Kaleidoscopic Motion and Velocity Illusions

Kaleidoscopic motion and velocity illusion. Physically, the red cog wheel rotation below is perfectly smooth, but it seemingly jolts ever so often. Depending on conditions, contrast to the background, and between the stationary and rotating part. The effects here are probably caused by color assimilation and/or ambiguous figure-ground segregation. Peter van der Halm, 2007.

Stroboscopic Alternative Motion or Motion Quartet

Stroboscopic Alternative Motion (SAM) Optical Illusions. What is the real motion of the red balls? There is no real motion. There are actually 4 red balls staying put, just their visibility is switched. The grouping to horizontal, vertical or rotatory motion occurs in our brain. They are seem moving/hopping horizontally, vertically, clockwise or counter-clockwise. This belongs to the class of multistable figures and countless research papers have been written on it, starting with Peter von Schiller 1933. The figure is also known as motion quartet and, unfortunately, recently a new name ambiguous quartet.