<P> An Ames room is a distorted room that is used to create an optical illusion . Likely influenced by the writings of Hermann Helmholtz, it was invented by American ophthalmologist Adelbert Ames, Jr. in 1946, and constructed in the following year . </P> <P> An Ames room is viewed with one eye through a pinhole such as to avoid any clues from stereopsis, and it is constructed so that from the front it appears to be an ordinary cubic - shaped room, with a back wall and two side walls parallel to each other and perpendicular to the horizontally level floor and ceiling . However, this is a trick of perspective and the true shape of the room is trapezoidal: the walls are slanted and the ceiling and floor are at an incline, and the right corner is much closer to the front - positioned observer than the left corner (or vice versa). (See overhead view diagram to the right) </P> <P> As a result of the optical illusion, a person standing in one corner appears to the observer to be a giant, while a person standing in the other corner appears to be a dwarf . The illusion is so convincing that a person walking back and forth from the left corner to the right corner appears to grow or shrink . </P> <P> 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 . </P>

The ames room uses which of the following principle to achieve its effect