Recruitment of the speech motor system in adverse listening conditions

Abstract

Background noise is detrimental to speech comprehension. The decline-compensation hypothesis posits that deficits in sensory processing regions caused by background noise can be counteracted by compensatory recruitment of more general cognitive areas. We are exploring the role of the speech motor system as a compensatory mechanism during impoverished sensory representations in the auditory cortices. Prior studies using functional magnetic resonance imaging (fMRI) have revealed an increase in prefrontal activity when peripheral and central auditory systems cannot effectively process speech sounds. Our research using event-related fMRI revealed a negative correlation between brain activation and perceptual accuracy in speech motor regions (i.e., left ventral premotor cortex (PMv) and Broca’s area), suggesting a compensatory recruitment of the motor system during speech perception in noise. Moreover, multi-voxel pattern analysis revealed effective phoneme categorization in the PMv and Broca’s area, even in adverse listening conditions. This is in sharp contrast with phoneme discriminability in auditory cortices and left posterior superior temporal gyrus, which showed reliable phoneme classification only when the noise was extremely weak. Better discriminative activity in the speech motor system may compensate for the loss of specificity in the auditory system by forward sensorimotor mapping during adverse listening conditions.