Disorganizing biological motion

The rapid and seemingly effortless organization of visually impoverished point-light displays of humans walking is often held up as a compelling example of the perception of form from motion. Here we show that motion information is not sufficient for the impression of a human walker to be extracted from a point-light display. We manipulated the 13 small dots out of which the typical point-light walker is constructed. Attempts to use size, color, or shape changes to disrupt walker perception had only modest impact on its robustness. But when all the local elements of the walker were replaced with complex unique objects, perception of the walker was severely disrupted. Of seventy-seven naive observers presented with this array for one full gait cycle, none perceived a human walker, even though movement paths were unchanged. We conclude that the spontaneous perception of a human walking is not an inevitable consequence of the motion of the points in a point-light walker but depends on the points themselves being relatively simple and uniform.