Japanese artist jagarikin has created an incredible optical illusion that makes it look like two three-dimensional boxes are rotating in place. The boxes, which are colored blue and outlined in various shades of gray, appear to spin while the background flashes from white to black.
— じゃがりきん (@jagarikin) February 14, 2020
This type of visual phenomena is known as Reverse Phi, which legendary optical illusionist Michael Bach explains as the brain’s perception of movement when opposing tracks (positive and negative) are played at the same time.
The reason for the seemingly continuous forward motion is that our motion detectors are sign-dependent. Simultaneous inversion of contrast and motion direction does not reverse perceived motion direction. This effect is also known as “four stroke motion”. The disconcerting effect when watching this arises from a conflict: (1) our motion detectors indicate continuous motion, but (2) feature tracking indicates a forward-backward jump.
jagarikin also posted an amusing example of this with a cartoon hippopotamus.
— じゃがりきん (@jagarikin) February 25, 2020