NARRATOR: Too often, we take our bodies for granted,
but under pressure, our bodies can show us
how extraordinary they truly are.
This complex machine grew
out of millions of years of evolution.
So intricate, we're still mystified
by many of the things going on inside us.
A hidden world,
but one we can now explore in 3-D as never before.
Our sight relies on the most complex system in our bodies.
Using three-quarters of our brain power'
when we're challenged,
our eyes focus on the smallest detail at lightning speed.
They allow us to see in the dark'
even to see to the magic of the impossible.
Our brain allows us to see even while we sleep.
And someday, we may be able to see without our eyes.
That's how extraordinary our sight truly is
when we're pushed to the limits.
[ Siren wailing ]
[ l ndistinct talking on radio ]
A murder suspect races through downtown Los Angeles.
[ Tires screeching ]
Pursuing him is LAPD officer Stan Berry.
What he's got to do in this superfast world
is to figure out what matters and what doesn't
at 1 00 miles an hour.
MAN: 1 4, there's two occupants in the car.
[ Horn blares ]
NARRATOR: And to keep up with the suspect without crashing.
BERRY: l need to know about the traffic to the right of me,
traffic coming to the left of me.
But you also need to focus on what's ahead of you.
ls there pedestrians walking down the street?
And then also try to keep up
with the fleeing suspect' as well.
NARRATOR: Nature designed the eyes to let him do just that.
Sight guides the human body.
[ Tires screeching ]
[ Siren wailing ]
2- 1 -900, l am west...
NARRATOR: Many animals have special kinds of vision.
But in humans, we can do it all.
Like no other creature on Earth,
our vision can distinguish around 1 0 million colors...
[ Horn blaring ]
...switch focus from infinity
to mere inches in a fifth of a second...
... pinpoint detail in the brightest sunshine
or darkest shadow...
...take in a wide-angle view of almost 1 80 degrees.
All of this takes the massive power of the human brain.
70% of the neurons in the brain
in some way subserve the visual system.
lt's been given an extraordinarily high degree
of emphasis
by all the mechanisms that have gone into its creation.
[ l ndistinct talking on radio ]
NARRATOR: Human eyes function as survival sensors,
giving us essential information at the crucial time.
Berry constantly relies on them.
The eyes' mechanics are the most complex in the body.
Their intricacy is unmatched.
As a ball, the eye pivots in all directions,
locking onto moving targets.
lt does so with the help of unlikely allies --
two cups of fat -- shock absorbers for the eyeballs.
Light enters through an aperture in the iris,
an elastic mesh of interlocking fibers.
l n bright light' it snaps down to the size of a pinhole
in a fifth of a second.
Light hits the lens --
not a hard disk' but a bag of fluid.
The lens projects an image the size of a large postage stamp
onto the retina at the back of the eye.
Then the retina' a mass of nerves,
sends impulses to the brain.
Surprisingly, the right eye
signals the left side of the brain,
and the left eye transmits to the right side.
Our eyes have evolved a crucial feature
that still keeps us from going extinct.
20 minutes into his chase,
Officer Berry is about to test that feature to its limits.
Speeding into a dangerous intersection,
he faces questions literally involving life or death.
[ Engine revving ]
ls anything moving?
Where is it?
What is it?
[ Siren wailing ]
A vehicle is stopped ahead, blocking the way.
To the right' a car speeds toward the intersection.
On the left' a third driver about to move.
[ Horn blares ]
But suddenly, something else comes into view.
And here's where the human eye's design pays off.
At the back of the eye,
most of the retina consists of millions of rods.
These cells see no color or detail.
But let anything anywhere in our field of view move,
and the rods spot it.
The eyes swivel to look directly at the vehicle.
Now other cells at mid-retina kick in.
A pinhead-sized dot holds six million cells called cones.
They're all about color and detail.
DR. D'AM l CO: That's why, when we look at something,
we look directly at it --
because we have our highest visual acuity
right in the center.
