Your visual system adapts to spinning motion in SPINNERS. When you first stare at a spinning spiral, it appears to move in and out. If you continue to stare for 15 or 20 seconds, one set of motion detectors in your eye becomes tired, and the motion of the spiral appears to stop. When you look away from the spiral at something stationary, the opposite set of motion detectors takes over and you briefly see motion in the opposite direction.