Dogs are (rightly) famous for their amazing sense of smell, but what about their other senses? How does a dog’s sense of sight, hearing, taste or touch compare to our own?
Our dogs’ wolf ancestors hunted prey that was most active during dusk and dawn, and therefore they evolved eyes that are especially sensitive in low light conditions, and especially attuned to motion. Compared to people, dogs have a panoramic view of the world: their field of vision encompasses 250-270 degrees, as opposed to our 180 degrees. Objects directly in front of a dog’s face, however, are not as sharply in-focus as they are for us. Dogs will often overlook small objects directly in front of them (such as a treat lying on the ground), because the lense of their eyes cannot adjust to accommodate nearby sources of light. They can still sniff out that treat with their sensitive nose though!
Contrary to popular belief, dogs are not completely colour-blind, but they do not see the same range of colours that we do. A dog’s eyes have receptors for blue and greenish-yellow colours, as opposed to human eyes, which have receptors for green, yellow and red. Dogs can often still distinguish between other colours by their level of brightness though. For example, a yellow ball will appear brighter to a dog than a red one, even though they can’t directly perceive the colour.
Dogs, whose eyes are attuned to motion, can literally see faster than we do. The cells in both dog and human eyes take light coming into the eye and turn it into electrical signals in the brain; this is how we see. The rate at which the cells do this is called the flicker-fusion rate. While human eyes can process about 60 still images per second, dogs can process about 70 to 80, and this affects the way dogs perceive film. In order for a film to appear as a moving image to us, rather than a series of still images, it must slightly exceed our flicker-fusion rate. Dogs, with their faster flicker-fusion rate, still perceive the film as a series of still images, and can even see the dark gaps between each image…on an old-fashioned piece of film, anyway. The shift to digital tv eliminates this problem.
Dogs can hear a much wider range of sounds than we can. While the typical human range of hearing is 20 – 20 000 Hz, dogs can hear sounds ranging from 40 – 45 000 Hz. Dogs can hear many sounds that are completely undetectable to human ears, such the high-pitched sounds emitted by crystal resonators in devices such as cell phones and digital clocks.
A dog’s ears are controlled by at least 18 muscles, which allow them to tilt and rotate to determine the exact direction a sound is coming from. In the wild, this would have helped dogs’ ancestors pinpoint the location of prey. In domestic dogs, the shape of the ear affects how well they can do this. Breeds with upright ears, such as German Shepherds, have better hearing than floppy-eared breeds, because the shape of their ears is better for capturing and amplifying sound.
Dogs, on average, have 1700 taste buds, compared to 9000 for humans (and only 470 for cats). This means that dogs are actually not as sensitive to taste as people are. Dogs respond to the same basic tastes as we do: sweet, salty, sour and bitter. The taste receptors for salt, however, are not nearly as well-developed as they are in humans. This is because dogs’ wild ancestors primarily ate meat, which is high in sodium. Therefore, they did not need to crave or seek out extra sources of salt.
In addition to taste receptors for salty, sweet, sour and bitter flavours, dogs have additional taste receptors for fats and meat-related chemicals, which is why dogs prefer meat and meat-flavoured treats above other foods.
Dogs also have specific taste buds, not found in humans, which are tuned for water. These taste buds are most sensitive after a dog has eaten salty or sugary foods. Since dogs’ wild canid ancestors ate diet consisting of mostly meat, which is high in sodium, these special taste buds help motivate a dog to seek out water to maintain proper fluid balance in the body.
Dogs, like humans, are social animals, and have an innate drive for contact. Puppies, born blind and deaf, have an instinct to huddle with their mother and littermates. Wolves have been observed to make a move to touch one another approximately 6 times per hour. Also like people, dogs have individual preferences when it comes to the amount and type of contact they prefer. Nearly all dogs, however, do not like to be touched directly on the head or muzzle. Above a dog’s eyes, below their jaw and on their muzzle are special whiskers called vibrissae. These whiskers have pressure-sensitive receptors at their ends, and can detect air currents and subtle vibrations, making the head an especially sensitive part of a dog’s anatomy. Many dogs are more comfortable being pet on the chest, shoulders and base of the neck; a good thing to remember when you’re interacting with an unfamiliar dog.
Horowitz, Alexandra, Inside of a Dog: What Dogs See, Smell and Know (New York: Scribner, 2000).