Dogs: An Exciting Journey Through Their Sensory Worlds (2024)

In a series of previous essays, I summarized the five major senses dogs use to navigate their social and nonsocial worlds either singly or by combining them into what ethologists call composite signals.¹ A major message of Jessica Pierce and my book Unleashing Your Dog: A Field Guide to Giving Your Canine Companion the Best Life Possible is that dogs need to be allowed to exercise their senses as well as their bodies, and when we permit them to do so they have better lives, leashed or unleashed. Jessica and I offer numerous suggestions for living with dogs in ways that enhance everyone’s quality of life and expand the freedoms for dogs to really be dogs. Allowing dogs to exercise their senses is critical for giving dogs the most freedom possible. All in all, dogs want and need much more than they usually get from us.

A number of people asked if I would summarize some general facts about dog sensory capacities, so that's what I do here in this brief fact-filled primer. Knowing how dogs smell, taste, touch, see, and hear the world around them is critical for understanding what they want and need and how we can allow them to be dogs.

Smell:

"It is said that a dog who has lost its sense of smell is no longer a dog." (Dr. Frank Rosell)

Dogs love to use their noses. It's been estimated that dogs sniff around 33% of the time when they're moving here and there and this is how they pick up all sorts of information about who's been there, whether a female is reproductively active (we don't know about males), how big they are, and perhaps what they're feeling. We all know that dogs' noses stray here and there, and often wind up in places that we label as disgusting or inappropriate, such as butts and groins of canine and human companions. Butts and noses often go together, because butts are a critical communication center for dogs. If dogs used social media, their version of Facebook would be nose-centered and likely be called Buttbook. For dogs, it's perfectly normal and dog appropriate to sniff wherever their noses lead them.

As visual creatures, the canine sense of smell is difficult for humans to understand and to appreciate. We can’t see odors. However, the dog’s nose is the organ most people are curious about because it’s so much more sensitive than our own, and dogs use it most of the time, often in ways we wish they didn’t. On many occasions, we simply don’t understand why they’re doing what they're doing as their nose leads the way. However, when we understand that "With 300 million receptors to our mere 5 million, a dog’s nose is estimated to be between 100,000 and 100 million times more sensitive than a human’s." Some details about which I write in "Dogs Should Be 'Unleashed' to Sniff to Their Noses' Content" include the following facts. The section of a dog's brain related to processing smells is almost seven times larger than ours. In addition, the dog’s fantastic sense of smell can be explained by the fact that dogs don’t exhale when sniffing a faint scent. This enables the dog to sniff faint odors without disturbing or destroying them. Dogs have a wing-like flap in each nostril that determines the direction of the airstream in and out of the nose. When the dog inhales, an opening above and beside this flap allows air to pass through. When the dog exhales, this opening closes and the air comes out below and beside this flap through another opening, enabling the dog to increase its collection of odors. As a result, the warm air that is exhaled flows backward and away from the odor being sniffed, preventing them from mixing. Dogs also use their nostrils differently according to the nature of the scent. During behavioral trials, when dogs sniffed at unfamiliar smells that were not dangerous, first they used the right nostril and then switched to the left nostril to sniff at the odors again. Once they had become familiar with the smell, the left side of the brain took over. When they sniffed sweat odors from veterinarians who worked at a kennel, they used only the right nostril. In short, the left and right sides of the brain take in different kinds of information. The right side of the brain is associated with intense feelings, such as aggression, flight behavior, and fear. For most dogs, a veterinarian is a frightening person.

Clearly, dogs love to use their noses and we should let them use this amazing organ as much as possible. It's also known that allowing dogs to sniff helps them think positively, so why not let them do something they love to do that's also good for them?

Taste: A dog's sense of taste is far less sensitive than our own. They only have around 1,700 taste buds, whereas we have about 9,000. Humans can taste all five flavors: salty, sweet, sour, bitter, and umami (savory). Dogs (as far as we know) taste only salty, sweet, sour, and bitter. It’s interesting to note how much variation there is in how well and what sorts of things other animals can taste. For example, pigs have a more sensitive sense of taste than we do, possessing about 14,000 taste buds. Chickens have only about 30 taste buds, while cats have around 470. During their evolution, cats lost the gene that detects sweet flavors.

