Action Categories and the Perception of Biological Motion

TLDR

The study extends Johansson’s finding by examining detection and recognition of locomotory, instrumental, and social actions under normal, inter‑joint, and upside‑down light‑spot conditions to determine how human actions are perceived from biological‑motion cues, and discusses implications for computer vision, perceptual models, and mental representations. The authors presented locomotory, instrumental, and social actions in the three Johansson display conditions and measured subjects’ verbal responses and recognition times. Locomotory actions were recognized better and faster than social and instrumental actions, and biological motions were recognized much better and faster in the normal orientation than upside down, with only a slight impairment under the inter‑joint condition; the results suggest that perceptual analysis of actions begins at an intermediate action‑coding level and involves early coding of dynamic phase relations and semantics.

Abstract

Johansson filmed walkers and runners in a dark room with lights attached to their main joints and demonstrated that such moving light spots were perceived as human movements. To extend this finding the detection and recognition of Johansson displays of different kinds of movements under three light-spot conditions were studied to determine how human actions are perceived on the basis of biological-motion information. Locomotory, instrumental, and social actions were presented in each condition, namely in normal Johansson (light attached to joints), inter-joint (light attached between joints), and upside-down Johansson. Subjects' verbal responses and recognition times were measured. Locomotory actions were recognised better and faster than social and instrumental actions. Furthermore, biological motions were recognised much better and faster when the light-spot displays were presented in the normal orientation rather than upside down. Recognition rate was only slightly impaired under the inter-joint condition. It is argued that the perceptual analysis of actions and movements starts primarily on an intermediate level of action coding and comprises more than just the similarity of movement patterns or simple structures. Additionally, coding of dynamic phase relations and semantic coding take place at very early stages of the processing of biological motion. Implications of these results for computer vision, perceptual models, and mental representations are discussed.