When does perceived lightness depend on perceived spatial arrangement?

Experiments have recently been reported in which a decisive change in perceived light~ess was produced by a change in perceived spatial position, with no important change in the retinal image. A number of previous studies had found Little or no such effect. Experiments of the kind that produced these effects and of the kind that do not produce these effects are presented here. The main differences between these two kinds of experiments are discussed. One difference is whether the display allows the target to be part of one ratio in one spatial position but another in the other spatial position. Another differmce concerns the range of luminances within the display. Also discussed are the implications of these findings for cognitive vs. S-R theories, the order of processing depth and lightness, laboratory data vs. experience, the role of lateral inhibition in lightness perception, and theories of lightness perception in general. The percentage of light a surface reflects is called the reflectance (or albedo) of the surface. The phenomenal counterpart of reflectance is called lightness. The simplest and most obvious determinant of lightness would seem to be the absolute amount of light (luminance) reflected by a surface, as measured by the eye. This acccunt immediately fails because the amount (as opposed to percentage) of light a surface reflects is determined as much by the amount of light striking the surface as by the reflectance of the surface. The remarkable fact is that we perceive surface reflectance with rough accuracy despite wide variations in illumination. These facts produce what has been called the constancy question, that is, how the apparent lightness of surfaces remains so constant when variations in the amount of illumination create great variations in the absolute amount of light that these surfaces reflect. An additional question, made relevant by theoretical differences, conceins what role, if any, processes of depth perception play In lightness constancy. Consider how the major theories of lightness perception answer these questions. For many years, the conventional explanation of lightness constancy was that of Helmholtz (1867/1962), who maintained that the level of illumination is unconsciously taken into account in evaluating the intensity of the reflected light. Such a theory makes intuitive sense since we do seem to be aware of different levels of illumination, both over time and within a single scene. Moreover, depth perception plays a central role in this theory since an assessment of the …