NARRATOR: Locking his eyes on the moving object'
Officer Berry can judge speed, direction, and danger.
The brain responds,
sending signals at an amazing 1 80 miles per hour
to his hands and feet in time to clear the intersection.
[ Horn blares ]
[ Siren wailing ]
This is one of hundreds of life-or-death decisions
that Officer Berry makes
to bring the 40-minute chase to a safe end.
[ l ndistinct talking on radio ]
He does this thanks to the eye's incredible skill at adjusting
when information threatens to overload what we're seeing.
This ability matters as much today
as it did for our ancestors.
Evolution left us with another skill,
one that's still priceless.
l n the dark' we can make out the world
with only the smallest of clues.
The will to live through a fire depends on our skill
at navigating the murderous darkness of smoke-filled rooms.
Firefighters reach a house in Bradenton, Florida.
Agent 56, go ahead and charge the line.
NARRATOR: But they don't know if anyone's trapped inside.
l'm set.
Ready?
NARRATOR: Now firefighter Dan Fleming
enters a dangerous world of shadows and shapes...
...so murky and cloudy,
you'd think it impossible to see anything.
Dan struggles to build a picture of the whole house
from frag ments he makes out in the haze.
[ Heavy breathing ]
How is the house laid out?
Where is the fire?
Are there any survivors?
You're trying to determine what the house looks like,
what the occupants are about' who would be inside this home.
NARRATOR: Despite the darkness,
Dan's eyes im mediately start to adjust.
They have amazing sensitivity.
l n complete darkness, from 1 4 miles away,
we can detect the light from a single candle.
You try to find bits and pieces of light
to help you find your way through.
[ l ndistinct talking on radio ]
NARRATOR: l n low light' we rely on the rod cells
that cover most of the retina.
Highly sensitive, they only register black and white.
But Dan needs to see in color.
He's searching for a fire.
FLEM l NG: lt was very faint at first.
l thought to myself' "That must be the seat of the fire."
very orange glow -- l mean, it was really orange.
NARRATOR: To see color'
you use cone cells at the retina's center.
We get all our color vision
from being able to distinguish only three colors.
SADU N: The cones are sensitive to different colors.
There's those that are particularly sensitive
to blue light' those to green light' and those to red light.
And they need a lot more light to fire.
So if they get enough of the photons of the right color'
they fire and say to you,
"There's a spot of green or red or blue at this point."
NARRATOR: Using these red, blue, and green signals,
the brain creates an impression
spanning the entire visual spectrum...
...a range of over 1 0 million colors.
[ l ndistinct talking on radio ]
Color vision leads Dan straight to the fire.
FLEM l NG: To my surprise, it went out very quickly.
And l started scanning around to see what else was in that room.
Whenever you can get glimpses, that's so important'
but l'm taking the whole room in as l'm scanning.
NARRATOR: l n a flash,
Dan's brain calculates what has to be there,
even though he sees only tiny frag ments.
This is what our brains do constantly --
fill gaps with data from our visual memory bank.
l n fact' our brain interprets most of our vision
out of a lifetime of stored images.
Then Dan recognizes something.
A white shape -- a cup of coffee.
Black and white squares -- a half-completed crossword.
Are these crucial signs
that someone could still be in the house?
There, through the smoke,
Dan sees a blurred and unusual shape.
FLEM l NG: My initial instinct was there's something on the couch.
l'm not sure what it was.
Requesting backup!
We have a saying --
When in doubt' check it out' and that's what l did.
Give me a hand! l got a victim!
Get the gurney in here, guys.
NARRATOR: Dan Fleming has used his brain's visual memory
to transform a blur into the outline of a body,
saving a man's life.
The power of human sight
comes from millions of years of evolution.
We can't even understand it.
And technology today can't begin to match the sophistication
of our incredible eyes.
But for the first time,
science is pushing human vision to new limits
by connecting directly with the brain's vision center.
