Adaptive changes in locomotory control and perception occur in environments where the normal relationship between effort and body displacement is altered (1,2). We have further investigated this plastic relationship by altering visual feedback during voluntary walking in place on a rotary treadmill. When the velocity of optical flow was increased or reversed relative to normal for the steps being made, subjects reported changes in perceived self-motion, the size, rate, and/or direction of their voluntary steps, the extent of voluntary effort required, and the apparent stability of a hand-held support bar. The floor and the visual environment were perceived as stable. We will show that these perceptual remappings obey "terrestrial constraints."