Original subtitles

(soft rock music)

A lotta people ask me "What does my dog see?"

We could guess what a dog sees, but we can't

really tell you what its brain is processing.

Their sensory worlds are not like our sensory world.

They're living in a world that we would probably

love to occupy for a little while, but it's not like ours.

Vision doesn't play the role in their lives

that it plays in ours, they don't have the kind

of sharp detail vision that we have,

so they don't see the fine structure of things

that we're able to see, and their color vision

is somewhat simplified compared to ours.

So they don't see anything in the reds,

so their vision is concentrated in blue and green.

And frankly, they don't care much about color.

It's just not important to them.

They care about brightness and motion and shape.

They have better vision at night

than we have, probably, if you take a photograph

of your dog, you'll often get some eye shine back.

So there's a layer behind the retina

and its function is basically to return light

back through the photoreceptors.

So, it provides a second chance for any light

that wasn't absorbed on the first passage

to be absorbed on the second passage

as it bounces back out through the eye.

For example, you can find animals,

often by using a headlight, and you'll see the eyes

of animals looking at you, and it's because it's

reflective lighting on the back of the eye.

(soft music)

You see a lot more eye shine in something like a cat

than you do in a dog.

I mean, a cat probably can see in light

about half as bright as we can,

which might not seem like a big change,

but, in fact, that takes them into a whole range of vision

where we're not seeing anything

and they're seeing things reasonably well.

You'll see often, these sort of night camera views

of a cat looking for prey, and I think

it's not completely unreasonable,

as to what they might, at least be able to pick out

that we would miss entirely, even looking

at exactly the same thing, with the same lighting,

it's not gonna be the same for a cat's eyesight.

In general, predators have anteriorly placed eyes.

So if you look at any of the cats,

any of the dogs, you're gonna see eyes

in the front of their faces.

They're predators, they're looking forward,

they're looking for prey.

Prey animals have laterally placed eyes,

and the benefit of a laterally placed eye

is it gives the animal full, 360 degree coverage

of the horizon at all times.

If a predator occurs anywhere, they don't want to miss it.

So the best way to do that is to have good vision

in the regions where you expect a predator to be.

If you're a prey animal, you're normally

in an environment where the horizon's fairly flat.

You're in some kind of open country,

and you're looking at the horizon.

Predators are gonna appear somewhere on the horizon.

If they're near to you, if you're unlucky,

maybe far away, but wherever they're gonna be,

they're gonna be at your level.

So, how do you solve the problem

of looking in all directions?

Well, on most animals, that have eyes built like ours,

have a part of the retina that's adapted

for the highest quality of vision.

We have a thing called a fovea at the back of the eye.

Fovea means a hole or a dimple, that's our fovea.

And in there are the cone cells

that are adapted for best vision.

Prey animals have what's called a strip fovea.

The fovea actually extends along the back of the retina

in a line reaching almost from one side to the other,

and so, as it looks at the horizon,

it's seeing good detail at all points

along the horizon level, so anything

that occurs in there that's moving,

or that doesn't look right, it can pick out very quickly,

and therefore take evasive action.

If we're talking about eyes that have really

excellent acuity, then we have to turn to the birds,

because the birds have eyes

that are the most adapted for high quality vision.

Birds have incredibly variant ecologies,

they dive, they are fruit eaters,

they are predators. (bird shrieks)

The ones that always capture human imagination

are the raptors, and the reason is

because they do, in fact, have the best vision

of any animal, with the highest acuity

of any animal that we know of.

Raptors also have a fovea, but it is deeply indented

into the eye, much more deeply

than ours is, and so that has much greater surface area

than just a cup shaped fovea has.

So as light enters this deep pit,

it actually diverges and magnifies the image

to a small extent, so it's like having binoculars.

A very small patch, but with extremely high acuity.

So to have, like, a peregrine falcon,

the eyes are almost the same size as ours

in an animal that's immensely smaller than us,

and its acuity is about five to seven times ours,

and so when a peregrine is flying,

a thousand meters high in the sky,

it's still capable of picking up movement on the ground

at great distances, and to locate prey

and to decide which are useful to attack

and which ones are not worth attacking.

