Sensorimotor
interactions in speech perception: evidence from functional neuroimaging
UCLA,
We investigated the role of motor areas in speech perception in two functional magnetic resonance imaging (fMRI) studies. In the first study, subjects listened passively to meaningless monosyllables, and produced the same speech sounds. Listening to speech activated a superior part of ventral premotor cortex which largely overlapped a speech motor area centered just posteriorly. This overlap supports the idea that speech motor areas are also involved in speech perception. In the second study, subjects listened to unfamiliar non-native phonemes varying in the extent to which they can be articulated. Both superior temporal (auditory) and precentral (motor) areas distinguished non-native from native phonemes, with greater signal change in response to non-native phonemes. However, only in auditory areas did activity covary with the producibility of non-native phonemes. We propose that the motor system generates internal models of candidate phonemes, which are then compared to the acoustic input in auditory areas. Taken together, these data suggest that speech perception is neither purely sensory nor motor, but rather a sensorimotor process.