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[email protected]. Chapter 14 The Perception of Movement Irvin Rock Why does the perception of movement present a problem ? It would seem plausible to believe that when an object moves, its image will move on the retina and this image movement is interpreted by the perceptual system as movement of the object . If this were the case, movement perception would not present a problem . Indeed, insofar as lower animals are concerned, this account may be correct , but as an explanation of the perceptual experience of human observers, it is grossly inadequate. The perceptual experience of movement is analogous to other qualities of sensory experience such as color or size----we perceive movement as a property of the object . The ability to perceive movement is clearly very fundamental in animals; it is necessary for survival . Various animals react to movement but not to stationary objects. In man, movement of an object in the periphery of the field can be detected before its exact form is . apprehended " " Movement is an either -or experience. An object either appears to be moving or it appears to be stationary (although of course its perceived speed may vary ). There is no middle ground . If an object is moving too - slowly - as in the case of the minute hand of a watch it will not appear to move at all, although after a while a change in position is detected .