Retrieving Information from Human Movement Patterns

Biological motion—that is, the movement patterns of animals and humans—provides a rich source of information that helps us to quickly and reliably detect the presence of another living being; to identify it as a predator, prey, or conspecific; and to infer its actions and intentions in order to respond with adequate behavior. Once we know that we are being confronted with another person, we are able to use motion as a source of information about identity, gender, age, emotional state, and personality traits and as a complex means for signaling and communi-cations. More than 30 years ago, the Swedish psychologist Gunnar Johans-son (1973) introduced a stimulus into experimental psychology that allows us to disentangle to a large degree the information contained in the kinematics of a moving body from other sources of information about action and identity. His work showed that a few light dots placed strategically on a moving human or animal body are instantaneously organized into the coherent percept of a living creature (also see Chap-ter 11 in this volume). The observation goes back to the earlier work of the pioneers of cinematography (Muybridge, 1887/1979) and bio-mechanics (Marey, 1895/1972), but it was Johansson (1973) who first RETRIEVING INFORMATION FROM MOVEMENT PATTERNS 309 appreciated the signifi cance of the tremendous saliency of biological motion point-light displays, and the eff ortless perceptual organization with which the visual system responds to them. Fewer than 10 isolated dots and display times of 200 ms are suffi cient for a vivid percept of the articulated structure of a human body (Johansson, 1976). Subsequent research concentrated on several aspects of this general phenomenon. It was shown that biological motion perception is very robust in the presence of many types of distracting masks (Cutting, Moore, & Morrison, 1988) and that it reveals more than just the pres-ence of a person: point-light displays convey information about se