50x09 - Your Brain: Perception Deception

[bunniefuu]

♪ ♪

♪ ♪

ANIL SETH: The brain is one
of the most complex objects

that we know of in the universe.

BOBBY KASTHURI: There are
more connections in your brain

than there are stars in
the Milky Way galaxy.

So, we literally walk around
with about 10,000 galaxies'

worth of neuronal connections

in one of our brains.

HEATHER BERLIN: That vast
web of connections creates you.

But how?

NANCY KANWISHER: Figuring out
how the brain implements the mind

is a massive challenge.

♪ ♪

SETH: It seems as though

the world just pours
itself into the mind

through the transparent
windows of the eyes

and the ears and, and
all our other senses.

♪ ♪

BERLIN: But is what we see,

hear,

and feel real?

You might think that the reality

outside is actually
what you're perceiving.

And the answer
is no, it really isn't.

Almost at the very first moment,

we are transforming reality.

It feels so real

because we don't know better.

Think about illusions.

ROSA LAFER-SOUSA:
Do you remember the dress?

Of course... it's like
a celebrity, the dress.

A polarizing debate

that took over the internet.

White and gold. Blue and black.

SETH: Illusions are fascinating;

they're like fractures
in the matrix.

BERLIN: Ow!

Isn't that interesting? Whoa!

They reveal to us that the way

we perceive things isn't
necessarily the way they are.

BERLIN: Could you be
the biggest illusion of all?

SUSANA MARTINEZ-CONDE:
Your sense of who you are is an illusion

as everything else;
you're no exception.

BERLIN: "Your Brain:
Perception Deception."

Right now, on "NOVA."

♪ ♪

MAN: Okay, rolling.

♪ ♪

Take three.

BERLIN: Have you ever
thought about what's real?

[echoing]

Somehow the whole world
out there gets inside my head.

How do I know what
I see, what I hear,

what I feel is right?

It's a question
that's fascinated me

ever since I was a little girl.

I couldn't sleep one night,

and I had this thought
for the first time:

And then I thought, well,
even if I don't have a body,

can I at least keep
my own inner thoughts?

So I asked my dad the next day,

"Dad, where do my
thoughts come from?"

And he said, "They
come from your brain."

[expl*si*n echoes]

♪ ♪

"Your brain." I was hooked.

This bag of jelly
between my ears,

how does it work?

STANISLAS DEHAENE: I think
it's one of the ultimate mysteries.

How matter becomes thought.

ANDRÉ FENTON: To answer
that question would be perhaps

the highest human
achievement to date.

DANIELA SCHILLER: I mean,
forget about scientific quest.

It's a human quest.

♪ ♪

BERLIN: To find answers,

I became a neuroscientist
and a psychologist.

I'm Heather Berlin,

and my journey to understand
my brain begins with a question.

How does the world out there,

with all its beauty
and complexity,

get inside our heads?

♪ ♪

Think about it.

Imagine for a
second you're a brain,

sealed inside your skull.

There's no light, no sound.

KASTHURI: You're
a massive collection

of billions and billions
of cells that are living

in this weird pond
that is entirely devoid

of all of the sensations,
and that somehow,

through chemistry and
electricity, all of these

perceptions and
memories of the world

originate in our brains.

BERLIN: All brains...
From the tiny fish

to the enormous elephant...
Contain microscopic cells

called neurons, and one of
their jobs is to translate input

from the external world,
whether that's light,

heat, sound, or
pressure, for instance,

into electrochemical signals
the organism can use to act.

What might be
surprising to you is that

as neurons process
sensory signals,

they create an edited
version of reality,

even on the most basic level.

KASTHURI: We're deciding
to throw away 99% of the world.

Almost at the very first moment,
we are transforming reality

into something we could use.

BERLIN: Neurons transform
reality by competing with each other.

When a creature touches,
smells, sees, or hears something,

its sensory neurons fire;
some a little, some a lot,

depending on where the
physical signal is strongest.

But follow those signals
down towards its brain,

you'll see that the weaker
ones get stamped out.

For simple brains,
say, the brain of a crab,

a diffuse light to the eye
becomes a sharp beam.

For more complex
brains like ours,

it's in part what
makes you think

that these two squares are
completely different colors,

but actually, they're identical.

♪ ♪

MARTINEZ-CONDE:
Think about illusions.

First, they're a lot of fun,
but as neuroscientists...

Whoa...

MARTINEZ-CONDE: illusions
are very important to us.

Because of this discrepancy
between objective reality

and subjective perception,
we can use these illusions

as a handle to try to
understand what the brain

is doing all the time.

BERLIN: Susana Martinez-Conde,
along with her partner

and collaborator
Stephen Macknik,

are among the world's
preeminent experts

on illusions and perception,

and what they tell us
about how the brain works.

Ha, now what?

[both laughing]

MARTINEZ-CONDE: To
give a different example,

Adelson's checkerboard
illusion, this is so striking because

you see some of the checks
as dark and others as bright,

but you realize that it is
exactly the same shade of gray.

BERLIN: Don't believe it?

Look at the squares
labeled A and B.

A looks darker, right?

Wrong... that's the illusion.

That's because your brain
is adjusting for the shadow.

MARTINEZ-CONDE: What's
happening is that your brain is considering

the light source and basically
subtracting that light source

from your resulting perception.

Your brain is performing
an interpretation,

a shortcut, if
you will, to arrive

at a perception.

