Neurobiological monitoring has shown that the brain is most aroused by patterns in which there is about 20 percent redundancy of elements or, put roughly, the amount of complexity found in a simple maze, or two turns of a logarithmic spiral, or an asymmetric cross.
It may be a coincidence (although I think not) that about the same degree of complexity is shared by a great deal of art in friezes, grillwork, colophons, logographs and flag designs. It crops up again in the glyphs of the ancient Middle East and Mesoamerica, as well as in the pictographs and letters of modern Asian languages. The same level of complexity characterizes part of what is considered attractive in primitive art and modern abstract art and design.
The source of the principle may be that this amount of complexity is the most that the brain can process in a single glance. When a picture is more complex, the eye grasps its contents by saccades or consciously reflective travel from one section to the next.
A quality of great art is its ability to guide attention from one of its parts to another in a manner that pleases, informs and provokes.
Source: The Social Conquest of Earth, Edward O. Wilson