“The spectral opposites of black and white embody the most
extreme visual contrast and can summon myriad optical effects,
including spatial illusion, virtual motion, after-images, and phantom
color. Goethe made observations on such phenomena in his theories on
optics and color, but it was Gestalt psychologists who later explained
how the brain interprets perception to create these phenomena in the
mind. . . . Optical illusions, which accentuate the disjuncture between
knowledge and vision, became an early subject of interest to perceptual
artists.”

 —John Houston, Optic Nerve: Perceptual Art of the 1960s, 2007.