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Alessandro Soranzo, Tiziano Agostini; Perceptual grouping in illumination-independent lightness constancy. Journal of Vision 2003;3(9):418. doi: 10.1167/3.9.418.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction. In a two frames of illumination stimulus, illumination-independent lightness constancy is improved by adding equal reflectance surfaces in each field of illumination. (Soranzo & Agostini, ECVP 2002). We suggested that the number of luminances having different values but leading to the same luminance ratio, could be the relevant factor for the increase of illumination-independent lightness constancy. In this context, we performed a new experiment where a two fields of illumination display has been used to measure the effect of perceptual grouping on illumination-independent lightness constancy. Experiment. We systematically manipulated two factors under controlled conditions: i) the strength of belonginess between surfaces having the same reflectance and standing in both fields of illumination, and ii) the number of surfaces crossed by the illumination edge. Results. We found that 1) lightness constancy increases as the strength of belonginess increases, and 2) lightness constancy do not depend from the number of surfaces crossed by the illumination edge. Conclusions. The results of this experiment confirmed that the number of luminances having different values but leading to the same luminance ratio, increases the degree of illumination-independent lightness constancy. This effect depends on the belonginess relationship between surfaces sharing the same luminance ratio rather than on the number of surfaces crossed by the illumination edge. We conclude that the number of different surfaces that strongly belong to each other and share the same luminance ratio of the bipartite field is strongly interpreted by the visual system as a change in the illumination rather than as a change in the reflectance.
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