Objects can be localized at positions that are inconsistent with the relative disparity between them

The presence of a more distant object helps judge an object's position in depth. To find out why, we examined whether misjudging a distant cube's location induces a corresponding misjudgment of a nearer sphere's location. Various configurations of a distant cube and a near sphere were presented in total darkness. Each configuration was presented twice: in one presentation, subjects localized the sphere with their unseen index finger, and in the other presentation, they localized the cube in the same way. Three cube sizes were used. Most subjects judged a larger cube to be nearer than a smaller one that was at the same position. For about half of the subjects, cube size had a significantly smaller effect on the judged distance of the sphere in terms of target vergence. Thus, the distance between the judged positions of the two objects was inconsistent with the relative disparity between them. This contradicts claims that the furthest object is localized and used as an anchor point for distance judgments based on correctly perceived relative disparity.