When the black and white bars switch places, on a dark surround (left) the white bar appears to jump, but on a light surround (right) the black bar appears to jump. The bar with the higher contrast wins out. The mid-grey at which the motions balance is the arithmetic (not geometric) mean of the black & white, suggesting linear, not logarithmic processing of luminance. (Anstis & Mather, Perception 1986).
Ambiguous apparent motion. The two spots move either vertically or horizontally. Can you control the direction by willpower?
Proximity: Motion is seen between nearest neighbors, horizontally on the left, vertically on the right. Shorter motion paths win out.
The motion path changes gradually from a tall, skinny rectangle to a wide, flat rectangle. Perceived motion is always along the shorter side of the rectangle. Proximity wins.
Visual inertia drives ambiguous apparent motion. Each spot appears to follow a horizontal path, not jumping up or down halfway across. Straight motion paths are preferred to going round corners.
Do these all move together or do they move individually?
The center dot simply flashes on and off but it gets entrained by the other dots and seems to disappear and reappear from behind the green square. [V.S. Ramachandran]