Median-plane sound localization as a function of the number ofspectral channels using a channel vocoder

摘要

Using a vocoder, median-plane sound localization performance was measured in eightnormal-hearing listeners as a function of the number of spectral channels. The channels werecontiguous and logarithmically spaced in the range from 0.3 to 16 kHz. Acutely testing vocodedstimuli showed significantly worse localization compared to noises and 100 pulse/ s click trains,both of which were tested after feedback training. However, localization for the vocoded stimuli wasbetter than chance. A second experiment was performed using two different 12-channel spacings forthe vocoded stimuli, now including feedback training. One spacing was from experiment 1. Thesecond spacing (called the speech-localization spacing) assigned more channels to the frequencyrange associated with speech. There was no significant difference in localization between the twospacings. However, even with training, localizing 12-channel vocoded stimuli remained worse thanlocalizing virtual wideband noises by 4.8° in local root-mean-square error and 5.2% in quadranterror rate. Speech understanding for the speech-localization spacing was not significantly differentfrom that for a typical spacing used by cochlear-implant users. These experiments suggest thatcurrent cochlear implants have a sufficient number of spectral channels for some vertical-planesound localization capabilities, albeit worse than normal-hearing listeners, without loss of speechunderstanding.