Is Limb Proprioception a Function of the Limbs' Intertial Eigenvectors?

The ability of humans to match the spatial orientation of occluded contralateral limbs was investigated. We hypothesized that this ability is tied to the inertial eigenvectors of each limb, which correspond to the limb's axes of rotational symmetry. In two experiments, the coincidence between the eigenvectors and the spatial axes of a forearm was broken with the expectation that the matching of occluded forearms would vary as a function of the eigenvectors. Overall, the angles at which the limbs were positioned were affected by the direction in which the eigenvectors were oriented by small appended masses. Discussion focused on the importance of physical invari- ants for perception, and their relation to hypothesized frames of reference for proprio- ception and motor concrol.