This means that one day, we might even see
in the invisible worlds of infrared, have X-ray vision,
or plug video games straight into the brain.
Cheri Robertson from Missouri
is about to step into this virtual world.
l was in a car accident when l was 1 9 years old.
l was a passenger in the car.
And the driver fell asleep at the wheel, and we hit head-on
with a small truck'
and both of my eyes were just destroyed.
NARRATOR: Hoping to regain her sight'
Cheri volunteers for a pioneering procedure.
lt involves marrying technology
to the huge processing power of the brain's visual cortex.
lt was a chance for me to be able to see again
when the doctors had always told me l would never see anything.
NARRATOR: Cheri is about to have an extraordinary experience.
Doctors drill through both sides of her skull,
exposing her brain.
Then they implant two triangular plates,
each holding 200 tiny electrodes,
directly onto Cheri's visual cortex.
Finally, the surgeons string cables
from the plates to terminals sticking out of her skull.
Next' the electrodes run through a computer
to a camera on Cheri's eyeglasses.
All of this technology is designed
to help Cheri regain some sight.
ROBERTSON: lt was, l guess, quite a shock for me
when l felt my head
and l felt these terminals sticking out behind my head.
'Cause l guess l really wasn't expecting that.
NARRATOR: But for her to see what the camera sees,
many things have to happen.
And that requires a step into the unknown.
Each electrode touches a different part of Cheri's brain.
When the system triggers an electrode,
she sees a flash somewhere in her visual field.
Where, the doctors don't know.
Now.
NARRATOR: So they trigger each electrode one by one
to learn where in her visual field Cheri sees flashes.
MAN: Now.
ROBERTSON: Oh, wow. That was right there.
Okay.
NARRATOR: When she sees a flash,
Cheri points to top, bottom, left' or right.
[ Beeping ]
With every electrode mapped, the doctors connect the camera'
making certain that what it sees
matches the flashes in Cheri's brain.
ROBERTSON: Yeah. Right in the same spot.
So it works for us.
NARRATOR: Finally, with the camera mounted,
Cheri's mother helps connect the gear to try the new settings.
WOMAN: Ready?
l think my computer gained weight.
[ Laughs ]
NARRATOR: Has technology helped bring Cheri's sight back?
Oh!
Wow!
Oh, wow.
[ Laughs ] Oh, wow.
When l finally saw my first light' it took my breath away.
l could not believe it.
We knew it worked,
and that was very, very thrilling for me.
Oh, something's lighting me up.
NARRATOR: We can't know what Cheri sees.
But we do know what she describes.
Whoa. l'm seeing two big dots of light.
And they are white with a little bit of red in them.
Wow. Those were two really big flashes, and they moved.
Wow. l saw a big flash of light there.
NARRATOR: This early in the project'
doctors have activated only some of Cheri's electrodes.
Eventually, they hope to connect many more,
vastly improving the scope of her vision.
Oh, wow.
Because l can only use 1 0 of my electrodes,
whenever an object goes in front of my camera'
l will see two flashes of light.
And they're about the size of a big peanut M&M --
just one on top of the other.
Saw a couple more. l'm not sure if it's the waves.
And that way, l know that there is an object there.
Now, l'm not sure what it is.
They're sailboats?
ls that it still here?
That is cool.
When l am able to use all of my electrodes, however'
l will be able to see
the outlines of things l'm looking at.
So l'll know if l'm looking at a tree or a person or a car.
So l'll actually know what l'm looking at.
NARRATOR: No one pretends that Cheri's vision is back.
But the fact she can sense any of the visual world
makes her an extraordinary pioneer.
l magine if one day we could feed complete vision signals
directly to the brain.
What could we see?
We might see a world that we've been blind to,
as if we were seeing through night-vision lenses,
infrared cameras, even X-ray vision.
l magine a sum mer weekend
on a California beach dense with bodies.
But for one onlooker' this seemingly calm scene
may be a series of accidents waiting to happen.
