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 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.
Zeng
Fan-Gang
FG
Department of Otolaryngology, University of California, Irvine 92697, USA. fzeng@uci.edu
Grant
Ginger
G
Niparko
John
J
Galvin
John
J
Shannon
Robert
R
Opie
Jane
J
Segel
Phil
P
D000328:Adult; D019929:Cochlear Implantation; D003638:Deafness / Q000534:rehabilitation*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009622:Noise / Q000009:adverse effects; D010699:Phonation / Q000502:physiology; D010700:Phonetics; D013060:Speech / Q000502:physiology*; D013067:Speech Perception / Q000502:physiology; D013068:Speech Production Measurement