A new binocular cue for absolute distance: Disparity relative to the most distant structure

When an object is presented binocularly at various distances in complete darkness the range of distances is usually underestimated. We found that adding a second object can reduce the extent to which the range of distances is underestimated. However this only happens if the second object is further than the one of which the distance is to be judged. We propose that the relative disparity between the two objects limits the possible distances of the nearer object because the lines connecting the further object to each of the two eyes must converge in the distance.