Graeme Clark Collection
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ItemSpeech processing for a multiple-channel cochlear implant( 1980)A laboratory speech processor has been developed for a multiple-channel cochlear implant prosthesis. The speech processor accepts the speech waveform as an input and produces a pattern of electrical stimulus data as output. The electrical stimulus data are transmitted to the implanted receiver-stimulator by a transmitter which is external to the speech processor. Four speech signal parameters were estimated every 20 ms in the parameter estimation section of the speech processor. These parameters included the fundamental frequency (FO), a low frequency energy measure (AO) , the second formant frequency (F2) and its amplitude (A2).
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ItemSpeech processor design for a multiple-channel cochlear implant( 1980)This paper outlines the strategy adopted for a laboratory-based speech processor used to provide speech information to patients with a multiple-channel cochlear implant It also presents the results of vowel and consonant recognition studies and speech test using open sets of words and sentences.
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ItemSpeech comprehension with multiple-channel electrical stimulation of human auditory nerve fibres [Abstract]( 1980)The psychophysics of multiple-channel electrical stimulation of residual auditory nerve fibres has been studied in two postlingually deaf patients with total hearing losses, and the information used to design a speech processing strategy that enables them to understand connected speech in everyday situations when used in conjunction with lipreading. A constant rate of stimulation of different groups of auditory nerve fibres produced different pitch sensations which could be scaled from low to high, and this was consistent with the place theory of frequency coding. The me patients were also able to associate the different percepts produced by each electrode with different vowel colours and sharpnesses. In addition, the patient reported that pitch increased with pulse rate and loudness increased with current level. A speech processing strategy was developed whereby the parameters for voicing determine the rate of stimulation for all electrodes, and the parameters for the dominant spectral peak in the mid-frequency range determine the site of electrode stimulation and current level.
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ItemThe rehabilitation of patients with a total hearing loss using a multiple-channel cochlear implant [Abstract]( 1980)Two profoundly deaf patients who have multiple-channel cochlear implants receive speech information through a speech processor. The speech processor encodes second formant and fundamental frequency information. Rehabilitation is concerned with evaluating the speech processor and training patients to improve speech perception. The patients have scores up to 37% and 27% on AB word lists, and 36% and 34% on NAL Everyday Sentences using the cochlear implant alone and repetition of the stimuli. However, to gain a better insight into the capabilities of the speech processor and to demonstrate its potential for the patients more investigative procedures have been used. These include the speech tracking method described by DeFillipo and Scott (1978) using the cochlear implant in conjunction with speech reading. Results indicate that patients have gained a two-fold and four-fold improvement in tracking rates (words per minute) using speech reading and the cochlear implant as opposed to speech reading alone.
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ItemParameter selection and programming recommendations for the ACE and CIS speech processing strategies [Abstract]( 1999)The Nucleus 24 Cochlear Implant system with the SPrint processor provides access to multiple speech processing strategies and a wide range of programming parameters. Strategy comparison studies have suggested that the optimal parameter set and coding strategy varies from individual to individual. It is necessary, however, to establish some default programming parameters and fitting guidelines. Therefore we have investigated the effect of stimulation rate and the number of channels or maxima in the ACE or CIS strategies, as well as the optimal programming strategy for subjects with a limited number of available electrodes. Speech perception was tested using monosyllabic words and sentences in noise, with the evaluation protocol designed to take into account learning effects. Take-home experience was provided with all programs, and subjects were asked to complete a comparative performance questionnaire regarding program preference. Six or eight subjects were enrolled in each study.
