Graeme Clark Collection
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ItemThe multi-channel cochlear implant and the relief of severe-to-profound deafness.(Informa UK Limited, 2012-05)This personal reflection outlines the discoveries at the University of Melbourne leading to the multi-channel cochlear implant, and its development industrially by Cochlear Limited. My earlier experimental electrophysiological research demonstrated temporal coding occurred for only low frequencies, i.e. below 200-500 pulses/second. I was able to confirm these findings perceptually in behaviourally conditioned animals. In addition, these studies showed that temporal discrimination occurred across spatial coding channels. These experimental results correlated with the later conscious experience for electrical stimulation in my implant patients. In addition, the mid-to-high frequencies were coded in part by place of stimulation using bipolar and monopolar stimulation to restrict current spread. Furthermore, place of stimulation had the qualities of sharpness and dullness, and was also experienced as vowels. Owing to the limitation in coding speech with a physiological model due to the overlap of electrical current leading to unpredictable variations in loudness, a speech coding strategy that extracted the most important speech features for transmission through an electro-neural 'bottle-neck' to the brain was explored. Our inaugural strategy, discovered in 1978, extracted the second formant for place of stimulation, voicing for rate of stimulation, and sound pressure for current level. This was the first coding strategy to provide open-set speech understanding, as shown by standard audiological tests, and it became the first clinically successful interface between the world and human consciousness. This strategy was improved with place coding for the third formant or high-frequency spectrum, and then the spectral maxima. In 1989, I operated on our first patient to receive a bilateral implant, and in 1990, the first with a bimodal processor. The psychophysics and speech perception for these showed that the stimuli from each side could be fused into a single image, and localized according to differences in intensity and time of arrival of the stimuli. There were significant improvements for speech perception in noise. In 1985, I implanted our first children with the multi-channel prosthesis and found that speech understanding and spoken language were greatly improved the younger the child at surgery, and especially when younger than 12 months. Speech understanding was strongly related to the development of place coding. In 1990, the US Food and Drug Administration approved the implant for deaf children, the first by any world health regulatory body making it the first major advance in helping deaf children to communicate.
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ItemContinuing improvements in speech processing for adult cochlear implant patients( 1995)The Cochlear 22-channel cochlear implant has employed a succession of improved speech-processing strategies since its first use in an adult patient in Melbourne in 1982. 1 The first patients received the F0F2 coding strategy developed by the University of Melbourne, in the Wearable Speech Processor (WSP). The F0F2 coding scheme presented the implant user with three acoustic features of speech. These were 1) the amplitude of the waveform, presented as the amount of current charge, 2) fundamental frequency (F0) or voice pitch, presented as rate of biphasic pulsatile stimulation, and 3) the spectral range of the second formant frequency (F2), which was represented by varying the site of stimulation along the electrode array.
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ItemCochlear implants in children( 1995)Cochlear implants are devices that are used to artificially excite hearing nerves with patterns of stimulation that convey speech information and environmental sounds when a person's inner ear has been destroyed by disease or not developed at birth. In this situation they cannot benefit from the amplification of sound with a hearing aid.
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ItemThe University of Melbourne Department of Otolaryngology( 1995)The University of Melbourne Department of Otolaryngology runs a general ENT Clinic as well as a Cochlear Implant Clinic. It forms the core of a Multicentre research group for deafness research, is heavily involved in teaching and education, and includes a School of Audiology. This article presents an overview of the activities of the Department.
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ItemMultichannel cochlear implant speech processing: further variations of the spectral maxima sound processor strategy( 1995)The spectral maxima sound processor (SMSP) was first developed at the University of Melbourne in 1989. A full description of the SMSP has been given by McDermott et al.1 In short, the SMSP utilizes an ear-level microphone to measure acoustic sound pressure. A 16-channel band-pass filter bank is used to analyze the sound spectrum at discrete time intervals. Each of the 16 filters is assigned to one of the 16 intracochlear electrodes according to frequency. Within each time interval the six channels with the largest band-pass filter amplitudes are selected and used to stimulate six corresponding electrodes in quick succession. The current implementation of the SMSP2 differs from the original in that a digital signal processor is used in place of the analog filter bank and the microprocessor. The filter bank has been implemented with a discrete Fourier transform. Also, the input dynamic range has been improved by increasing the resolution of the analog-to-digital converter from 8 to 12 bits.
