The Illusion That Makes You Question Reality (1)
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How can you see a cube that isn't really there?
Why does this window spin one way and then the other?
How can something shrink before your eyes?
And then grow again?
And why do you see a chair where there is none?
Optical illusions like these are more than just tricks.
They can actually help us unlock the secrets
of how we make sense of the world around us,
and even how we construct reality itself.
In this video, we're going to explore a whole bunch
of really mind-bending optical illusions
and dig deep into how they work,
to try and answer to one important question:
How do you know that what you see is real?
Hey smart people, Joe here.
Every waking minute of every day,
your brain is doing something truly incredible.
It's taking a gazillion tiny electrical impulses
from your eyes and creating a fully functional
three-dimensional reality.
It's pretty impressive when you put it like that.
The scientific term for this is spatial perception
And it's one of the most fundamental ways
that you make sense of the world around you.
I mean, think about it,
if you want to move around your environment
you gonna be able to detect obstacles,
to know how they are arranged.
What kinda space is between them.
I mean, I don't care if you want to do something
as complex as brain surgery,
or as simple as picking that book off the table,
Your brain needs a really accurate picture
of how big things are and how far away they really are.
And that's much harder than it sounds.
Space has 3 dimensions.
If you look at it sort of mathematically,
those 3 dimensions are basically identical.
But when it comes to how your eye sees the world,
those 3 dimensions are not created equal.
Because your brain has to make sense of a 3D world
using a 2D picture.
You can put objects in order in the up-down dimension
by how those images land on your retina bottom to top.
Same with left to right,
those images hit the back of your eye in different spots,
so it's easy to put them in order
in the side to side dimension.
But how do you figure out that other dimension:
how far away an object is?
Well, even though all the light coming into your eye
hits the back as a flat image,
hidden in that 2-dimensional picture are clues.
There's many different kinds of clues.
And we use these bits of information, these clues,
totally unconsciously, to build our picture of reality.
These circles are the same size.
But how far away is each circle?
And which one is farther away now?
Looking from here, you can clearly see which one's closer,
and that one circle is actually bigger than the other one.
I can just slide this closer or farther away.
The illusion worked,
you couldn't figure out size and distance,
because you didn't have enough clues.
When you look through here, the only information
that your eye has is which circle is bigger?
And well, size matters!
When things are closer, they literally take up more area
on the back of your eye than when they're far away.
So with no other clues present,
your brain thinks the bigger thing is close,
and the little thing is far,
even though they're the same distance away.
And when they look the same size,
they can look the same distance away, even when they're not.
Of course, if you have more clues,
you can get a better picture of reality.
I'm in front of all that stuff back there.
But how do ya know that?
One clue is that it's maybe slightly out of focus
but you also can't see all of these things.
I cover up that stuff, so I'm in front and it's in back.
It's the reason this turtle's in front of this one,
who's in front of this one, who's in front of this one.
It's turtles all the way back.
If you can't see all of something, then it's farther away
than the thing that you can see all of.
At least that's true most of the time.
You need more clues!
Magic.
And another one of those clues
explains why the drawings you did in kindergarten
look so awful.
The first thing you do is draw the ground, right?
Then maybe you put a tree over here.
And here's a house, and here's a person.
But how do you tell what's closer
and what's farther away
when they're all standing flat on this line?
You can't!
If you can't see the ground and the horizon,
you can't tell how far away things are.
But if you can and when you add in those other clues:
how big things are, what's on top of what,
then you can start to build a three dimensional reality.
Take a picture like this.
It's full of clues!
These trees closer to the horizon,
they're higher up in the picture, so they're farther away.
And these trees down here are overlapping those other trees,
so they're closer
But the most important clue in this image
is linear perspective.
Even though a path like this is made of two parallel lines
the same distance apart,
they appear to meet at a point on the horizon
called the vanishing point.
Sensing these parallel lines, seeing things converge
on a vanishing point
is what creates the sensation of perspective in your brain,
and it's a really powerful clue.
You know, noticing this linear perspective clue
in the world,
that's one of the big things people in Europe figured out
around the beginning of the 15th century,
and it's why art went from looking like this
to looking like this.
These are a few of the clues you use every day
to build your reality.
And you don't even have to consciously think about them!
You just DO it. That's incredible!
Give yourself a pat on the back.
And that brings us to one of the all-time great
mind-breaking illusions ever constructed, the Ames window.
