Inappropriate focus cues cause biases in perceived depth
Three-dimensional (3D) displays are playing an increasingly important role in society. As well as research into human depth perception, their applications now include scientific visualization, entertainment and medical procedures such as minimally invasive surgery. A well-known problem with such displays, however, is that perceived depth often differs from the portrayed object or scene, even when the display creates geometrically correct 2D retinal images. One possible reason for these distortions is that conventional displays present stimuli at only one focal distance because the light comes from a single surface. This means that depth information from accommodation and blur â€“ typically not considered significant cues to depth â€“ is inconsistent with the portrayed scene. We conducted two studies which demonstrate that focus cues do affect 3D percepts, both (i) directly, by providing information about local depth variations and (ii) indirectly, by influencing the process of disparity scaling. These results are consistent with the hypothesis that the visual system makes use of all available sources of depth information (weighted according to their reliability) to estimate scene parameters, and suggest that the design of future 3D displays needs to address the problem of inappropriate focus cues. With this in mind we have devised and implemented a novel display technique that uses multiple image planes to present stereoscopic stimuli at near-correct focal distances. Preliminary experiments suggest that this approach provides a practical solution to some of the problems created by conventional displays.