Graeme Clark Collection

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    Signal processing for multichannel cochlear implants: past, present and future [Abstract]
    DOWELL, RICHARD ; SELIGMAN, PETER ; MCDERMOTT, HUGH ; Whitford, Lesley ; BLAMEY, PETER ; Clark, Graeme M. ( 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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    A clinical report on vocabulary skills in cochlear implant users [Abstract]
    Dawson, P. ; Blamey, P. ; Dettman, S. ; Rowland, L. ; Barker, E. ; Cowan, R. ; Clark, Graeme M. ( 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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    Bisensory and unisensory training of auditory-visual speech perception [Abstract]
    Oerlemans, Michael ; BLAMEY, PETER ; WALES, ROGER ( 1994)
    The choice of strategy in auditory-visual training remains a controversial topic. Bisensory training involves exposing the subject to both of the main sources of information (auditory-visual). Unisensory training, on the other hand, focuses individually on each of the main modalities of sensory input (auditory, visual). Proponents of the bisensory training view suggest that auditory-visual training is most appropriate since this is the dominant mode of interaction in conventional communication settings. Those advocating unisensory training, suggest focussing on each modality separately prevents interference from one sense inhibiting training of the other sense. A training study is presented where three groups of four normally hearing subjects were given thirty-six sessions of analytic training using discrimination recognition and repetition tasks. Subjects were allocated to one of three groups based on their score on the CNC word test at the first evaluation; bisensory training (BS), bisensory input with unisensory training (BSUT) and unisensory training (US). Auditory stimuli were filtered (300Hz low-pass) and all stimuli were presented in the context of 50dB of white noise. Evaluations were conducted at five points (two pre-training and two post-training) to measure improvement of five phoneme, word and sentence tasks. The evaluations were conducted in all of the modalities of interest (auditory-visual, auditory, visual). In general there were no group differences across the training tasks, although the US group showed greater improvement that the BSUT and BS groups on vowel perception. Results of a phonetic feature analysis of word level performance will be presented. There is a tendency for bisensory training to result in better sentence level performance that unisensory training. Results are discussed in the light of current models of auditory-visual interaction.
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    Issues in long-term management of children with cochlear implants and tactile devices [Abstract]
    COWAN, ROBERT ; DOWELL, RICHARD ; Barker, Elizabeth ; GALVIN, KARYN ; DETTMAN, SHANI ; SARANT, JULIA ; RANCE, GARY ; Hollow, Rod ; BLAMEY, PETER ; Clark, Graeme M. ( 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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    The Tickle Talker: a speech perception aid for profoundly hearing impaired children [Abstract]
    Cowan, Robert S. C. ; Sarant, Julia Z. ; Galvin, Karyn L. ; Alcantara, Joseph I. ; Blamey, Peter J. ; Clark, Graeme M. ( 1990)
    Fifteen prelingually profoundly hearing-impaired children participated in speech perception training and evaluation, to assess potential benefits from use of the Tickle Talker. This device, a multichannel electrotactile speech processor, developed by Cochlear Pty. Ltd. and the University of Melbourne, presents speech as a pattern of electrical sensations felt on the fingers. The eight small electrodes are located over the digital nerve bundles, on both sides of the four fingers of the non-dominant hand. Speech processing hardware is similar to that used in the 22-channel cochlear implant. In the encoding strategy, second formant frequency (F2) is presented as electrode position, speech waveform amplitude as stimulus strength, and fundamental frequency (FO) as rate of stimulation. Each child participated in an ongoing training program involving clinicians, teachers and parents. The evaluation program included measures of sound and speech detection thresholds, and discrimination of speech features, words and open-set sentences. Both individual and mean scores for all the children demonstrate significant improvements in speech perception scores when input from the Tickle Talker is combined with either aided-residual hearing, or aided residual hearing and lipreading. These results are consistent with those previously reported for profoundly hearing-impaired adults using the Tickle Talker, and indicate that children are able to integrate speech information provided through the tactual modality with information from vision or residual hearing.
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    Speech feature recognition by profoundly deaf children using the University of Melbourne multichannel electrotactile aid [Abstract]
    Alcantara, Joseph I. ; Whitford, Lesley A. ; Blamey, Peter J. ; Cowan, Robert S. C. ; Clark, Graeme M. ( 1989)
    Abstract not available due to copyright.
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    Speech perception with cochlear implants and tactile aids [Abstract]
    Blamey, P. J. ; Clark, Graeme M. ; Dowell, R. C. ( 1988)
    Abstract not available due to copyright.
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    A clinical protocol for multiple electrode cochlear implants in children [Abstract]
    Dowell, R. C. ; Busby, P.A. ; Roberts, S. A. ; Clark, Graeme M. ; Nienhuys, T. G. ; Blamey, P. J. ; Tong, Y. C. ( 1986)
    A clinical protocol for an experimental study to evaluate the speech perception and production, and communication skills using the multiple electrode cochlear implant in pre-adolescent children has been developed. A single-subject time-series design has been adopted to regularly assess these abilities. During the pre-operative stage the subject's current hearing aids or tactile device are used, and for the post-operative stage the Nucleus multiple electrode intracochlear implant. Training is provided in both stages of the study. Also included in the pre-operative stage are the audiological and medical evaluations to determine whether the subject meets the selection criteria. Speech perception and production, and communication skills are assessed from a large selection of language and developmental-age appropriate materials. Psychophysical studies are also undertaken to measure the subject's abilities to discriminate simple stimuli differing in electrical parameter values.
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    Studies in tactile speech perception using the University of Melbourne Tickle Talker [Abstract]
    Galvin, K. L. ; Cowan, R. S. C. ; Blamey, P. J. ; Oerlemans, M. ; Ginis, J. ; Mavrias, G. ; Moore, A. ; Lu, A. ; Millard, R. ; Clark, Graeme M. ( 1998)
    During the past four years, a series of studies have been undertaken investigating the perception of speech presented through the tactile modality. These studies formed part of a project to develop an effective and safe electro tactile speech perception device for those children and adults requiring additional communication assistance to that provided by hearing aids, but unable to benefit from cochlear implants.