How does a lifeguard know
when a raised arm means, " l need help "'
not' "Hey, this is fun"?
The guard's skill at spotting that one desperate person
among thousands is phenomenal,
truly testing his sight and understanding.
We see the way we do so we can spot danger to ourselves.
l call!
NARRATOR: But nothing is threatening the lifeguard.
l n fact' the eye,
observing a harmless pattern across its view,
normally relaxes.
Motion-sensing rod cells switch off
when they detect action that's consistent and constant.
So the lifeguard has to trick his eyes.
He does this by scanning,
forcing his eyes to lock onto small details.
TU RN ER: Our frontline defense are the tower guards.
Their job is to scan the water'
so their eyes are moving across the water
and letting their brain filter out that information they see,
looking for something wrong,
looking for that odd one out that truly is in danger.
NARRATOR: Taking in all this information is hard work.
Human sight has only two degrees of detail vision at the center.
To check the whole beach, the lifeguard sweeps...
...jumping from point to point for detail.
Each jump is called a saccade.
A saccade is the movement that the eyes make together
when they're looking directly at one thing
and all of a sudden, they look at something else.
We have mechanisms that wire the muscles that move our eyes
to the image.
And we can quickly lock onto a new image all at once.
NARRATOR: The saccade function lets him jump visually
from each potential risk to the next.
He repeatedly scans his field of vision,
updating his visual memory every few seconds.
But even more is going on as he uses another complex skill --
interpretation of detail.
KAF ORD: Being a seasoned lifeguard,
l can recognize distressed victims in the water'
whether they look really labored,
whether they're comfortable or not' by their body language.
Those are sort of indicators
that allow you to recognize a rescue before it happens.
NARRATOR: The muscles rotating our eyes
give us an astounding breadth of view.
Even while perfectly still,
we can rotate our eyes from far left to far right
in a quarter of a second.
So when a riptide suddenly overcomes a swim mer'
Drew knows within moments.
Now he has to judge whether the swim mer can get back to shore,
whether he's too far out for a rescue attempt'
or whether' despite the riptide,
Drew has a chance of reaching him.
That split-second call demands an accurate sense of distance.
We have two eyes, and they're separated by this distance,
and that permits each image
to be slightly different than the other image.
And that slight dissimilarity
gives me a sense of how far away something is.
NARRATOR: We constantly judge shifting distances,
hardly giving the process a thought.
But this special process only occurs
in humans and other predators for spotting and catching prey.
That's the hunting skill the lifeguard uses
to home in on the struggling swim mer.
We can all find the detail we need in a busy scene
when it's for our own safety.
But when guarding the lives of others,
that same skill requires training and intense focus.
l n day-to-day life, we fill in parts of the passing picture
as our visual memory makes shortcuts and assumptions,
putting together a picture of the world that seems complete.
What happens when those assumptions prove wrong?
That's where we get the phrase "smoke and mirrors "'
the tools of visual confusion illusionists use
to exploit the science of sight to fool our vision.
Movies present spectacular sights and grand illusions.
This is a movie set' but how big?
[ Alarm blaring ]
What looks like a space station on an alien planet...
MAN: Cut!
NARRATOR: ... is a trick.
WOMAN: 68 "B "' take 1.
NARRATOR: A tiny model near the camera
and a full-size stage further away.
Film makers are essentially the masters of illusion.
Here we see the two actors.
We assume they're in a massive set'
because we don't have the ability
to think' "Hold on a second.
This is just a small set' and the actors
are a considerable distance away from it."
MAN: Cut!
visual illusions trip up the perceptual system,
the system that is normally right.
Here we're exploiting the loopholes,
when suddenly, we're very, very wrong.
NARRATOR: l llusions exploit how we see the world.
They rely on the difference between what the eye sees
and what the brain understands.
Magicians have always relied on this delicate confusion.
Hi, there.
[ Echoing ] l'm Marco Tempest.
l'm a magician.