In "Oh Goodness, Why'd My Dog Erin Just Eat Something So Foul?" I note that taste is an evolutionary adaptation for assessing whether something is edible, although the definition of “edible” clearly varies between dogs and humans. If you’ve ever watched dogs eat, you may wonder whether they taste anything at all as they vacuum down snacks and meals, chomping and spraying food far and wide. Although the table or bowl manners of many dogs are appalling by human standards of etiquette, they certainly enjoy what makes it into their mouths. In Unleashing Your Dog Jessica and I also discuss such topics as Tasting to Help Smell: A Dog’s “Second Nose," Eating Gross Stuff: Tasting the Wild, Always Provide Fresh Water, Let the Drool Fly, The Joys of Working for Food, Offer Food in Ways That Suit Your Dog, Help Your Dog Stay Fit and Trim, and Chewing Is Important. In Tasting to Help Smell we write about what some people refer to as a Dog's “second nose,” a structure called the vomeronasal organ (VNO) or Jacobson’s organ that has sensory neurons that detect chemicals and is used to enhance an odor by adding taste. Sometimes a dog’s teeth will chatter after they lick urine or some other strongly scented area, and they may engage in what some call “tonguing,” where the tongue is pressed rapidly and repeatedly against the roof of the mouth to help move chemicals into the VNO and thus help analyze a scent. It's also essential to remember that dogs don't agree with what we find to be icky, nasty, gross, rank, disgusting, and foul. Becoming "fluent in dog" and "dog literate" will help us understand what they want and need and why they do the things they do, When we do, it's a win-win for all.

Touch:

"Listen to what a dog is telling you and respect and honor and their preferences: Some dogs are touchy about being touched."

Dogs touch the world, quite literally, when they walk, run, play, and sniff. Part of an exploration of touch, then, involves physical activity, such as going on walks, romping around a dog park, and riding in a car. Dogs touch noses when they say hello, they may touch nose-to-butt to gather information about one another, and they touch us when they rub against our legs or curl up next to us in bed. And, of course, we touch our canine friends when we pet, groom, and hug them.

We know less about the canine sensory experience of touch than we do about their senses of smell or taste. We know little, for example, about how dogs perceive human touch and why some dogs seem to like being touched while others don’t. Does an aversion to touch develop during the socialization process, and what kinds of early experiences might lead dogs to feel uncomfortable rather than soothed by human touch? Why do some dogs simply seem to dislike human hands? In cases where a dog has an aversion to being touched, this needs to be honored, and we should always touch dogs on their terms, not ours. As with human-human touching, consent is important.

In Unleashing Your Dog, Jessica and I consider the following general topics that involve touch: Collars and Leashes: The Balance between Control and Freedom; Walking the Dog: On Exercise, Shared Time, and Power Struggles; Unleash Your Dog: Give Ample Off-Leash Time; Nurture Your Dog’s Friendships; Know Your Dog’s Petting Preferences; Signs of Affection: Hugging and Licking; Whiskers Are Sensational; and Dogs Dig Together Time; Dogs Also Need Alone Time. One of the most universal ways in which dogs are touched involves our leashing or otherwise tethering them. We mediate and control access to the physical and social worlds of our dogs quite a bit. We do this by deciding when, where, and for how long dogs get to be outside each day and, perhaps more subtly, by imposing the physical constraints of collars and leashes, which guide the speed and direction of a dog’s movements. These tools of control are often necessary, but we should remain alert to the diverse ways in which they can inhibit a dog’s freedoms and the ways these devices can themselves be harmful. Our goal should be to use these tools to facilitate access to a wide variety of positive physical and social experiences and to allow our dogs as much agency as possible. They should be leashed more for their safety, rather than for our convenience. Ultimately, a leash is simply a tool, a kind of umbilical cord between human and dog that can be used well or poorly. Used well, it gives dogs access to their world and can be a critically important freedom enhancer. Without leashes, dogs wouldn’t be able to go many places with us. Used poorly, the leash can become a source of severe physical and sensory deprivation and harm.

Concerning petting and hugging they're usually okay if it’s done on the dog’s terms, and the best advice is to err on the side of caution: When or if you’re unsure, don’t pet or hug. As always, pay close attention to the personality of the dog. Understand their preferences and signals of consent."

The bottom line is simple. Always, pay close attention to the personality each and every individual dog and what they like and what they don't like and pay careful attention to what they're telling you. By understanding and honoring their preferences and signals of consent, we can respect their individuality and not trespass into their personal space.

Sight: To become fluent in dog, it's essential to know how their eyes work and to consider the canine visual cosmos. 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. 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, 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.

Among the 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? It turns out that they can change how they rely on other senses when they've lost their tails. It also remains a mystery how dogs seem quite able to recognize "dog" and to read their mood from afar. (See "Do Dogs Recognize "Dog" and What They're Feeling From Afar?") It also turns out that visual and olfactory stimuli might combine to form a composite signal, such as when dogs scratch the ground after peeing or pooping or when they raise a leg but don't actually urinate. (See "Ground Scratching by Dogs: Scent, Sight, and Ecstasy" and Canine Confidential: Why Dogs Do What They Do.)

