Sensory effects of action observation: evidence for perceptual enhancement driven by sensory rather than motor simulation.

Recent neurophysiological and behavioral studies suggest that the brain simulates the sensorimotor processing of observed actions. The relative contributions of sensory and motor simulation in this process remain unclear. Here, we use the well-established phenomenon of sensorimotor gating as a hallmark of motor representation. Perceived intensities of external stimuli are routinely suppressed during motor preparation and execution. Therefore, motor simulation should result in reduced perceptual intensity of sensory stimuli delivered during action observation. We obtained magnitude estimates for vibrotactile stimulation of the upper lip during observation of silent speech (lip-reading). Perceptual enhancement was consistently found across three experiments. The effect appeared to be specific to the observed action, somatotopically organized, and distinct from general attentional and response biases. We conclude that action observation produces perceptual enhancement. The experience of observing others' actions may be driven more by sensory simulation than by motor simulation.