The perception of vocal-tract length in cochlear implant users: Can it be improved?
Étienne Gaudrain, Nawal El Boghdady, Deniz Başkent · The Journal of the Acoustical Society of America · 2015
When trying to understand a speaker among competing speakers, normal-hearing listeners take advantage of differences in the voices of the talkers. However, cochlear implant (CI) users do not seem to benefit from such voice differences. Roy D. Patterson's group in Cambridge has applied psychophysical methods to voice perception in order to isolate the acoustic cues that allow listeners to identify and segregate voices [e.g. Smith, Patterson, Turner, Kawahara and Irino, 2005, J. Acoust. Soc. Am., vol. 117, pp. 305–318]. In our group, we have extended these methods to CI listeners to fully characterize the limitations CI users experience in utilizing voice characteristics. More specifically, we have shown that while voice pitch (F0) is sufficiently salient through the implant to allow gender categorization, the perception of vocal-tract length (VTL) is severely degraded, leading to erroneous gender perception. With the help of acoustic simulations mimicking the CI processing, the potential factors explaining this lack of sensitivity for VTL were explored. Poor spectral resolution, spectral quantization, and spectral distortion were all found to affect VTL just-noticeable-differences. These results have yielded a number of potential solutions to improve VTL representation — and hence concurrent speech perception — in the implant.