BERLIN: If the brain's
shortcuts distort reality this much,

how much of the world
are we really seeing?

STEPHEN MACKNIK:
What you need to understand

is that we really can't see
most of the world around us.

We're effectively blind

to 99.9% of the world
around us at any given time.

If you hold out your
thumb at arm's length...

Mm-hmm. And you straighten your
elbow and you look at your thumbnail,

your thumbnail is about one
degree of visual angle here,

and it turns out that
that's the only place

we can actually see
with 20/20 vision.

Wow. And everywhere
else, we're legally blind.

BERLIN: It might
sound hard to believe,

but human vision
is really like this.

You actually only see detail

in about one percent
of your visual field.

That's because only a
tiny portion of the world

can be processed
in detail by the retina.

It feels like I'm seeing the
whole world in 20/20 vision.

And it's almost all completely
made up in your brain,

based on assumptions and
models of how the world works

and just a tiny bit of
high-quality visual information.

Let me demonstrate this to you.

I know it's kind of hard
to believe... Mm-hmm.

Because you've been
having your whole life

where you feel like everything's
continuous. Yeah, show me the data.

[laughs] Show me the evidence.

Let's look at an eye-tracker
and look at your eyes

and how they actually work.

And if you put your
head in this headrest...

Mm-hmm... we'll point
the camera at your eyeballs

and we'll actually
be able to see

where your eyeballs point
during this demonstration.

Feels like "Clockwork
Orange." [chuckles]

"Buck lived at a big house

in the sun-kissed
Santa Clara Valley."

BERLIN: First up,
a reading demo.

Though most of your
screen may be filled with Xs,

to me, it just feels
like normal reading.

I barely see the Xs,

and that's because
the display of letters

is tied to my eye movements.

BERLIN: Well, it's
just, the words are being

revealed depending
on where I look.

That's right, so as
you move your eyes...

So weird... the words
are revealed to you.

But we don't move our
eyes in the same way you do.

So we just see a bunch
of Xs most of the time.

BERLIN: What turns out to be
critical is my eye movements.

MACKNIK: So our eye
movements program what part of this

high-quality piece
of visual real estate

we're going to put
where and at what time.

BERLIN: The human eye moves
about three times per second.

We take it for granted, but
without these movements,

we'd be basically blind,

as Steve is about to show me.

MACKNIK: In this
demonstration, it's the opposite.

Here we're blocking what
you can possibly see, right?

BERLIN: Though you may see a whole
scene with a square moving around,

all I see is the square!

I can tell something is around
the edges, but it's blurry.

Whenever I try to look, the
square moves with my eyes

and it's blocked.

BERLIN: This is so
frustrating, this one.

Who has their hand
up in this image?

BERLIN: Uh... I think
that guy down there?

MACKNIK: That's right, but
it's very hard for you to see,

right? Every time I
look at him, it, yeah.

It disappears because
this block, it blocks it.

MACKNIK: This
actually is interesting

because it's in high-quality
vision wherever you look,

but it's blurry in the surround.

BERLIN: Now the
scene looks normal to me,

but mostly blurry to you

because your eye
movements don't match mine.

MACKNIK: Wherever
you happen to look,

you have high-quality
image processing happening

and the surround
is completely blurry.

This kind of represents
exactly what your visual system

looks like all the time anyway.

So why would our
brains be built this way?

Well, think about
what the alternative is.

What if we didn't
have eye movements?

Well, if we didn't
have eye movements,

and we just wanted
to see the entire world,

we'd need to have our retinas

see everything in
very high quality.

Our brains would
be 600 times bigger,

and you gotta remember, the
visual system's our best sense.

This is our richest sense.

So our other senses are,
are even more impoverished.

BERLIN: Here's how your
brain really sees the world.

It's easy to
think it's like this.

You open your eyes and
the whole world pours in.

But really, it's like this.

Your eyes sample
tiny pieces of the world

and the brain fills in the
rest... constantly, all the time.

KANWISHER: We feel like we have

this incredibly rich,
wide, full, detailed percept

of what's going on
moment to moment,

and that's probably
pretty illusory.

What we're actually
aware of is a tiny subset

of the information that
comes in through our eyes.

BERLIN: Don't believe it?

Consider this:

your optic nerve is what
connects your eye to your brain,

and its location near
the center of your retina

effectively creates a blind spot

near the center
of your visual field.

And yet, you don't experience
the blind spot... why?

The brain samples the
area near the blind spot

and fills in the gap
with its best guess.

KASTHURI: It's probably not fair

to say that we completely
confabulate the world,

it's just that we
probably represent

one percent of it at any
particular moment in time.

So, it's a constant updating
between what I see with,

versus what I remember,
versus what I expect.

And it's that dance
between those three

that actually gives
us our sense of reality.

BERLIN: And amazingly,
that edited reality...

Despite its limitations...

Serves us quite well.

KASTHURI: You might
ask, "If I'm just keeping track

"of one percent of the
information in the world,

how can I drive a car?"

And it turns out
that first one percent

of the information that
comes in from the world

is actually an enormous
amount of information. [chuckling]

If we had to
actually pay attention

to everything on the road
at the, at one particular time,

it would take minutes,
maybe even longer,

before I decide to
turn the wheel right

or to turn the wheel left.

♪ ♪

BERLIN: By understanding
how my senses really work,

I'm getting a peek
behind the curtain:

what my brain is really up
to outside of my awareness.

