In the “chopstick illusion” (Anstis 1990, 2003) a vertical and horizontal line overlapped to form a cross and followed clockwise circular orbits in counterphase, with one line being at 6 o'clock when the other was at 12 o'clock. The intersection of the lines moved counterclockwise, but it was wrongly perceived as rotating clockwise. This chopstick illusion reveals how moving objects are parsed, based upon the intrinsic and extrinsic terminators of lines viewed through apertures. We conclude that intersections were not parsed as objects, but instead the motion of the terminators (tips) propagated along the lines and was blindly assigned to the intersection. In the similar “sliding rings illusion,” we found that observers could use their eyes to track intersections only when these appeared rigid and not when they appeared to slide. Conclusion – smooth pursuit eye movements are under top-down control and are compelled to rely upon perceptual interpretation of objects.
In the “flash-lag” effect, a static object that is briefly flashed up next to a moving object appears to lag behind the moving object (Nijhawan 2002). We superimposed a flashed spot on a chopsticks intersection that appeared to be moving clockwise along a circular path but was actually moving counterclockwise. We found that the flash appeared displaced clockwise. This was appropriate to the physical, not the subjective direction of rotation, indicating that the flash-lag and the chopstick illusions coexist without interacting. Similarly, the flash-lag effect was unaffected by reversed phi. […]
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