AMES ROOM

People inside an Ames room appear to have odd sizes. In the left corner we see them as being significantly smaller than in the right corner. In fact, this difference is not due to differences in their actual height, as it might seem, but rather because of a difference in the distance from our eyes (or a camera). Indeed this room, although it seems to have a rectangular room, it actually has an irregular shape. The floor, the ceiling and the two walls are trapezoidal in shape. This is also true of the pattern on the floor and window frames. The floor also slopes and is not parallel with the ceiling. Additionally, the front and the back walls of the room are not parallel to each other.

All these structural changes cumulatively mean that, from a specific vantage point, the pattern of light reaching the eye from the Ames Room is identical to that produced by a normal room. (In fact, the possible forms of Ames Room are endless.) Because the observer’s vision is limited to a single viewing point, both rooms – the trapezoidal and rectangular – look indistinguishable.

But then how come we cannot see the room’s true shape? When presented with an ambiguous stimulus we tend to rely on our experience and we see the scene in its typical and simplest way (here a rectangular room) – in a similar way to the exhibits in the first room. The illusion of normality of the Ames Room is so convincing and the inability to see the room as another shape is so powerful that we believe that the people or other objects in the room are of different sizes. As a consequence, the dimensions of the characters are scaled, depending on the size and shape of the room.

There is an alternative interpretation of the Ames room illusion in which the horizon ratio is crucial. It is expressed as a proportion between the height of the person and their body parts between ground level and the horizon. Under natural conditions, this ratio remains the same regardless of the object’s distance; it is an optical invariant. This helps us perceive the size of an approaching or receding person as the same even though the size of their image on the retina grows and shrinks respectively. However, because of the inclination of the floor in Ames room, the overall ratio between the size of the person above and below the horizon stays the same.

Ames room was designed by Adelbert Ames in 1946. The principle is used repeatedly in the visual arts, especially in films such as Alice in Wonderland, The Lord of the Rings and Charlie and the Chocolate Factory.

/ Ittelson, W. H. & F. P. Kilpatrick. (1951). Experiments in perception. Scientific American, 185, 50–55. /