How do dogs “see” with their noses? – Alexandra Horowitz


“Hi, Bob.” “Morning, Kelly. The tulips looks great.” Have you ever wondered
how your dog experiences the world? Here’s what she sees. Not terribly interesting. But what she smells,
that’s a totally different story. And it begins at her wonderfully
developed nose. As your dog catches
the first hints of fresh air, her nose’s moist, spongy outside helps
capture any scents the breeze carries. The ability to smell
separately with each nostril, smelling in stereo, helps to determine the direction
of the smell’s source so that within the first
few moments of sniffing, the dog starts to become aware of not
just what kind of things are out there but also where they’re located. As air enters the nose, a small fold of tissue
divides it into two separate folds, one for breathing
and one just for smelling. This second airflow enters a region filled with highly specialized
olfactory receptor cells, several hundred millions of them,
compaired to our five million. And unlike our clumsy way of breathing
in and out through the same passage, dogs exhale through slits
at the side of their nose, creating swirls of air that help
draw in new odor molecules and allow odor concentration to build up
over mulitple sniffs. But all that impressive nasal architecture
wouldn’t be much help without something to process the loads
of information the nose scoops up. And it turns out that the olfactory system
dedicated to proessing smells takes up many times more relative
brain area in dogs than in humans. All of this allows dogs to distinguish and remember a staggering
variety of specific scents at concentrations up to 100 million times
less than what our noses can detect. If you can smell a spritz of perfume
in a small room, a dog would have no trouble smelling it
in an enclosed stadium and distinguishing its ingredients,
to boot. And everything in the street,
every passing person or car, any contents of the neighbor’s trash, each type of tree, and all the birds and insects in it has a distinct odor profile telling
your dog what it is, where it is, and which direction it’s moving in. Besides being much
more powerful than ours, a dog’s sense of smell can pick up things
that can’t even be seen at all. A whole separate olfactory system, called the vomeronasal organ,
above the roof of the mouth, detects the hormones all animals,
Including humans, naturally release. It lets dogs identify potential mates, or distinguish between friendly
and hostile animals. It alerts them to our various
emotional states, and it can even tell them
when someone is pregnant or sick. Because olfaction is more primal
than other senses, bypassing the thalamus to connect
directly to the brain structures involving emotion and instinct, we might even say a dog’s perception
is more immediate and visceral than ours. But the most amazing thing about
your dog’s nose is that it can traverse time. The past appears in tracks
left by passersby, and by the warmth
of a recently parked car where the residue of where you’ve been
and what you’ve done recently. Landmarks like fire hydrants and trees are aromatic bulletin boards
carrying messages of who’s been by, what they’ve been eating, and how they’re feeling. And the future is in the breeze, alerting them to something or someone
approaching long before you see them. Where we see and hear something
at a single moment, a dog smells an entire story
from start to finish. In some of the best examples
of canine-human collaboration, dogs help us by sharing
and reacting to those stories. They can respond with kindness
to people in distress, or with aggression to threats because stress and anger
manifest as a cloud of hormones recognizable to the dog’s nose. With the proper training, they can even alert us
to invisible threats ranging from bombs to cancer. As it turns out, humanity’s best friend is not one who experiences
the same things we do, but one whose incredible nose reveals
a whole other world beyond our eyes.

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