The relation of lightness and stereoscopic depth in a simple viewing situation

The effect of stereoscopic depth on perceived lightness was studied using a simple, achromatic stimulus arrangement. In Experiment 1, depth/lightness interactions were sought between a single test field and a single induction field. In Experiment 2, depth/lightness interactions were looked for between a single test field and two induction fields. Stimuli were presented on a computer screen and viewed with a stereoscope. The subjects reported perceived lightness of the achromatic test field by rating its apparent blackness along a dimension of 0%-100%. In Experiment 1, they reported lightness judgments of the test field across 13 perceived depth levels and 8 contrast levels. In Experiment 2, they gave lightness judgments of the test field across 7 perceived depth levels and 16 contrast levels. We were particularly interested in observing the generality of Gilchrist's coplanar ratio hypothesis. The results showed that when stereopsis and contrast levels are the available cues, depth and lightness percepts are independent, and it is retinal ratios, not coplanar ratios, that dictate lightness perception. We conclude that before the relative depth location of an object is determined, its lightness value is known through sensory-level processes.