Office of Aerospace Medicine Technical Reports
FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute
Report No: DOT/FAA/AM-71/31
Title and Subtitle: The spiral aftereffect: III. Some effects of perceived size, retinal size, and retinal speed on the duration of illusory motion
Report Date: July 1971
Authors: Mehling KD, Collins WE, Schroeder DJ
Abstract: 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 1/2, 1, 2, 4, and 8 deg with seven rates of retinal speed (10-100 minarcs/sec) 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 minarcs/sec) 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.
Key Words: Spiral Aftereffect, Illusory Motion, Perceptual Constancy, Retinal Speed, Visual Angle Response time, Visual perception, Illusions, Vision
No. of Pages: 11
Civil Aerospace Medical Institute
Report No: DOT/FAA/AM-71/31
Title and Subtitle: The spiral aftereffect: III. Some effects of perceived size, retinal size, and retinal speed on the duration of illusory motion
Report Date: July 1971
Authors: Mehling KD, Collins WE, Schroeder DJ
Abstract: 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 1/2, 1, 2, 4, and 8 deg with seven rates of retinal speed (10-100 minarcs/sec) 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 minarcs/sec) 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.
Key Words: Spiral Aftereffect, Illusory Motion, Perceptual Constancy, Retinal Speed, Visual Angle Response time, Visual perception, Illusions, Vision
No. of Pages: 11
Last updated: Friday, June 1, 2012