How do other animals see the world?
Is their vision the same as ours?
All animals see by gathering light rays,
and although to a gorilla
we appear very different,
our eyes capture light in exactly the same way.
(Child) Mummy, Mummy! See?
But for both of us, the image received
on the light-sensitive retina
is not what the brain ultimately sees.
It is upside down and only the centre
shows any real detail.
0n the retina, this area contains
a high concentration of light-sensitive cells.
Full colour and definition
is confined to this inner circle.
(Child) Mummy, see?
The brain not only inverts the image,
but also fills in all the missing information.
Also, like ours, a gorilla?s brain
is involved in judging distance.
The right eye has a slightly different view
from the left.
From these two separate images,
the brain constructs a three-dimensional picture.
Judging distance becomes precise.
The brain is involved in the vision of all animals,
but away from our closer relatives,
we can only guess at how less familiar eyes
finally interpret the view they see.
The starling?s eyes are far more mobile
than our own.
They can be brought together
to increase the overlap
and so improve the central image.
0r be moved apart to widen the view.
The eyes also converge when searching for food.
And move apart to spot predators.
(Squawks )
Like most prey animals, the starling?s eyes
are placed to the side of its head
to give a panoramic view.
Eye movements add to the coverage.
No animal has a wider view than the woodcock.
Without moving its eyes,
it can even see behind itself.
The eyes placed centrally
on either side of its head
give total wraparound vision.
(Jeep approaches )
With this 360-degree view of the world,
the camouflaged woodcock shows no hint
of movement as it watches for danger.
The eyes of a predator face forward,
and concentrate on the scene ahead.
(Fox panting)
A fox?s view may be narrower,
but it has little to fear from danger behind.
Like many mammals,
the fox has limited colour vision,
but like us, it sees true detail
in only the centre circle.
The brain fills in the rest.
The lion too has the forward-facing eyes
of a predator.
But its vision differs from the fox?s in a way
common to animals of the savanna.
0n this flattened landscape,
prey animals always appear to be
on the horizon.
To take advantage of this,
the lion?s detailed view is elongated into a strip.
This lateral strip gives
greatly increased definition,
and again the brain constructs
the missing details in the surrounding areas.
Like the eyes of all animals, those of
the wildebeest respond best to movement,
so the lion moves as stealthily as it can,
making the most of any cover.
The wildebeest?s clearest view
also lies in this lateral strip.
(Roaring)
(Bellows )
The kill will also provide food
for sharp-eyed scavengers.
The vulture has perhaps the keenest eyesight
of any animal.
As the sun heats the ground,
the birds rise up on currents of warm air.
These thermals will provide uplift
to heights of 2,000 metres or more.
When they reach this height, the vultures will
be able to survey many kilometres of savanna.
With thousands of these flying eyes
scouring the ground,
no carcass will be left for long.
Their renowned eyesight
relies on remarkable adaptation.
The central portion of their view
is magnified two and a half times.
0n the retina, this enlarged area has
a high concentration of light-sensitive cells.
These resolve the finest detail.
The vultures not only scan for carrion,
but are also guided by the behaviour
of other animals.
A gathering of other scavengers
is a certain sign of food.
(Shrieking)
They may search communally,
but at the carcass it?s every vulture for itself.
(Shrieking)
(Shrieking continues )
(Flies buzz )
(Chirping)
(Roaring)
This eerie science-fiction spectacle
is caused by an intriguing science fact.
Eyes adapted to darkness often have a mirrored
layer at the back of the retina to reflect light.
This gives the eyes a second chance
to absorb even the faintest glimmer.
Most nocturnal mammals
show this mirrored vision.
The net-casting spider needs neither mirrors
nor artificial light to see at night.
Its enormous lenses let through
every available ray,
and its retinas have huge light-gathering cells.
In addition, its eyes have a totally
overlapping view, doubling sensitivity.
The spider can see in one tenth of the light
we need,
so on the darkest night it can still hunt.
It first constructs a unique kind of web,
one that is held by its legs.
Poised like a miniature gladiator, the spider
relies on good vision to entrap its victim.
Its eyes are not only sensitive to light,
but react to the slightest movement.
Although far simpler, the spider?s eyes
are similar in design to our own.
But there are many animals with vision
that is remarkably different.
The rising sun?s light filtered by the atmosphere
appears to us as red.
Insects like these are blind to this colour,
but they see parts of the spectrum
invisible to us.
0ur colour vision is sensitive to green,
blue and red,
but the bee is sensitive to green,
blue and ultraviolet.
With only three basic colours,
we both create a full colour picture,
but the bee?s world looks very different.
(Buzzing)
The spectrum has shifted towards the ultraviolet,
and its compound eye
provides a far coarser view.
Seen through a bee?s eye,
flowers become strangely unfamiliar.
This ultraviolet bloom is actually a buttercup.
These are perhaps the true colours of flowers.
The colours we see have no real relevance.
