At first it was believed that as the objects move, the retinal image caused by it also moves across the eye, feeding information of the movement to the brain. Though the movement of the energy across the retina is an essential factor in the perceived motion, it is not the only factor. There are two types of movement perception: 1. Real Motion; and 2. Apparent Motion.
When we perceive the physical movement of objects in the word it is called as the perception of real motion. Psychologists have come forward with a number of explanations to account for real motion, most of which emphasize the role of mechanisms in the central nervous system.
It has interested psychologists mostly. In contrast to real motion, apparent motion is movement perceived in the absence of retinal image movement or movements of eyes, head or body. Thus, the basis of perceived movement is not in a physical movement of the stimulus or the body. Apparent motion demonstrates, once again that there is more to the perception of motion than a moving retinal image.