Spectral Subband Centroids for Tone Vocoder Simulations of Cochlear Implants

Abstract

Cochlear Implants (CIs) have long been used to partially restore hearing in profoundly deaf individuals through direct electrical stimulation of the auditory nerve. Changes in pitch due to electrode selection have been shown to conform to the tonotopic organisation of the cochlea; i.e., each electrode corresponds to a localised band of the human hearing spectrum. Studies have shown that it may be possible to produce intermediate place percepts in some patients by stimulating pairs of adjacent electrodes simultaneously. Tone vocoder simulations with 2-16 output channels were used to evaluate the effect of producing place cues similar to spectral subband centroids of each spectral analysis band. Signals were generated as a sum of sine waves positioned at the spectral subband centroid (rather than the usual centre frequency) of the frequency band relevant to each channel. Results showed improved vowel and consonant intelligibility, even with as low as 4-6 output channels.