Every species existing on earth has its own orchestra of senses, and a uniquely designed mental processor designed to assemble sensory input into enough coherency to survive and reproduce. Cats most efficiently target small prey at dusk and dawn, Polar bears can walk in a direct line to food located 20 miles across the ice in still air. And dogs rely far more on their noses than on their eyes.
Sight
A dog has such poor vision compared to a human that you and I would feel nearly blind with a dog's eyes in daylight. However, dogs see better than do humans in very low light. I suppose the dog would feel blind at night with our eyes.
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| Canine Vision |
To see life through the mind of a dog, you must resist the natural inclination to imagine that a dog has a version of your senses like the images above. To help you enter the mind of a dog, consider how a human sees color and detail in our environment.
It seems that what we see on a sunny day are the very photons that reflect off objects in our field of vision. In fact, the reflected light never reaches our brain; that's not what we see. The photons die at the back of the eye where they trigger electrical impulses that carry the encoded visual information (in the darkness of our skull) through nerve cells to the brain. Then, incomprehensible (to me), the brain decodes the information and "displays" a detailed, colorful, three-dimensional view of the world around us. This is important because what we "see" is the product of the brain, not the light "out there".
Humans have distinct senses that are only loosely integrated by the brain. We hear thunder but unless we see the lightning we have only a vague notion of the direction it traveled to reach us because our sense of directional sound (called binaural spectral-difference cueing) is relatively weak. We smell a skunk but can't pinpoint its precise past or present location because our sense of smell also is not highly directional. The location of things in our environment is only precise for our sight and touch. Our sight precisely locates objects using biocular vision that our brain decodes by combining separate impulses from each eye, and processes a three dimensional model of our environment.
Scent
In contrast to humans, dogs have tightly integrated senses. Dog's collect far more non-visual sensory information than humans and the dog's brain processes that information very differently. We know more about a dog's sense of smell than about the other canine senses. For example, dogs breathe in through two nostrils much like humans. But the similarity in the sense of smell ends there. As the air enters the nose, sensors in the nasal cavity capture and sort molecules using about 200 - 300 million scent receptors compared to our 5 million. These scent receptors send electrical impulses to the olfactory bulb in the dog's brain and send information on to the frontal cortex for recognition, and on further to other centers in the brain that sort out memories, emotions, etc. The frontal cortex and the other centers in the brain are interconnected in ways that have no human counterpart but we can surmise that the dog's scent-filled world is as brightly displayed in their minds as is our vision. Just as we can spot a dandelion in the middle of a lawn, a dog can "spot" a single pea in a beef stew.
In addition to the traditional scent receptors, dogs have an odd sense receptor completely unfamiliar to humans called Jacobson's Organ (aka the Vomeronasal Organ). As air enters the dog's nostrils, it is partly routed to Jacobson's Organ where large molecules, often having no detectable odor, are sorted and encoded to be interpreted by portions of the brain beyond the normal sense of smell. The two separate scent systems are integrated by the brain to provide more information combined than the sum of the two alone.
Dogs have many more superior sensory abilities. For the sake of brevity, I will summarize them: 1) air enters the dog's nostrils but exits through separate holes in the nose to enhance the mixing and sorting of odors; 2) dogs have the scent equivalent of biocular vision and can precisely locate the source of scents much like our eyes; 3) dogs have the ability to detect the age of scents even to the extent of knowing in which direction a person walked by smelling a couple of footsteps hours old; 4) while dogs lack acute vision, their ability to detect motion (the Frisbee) is much more acute than is ours. Think of a dog's sense of smell as being as rich and useful to them as our sense of sight is to us. In fact, dogs devote proportionately more of their brain to smell than we do to sight. Their brain is 10% the size of ours on average but the portion of the brain devoted to smell is 40 times larger. It must result in a brilliant display of their environment.
Hearing
Hearing is the dog's second-best sense. Dogs can hear sounds 4 times farther away than you and I. They can hear frequencies twice as high as we mere humans. What I found most interesting about high-frequency hearing is not only that prey (rodents, for example) make high-frequency sounds, but that binaural spectral-difference cueing is much more precise at high frequencies. When sound arrives at a dog's ears, it casts a "shadow" on the ear farthest from the sound. The brain then uses this shadow to locate the source of the sound.
This shadow cues a dog to the direction of the source of the sound analogous to how your shadow tells you where the sun is located. The higher the frequency and the farther apart are the ears, the more distinct is the cue. Large dogs do well with frequencies in the range of 40kHz, about twice what humans can hear. A mouse needs twice that, near 90kHz to get similar directional acuity because the rodent's ears are much closer together. The result is that dogs hear frequencies higher than do humans to more precisely locate the location of a sound.
But that's not the end of the difference between dogs' and human's hearing. Dogs have nearly 20 muscles in their ears to fine-tune the shape and position of ears to enhance sound locations. The result is that dogs can locate sound sources nearly as accurately as humans use sight.
