July 2012 Discussion - animal intelligence

[Steve]

Document containing 5 brief articles (minus photos) on "Crittervision"
about how some animals see the world:

Crittervision: See like a bee
22 August 2011 by Caroline Williams
When a bee flies into your garden, it doesn't see what you and I see.
Flowers leap out from much darker-looking leafy backgrounds, and they
have ultraviolet-reflecting landing strips that show the way to the
nectar. Some spiders might even have evolved to exploit these
displays, spinning UV patterns into their webs that could work to fool
a bee into thinking that it was making a beeline for a tasty treat.
If the bee manages to resist the spider's trap, she finds her way back
home by checking the pattern of polarised light in the sky. All this
is seen through the pixellated window of mosaic vision, with each unit
of the insect's compound eye providing one of the 5000 dots that make
up an image.
It's a world of vision that it is difficult to imagine, but we might
get some clues from people with aphakia: a condition in which the lens
of the eye - which normally absorbs UV light before it can reach the
retina - has been removed in surgery or lost in an accident. Bill
Stark, an insect-vision researcher at Saint Louis University in
Missouri, lost the lens in his left eye after an accident when he was
10 years old. He says he can see UV light as a kind of "whitish blue",
which he would see washing the scenery at a funfair, for example.
Because the sight in his left eye is not great, however, he cannot see
the subtle patterns in flowers that bees do.
Mind you, even if Stark's vision was corrected his experience of UV
could not match that of a bee, says Lars Chittka, a sensory and
behavioural ecologist at Queen Mary, University of London. "Bees have
a specific UV receptor - humans don't," he explains. "These people see
UV with their blue receptors, because the sensitivity of our blue
receptors extends weakly into the ultraviolet. But humans can't
perceive UV as a separate colour."
The complexity of the bee's colour system is nevertheless comparable
to human vision, since, like humans, they only have three colour
receptors - for UV, blue and green, compared with the human set-up of
blue, green and red. This means that false-colour photographs, in
which red has been filtered out and UV has been added in a colour
visible to human eyes, gives us a close approximation of the patterns
a bee sees.
Besides their UV vision, bees can also detect the polarisation of
light. "Just like you see red from blue they see one polarity from
another," says Stark. Air molecules in the atmosphere scatter photons
to create a pattern of polarised light arranged around the sun, for
example (see diagram). This helps bees to navigate by the position of
the sun even when the sky is cloudy. Since polarised light is
measurable using relatively simple detectors, we can again create
images of the kind of information they can pick up.
If a bee's-eye view of the world seems alien to our own, it is nothing
compared with that of some insects and birds, which have four, five or
even six colour receptors, allowing them to perceive colours that it
is impossible for us to experience or even imagine. For them, the
three-colour world of human vision would be as dull as greyscale.

Crittervision: Turtles surf the magnetic ocean
23 August 2011 by Caroline Williams
The idea that animals can navigate using their own internal compass is
so startling it was once dismissed as pure fantasy. Now there is good
evidence that many species - including pigeons, sea turtles, chickens,
naked mole rats and possibly cattle - can detect the Earth's
geomagnetic field, sometimes with astonishing accuracy.
Young loggerhead turtles, for example, read the Earth's magnetic field
to adjust the direction in which they swim. They seem to hatch with a
set of directions, which, with the help of their magnetic sense,
ensures that they always stay in warm waters during their first
migration around the rim of the North Atlantic. Over time they build a
more detailed magnetic map by learning to recognise variations in the
strength and direction of the field lines, which are angled more
steeply towards the poles and flatter at the magnetic equator.
What isn't known, however, is how they sense magnetism. Part of the
problem is that magnetic fields can pass through biological tissues
without being altered, so the sensors could, in theory, be located in
any part of the body. What's more, the detection might not need
specialised structures at all, but may instead be based on a series of
chemical reactions.
Even so, many researchers think that magnetic receptors probably exist
in the head of turtles and perhaps other animals. These might be based
on crystals of magnetite, which align with the Earth's magnetic field
and could pull on some kind of stretch receptor or hair-like cell as
it changes polarity. The mineral has already been found in some
bacteria, and in the noses of fish like salmon and rainbow trout,
which also seem to track the Earth's magnetic field as they migrate.
The tug of the South
If this is the case, what might a migrating turtle feel as it set off
on its 14,000 kilometre jaunt around the North Atlantic? One analogy,
says Kenneth Lohmann at the University of North Carolina at Chapel
Hill, might be to "imagine swimming while paying attention to two
tufts of hair, one on the right side of your head and one on the left.
When you go north, neither tuft is pulled. When you go east, the
sensation is one of someone gently pulling on the tuft of hair on the
left side of your head; when you go west, you feel a tug on the tuft
on the right side. And when you go south, both tufts of hair are
pulled." Holding a steady course would be a matter of making sure the
sensation didn't change.
That is one possibility. Another is that there may be photopigments in
the eye called cryptochromes that detect the magnetic field chemically
and provide a visual cue that an animal can use as a kind of compass.
If so, the animal may see the magnetic field as a shifting pattern,
such as an array of lights or colours that change depending on the
direction it faces.
There is some evidence that this may be the case for at least some
kinds of animals. Cryptochromes are found in the retina of migratory
birds and seem to be activated when birds are navigating using the
magnetic field. What's more, the retinal cells containing
cryptochromes connect with a brain region which, when removed, hinders
the bird's ability to navigate by the magnetic field.
Until we find out how these animals detect the field, however, we
won't come close to knowing what animals see and feel when they sense
it. There is some hope, though, in the recent discovery that well-
studied species such as fruit flies and zebrafish can detect magnetic
fields. Their smaller and simpler brains make them far easier to study
than wild turtles and pigeons, and so may one day provide some
answers.

