Controllable Point-Light Displays Implemented in a game engine for biological motion research

Abstract

Biological motion perception plays a critical role in survival and social communication across species. Point-light displays (PLDs), which represent body movement using only a small set of joint markers, have long served as an effective tool for isolating motion cues from other visual features. However, existing methods for generating PLDs, ranging from filmed actors with reflective markers to markerless motion extraction and motion-capture datasets, present limitations in cost, accessibility, flexibility, or ecological validity. In particular, many laboratories lack the resources to create customizable stimuli that allow systematic manipulation of movement parameters. In this article, we introduce a practical and easily modifiable method for producing fully controllable 3D PLDs using freely available animation rigs and the Unity game engine. Our approach enables real-time control of depth cues and directional motion without the need for motion capture equipment or specialized filming environments. To demonstrate the utility of the method, we conducted a psychophysical experiment comparing the perception of biological and non-biological motion. The results replicate the well-documented forward-motion perceptual bias for biological stimuli and highlight differences in how observers interpret motion direction across stimulus classes. This method offers a convenient, accessible, and adaptable tool for research on motion perception and social cognition.