Abstract
The present study is to determine the effects of background noise on the hemispheric lateralization in music processing by exposing 14 subjects to four different auditory environments: music segments only, noise segments only, music + noise segments, and the entire music interfered by noise segments. The hemodynamic responses in both hemispheres caused by the perception of music in 10 different conditions were measured using functional near-infrared spectroscopy. As a feature to distinguish stimulus-evoked hemodynamics, the difference between the mean and the minimum value of the hemodynamic response for a given stimulus was used. The right-hemispheric lateralization in music processing was about 75% (instead of continuous music, only music segments were heard). If the stimuli were only noises, the lateralization was about 65%. But, if the music was mixed with noises, the right-hemispheric lateralization has increased. Particularly, if the noise was a little bit lower than the music (i.e., music level 10~15%, noise level 10%), the entire subjects showed the right-hemispheric lateralization: This is due to the subjects' effort to hear the music in the presence of noises. However, too much noise has reduced the subjects' discerning efforts.
Highlights
Asymmetry in functional responses in the right and left hemispheres of a human brain has been observed (Toga and Thompson, 2003)
Shtyrov et al (1998) showed that, in a noisy environment, the involvement of the left auditory cortex in discerning speeches considerably decreases, while that of the right hemisphere increases. This reveals that the existence of background noise in spoken words diminishes the dominant role of the left hemisphere in the speech processing (Wong et al, 2008)
We examined the hemodynamic responses from 44 channels for three noise categories in both hemispheres
Summary
Asymmetry in functional responses in the right and left hemispheres of a human brain has been observed (Toga and Thompson, 2003). Notable brain asymmetries include the dominance of the auditory cortex in the left hemisphere for speech processing (the left-side planum temporale region for consonant-vowel syllables, see Jancke et al (2002), the theory of asymmetric sampling in time (Giraud et al, 2007), and that in the right hemisphere for music processing (Bever and Chiarello, 1974; Tervaniemi and Hugdahl, 2003). This asymmetric response is observed even in infants: speech (Dehaene-Lambertz et al, 2002) and music (Perani et al, 2010). The objectives of this study are first to investigate whether, in the presence of noise, the right-lateralization of music processing (in contrast to the speech processing) is destructed or not and second to characterize the noise levels in the music to any differences in the hemodynamic responses between the right and left auditory cortices
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