Human Body: Pushing the Limits Page #3

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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:

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.

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