Graeme Clark Collection
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ItemImpedance measurement of the Nucleus 22-electrode array in patients( 1995)By means of a prototype 22-electrode cochlear implant with a telemetry ability, electrode voltage and impedances have been measured in three patients over a 2-month period. A simple electrical model of the electrode-tissue interface is described to explain the results.
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ItemArchitecture of the Spectra 22 speech processor( 1995)The Spectra 22 is a logical extension in the development of the speech processing for the Cochlear Mini 22 system. It can implement the new coding strategy (Speak) that has provided significant improvement in patient benefit.
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ItemCoding of voice source information in the Nucleus cochlear implant system( 1995)Two studies are reported in which the effectiveness of explicitly coding voicing and fundamental frequency information for the Nucleus cochlear implant was investigated. ln the first study, the voicing perception of a group of three experienced Multipeak users was evaluated when they were using Multipeak and a modified Multipeak in which the explicit fundamental frequency and voicing cues were eliminated and replaced with a 250-Hz constant rate of stimulation. The results of consonant and monosyllabic word tests showed that there was no significant difference in the subjects' ability to discriminate voicing. In the second study, the ability of a group of five experienced users of the constant rate spectral maxima sound processor (SMSP) strategy to discriminate suprasegmental contrasts was evaluated when they were using the SMSP strategy and a modified SMSP strategy that included a rate-encoded representation of the fundamental frequency on the most apical stimulation channel. The results of intonation, roving stress, and question-statement tests showed that there was no significant difference between the scores recorded with these strategies. Since the temporal voicing cue is not a primary cue to voicing discrimination for Multipeak users, and the provision of an additional rate cue to the SMSP strategy does not improve SMSP users' ability to discriminate suprasegmental contrasts, the results of these studies indicate that in the cases investigated, the coding of voice source information by rate of stimulation does not significantly augment the cues present in the spatially distributed constant rate stimulation pattern.
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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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ItemEvaluation of a new Spectral Peak coding strategy for the Nucleus 22 channel cochlear implant system( 1994)Sixty-three postlinguistically deaf adults from four English-speaking countries participated in a 17-week field study of performance with a new speech coding strategy, Spectral Peak (SPEAK), and the most widely used strategy, Multipeak (MPEAK), both of which are implemented on wearable speech processors of the Nucleus 22 Channel Cochlear Implant System; MPEAK is a feature-extraction strategy, whereas SPEAK is a filterbank strategy. Subjects' performance was evaluated with an experimental design in which use of each strategy was reversed and replicated (ABAB). Average scores for speech tests presented sound-only at 70 dB SPL were higher with the SPEAK strategy than with the MPEAK strategy. For tests in quiet, mean scores for medial vowels were 74.8 percent versus 70.1 percent; for medial consonants, 68.6 percent versus 56.6 percent; for monosyllabic words, 33.8 percent versus 24.6 percent; and for sentences, 77.5 percent versus 67.4 percent. For tests in noise, mean scores for Four-Choice Spondees at +10 and +5 dB signal-to-noise ratio (S/N) were 88.5 percent versus 73.6 percent and 80.1 percent versus 62.3 percent, respectively; and for sentences at +15 dB, +10, and +5 dB S/N, 66.5 percent versus 43.4 percent, 61.5 percent versus 37.1 percent, and 60.4 percent versus 31.7 percent, respectively. Subjects showed marked improvement in recognition of sentences in noise with the new SPEAK filterbank strategy. These results agree closely with subjects' responses to a questionnaire on which approximately 80 percent reported they heard best with the SPEAK strategy for everyday listening situations.
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ItemFormant-based processing for hearing aids( 1994)A body-worn hearing aid has been developed with the ability to estimate formant frequencies and amplitudes in real time. These parameters can be used to enhance the output signal by "sharpening" the formant peaks, by "mapping" the amplitudes of the formants onto the available dynamic range of hearing at each frequency, or by resynthesizing a speech signal that is suited to the listener�s hearing characteristics. Initial evaluations have indicated small improvements in speech perception for three groups of subjects: users of a combined cochlear implant and speech processing hearing aid, normally hearing listeners in background noise, and a hearing aid user with a severe hearing loss.
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ItemCombined electrical and acoustical stimulation using a bimodal prosthesis( 1993)A new device incorporating a cochlear implant speech processor and a speech-processing hearing aid for the un-implanted ear has been designed and tested with four severely hearing-impaired patients. The aim of the device is to provide a more acceptable and effective combination of electrical and acoustic signals to the two ears. When used monaurally, and binaurally in conjunction with the cochlear implant, the speech-processing hearing aid mean scores for open-set sentences, words, and consonants were as good as or better than the mean scores for the patients' own conventional hearing aids. Some patients improved much more than did others. Although not conclusive, these results are encouraging, especially as they were achieved with a laboratory prototype that did not allow the patients to become accustomed to the processor in everyday situations.
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ItemRecent developments with the Nucleus 22-electrode cochlear implant: a new two formant speech coding strategy and its performance in background noise( 1987)A clinical evaluation of speech processing strategies for the Nucleus 22-electrode cochlear implant showed improvements in understanding speech using the new F0F1F2 speech coding strategy instead of the F0F2 strategy. Significant improvement in closed-set speech recognition in the presence of background noise was an additional advantage of the new speech processing strategy.
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ItemEvaluation of a two-formant speech-processing strategy for a multichannel cochlear prosthesis( 1987)Initial results with the two-formant speech-processing strategy (F0FIF2) confirm the advantage of a multichannel cochlear prosthesis capable of stimulating at different sites within the cochlea. The successful presentation of two spectral components by varying the place of stimulation leads to the possibility of presenting further spectral information in this manner. Because virtually all multichannel implant patients demonstrate good "place" (electrode site) discrimination, these more refined coding strategies should lead to benefits for the majority of implantees. Already, with the F0FIF2 strategy, we have a system that appears to provide some effective auditory-alone communication ability for the average patient.