Further informationson the exhibit "Spiral disc"
The phenomenon that can be observed here is known as the "afterimage effect" or "waterfall effect". If you focus on the moving spiral disc for several seconds, it seems as if you are looking into a rotating tunnel. If you look at your hand, this image has an effect on the retina, and you get the impression that your hand briefly pushes in the opposite direction, i.e. that it bends towards you or approaches you.
If you turn the disc in the opposite direction (to the left), the effect is reversed, and you get the impression that the hand curves inwards or moves away.