Regarding the social functioning of humans, it has been suggested that the visual system has specialized mechanisms to detect and recognize biological motion patterns. Since the studies of Johansson (
1973), this phenomenon has been regarded as a major example of the resourcefulness of the visual system. When a cloud of points corresponding to the head and main joints of the human body—a Point Light Walker (PLW)—is animated with the common translational component removed, observers instantaneously recognize a human motion pattern. The seminal findings of Johansson have been replicated and extended to the recognition of actions such as running, jumping, eating, or dancing (Dittrich,
1993; Norman, Payton, Long, & Hawkes,
2004), gender (Pollick, Kay, Heim, & Stringer,
2005; Troje,
2002), specific identity of walkers (Cutting & Kozlowski,
1977; Troje, Westhoff, & Lavrov,
2005), one's own walking pattern (Beardsworth & Buckner,
1981), emotions (Atkinson, Dittrich, Gemmell, & Young,
2004; Pollick, Paterson, Bruderlin, & Sanford,
2001), and even to the estimation of the weight of lifted objects from only observing the lifting motion (Bingham,
1993). The results obtained from this kind of discrimination tasks have demonstrated that observers might detect subtle variations in gait, gesture, or action from biological motion displays.