Abstract
Three experiments are described in which hypotheses are examined for the activity of human stair climbing, by varying riser height with respect to leg length. The perceptual category boundary between "climbable" and "unclimbable" stairs is predicted by a biomechanical model, and visually preferred riser height is predicted from measurements of minimum energy expenditure during climbing. It is concluded that perception for the control of action reflects the underlying dynamics of the animal- environment system.