Judging the Center of Human Figures: Evidence for Dynamic Perception

In our first experiment we presented outlines of human figures in various poses to a group of undergraduate psychology majors. We asked them to indicate where the perceived centers of the figures were by placing a small dot. The stimuli fell into two major categories. The first group was symmetric, with both arms held in equivalent positions on both sides of the body. The second group was asymmetric where an arm or an arm and a leg were extended to either side at different angles. We calculated accuracy, measured as the distance between the true and the perceived center of mass, as well as orientation, measured as the direction of the response distribution. Accuracy was best in the symmetric conditions where responses were aligned vertically along the body midline. In the asymmetric cases accuracy was lower and responses were shifted in the direction opposite the limb extensions. This occurred even though the true center was always shifted in the same direction as these extensions. The results are replicated in a second experiment with physical education majors who were trained on the concept of center of mass and who had already had experience calculating it. The data support the notion that observers infer where the centers should be in order to rebalance the figure. They anticipate the future motion of the figures in unbalanced poses rather than treat them as static forms. We discuss these results as examples of agency and dynamical perception.