What are Point Light Displays?
Faculty Associate, Partnership for Urban Health Research
Point Light Displays are comprised of reflective tape or small light bulbs attached to the joints of a person with the surrounding area darkened and presented on videotape. When the individual moves, only a dynamic array of correlated moving lights is seen. Despite the seemingly impoverished nature of these stimuli, participants consistently report that the moving lights represent a human being. From these PLDs individuals are capable of recognizing friends by their gait, can discriminate between male and female walkers, know when target individuals attempt to engage in gender-deception, can tell how much weight an individual is intending to lift, and are able to discern the age of target walkers.
The PLD procedure enables investigators to isolate abstract patterns of motion independent of those structural aspects of the human figure to which perceivers normally attach meaning (such as gender cues, facial expressions, clothing, age, etc.). What remains are the simple dynamic qualities of movement from which people can directly discern action and base subsequent inferences. In addition, PLDs, unlike the static stimulus displays most often used in social research (such as photographs, written descriptions of events, vignettes, and questionnaires), provide perceivers with information that is specified in what changes (transformational invariants) as well as what does not change (structural invariants) during an event, and they do so in real-time. Such naturalistic information is not available in static displays.
Stimulus Construction: Two males of the same approximate height, weight, and age and served as actors. They wore tight fitting dark clothing during the recording session and had reflective patches affixed to their ankles, knees, hips, elbows, and shoulders. The actors were filmed in a brightly lit room with a black cloth background. The resulting videotape was edited with the contrast increased to its maximum and brightness to near minimum so that the display manifested only the reflective patches as points of light. The display presented the two actors "interacting" for brief (5-7 sec.) intervals. A number of stimulus segments were created for this study; (a) actor A approaching actor B from the front and slowly tapping him on the shoulder slowly; (b) at medium speed; and, (c) at fast speed. Actual rate of movement was governed by an electronic metronome count. Slow movements were defined as one step every .9 sec; medium at every .7 sec., and; fast at every .5 sec. PLDs are presented to the participants on a computer screen. They view each of the three displays in randomized fashion and respond to questionnaire items asking them to make judgments regarding the nature of the displayed interactions.