Now, here's a little optical illusion.
Now, let me show you just how easy it is to fool the eye.
l have a three-dimensional object right here.
And l also have a two-dimensional object'
this paper disk.
Now, if l place this three-dimensional object
next to the two-dimensional object'
something very strange is happening.
Check this out.
lt looks like
the two-dimensional object has become three-dimensional.
But if we get rid of the three-dimensional object'
something else is happening.
Check this out.
Do you see?
The cube now looks like it's completely two-dimensional.
All right. Here we go.
NARRATOR: From another angle, the secrets reveal themselves.
l also have a two-dimensional object'
this paper disk right here.
Now, if l place the...
NARRATOR: Underlying the trick
is a genuine scientific principle,
explaining how our brains
build a three-dimensional visual world.
Check this out.
This is all about how we read perspective.
The three-dimensional cube,
once established as being three-dimensional,
stays three-dimensional in our minds.
Even when we look at the taped lines,
it still looks three-dimensional to us.
lt's almost like our eye fills in the missing information
and wants the object to be three-dimensional.
And that's where l get you.
All right.
NARRATOR: Our world is filled with visual information.
The brain copes by creating shortcuts,
relying on experience to fill gaps with informed guesswork.
Light and shadow.
The size, shape, and distance of objects.
We assume the world operates according to fixed rules.
But sometimes we're just plain wrong.
Take this ordinary-looking room.
l look to be much, much larger than Sarah.
And this isn't camera trickery.
l nstead, it's an incredible illusion.
Because when l'm in this corner'
Sarah suddenly looks much, much larger than me.
Now, in reality, the two of us are roughly the same size.
lt's all to do with the amazing way
in which this room has been constructed.
NARRATOR: Not regular in shape at all,
the room has a bizarre geometry that's disguised as normal.
We see square rooms so often...
...we fool ourselves into thinking this is one, too.
lt's amazing how easily our eyes get fooled.
We see an umbrella' and we im mediately think of rain.
But on a beautiful day like today...
[ Echoing ]...we don't really need an umbrella.
NARRATOR: Magicians exploit more than our assumptions
about the objects and spaces around us.
You're about to see what looks like a simple trick.
But it has a deeper' more elusive level.
Welcome to the color-changing card trick'
using this blue-back deck of cards.
Now, the idea is very simple.
l'm just going to spread the cards in front of Sarah
and ask her to push any card towards the front of the table.
SARAH: Okay.
l'm going to go for this card here.
Wl SEMAN: Excellent.
Sarah could've chosen any of the cards in the deck'
but she selected the one
which is now laying facedown on the table.
l'm going to ask her to look at the card
and tell us what it is.
The card l chose was, in fact' the 3 of clubs.
Wl SEMAN: The 3 of clubs. Excellent.
That comes back into the deck.
l'm now going to spread the cards faceup on the table.
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 ]
40 years later' he underwent 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 dreams recur throughout history,
and the meaning of these night visions
has always fascinated us.
3,000 years ago, the Egyptians compiled a book of dreams.
lt listed familiar dream images
and offered interpretations of them.
DR. PARKl NSON : Dreams were a sort of moment
when the boundaries between this world and the next world
seemed very thin.
But for many of the dreams in the dream book'
it's clearly a search for what will happen in the future.
NARRATOR: Now we explain bad dreams as useful
in helping us conquer deep, often universal fears,
just as we see good dreams as fulfilling our fantasies.
Sights seen in dreams may well connect us
to our ancestors' instincts and fears --
yet another example of how our sense of vision
has always dominated our lives.
Our visual system shows better than any other
how intricately our bodies work.
Throughout history, it has supercharged human development'
and it could allow us to take charge of our future.
Sight dates back to our deep past --
unsung, unnoticed, a faculty we take for granted.
But when revealed, sight shows how everyday life depends on it.
Pushed to the limits, we can see the superhero inside us all,
the human body.