Human Body: Pushing the Limits Page #4

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A click of the fingers,

and Sarah's card

still has a blue back.

What's more surprising

is that all of the other cards

now have red backs.

And that is the amazing

color-changing card trick.

NARRATOR:
But this trick really

doesn't involve cards at all.

lt clearly shows

how the brain picks up

only a tiny bit

of the available

visual information.

l n fact'

as the trick was occurring,

four other color changes

went on.

Welcome to the color-changing

card trick'

using this blue-back deck

of cards.

NARRATOR:
As the trick unfolds,

the camera stays on the cards.

...which is now laying facedown

on the table.

NARRATOR:

Most of us don't notice changes

in clothing and background

made off-camera.

The color-changing card trick

exploits this idea

that we have a very good idea

of what's happening

right in front of our eyes.

l n fact' 90% of that information

we're just not seeing.

lt doesn't feel like that.

lt feels like,

as we look around,

we're perceiving the whole

of the world.

That's not the case.

We really are only just focused

on a tiny, tiny area.

NARRATOR:
l llusions are about

more than entertainment.

They reveal how what we see

depends on assumptions

our brains make.

Our eyes and brain collaborate

to make sense of the world.

But our brains need years

of training

before they can turn

what our eyes see

into a meaningful image

in an instant.

F ollow a blind man as he uses

his eyes for the first time,

and hear him describe

what his brain can see.

Michael May has undergone

radical surgery

to repair eyes ruined

in a boyhood accident.

He hopes that when

the bandages come off'

he'll be able to see

for the first time in 40 years.

MAY:
l didn't expect

anything to happen

for at least a couple of weeks.

So to go into that room and

have the bandages peeled back

and then to actually

see light coming in

was more than words

can really describe.

All of a sudden,

there's the overwhelming whoosh

of visual input'

things resolving into colors

and shapes,

images whooshing everywhere.

NARRATOR:

Rebuilt eyes allow light

to reach Michael's retinas.

First thing you should see

is your wife.

NARRATOR:

But Michael has a problem.

After 40 years in the dark'

his brain doesn't recognize

what his eyes can see.

vision wasn't as simple

as just turning on the sight

and all of a sudden

being able to read a book.

lt's much more complicated

than that.

vision isn't something

where you flip a switch.

Come here, baby.

NARRATOR:
So, what visual sense

will Michael have

of a world he hasn't seen

in 40 years?

Once blind,

Michael May's repaired eyes

now work almost perfectly.

But surprisingly,

he can hardly see.

The reason is the age

at which Michael lost his sight.

A freak chemical explosion

at age 3 blinded him.

[ Monitor beeping ]

an experimental procedure

to restore his sight.

Doctors replaced a key part

of the eye

destroyed in the accident'

his cornea.

This clear' paper-thin coating

protects the eye

and helps it focus.

The damage to Michael's eyes

kept him from making out

anything.

He hoped that new corneas

would mean another chance

to see the world.

...you should see is your wife.

NARRATOR:

But 40 years of blindness

left him with a larger problem.

MAY:
l was trying to

latch on to images

and make sense of the world.

lt wasn't as though l saw a face

and said, "Oh, that's a smile "'

automatically.

l had to intellectualize

this whole process,

dissect it'

and then figure it out.

NARRATOR:
Michael May has

no visual memory of the world.

Are you making a funny face?

NARRATOR:
lt's not something

we're born with.

At birth,

everything we see is new,

but we archive the images,

learning their content

and meaning.

We build our visual memory

through experience.

At the back of the brain,

over half a billion brain cells

make up our visual cortex'

the processor and storehouse

for vision.

Early in our lives,

we build our visual memory.

And as long as we live,

that library helps us

make sense of the world.

SADU N :

The interpretation

and therefore the recognition

of certain things

takes a tremendous amount

of experience.

l n this sense,

the brain is learning to see.

And this is taking place

over the first six years

or' to a smaller extent'

even the first nine years.

NARRATOR:
But when Michael

was blinded at 3,

he'd only just started

to understand the things

that make up his ability

to see.

Size, shape, and distance,

light and shade.

MAY:
ls that a curb, a step

down, a step up, or a shadow?

Just in terms of the brain's

ability to analyze the depth,

to see the edge and to realize

that there's a 6-inch drop

to the curb, l'm just not able

to perceive that information.

lf he had spent

a childhood seeing

and playing with his bicycle

and riding off curbs

of different sizes,

he would have learned subtle,

different cues

that lets him distinguish

between a 3-inch curb

at one distance,

a 6-inch curb a little further'

and a 9-inch curb

further than that.

Deprived of that experience,

it gets to be very hard to do so

on an optical basis alone.

NARRATOR:
Now Michael's

adult brain has to struggle

to catch up on the learning

it missed as a child.

But Michael does recognize

and enjoy some things.

MAY:
l'll use a cane to deal

with what's in front of me.

And then l can look around

and appreciate the things

that l can perceive --

bright-colored flowers,

landmarks, people walking by --

things like that

that l can use my vision for.

And l don't even think

about what's in front of me.

NARRATOR:
Michael May inhabits

a weird world

between blindness and sight'

frustrated by his lack

of visual memory.

F or most of us,

this same visual memory

unlocks another universe,

the world of dreams.

When you're in a dream,

that is your reality.

You visually are seeing things.

You are hearing things.

You can literally feel things.

You can see your body moving,

et cetera.

And you can experience anything

that you would experience

in waking life in a dream.

NARRATOR:
Dreams consist

of images we've collected

with our eyes.

Like a film editor'

the brain reassembles them.

M l LLER:
l'm usually

on my stomach with my arms out'

kind of like Superman,

and l'm gliding

over different sceneries.

l find it a bit of a high to go

in between, dodge the buildings,

and go fast

and go up and down and over.

l feel like a bird soaring

in the air.

l've always wished l could fly.

NARRATOR:
l nterestingly, many

people share the dream of flying

and endure the nightmare

of being pursued.

The brain can create

utterly realistic scenes,

even though

we've never experienced them.

WOMAN :

Someone's following me,

and l have this urge

to just run away.

MAN :
l started running away

from it' seeking higher ground.

WOMAN #2 :

He was faster than me.

WOMAN #3:
But l ran into

the back door of the hospital.

NARRATOR:
Reports of such bad

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