Encoding a Melody Using Only Temporal Information for Cochlear-Implant and Normal-Hearing Listeners

Abstract

One way to provide pitch information to cochlear implant users is through amplitude-modulation rate. It is currently unknown whether amplitude-modulation rate can provide cochlear implant users with pitch information adequate for perceiving melodic information. In the present study, the notes of a song were encoded via amplitude-modulation rate of pulse trains on single electrodes at the apex or middle of long electrode arrays. The melody of the song was either physically correct or modified by compression or expansion. Nine cochlear implant users rated the extent to which the song was out of tune in the different conditions. Cochlear implant users on average did not show sensitivity to melody compression or expansion regardless of place of stimulation. These results were found despite the fact that three of the cochlear implant users showed the expected sensitivity to melody compression and expansion with the same task using acoustic pure tones in a contralateral acoustic ear. Normal-hearing listeners showed an inconsistent and weak effect of melody compression and expansion when the notes of the song were encoded with acoustic pulse rate. The results suggest that amplitude-modulation rate provides insufficient access to melodic information for cochlear-implant and normal-hearing listeners.