We see birds fly in the sky. We see the movement of different types of vehicles. We see the movement of people around us. How do we perceive movement? Do we perceive the moving objects the same way that we perceive objects, which are static? There are situations, where the objects are not actually moving, but we see a movement. What psychological processes are involved in the perception of movement?

How do we perceive the real movement of objects? One may say that we perceive motion of objects because the real motion correspondingly stimulates different parts of the retina serially. The serial nature of sensation in retina gives the impression of actual movement of the object. This phenomenon also holds true because of some laws of perceptual organization.

However, movement perception can be attributed to these serially changing stimulations in the retina only partly, because sometimes we also perceive movement without actual movement of the object in the environment. This phenomenon is called apparent motion in which, without any energy movement across the receptor surface of the retina, we still perceive movement.

1. Real Motion:

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To understand how we perceive real movement, recall what it is like to be on a train that has begun moving out of the station while the train on the adjacent track remains stationary. If your train does not lurch as it moves, you might think at first that the other train is moving. Sometimes, you may be in confusion with regard to which train is moving.

In order to be sure about the movement of your train, you look for objects you know are stable, such as the tea stall on the platform, signboards, houses, trees, etc. If you are stationary in relation to them, you can know that your train is not moving. Observing people walking on the platform may not provide the answer as they are also moving and changing their positions in relation to stationary objects. You can also feel the movement in your body, though it is very difficult to say how.

Therefore, perception of real movement is based on change of position relative to other objects within the visual field. Whenever there is movement, the perceptual system must decide what is moving and what is stationary with respect to some frames of reference.

2. Apparent Motion:

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Apparent motions are illusions of movement in which there is the perception of motion without any actual movement of the object. In other words, with our eyes, head, and body steady, and with no physical movement of an object, we see motions. Psychologists have studied several kinds of apparent movement.

These include auto-kinetic effect, stroboscopic motion, and the phi phenomenon.

i. Auto-kinetic Effect:

It is the tendency to perceive a stationary point of light in a dark room as moving. For example, if a person stares at or fixates on a small stationary spot of light in a completely darkroom, the spot will eventually appear to move. The auto-kinetic effect has been the subject of many experiments, but there is still no adequate explanation as to how it exactly happens. However, it has been observed that auto-kinetic effect is somewhat influenced by suggestion and subject’s prejudice.

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ii. Stroboscopic Motion:

It is a visual illusion in which the perception of motion is generated by a series of stationary images that are presented in rapid succession. It is a kind of motion that we see in movies and television. The so-called motion pictures do not consist of images that really move. Rather, with the help of a projector, 16 to 22 pictures, or frames per second are successively shown. Each frame differs slightly from the one preceding it. Hence, showing the frames in rapid succession provides the illusion of movement, and continuity is observed because of minor systematic variations in the pictures. It has been observed that if fewer than 16 frames per second are presented to observer, the motion picture looks jumpy and unnatural.

iii. Phi-Phenomenon:

It is the perception of movement as a result of sequential presentation of visual stimuli. We all have seen the light decoration in the streets during the festival. It appears as if a light is moving in a row from one end to the other. Actually, the light does not move in a row. A large number of bulbs are alternatively connected in a row. The switch is so arranged that the two sets of light alternatively get on and off in quick succession. This quickness in the presentation of light gives the impression of movement of the light. Instead of perceiving a series of stationary lights, we perceive a linear movement of light across the row. This illusory movement of light is called the Phi-phenomenon. The stroboscopic motion and the Phi-phenomenon could be explained in terms of the laws of perceptual organization.