Action's influence on spatial perception: resolution and a mystery

Despite the impression that perception of spatial layout including distance, slant, and size is objective and geometrically accurate, spatial perception is influenced by a perceiver's ability to act. Hills appear steeper when the perceiver is fatigued, and balls appear faster when they are harder to block. The same environment looks different when the perceiver is better able to act than when actions are constrained. Claims of action's influence on spatial perception have been met with much controversy, and spurred many experiments designed to explore alternative explanations. In at least one case, these alternative explanations have failed to account for action's effect, thereby leading to the conclusion that the potential for action can truly influence spatial perception. The mystery remains, however, as to how action exerts its influence.