The Illusion Only Some People Can See

I am going to turn myself into an optical illusion by going through this window right here. Ah, (grumbles) huh. Okay, I'm good, oh, not good. I was gonna say I'm good, I'm not good.

Okay, so you're looking at this window and it looks like it's turning around, except here it stops. Now I keep rotating, but the window is rotating through me. What is happening?

This video is sponsored by NordVPN. They help you create the illusion that you could be anywhere in the world. Let me backup for a second. This is the first part of a three part illusion. What do you see? Well, there's a window and it's turning, except it stops and reverses direction. So the window is oscillating back and forth. That's what most people see when they look at this illusion except that's not what the window's actually doing.

It's on this turntable and it is rotating continuously. This is known as the Ames window illusion. And I saw it on an old Australian TV program called the Curiosity Show. And I was curious. So in this video, I'm gonna dig deeper into this illusion than anyone has before. You know the window itself is not a rectangle, but a trapezoid. You can see this side here is much shorter than this side over here.

And that is essential to the illusion. Also essential, it is shaded to make it look 3-D, but it's actually just a two dimensional card with the same image on both sides. So now that you know exactly what this object looks like and what it's doing, can you correctly perceive the rotation rather than the oscillation?

I still can't. It still looks to my brain like this window is going back and forth. Okay, here's an idea. I'm going to attach this Rubik's Cube to the short side of the trapezoid so we can keep track of it as it goes around. Are you ready? Okay. (dramatic music)

Okay, the Rubik's Cube is going around. Everything seems normal. But now what is that? It looks like the Rubik's Cube is continuing to go around, but the window is oscillating back and forth. There it goes, the Rubik's Cube around the back. I don't even know what's happening. (dramatic music)

Whoa, look at that. It looks like the Rubik's Cube is out drifting by itself out in front of the whole illusion. What is happening? Okay, new plan, I'm going to take off the Rubik's Cube and I'm gonna put a ruler right through the middle of the window. And so we can't possibly be fooled by the illusion, right? Okay, here we go.

Okay, the ruler is rotating around, but wait now the window is going backwards whoa, whoa! The ruler is going through the window. It is doing things which I know are physically impossible but that is how my brain is seeing it. Look, here we go again. The ruler is turning around with the window but right about here the windows starts going backwards but the ruler keeps coming.

What is even like, how is this possible? This doesn't make any sense. But that is the way my brain interprets this. It clearly prefers the illusion over seeing what's really happening, the continuous rotation.

So why is this, how does the illusion work? Well, it was created by Adelbert Ames back in 1947. And before becoming a researcher, he wanted to be a visual artist. So he was fascinated by how people perceive shapes and shading. And according to him, the key to this illusion is that we're all used to living in rectangular boxes, essentially.

You know houses and rooms where virtually all of the corners we see are 90 degree angles. Doors, windows, tables and chairs are full of 90 degree angles. This is called the carpentered environment. But unless we're looking straight on at something, the angles we actually see are not 90 degrees.

I mean, the images that form on our retinas are typically trapezoids of different shapes and sizes. Now from extensive experience, our brains know they really should be rectangles and right angles. So our brains use these strange shapes to infer depth information, which in our rectilinear world is almost always correct.

But not in the case of a trapezoidal window that our brains assume to be rectangular, hence the illusion. Now, if this carpentered world hypothesis is correct, well then you'd expect people with less experience of rectangles in their environments to be less susceptible to the illusion.

And to test exactly this, in 1957 Harvard psychologists tried the Ames window illusion in South Africa with 80 children, aged 10 to 14. 40 of them were living in the city of Durban full of rectangular buildings, doors and windows. The other 40 were from nearby rural communities where they lived in round huts with few prominent 90 degree angles.

When subjects were seated 10 feet away from the rotating Ames window with both eyes open, 60% of the urban group reported seeing the window oscillating. But in the rural group, only 17.5% saw the same thing. So the results were consistent with the carpentered world hypothesis. The kids with less experience of rectangles were less likely to fall for the illusion.

But that's not the whole story. When seated 20 feet away and with one eye closed, the illusion was much more convincing. Now, 90% of all participants saw the window oscillating and there was no significant difference between urban and rural groups. That means something else must be going on over and above our experience with rectangles.

In fact, you can get a similar illusion without any straight lines at all. This is the de Heer circle, when rotating continuously, it also appears to oscillate back and forth. So what's going on? Well, both of these illusions make use of a technique called anamorphosis which has been used by artists for centuries if not millennia.

This is a painting from 1533 called The Ambassadors by Hans Holbein the Younger. It clearly shows two prominent figures, but there's also this distorted shape over the floor. Only when viewed from the correct position either of the top right or bottom left, does it become clear that the image is actually a detailed depiction of a human skull.

It's suspected that the painting was meant to be hung in a stairwell where presumably out of the corner of your eye, you would spot the striking image of the skull reminding you of your own mortality. But if you were to look at the painting head-on well, the skull would be pretty hard to see.

