Effect of brightness on perceived distance as a figure-ground phenomenon

Two experiments were performed to compare the effects of brightness on perceived distance in the situations in which a target appeared either as figure (experiment 1) Or as ground (experiment 2). In experiment 1 the stimulus array consisted of two small homogeneous target regions and a homogeneous surrounding region common to both; in experiment 2 it consisted of two large homogeneous target regions and a textured surrounding region. Subjects were asked to indicate which of the two targets appeared nearer and to make a verbal judgment of perceived depth between them. The results showed that the target having the greater brightness contrast with the surround is apt to be judged nearer when the targets appear as figure, and farther when they appear as ground. These findings support Egusa's hypothesis that the effect of brightness on perceived distance can be attributed to figure-ground differentiation between the target region to be judged and its direct surround.