Temporal "Bubbles" reveal key features for point-light biological motion perception.

Humans are remarkably good at recognizing biological motion, even when depicted as point-light animations. There is currently some debate as to the relative importance of form and motion cues in the perception of biological motion from the simple dot displays. To investigate this issue, we adapted the "Bubbles" technique, most commonly used in face and object perception, to isolate the critical features for point-light biological motion perception. We find that observer sensitivity waxes and wanes during the course of an action, with peak discrimination performance most strongly correlated with moments of local opponent motion of the extremities. When dynamic cues are removed, instances that are most perceptually salient become the least salient, evidence that the strategies employed during point-light biological motion perception are not effective for recognizing human actions from static patterns. We conclude that local motion features, not global form templates, are most critical for perceiving point-light biological motion. These experiments also present a useful technique for identifying key features of dynamic events.