Perceived depth as a function of relative height under three background conditions.

The hypothesis was proposed, that the perceived depth, which results from the relative height cue, depends on optical adjacency. A 3 X 3 factorial experiment was conducted to examine this hypothesis. The 2 factors were vertical separation (3.5, 5.5, 7.5 in.) and background conditions (0 background, outline background without surface texture, textured background). Verbal estimates of the depth between pairs of frontal parallel points were obtained under the 9 conditions. In one experiment, the backgrounds simulated a floor surface, and in another, the backgrounds simulated a ceiling surface. The results in both experiments were comparable. Both main effects, separation and background, and the interaction effect were significant. All the effects were in the direction predicted by the optical adjacency hypothesis. Relative height is often included in general discussions of the cues for perceived depth. The higher of two objects will generally appear more distant. A search of the literature has failed to uncover any systematic experimentation dealing with this cue. Apparently the assertion that there exists a lawful relationship between relative height and relative perceived distance is based on informal observations and demonstrations. Two interesting demonstrations are provided by Gibson (1950, Fig. 72) and Kilpatrick