Lightness in Stereoscopic Depth

In the present study I tested the effect of stereoscopic depth on the lightness of two targets equal in size, presented simultaneously so that one target appeared in depth coplanar to the background and the other appeared floating in a frontal plane closer to the observer. When targets were equal in luminance, the target that appeared more distant from the observer appeared also more contrasted to the background: when targets were increments with respect to the luminance of the background the distant target appeared lighter than the closer one; vice versa when targets were decrements the distant target appeared darker. Results are discussed with respect to the Gestalt factor “belongingness”, and to more recent finding of the effect of perceived size on lightness in the Delboeuf and the Ebbinghaus Illusions.