(string music)

Let's talk about owls for just a minute.

Owls have eyes that are sort of tubular shaped,

in other words, the eye is not

a perfect sphere like our eyes are.

And by making it tubular, the animal is essentially

disposing of part of the volume of the eye in the head,

and can make more of that volume available

for frontal vision as a result, so the two eyes

can be packed relatively close to each other,

but they can still have really large magnifications,

which means that the image is large on the retina,

which means that the owl has good detail vision.

(birds chirp)

Now, interestingly enough, eyes like that of an owl

turn up in one other place in the world,

and that is in the deep sea.

Deep sea fishes often have tubular eyes.

A good example is the hatchetfish.

Hatchetfish have gorgeous tubular eyes.

This is adapted for restricting the visual field

to just looking overhead of the fish.

If you're in the deep sea, the best place

to look for something is directly overhead,

because that's where the light field is.

The light is compressed by the refraction

at the waters' surface into a circle of light

straight up over the fish.

And that circle of light can have prey in it,

or it could have predators in it,

and so these animals often will build eyes

that can just see that little bit of the world,

looking straight up and look for prey in that part.

And hatchetfishes hunt by looking up

and then striking from below.

The big advantage of vision, and the reason

why it comes up again and again in animals,

is it gives you fairly quick information, and it gives you

extraordinarily good directional information,

much better than any other sense does.

So, that's why it's evolved over and over again in animals.

Making an eye is ridiculously easy, evolutionarily,

it turns out, it's not at all complicated.

The simplest thing you could have is just a photoreceptor.

It detects light, tells the creature

whether the light's present or absent,

which is useful, 'cause even that can tell an animal

something weird is going on,

the light suddenly dipped really quickly.

I don't think they're thinking this, but the evolution

is saying, this is a good time to get outta here.

So the next step is to take that cell and multiply it

times 10 or a hundred, or a thousand,

and then lay out an array of these cells

that can see a little bit of information

about shape and direction of things.

It doesn't necessarily see anything,

but it can respond to things.

If you look at a flatworm, like a thing called planaria,

and each of those little eyes is a black pigment,

which is what you see, and within that pigment

there's a group of photoreceptor cells,

and those creatures are then sampling

a little region of space with each eye,

and it can tell them which way to swim

or which way to go if the light changes suddenly

or if they're, they wanna go towards the light,

they can orient their body so they head towards that light.

From there, the obvious thing is to add more receptors,

a step that every animal has gone through

at some point in its ancestry is to add additional receptors

until you get a large number, maybe a hundred,

in this eye cup that you've got.

There's no optics there, to speak of,

except for the shape of the eye.

So, what do you do?

Well, one solution is to restrict where light

comes to that receptor array, and so an animal

can build what's called a pinhole eye,

basically close down the opening to that cup

so it's smaller and smaller, which means

that the image formed becomes sharper and sharper.

There's only one really good example

that can be illustrated today,

that's the nautilus, which is a deep sea creature.

You would never expect that would be the one place

to find a pinhole eye, because deep sea creatures

don't get much light, and pinhole eyes

are inherently very insensitive

because they have a very small opening,

so not much light gets into an eye of that type,

and they don't focus it beyond restricting an aperture.

So the image is extremely dim,

and why a nautilus, which is a pretty big animal,

with at least moderately complicated behavior,

has been happy to sit around with an eye like this

is kind of a mystery, but nautiluses

do what they have to do, they don't seem to mind.

So, nautilus is a real outlier there.

I think the main thing is the more that I work with animals,

and the more that I work with marine creatures

is that these creatures have their own lives

and that their lives are so utterly different from ours

that their experience of the world is truly alien.

(eerie music) So there are jellyfish,

it's kind of terrifying to think this,

there's lethal jellyfish out there,

jellyfish that can kill a person

who have eyes that have beautiful, perfect lenses in them.

They look like a small version of our eye,

a tiny version of our eye, and they work the same way.

Now, jellyfish don't have brains,

they have a ring of nerves that run around the body

that analyze something, and these creatures

can make directed responses, they can move towards shadows

or move towards light, depending on what's motivating them.

Why they have these insanely complicated eyes

is not obvious.

