Graeme Clark Collection
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ItemA clinical report on receptive vocabulary skills in cochlear implant users( 1995)Objective: The aim was to measure the rate of vocabulary acquisition for cochlear implant users and compare the pre- and postoperative rates with published data for other groups with normal or impaired hearing. The hypothesis was that the postoperative rate would be greater than the preoperative rate. Design: The Peabody Picture Vocabulary Test (PPVT) was administered to 32 children, adolescents, and prelinguistically deafened adults implanted with the 22-electrode cochlear implant. Age at implantation ranged from 2 y r 6 mo to 20 yr and implant use ranged from 6 mo to 7 yr 8 mo. Results: The group mean postoperative performance at various postoperative intervals was significantly higher than mean preoperative performance. Single-subject data indicated statistically significant gains over time on this test for 13 of the subjects. The mean postoperative rate of vocabulary acquisition of 1.06 times the rate for normally hearing children was significantly greater than the mean preoperative rate of 0.43. Conclusions: These rates of improvement were in accord with previous reports on smaller numbers of implant users, but could not be attributed unambiguously to use of the implant because no control group was used for this clinical work. Variables such as age at implantation, duration of profound deafness, communication mode, and speech perception skill failed to significantly predict rate of improvement on the PPVT.
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ItemA clinical report on speech production of cochlear implant users( 1995)Objective: The aim was to assess articulation and speech intelligibility over time in a group of cochlear implant users implanted at 8 yr or over. The hypothesis was that the postoperative speech production performance would be greater than the preoperative performance. Design: A test of intelligibility using sentences and an articulation test measuring non-imitative elicited speech were administered to 11 and 10 subjects, respectively, who were implanted with the 22-electrode cochlear implant. Nine subjects received both tests. Age at implantation ranged from 8 yr to 20 yr and implant use ranged from 1 yr to 4 yr 5 mo. Results: For both the intelligibility and articulation tests roughly half of the subjects showed significant improvements over time and group mean postoperative performance significantly exceeded preoperative performance. Improvements occurred for front, middle, and back consonants; for stops, fricatives, and glides and for voiceless and voiced consonants. Conclusions: Despite being deprived of acoustic speech information for many childhood years, roughly half of the patients assessed showed significant gains in speech intelligibility and articulation postimplantation. The lack of a control group of non-implanted patients means that we cannot separate out the influence of the implant on speech production from other influences such as training and tactile-kinaesthetic feedback.
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ItemAssessment of intracochlear ossification by three-dimensional reconstruction of computerised scans( 1995)The aim of the study was to investigate whether the three-dimensional (3-D) images from computed tomography (CT) scans of the ears could adequately define the site and extent of new bone in the cochlea, and how these images compared with those created by magnetic resonance imaging (MRI). The patients whose investigations were used in the study were being assessed for a cochlear implant and were selected on the basis of their history and the appearance of their two-dimensional (2-D) CT scans. Four patients had progressive mixed deafness, a family history of deafness, and stapedectomies. They were considered to be deaf from otosclerosis and needed further assessment because their scans showed either obstructed cochleas from new bone, or demineralized otic capsules to the point that we could not determine whether new bone was present or not. The fifth patient was being assessed within 3 months of suffering deafness from meningitis. In one ear he had extensive ossification, and in the other the degree of opacification shown in axial and coronal cuts of the basal turn was inconsistent. Essentially the problem is that at the magnification used in examination of the inner ear, the resolution of 2-D CT scans gives indistinct borders between bone and water. Magnetic resonance imaging has commonly been used in these cases. The study showed that it is now possible to confirm whether or not there is new bone and to demonstrate the site and extent of new bone with both 3-D and MRI images. It is not possible to give a degree of sensitivity and specificity for this observation because of the small group of subjects in the study. It should be worth applying the reconstruction software to scans from helical scanners with a view to assessing whether the resolution of the 3-D images can be improved further.
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ItemComparison of monaural acoustic and electric stimulation: unit types in the cat inferior colliculus( 1995)This study has shown that 1) the ratio of excitatory and inhibitory inputs to units in the central nucleus of the inferior colliculus is altered when one cochlea is neomycin-deafened and/or electrically stimulated; 2) prestimulus threshold shift and lateral inhibition mechanisms can be used to explain these results; and 3) at high current levels a leakage current into the modiolus can evoke unit population responses.
