Graeme Clark Collection

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Author: Clark, Graeme × End date: 1989 × Start date: 1980 × Type: Journal Article × Subject: hearing prosthesis ×

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    Perception of connected speech without lipreading, using a multi-channel hearing prosthesis
    Dowell, Richard C. ; Clark, Graeme M. ; Seligman, Peter M. ; Brown, Alison M. ( 1986)
    Four of 13 totally deaf patients implanted with the Nucleus multi-channel hearing prosthesis at the University of Melbourne have demonstrated the ability to understand connected speech without lipreading or other visual cues. These patients were able to repeat verbatim unknown material read by a tester at rates of up to 35 words per minute. They were also able to understand an average of 78%, of key word, in everyday sentences in ideal acoustic conditions and 51% of equivalent material over the telephone. These results show that with a good proportion of postlingually deaf patients the multi-channel hearing prosthesis can not only act as an aid to lipreading. but also restore effective speech understanding without lipreading.
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    A signal processor for a multiple-electrode hearing prosthesis
    Seligman, P. M. ; Patrick, J. F. ; Tong, Y. C ; Clark, Graeme M. ; Dowell, R. C. ; Crosby, P. A. ( 1984)
    A 22-electrode implantable hearing prosthesis uses a wearable speech processor which estimates three speech signal parameters. These are voice pitch, second formant frequency and flattened spectrum amplitude. The signal is monitored continuously for periodicity in the range 80-400 Hz and, if this is present, stimulation occurs at the same rate. Otherwise, as in the case of unvoiced sounds, it occurs at the random rate of fluctuation of the signal envelope. The second formant is obtained by filtering to extract the dominant peak in the midband region and by continuous measurement of the zero crossing rate. The amplitude measured is that of the whole speech spectrum pre-emphasized by differentiation. The values that are presented to the patient are the parameter estimates immediately prior to the stimulation pulse. Second formant frequency is coded by selection of an appropriate electrode in the cochlea and amplitude by a suitably controlled current. Automatic gain control is used to keep the dynamic range of the amplitude estimate within the 30 dB range of the circuitry.