The visual perception of objective motion and subjective movement.

The perception of motion in the visual field, when recognized as a psychological problem instead of something self-evident, is often taken to present the same kind of problem as the perception of color or of form. Movement is thought to be simply one of the characteristics of an object, and the only question is "how do we see it?" Actually, the problem cuts across many of the unanswered questions of psychology, including those concerned with behavior. It involves at least three separable, but closely related problems: How do we see the motion of an object? How do we see the stability of the environment? How do we perceive ourselves as moving in a stable environment?