Crittervision: Enter the bat's world of sound
24 August 2011 by Caroline Williams
A bat would probably have no trouble imagining how it is to see like a
human: some species have eyesight that is at least as good as ours,
and some see better than us in dim light. For us to imagine their
world, though, is somewhat trickier. Insect-eating bats and some fruit-
eaters get much of the detail they need to find food through
echolocation: clicks, squeals and screams that they belt out at up to
120 decibels. That's the volume of a passing ambulance siren.
Thankfully they do it in ultrasound, above the range of human hearing.
The echoes of these sounds give them a huge amount of information
about their surroundings. The time it takes for an echo to return, for
example, reveals the distance of an object, and the changes in the
sound's frequency as it bounces off another creature can even reveal
the speed and direction of the animal's movement.
The sensitivity of echolocation is phenomenal. A study published last
year found that some bats can detect differences in the distance
between themselves and their prey with an accuracy of between 4 and 13
millimetres (Journal of the Acoustical Society of America, vol 128, p
1467). For an insect-eating bat, that's enough to scoop up the insect
with its wings before passing it to its mouth. Subtle differences in
the tone of these sounds, meanwhile, reveal a bat's identity to its
peers, in much the same way that we recognise someone's speaking voice
(PLoS Computer Biology, vol 6, p e1000400).
Imagining this world of sound is difficult for humans, who rely so
predominantly on visual information, but there are some people who
perceive the world in a similar way to the bats. Daniel Kish is one.
He has been blind from birth, but as a toddler began to make sense of
his surroundings by making clicks with his tongue and listening to the
echoes that bounced back from people and objects. He describes the
echoes produced by sounds in the environment, and the mental images he
gets from this, as being like "flashes of light in otherwise total
darkness", but it is enough to allow him to cycle on quiet roads and
hike independently. As we talk over the phone, Kish even describes the
room I am sitting in and the kind of furniture that I have from the
echoes that he can hear.
There are limits to this impressive ability, however. Unlike a bat, he
cannot trace the movement of objects with the echoes of his clicks.
And while bats can use echolocation to tell one kind of insect from
another, Kish's is not sensitive enough to distinguish different
people, or even a face from a basketball. What he can do, however, is
use his large, human brain to fill in the gaps. This way he can still
play basketball by listening to where other players are and where the
ball last bounced.
His skills may be related to those of a bat, but we don't know whether
bat brains represent the information in a similar way. Human
echolocators like Kish seem to use the brain's visual circuitry,
rather than the auditory centres, to decode the acoustic information
and form a mental image of their surroundings (PLoS One, vol 6, p
e20162). Whether bats also visualise the information from their echoes
and if so, whether they are able to switch from vision to echolocation
as they hunt, remains a mystery.
In any case, learning Kish's method is the closest a human can get to
experiencing the world like a bat. Kish suggests practicing outdoors,
preferably somewhere quiet like a field or a large room that isn't too
echoey. Put on a blindfold and ask someone to stand behind you so
their body doesn't become the main target for your echolocation. Then
ask them to hold a large, resonant object - a deep bowl, say - a few
centimetres in front of your face while you click loudly with your
tongue and listen. With a bit of guesswork you should be able to
identify the shape. Then move on to a trickier one, such as a shallow
metal platter, to slowly build up your awareness of how different
objects sound. With time you may even start to "see" different objects
in your mind's eye - perhaps in the same sort of way that a bat
visualises their world.

