- CRITTER TALK
Here’s how our doggies make their way in the world:
A dog’s sense of smell is remarkable. In comparison to humans, dogs have over 40 times the number of scent receptors in their noses, and a large proportion of the canine brain is dedicated to decoding what they smell. Scientists estimate that the canine sense of smell is anywhere between 40 and one million times stronger than ours, depending on the breed and the type of odor tested. Remember this the next time you are out for a walk. Try to be patient while your dog endlessly sniffs the same patch of ground. Who knows what type of information he is gathering?
One of the more fascinating ways that the canine nose is being put to use to benefit people is in the detection of some types of human cancer. For example, a study published in England tested whether dogs were able to determine if bladder cancer was present by sniffing samples of urine. Overall, they did a very good job, but most interestingly, the dogs kept insisting that one of the samples was positive for cancer while the researchers were sure it was not. Finally, the patient was retested and the doctors, not the dogs, were wrong.
Dogs have a good sense of sight, but if we could see through their eyes, we would be shocked at how different everything looks. The retina is the tissue at the back of the eye that converts light energy into nerve impulses to be sent to the brain. Cells in the retina called rods are primarily responsible for vision under low light conditions and for the detection of movement. Dogs have a greater number of rods in their retinas in comparison to people.
Dogs also make use of another ocular structure, the tapetum lucidum, to reflect light within the eye. This is also what causes the eyes of some animals to glow when light shines into them in just the right way. More rods and the tapetum lucidum allow dogs to see in dim light and pick out a moving object much better than we can.
Trade-offs are the name of the game in nature, however. The canine investment in rods comes at a cost: fewer cones — the retinal cells that are involved in color vision and the ability to see fine detail. Dogs are not completely color blind, but studies show they have difficulty differentiating between greens, yellow-greens, oranges, and reds; and greenish-blue colors probably appear grey to dogs. Also, canine eyes are set farther apart than are human eyes, so dogs have better peripheral vision but poorer depth perception than we do.
The standard for human vision is 20/20, but most dogs seem to be limited to about 20/75. To get an idea of what this means, stand 75 feet away from an object. For your dog to see it as well as you do, he would have to be only 20 feet away. Consequently, if you need to get your dog’s attention from a distance, don’t just stand still, try waving your arms, moving back and forth, or calling out his name.
Dogs hear very well. They are able to pick up sounds at much lower intensities than people can, which means they can hear things from much farther away. This may be part of the explanation for the uncanny ability of some dogs to know when a loved one will appear long before they actually arrive. Perhaps they are picking up on the unique sound of the family car or their favorite person’s footfalls at a much greater distance than we can even imagine. Dogs are also able to hear sounds at a much higher pitch than we do. In general, the upper threshold for human hearing is around 23,000 Hz, while it goes up to about 75,000 Hz for dogs.
Some breeds of dogs have a better ability to hear than do others. Large, erect ears that can be turned towards a noise act as funnels, focusing sounds down the ear canals. The floppy, pendulous ears of other breeds, like Cocker Spaniels, actually make it harder for them to hear.
Dogs have only about one-sixth the number of taste buds on their tongues in comparison to people, but they are still able to detect the four primary flavors: salty, sweet, sour, and bitter. While taste is actually a fairly limited sense, it is greatly enhanced by what an animal smells. Think back to the last time you tried to eat your favorite meal while suffering from a stuffy nose…disappointing, right? Therefore, even though dogs have a limited number of taste buds, their fantastic sense of smell probably allows them to “taste” what they eat very well.
If you’ve ever seen a dog enjoy a good belly rub or back scratch, you probably already know that they have an excellent sense of touch. Dogs have sensory nerve fibers throughout their skin. Some of these nerves are closely associated with hair follicles, which allow them to feel even the lightest touches to their fur. Specialized hairs called vibrissae around the eyes, under the chin, and on the muzzle (i.e., whiskers) increase a dog’s sensitivity in these areas.
Dogs not only have what can be thought of as the five traditional senses — smell, sight, hearing, taste, and touch — but also the ability to detect pheromones produced by other dogs using a structure above the roof of the mouth called the vomeronasal, or Jacobson’s organ. Pheromones are special chemicals produced by the body that are usually associated with reproduction or social communication within a species.
The presence of a functional vomeronasal organ in people is somewhat controversial, but there is no doubt that dogs respond to their own species’ pheromones. One obvious instance is when a male dog smacks his lips and chatters his teeth after smelling a female’s urine. This is called the Flehmen response, and it probably helps him move any pheromones left behind by the female towards his vomeronasal organ.
I like to think of the canine and human senses as complimenting one another. Together, we make a pretty good team.
Dr. Jennifer Coates writing for PetMD