Whenever we look at a flat surface, like a picture or a television screen, and assume we are looking at spaces and objects that have depth, we are accepting a set of visual signals that create an illusion of three dimensional space. 3D cues are so common today that we are almost unaware of them. However, these signals were not always used and understood; even today in some preliterate societies, people may have difficulty understanding 3D illusions. Understanding how these illusions work is a key to developing our ability to think spatially. Spatial concepts come into play whether we are trying to find our way through the streets of a strange town, figure out how to wrap cloth around a body to achieve a fashion idea, envision the inner structures of a complex mechanism or body part, or simply do an accurate drawing of what we see. The ancient Romans had the ability to depict depth in their paintings. However during the Middle Ages European artists lost the skill of depicting three dimensional illusions accurately. All this changed in the late 15th century, when architects and artists discovered the value and power of three dimensional effects in drawing and painting. This blended with the intellectual explorations of the period, in which truth, realism, and individuality were prized. Three dimensional effects were greeted as a sensational, almost magical illusion that made painting into a kind of magic window into a very believable world. The modern artist challenges
