The distance perception has been that of a stationary observer. The stimulus of retinal motion perspective as a basis for distance has been described only in part. The general rule may be formulated that whenever the observer himself moves, the retinal image corresponding to the whole visual field undergoes deformation. The importance of the distinctions lies in the fact that deformation of the retinal background-image yields not only the perception of subjective motion but provides a powerful stimulus for space perception. The differences in the rate of flow are dependent on differences in distance, since the nearer points change their direction from the observer, and are retinally displaced, faster than the further points. The gradient of retinal velocities with respect to their direction is therefore unaffected by pursuit movement of the eyes. Retinal motion therefore vanishes both on the rim of the horizon and at another point in the field—the center from which the motion radiates.