Speech dynamic range and its effect on cochlear implant performance

This study examines optimal conversions of speech sounds to audible electric currents in cochlear-implant listeners. The speech dynamic range was measured for 20 consonants and 12 vowels spoken by five female and five male talkers. Even when the maximal root-mean-square (rms) level was normalized fo...

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Bibliographic Details
Published in:The Journal of the Acoustical Society of America 2002-01, Vol.111 (1 Pt 1), p.377-386
Main Authors: Zeng, Fan-Gang, Grant, Ginger, Niparko, John, Galvin, John, Shannon, Robert, Opie, Jane, Segel, Phil
Format: Article
Language:English
Subjects:
Adult
Cochlear Implantation
Deafness - rehabilitation
Electric currents
Female
Humans
Implants (surgical)
Male
Middle Aged
Noise - adverse effects
Phonation - physiology
Phonetics
Speech - physiology
Speech Perception - physiology
Speech Production Measurement
Speech recognition
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Summary:This study examines optimal conversions of speech sounds to audible electric currents in cochlear-implant listeners. The speech dynamic range was measured for 20 consonants and 12 vowels spoken by five female and five male talkers. Even when the maximal root-mean-square (rms) level was normalized for all phoneme tokens, both broadband and narrow-band acoustic analyses showed an approximately 50-dB distribution of speech envelope levels. Phoneme recognition was also obtained in ten CLARION implant users as a function of the input dynamic range from 10 to 80 dB in 10-dB steps. Acoustic amplitudes within a specified input dynamic range were logarithmically mapped into the 10-20-dB range of electric stimulation typically found in cochlear-implant users. Consistent with acoustic data, the perceptual data showed that a 50-60-dB input dynamic range produced optimal speech recognition in these implant users. The present results indicate that speech dynamic range is much greater than the commonly assumed 30-dB range. A new amplitude mapping strategy, based on envelope distribution differences between consonants and vowels, is proposed to optimize acoustic-to-electric mapping of speech sounds. This new strategy will use a logarithmic map for low-frequency channels and a more compressive map for high-frequency channels, and may improve overall speech recognition for cochlear-implant users.
ISSN:0001-4966
1520-8524
DOI:10.1121/1.1423926