Gravity and its Role in Biological Motion Perceptions

Gravity links spatial and temporal aspects of the behaviour of objects in our visual environment. Gravity also imposes constraints on moving animals. Our visual system employs knowledge about these constraints in order to detect, perceive and adequately interpret biological motion. Psychophysical experiments show how this is achieved.

Size and speed demo

This demo simulates an experiment (Jokisch and Troje, 2003) in which a quadruped point-light animal, walking with different gait frequencies through a structured environment, was presented to observers. They had to adjust its size to look “as natural as possible”. In doing so, they basically reproduced the inverse quadratic relation between size and frequency as formulated in the pendulum law.


  • Jokisch, D. and Troje, N. F. (2003) Biological motion as a cue for the perception of size. Journal of Vision, 3:252-264, Full Text
  • Troje, N. F. (2003) Reference frames for orientation anisotropies in face recognition and biological-motion perception.Perception 32:201-210.Full Text
  • Troje, N.F. (2004) Inverted gravity, not inverted shape impairs biological motion perception. Paper presented at the Vision Science Society meeting, Sarasota, FL. Poster / Abstract