A visual illusion in which a lattice of black lines with the regions around their intersections erased appears to have white discs with illusory contours at the intersections, seemingly occluding the lines and appearing lighter than the background (see illustration). If the colours are reversed, then illusory dark discs appear at the erased intersections. Also (ambiguously) called the Ehrenstein illusion. Compare Ehrenstein's square illusion, Hermann grid. [Named after the German Gestalt psychologist Walter Ehrenstein (1899–1961) who discovered it in 1939/40 and published it in 1941]
Ehrenstein's brightness illusion. The white patches at the intersections of the lines are illusory.