Sight
In humans
People can perceive light because of two types of photoreceptor cells in our retina, called cones and rods. It's specifically the photoreceptor cones which enable the human eye to decipher millions of different colours. Cones are grouped into 3 types, broadly based on their ability to perceive shades of red, green and blue. A technicolour world reveals itself to us each time we open our eyes, thanks to these photoreceptors—except, of course, when we're watching a Charlie Chaplin film!
In dogs
In the past, we thought that dogs were unable to perceive colour and that they lived in a world that's exclusively black and white. We now know, however, that this is not the case. Dogs have two types of photoreceptor cones, which are sensitive to shades of blue and yellow. Dogs likely experience colour in much the same way as do people we call “colour blindâ€. Despite this apparent disadvantage, dogs are better adapted for low-light vision than humans and see better at night.
Smell
In humans
There's a reason why dogs—and not human beings—are employed to sniff out suitcases at the airport! The typical person has roughly 5 million olfactory cells. A paltry total compared to the average dog's 220 million olfactory cells. When it comes to smell, dogs leave people in the dirt!
In dogs
The nasal tract of the tiniest Chihuahua can “out track†even the biggest human nose. Researchers believe that the mucus coating a dog's nose helps contribute to its extraordinary sense of smell. A dog's sense of smell is so advanced that it's frequently a crucial factor in criminal investigations. Dogs can also be trained to detect an acetone-like odor, which can indicate hyperglycemia in diabetic patients. So, if your dog starts looking at you strangely, it might be time to go to the doctor!
Touch
In humans
Our hands have one of the highest concentrations of nerve endings in the entire body, which helps explain why the human sense of touch is so developed. What's more, when we touch a person we love, the nerves in our hands communicate with our central nervous system and release a “feel-good†hormone. Fingerprints may play a role in this process, possibly by amplifying the skin's vibrations.
In dogs
The sense of touch is likely the sense that's the most similar in dogs and people. It's the first sense to be solicited at birth—when a mother licks her puppies she's establishing a connection with her litter. We also calm and comfort our dogs by stroking them. When they snuggle up to us, dogs seek reassurance and, in return, give it right back to us. The extraordinary complicity between a person and her dog wouldn't be the same without the sense of touch!
Hearing
In humans
In terms of hearing, humans—with our inflexible ears and our limited range—are definitely at a disadvantage compared to dogs. It's also likely that we experience greater hearing loss as we age, though some dogs, depending on breed and genetics, may also go a little deaf as they age.
In dogs
Dogs can detect noises that are 4 times further away from them than humans can. Dogs have floppy, flexible ears which amplify sounds, and several specialized muscles which localize and isolate them. Dogs also have a broader range of hearing, allowing them to hear both low and higher frequency sounds, which escape the human ear. What gives when your dog barks for no apparent reason? She's probably just heard something that's way out of your hearing range!
Taste
In people
Contrary to popular belief, taste buds are not only found on our tongues. They're also on the palate, throat, cheek and even in the upper esophagus. It varies from person to person but typically humans have somewhere between 2,000 and 9,000 taste buds—many more than dogs. The quantity of our taste buds decreases as we age: our capacity to distinguish tastes—sweet, sour, salty, bitter, and savory—diminishes considerably after the age of 60.
In dogs
How can your dog dig into her bowl—and devour the same food—with the same gusto, day after day? For one thing, dogs have fewer taste buds than we do, as few as 1,700. What's more, canine taste buds are likely less sensitive to taste than ours. Ultimately, when it comes to food, a dog is guided more by smell than taste. This helps explain why a dog will wolf down its chow—or whatever he picks up on the street!—without savouring it. A dog just doesn't appreciate taste the way we do!