Perceived Lightness Depends on Perceived Spatial

A change in the perceived spatial position of a surface can change its perceived color from black to white or from white to black. This Anding challenges the widespread view that denies any substantial role of depth perception in the perception of surface lightness (the shade of gray between white and black). Since 1948, when Hans Wallach published his classic experiments in lightness constancy (1), a consensus in this field has held that perceived lightness is a function of luminance ratios between adjacent parts of the retinal image, regardless of where those parts are perceived to lie in threedimensional space. Moreover, because of Wallach 's emphasis on retinal adjacency, many researchers (2) have concluded that lateral inhibitory connections among retinal cells provide the neural mechanism underlying the ratio principle. A number of investigators (37) have sought to show that retinal ratios do not tell the whole story. Essentially the approach has been to change the apparent spatial position of a target surface so that it either appears to lie in the same plane as that of its surrounding surface or in a different plane in order to determine whether the apparent spatial separation between the surfaces reduces their interaction and thus produces adifferent perceived color in the target even though the twodimensional retinal pattern remains unchanged. Two studies (3, 4) reported changes as great as one and a quarter steps on the Munsell scale (8), or 17 percent of the difference between black and white. Most (57) have reported little or no change. With a few exceptions (9), it is now generally agreed (10) that perceived lightness is essentially determined by the relative intensities of adjacent parts of the retinal array. The experiments that I report here grew out of a seeming inconsistency between the retinal ratio theory and