Graeme Clark Collection
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ItemPitch comparisons of acoustically and electrically evoked auditory sensations( 1996)Cochlear implant users with some residual hearing in the non-implanted ear compared the pitch sensations produced by acoustic pure tones and pulsatile electric stimuli. Pitch comparisons were obtained for pure tones and electrical stimuli presented at different positions (electrodes) in the scala tympani, keeping the electric pulse rate fixed at 100, 250, or 800 pps. Similarly, pitch comparisons were obtained for electrical stimuli with variable pulse rates presented to two fixed electrode positions (apical and basal) in the cochlea. Both electrode position and pulse rate influenced the perceived pitch of the electrical signal and 'matched' electric and acoustic signals were found over a wide range of frequencies. There was a large variation between listeners. For some stimuli, listeners had difficulty in deciding whether the acoustic or electric stimulus was higher in pitch. Despite the variability, consistent trends were obtained from the data: higher frequencies tended to be matched by more basal electrodes for all pulse rates. Higher frequencies tended to be matched by higher pulse rates for both electrode positions. The electrode positions that 'matched' pure tones were more basal than predicted from the characteristic frequency coordinates of the basilar membrane in a normal human cochlea.
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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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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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ItemTwo-component hearing sensations produced by two-electrode stimulation in the cochlear of a deaf patient( 1983)http://www.sciencemag.org/cgi/content/abstract/219/4587/993?ijkey=v6jEOhdpzPCxw&keytype=ref&siteid=sci
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ItemPsychophysical studies for two multiple-channel cochlear implant patients( 1982)Abstract not available due to copyright.