In this article the author uses projective relations as the theoretical foundation of his investigations of visual space and motion. Several laboratory experiments involving perceptual vector analysis and its geometric basis are described. In most of the experiments the visual stimuli consisted of computer-controlled patterns displayed on a televisionlike screen and projected into the eyes of subjects by means of a collimating device that removed parallax as well as the possibility of seeing the screen. A common characteristics of the experiments was that the observer was evidently not free to choose between a Euclidean interpretation of the changing geometry of the figure in the display and a projective interpretation. For example, the observer could not persuade himself that what he was seeing was simply a square growing larger and smaller in the same visual plane; his visual system insisted on telling him that he was seeing a square of constant size approaching and receding. Hence he perceived rigid motion in depth, rotation in a specific slant, bending in depth and so on, paired with the highest possible degree of object constancy. Further experiments were conducted to determine if the principles of perceptual analysis hold true for the more complex paterns of motions encountered in everyday life. These experiments led to the conclusion that during locomotion the components of the human visual environment are interpreted as rigid structures in relative motion.