Human Body: Pushing the Limits Page #5

---

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.

Rate this script:0.0 / 0 votes