Lateralization of processing spectrally-degraded music in the auditory cortex: An fNIRS study.

Abstract

Music processing is one of the most complex cognitive activities that human brain performs. The mechanism of music processing when musical sounds are perceived by listeners fitted with a cochlear implant (CI) is not well understood yet. The present study examined the effect of spectrally-degrading processing (via a noise-vocoding processing to simulate CI speech processing) on the hemispheric lateralization in music processing using functional near-infrared spectroscopy (fNIRS). The hemodynamic responses in both hemispheres caused by the perception of the original, 32-channel noise-vocoded and 16-channel noise-vocoded musical sounds were measured using fNIRS. The right-hemispheric lateralization in the original, 32-channel noise-vocoded and 16-channel noise-vocoded music processing was about 72%, 67%, 56% of all participants, respectively. The activation level of the auditory cortex caused by the perception of the original music was higher than that of the noise-vocoded music, and the activation level reduced when decreasing the number of channels in the noise-vocoder processing. The activation levels in the right auditory cortex in all conditions were higher than those in the left auditory cortex; however, the difference of the contrast values between the right and left hemispheres reduced when decreasing the number of channels in the noise-vocoder processing. Results in this work indicated that the spectrally-degrading processing in CI speech processing may diminish the dominant role of the right hemisphere in music processing.