From: veritasium
Our perception of reality is not always a direct representation of external reality; instead, our brains often interpret ambiguous visual information, leading to illusions and highlighting the subjective nature of what we “see” [09:33:00]. These perceptual phenomena offer a metaphor for how we approach scientific theories and even life itself [14:27:00].
The Ames Window Illusion
The Ames window illusion involves a trapezoidal card that appears to oscillate back and forth, even though it is continuously rotating on a turntable [00:43:00], [01:00:00]. This illusion was created by Adelbert Ames in 1947 [03:58:00].
Key features of the Ames window that contribute to the illusion:
- Trapezoidal Shape The window is not a rectangle but a trapezoid, with one side significantly shorter than the other [01:19:00]. This shape is essential to the illusion [01:29:00].
- Shading It is shaded to give the appearance of a 3-D object, despite being a 2-D card with the same image on both sides [01:32:00], [01:35:00].
- Brain’s Preference Even when aware of its actual continuous rotation, the brain persists in perceiving the window as oscillating [01:40:00], [01:49:00].
Experiments to demonstrate the illusion’s power:
- Attaching a Rubik’s Cube When a Rubik’s Cube is attached to the short side, the brain perceives the cube continuing to rotate while the window oscillates independently or even appears to ‘out-drift’ the illusion [02:15:00], [02:26:00], [02:44:00].
- Inserting a Ruler A ruler passed through the middle of the window appears to go through the window itself or keep rotating while the window goes backward, defying physical possibility as perceived by the brain [03:10:00], [03:17:00], [03:21:00].
The illusion works because when the larger side of the trapezoid moves to the back, it still occupies a larger portion of our field of view than the small side, leading our brain to incorrectly perceive it as closer and rotating in the opposite direction [11:59:00], [12:07:00].
The Carpentered World Hypothesis
Adelbert Ames believed the illusion’s key lies in our environment: we are accustomed to living in “rectangular boxes” like houses and rooms, where corners are typically 90 degrees and objects like doors and windows are rectangular [04:11:00], [04:21:00]. This is known as the carpentered environment [04:30:00].
Our brains learn from extensive experience that trapezoidal images on our retinas should generally correspond to rectangles and right angles in reality [04:40:00], [04:46:00]. This allows our brains to infer depth, which is usually correct in a rectilinear world, but it fails with the trapezoidal Ames window, which the brain assumes is rectangular [04:52:00], [05:00:00].
Cross-Cultural Studies
In 1957, Harvard psychologists tested the Ames window illusion in South Africa with 80 children aged 10-14 [05:16:00], [05:21:00]:
- Urban Group 40 children from Durban, living in environments with many rectangular buildings [05:27:00].
- Rural Group 40 children from rural communities, living in round huts with few prominent 90-degree angles [05:33:00].
When seated 10 feet away with both eyes open, 60% of the urban group saw the window oscillating, while only 17.5% of the rural group did [05:41:00], [05:46:00]. These results supported the carpentered world hypothesis, suggesting that less experience with rectangles correlated with less susceptibility to the illusion [05:56:00].
However, when subjects were seated 20 feet away with one eye closed, 90% of all participants perceived the oscillation, with no significant difference between urban and rural groups [06:07:00], [06:12:00]. This indicates that factors beyond just experience with rectangles also play a role in the illusion [06:20:00].
The De Heer Circle
A similar illusion can be observed without any straight lines. The de Heer circle, when continuously rotating, also appears to oscillate back and forth [06:26:00], [06:31:00].
Anamorphosis
Both the Ames window and the de Heer circle utilize anamorphosis, a technique where a distorted projection of an object is created [06:39:00], [06:41:00], [07:29:00]. To see the proper proportions, the viewer must look from a specific position or use a particular device [07:32:00].
Historical examples of anamorphosis include:
- The Ambassadors (1533) by Hans Holbein the Younger This painting features a distorted shape on the floor that reveals a human skull only when viewed from the top right or bottom left, suggesting it was meant to be seen from a specific vantage point, like a stairwell [06:48:00], [06:56:00], [07:02:00].
- Leonardo’s Eye by Leonardo da Vinci This work takes its proper form only when viewed from the side [07:40:00], [07:42:00].
- Lascaux cave paintings (17,000 years ago) Some argue these might be the first examples of anamorphic art, as artists would have considered how their animal figures would appear from different vantage points on uneven surfaces [07:52:00], [08:00:00].
The Ames Room
Anamorphosis is also central to Adelbert Ames’s most famous illusion, The Ames Room, designed in 1934 [08:15:00], [08:21:00]. From a single, privileged viewpoint with one eye, it appears as an ordinary rectangular room [08:25:00]. However, when people move within the room, its distorted nature becomes evident [08:31:00].
An Ames Room is constructed by taking a rectangular room and adding a diagonal wall [08:40:00], [08:42:00]. Lines connecting key parts of the room (corners, windows) to the privileged viewpoint are used to mark where they intersect the diagonal wall [08:47:00]. The floor and ceiling are then added, appearing tilted and warped if the projection is done correctly, and connected by trapezoidal walls [08:58:00], [09:01:00], [09:07:00]}.
Ames recognized that an infinite number of different distorted room geometries could produce virtually identical images of a normal room when viewed from the privileged position [09:20:00], [09:26:00].
The Development of Depth Perception
The ability to interpret depth cues appears to be an innate ability that develops very early in human development [12:28:00], [12:33:00]. Experiments showing the Ames window illusion to babies across different age groups (five and a half, seven and a half, and nine months) used their preference for novelty as an indicator [12:39:00], [12:54:00]. While five-and-a-half-month-olds showed no special preference for the Ames window, the older babies (seven and a half and nine months) were significantly more interested, suggesting they perceived it as oscillating [13:09:00], [13:14:00].
Philosophical Implications of Perception
The Ames illusions highlight that our perceptions are far from a transparent representation of external reality; our brains constantly face ambiguity and must subconsciously decide which of infinite possibilities we are looking at [09:33:00], [09:41:00]. This is evident in situations like depth perception, where it can be ambiguous which objects protrude outwards versus which are impressions, only becoming clear through motion [09:50:00], [09:53:00].
Metaphor for Science and Life
These illusions serve as a powerful metaphor against the misconception that scientific theories are simply decided by looking at data [13:30:00], [13:34:00]. In truth, the same data can often come from very different external realities, meaning data alone does not always discriminate between competing theories [13:44:00], [14:23:00].
Examples of theories where data doesn’t fully discriminate include:
- Whether the sun goes around the Earth or the Earth rotates on its axis [13:51:00].
- Whether the wave function collapses or the universe branches when a quantum measurement is made [14:07:00].
- Whether the speed of light is truly the same in all directions, or if only the roundtrip speed is observed [14:14:00].
The Ames illusions also serve as a metaphor for life [14:30:00]. Just as a person looking into an Ames Room feels they directly perceive external reality, there are infinite different geometries that would all look the same [14:35:00]. In a world where people receive the same information but reach very different conclusions about reality, it is important to remember how easily our brains can be fooled [14:48:00], [15:01:00]. This calls for approaching the world and our conclusions with greater humility and less certainty [15:08:00].