Structural processing in biological motion perception.

To investigate the basis for biological motion perception, structural and motion information were manipulated independently in a dynamic display using a novel stimulus with multiple apertures. Performance was compared in discrimination of global motion (translation and rotation) and biological motion. When structural information in the display was eliminated but motion information was intact, human observers were able to perceive global motion yet were at chance in discriminating walking direction of biological movement. In contrast, when the display provided even noisy and impoverished structural information, walking direction became identifiable. The present findings thus provide direct psychophysical evidence that motion information is insufficient and structural information is necessary for the identification of walking direction in biological movement. These findings imply that computational models must utilize a structural representation of the human body to account for perception of biological movements.