A dog is ten times more sensitive to peripheral movement than we are. He picks up movement on either side of him better than we ever could, in part because most dogs’ eyes are closer to the sides of their heads than ours are. A dog’s vision is poor up close, but he can see quite well at a distance.
Anatomy of the Eye
The dog’s eye is different from ours. Our eyes are better at defining detail in bright light. The dog’s eye has a reflective layer that intensifies light and helps the dog (as it did his predecessor, the wolf) to see more when he needs it most: for hunting at dawn and dusk. At night, when you see a car’s headlights reflect brightly off a dog’s eyes, what you are seeing is that reflective layer. Dogs can see in low light but they cannot see in the dark — they do not have the mechanisms that a cat does to allow that.
Dogs see in black and white when there is low light, but when it is brighter they do see some color.
Some dogs have very good eyesight because the work for which they were originally intended required great vision. Many retrievers and the so-called sight hounds — for example Salukis and their descendants like Afghan Hounds, Borzois and Greyhounds — have amazing vision. These dogs have frontally placed eyes, as people do.
Many terriers have slanted eyes — they’re physically frontal, but the slant allows them to see around corners.
Guardian dogs like German Shepherds and Akitas have more laterally placed eyes.
There are also many breeds that depend much more on their sense of smell and even on their hearing, so their vision is unremarkable.
“Progressive retinal atrophy” is an inherited blindness that can strike dogs in breeds that are at risk for it. There are times when people think an otherwise healthy dog is going blind because they notice that she cannot see a toy “right in front of her.” However, the inability to see something “right in front of her nose” is not a cause for concern, because due to where a dog’s eye is placed on her head, the toughest place to see anything is directly in front.
Dogs’ hearing is more acute than ours. They can hear high-pitched noises that are inaudible to us — this may have allowed their wolf ancestors to pick up the high-pitched squeaks of small mammals such as mice. However, their hearing ranges over eight and a half octaves, just like ours, while a cat can hear more than ten octaves.
It is the pitch that dogs are able to discriminate that makes their hearing abilities seem so impressive, which also explains how they are able to pick out the sound of their mistress’ car engine as it approaches home. More of the dog’s brain is devoted to sound than ours — plus they have mobile ears that scan and then collect the sound waves.
A dog’s acute hearing explains why a sudden loud noise can be upsetting to him, although as with everything in the dog world, these are individual issues. Some dogs hate the suddenness of noise and others cannot stand loudness — and yet there are plenty of dogs who seem oblivious to a racket. For example, it isn’t clear why some individual dogs become terrorized by the sound of gunfire or thunder, while others don’t even raise their heads although they have perfectly good hearing. It may be that hunting dogs from breeds originally raised to accompany men with guns may be somewhat genetically desensitized to the loud cracking report of a gun.
SENSE OF SMELL
Dogs are among several animals that have an extra organ in the nasal cavity called the Jacobson’s organ. These animals can literally smell the air — which is why you often see a dog tip his nose up into the air and see his nose twitching to “read” the smells wafting on the breeze. What the dog is actually doing has been described not so much as smelling the air but “tasting” it. This is a concept that is hard for creatures like us to really understand, since we’re so limited in the olfactory department.
The dog’s nose has sensory tissue that is directly exposed to the world around her. It is made up of three different kinds of cells, one of which is the sensory receptor. There are tiny, hair-like “cilia” on those cells that pick up the chemicals that make up a smell. The amount of cilia per cell is connected to the acuteness of an animal’s sense of smell.
A comparison of the cilia in a dog vs. that in the human nose shows that people have six to eight cilia per cell, while dogs have 100 to 150.
Sensitivity to odors is partly inherited and can be increased by selective breeding and training. Examples of this selection for “great noses” are the Beagles that sniff at airports for contraband, and the Bloodhounds that are used to track criminals and lost people.
“Air-scenters” include dogs like Collies, which run along a scent trail in the air, weaving back and forth with their heads held high. They circle when they lose the scent and go in widening circles until they pick it up again.
SENSE OF TASTE
People have a more refined sense of taste than dogs do, which seems contradictory when you consider that their sense of smell is so much more powerful and complex than ours. Humans have about 9,000 taste buds on their tongues — dogs have less than twenty-five percent of that.
Dogs do register salt, sugar, sweet and sour, but these do not register as they do in people. The odor of food is what first attracts a dog, but after she starts eating, the smell has no effect on her more limited sense of taste. Lab tests on dog’s taste preferences have shown some surprising results:
DOGS’ TASTE PREFERENCES
- Canned meat over fresh
- Cooked meat over raw
- Meat over cereal
- Warm food over cold
Dogs have additional primary taste receptors that respond to water (cats and pigs have these, too). So if you’ve noticed your dog being picky about the water in his bowl, it may be that his “water sensor” is on the job. It is thought that dogs may actually be able to taste the differences between types of water from different sources or from different receptacles. Not much is known about this sensitivity, and it’s not really feasible to set up a test to determine levels of sensitivity, since each dog has varying degrees of sensitivity and might very well not show a measurable response to the differences that he tastes.
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Copyright © Tracie Hotchner – Originally appeared in The Dog Bible: Everything Your Dog Wants You to Know by Tracie Hotchner