The Ames Room
Source: Laboratory of Jonathan Flombaum—Johns Hopkins University
The most difficult challenge of visual perception is often described as one of recove…
1. Materials
- To build an Ames Room you will need four pieces of cardboard, each 1-ft high. The four pieces should vary in length, including a 2-ft piece, two 1-ft pieces, and one piece that is 1.5-ft long.
- You will also need two figurines of some kind, action figures, toy soldiers, even stuffed animals will do the the trick. The two should be roughly the same height and shorter than ¾-ft tall.
- A box cutter and glue or tape will also be necessary.
2. Assembling the Ames Room
- Start with one of the two 1-ft pieces of cardboard. Put a penny on it, right in the center, and use the box cutter to cut around the penny to produce a hole. This will be the aperture for the Ames Room.
- Figure 1 schematically depicts the three initial steps of assembly, described in 2.2.-2.4. Stand up the piece with the hole, and to its right attach the other 1-ft piece of cardboard, so that the two form a right angle. You will have an object that looks like the one in Figure 1a, when looked at from above.
Figure 1: Building an Ames Room amounts to building (from cardboard) an irregular four-sided polygon. The first step is to carve a penny-sized peephole in a 1-ft piece of cardboard. Then attach an equally sized piece of cardboard to produce a standing, right-angle like the one shown in (A). Next, attach a 2-ft piece of cardboard, also at a flush right angle, on the left of the piece with the peephole. The outcome is schematized in B. Finally, attach a 1.5-ft piece of cardboard to close the polygon. The final product is shown in C.
- Now attach the two-ft piece on the other side of the piece with the aperture. You will have an object that looks like the one in Figure 1b when looked at from above.
- Finally, attach the 1.5-ft piece to close the structure. You will have a four-sided polygon like the one in Figure 1c.
- To complete the Ames Room and produce the illusion take the two figurines and place one at each of the vertices where the 1.5-ft cardboard attaches to the rest of the structure. In Figure 2, these two locations are denoted by green circles. The figurines should be facing the aperture.
Figure 2: The green dots denote the relative placement of figurines within the Ames Room. To produce the strongest illusion, it is critical that the two figurines be placed at the two non-right angle vertices of the polygon.
3. Seeing the illusion
- To see the illusion, just look into the Ames Room by looking through the aperture.
Visual illusions often exploit the fact that a person receives input from both eyes to see the world in three dimensions.
For example, if someone is talking to a friend through their open apartment door, they?ll discern this individual as standing a few steps in front of the hallway wall. This perception is due, in part, to the fact that the person?s brain receives and combines two images of the friend?one from the right eye, and another from the left.
However, if the door suddenly slams shut and the renter is forced to look at their friend with one eye through a hole?size and depth become more difficult to judge.
The Ames Room?a structure named after its ophthalmologist inventor Aldebert Ames?manipulates this binocular aspect of vision, and cleverly uses geometry to trick the visual system into identifying objects? sizes as being different when in fact they are the same.
This video demonstrates how to design an Ames Room, documents the illusion it creates, and discusses how such deception is used in special effects for movies.
In this experiment, participants view a distorted exhibit with a single eye by peering through an aperture?the entire setup is the Ames room. The forced perspective ensures that the brain receives only one image of the scene, and no depth cues from the contralateral eye.
The geometrical trick here is that the display is constructed with sidewalls of irregular length, making the back wall diagonal rather than parallel to the front wall. Such construction does not produce the right angles that are expected in a room.
Instead, a situation is created where two equally sized figurines?placed in the back corners?vary in distance from the aperture. That is, the one on the left is farther away than the one on the right side.
Participants are asked to report what they see, and their responses are recorded as the dependent variable. It?s expected that they will report the character on the right as being much larger, even though they are the same size.
Before participants arrive, assemble a small-scaled version of the Ames Room, using scissors or a knife, tape, a ruler, four, one-foot wide cardboard pieces of varying lengths, and two, equally sized action figures.
First make the aperture: Trace around a penny in the center of one of the foot-long pieces. Cut around this outline and then push the part out to leave a small hole. Stand this segment up, and with tape, attach it to the other one-foot long portion of cardboard to form a 90? angle on what will be its right side.
Now fasten the two-foot piece on the left side, forming another 90? angle. Finally, connect the remaining one-and-a-half-foot section to close the polygon. Note that the backside should not form right angles.
With the display assembled, place two figures of the same height in the back corners?one at each vertex.
