(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)