What is biological motion?

Everyone in visual psychology seems to know what Biological Motion is. Yet, it is not easy to come up with a definition that is specific enough to justify a distinct label, but is also general enough to include the many different experiments to which the term has been applied in the past. I will present a number of tasks, stimuli, and experiments, including some of my own work, to demonstrate the diversity and the appeal of the field of biological motion perception. In trying to come up with a definition of the term, I will particularly focus on a type of motion that has been considered “non-biological” in some contexts, even though it might contain -- as more recent work shows -- one of the most important visual invariants used by the visual system to distinguish animate from inanimate motion.