Abstract
Rapidly moving stimuli appear blurred and this correlation between speed and blur may cause blur itself to be taken as a cue to apparent speed. To investigate the effect of visual blur on speed perception, subjects were asked to compare the rotation speed of a sinusoidal radial grating with that of a square wave radial grating. The gratings were presented consecutively for one-second intervals in the center of the display and subjects were asked to adjust the speed of the sinusoidal grating to match that of the square wave grating. Results showed that the sinusoidal grating is perceived to move significantly (15–20 %) faster than the square wave grating. In the second experiment, using sinusoidal gratings with different spatial frequencies, it was shown that increasing spatial frequency while keeping the speed constant increases the apparent speed. Therefore the relative slowing of the square wave grating (compared to sine wave) cannot be attributed solely to presence of higher spatial frequencies but is more likely a result of the alignment of frequency components that produces a sharp edge . These findings show that a blurred stimulus appears to move faster than a sharp stimulus of equal contrast.