Anamorphosis involves making a distorted projection of an object. So to see its proper proportions, you need to look at the work from a particular position or with a particular device, often a mirror. There are earlier examples like Leonardo's Eye by Leonardo da Vinci, which only takes its proper form when viewed from the side.

Clearly, Leonardo knew how to give side-eye. And some might argue that the cave paintings at Lascaux France from 17,000 years ago provide the first examples of anamorphic art. Due to the uneven painting surface, artists would have had to consider how their animal figures would be perceived from different vantage points.

(dramatic music) Anamorphosis is also central to perhaps Ames most famous illusion, The Ames Room. Ames designed his first distortive room in 1934. And with one eye, from one privilege perspective it just looks like an ordinary room. But when people move around the room, it becomes obvious that something is not quite right.

An Ames Room is constructed by taking an ordinary rectangular room and adding a diagonal wall through the middle of it. Then draw lines connecting all the key parts of the room like corners, windows, and so on to the privileged viewpoint. Mark where those lines intersect the diagonal wall.

Then add a floor and a ceiling. If the projection is done properly, they will not only be tilted but also warped. Then connect the floor and ceiling with trapezoidal walls and voila, you have an Ames Room.

(gentle music) Ames realized there are an infinite number of different distorted room geometries which when viewed from the privileged position create virtually identical images of a normal room. So our perceptions far from transparently representing external reality are constantly faced with ambiguity.

And our brains below the level of consciousness have to decide which of the infinite possibilities we're actually looking at. One form of ambiguity relates to depth perception. Which of these masks protrudes outwards towards the camera, and which is an impression? Only through motion does it become obvious, which is which.

We are subconsciously attuned to visual cues that indicate how close or far away something is. Closer objects are typically bigger and brighter, plus they obscure objects behind them. But we can play with these attributes in order to create situations that defy our expectations.

Now I have been obsessed with getting the Ames window illusion to work. Look at how many different Ames windows I have been making. And I made them small initially, and then bigger. There used to be a disco ball in this room, I never thought that this would come in handy.

Then I thought about the question, how could I make myself like the ruler that passes through the Ames window? And of course, then I would need a very large Ames window. So it's been this holiday season, like we're living in a weird, surreal art museum or something. It needed to be at least eight feet on its longest dimension. It's actually made out of six pieces of plywood, glued, screwed together.

(saw cutting) One of the challenges is to make it really thin because ideally it should just be two dimensional. So we had to bevel these edges here. (gentle music) So then I would twist up these metal cables that hang it to the ceiling and then jump in the window and let them unwind.

Ah, (grumbles) huh, okay. So I'll show you some of the best shots I was able to get and you let me know, does this work for you? Do you see it oscillating or do you just see it rotating as it actually is?

I found lighting is really important. The lighting needs to be really even on both sides to convince you that it is really oscillating. When the large side of the trapezoid is close to us, we perceive it rotating exactly as it is. But when the large side moves around to the back, it is still larger in our field of view than the small side.

So our brain perceives it as closer and rotating in the opposite direction. This is why the window appears to oscillate. Half the time we're seeing the window as it is, and half the time we're seeing the bigger side as closer to us, even though it's farther away.

But how do we develop the ability to interpret depth cues in the first place? Well, it seems to be an innate ability which forms very early in our development. They've actually shown babies in three different age groups five and a half months, seven and a half months and nine months the Ames window illusion.

Do they see the window oscillating? And how would we know if they did? Well, babies have a well-known preference for novelty. They look longer at things that are new to them. So experimenters first exposed them to an ordinary rotating circle. And then they showed them simultaneously the Ames window and a rotating rectangular window.

The five and a half month old babies showed no special preference for the Ames window. But the seven and a half and nine month olds were significantly more interested in the Ames window. Suggesting they perceive it as doing something different, presumably oscillating.

The reason I have been so obsessed with this illusion is because I think it confronts one of the big misconceptions about science. Which is this idea that scientists propose competing theories, and then all you have to do is look at the data to decide which is the best theory.

The truth is there are many circumstances in which the same data could come from very different external realities. To use a classic example, does the sun go around the earth or does the earth rotate on its axis? The observation of the sun moving across the sky doesn't in itself resolve that debate.

Or to use more modern examples, when you make a quantum measurement does the wave function collapse or does it branch the universe? Is the speed of light really the same in all directions or does it differ and only the roundtrip speed is seen? As of right now the data do not discriminate between those theories.

And I think we can extend this beyond science. I mean maybe the Ames illusions are a good metaphor for life. We feel as though we can directly perceive external reality like a person looking into an Ames Room, but the truth is there are an infinite number of different geometries that would all look the same.

You know these days, a lot of people are getting the same fundamental information but coming to very different conclusions about the state of reality. So I think in that context, it's important to remember that something as simple as a little rotating picture can fool our brains in fairly spectacular ways.

So we should approach the world and our conclusions about it with a little more humility and a little less certainty. (dramatic music)

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