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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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ItemExperimental animal model of intracochlear ossification in relation to cochlear implantation( 1995)Histopathologic examinations of the temporal bones of implanted human patients and experimental animals have demonstrated various degrees of abnormal fibrous tissue or new bone formation within the cochlea; in some cases, extensive new bone formation was reported. The presence of new bone following cochlear implantation is undesirable, since it may adversely affect current distributions in the electrically stimulated cochlea. The pathogenesis of intracochlear osteoneogenesis as a direct result of cochlear implantation is unclear. The aim of this study is to use an experimental animal model to investigate some of the factors underlying the formation of new bone and fibrous tissue within the implanted cochlea, especially the role of insertion trauma and bone chips, and also a possible way of inhibiting such a process using an anticalcific agent of the diphosphonate family, disodium ethane-1-hydroxy-1, 1-diphosphonate(EHDP). The local release of EHDP from a polydimethylsiloxane (Silastic silicone rubber, Dow Corning Corp) controlled delivery system has been shown effective in the context of bioprosthetic heart valve. Its application within the cochlea has not been documented, to our knowledge.
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ItemImplant designs for future coding strategies( 1995)This paper briefly describes the history of speech processing developments leading to the presently available Speak processing strategy. The similarities and differences of the Speak and Continuous Interleaved Sampling (CIS) strategies are then discussed and some recent key experimental observations are examined as a guide to potential future coding strategies. Key issues for future coding strategies and implant designs are the number of electrodes and stimulation rates in use. Consideration of these issues has led to development of a prototype implant to be used for advanced speech-processing research.
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ItemDischarge rate-level functions from dorsal cochlear nucleus single units in response to acoustic and electrical stimulation of the auditory nerve( 1995)Discharge rate-level (I/O) functions possessed by dorsal cochlear nucleus (DCN) units were examined, in response to bipolar electrical stimulation of the cochlea of the barbiturate-anesthetized cat. Spontaneously active units usually possessed nonmonotonic functions with a minimum, and spontaneously inactive units usually possessed monotonic functions or nonmonotonic functions with a maximum (NM+). In response to acoustic high-pass filtered noise, the function relating discharge rate and cut off frequency resembled the same unit's I/O function to electrical stimulation. The I/O functions to acoustic characteristic tones were usually monotonic or NM+. These results suggest that in the DCN, a prerequisite for the generation of acoustic-like responses with an electrical stimulus may be the matching of the cochlear place and spatial extent activated by each stimulus.
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ItemManikin and cochlear implant patient test results with a portable adaptive beamforming processor to suppress the effects of noise( 1995)A simple adaptive beamformer (ABF) was implemented in a real-time portable speech processor and tested with four cochlear implant patients. The ABF algorithm used signals from only two microphones - one behind each ear - to attenuate sounds not arriving from the direction directly in front of the patient, and was compared with a strategy in which the two microphone signals were simply added together (two-microphone broadside strategy). Tests with the four patients were conducted in quiet and in noise. Results at a 0 dB signal-to-noise ratio showed large improvements in speech intelligibility for all patients, when compared to the two-microphone broadside strategy. Physical measurement of the directional characteristics of the ABF processor were made with a Kemar manikin. The effects of reverberation were explored by placing the manikin in different acoustic environments and observing the attenuation of the noise alone at various angles. A near-anechoic environment allowed the noise to be attenuated by as much as 21 dB, whereas in a highly reverberant concrete stairwell, the ABF processor was unable to provide any directional gain beyond about 3 dB.
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ItemFusion and lateralization study with two binaural cochlear implant patients( 1995)Psychophysical studies have been completed with two binaural cochlear implant patients. Results from a fusion and lateralization experiment with both patients are described. As found in an earlier study with the first binaural patient in Australia, the second patient also showed good sensitivity to interaural amplitude differences but poor sensitivity to interaural time delays when compared with normal-hearing subjects. The implications of this result are discussed.