For these hidden hues have evolved
to attract insects.
It?s not only bees
that have this ultraviolet vision.
To our eyes, male and female clouded yellows
look the same.
But to a bee or another butterfly,
the ultraviolet courtship flashing of the male
is strikingly visible.
Insects are also sensitive
to another kind of light invisible to us -
patterns created as the atmosphere
polarises the sun?s rays.
(Buzzes )
These patterns create a sky map
which the bee can use to navigate.
Although normally invisible to us, these patterns
can just be made out with polarised sunglasses.
The bee needs to see only a small portion
of the sky map to find its way home.
Like the bee, the water boatman
has a compound eye.
This consists of an array of tiny lenses.
Although each lens views
only a fragment of the scene,
they combine to create a single view.
The water boatman?s eyes attune
to the polarised light reflected from water.
0ur polarised glasses cut down these reflections,
but the water boatman?s eyes enhance them.
They help it find new breeding pools.
The dragonfly has the ultimate compound eye.
Its vision is four times better
than the water boatman?s.
Good vision is essential
for this aerobatic marvel,
for the dragonfly not only hunts,
but also fights on the wing.
30,000 lenses gather enough information
for skilled manoeuvres.
But this view is still 30 times poorer
than our own.
To match our eyesight, its compound eyes
would have to measure a metre across.
Like us, the dragonfly has eyes
with areas of high resolution.
These are used to spot flying insects
against the sky -
either food, mates or rivals.
Territorial disputes are resolved
by air-to-air combat.
The victor returns to patrol its territory.
(Quacks )
Birds have the most complex colour vision
of any animal.
The light-sensitive cells of the eye
contain up to five different colour pigments.
These pigments detect many more colour hues
than we can see.
The cells of the eye also contain
coloured oil droplets.
These act like miniature filters
and reveal even more colours.
While many birds appear to use oil droplets
to improve their colour vision,
sea birds may use them for a different purpose.
The eyes of terns have a high concentration
of red oil droplets.
It is believed that these act as haze filters
cutting out the reflected blue light of sea mists.
For terns and gulls that feed communally,
these haze filters may help individuals
locate feeding flocks.
The terns concentrate over schools of sand eels.
As they hover, they use sight to single out
a fish from the shoal.
Their eyes cannot focus under water,
so they simply take aim, then dive.
(Squawking)
Although terns cannot cope
with the change of focus needed below water,
there are some fishing birds that can.
Like most animals, a cormorant focuses light
using both a lens inside the eye,
and a cornea on the outside.
In air, the cornea starts to focus light
which is then fine-focused by a lens
that can change shape.
Under water the cornea can no longer focus,
which is why we see only a blur.
But the cormorant?s vision is still crystal-sharp.
By distorting its lens,
it can compensate for the now useless cornea
and focus better than any other animal.
A cormorant?s eyes may outwit a fish,
but in Mexico there are fish
with vision to outwit birds.
These strange floating blobs are actually eyes.
This is what they see.
The eyes belong to anableps,
better known as the four-eyed fish.
Each eye is divided.
The top half looks for predators such as birds,
the bottom half looks for food.
In this way it can see food and danger
simultaneously.
This distracting display confuses the vision
of predators both above and below the water.
The Great Barrier Reef is home to perhaps
the strangest eyes in the animal world.
Their vision is as bizarre as their appearance.
They belong to a creature
known as a mantis shrimp.
The central band of the eye is the most complex
colour analyser of the animal world.
As it sweeps the scene,
it not only scans for visible colours,
but also for ultraviolet and polarised light.
The eyes are searching for anything
that might be alive.
0nce it?s found a possible source of food,
an analyser is swept across it.
It then brings the second analyser into play,
lining up the scanning lines
like the cross wires of a gun sight.
In the dark and murky waters of the Amazon,
live fish with eyesight as formidable
as their predatory reputations.
In water coloured red by organic decay,
the piranha has eyes that can pierce the gloom.
Its eyes can see rays of light invisible to us.
Here the light we see is rapidly absorbed,
but far-red light still penetrates.
As they hunt for prey, these killing shoals
rely on far-red light to cut through the murk.
For the catfish there is no escape.
Even a mere goldfish has
the visual powers of a piranha.
In our hi-tech world, we use
far-red light for our own protection.
Many security systems use this light,
sometimes known as infrared,
to illuminate guarded premises.
Invisible to human eyes,
but picked up by special cameras,
the far-red light shows up any intruders.
As the truck disappears into darkness,
it is still seen by the security cameras.
The goldfish?s eyes can see it too,
lit by the far-red lamps.
A visual system that evolved
to cope with murky water
is here paralleled by
one of our latest inventions.
But the goldfish has other visual powers.
It not only sees far-red,
it can also see ultraviolet,
a colour at the other end of the spectrum.
A creature we take for granted can see a greater
range of colours than any other animal.
0n our next journey,
Super Sense will explore the world of sound.
