VISUAL CONTROL OF POSTURE DURING WALKING - FUNCTIONAL SPECIFICITY

Three experiments examined the functional specificity of Visually cont rolled posture during locomotion by presenting large-screen displays t o participants walking on a treadmill. Displays simulated locomotion d own a stationary hallway, a hallway that traveled with the observer, o r a frontal wall that traveled with the observer. A superimposed oscil lation specified postural sway in 6 possible directions. With the wall , sway amplitude was isotropic and directionally specific in all condi tions, However, with the hallways, sway was anisotropic (lateral > ant erior-posterior [AP]), and diagonal responses were flattened into the lateral plane. When the treadmill was turned 90 degrees to the hallway , both the anisotropy and flattening were reversed (AP > lateral), ind icating that they are determined by the visual structure of the scene. ?he results can be explained by postural control laws based on both o ptical expansion and motion parallax, yielding biases in planar enviro nments that truncate parallax.