Visual representations of dynamic actions from static pictures.

We investigated how subjects used their knowledge of biomechanical constraints when judging whether different items were in balance or in the process of falling, as a function of their angle of slant. In the first experiment, the stimuli were pictures of postures of a human body, of a wooden mannequin, and of a skeleton. The results show that for these 3 items, fall responses appeared for a smaller slant angle for a backward slant than for a forward one. This difference may reflect the influence of biomechanical constraints. To verify whether the asymmetry of the responses to the mannequin and the skeleton was genuine or due to some semantic context effect, a second experiment was run with only pictures of a wooden mannequin. The same asymmetry was observed. In a third experiment, falling judgments were obtained for pictures of a human body and of a structurally comparable artifactual object. The asymmetry of the fall responses appeared only for the human body.