Five Basic Senses of the Dog
Dogs have the same five basic senses as people – hearing, taste, olfaction, sight and touch. However, dogs have each of these senses in different degrees than people. This can cause communication difficulties between dogs and people, since each perceives his environment in a different way. This paper will summarize the five basic senses of the dog, and how they compare to the five basic senses of people.
A dog’s ability to hear is overall greater than a human’s ability. Dogs are able to hear sounds at a much higher frequency, which are inaudible to humans. They can also hear sounds at a much lower intensity (quieter or farther away) than humans. Many dogs also have the capability to move their ears independently in all directions, to help them determine where a sound is coming from. This ability is of course stronger in dogs with pricked ears than those with floppy ears. Dogs have been able to place a source of a sound to within 4 degrees of its location by moving each ear independently to trace the sound. (Beaver, 1999, p. 50) Most humans can hear sounds at a frequency between 20Hz and 20,000Hz, while dogs can hear sounds between approximately 20Hz and 40,000Hz. (Page, 2007, p.117) Some dogs can hear sounds at up to 100,000Hz. (Beaver, 1999, p.50)
The sense of taste is similar in people and dogs, but people have a much greater ability to taste than dogs. Humans have around 9,000 taste buds while a dog has less than 2,000. (Page, 2007, p.106) Dogs also do not have any taste buds that respond to salt. They are generally repelled by sour or bitter things, hence the success of products like “Bitter Apple” – a taste deterrent used to keep dogs from chewing on unwanted objects. Dogs are carnivores and prefer meat to vegetables. They have also been shown to prefer their meat cooked instead of raw. If a dog is given a wide variety of foods as a puppy, it will be more likely to adjust to new foods later in life, similar to humans. However, studies of dogs trained to validate specific flavors show their selections are made primarily by the sense of smell instead of taste. (Beaver, 1999, p. 51)
Dogs have a much stronger sense of olfaction than humans. Human brains are structured around vision and processing light-related data, while dog’s brains are structured to process scents. A dog’s brain devotes about 40 times more of its brain to scent than the human brain does. According to recent research, animals with better vision generally had a worse sense of smell. In humans, about 60% of the 1000 genes for olfactory receptors are so-called pseudogenes that have been decommissioned. But dogs, which are colorblind, have only about 20% pseudogenes. (Holden, 2004) Scientists theorize that the tradeoff is likely due to anatomical constraints.
It has been estimated that dogs can identify smells somewhere between 1,000 to 10,000 times better than humans can. (Coren, 2004, p.51) Dogs can move one nostril at a time, which helps them to determine what direction a scent is coming from. Different breeds have various numbers of scent receptors. A bloodhound has about 300 million scent receptors, while a dachshund has 125 million. Humans, in comparison, have around 5 million scent receptors. While humans are more likely to sense just one scent at a time - whichever is strongest; a dog can smell several scents and separate them in his brain at the same time.
Dogs cannot see in detail or color in the same way people can. The visual acuity in dogs is much less than a normal human. They also do not see in colors as well as people. However, they can see better in dim light, and have better motion perception ability. Dog’s eyes are structured differently than human’s eyes. Dogs don’t have foveas, so their vision is grainy and they have a reduced depth of field. Instead, they have a horizontal streak of cones across the retina, which provides them with high acuity in seeing anything in motion. Dogs can discriminate individual flickers of light at rates much higher than humans. Humans can detect 50-60 Hz, while dogs can detect 80+ Hz. (Beaver, 1999, p. 47) Dogs have a reflecting tapetum behind the retina of the eye, which acts as a mirror to make use of any light that was not picked up by the photosensitive cells. This tapetum is what causes a dog’s eyes to “glow”, or reflect light, at night. The tapetum basically increases the sensitivity of the eye in low light, but in return it reduces the level of detail that dogs can see. Dogs see some colors, but not as many as humans. Their “rainbow” is restricted to basically yellow, gray and blue. This is known as dichromacy, and it is because they have a different type of cone photo-receptors than humans. (Neitz, Carroll & Neitz, 2001) Dogs also see in a wider arc than humans, so they have much better peripheral vision. However this means they have a reduced range of depth perception, since depth is determine by seeing the same object with both eyes.
Touch is the earliest and according to some veterinarians, the most important of all the canine senses. (Page, 2007, p.102) Just like in human babies, touch is crucial to the development of puppies. While touch is an important sense for both dogs and people, the main difference is in where the touch receptors are located. Some areas of a dog’s body are more sensitive to touch than others, because touch receptor nerves are present in greater numbers in those areas. This includes the muzzle and the lips, as well as the foot pads in dogs. A dog’s foot pads have specialized nerves that react to vibration, in order for the dog to know how stable the surface is. The vibrissae in dogs are also very sensitive. Almost half of the area of a dog’s brain that is involved in touch is lit up by touches to the face, and in particular the upper jaw where the vibrissae are (Page, 2007, p.103). Vibrissae can help dogs “see” in the dark by sensing air currents that will let the dog know when he gets too close to an object.
Because human and canine senses are experienced in different degrees, it is helpful for humans to be aware of how their dog senses the world. For example, if you are trying to get the attention of your dog from a distance, it is important to note that the dog will see you much better if you are moving. Also, dogs that are blind can be helped by placing scents, such as peppermint extract, around doorways to help them navigate in a house. By knowing how a dog uses his senses to perceive the world, humans can find new ways to communicate more effectively with their dogs.
References:
Beaver, B. (1999) Canine behavior: a guide for veterinarians. Philadelphia: W.B. Saunders Company.
Coren, S. (2004) How Dogs Think. New York: Free Press.
Holden, C. (1/30/2004) An Eye for a Nose. Science, 303(5658), 621-621.
Neitz, J., Carroll, J., Neitz, M. (January 2001) Color Vision. Optics & Photonics News, 26-33.
Page, J. (2007) Dogs: A Natural History. New York: HarperCollins Publishers Inc.
