Film (Cinema) Perception

Moving Pictures

Movies consist of a series of still images, known as frames, projected onto a screen at a rate of 24 frames per second. Even though the frames are stationary on the screen and are momentarily blanked as a new frame replaces the old, we experience film as a continuous image containing real motion. The two perceptual phenomena contributing to this experience are persistence of vision and apparent motion.

Persistence of vision refers to the continued perception of light after the stimulus light has been turned off. During film projection, the light is obscured by the closing of a shutter as the film moves from one frame to the next. This creates an alternation between light (shutter open—frame projected) and darkness (shutter closed) 24 times per second. Persistence of vision “fills in” the dark interval, but only partially, because a shutter rate of 24 frames per second results in a noticeable flicker. Early film used shutter rates between 12 and 24 frames per second earning them the nickname “The Flicks.” Modern film projectors eradicate this flicker by blanking each frame three times, which increases the flicker rate above the critical flicker fusion rate of 60 hertz (Hz) and ensuring that the perception of light is continuous because of persistence of vision.

The motion we perceive in film is apparent because it is based on static visual information rather than real motion. Apparent motions can be broadly classified as long-range and short-range according to the conditions under which they are perceived. Long-range apparent motions, such as beta movement, are perceived when two objects are alternately presented at two different locations about 10 times a second. The two objects are perceived as a single object moving smoothly between the two locations. Because of the slow rate of presentation and the large distances covered by the apparent motion, long-range apparent motions are thought to be processed late in the visual system and require inferences based on knowledge of real motion and the most likely correspondences between objects in the image sequence.

Short-range motions occur when static images depicting only slight differences in object location are presented rapidly (> 13 Hz). Short-range motion processing occurs early in our visual system, does not require perceptual inferences to understand the motion, and is the same system used to perceive real motion. It is commonly believed that the apparent motion perceived in films is beta movement. However, although beta movement and other long-range motion phenomena such as apparent rotations and transformations may occur during film perception, they cannot account for most motion perceived in film. The 24-Hz presentation rate used in film is too fast for long-range motion and film frames are too complex, making the task of identifying corresponding objects in subsequent frames too difficult. Instead, apparent motion in film results from the same short-range motion system used to detect real motion. Motion detectors in the early visual system respond in the same way to the retinal stimulation caused by real motion and by rapidly presented (> 13 Hz) static images that depict only slight differences in object location. [Page 459]This results in a sensory experience of film that is indiscernible from reality.

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