Created by Erica Dixon, Arthur Shapiro and Kai Hamburger “Grouping by Contrast” presents luminance levels of four disks modulating in time. The top two disks become white when the bottom two disks become black (and viceversa), but when they are placed against a split background, the disks group together along the diagonals giving the illusion their modulation is out of sync. This grouping pattern follows the contrasts of the disks relative to their backgrounds. You are welcome to test this theory by playing with the interactive button below.