Bistable Alternation of Point-Light Biological Motion

Abstract

The facing-in-depth of point-light biological motion is ambiguous: the frontal and back view look the same. However, since earlier studies found a very strong perceptual bias in point-light biological mtion, it is unknown whether it evokes an alternating (bistable) percept. In the present study, naive, untrained observers viewed point-light stimuli in half-profile view. All participants experienced spontaneous flipping of the orientation-in-depth, both for biological motion and necker cube displays. The number of perceptual flips was lower for the rocking cube than for the static one; and higher for biological motion than for rocking cubes. Contrary to earlier findings the participants did not have a perceptual bias. We conclude that ambiguous biological motion does evoke a bistable percept.