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March 10 How Do Dogs Hear?If dogs could talk, they'd almost certainly proclaim hearing as their second most important sense. Smell being their first most important sense. Because people are so verbally oriented, we expect our canine counter parts to listen a lot, and they're remarkably willing. If you watch even a sleeping dog, you'll notice their ears swivel, reacting to sound.
Humans and canines share many of the same anatomical characteristics of the ear. The difference is the outermost section. Our ears are very much plastered to our heads, and the ability to wiggle them even a tiny bit is considered amazing. A dogs ears are made to collect sound. Some may be floppy or erect, but they are far superior to ours. A dogs ears can move independently from eachother, making it easier for them to discriminate and pick up sounds all around them.
The external auditory canal leads down from the base of the outer ear called the pinna. It then makes a nearly right angle turn inward to the eardrum. Vibrations reaching the eardrum pass through the tympanic cavity via three tiny bones known collectively as the auditory ossicles. This section comprises the middle ear.
The inner ear is responisble for turning vibrations into nerve impulses. Vibrations pass through a snail-shaped tubular structure called the cochlea. This converts the vibrations into nerve impulses and then sends them along the auditory nerve to the brain for processing.
Ok, so now you know how the canine ear hears.. now lets talk about what it hears. Sound is measured in vibrations, or cycles, per second, termed either cps or hertz. It is accepted that humans can hear 20 to 20,000 hertz, with the optimum range between 1,000 and 4,000 hertz. Agreement among scientists about canine hearing, however, differs. While it is generally acknowledged that dogs hear somewhat less in the ultra-low range and considerably more in the high-frequency range, actual numbers vary widely. Most experts cite upper limits of 35,000 to even 100,000 hertz! It is said that Pavlov (famous for making a dog salivate by ringing a bell) demonstrated that dogs react to sound at 75,000 hertz. Whatever the upper number may be, it is far greater than ours!
So having a high hearing range means that dogs are flooded with sounds. One impressive talent dogs seem to have is the ability to screen incoming sounds. If you've watched your dog sleeping soundly suddenly spring into alert at the sound of the can opener or the crinkling sound of a bag after sleeping through loud music, a blasting t.v., or the family wrestling match, you've witnessed sound screening at work.
Dogs also have the ability to locate the exact point where the sound is coming from. Which isn't really suprising if you think about it. A wolf or wild dog hearing the sound of a rabbit, but misjudging it's location by a few yards wouldn't make for a well fed dog.
Probably the most intiguing element of canine hearing is the mobile ear flap. Dogs can foucus and capture sounds with each ear independently. Police have learned to watch their dogs' ears for clues to a situation. Both ears focused in the same direction as the muzzle indicates a suspect in that direction, while one ear flicking repeatedly away from the forward direction to some other consistent position likely indicates a second person in the area.
So now you know how dogs hear, and what they can hear. If you'd like to test your dogs' hearing try putting your dog in another room with someone else and have that person distract them by talking to them. Then go into the kitchen and crinkle a bag of chips or of their favorite treats and watch them come running! Another way to test your dogs' hearing is to wisper a command to them while they are just laying around, even if they don't obey the command, you'll more than likely see their ears move in your direction!
The following are some ways to recongnize hearing problems in your dog:
Pups are born deaf. As a matter of fact their ears don't open until they are 10 to 14 days. If your pup is not responding to sound after that time, it may be congenitally deaf. This problem is often associated with white coat coloring, and occurs more in Dalmations, Bull Terriers, Jack Russells, and Australian Shepherds/Cattle dogs.
Any dog that does not seem responsive to sound, no matter it's breed or age, should be checked for effective hearing. You can preform a very rough test by standing behind your dog and clapping your hands loudly, but your veterinary neurologist can preform an actual hearing test called a BAER, or brainstem auditory evoked response, test. This test simply measures the degree of hearing loss in each ear.
Since the middle ear is long and curves at a near right angle, it is important to clean your dogs ears regularly. The middle ear is a great place for bacteria and yeast to grow, especially if your dogs ears are floppy. Bacteria and yeast can cause painful ear infections and block, even destroy in worst cases, your dogs hearing.
So remember, if you call your dog to you and he/she doesn't respond, have him or her checked out by a vet. If everything is ok with your dogs ears, he/she may just have changed their name for the day! February 13 How Do Dogs Smell?Ah, smell.. or olfaction as it's often known. Olfaction is a dog's primary sense. They trust their sense of smell over every other sense. However, not all dogs have equal abilities when it comes down to the sense of smell.
To break it down, a dogs nose is designed for superior smell. The nasal plane (end of nose containing nostrils) is kept moist to dissolve and release scent particles. The nostrils are comma shaped to swirl the scent throughout the nose. This helps dogs to smell in detail. For example, if you let your dog smell a plate of ketchup, he not only smells the ketchup, but also every.. single.. ingredient with in the ketchup.
