spectral opposites

“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.