To begin the experiment, make sure that the back is covered to avoid revealing the exhibit?s skewed geometry and seat a participant in front. Explain that she is to look into the aperture and report which of the two characters is larger.
At this point, allow the participant to lean in. While she is peering inside, ask her which one is larger and note her response. [Participant says: Right is larger.]
In this demonstration, the participant was tricked into thinking that the characters differed in size. In this case, she reported the right figure as being larger than the left one.
Here, the underlying expectation was based on previous experiences?that walls should attach at right angles. Because the brain could not gather countervailing evidence?like that which could be provided by the other eye?it therefore applied the assumption. This resulted in the room appearing rectangular, with the far wall occupying the position shown.
The implication then was that the two figures were side-by-side. Now, what appeared on the retina?two differently sized projections?was interpreted by the brain as a size difference, rather than one caused by the objects standing at different distances from the viewer.
Now that you are familiar with the Ames Room illusion, let?s look at how its principles are applied in situations involving special effects and virtual-reality viewing.
Many movie scenes have been filmed inside an Ames Room set. Because the frames are captured through the apertures of cameras, directors can depict an actor as being super small and a robot as being much larger than it really is by simply positioning them appropriately around the room.
By helping us understand the cues needed by humans to perceive the visual world in 3D, the Ames Room has also helped researchers design better virtual reality tools that employ size illusions.
Such systems can actually help individuals visualize home remodeling and design projects. By using virtual reality devices, objects can be positioned so that viewers can perceive the actuality of appearance within a given space.
You?ve just watched JoVE?s video on the Ames Room. Now you should have a good understanding of how to design the exhibit and run the demonstration, as well as how to interpret responses and apply the principles behind the illusion.
Thanks for watching!
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Q1: How does the Ames Room use geometry to create a size illusion?
The Ames Room manipulates binocular vision by constructing sidewalls of irregular length, making the back wall diagonal rather than parallel to the front. This creates a non-rectangular space where two equally sized figures placed in back corners are at different distances from the viewer. When observed through a single aperture, the brain assumes right angles and interprets the differently sized retinal projections as size differences rather than distance variations.
Q2: Why does viewing through one eye make the Ames Room illusion work?
Monocular viewing through an aperture eliminates depth cues that the second eye would normally provide. The brain cannot gather countervailing evidence about actual distances, so it applies the assumption that walls attach at right angles. This forces the visual system to interpret size differences on the retina as actual size variations rather than perspective effects caused by different distances from the viewer.
Q3: What materials and measurements are needed to build a small-scale Ames Room?
Construct an Ames Room using four cardboard pieces of varying lengths: one foot, one foot, two feet, and one-and-a-half feet wide. You'll also need scissors, tape, a ruler, and two equally sized action figures. Create an aperture by tracing and cutting a penny-sized hole in one piece. Assemble the pieces at 90-degree angles on the front, but ensure the back does not form right angles to create the distorted geometry.
Q4: What assumption does the brain make when viewing the Ames Room illusion?
The brain assumes that rooms have rectangular geometry with walls meeting at right angles, based on previous visual experiences. When viewing the Ames Room through a single aperture, this assumption persists even though the actual structure is geometrically distorted. The brain cannot verify this assumption with binocular depth cues, so it misinterprets the scene and perceives the figures as different sizes.
Q5: How is the Ames Room principle applied in movie special effects?
Movie directors film scenes inside Ames Room sets and capture frames through camera apertures, which function like the single-eye viewing hole. By positioning actors and objects strategically around the distorted room, filmmakers can depict one character as extremely small and another as much larger than reality. This forced perspective technique creates convincing size illusions without digital manipulation.
Q6: What role does the retina play in three-dimensional depth perception?
The retina receives two-dimensional projections of three-dimensional objects, collapsing distance information onto its surface. Objects at different distances cannot produce more distant stimulations on the retina compared to nearby objects. The brain must apply assumptions and heuristics to infer actual distances from these flattened retinal images, which is why visual illusions like the Ames Room can successfully trick the visual system.
Q7: How does the Ames Room contribute to virtual reality design?
By revealing how the brain uses assumptions about rectangular geometry to perceive depth, the Ames Room has helped researchers design better virtual reality tools that employ size illusions. Virtual reality systems can position objects so viewers perceive their actual appearance within a given space, enabling applications like home remodeling visualization where spatial relationships and object sizes appear realistic despite the two-dimensional display.