We interpret Japanese rock garden design, from a visual psychological stance, to understand how and why design effects are achieved, and how this may relate to the sense of calm typically evoked in these gardens. We found that classical design guidelines attempt to balance the visual prominence of design elements on multiple spatial scales; neither the "whole" nor the "parts" create an unequal bias for visual attention. We analyse the structure of visual figure and visual ground, since visual structure is the foundation of visual perception. The figures (rock clusters) in Japanese "karesansui" gardens approximate vertically inverted, tree-like branching structures that converge away from the viewer, while visual "ground" is essentially an upright, dichotomously branching structure, converging towards the viewer. We conclude that some "karesansui" gardens employ a structural scaffold of the "whole" design to facilitate effortless visual perception, with a calming effect, and specific aesthetic consequences.