Graeme Clark Collection

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    Vowel perception and hearing impairment
    Fairbank, K. ; Wals, R. ; Clark, Graeme M. ( 1981)
    The perception of vowels by young hearing-impaired and normal-hearing children was investigated in two experimental versions, one which required the child ~o make discriminations among minimal pairs, the other which was based on free choice. Each version focused on three lists which comprised monosyllabic real word-pairs whose initial and final consonants were identical. These lists were constructed around high and low frequency components of vowel spectra in order to explore those acoustic aspects which have been hypothesized (Ling, 1978) as being maximally problematic in high-frequency hearing loss. Results indicated that the normal-hearing children, in contrast to the hearing-impaired, made virtually no errors in either task. The hearing-impaired children made significantly more errors in the free-choice task and in the lists whose vowels contained the highest frequency spectra and among those word-pairs which commenced with nonstops.....
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    Multiple-channel cochlear implant
    Clark, Graeme M. ; Tong, Y. C. ; Bailey, Q. R. ( 1981)
    Receiver-stimulator units and multiple electrode arrays were implanted in the scala tympani of one totally deaf patient on 1 August 1978, and one profoundly deaf patient on 17 July 1979. The first patient, a 46 year old male, lost all hearing following a head injury 18 months prior to surgery. Pure tone and speech audiometry showed no hearing in either ear at the maximum output levels of the audiometer, and no vibro tactile responses were elicited. The second patient, a 63 year old male, had a progressive sensorineural hearing loss extended over 30 years due to bomb blast and chronic infection, and had no help from a hearing aide for 13 years prior to surgery. Pure tone audiometry under headphones showed no hearing in the left or operated ear, and in the right he had the following thresholds: 0.125 kHz � 125 db SPL; 0.25 kHz � 115 db SPL and 0.5 kHz � 117 db SPL. There was no speech discrimination in either ear under headphones or in a monitored sound field.
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    Frequency discrimination and the spiral ganglion cell population in cats [Abstract]
    Black, Raymond C. ; Steel, A. C. ; Clark, Graeme M. ( 1981)
    Our previous studies on electrical stimulation of the cochlea and auditory nerve have been performed to provide information about cochlear current distributions and electroanatomy, as well as indicating ways of exciting discrete auditory nerve fibre populations to aid in the design of a multiple channel cochlear implant (Black &Clark, 1980). The present study has been carried out to examine the relationship between the size of the spiral ganglion cell population which remains after experimentally-induced graded degeneration of the auditory nerve has occurred and the ability of an animal to perceive certain electrically induced sounds. This is of special interest for a cochlear hearing prosthesis which requires a residual auditory nerve population large enough to adequately relay the electrically induced activity to higher centres.
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    Speech processing for a multiple-channel cochlear implant
    Tong, Y. C. ; Millar, J. B. ; Clark, Graeme M. ; Martin, L. F. ; Busby, P. A. ( 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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    Psychophysical studies for a multiple-channel cochlear implant
    Tong, Y. C. ; Millar, J. B. ; Clark, Graeme M. ; Martin, L. F. ; Busby, P. A. ( 1980)
    This paper describes the results obtained in a series of psychophysical studies conducted with our first multiple-channel cochlear implant patient. The variations of apparent loudness and pitch for single-electrode stimulation were determined by the method of magnitude estimation. The results showed that the loudness growth due to increases in current level was much steeper than the growth for acoustic stimulation in normal hearing subjects. The pitch produced by electrical stimulation was found to increase with pulse rates below 200 pps, while the increase in pitch with pulse rate was less pronounced above 200 pps. For a constant rate of stimulation, the pitch varied with the electrode position. Furthermore, the same pitch estimate could be obtained by driving single electrodes with different pulse rates.
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    Speech processor design for a multiple-channel cochlear implant
    Tong, Y. C. ; Clark, Graeme M. ; Busby, P. A. ; Millar, J. B. ; Martin, L. F. ( 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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    Speech comprehension with multiple-channel electrical stimulation of human auditory nerve fibres [Abstract]
    Tong, Y. C. ; Clark, Graeme M. ( 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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    Evoked responses in humans to tones which are sinusoidally amplitude modulated [Abstract]
    Rickards, F. W. ; Clark, Graeme M. ( 1980)
    Evoked responses have been recorded from the scalp of normal human subjects to continuous sinusoidally-modulated Amplitude-modulated tones. The responses were periodic in nature, and a Fourier transform was used to quantify the amplitude and the phase of the constituent fundamental frequency and harmonic components. The fundamental frequency of the response equalled the frequency of the modulation envelope and the amplitude of the harmonic components was usually less than the fundamental. The responses were also found to be invariant with time for periods exceeding 30 minutes.
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    The rehabilitation of patients with a total hearing loss using a multiple-channel cochlear implant [Abstract]
    Martin, L. F. A. ; Tong, Y. C. ; Clark, Graeme M. ( 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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    A speech processing strategy for an electro-tactile vocoder [Abstract]
    MacLeod, G. A. ; Clark, Graeme M. ; Pengilley, C. J. ( 1980)
    Past attempts at using the skin for recognition of tactile patterns derived from acoustic speech signals have largely been unsuccessful for perception of running speech. Problems facing researchers in this field include: frequency discrimination, especially for electrical stimulation, temporal and spatial resolution, real time speech processing and tactile pattern configuration strategies. It is considered that recent developments in speech processing which allow real time estimation of formant frequencies and vocal tract area functions will enable a successful speech aid to be developed. Based on results of the Tadoma (or Hofgaard) Method, in which speech is perceived by the deaf-blind using tactile and kinesthetic senses to determine movements of a speaker's articulators, a model is evaluated which enables a tactile display of articulatry information derived from parameters extracted from the speech signal by real time speech processing. Psychophysical measurements of percepts of computer derived patterns were carried out concentrating in particular on patterns more likely to be important for phonemic and speech discrimination. In this way it is hoped to validate the model as a useful speech aid for the profoundly and partially deaf.