Their experience of the world is truly alien.

I don't think that we could find anything more alien

in another galaxy than we find right here on our planet,

in terms of the way in which it interacts

with its world and what it needs to know from its world

and what is important to it.

Scallops go off in a totally new direction.

Scallops have about 60 eyes, arranged around the edge

of their mantle, the part that we don't eat.

These eyes look around all the margins of the shell

in all different directions.

Each eye sees a patch of the world,

and sees enough detail to tell the scallop

what's going on in its part of the world.

The scallops don't even have much of a brain,

in fact, it'd be hard to define the brain of a scallop.

They have a bunch of ganglia, which are cell groups.

We suspect that these ridiculously complicated eyes

are probably mostly there just to tell the scallop

when it's time to either close its shell

or possibly initiate an escape response.

Scallops are really interesting because they're a mollusk.

Mollusks have the greatest diversity

of eyes of any group of animals.

They go from extraordinarily simple eyes

that can just barely see whether a light's on or off,

to eyes like the eyes of a giant squid,

which is the biggest eye that

we know of that's ever evolved.

Other mollusks are things like octopuses and squids,

and octopuses are interacting with their world all the time,

they're looking for things to eat,

they're particularly alert for predators,

being soft bodied creatures, they're very vulnerable

to predation by anything with teeth or claws,

so it's necessary for them to be aware

of what's happening around them.

Octopus have good vision, they have large eyes,

they have good optics, beautiful optics,

so they can see quite clearly.

So they probably have a sense of vision

that is not so totally different from ours,

but, of course, what an octopus sees

depends on what an octopus needs to see,

and I'm not really able to tell you that.

We give volition to all kinds of things.

But what they're doing is what they do. (laughs)

It's not necessarily what we interpret them doing.

Take the shark, for example, sharks are impressive animals,

they're beautiful animals, but it's difficult

to imagine a shark that's anything other than a machine.

I don't think anybody would say that a shark

is thinking about things, it's doing things.

If you could talk to a shark, it would just say,

"Fish, danger, friend, enemy, mate."

That's kind of the whole world of a shark's existence.

It doesn't sit there and say, "Why did God make me a shark?"

or "Why do Chinese people want to eat my fins?"

It doesn't, that's not its world.

We know a lot about their vision.

Sharks are vertebrates, they're related to us.

Their eyes are related to our eyes,

they're extremely good eyes, they're acute,

they have a lot of receptors, they have cone cells

and rod cells, so they can see color,

as well as shades of brightness and darkness.

So the quality of the eye in a shark

is comparable to our eyes, and possibly

even better than our color vision.

(bubbles gurgle)

Fish have beautiful color vision,

they have better color vision than humans have.

In fact, most fishes have a higher dimensionality

of color than we have.

In addition to the receptors that are much like ours,

blue, green and red, they have ultraviolet

sensitive photoreceptors yet, so they can see in the UV.

Many coral reef fishes have a receptor set

very much like this, so they're seeing colors

that we don't even know about.

So color vision in humans is important and good,

but it's nothing extraordinarily special.

(birds chirp) Now, insects,

they actually have more color classes of receptors

than we have, they actually see basically four primaries,

two kinds of UV, blue and green,

and they put those together somehow,

and can interpret that as a color signal.

They all have compound eyes.

Compound eye consists of many many essentially identical

units that sample the world point by point,

and the whole image is sometimes called a mosaic image.

Each unit sees one point in space.

It doesn't see an image of that point,

it just sees how much light there is

and how much color there is at that point.

Their acuity is extremely poor,

only maybe 1/100 of our acuity.

So they're seeing, when we see a face,

they're just seeing a blob with maybe a couple of dark areas

where the eyes would be, that's about

all they're gonna pick out.

Their motion vision is fantastically good,

because they have to fly through spaces and not crash

into things, so they have almost unbelievable motion vision.

They have a much simpler nervous system,

so things are processed really quickly,

and everything's more compact,

which makes everything faster.

So their vision is very fast, and it's very reflexive,

so they're able to see a motion extremely early

and make a decision about what it means

(tape squeals)

and where it's coming from, and then evade.