The inner nose is compiled with olfactory receptor cells to process scents. Dogs with longer muzzles have more olfactory receptor cells than dogs with short muzzles. In example, humans only have 5 million olfactory receptor cells, where as a German Shepherd Dog has 220 million! A dachshund has 125 million, and a fox terrier has 147 million. So different dogs have different scenting abilities, but they all out rank us humans. Another reason dogs smell so well is that at the end of each of these olfactory receptor cells, there are cilia. The cilia are tiny hairs coated in mucous and help to trap scents with in the nose. Humans have about 6 to 8 cilia at the end of each olfactory cell, but dogs have 100 to 150. Each of the olfactory receptor cells connect to nerves that lead to the olfactory lobe in the brain. In a dogs brain, this lobe is the size of a large walnut, where as in a human it is the size of a pea.
One other thing that makes a dogs sense of smell so incredible, is that they can actually smell under water! Thanks to the vomeronasal organ, or more commonly refered to as the Jacobs organ. It runs along the bottom of the nose, just behind the teeth, and is directly connected to the olfactory lobe via 608 nerve bundles. In the skull, there are two small holes in the roof of the mouth, in a live dog they are not visible, that they can somehow pull a scent through with out inhaling. They use this organ to draw in smells while diving in water to smell what they are looking for.
Dogs tend to associate many memories with their sense of smell. Because this is their primary sense, they trust it with their lives. In a previous entery, I explained how a dog sees. They are considered near sighted, so if you've ever thrown a treat on the ground close to a puppy and it's taken him awhile to find it, it's because he is not trusting his eyesight, even if he might see it. He is trusting his nose to find it.
It is very important to take care of your dogs teeth because any kind of infection or problem with his teeth can effect his olfaction, similar to when we get a headache and it effects our eyesight. So if your dog developes a behavior problem, have him checked by a vet to see that his senses are all in order. Imagine how you'd act if your primary sense wasn't working correctly.
February 12 How Do Dogs See?
By disecting the eyeball of a dog, researchers found that about 10% of the photoprecepters are cones. Cones are responsible for helping the brain detect colors. The photoreceptors in our eyes are 100% cones. This means that we can process all the colors and see them more vividly. A dog can't tell the difference between red, yellow, orange, or green but they can see whites light blues, purples and different shades of grey.
Besides just the cones, there are other photoreceptors known as rods. Rods can only detect black and white, but they also process movement extremely well and help to see in the dark. A dogs photoreceptors are mostly rods. This means they can see exceptionally well in low light conditions and see different shades of grey to a higher degree than we can. They can also differinciate the tiniest movements you make. If you've ever stood still with your dog in the back yard at night in a shaded area, and caught him by suprise, your dog has probably barked at you. This is because while you are standing still, he doesn't know who you are. Once you move, even wiggle your finger, he knows its you. This is helpful to an animal that hunts in the dark! On top of having an eye full of rods, they also have a reflective layer that helps to reflect light, helping them to see even better in the dark. This reflective layer is the glow that we see when we shine a light on a dogs eyes in the dark. As a matter of fact, it is believed that a dog can see in 4 times lower light levels than we can because of this reflective layer.
Another thing that comes into factor when talking about a dogs vision abilities is that they can see 240 to 250 degrees around them without moving their eyes. Our field of vision is only 180 degrees. So even if you are standing diagonally behind your dog, chances are he sees you.
Even though dogs are able to see all of these different things with their eyes, vision is not their primary sense. Actually, dogs are considered nearsighted. They really don't trust their eyes as much as we trust ours. Instead, they trust their sense of smell. To them, the phrase "follow your nose" is a way of life. I'll write more about that in another blog entery.
So what about T.V.? Do dogs enjoy watching T.V.? Well, T.V. is a series of flickering pictures that are streamed together to make a moving picture. The pictures are broadcast at a rate of about 60Hz, which is how fast they need to move for us to see them as a moving, flawless picture. To a dog, watching T.V. is a lot like watching and old scratchy silent film because their flicker fusion seems to occur at a rate of 70 to 80Hz. So they see the pictures flicker slower and there for it seems choppy to them. So chances are that if your dog likes to watch T.V., it's probably because of the sounds. Hearing is a dog's secondary sense, and I will discuss that in another blog entery.
So there you go. You now know the basics of how a dog sees his world. Keep in mind that this is usefull information to have in the training field. Because dogs are so adapt to detecting movement, they often respond to hand signals better than to voice commands. It's a good idea to teach your dog both. I hope you feel closer to you canine friend now that you understand a bit better how he or she precieves the world. |
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