Saturday, August 25, 2012

Sight, hearing, smell: the differences between dogs and humans

It's been a fact for many years that dogs only see in black and white. I'm here to tell you it's a total myth. Dogs can actually see colors that are equivalent to red-green color blindness in humans. If you were to compare the vision of a human vs. a dog, the dog would win the contest for noticing the most in its surroundings because a dog has much better vision for catching motion, however, dogs can only see about half the brightness level than their human counterparts.

Now that you know dogs can see in color, let's take it sense by sense and compare the sensory systems of dogs and humans, starting with hearing:

Dogs can hear what?
Dogs can hear in frequencies ranging from around 40 Hz to 60 kHz, depending on the breed and age. Dogs have more than 18 muscles that enable them to move their ears so they can more precisely locate a sound. In addition, dogs can hear sound up to four times farther than us humans. So the next time you hear your dog barking at the wind, he/she may be hearing something quite interesting.

Humans can hear what?
Humans can hear in frequencies ranging from 12 Hz to 20 kHz (give or take). As we get older, that range can shrink, depending on the level of hearing loss you experience. Women tend to be more sensitive to higher frequencies than men. This is most likely due to the fact that women have to be more aware of their offspring.

Dogs can smell what?
Dogs have a brain that is built to sense smell. The olfactory cortex is the part of their brain that enables them to have superior smelling capabilities. The olfactory cortex is fourty times bigger in dogs than it is in humans and up to 100 million times more sensitive. Bloodhounds have an extremely superior sense of smell, hence the “100 million times more sensitive” figure. Other breeds don't have quite that capability. Dogs use their wet noses to detect what direction a smell is coming from. Dogs can use each nostril separately to further increase their smelling abilities. The sense of smell is the most highly evolved sense a dog has.

Humans can smell what?
The human nose can sense up to 4,000 to 10,000 different smells (dogs can sense around 30,000 to 100,000). Humans who do not have any sense of smell have a condition called Anosmia. Our sense of taste is largely influenced by our sense of smell. In fact, it can influence our sense of taste by up to 80 percent! Dogs can sense smells that are 100 million times less concentrated than what us humans can smell. So I guess that puts our sense of smell in perspective.

Dogs can see what?
Dogs are not color blind. They can see in ranges that are similar to red-green color blindness in humans. As twilight hunters, they have a section of their eye called the tapetum lucidum, which gives them something like night vision. You can often see the tapetum by shining a light into a dog's eye. It's that reflective eye-shine you can see when light reflects in their eyes in the dark. Dogs don't have the greatest clarity of vision, but they can see motion much better than us humans. For example, dogs have been shown to be able to differentiate between their owners from distances of up to 900m. However, that's only the case if you are moving. If you were to stay in one place, the distance they can differentiate goes down to around 500m. Some researchers believe that dogs may see television as a flickering screen. The visual abilities of a dog varies by breed. Greyhounds have been touted as having the best eyesight compared to other breeds, however, it hasn't been thoroughly proven.

Humans can see what?
Humans can distinguish about 10 million different colors. Dogs on the other hand, cannot see nearly as many colors as humans. The overall visual acuity (clarity) in humans is much better than it is in dogs, however, dogs have a much better ability to notice motion and the ability to see well in the dark. It takes roughly 30 minutes for the human eye to fully adjust to darkness. If we were to compare the sight of humans and dogs, humans would win on the clarity front and dogs would probably win everywhere else. Of course none of this matters if you are blind or have some other unfortunate visual disability.

Chihuahua. Credit: Danielle deLeon

Conclusion
As you can see, there are many differences between humans and dogs. However, with all of our differences, dog is still man's best friend!