Depth cue integration: stereopsis and image blur

Depth-of-focus limitations introduce spatial blur in images of three-dimens ional scenes. It is not clear how the visual system combines depth informat ion derived from image blur with information from other depth cues. Stereos copic disparity is the pre-eminent depth cue, so experiments were conducted to investigate interactions between image blur and stereoscopic disparity. Observers viewed two random dot stereograms (RDSs) in a 2AFC task, and wer e required to identify the RDS depicting the greatest depth. In control obs ervations, all dots in both RDSs were sharply defined. In experimental obse rvations, one RDS contained only sharply defined dots, but the other contai ned differential spatial blur to introduce an additional depth cue. Results showed that the addition of differential blur made only a marginal differe nce to apparent depth separation, and only when the blur difference was con sistent with the sign of disparity. Cue combination between blur and dispar ity cues is thus weighted very heavily in favour of the latter. It is shown that blur and disparity cues co-vary according to geometric optics. Since the two cues are effective over different distances, the visual system is n ot normally called upon to integrate them, and is most likely to make use o f blur cues over distances beyond the range of disparity mechanisms. (C) 20 00 Elsevier Science Ltd. All rights reserved.