Perception of Animacy from the Motion of a Single Object

We demonstrate that a single moving object can create the subjective impression that it is alive, based solely on its pattern of movement. Our displays differ from conventional biological motion displays (which normally involve multiple moving points, usually integrated to suggest a human form) in that they contain only a single rigid object moving across a uniform field. We focus on motion paths in which the speed and direction of the target object change simultaneously. Naive subjects' ratings of animacy were significantly influenced by (i) the magnitude of the speed change, (ii) the angular magnitude of the direction change, (iii) the shape of the object, and (iv) the alignment between the principal axis of the object and its direction of motion. These findings are consistent with the hypothesis that observers classify as animate only those objects whose motion trajectories are otherwise unlikely to occur in the observed setting.