MARTINEZ-CONDE: Based on
this very tiny amount of information,

we construct this
grand simulation

of the visual world around us.

It feels so real because
we don't know better.

BERLIN: And most of the time,
we all agree on that simulation.

It's when we don't that
we can learn something.

So do you remember
the dress? Of course.

Did you see this
dress or this one?

It's a simple question,

but the answer has
divided friends and family.

White and gold. Blue and black.

I remember it caused
quite the stir, right?

Massive stir.

A polarizing debate

that took over the internet.

♪ ♪

LAFER-SOUSA: People had
existential crises over this image.

People tweeted things like,

"If that's not white and gold,

my life has been a lie."

Swear on your mother's grave.

Because that dress
is white and gold.

Out of her [bleep] mind.

LAFER-SOUSA: Massive arguments.

I watched videos of people
screaming at each other.

GRAYSON DOLAN:
This is white, dude!

ETHAN DOLAN:
White? That is dark blue!

It's purple-blue!

LAFER-SOUSA: I bet there
was a divorce here or there

over this image.

BERLIN: So when
you first saw that dress,

as a, as a vision scientist,
what did you think?

Well, when I first
saw the dress,

I thought it was blue and black.

And I thought that the
internet was yanking my chain.

Right... to get the goat
of vision neuroscientists.

Sure. [chuckles]

But in the morning, when
I looked at my phone,

I saw white and gold.

And now, of course,
I was obsessed.

So I said, "Well, if this
is an ambiguous image,

all I have to do is
disambiguate it."

So I set to work, I
got into Photoshop,

cut out the dress, put it into
a scene with lots of rich cues.

BERLIN: Hm.

LAFER-SOUSA: And
all of a sudden, boom:

you can see the
dress is white and gold.

Wow. Now, the pixels,

the pixels that make
up the dress there,

are identical to the
original image. Okay.

BERLIN: Now, this
doesn't work for everybody,

but for most, the visual context

can make all the difference.

LAFER-SOUSA: What's different
here is, her skin is tinted blue,

the background has
blue light cast on it,

she's standing in the
shadow of that cube,

and so your brain says,
"Aha, I need to ignore

"some amount of blue light

"that is in this signal
that's hitting my eye

and render this
as white and gold."

BERLIN: And if we
flip things around?

LAFER-SOUSA: Same dress,
pasted it into this other scene.

Her skin is tinted yellow, the
background has a yellow cast,

she's standing no longer in
the shadow but in the light.

Boom! Blue and black.

Amazing, that's really amazing.

So again, the dress,

the pixels are exactly the same.

LAFER-SOUSA: Identical.

BERLIN: The dress
is a powerful example

of how color really
works in the brain.

Does that mean
we're creating color

in our mind, or does color
actually exist in the world?

Color takes place in the brain,

and I've prepared a
little illusion for you

that should
convince you of this.

LAFER-SOUSA: So I have
a picture of four cars here.

I want you to tell me,
what color are these cars?

Let's start on the top left. BERLIN:
Okay, so the one on the left looks red,

then the one next
to it looks blue.

I'd say the one,
the bottom there,

bottom left looks green,

and then the one
next to it looks orange.

LAFER-SOUSA: Okay. Mm-hmm.

What if I told you

that all of those pixels
are not only gray,

they are the same gray?

BERLIN: How is this possible?

It's because the light
that enters your eyes,

contrary to what you might have
learned in school, is not color.

Color is an interpretation
of your brain.

Here's how it works.

Light shines on the world

and bounces off objects...
This part you know.

And light comes in

different wavelengths,

each corresponding
to a different color.

What you might not
have heard in school

is how those wavelengths change

when they hit
different surfaces...

Rough, smooth, wet, et cetera.

This signal that
gets into your eye

is actually a product of
the reflective properties

of the object and the
wavelength of light hitting it.

Then that signal is
focused on the retina,

the back of the eye,

where we have about 130
million light-sensitive cells.

Three types called
cones are involved in color,

each sensitive to different
wavelengths of light:

long, medium, and short.

But that light
still isn't color.

For that to happen,
our brain has to take

that three-piece
code from the retina

and use the relative response
of the cones to encode color.

It's not until that signal
gets to an area called V4

that we get a neural
representation of color

that corresponds to our
perceptual experience.

So why would our
brains be built this way?

Well, if our brains
weren't built this way,

objects would appear to
change in color all the time,

and that would render color

a pretty useless
signal in the world.

♪ ♪

BERLIN: That's because objects
reflect different wavelengths

into your eye depending
on the lighting conditions.

If your brain didn't
compensate for this,

a red berry would
appear gray in a cave,

blue at dawn, and
orange at dusk.

But instead, your
brain carefully calibrates

your experience to
hold color constant.

Similarly, color
vision in other animals

is tuned to their needs.

SETH: Different species have
very different kinds of color vision

that are suited to their
particular environments

and their particular
challenges for staying alive.

BERLIN: Dogs rely on smell, so
they have fewer types of cones,

and thus see
the world like this.

Birds need to recognize
tiny color differences

from great distances.

So they have an extra type
of cone that allows them

to see more colors than we do.

And bees need to find
flowers rich in nectar,

so they see ultraviolet
light that's invisible to us.

LAFER-SOUSA: Color provides
a lot of valuable information

about the world,

but only if we can
faithfully extract

something about the object.

