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Stuart Anstis, Hiroyuki Ito; Background stripes affect apparent speed of rotation. Journal of Vision 2005;5(8):1060. doi: 10.1167/5.8.1060.
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© ARVO (1962-2015); The Authors (2016-present)
A gray line that rotated at constant speed against a stationary background of vertical stripes appeared to double in perceptual speed as it rotated through the vertical position and was momentarily aligned with the background. Two stimulus features might be at work: landmarks, where the tip of the moving vertical line moves horizontally across the maximum number of stationary stripes, and moiré intersections between stripes and moving lines, which move most rapidly when the line is near vertical. To isolate the contribution of landmarks, a white ring was as placed over the grating, and short radial lines ran around this ring. This provided landmarks but no intersections, and the illusion disappeared. To isolate the contribution of intersections, a slit in a virtual black occluder rotated in front of the grating, which was thus seen only through the slit. This provided moiré intersections but no landmarks, and the illusion increased. We conclude that the moiré intersections are entirely responsible for the perceived speed changes. Consistent with this, we find that when a line rotates on a plain grey background, dots that run back and forth along the length of the line can modulate its perceived speed, which indicates a failure to decouple radial from tangential velocity components.
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