Hand processing depends on the implicit access to a spatially and bio-mechanically organized structural description of the body

Recent evidence using a modified Simon task suggests that hand processing involves implicit coding of the spatial position of the hand relative to the side of the body to which it is attached from the viewer's reference point. This effect, called the Sidedness effect, has been found to emerge only when at least the forearm is present (the forearm thus providing the spatial reference for representing the rest of body) and it has been interpreted within the framework of the structural representation of the body. In this study we use the same modified Simon task to investigate whether hand processing involves the implicit access to a spatially and bio-mechanically organized structural body representation. In a first experiment the hand stimuli were attached to a body inappropriately without respecting the bio-mechanical constraints and no Sidedness effect was found. In Experiment 2 where the hand stimuli were presented attached to a non-bodily shape the Sidedness effect was observed only when they were attached appropriately. Whilst previous research has involved explicit representational processes, our results suggest that we can implicit access to a ‘structural description of the body’ and elaborate the anatomical and bio-mechanical plausibility.