Motion Perception: Social

Background

The scientific study of biological motion perception enjoys a long history, dating back to the 19th [Page 582]century. Yet research in the perception of biological motion did not take firm hold in the perceptual sciences until the early 1970s when it carved a prominent place. This was largely due to the development of an elegant experimental manipulation that permitted researchers to isolate the body's motion by affixing either lights or reflective material to the major body joints of a person who was filmed in the dark engaging in an activity. When played back to observers, only the lights were visible. Fittingly, such stimuli came to be known as point-light displays. With his early reports, Gunnar Johansson set the stage for an explosion of research in the perception of biological motion. Much of the earliest work in this area documented observers' ability to differentiate between human and nonhuman motion or to categorize the action being depicted (e.g., running, walking, jumping jacks). Yet research in the perception of biological motion quickly took a turn to interpersonal judgments.

Building on early observations, researchers became interested in observers' ability to discern personal attributes about the people depicted in point-light displays. Three of these domains, in particular, have been and remain to be important aspects of person perception from a social perspective. These include how the perception of social categories, identity recognition, and emotion recognition are supported by perception of the body's motion.

Perceiving Social Categories

Since Gordon Allport's early work, scholars have recognized the importance of social categorization as a means to facilitate person perception. Once social categories are known, they set forth processes that are difficult to recall. Even when observers do not endorse stereotypes associated with a particular social category, it is difficult to escape the effects of group-based expectations and evaluative tendencies. Indeed, decades of research in social psychology suggest that social categorization is sufficient to arouse stereotypes associated with the category, which subsequently affect attitudes about and behaviors directed toward others. Three major categories tend to dominate social perception—sex, race, and age.

Of these, sex cate gorization has received the most empirical attention in the perception of biological motion.

The body's motion is sexually dimorphic, and observers can reliably identify the sex category membership of people depicted in point-light displays. Some have argued that the motions of men and women are distinct because their body shapes differ. Differences in body shape correspond to distinct motion patterns. By this reasoning, body motion is structurally mediated, and observers' ability to categorize others according to sex reflects an ability to recover the body's form from its motion. The reasons underlying accurate sex perception remain the focus of empirical research, but the finding that observers can discern sex category highlight a privileged role of body motion for the perception of the interpersonally relevant social category, sex.

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