introduced by Gunnar Johansson (1911-1998) in 1973, it typically consists of small light sources or reflective markers attached to the main joints of the body, especially, the elbows, wrists, hips, knees and ankles. As the person moves in a darkened environment dressed completely in black, an almost immediate impression is created of a coherent and recognisable movement pattern that might be perceived to be sex-related or that of familiar person. Another example is when a person performing under such conditions demonstrates lifting a weighted object, it results in the observer judging the actual weight with an accuracy of 3-4 kg. This leads to the intriguing question, still not completely answered, as to how dynamics (i.e., forces required to lift a particular weight) are derived from kinematics in such displays. Infants as young as 3-5 months of age show some evidence of being able to detect biological motion from point-light displays, and even changes in phase relations between the component parts when they have been perturbed.
See Biological motion, Kinetic depth information, Motion perception, Perception