Plateau’s spiral
a stimulus used to create a vivid motion aftereffect, consisting of a black and white spiral rotated around its central point. Depending on the direction of rotation, the spiral will appear to expand or contract when steadily viewed while it is rotating. However, when the spiral is stopped, it will appear to move in the opposite direction, producing a perception of expansion or contraction. Moreover, the illusory expansion or contraction will apply to any other stationary object viewed immediately after stopping the spiral. [Joseph Antoine Ferdinand Plateau (1801–1883), Belgian physicist]