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The Spiral Aftereffect. III. Some Effects of Perceived Size, Retinal Size, and Retinal Speed on the Duration of Illusory Motion,
CIVIL AEROMEDICAL INST OKLAHOMA CITY OKLA
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Many safety problems encountered in aviation have been attributed to visual illusions. One of the various types of visual illusions, that of apparent motion, includes as an aftereffect the apparent reversed motion of an object after it ceases real movement. The study examined some effects of perceived size, perceived distance, and perceived stimulus speed on the persistence of illusory motion in the spiral aftereffect. Two major conditions were used Size Constant a 4-inch spiral was positioned to subtend visual angles of 12, 1, 2, 4, and 8 deg with seven rates of retinal speed 10-100 minarcssec used at each angle Angle Constant three sizes of spirals were positioned so that each subtended visual angles of 2, 4, and 8 deg with physical speed held constant 75 rpm in one case, and retinal speed 45 minarcssec held constant in another. Durations of the illusion were significantly affected by low retinal speeds, by small visual angles, and by perceived size per unit of retinal size. The results suggest that complex interactions of physical and perceptual factors can significantly alter the presence and the magnitudes of visual illusions of motion. Author
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