A little more conversation, a little less action - candidate roles for the motor cortex in speech perception

Imaging studies show activation of the motor cortex during speech perception. In this Perspective, Scott and colleagues discuss different possible roles for the motor system in speech processing and propose that it has a specific function in conversation. The motor theory of speech perception assumes that activation of the motor system is essential in the perception of speech. However, deficits in speech perception and comprehension do not arise from damage that is restricted to the motor cortex, few functional imaging studies reveal activity in the motor cortex during speech perception, and the motor cortex is strongly activated by many different sound categories. Here, we evaluate alternative roles for the motor cortex in spoken communication and suggest a specific role in sensorimotor processing in conversation. We argue that motor cortex activation is essential in joint speech, particularly for the timing of turn taking.