How Dogs See the World: Some Facts About the Canine Cosmos
To become fluent in dog, it's essential to know how their eyes work.
Posted March 5, 2019
We tend to think of humans as visual mammals and dogs as olfactory and auditory mammals, but science is challenging these stereotypes. The visual world we make available to our dogs is worth considering because it can impact their well-being. Let’s consider the canine visual cosmos.
Visual acuity in humans is often described using what’s called the Snellen fraction, which is the well-known ratio of “20/20” or “20/40” that represents the quality of one’s eyesight. Dogs have a Snellen fraction of 20/75. This means that what we can see at 75 feet, a dog can see only at 20 feet. Using this method of measuring acuity, dogs have worse vision than humans. But it would be wrong to claim that dogs don’t see as well as humans since the Snellen fraction provides only one small window into the larger sense of sight. It would be more accurate to say that dogs and humans see the world differently. The visual acuity of dogs evolved to meet dogs’ unique needs, and different doesn’t necessarily mean better or worse.
Dogs are visual generalists, meaning that their eyes work well in a range of different light levels. They likely can see better at dusk and in the dark than humans. It’s been estimated that dogs can see in light about five times dimmer than humans can. Dogs are also better adapted than humans for identifying movement in their peripheral vision. However, dogs are not as good as humans at seeing things in detail. One reason for this may be that dogs can’t easily distinguish between the colors red and green. A red ball thrown in a field of green grass will be challenging to see even for a Labrador retriever. Other aspects of vision include depth perception, the visual field of view, and sensitivity to motion. In each of these areas, dog vision is different from human vision, as visual capacities have adapted to each species’ needs.
One of Jessica Pierce and my mantras throughout Unleashing Your Dog: A Field Guide to Giving Your Canine Companion the Best Life Possible is that there is no universal “dog.” Dogs come in a huge variety of shapes and sizes, and their sensory capacities may vary based on these differences. In the realm of sight, for instance, different breeds appear to have different visual strengths. In her book Being a Dog: Following the Dog Into a World of Smell, Dr. Alexandra Horowitz suggests that variations in canine visual acuity may be related to the shape and size of the nose (Pages 204-205). Short-nosed dogs like pugs tend to have better up-close vision, while dogs with long noses have better panoramic and peripheral vision. This may help explain why short-nosed dogs are often less interested in chasing balls and Frisbees than their longer-nosed kin. It is more difficult for them to see a ball and track its movement, which makes it a lot less interesting to chase.
Many human companions report that their dog will bark at someone wearing a hat or sunglasses or walking on crutches. Dogs often get spooked by things they don’t visually recognize. Loss of visual acuity is common in older dogs, just as it is in people, and dogs who are visually impaired need a little extra help in interacting with their world. Their behavior may change, too. At 15 years of age, Jessica Pierce's dog Maya has lost the use of one eye and has relatively poor vision in the other. She’s started to bark at people on walks, particularly people who stand about three feet away, right in what seems to be a blind spot. Loss of vision can lead to anxiety and social withdrawal if we aren’t careful to help our canine companions adapt. That said, loss of sight, even complete blindness, does not mean that a dog has a poor quality of life. Blind and visually impaired dogs can adapt quite well to their disability, though they need special care and consideration. Often these dogs adapt by relying more heavily on other sensory input, such as sound and smell, and they can be trained to follow olfactory cues or “smell hints,” such as a puff of citrus essential oil.
A challenge for future research with dogs is to learn not only how each sense works on its own, but also how dogs combine and use the input from multiple senses — how they use composite signals — to understand the world and to make decisions. For instance, one study by dog researcher Ludwig Huber showed that captive dogs could integrate information from sight and sound to identify other dog breeds correctly. In this study, dogs matched a projected visual image of dogs of different sizes with the vocalization that is usually made by dogs of each size. This kind of composite signal may help Maya determine, from quite far off, that she sees a poodle so that she can get her hackles raised in anticipation. For whatever reason (and no offense intended), Maya is not too keen on poodles.
