussed along with the latest speech perception results obtained with the new SPEAK processing scheme for the Australian 22-channel cochlear implant. Initial results for SPEAK show mean scores of 70% (equivalent to 85-90% phoneme scores) for open set monosyllabic word testing for experienced adult users. Although there remains a large range of performance for all users of cochlear implants, average speech perception scores for all implanted adults have also improved significantly with the developments in signal processing. It appears likely that multichannel cochlear implants will be a viable alternative for the treatment of severe hearing loss in the future.
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ItemPreoperative residual hearing as a predictor of postoperative speech scores for adult cochlear implant users [Abstract]( 1994)The development of multiple channel cochlear implants has been a significant advance in the rehabilitation of profound hearing loss. Speech perception benefits have been particularly evident for postlinguistically deafened adults, who as a group have shown not only supplementation of lipreading scores but also significant comprehension of words and sentences using an implant alone, without the aid of lipreading. In many cases, patients are able to use their implant for telephone conversation. Speech perception benefits for adult users have increased with advances in speech processing and improved means of habilitation. These improvements in open-set speech benefits for adult users have resulted in a steady increase in group mean scores and a reevaluation of selection criteria for cochlear implantation. In the initial development of cochlear implants, only those with little or no residual hearing were considered as candidates. Current selection criteria now include those with substantial residual hearing, who may score up to 40% in the best-aided condition on word and sentence speech perception tests. In order to provide realistic expectations for prospective cochlear implant patients, it is important to establish the relationship of many preimplant factors to postimplant speech perception benefits. For severely hearing impaired adults, the relationship between preoperative residual hearing, as measured by aided word and sentence speech perception test scores, and postoperative speech perception benefits is of significant interest. Analysis of data collected over a 15 year period for adult patients is presented. The rationale for conducting full speech perception assessments for all potential cochlear implant patients is stressed.
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ItemA clinical report on vocabulary skills in cochlear implant users [Abstract]( 1994)Receptive vocabulary results are reported for 32 children, adolescents and prelinguistically deafened adults implanted with the 22-electrode cochlear implant at the Melbourne Cochlear Implant Clinic. Age at implantation ranged from 2 years, 6 months to 20 years and implant use ranged from 1 year to 7 years, 8 months. There were significant gains from pre- to postoperative assessments on the Peabody Picture Vocabulary Test (PPVT) for the majority of subjects. Rates of improvement found are compatible with previous reports on smaller numbers of implant users, but cannot be attributable unambiguously to use of the implant. The group postoperative performance was significantly higher than mean preoperative performance (n =25). The relationship of variables such as duration of implant use, duration of profound deafness and speech perception ability to improvement on the PPVT is discussed. Expressive vocabulary results on the Renfrew Word Finding Vocabulary Scale are reported for 11 of the subjects. Less substantial gains were made on this measure.
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ItemIssues in long-term management of children with cochlear implants and tactile devices [Abstract]( 1994)For many children with severe and profound hearing losses, conventional hearing aids are unable to provide sufficient amplification to ensure good oral communication and/or in the case of very young children, development of speech and language. Traditionally a number of these children have opted for the use of sign language alone or in Total Communication approaches as a primary means of communication. The advent of multiple channel cochlear implants for children and the continuing development of multiple channel speech processing tactile devices provide auditory approaches to resolving communication difficulties for these children. The successful use of such devices depends on a number of factors including the information provided through the aid; the ease of use, convenience and reliability of the aid; the individual communication needs of the child; and the habilitation and management program used with the device. Long-term data has shown that children continue to show increased speech perception benefits from improvements in speech processing and from further experience with these devices. Habilitation and management programs must therefore be geared to meet the changing needs of children as they progress and of families as children mature and face new challenges. Habilitation must address specific individual needs in speech perception and in speech production. For very young children, benefits of improved speech perception should have an impact on the development of speech and language, and habilitation and management must emphasise the need for language growth.
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ItemCombined cochlear implant and speech processing hearing aid for implant users with a severe to profound hearing loss in the contralateral ear [Abstract]( 1994)The bimodal device was developed for cochlear implant users who simultaneously wear a hearing aid in the opposite ear having residual hearing of a severe to profound degree. The aim was to create a single device to provide both input signals in a more compatible manner and thus maximise use of the individual's total hearing capabilities. The acoustic component of the bimodal device is very flexible and can implement various speech processing strategies with speed, ease and precision. The Frequency Response Tailoring strategy utilises three filters to fit a frequency gain curve to within 1-2 dB of that desired. Modifications at discrete frequencies, ranges or slopes can be readily made. The Peak Sharpening or Spectral Enhancement strategy amplifies the formant peaks in speech for potential improvement of formant resolution and speech perception in the presence of background noise. The Resynthesis strategy presents specifically selected components of speech in selected combinations and includes the ability to transpose higher frequency information to lower frequency ranges for individuals with no aidable high frequency hearing levels. Different fits can be quickly and easily interchanged for comparison and evaluation and subsequent modifications indicated can be readily effected. Any combination of acoustic and implant speech processing strategy can be presented to optimise speech perception for the individual user.
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ItemAccuracy of behavioural threshold prediction using steady-state evoked potentials [Abstract]( 1994)This paper examines the confidence with which predictions of hearing level can be made using the steady-state evoked potential (SSEP) technique. Steady-state evoked potentials are scalp potentials that can be elicited in response to sinusoidally amplitude and/or frequency modulated tones in sleeping or awake subjects. SSEP thresholds were obtained using frequency specific stimuli at octave frequencies between 250Hz and 4000Hz in 25 children and 35 adults with varying degrees of sensori-neural hearing loss. These levels, determined automatically by a computerised detection system, were then compared with thresholds obtained behaviourally. Linear regression analyses of this data have shown that the SSEP procedure allows objective estimates of hearing level to be made for a range of carrier frequencies to within 10dB accuracy on 96% of occasions.
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ItemThe diagnostic assessment of infants using steady-state evoked potentials [Abstract]( 1994)This paper examines the relationship between the steady-state potential and behavioural thresholds obtained in two groups of young children. The first group consists of 10 babies referred to the Victorian Children's Hearing Centre following abnormal findings on screening ABR assessments. The second group contains 20 difficult to test infants who had unconfirmed hearing losses at the time of the SSEP assessment. The hearing levels predicted by the regression lines (described in the companion paper presented at this conference) were in close agreement with the behavioural levels obtained subsequently from children in both groups.