Crittervision: What a dog's nose knows
25 August 2011 by Caroline Williams
Ever wondered how a dog, with a sense of smell that may be thousands
of times more sensitive than ours, can bear to bury its face in the
trash can? Alexandra Horowitz, a dog-cognition researcher at Columbia
University in New York City and author of Inside of a Dog: What dogs
see, smell, and know, says it's because the dog isn't simply smelling
a stronger version of the revolting mono-stench that we smell. "It is
not that smells are 'louder'," she says. "The smells have different
layers, which probably give dogs a much bigger range of types of
information." She compares it to the way we might enjoy a painting
from across the room, but appreciate it in a different way when we can
get up close and see the brush strokes.
This makes a dog's experience fundamentally different to our own. When
we go out for a walk, for example, we get almost all of our
information from vision. But the dog's eyes are just a back-up. This
was shown when police tracker dogs were given a scent trail that
seemed to run in the opposite direction to a set of footprints on the
ground; they invariably followed their noses and ignored the
contradictory visual cues (Applied Animal Behaviour Science, vol 84, p
297). This reliance on smell explains why a dog that isn't expecting
to see its owner will often stop a metre or so away for a quick sniff
before jumping all over them.
To imagine the scent-based world of a dog, says Horowitz, look around
and imagine that everything you see has its own individual scent. And
not just each object - different parts of the same object may hold
different types of information. Horowitz gives the example of a rose:
each petal might have a different scent, telling the dog it has been
visited by different insects that left telltale traces of pollen from
other flowers. Besides picking up on the individual scent of humans
that had touched the flower, it could even guess when they may have
passed by.
Passing Time
In this way, smell might give a dog a way of understanding the passage
of time, Horowitz suggests. A dog can perhaps perceive the past by
smelling that a dog urinated here long enough ago that the scent has
changed in character and become weaker. One recent study, from 2005,
showed that dogs may even be able to detect the subtle differences in
odour from one footstep to the next as they follow a human's scent
trail (Chemical Senses, vol 30, p 291). The dog could imagine the
future by picking up the scent of the dogs, humans or other objects
coming towards them on the breeze.
Unfortunately there's no way for a mere human to get inside this
highly detailed world. Even if we get down on the ground and sniff, we
cannot do it like a dog. When we sniff we are sporadically blind to
scent as we breathe in and out through the same holes. A 2009 study of
the fluid dynamics of the dog's sniff showed that their system is far
more complex. Each nostril is smaller than the distance between the
two, which means that they inhale air from two distinct regions of
space, allowing the dog to decipher the direction of a scent. The
sniff also funnels stale air out through the sides of the nostrils, an
action which pulls new air into the nose. Once inside the nose the air
swirls around up to 300 million olfactory receptors, compared with our
measly 6 million (Journal of the Royal Society Interface, vol 7, p
933).
Even if humans could gather this information, our brains wouldn't know
what to do with it: the dog olfactory cortex, which processes scent
information, takes up 12.5 per cent of their total brain mass, while
ours accounts for less than 1 per cent.
While we can never truly experience the world of the dog, we can at
least imagine the kinds of fascinating information that a dog might
get from sniffing that lamp post. And maybe, just occasionally, we
will resist the temptation to tug the lead to get somewhere more
"interesting".

Crittervision: Heat-seeking snakes
26 August 2011 by Caroline Williams
Pythons, boas and pit vipers (the family that includes rattlesnakes)
see the world pretty much as we do, but with a twist: they can "see"
in infrared too. This allows them to track their prey by their body
heat from up to a metre away.
They do this using relatively simple organs, called pits, which lie
near their nostrils. These differ slightly among different snakes but
are always a small dip containing a membrane that is packed with heat-
sensitive nerve endings which act as infrared receptors. The pit
organs were first described in 1952 but it was only last year that the
specific protein channels that react to heat were identified (Nature,
vol 464, p 1006). These are found on nerve cells that are part of the
sensory system that detects touch and temperature, and registers pain.
Yet while this is completely separate from the visual system, both
sets of information end up in the same place: a part of the brain
called the optic tectum. "There, the two maps of space - visual and
infrared - merge into one," says Michael Grace, a neuroscientist
investigating pit viper thermal sensing at the Florida Institute of
Technology in Melbourne.
Grace speculates that this allows the snake to see in infrared and
visible light at the same time, or to switch between one and the
other. When hunting in a dark burrow, for example, it can use infrared
to hunt its prey and to find its way to the warmer air at the surface
of the burrow, and then return to regular vision when it emerges into
a hot desert day where there are few differences in temperature. The
snakes may be able to use both senses at once in early morning, when
there is enough light to see and it is still cool enough for its warm-
blooded prey to pop out as being much hotter than their surroundings.
Our understanding of how snakes "see" in infrared is far from
complete, but a combination of normal video and thermal video footage
gives us a fair stab at imagining what this world might look like.
Caroline Williams is a writer based in Surrey, UK

[Steve]

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