It’s important for dogs to be able to read one another accurately in order for social interactions to go well. The same is true in the human realm, which is one reason that highly successful people tend to be those with high levels of emotional intelligence and well-honed social skills. One of the reasons dogs can get into sticky situations with one another is when they misread visual or other signals, and some dogs are much better at reading signals than others. Spend any time at a dog park, and you will certainly notice a few dogs who are socially awkward and don’t seem very good at interacting with other dogs. Oftentimes, these dogs have trouble finding play partners. In Canine Confidential: Why Dogs Do What They Do, I noted that there often seems to be a relationship between the social skills of a dog, or lack thereof, and those of their human, but that’s another story.
How do dogs recognize "dog"?
One of the mysteries of a dog’s world is how they recognize other dogs as belonging to the category “dog.” Obviously, dogs recognize other dogs by smell, but they also seem able to recognize other dogs using only sight. A very interesting study conducted by Dominique Autier-Dérian and her colleagues found that dogs can identify other dogs using facial features alone, in the absence of other cues such as movement, scent, and sound. Dogs were very good at picking out the faces of other dogs, among human and other domestic and wild animal faces. C. Claiborne Ray, discussing this study, remarked, “Ranging in size from a tiny Maltese to a giant St. Bernard, and showing myriad differences in coats, snouts, ears, tails and bone structure, dogs might not always appear to belong to one species. Yet other dogs recognize them easily.”
In an essay called "Do Dogs Recognize "Dog" and What They're Feeling From Afar?" I discuss observations from people who claim their dog knows "dog" from great distances and if they're friendly or not. Currently, we really don't know how they do this, but it's possible that composite signals consisting of input from smell, sight, and sound might help them discriminate "dog" and perhaps mood. However, this doesn't seem likely under the conditions in which it's been reported, "My dog knows 'dog' from afar." Given what we now know about the sensory systems of dogs and the information that might be used for them to be able to know "dog" and perhaps assess mood from afar, I wonder if there's some sort of "dog-gestalt" that dogs are able to use, a composite signal perhaps, but we don't have any data that support this possibility. Along these lines, some people have suggested that gait is a key variable, so sight might be paramount in combination with input from other senses. While I also lean toward sight being a key variable, we don't know if this is so.
We often hear dog owners say something like, “My vizsla loves other vizslas more than any other kind of dog, and she also knows they are vizslas.” Can dogs really recognize other dogs of the same breed? Nobody knows, but a lot of anecdotal evidence suggests that they might. If they do, it is likely that the cues lie in the dog’s olfactory sense, and perhaps in the identification of what’s called the major histocompatibility complex, or MHC. The MHC is a set of surface proteins found on the cells of all mammals, and it is involved in immune function. It’s thought to play a role in the selection of mates who are not too closely related genetically. The MHC may present as a kind of olfactory “signature” allowing dogs to determine genetic familiarity, but there hasn’t been any research in this area. Nonetheless, many people believe their dog shows a preference for others of their same breed.
Other topics we consider in Unleashing Your Dog in the section called "Sight" are "Let Dog-Dog Interactions Flow," "Tales about Tails," "Dogs 'Speak' with Their Ears," "Face the Facts: Expressions Matter," and "Your Dog Is Watching: Nonverbal Communication and Emotional Intelligence." In our discussion of the importance of dog tails, we also consider the question: What if a dog loses their tail? Stanley Coren tells a story about a dog whose tail had to be amputated after an unfortunate dog-motorcycle collision. Other dogs seemed unable to understand what she was trying to communicate. My friend, Marisa Ware, told me the story of her dog, Echo, who lost her tail in an accident. After the loss, Echo changed the way she communicated with dogs and people by using her body and ears to compensate for the loss of her tail. Tailless Echo now relies more heavily on her ears to express her feelings. When she is excited to see someone, she puts her ears very far back and will almost wiggle them. She also has developed a kind of “hop-wiggle,” taking a little hop and wiggling her butt very quickly if she is excited to see someone. Echo never did the “hop-wiggle” before losing her tail. The long and short of it, if you will, is that tails are important to dogs. Thus, tail docking is a freedom inhibitor (and a form of disfigurement) that limits a dog’s ability to communicate. We are in support of enlightened breed standards that don’t involve cutting off puppies’ tails.
