The inversion effect in biological motion:
Maybe there are two of them!

If biological motion point-light displays are presented upside down, performance in almost any visual task will decline. The inversion effect in biological motion shows characteristics that make it comparable to the inversion effect described for face recognition. Particularly, there exists evidence that this inversion effect is due to impaired processing of the familiar shape of an articulated body.

Recently, we have demonstrated that scrambled biological which is completely devoid of structural information not only retains information about the direction of a walking human or animal, but also is subject to a pronounced inversion effect. Furthermore, we could show that the information conveying direction and carrying the inversion effect is entirely due to the local motion of the feet.

Apparently, our visual system responds sensitively to an invariant signature contained in the movement of the feet of a locomoting, terrestrial animal constrained by gravity and the attempt to move energetically efficient. We speculate, that a simple visual filter tuned to the resulting velocity profile functions as a general “life detector”. It might be evolutionary old and shared with other animals, a speculation corroborated by recent work on filial imprinting behaviour in chicks (Vallortigara & Regolin, 2006).

Publications:

• Troje, N. F. and Westhoff, C. (2006) Inversion effect in biological motion perception: Evidence for a "life detector"? Current Biology 16:821-824.Troje, N. F.


• Johnson, M. H. (2006) Biological motion: A perceptual life detector? Current Biology 16:R376-R377

Direction from scrambled motion

This animation contains stimuli that demonstrate our ability to derive information about the direction from scrambled biological motion. If the stimulus is inverted performance declines to chance level. [Demo]