Now, insects have an infinite arrangement,

just almost uncountable arrangement of ecological roles.

They can be down in the grass,

they can be flying, they can be living in trees,

they can be out hunting, they have many many different ways

of making a living, and there's so many possible choices

that each demands an eye that's specialized

to be best at that job, in fact,

the world's most efficient aerial hunter

is not a hawk, it's a dragonfly.

Dragonflies can successfully capture prey

on up to 90% of their predatory attacks.

It's pretty fabulous.

What they're doing, is they're visually inspecting space

above them for small dots that are flying.

(insects buzz) And they spot a dot

of appropriate speed and appropriate size,

their little dragonfly brains say,

that's prey, that's an insect, I can catch that,

and they'll make a quick, flying ascent

and snatch that prey out of the air.

And the way that they can see this

is that the whole top part of the eye

is adapted for seeing overhead with extreme detail.

They can see very very well looking up,

and see rather poorly looking in front,

and they see very poorly looking down,

but looking up they have excellent vision,

especially up at slightly in front of them,

so they try to place their prey item

in that part of the visual field and chase it down

with a very quick flying attack.

(insect crunching)

So that's an insect eye that's really adapted

for that job, of pursuit and prey capture.

But there's other ones like that's for other jobs,

so if we think about something like a honeybee,

honeybee eyes are adapted primarily for finding flowers

and for finding their way around.

They'll always know where they are,

because as they fly, they look at the sky

and they monitor either the position of the sun

or the position of a field of light

called the polarized light field

that we don't see, but that honeybees see very well.

And use that information to orient what direction

they're traveling. (bees buzz)

And so, doing that, they can tell what direction

they're flying, and by monitoring

their speed through the air, they can tell how far

they've flown so they know pretty much where they are

all the time. (bees buzz)

Bess have ultraviolet vision, and they use it

for identifying flowers and for looking for patterns

of flowers that guide them to where the nectar is.

And if they encounter a patch of flowers,

they can return to the hive,

'cause they've been keeping track of where they are,

using the sun and the sky the whole time.

They can use that same information to get back home again.

And once they get home, they use that very same information

to then do this waggle dance that bees are so famous for.

And tell other bees in the hive

that food can be found at a given distance,

in a given direction, so they'll tell other bees

if you fly three degrees left of the sun

and you fly for 200 meters, there'll be flowers there.

Go there and get some food.

(bees buzz) (birds chirp)

The animal that I started my research on,

when I was working on visual physiology of marine animals

was, strangely enough, an animal that has

probably the most remarkable known visual system of all,

and that's vision in mantis shrimps.

Friend of mine calls them shrimps from Mars,

and that's pretty much what they are.

They have amazing eyes, unique to mantis shrimps.

Each eye is actually three eyes in one,

it has a top half and a bottom half,

those are two of the parts, and they're pretty much

like the compound eyes on bumblebee or a dragonfly.

But in the middle of this regular split eye,

there is a thing called a midband.

And it's the midband that contains all of the receptors

that are sensitive to the special properties of light.

So, ultraviolet color receptors,

and even some special polarized light receptors

are all found just in the midband.

The midband only sees a little strip of space.

It's like you looking through a very very narrow slot.

You can only see a little tiny bit of the world

through that little narrow slot,

so to see more of the world,

you have to move that slot around,

so mantis shrimps see the world

by moving their eyes around a lot.

That's how they manage to sample the world

with this very narrow midband.

Now the rest of the eye sees the whole world,

but it doesn't see it in color at all.

The midband adds a lot of information.

So, basically the eye is being moved around

on the world, to color in the world by these movements.

What's special about their eyes besides all this stuff,

and that is that they have more kinds of photoreceptors

than any other animal that we know of today.

They have eight classes of primary photoreceptors.

Remember, we have three, we have red, green, blue.

They have eight classes in the visible,

so they have violet blue, blue green,

green, green yellow, yellow and orange.

They also have four more ultraviolet color classes,

so they have a total of 12 color classes.

So give them a great color vision,

and it looks like, behaviorally, it's not necessarily

as good as ours is, it's really hard to say for sure,

but probably all this apparatus is there

not to give them fabulous color vision

but to give them a simple way of categorizing colors.