Like a tail, a dog’s ears are an important visual signal in dog-dog and dog-human interactions. Take the time to watch your dog’s ears closely, since they can be a good indicator of how your dog is feeling. Ears are part of the group of composite signals — which include a dog’s face, body, tail, vocalizations, gait, and odors (some of which we are only partially privy to) — that complete the sentence of what a dog is feeling.
Dogs also rely on vision to read human faces. In one study of dogs and human facial expressions, a team of scientists led by Corsin Müller demonstrated that dogs differentiate between happy and angry human faces and that dogs find angry faces to be aversive. In a related study, Natalia Albuquerque and colleagues examined the behavior of dogs in response to emotionally relevant visual cues from humans. The team compared the responses of dogs to happy and angry human facial expressions and found that dogs engaged in mouth-licking in response to angry expressions. Dogs mouth-licked when they saw images of angry human faces, but not when they heard angry voices, emphasizing the importance of the visual cues. Mouth-licking can be an appeasement signal during dog-dog communications, and it may similarly serve as a way for a dog to respond to perceived negative emotion in a human companion. (An “appeasement behavior” inhibits or reduces the aggressive behavior of a social partner.) In the study, dogs engaged in mouth-licking more often when looking at images of humans than of other dogs, suggesting that dogs may have evolved their sensitivity to human facial expression to facilitate interactions with us. Dogs can also tell us we're angry when we don't know we are. (See "Can Dogs Tell Us We're Angry When We Don't Know We Are?")
In another study, researchers found that the hormone oxytocin (which is associated with feelings of trust and affection) made dogs interested in smiling human faces and less threatened by an angry face. They concluded, “Oxytocin has the potential to decrease vigilance toward threatening social stimuli and increase the salience of positive social stimuli thus making eye gaze of friendly human faces more salient for dogs.” In other words, oxytocin likely plays a key role in the development of the human-canine bond.
We also know that dogs watch us very closely, and it’s astonishing how skilled dogs are at untangling the complicated signals we send. We expect our dogs to understand us, but our communications are garbled. Most dog owners are “messy” signalers, in that they may give a verbal command without realizing that they are also giving visual signals. We tend to blame it on the dog when they don’t respond in the way we want; we think they are being stupid or stubborn. More likely, we are simply not being clear. One thing we can do to help our dogs is to approach training or teaching with an understanding of how closely dogs pay attention to all our signals, and we can try to align our verbal and nonverbal cues into a consistent and clear message. Paying closer attention to the nonverbal aspects of training could help many people and dogs work better together. Research conducted by Anna Scandurra and colleagues suggests that gestures are more salient to dogs than verbal cues.
Even a leashed or otherwise tethered dog can be "unleashed" and given the freedom to allow them to sense what's around them. There are large individual differences among dogs, and it's essential to pay close attention to what each dog wants and needs. When it comes to dog-human interactions, non-verbal visual signals, including gestures and facial expressions, may be equally or more important than verbal signals.
The more we learn about how dogs sense the world, the more we can do to give them — and us — the best lives possible. People who choose to share their homes and their hearts with dogs, along with those who try to train/teach dogs to interact with other dogs and to live in a human-oriented world, will benefit from becoming dog literate. It's not asking too much for them to become fluent in "dog"; it's a lot of fun to do, it's a good way to develop strong and long-lasting bonds, and it's a win-win for all.
Some of this text is excerpted from Unleashing Your Dog: A Field Guide to Giving Your Canine Companion the Best Life Possible. I thank Jessica Pierce for her collaboration on this and other projects.
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