Complex pitch perception via vocoder simulations of cochlear-implant processing

Abstract

Melodic pitch perception in cochlear implants (CIs) is limited at least in part by spectral resolution, which in turn is limited by the number of spectral channels as well as interactions between adjacent channels. Future technical improvements may lead to greater numbers of functional channels within CIs; however, the target number of channels required to extract the fundamental frequency from a harmonic sound is not known. The present study used noise-vocoded simulations of CI processing to parametrically study melodic pitch perception, with other potential cues, such as temporal-envelope rate and lowest spectral component, removed. The number of spectral channels was parametrically varied, along with the degree of channel interaction. In contrast to earlier studies, preliminary results suggest that 32 channels are not sufficient to elicit the perception of complex pitch, even in the absence of any significant channel interactions. Even when pitch perception was possible with higher numbers of channels, performance was degraded by introducing varying amounts of channel interaction. The results suggest that spectrally based pitch is unlikely to be generated in CI users without a substantial change in technology and/or site of stimulation. [Work supported by NIH grant R01DC005216.]