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ItemEffects of rate and pulse manipulations of the spectral maxima speech processor upon speech production( 1993)Postlingually deafened adults experience many changes in their speech as a consequence of late-onset deafness. Previous studies have indicated changes in fundamental frequency, duration, intensity, and vowel formant frequencies in postlingually deafened adults. Postlingually deafened adults who receive multichannel cochlear implants demonstrate improved control of fundamental frequency and intensity. Shifts in formant frequencies to values similar to normal hearing. speakers also appears in some adult implant users. In order to examine how adult implant users adjust their vowel production in response to map changes, we examined vowel production following manipulations to the processing strategy of the Spectral Maxima Speech Processor. This processor uses a speech processing scheme in which six spectral maxima from the outputss of 16 bandpass filters stimulate the cochlea on a place basis at a constant rate. The rate of sampling of the filterbank output is 250 Hz, so six biphasic pulses are presented every 4 msec and there is no attempt to extract fundamental frequency or to find the formant peaks in the speech signal. Two manipulations to the scheme were examined. In the first condition, the rate of sampling remained at 250Hz but eight biphasic pulses were presented rather than six. In the second condition, six biphasic pulses were presented but the rate of sampling of the filterbank output was increased to 400 Hz. Speech samples also were acquired using the standard spectral maxima processor .and with no auditory feedback when the processor was turned off. Speech samples from three �subjects were acquired immediately after receiving the manipulated speech processors and after two weeks experience with the various processors. Preliminary data indicate one subject experienced increased fundamental frequencies while using the 400 Hz high rate strategy. No significant changes were observed in fundamental frequency between the normal SMSP processor and the eight pulse variation. Elimination of feedback resulted in significantly lower fundamental frequencies. The high rate and eight pulse variations resulted in significantly higher first formant frequencies. Second formant frequencies also appear to be influenced by the processing strategies. Comparisons of values produced immediately after receiving a new strategy versus those produced after two weeks use show shifts in primarily first formant values. Data will be presented for all three subjects and discussed in regard to sensitivity to variations in speech processing schemes and the influence of experience with manipulated schemes. (Work supported by the N1H-NIDCD).
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ItemAn improved speech processor for a 22-electrode cochelar implant [Abstract]( 1992)A spectral maxima speech processing strategy ( SMSP) has been developed as a result of research to improve the speech perception performance of a multiple-channel cochlear implant. With this speech processing strategy. the six spectral maxima from the outputs of 16 band pass filters are used to stimulate the cochlea on a place basis at a constant rate. This SMSP strategy has been compared with the MSP-MULTIPEAK strategy, the present speech processor provided by Cochlear Pty. Limited, on four postlinguistically deaf adults. The study showed that the SMSP strategy was significantly better than the MSP-MULTJPEAK for the recognition of closed-set vowels and consonants, and open-set monosyllable words and sentences in background noise.
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ItemDevelopment of an advanced electrotactile speech processor [Abstract]( 1992)Initial studies with a multiple channel electrotactile speech processor ('Tickle Talker') showed that profoundly hearing-impaired adults and children could achieve significant improvements on speech perception tests through use of tactual-encoded estimates of fundamental frequency, second formant frequency and amplitude envelope. Results showed that the device provided tactual cues which could be used to discriminate speech features such as vowel length and place, and consonant manner and voicing. However, discrimination of initial consonant voicing was not as consistent as for other features. Accurate discrimination of consonant voicing and manner (particularly high frequency information) is critical, since this Information is generally inaudible through hearing aids, and difficult to lipread.
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ItemTraining and assessment of children using a multi-electrode cochlear implant [Abstract]( 1986)A training and assessment protocol has been developed for a research study on deaf children using multi-electrode cochlear implants. The areas of assessment and training include speech perception and production, language and communication skills. Material which is appropriate for language-and developmental-age is selected from a large battery of: tests to ensure that the individual abilities of children are addressed. A single-subject, time-series design has been adopted for regular assessment of the child's performance. The participating child receives a minimum of six months' pre-operative training and assessment using high gain hearing aids or a tactile device. Also included are audiological and medical evaluations to determine the child's suitability for inclusion in the study. Approximately two months are allocated for pre-operative, operative and postoperative surgical management as well as fitting and setting the external speech processor. Post-operatively, the same training and assessment procedures continue for a number of years. Extensive psychophysical studies are also undertaken to measure the child's abilities to discriminate simple stimuli which differ in electrical stimulus parameter values.