So we don't actually see
color as it is in the real world,

we just see it in terms
of how it's useful for us?

Absolutely.

And the dress is probably
the best example of that.

It's a really powerful
demonstration

of how our color
machinery works.

BERLIN: So why do
people see this image

of the dress differently?

It comes down to your
brain's assumptions

about the lighting conditions.

It seems that the more time
you spend working indoors

under artificial light, which
is predominantly yellow,

the more likely you are to
say the dress is black and blue,

because your brain
assumes it is lit by artificial light

and subtracts out the yellow.

Conversely, if you
spend more time

in natural light,
which is bluer,

you are more likely to
see it as white and gold.

So then what is the
actual color of the dress?

Well, Heather, I happen
to have brought it with me.

[chuckles]: Wow.
So what color is it?

Uh, it's obviously, I
was right, blue and black.

Team blue and black
for the win. Yes, yes.

I can't believe this
is the actual dress.

BERLIN: I feel like
I'm holding, like...

It's like a
celebrity, the dress.

I know, it should be in a
museum, not in my closet. Yes!

[both laugh]

Before the dress, people
hadn't really realized

we differ so much
between individuals.

We're now quite used to the idea

that we all differ
on the outside.

We all have differences in
skin color, in height, in shape.

But just as we all
differ on the outside,

we all differ on
the inside, too.

And this inner diversity
is very important.

It gives us a certain humility
about our own ways of seeing.

BERLIN: Illusions
give us a ringside seat

to watch how the
brain creates our world.

And it's not just
the visual domain.

Try listening to this.

[staticky computerized
voice playing]

Brainstorm, right?

Simple enough.

Now, listen to this.

[staticky computerized
voice playing]

Green needle.

Okay, so you're thinking,
"What's the big deal?"

But, what if I tell you that the
two audio clips I just played

were exactly identical?

For most people, what you hear
depends on which label you read.

Sounds unbelievable?

Here, try it again, but
this time, just read one.

[staticky computerized
voice playing]

Okay, now read the
other and listen again.

[staticky computerized
voice playing]

Now, when I first
encountered this,

I was floored, too.

Even though I know
what's going on.

When your brain
encounters uncertainty,

it fills in the gaps
with its best guess.

In this case, we have
a degraded audio clip,

and when you're primed
with a certain word to go with it,

your brain automatically
jumps to the best fit.

For most of us, we literally
hear what we want to hear.

And it gets even
worse... let's try one more.

Another internet sensation

that lit up debates
across the country.

[cleaner computerized
voice playing]

Once and for all, is
it yanny, is it laurel?

It's not yanny, it's
laurel. It's yanny!

Did you hear yanny?

[cheering and applauding]

Who heard laurel?

[cheering more loudly]

It is laurel and not yanny.

[remix of computerized
voice playing]

It's like that
stupid dress again

all over, but in audio form!

This is not saying "laurel,"
this is only saying "yanny."

Exactly, it's laurel!

Now, about half
of you hear yanny,

and the other laurel,

and unlike the first illusion,
I can't get most of you

to experience this
one any other way.

You're locked into
your version of reality.

Experts aren't exactly
sure why, but some of us

seem to pay more attention
to the low frequencies, laurel,

and others to the high, yanny.

The divide stems from
the fact that the audio file

is an ambiguous signal made up

of both high and
low frequencies.

But by manipulating
the frequencies,

I might be able to
change what you hear.

[computerized voice
playing at mid frequency]

High...

[voice plays at high frequency]

[voice plays at
low frequency] Low.

All of this goes to show

how much the brain

is an active interpreter
of sensory input.

Our perception of
the external world

is actually much less objective
than we'd like to believe.

Most of the world
around us is very real,

but you just never
lived there, okay?

You lived in your mind,

which is a perception of
that world that's being filtered

through a bunch of salt
water sacks of proteins

and electrochemical signals,
which can't possibly be making

completely accurate
determinations

of what's actually
in the outside world.

Not convinced? Or maybe
you're just asking, "Why?"

Well, try watching for
when the green dot flashes.

Does it line up
with the red dot?

If you are like most people,

the red one always
seems just a little bit ahead.

Now try again.

The red dot and the green dot
are actually perfectly aligned.

That's because some
neuroscientists would say

that it's not your brain's job

to perceive the
world accurately.

Rather, its job is to
predict what happens next.

To a certain extent, you
see what you expect to see:

a predicted path of motion.

And this is what
helps us hit a home run

or flinch from a punch
at just the right moment.

The brain is a
predicting machine.

Given a set of circumstances
in this story at this moment,

what are the likely plausible

next events in the story?

SETH: The brain is
using sensory information

to calibrate,

update, to fine-tune
these predictions

so they remain tied

to reality in ways that are
not constrained by accuracy,

but that are constrained
by how useful

the brain's perceptual
predictions are

in the business
of staying alive.

BERLIN: And to keep us
alive, the brain has evolved

to look for signals
of potential danger.

One of the most
important is pain,

and as neuroscientist Theanne
Griffith is about to show me,

sometimes that can be
a kind of illusion, as well.

BERLIN: So what is this?

GRIFFITH: This is
a thermal grill. Okay.

This is a machine that
could give us some insight

as to how pain
works in your brain.

All right, this is making
me nervous already

as I'm getting strapped
in! [Griffith laughs]

GRIFFITH: Don't worry,
it's all an illusion, actually.

Okay.

