Perceptual belongingness and spatial propagation of lightness contrast

Agostini and Proffitt (1993 Perception 22 263 - 272) showed that perceptual belongingness (the subsumption of some set of elements into a perceived whole) can cause simultaneous lightness contrast (SLC) to be seen in configurations in which the inducing elements are not adjacent to the target. The aim of this work was to measure the strength of belongingness in determining SLC when the numbers of inducing and induced elements are manipulated in Agostini and Proffitt-type configurations. Observers had to perform a nulling task. They adjusted the luminance of the gray dots organised with the black inducer dots to cancel the illusion and attain a subjective match with the gray dots organised with the white inducer dots. We found that even when there are few inducer elements, perceptual belongingness causes SLC to spatially propagate on all the gray induced dots. Simple lateral inhibition or retinex theories cannot account for the effects observed in these configurations. Higher-level processes must be factored in to explain lightness contrast.