Abstract
Perceptual estimation of a center of mass has been studied extensively using dot patterns and simple geometric shapes (Friedenberg & Liby, 2008). However, less work has examined center estimation for ecologically relevant shapes such as human figures. We have extensive perceptual and motoric experience with human forms. It is of theoretical interest to see if observers are as accurate with these biological forms and whether their estimates are biased by the same factors found in the literature. In this experiment, sixty undergraduates judged the perceived centers of male and female human figures with limbs extended to the left or right in a variety of configurations. In this way we could manipulate the location, orientation and length of elongation axes relative to the body's main vertical symmetry axis. The outer contours of these figures were presented in black against a white background. Participants indicated their responses by drawing in a dot. Errors were measured as the distance between the true and perceived center. The orientation of the responses in terms of angular deviation from the vertical was also recorded. There was a significant main effect of limb extension both for the error data F(17, 998) = 4.0, p <0.01 and for orientation skew F(17, 998) = 6.3, p <0.01. Accuracy was best for bilateral figures where the limbs were extended symmetrically to either side while orientation response distributions were skewed away from the direction the limbs pointed. The results are discussed in terms of a dynamic balance model.