And it's comprised of
these different metal bars

that are either set to a
cold or warm temperature.

So why don't you go ahead
and touch that first bar?

It's warm, right?

And then the next bar?

Cold. Mm-hmm.

GRIFFITH: And then
the next one, warm.

You see? So they're alternating cold,
warm, cold, warm. BERLIN: Mm-hmm.

Now, you want to
see what happens

when you put your hand down?

Not necessarily. [both laugh]

Go ahead. Okay.

Okay, here we go.

BERLIN: Ow!

GRIFFITH: Right? Isn't
that interesting? Whoa!

Yeah, what is going on there?

It sort of feels cold
at first, but then...

Then it gets this kind of
burning sensation, right?

Yes, very much so.

BERLIN: It feels super-hot,
like I'm getting burnt.

So it's not 100% clear
exactly how this is happening.

But what we think
might be going on

is that, basically, your brain

is getting a little
bit confused.

Okay. It's feeling cold,

and it's also feeling warmth.

And somehow, it's interpreting
these two signals as pain.

BERLIN: Here's what
neuroscientists think is going on.

In your hands, you have
separate sensors for heat,

cold, and pain.

Normally, when you touch
something slightly cold,

both your cold and pain
sensors are activated,

but the cold ones
override the signals

from the pain sensors,

telling your brain there's
nothing to worry about.

Unless, in this very
unnatural scenario

with the thermal grill,
you happen to be touching

something warm at the same time.

Here, the heat signals
cancel out the cold ones,

leaving you with just
the pain ones activated,

telling your brain, "Ouch!"

So in that respect,
is pain real?

Mm-hmm. Or is
it just an illusion

or a construct of the brain?

That's a really good question.

So noxious stimuli
is, is a real thing, right?

If you stick your
hand in boiling water,

that's an aversive stimulus.

The perception of a noxious
stimuli is real. Mm-hmm.

Pain is more of a
construct, right? Mm-hmm.

And it can vary from
individual to individual.

EMERY BROWN: Pain
is a construct of the brain.

How do we know that?

You touch a needle,
right? And prick your finger.

We can draw the anatomy
of what just happened.

We have very
well-defined pathways

saying, "This is
pain information."

We don't interpret it as
pain until it hits your brain.

BERLIN: Pain, not unlike
the experience of color,

is a construct of the mind.

Mama! Mama!

BERLIN: But just because
pain is in your brain

doesn't make it any
less critical for survival.

GRIFFITH: Pain is
a very important...

[gasps] ...learning
mechanism for children.

They learn what behaviors
they can engage in that are safe

and what behaviors, well,
they should not engage in

because they could
cause them bodily harm.

And there's, um, uh, different
mutations that people can have

in certain proteins
that make them

completely insensitive to pain.

And so kids do things
like bite on their lips

or on their fingers
when they're very young,

and as they get older, can
engage in risky behavior.

So pain is extremely
important for us to feel.

SETH: Illusions are fascinating.

They're like
fractures in the matrix.

They reveal to us that
the way we perceive things

isn't necessarily
the way they are.

MACKNIK: Illusions help us
find the cracks in the mortar

of that world we've
built for ourselves,

and understand what it is our
world is actually made out of

and what the brain
is actually doing.

So most people
think of the brain

reconstructing the world
more or less verbatim.

[dog growling] But
that's just not true.

What it's actually doing is,

it's getting very
little information

and it's using that
very little information

to make a big, grand
model of the world.

MARTINEZ-CONDE: We cannot
process the vast amount of information

that is constantly
bombarding our senses.

Illusions, you can think
of them as shortcuts.

Shortcuts make us faster,

more efficient
with less resources.

Based on these
snippets of information,

we build this more
complex simulation of reality.

And that simulation
of the world is

what we call consciousness.

BERLIN: Consciousness.

[alarm buzzing] We take it for
granted, but every time you wake up,

[alarm stops] your brain stitches
together all your sensory inputs...

The sound of a distant train...

[train whistle blowing]

the smell of coffee,

the warmth of the sun...

Into an experience of the world.

And that experience,

that awareness of the world,

is what scientists
call consciousness.

In neuroscience,
consciousness is the Holy Grail.

Humans have been
fascinated by consciousness

for thousands of years, probably
much longer than that. [chuckling]

Take three.

Now, of course, the
word "consciousness"

means a lot of things
to different people.

To some, consciousness
means being awake,

as opposed to asleep.

Or self-aware, or the
contents of my thoughts.

But that's not how we
neuroscientists think about it.

We think of it as something
much more basic...

It's just internal experience.

It feels like something
to see the color red.

To taste a strawberry.

[thunder rumbling]

To hear the crack of thunder.

[thunder crashing]

SETH: We are complicated
biological creatures,

but the most central
feature of our lives

is that we are
conscious creatures, too.

When I open my eyes,

it's not just that my brain does
some sophisticated processing

of the visual information.

I have an experience.

BERLIN: During the
course of my journey,

I've seen how our
experience of reality

is not what it seems.

If my conscious awareness

is built from my perceptions,
flawed as they may be,

how does that work
and what does it mean?

♪ ♪

So please take a seat.

BERLIN: Some of the first clues
trickled in from people like this.

LORELLA BATTELLI: Put
your chin on the chin rest.

BROWN: A lot of very
valuable information

comes from patients who've
had, part of the brain's damaged.

