Recruitment of the motor system in the perception of handwritten and typed characters


Many functional roles have been ascribed to the motor system due to its prevalent recruitment in perceptual/cognitive tasks other than motor production. We discuss findings suggesting the motor system takes on multiple roles that vary with context and the brain networks involved. Using single-pulse TMS, we measured the MEPs of the FDI muscle in primary motor cortex as participants viewed words that were either typed or handwritten. We observed consistent facilitation of corticospinal excitability during reading of handwritten text. Although we observed faciliatation during the presentation of typed text, this effect decreased with repetitive presentations of stimuli. We suggest the the facilitation during presentation of typed words is a case of action simulation, and that the diminishing facilitation in the case of typed stimuli is representative of sensory prediction by the motor system. These findings suggest we should consider multiple roles for motor recruitment during the observation of visual stimuli.

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