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ItemInvestigations on a curved intracochlear array( 1995)The electrode array of a multiple-channel cochlear implant lies against the outer wall of the scala tympani. From this position electrical current spreads to excite residual neural elements, particularly spiral ganglion cells within the modiolus. It is not clear whether the spread of current from the outer wall is optimal for multiple-channel speech processing, but placement closer to the target nerves could result in lower thresholds. This could have benefits through the use of shorter pulse durations and extended battery life. Computer modeling studies and animal experiments have suggested that for localized current the optimal electrode position is adjacent to the modiolus. At the University of Melbourne it was felt that an electrode with a curve matching the internal cochlear spiral would remain close to the modiolus after insertion. A curved electrode was developed and an inserting tool was designed and produced (Treaba et al, this suppl, this section). Preliminary studies suggested that the electrode array did indeed remain close to the modiolus. Before further development of this type of electrode design, it was necessary to determine whether modifications to the surgical technique for its insertion were required. It was also important to ensure that the curved electrode fabricated for clinical trial would lie closer to the modiolus than to the outer wall of the scala tympani. This study was undertaken to examine these issues.
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ItemVowel imitation task: results over time for 28 cochlear implant children under the age of eight years( 1995)With increasing numbers of implanted children under the age of 4 years, numerous researchers have reminded us of the need for valid, sensitive, and reliable tests of developing speech perception.1,2 In addition to studies of the efficacy of implanted prostheses, there is a need to investigate the many variables that influence children's communicative performance, such as changes in speech-coding strategy, updated speech-processing systems, the effects of various training regimens, and the selection of educational and communication modes.
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ItemSpeech perception in children using the advanced Speak speech-processing strategy( 1995)The Speak speech-processing strategy, developed by the University of Melbourne and commercialized by Cochlear Pty Limited for use in the new Spectra 22 speech processor, has been shown to provide improved speech perception for adults in both quiet and noisy situations. The present study evaluated the ability of children experienced in the use of the Multipeak (Mpeak) speech-processing strategy (implemented in the Nucleus Minisystem-22 cochlear implant) to adapt to and benefit from the advanced Speak speech-processing strategy (implemented in the Nucleus Spectra 22 speech processor). Twelve children were assessed using Mpeak and Speak over a period of 8 months. All of the children had over 1 year's previous experience with Mpeak, and all were able to score significantly on open-set word and sentence tests using the cochlear implant alone. Children were assessed with both live-voice and recorded speech materials, including Consonant-Nucleus-Consonant monosyllabic words and Speech Intelligibility Test sentences. Assessments were made in both quiet and in noise. Assessments were made at 3-week intervals to investigate the ability of the children to adapt to the new speech-processing strategy. For most of the children, a significant advantage was evident when using the Speak strategy as compared with Mpeak. For 4 of the children, there was no decrement in speech perception scores immediately following fitting with Speak. Eight of the children showed a small (10% to 20%) decrement in speech perception scores for between 3 and 6 weeks following the changeover to Speak. After 24 weeks' experience with Speak, 11 of the children had shown a steady increase in speech perception scores, with final Speak scores higher than for Mpeak. Only 1 child showed a significant decrement in speech perception with Speak, which did not recover to original Mpeak levels.
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ItemImproved electrotactile speech processor: Tickle Talker( 1995)The Tickle Talker, an eight-channel electrotactile speech processor, has been developed from continuing research at the University of Melbourne. 'The development of the device has focused on production of reliable speech-processing hardware, design of cosmetically and ergonometrically acceptable electrode transducers, implementation of acute and chronic biomedical studies demonstrating device safety, design and testing of alternative speech-encoding strategies to provide benefit to speech perception and production, and design and testing of appropriate training methods for optimizing benefits. The Tickle Talker has been shown to provide benefits in supplementing lipreading or aided residual hearing for hearing-impaired adults and children. Improvements in speech processing have resulted in an increase in benefits to speech perception, and open the way for more flexible approaches to encoding speech input. Continuing development of the electrode circuitry has now produced a device that is robust and has an extended battery life. Safety studies have clearly demonstrated that there are no long-term contraindications to device use. The results suggest that the device has a role to play in rehabilitation programs for severely and profoundly hearing-impaired adults and children.