By piecing these various parts
together, seeing what was lost,

we've come to
appreciate the role

that these various
brain regions play

in the creation
of consciousness.

We're going to
calibrate your eyes first.

SETH: A powerful example of this

is the phenomenon of blindsight.

BATTELLI: This is a
patient who had a stroke

in her visual areas,

in the back of the brain.

And this stroke is
affecting her visual field.

BERLIN: Three years ago,
she felt a pounding in her head.

WOMAN: I had what I
thought was a migraine.

I actually went to
the emergency room

because I'm walking around
with this area where I can't see.

BERLIN: The stroke
damaged a piece of the brain

devoted to vision, leaving
her with an apparent

total blind spot.

WOMAN: That blind spot,
it's enough that if you're driving,

an oncoming car
disappears into it.

It's a little anxiety-producing
and, and things like that.

BERLIN: In everyday tasks,

her eye movements
make up the difference.

But what happens when
she doesn't move her eyes?

Neuroscientist Lorella
Battelli wants to find out,

so she developed a clever
series of experiments to pin down,

just how blind is she
really in that spot?

BATTELLI: We're using EyeLink,

which is the eye-tracking system

to make sure she
doesn't move the eyes.

BERLIN: She keeps her eyes
focused on the center spot.

Every time she hears a beep,

she has to say if those
little dots inside the circle

are moving to the
left or to the right.

Left.

BERLIN: The eye tracker checks
that she's not shifting her gaze.

WOMAN: Right.

When you're
doing tests like this,

that blind area, what does
that kind of look like for you?

What does it feel like for you?

When that target pops
up in my blind area,

I don't see it.

[machine beeps]

Left.

BERLIN: Strangely, even
though she says she doesn't see

anything in the blind spot,

she gets it right
more often than not.

WOMAN: Right.

BERLIN: So that some information

is getting in. Yeah, so...

But they're not
consciously seeing it,

but they can respond to it
in different ways. Exactly.

BATTELLI: Even if they
say, "I didn't see anything."

Left. But you tell them,
"Please, just tell me

whether you saw it or not,"

then their response
would be above chance.

BERLIN: So just keep
your eyes closed, okay?

And...

BERLIN: What's going on?

To probe deeper, Lorella
lets me give the patient

a different version
of the challenge.

I put a miniature
screwdriver in her blind spot.

BERLIN: Okay, I'm going to
have you open your eyes and fixate.

Okay. Okay.

I see nothing.

You see nothing.

Nothing. Okay.

BERLIN: Even though she says

she sees nothing, look
at which tool she picks.

Now turn over there
and look at the objects.

Tell me what you think you saw.

WOMAN: The
screwdriver. BERLIN: Yep.

BERLIN: Now try another one.

BERLIN: Next, I
display a tiny wrench.

♪ ♪

Did you see anything?

No. No? Okay.

Look over there and guess
what you think you, was there.

I think the wrench? Yep.

WOMAN: I'm going
to guess the scissors.

Yeah, good job, great, scissors.

BERLIN: Time and time again,

she makes the right choice.

Amazing, so, you know, it seems

to me that you're saying
you're not seeing anything,

yet when I'm asking
you to choose,

you're pretty much
getting it correct,

so something is getting in.

BERLIN: How is this possible?

It's as if she sees the
tools, but doesn't know it.

BATTELLI: They
actually saw something.

Mm-hmm, certainly. But
they're not entirely aware of it.

Information is getting
in, affecting our behavior

and how we're responding
to the world around us,

without there being a
conscious perception

of that piece of visual
information. Correct.

WOMAN: I'm gonna go
with the hammer again.

BERLIN: Until patients like
this, we scientists had never seen

perception separate
from conscious experience.

And this tells us
that perception

and consciousness are
separate things in the brain.

But it also has me wondering,

if someone can still
use visual information

without awareness of it,

why do we have
consciousness at all?

What is consciousness for?

A clue might come from babies.

[cooing]

ALISON GOPNIK: Babies...
Everything we know suggests

that they're born conscious.

They're certainly
taking in information

from the time they're born.

REBECCA SAXE: They
are making rational choices

about what they learn
from extremely early on.

And they are forming memories
of their specific surroundings,

of their parents,

of their important
relationships.

We can see that
in their behavior.

BERLIN: And all that
behavior burns a lot of fuel.

GOPNIK: Brains are
expensive computing gadgets.

So while you're
just sitting here,

your brain is using up
about 20% of all the calories

that you have, so it's
using up quite a bit.

But if you think
about a two-year-old,

his brain is using


So almost all that food is just
going to keep his brain going.

BERLIN: To understand why young
brains might need so much more fuel,

check out the connections
in a toddler's brain

versus an adult's.

A two-year-old's brain has
about two quadrillion synapses.

By the time they hit adulthood,
that number is cut in half.

So if you think about
the difference between

the baby brain, the child's
brain, and the adult brain,

the child's brain is more
like back country roads

where you have
little, tiny roads

that are going from
one village to the next.

None of them are very efficient.

There's not a lot of traffic,

and the traffic doesn't
go very quickly,

but they connect lots
and lots of different places.

And the adult brain is
more like superhighways

that get you from one
place to another very quickly,

and take a lot of traffic,

but don't connect as
many different places.

BERLIN: As we age, in
the interest of efficiency,

we strengthen the
connections that are useful to us

and prune the rest.

MACKNIK: You basically take neurons
you don't need, you get rid of them.

