Distance Cues and Fields of View in Rear Vision Systems

The effects of image size on perceived distance have been of concern for convex rearview mirrors as well as camera-based rear vision systems. We suggest that the importance of image size is limited to cases-such as current rearview mirrors-in which the field of view is small. With larger, richer fields of view it is likely that other distance cues will dominate image size, thereby substantially diminishing the concern that distortions of size will result in distortions of distance perception. We report results from an experiment performed in a driving simulator, with static simulated rearward images, in which subjects were asked to make judgments about the distance to a rearward vehicle. The images showed a field of view substantially wider than provided by any of the individual rearview mirrors in current systems. The field of view was 38 degrees wide and was presented on displays that were either 16.7 or 8.5 degrees wide, thus minifying images by factors of 0.44 or 0.22. In contrast to previous studies of convex mirrors and camera-based rear vision systems, judgments about distance were not affected by image size, suggesting that distance cues other than size were available to subjects as they made their judgments. Further testing is needed to better understand the nature of the distance cues that drivers are able to use in camera-based rear vision systems, but these results suggest that, at least under some conditions, image size is not critical for reliable perception of distance.