The window appears to be turning normally.
Until this point,
when it stops and spins the other way.
Most people see this window
kinda oscillating back and forth infinitely.
Except that it's not. It's just rotating.
Round and round and round. Whee!
Very weird though.
This is an incredibly powerful illusion.
And it gets even stranger.
Watch what happens
when I put something through the middle here.
At first everything seems normal,
until the object appears to rotate backwards?
What in the cerebral cortex is going on here?
For a long time, people thought
this Ames window illusion works
because we live in physical spaces built out of rectangles
and right angles.
What has come to be known as the carpentered world.
Basically we're used to seeing rectangular things
that don't actually look like rectangles.
When researchers showed the Ames window illusion
to people who lived in rural areas
without many rectangles around,
well, they expected that people
who don't live in carpentered worlds
well, they wouldn't see the illusion as strongly.
But when viewed with one eye, as the illusion typically is,
both urban and rural subjects saw the illusion
basically the same.
So there must be something else going on here.
And I think the explanation is likely much simpler.
This trapezoid is built in such a way
that no matter how it rotates, the length of the longer edge
is always bigger on the back of your eye
than the length of the shorter edge.
And if there's no other clues available
in your visual field, your brain does what it always does:
it makes the best guess with what it has to work with.
What is bigger is closer.
And lines converging toward a vanishing point
are farther away.
Conclusion?
The window always appears to spin away from you.
(air whooshing)
These are visual cues that exist
regardless of whether the environment is built or natural.
Human brains seem to be wired to construct reality this way,
because that is what the world has always shown us.
Can that also explain this?
This is a room that can make things grow and shrink
right before your eyes.
I know what you're thinking:
This is a dark, evil magic.
But it's not. It's just a trick room.
It's called an Ames room.
The ceiling, the walls, the floor, the windows everything,
they're all skewed so when you view it
from one particular spot,
your brain ends up building a false reality.
In this case, your brain is getting the clues
that we talked about,
it's just that those clues are lying.
The really cool thing about these illusions
is that even when you know how they work,
when you know that you're getting tricked,
when you know that what you see
defies the very laws of nature,
well, that's still what you see.
Having more knowledge
doesn't really affect the illusion much.
I think that's kind of the most wonderful thing
about the Ames demonstrations.
They're what researchers sometimes describe
as cognitively impenetrable.
It doesn't matter what you think about politics or sports
or what you had for breakfast.
Your perception is going to work a certain way.
Now I mentioned that this illusion
only works from this one viewing angle,
this very specific spot.
This kind of distorted view,
where you only see the normal thing
from a specific vantage point,
is what's called an anamorphism.
Artists have been using anamorphic tricks for centuries.
One of the most famous examples is Hans Holbein's
"The Ambassadors".
When you view it from a very low angle,
a slash of gray becomes a skull.
Or the very flat ceiling of this church in Rome,
which was painted in 1690 to look like a dome.
You're probably more likely to see this illusion marking
a bike lane or something, though.
But the Ames room is one of the most striking examples
of anamorphosis, making a rectangular reality
out of a very non-rectangular room.
Okay, now it may seem like you're looking at a chair here.
But it's not a chair.
It's just a jumble of strings pointing this way and that.
But if you look here
this one is a chair.
And so is this one
This is an illusion called the Ames chair.
It's not as well known as the Ames window or the Ames room.
But it's actually my favorite.
Partly because this was a real pain in the butt to build,
so I have to tell myself it was worth all the trouble.
But it's also my favorite
because it shows you how sensitive your brain is
to certain patterns,
and how if you see a really special pattern,
you almost can't help but add meaning to it.
And the clue your brain is picking out in this one
is connectivity.
From that special point of view,
these edges come together to form nice neat corners.
And your brain is sort of doing a probability calculation:
If this really were a bunch of separate bits of string,
then of all the ways they could be arranged,
there's basically no probability
that they'd randomly find their way
into the arrangement of a chair, right?
So it's like your brain saying,
"based on the very limited information I have,
the most likely situation here
is that all of these lines are connected.
Because if they're not,
I'm in this very weird, chance situation."
Of course, it turns out right now
you are in a very weird, chance situation
where I have specifically arranged the strings
to make a chair shape.
But that would basically never happen in the real world.
Because in your normal experience,
those connections would never occur
unless they have meaning.
Conclusion? That's a chair.
Now, interestingly this idea of connectivity
