Allometry and Space Perception: Compression of Optical Ground Texture Yields Decreasing Ability to Resolve Differences in Spatial Scale

Robert E. Shaw and colleagues showed that allometric variations in biological forms provide visual information about the spatial and temporal scale of biological objects (Mark, Todd, & Shaw, 1981; Pittenger & Shaw, 1975a, 1975b; Pittenger, Shaw, & Mark, 1979; Pittenger & Todd, 1983; Shaw, Mark, Jenkins, & Mingolla, 1982; Shaw & Pittenger, 1977, 1978). In these studies, form changes due to growth of the human head and body were investigated. Subsequently, Bingham (1993a, 1993b) extended these ideas to plant growth and tree perception. Using extant models of tree growth and morphology, 2 allometric relations were simulated. One determined the thickness of tree branches and the other determined their numerocity. The investigations showed that the resulting tree forms could be used by observers to judge tree size. Trees appearing in the context of a ground texture gradient conferred metric scaling on the field that enabled observers to judge the size of other nonbiological objects appearing elsewhere in the context of the ground texture. Results were replicated using actual trees outdoors, pictures of actual trees, and computer generated simulations. In all cases, judgments were accurate at near distances and increasingly underestimated tree size at greater distances. The authors hypothesize that it becomes increasingly difficult to resolve differences in the size and distance of trees as the density of ground texture elements and of branches becomes high. The results of a single study support this surmise. The authors suggest that the accelerating compression of the previous judgment curves was due largely to this effect.