So, that basically, they're making a decision

about what color they're looking at,

not by analyzing it with complicated machinery

in the brain like we do, we don't know anything about color

till the signal gets to the back of our head

where it goes through a series of analytical stations,

one of which extracts color from the stimulus.

Mantis shrimps can do this right at the eye,

and avoid the brain entirely, so what the brain gets

is red, orange, yellow, green,

whatever in that object they're looking at at that moment.

So it's a way of making color sense operate very quickly

and very simply without a lot of neural machinery.

And we think that may be what's happening.

They are spectacularly pugnacious, violent animals.

They catch prey by having a pair of front arms

that are especially modified for very high speed attacks.

They can hit an object with the force

of a 22 caliber bullet, they have one of the fastest

movements ever recorded in animals, the force is huge.

They can break an aquarium wall in a large species.

They have to have good eyes to have an effective strike,

otherwise it's useless to them.

They have to know where their prey item is,

how far away it is, and, importantly as anything,

what is it?

Is it something, like a rock, which is gonna break my arm,

or is it actually something to eat, which is not.

And, is it another mantis shrimp?

'Cause that's really important.

Another mantis shrimp can fight back and can kill you

if you attack it, so it needs to know these things quickly.

The other thing that pushes it is,

in fact, they are dealing with other mantis shrimps.

They have to mate, they need to defend their burrows,

they need to get along in the world,

and to do that, they have to know who they're dealing with.

And so, mantis shrimps have evolved a really elaborate

set of colored signals in many species.

Those colored signals say to another mantis shrimp,

I am your species or not, I am angry or not,

I'm a female or a male, depending on who's doing it,

I'm feeling pretty cheerful right now or not.

All those things are signaled by colored signals

that mantis shrimps use.

But mantis shrimps have another pattern that we don't see,

and that's their polarized light patterns.

So they can reflect polarized light in ways

that make it possible to have one part

of their bodies stand off as being different

from other parts, and they use that to talk to each other.

And, in particular, some species use a little blue object,

which is along one of their front appendages

as a little part of it, it reflects blue polarized light.

They use that, we believe, in communicating

their sexual intentions to each other,

so this little blue polarizer looks blue to us,

but to another mantis shrimp, it looks like it's polarized,

and that polarization seems to be important.

If you destroy the polarization

of that little object on the front leg, male mantis shrimps

find it much more difficult to find a mate.

They're very interesting animals.

They make great pets as long as you wanna keep one animal

in an aquarium, because anything else that's in there,

it will kill it.

(dog pants) You know,

we've all been through our own evolutionary paths.

We've all gotten our senses through millions of years

of ancestors and the ancestors of dogs

separated from the ancestors of humans,

or of a cat or a mouse or a horse,

or whatever your pet is, a parrot, even a better example.

Their ancestors have separated from our ancestors

by millions to tens of millions

to hundreds of millions of years.

I think that human vision is pretty darn good.

The thing about humans is, we're not adapted.

We're really generalist animals.

We don't climb in trees very well,

like our ancestors, we can't outrun a cheetah,

some animal out there can excel us at anything,

including vision, but we don't have to feel bad about that.

I think we can, in general, say that human vision

is, for what we need, it's probably more than enough.

And it's one reason, probably, we depend on it so much

is that it's so well adapted to do

almost any kind of job we need.

If I was an animal, I would like

to be a lot of different animals for an hour each.

I don't think I wanna be only one,

I'd love to be a hawk and see what it's like

to see prey from a mile high in the sky.

I'd love to be an octopus and see what it's like

to catch prey when I'm down in the water.

(bubbles gurgle)

I'd love to be a mantis shrimp

and see what it's like to live in their colorful world,

and a world that's full of polarized light

and ultraviolet light, and just have a sense

of what it is they see out there,

but I must say, that if I put myself

in the mind of a hawk or in the mind of a mantis shrimp,

or in the mind of an octopus, I would have no idea

what was going on, because they don't have minds

like mine, and what they're sensing

is something that I really can't comprehend.

So, I'm afraid that it's something,

as much as I would like to be able to do it,

even in the world of virtual reality,

it'll never really happen.

(soft music)