Conclusions. Noise-induced masking has different effects on the two hemispheres during speech listening. Auditory-associated cortices in the left hemisphere were more affected by masking than the right side. However, activation of primary and secondary auditory cortices was not affected in both sides under the masking with high signal to noise ratio. Objectives. The purpose of this study was to investigate the effects of masking on the central auditory system during speech listening in white noise. Materials and methods. Twelve healthy young subjects with normal hearing participated in this study. Functional magnetic resonance imaging (fMRI) was performed while subjects were listening to speech sounds alone and speech plus white noise binaurally. Results. In humans, the activation of several regions including the middle parts of the superior and middle temporal gyri, parahippocampal gyrus, cuneus and thalamus of the left hemisphere was significantly reduced under the masking paradigm with +5 dB signal to noise ratio. In addition, reduced activation was also found at the lingual gyrus, anterior and middle parts of the superior temporal gyrus (STG), uncus, fusiform gyrus, and inferior frontal gyrus of the right hemisphere during masking.
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