Two related illusions of motion reveal links between human perceptual representations and the motor system. In the `sliding rods illusion' a vertical and a horizontal line overlap to form a cross, and each line moves along a separate counterclockwise circular path in antiphase, without changing orientation. The intersection of the lines moves clockwise, but it is wrongly perceived as rotating counterclockwise. The implication is that these intersections are not parsed as objects, and therefore their motion path is not extracted, but instead the motion of the terminators (tips) is assigned to the vintersection. In the `sliding rings illusion,' two rings overlapped in a figure-8 are rotated about the center of the figure-8. Small texture cues de-termine whether observers see the figure as breaking into two separate rings that slide over each other or as a rigid rotating figure-8. For both illusions, the eyes can readily track the intersections when the figure is perceived as rigid but not when it is perceived as non-rigid. Therefore pursuit eye movements are compelled to rely upon perceptual interpretation of objects.

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