Visuomotor priming by pictures of hand postures: perspective matters.

Observing hand postures interacts with the preparation of similar actions. This may be due to motor encoding of the observed displays and/or to enhanced visual processing induced by motor planning. We studied the effects of the observer's perspective on motor representation, using a visuomotor priming task with simple responses. Participants were asked to grasp a bar in horizontal or vertical orientation. In Experiment 1, the prime stimuli were pictures of a hand in either "Own" or "Other perspective", and their orientation could be congruent or incongruent with the pre-specified grasping action. An overall effect of congruency was found, providing strong evidence for the automatic encoding of the primes. The effects of prime perspective were moderated by the availability of preview of the hand stimuli: with preview, congruency effects only occurred for "Own perspective" stimuli. Conversely, without preview, congruency effects were restricted to "Other perspective" primes. In Experiment 2, we replicated the "Own perspective advantage" with hand preview. In addition, we manipulated the stimulus onset asynchrony between prime stimulus and go-signal and found congruency effects to be restricted to the shorter asynchronies. We interpret the "Own perspective advantage" as the result of an enhancement of action relevance of the prime stimuli during the preview interval, driven by motor planning. In contrast, we explain the "Other perspective advantage" as a stimulus-driven visuo-motor effect, based on more frequent experience with suddenly appearing hands of conspecifics than with suddenly appearing own body parts.