Conventional stereoscopic displays have one focal distance, at the plane of the screen. This is problematic because it frequently results in a mismatch between the stimulus to vergence and the stimulus to accommodation, leading to discomfort, fatigue, reduced stereoacuity and distortions in perceived depth. This problem could be eliminated if the stimulus to accommodation also varied continuously with portrayed depth. A proposed method to achieve this is to use multiple image planes to present images at different focal depths. Continuous variations in focal depth are achieved by distributing image intensity across planes - a technique referred to as depth-filtering (Akeley et al., 2004, ACM T Graphic). Here we evaluate this method and show that depth-filtered stimuli do produce a continuous accommodation response between discrete focal planes. We measured accommodation responses to monocularly-viewed, spatially broadband, stimuli at two “real” and five intermediate “simulated” focal distances. The real distances were presented by displaying 100% image intensity at one of two image planes, positioned 2/3 Dioptre apart. Simulated intermediate distances (∼0.1D steps) were presented by weighting image intensity across the two planes according to the ratio of the simulated object's dioptric distance from each plane. The accommodative state of the eye was monitored continuously using a Grand-Seiko WV-500 autorefractor. For all of our observers, mean accommodation responses to the depth-filtered stimuli were highly consistent with the simulated focal distance. Furthermore, variability in accommodation responses was equivalent for “simulated” and “real” stimuli. These findings are well predicted by a model of the changes in retinal image contrast that result from changes in accommodative state when viewing depth-filtered stimuli. We conclude that multiple focal plane displays, in conjunction with depth-filtering, can effectively simulate the continuous range of focal distances that occur in the real world, and therefore offer a promising solution for improving stereoscopic displays.
Supported by EPSRC and WICN.