On the right you see many horizontal black stripes and two vertical blue bars. Do the blue bars have identical luminance? They certainly differ in perceived brightness. Grab the slider with the mouse and observe the startling change in brightness when the black grating is moved away from the blue bars.
Lateral inhibition predicts the opposite effect, so the mechanism must be quite different. See Corney & Lotto (2007) for a promising new explanation approach. White (1979, 1981) described these luminance effects, called White's illusion or Munker-White illusion. When the horizontal stripes differ in color (not black/white as here), strong color shifts result, the Munker illusion.
Anderson BL (1997) A theory of illusory lightness and transparency in monocular and binocular images: the role of contour junctions. Perception 26:419–453
Taya R, Ehrenstein WH & Cavonius CR (1995) Varying the strength of the Munker-White effect by stereoscopic viewing. Perception 24:685–694
White M (1979) A new effect on perceived lightness. Perception 8:413–416
White M (1981) The effect of the nature of the surround on the perceived lightness of gray bars within square-wave test gratings. Perception 10:215–230
White M (2010) The Early History of White’s Illusion. Colour: Design & Creativity 5:7,1–7 [PDF]
Demo from Ted Adelson’s site
Corney D, Lotto RB (2007) What Are Lightness Illusions and Why Do We See Them? PLoS Comput Biol 3:e180