Hearing: Dogs’ ears come in many shapes and sizes—long and short, floppy and stiff, and all variations in between—and they are surprisingly mobile. More than 18 muscles control the pinna (or earflap) alone, which allows the nuanced movements that make dogs’ ears so expressive and so good at picking up sounds. Dogs move their ears to facilitate hearing; every dog owner will recognize the “pricked ears” of a dog who is suddenly attentive. The up-and-open ears allow dogs to best capture sound. The ear muscles also allow dogs to turn their ears like a periscope to follow the direction of a sound.

Dogs have far more sensitive hearing than humans and can detect much quieter sounds. Their sense of hearing is about four times as sensitive as ours, so what we hear at 20 feet, a dog can hear at about 80 feet. They also hear a lot of things we don’t because they can hear higher-frequency sounds. From available data, scientists suggest that dogs hear in frequencies as high as 67,000 cycles per second (also called hertz), while humans hear frequencies up to 64,000 cycles per second. This means there are some sounds that are inaudible to us but quite available to our dogs. For example, they can hear the high-pitched chirping of mice running around inside the walls or in the woodpile. Also, some of the electronics in our homes emit constant high-frequency sounds we don’t notice but which can be distressing to dogs.

In Unleashing Your Dog we consider different topics including Barks and Growls: The Language of Dogs, Whining and Whimpering: A Call for Help, Baby Talk and Your Dog, Turn Down the Volume: Protect Your Dog’s Hearing, Be Sensitive to Noise Phobias, and Dogs Need You, Not the Radio. Relatively little systematic research has been done on how dogs use sound and hearing in their interactions with the world and in their encounters with people and other dogs, but we do know that 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. Like a tail, a dog’s ears are an important visual signal in dog-dog and dog-human interactions.

People often want to know if dogs like basset hounds with long, floppy ears have a harder time communicating through ear positions. It’s possible that floppy ears don’t allow for quite as much expressiveness, but we really don’t know. As with tails, we support breed standards that don’t involve cropping or otherwise changing the natural shape of a dog’s ears. Doberman pinschers, Boston terriers, and Great Danes are a few of the breeds in which ear cropping is still common. During the ear-cropping procedure, the pinnae (earflaps) are altered. The pinna functions to funnel sound into the ear canal, and so dogs with cropped ears lose some acuity in their hearing; they also lose the ability to rotate the ear fully, and this makes it harder for them to communicate with their ears.

Take the time to watch your dog’s ears closely, since they can be a good indicator of how your dog is feeling. Watching dogs move their ears also is fun.

Play: A frenetic potpourri of the senses

One of the clearest examples of how different senses may be part of composite signals is play. Play obviously involves sight and touch, as dogs watch one another closely and chase, mouth, and wrestle with one another. Play also involves hearing and vocalizing, as dogs emit play pants and play growls, and smell might also play a role since odors are all-important to dogs. That only leaves taste, which is probably least important during play, but who knows? Perhaps when dogs mouth one another they are learning more than we realize. (See ".") When you watch your dog play, try to see how the their senses work with one another so that they can get the most out of romping around with their friends.

We must use what we know about how dogs sense their world to give them the best lives possible

I hope this journey into dogs' noses, mouths, fur and skin, eyes, and ears has been a useful exercise. It's a shame that many people know more about their mobile phones and other devices than their nonhuman companion. Companion dogs live highly constrained lives, and there's a lot we can easily do to give them considerably more freedoms and allow them to express their dogness in a human dominated world.

It's also important to remember that there is no "universal dog." Each and every dog is an individual with a unique personality. And, our relationships with dogs are grounded in and guided by personal values. Sometimes these are openly acknowledged, and sometimes they are unstated but reflected in our actions. People differ in how they choose to live with their nonhuman companions, but it is useful to make these values explicit if you have invited another animal into your life or plan to do so. The first question is the one we pose above: What do you consider to be a good life for your dog, and how can you help your dog achieve this kind of life? Make a list of your goals; write them down.

“Unleashing your dog” is both literal—dogs need more time off leash—and metaphorical. We need to continually work toward increasing the freedoms that our dogs experience, thereby unleashing their potential to live life to the fullest when they're untethered and when they're tethered. But, when we can, let’s unclip the leash and enhance the lives of the dogs we love so much. We must use what we know about how dogs sense their world even when it's not convenient to do so. As Jessica suggests, make a bucket list of what's good for your dog and try to dip into it each and every day. And always remember to let them exercise their senses along with their bodies. It's surely good for them, and what's good for them is also good for us and the relationships we form with our canine companions.

Some of the above 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.

¹For other essays about unleashing your dog whenever possible see "Dogs, Captivity, and Freedom: Unleash Them Whenever You Can," "Dogs Should Be 'Unleashed' to Sniff to Their Noses' Content," "Oh Goodness, Why'd My Dog Erin Just Eat Something So Foul?", "Being Touched Is Fine For Some Dogs, But Not for Others," "How Dogs See the World: Some Facts About the Canine Cosmos," "" and "10 Ways to Make Your Dog Happier and More Content."

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