of information about the true shape of the room are also removed by its designer. For example, by strategic lighting, the true far corner is as bright as the true near corner. For another example, patterns on the walls (such as windows) and floor (such as a black-and-white chequerboard of tiles) can be made consistent with its illusory geometry. The illusion is powerful enough to overcome other information about the true locations of objects in the room, such as familiar size. For example, although the observer knows that adults are all about the same size, an adult standing in the true near corner appears to be a giant, while another adult standing in the true far appears to be a dwarf. For another example, although the observer knows that an adult cannot change size, they see an adult who walks back and forth between the true far and true near corners appear to grow and shrink. Studies have shown that the illusion can be created without using walls and a ceiling; it is sufficient to create an apparent horizon (which in reality will not be horizontal) against an appropriate background, and the eye relies on the apparent relative height of an object above that horizon. Related phenomena Trompe-l'œil The Ames room has as a predecessor, from as early as the 15th century, the movement in art called trompe-l'œil, in which the artist creates the illusion of three-dimensional space, usually on a flat surface. "Anti-gravity" illusion and gravity hills Ames's original design also contained a groove that was positioned such that a ball in it appears to roll uphill, against gravity. Richard Gregory regarded this apparent "anti-gravity" effect as more amazing than the apparent size changes, although today it is often not shown when an Ames room is exhibited. Gregory speculated that "magnetic hills" (also known as gravity hills) can be explained by this principle. For such a location in Ayrshire, Scotland, known as the Electric Brae, he found that a row of trees form a background similar to the setting of an Ames room, making the water in a creek appear to flow uphill. For Gregory, this observation raised particularly interesting questions about how different principles for understanding the world compete in our perception. The "anti-gravity effect" is a much stronger paradox than the "size change" effect, because it seems to negate the law of gravity which is a fundamental