And what you have now
is a very lean machine

that does certain things
and it does them very well.

GOPNIK: We see this early
brain that's very exploratory,

that has lots and
lots of potential,

lots of possibilities.

Not very good at
putting on your jacket

and getting out to
preschool in the morning.

And then we have
this later brain

that's very good
at doing things.

Not so good at changing,

not so good at taking
in new information,

not so good at
doing something new.

BERLIN: What this
suggests is that maybe

what consciousness is for

is choosing what's
important for us to be aware of

at any given moment.

Kind of like a spotlight.

GOPNICK: For adults,
it's as if consciousness is

this bright spotlight
in one place

and everything
around it is dark.

BERLIN: While for
children and babies,

it would be more
like a flood light,

where nearly
everything is illuminated.

GOPNIK: You're conscious
of a lot more that's going on.

BERLIN: Consciousness
may be like an amplifier,

boosting the important
signals over the noise.

Is there any evidence?

This is where FMRI comes in,

a special tool in neuroscience
that takes pictures of the brain

while it's doing something
to map where blood flow

is in high demand.

The result is a
map of brain activity.

So where is
consciousness in the brain

and how does it work?

To find out,
neuroscientists designed

a clever series of
experiments that go like this.

They start by flashing a word

on a screen for
about 30 milliseconds.

[computer beeps]

DEHAENE: You flash this word,

and the person is not
able to see the word at all.

She says, "There was no word."

BERLIN: But in the FMRI scanner,
the visual cortex is activated,

even though people say
they don't see anything.

So the trick here is
to find the threshold.

Find the timing where sometimes

people consciously
see the image.

DEHAENE: So if you make
now the word a little bit longer,

suddenly, the person says,

"Oh, well, there is
a word, obviously."

And it's completely visible.

There is really a sort of
all or none phenomenon.

Either you see it or you don't.

And once you've done that,

you've got a really
powerful window

onto the neural correlates
of conscious perception.

BERLIN: When that happens,

suddenly, a suite of
different parts of the brain

shows a surge in
activity: the parietal cortex,

which integrates the senses,

the anterior cingulate,

which modulates drive
and decision-making,

and the prefrontal cortex,

which handles reasoning
and higher-order cognition.

An ignition of
distributed brain areas

that come online together,
speak to each other,

and broadcast this information
to the rest of the brain.

And this is what
we think is occurring

during conscious perception.

BERLIN: According
to some experts,

this communication
between brain regions

is the signature
of consciousness.

This discovery could
have real-world applications

in matters of life and death.

But that would
take one more step:

figuring out how to
measure consciousness.

♪ ♪

SETH: In science, when
we struggle to understand

a phenomenon that
seems quite mysterious,

it's often really important
to be able to measure it.

So a few hundred years ago,

this happened with heat... you
know, it was the development

of thermometers that
catalyzed our understanding.

Could something work for
consciousness the same way?

Could we have a
consciousness-ometer

that will lead us

to a deeper understanding
of what consciousness is?

BERLIN: That deeper
understanding could transform

the treatment of people
with brain injuries.

BRIAN EDLOW: So every year,
over a million people worldwide

will come into an intensive care
unit unresponsive, comatose.

The challenge that we face
is that our bedside exam...

Asking the person
to open their eyes,

pinching them and
seeing if they'll respond,

seeing if they move
their arms and their legs...

That bedside exam is
fundamentally limited.

BERLIN: Limited because
it often misses people

who are actually conscious.

In this case, we have
a healthy volunteer

from the "NOVA" team,

but what if she
were unresponsive?

How would we ever know
if she was conscious?

Brian Edlow's team at
Mass. General Hospital

is testing a new
technique to find out.

So tell me, what
are you doing here?

EDLOW: We are pinging
the brain with a magnetic pulse

and looking for
an electrical echo.

The ping is transcranial
magnetic stimulation,

or TMS.

The echo is the key;
if it dies out quickly,

the patient is unconscious...
They might be in a coma,

deep sleep, or under anesthesia.

If instead the echo
rings out across the brain

and becomes more complex,

the patient is likely to
be conscious and aware,

even if they appear
unresponsive.

EDLOW: The analogy
that we like to use

is throwing a pebble in a lake.

So the pebble represents the
TMS pulse to stimulate the brain,

and the brain waves,
the electrical ripples

that emanate from that pulse,
represent the waves in the lake.

The more complex
those waves are,

and the longer duration,

the more likely that
person is to be conscious.

BERLIN: To detect those brain
waves, Edlow's team uses E.E.G.,

a tool that measures
electrical activity

in the brain, to quantify
the amount of complexity

a patient's brain bounces back.

Here's how it works.

♪ ♪

All neurons, when
poked by a magnet,

will kick back an electrical
signal that looks like this:

a brain wave.

But if the surrounding
neurons aren't healthy,

those brain waves
won't get very far.

It turns out that in
conscious people,

even those who
appear unresponsive,

not only do those brain
waves spread all over the brain,

but they become more
complex too... it's as if,

to use music as the analogy,

what starts as a single
repeated note by a few neurons

eventually turns into a
coordinated symphony

of millions.

♪ ♪

DEHAENE: We find is that there
is this expl*si*n of complexity

only when the
person is conscious.

This complexity,

the way different brain
areas speak to each other,

is a signature, a
marker of consciousness.

BERLIN: Studies of hundreds
of patients in various states...

From deep sleep to
anesthesia to coma...

