The way our brains perceive and comprehend speech remains an essential issue in psychology and brain science. In recent years, consensus has gradually been made on that the speech motor system (SMS) contributes to speech perception in a modulatory and compensatory manner, especially under noise masking or speech degradation circumstances. Using functional magnetic resonance imaging, the current work investigates neural mechanisms of sensorimotor integration and compensation during syllable identification task in noisy conditions. Study 1 reveals an increment of the SMS involvement as the task difficulty increases. In addition, the SMS shows more robust specificity of phoneme representations than auditory regions in noisy conditions, as such a superiority climaxes at moderate noise levels. Study 2 finds that older adults with normal hearing have difficulty in syllable-in-noise identification. Compared with younger counterparts, the elders rely more on increased recruitment of the SMS and preserved speech motoric representations, which are less affected by noise and aging effects than auditory ones, to compensate for deficient auditory encoding. Our findings deepen the knowledge of neural mechanisms underlying cross-modal sensorimotor integration in speech perception and its life-span developmental changes. Moreover, new insights could be given on designing and implementing rehabilitative and training regimens for speech comprehension (e.g., SMS-targeted brain enhancement) in older adults with or without hearing loss.
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