Publisher Summary This chapter presents a theory of design based on the science of perception. A fundamental assumption underlying this theory is the idea that there is such an entity as “the human visual system.” All humans have essentially the same neural visual architecture, and that is more or less the same for all humans. The chapter provides a simplified three-stage model of the visual system that is useful to provide a framework. In Stage 1, every part of the visual image is simultaneously analyzed into color, motion, and the elements of form by massively parallel neural processes. In Stage 2, the visual world is segmented into regions and two-dimensional (2D) patterns. Finally, in Stage 3, only a few complex objects can be held in visual working memory. Although information flows from stages 1 to 3, the higher level processes can modify lower level processing through feedback loops.