Have enabled scientists to
develop a complexity scale.

A score above a
certain threshold

means you are conscious or
have the capacity for consciousness.

EDLOW: Multiple
studies have now shown

that 15% to 20% of patients
who appear unresponsive,

they don't express themselves
on our behavioral exam,

they are actually conscious.

So, you know, will this be able

to help people in those states?

When we speak to families

about what matters to them most,

it is that patient's current
level of consciousness

and their potential for future
recovery of consciousness.

If families were to have

that information, it could
fundamentally affect

the decisions they make about

whether to continue
life-sustaining therapy.

DEHAENE: Progress in the
clinic is extremely real and fast,

and people realize that the
problem of consciousness

is starting to be solved.

♪ ♪

BERLIN: Starting to be solved,

because while we
have several clues

about how conscious
awareness might work in the brain,

this is only the beginning.

How all of those pieces
of brain activation add up

to you, a distinct individual
with a sense of self,

is still a mystery.

I know my brain creates
an internal experience

by knitting together bits
of sensory information,

filling in the gaps
with its best guess

of what's out
there in the world,

but what are those
guesses based on?

Memory.

Each of us has a life rich
with experiences to draw from.

Where we were
born, went to school,

who we fell in love with.

Memories are the
cornerstone of our identities,

but as it turns out,

they have a very
shaky foundation.

I could swear by it,

and would pass every
lie detector test, that...

I had met Mother Teresa.

But I hadn't.

Something that I
wanted to happen

but it never did happen.

SCHILLER: The stories we tell

ourselves, or what we consider
our memory, is a construction.

We create these representations.

And they're very dynamic,
they constantly change.

You're kind of living a revision

of the story of
your life, constantly.

SETH: The more
often we recall things,

the less objectively accurate

our memories become.

BERLIN: It turns out that every
time you a recall a memory...

Your first kiss,

graduating from college,

the death of a loved one...

The very act of recollection
makes it vulnerable to change.

SCHILLER: So when you
experience a new event,

it has to be
stored in the brain.

And then, we used to think that

whenever you think
about that event,

you retrieve the
same original memory.

But what we got to realize
in the last few decades

is that whenever you
retrieve a memory,

it goes back to
an unstable state.

BERLIN: In 2000, memory scientist
Eric Kandel won the Nobel Prize

for showing that each
memory creates new synapses,

connections that
store the memory.

But what happens
when you recall it?

Every time you remember it,

you bring it up into
your working memory

and you perceive it,

and you destroy the
long-term memory.

And you actually have

to recast it into
long-term memory

when you re-remember it.

So every single time
you remember something,

you actually add
more noise to it,

so that it's more and
more and more false

throughout time.

BERLIN: This mechanism,
called reconsolidation,

was first discovered in rodents,

where neuroscientists
witnessed what happens

when a memory gets recollected:

for the memory to return
to long-term storage,

the connections between
neurons actually have to get rebuilt.

Recent experiments
have suggested

this is likely a mechanism
in human brains, as well,

because certain drugs known
to disrupt reconsolidation

have been shown to
alter human memories.

FENTON: We're stuck with the
problem of, how do we know what is true?

How do we know what's real?

And maybe

part of the recognition
is, some of those things

don't matter as much
as we think they do.

SCHILLER: If we think about the
fact that maybe our memories are not

as they originally happened,

it could be a scary thought,
because then, who are we?

I think you need to think
about it as something

more liberating,
because if you're stuck

with original representations,

you're kind of
stuck in the past.

BERLIN: Just like our perceptions,
our sense of self is dynamic,

built to serve
us in the present.

SETH: Our experience of, of self

is a construction at all
sorts of different levels.

What the brain is
doing, is interested in,

is weaving together
a kind of story.

FENTON: The brain is a
storytelling machine, right?

It's a machine that's
designed to make predictions.

KASTHURI: The narratives
that we tell ourselves

are the biggest illusions
that we ever participate in.

Your sense of who
you are is an illusion,

as everything else...
You're no exception.

BERLIN: But if even our
sense of self is an illusion,

where does that leave us?

MARTINEZ-CONDE [chuckles]:
Trust the illusion, that's the only thing

that we can be sure of,

that what we perceive
is not what's there.

BERLIN: So all
these years later,

in my quest to understand
where my thoughts come from

and how my brain works,

I've learned that my brain
is an exquisite machine

that perceives reality
in the service of survival,

not accuracy.

The world I carry
inside of my head

is a construction of my brain

built on bits of
sensory information

woven together with memory

to create a
conscious experience.

Now, to some this
might sound scary,

but to me, it's inspiring.

♪ ♪

SETH: The simple
act of opening our eyes

and seeing a world,

we should not take
that for granted.

And in realizing

what a miracle of
neural computation

is going on under the hood,

to give us even the
simplest experiences,

I think this adds value,

it adds meaning, it
adds depth to our lives.

♪ ♪

DEHAENE: I think it's
liberating to understand

that we rise from this
organization of matter.

It means that we can be
a little bit more humble.

We are gorgeous machines
designed by evolution

as well as by our environment,
education, friends, families.

All of that is
inscribed in our brains.

SAXE: Sometimes when I
wonder what I'm doing with my life,

I think how is it that a spatial

and temporal pattern
of electrical signals

passing between cells in our
brains makes us who we are?

That just being
a part of the team

asking that question is
worth keeping going for.

♪ ♪

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