Other Senses
Dogs also have many other senses we can't truly imagine by extrapolating our own experiences. I once blew into Pooch's face; he reacted as if I had punished him. This upset me and I never forgot it. What I now know is that 40% of the sensory cortex that provides dogs with information from different body areas is devoted to their muzzle. Dogs need a lot of information about what is going on near their snout. Whiskers act much like a blind person's cane. Blowing in Pooch's face kicked his cane away. Whiskers communicate information about the texture and location of objects and help avoid injury to the face in very low light conditions. Whiskers coordinate with trigeminal nerves in the face to sense chemical stimulation near, and in, the mouth.
A dog's thermoreceptors sense cold well but not heat. A dog's heat sensors are located around the nose. Dogs do however appear to sense heat but very differently than we.
One thing we do know about dogs is they love to be pet, especially on the chest, shoulder, belly, and base of the tail. Human touch causes a release of the bonding hormone, oxytocin. In humans, oxytocin is released in both mother and baby when they interact. Gazing into a dog's eyes and petting it has a similar effect. Both the dog and the human experience a rise in oxytocin lowering their blood pressure and reducing their heartbeat. The unique bond between humans and dogs is attributed to this hormonal relationship.
The Big Picture
We see that the pieces of a dog's sensory experiences are quite different than ours. However, perhaps the biggest difference between our human experience and that of a dog is in how the brain processes all the pieces. We piece together fragments of sound with fragments of sight to connect a train and its whistle. In other words, sensory connections are made with logic, reason, and neural connections unique to each species.
A dog assembles sensory information more directly and holistically. Your dog instantly and naturally reads your moods, intentions, pending actions, and other meaningful (to a dog) behaviors better than any other animal including humans and chimpanzees. The processing centers in a dog's brain connect to integrate emotions, memories, sight, smell, etc. into a single coherent understanding of your state of mind and its context. You hear that dogs live "in the moment". This likely is true. But that does not mean a dog has no history or can't learn from life's experiences. The past is embedded in the dog's brain as it pertains to the present. I doubt we as humans can ever really understand how profound an effect this has on how a dog sees the world. I don't try other than to recognize that the present context is what matters to a dog with it's past integrated into the "now" in ways we cannot truly understand.
Context is particularly critical to a dog's understanding and behavior. One woman writes that her dog learned to find her husband. "Go find Jim" would trigger a search through the house ending at Jim. She then transferred the command to anticipating Jim's arrival from work. The command would send the dog to the front window eagerly watching for Jim. One day, the dog and Jim were in the same room. "Go find Jim" sent the dog running to the window in eager anticipation of - well, something exciting that only a dog can understand.
Hearing is the dog's second-best sense. Dogs can hear sounds 4 times farther away than you and I. They can hear frequencies twice as high as we mere humans. What I found most interesting about high-frequency hearing is not only that prey (rodents, for example) make high-frequency sounds, but that binaural spectral-difference cueing is much more precise at high frequencies. When sound arrives at a dog's ears, it casts a "shadow" on the ear farthest from the sound. The brain then uses this shadow to locate the source of the sound.
This shadow cues a dog to the direction of the source of the sound analogous to how your shadow tells you where the sun is located. The higher the frequency and the farther apart are the ears, the more distinct is the cue. Large dogs do well with frequencies in the range of 40kHz, about twice what humans can hear. A mouse needs twice that, near 90kHz to get similar directional acuity because the rodent's ears are much closer together. The result is that dogs hear frequencies higher than do humans to more precisely locate the location of a sound.
But that's not the end of the difference between dogs' and human's hearing. Dogs have nearly 20 muscles in their ears to fine-tune the shape and position of ears to enhance sound locations. The result is that dogs can locate sound sources nearly as accurately as humans use sight.
Other Senses
Dogs also have many other senses we can't truly imagine by extrapolating our own experiences. I once blew into Pooch's face; he reacted as if I had punished him. This upset me and I never forgot it. What I now know is that 40% of the sensory cortex that provides dogs with information from different body areas is devoted to their muzzle. Dogs need a lot of information about what is going on near their snout. Whiskers act much like a blind person's cane. Blowing in Pooch's face kicked his cane away. Whiskers communicate information about the texture and location of objects and help avoid injury to the face in very low light conditions. Whiskers coordinate with trigeminal nerves in the face to sense chemical stimulation near, and in, the mouth.
A dog's thermoreceptors sense cold well but not heat. A dog's heat sensors are located around the nose. Dogs do however appear to sense heat but very differently than we.
One thing we do know about dogs is they love to be pet, especially on the chest, shoulder, belly, and base of the tail. Human touch causes a release of the bonding hormone, oxytocin. In humans, oxytocin is released in both mother and baby when they interact. Gazing into a dog's eyes and petting it has a similar effect. Both the dog and the human experience a rise in oxytocin lowering their blood pressure and reducing their heartbeat. The unique bond between humans and dogs is attributed to this hormonal relationship.
The Big Picture
We see that the pieces of a dog's sensory experiences are quite different than ours. However, perhaps the biggest difference between our human experience and that of a dog is in how the brain processes all the pieces. We piece together fragments of sound with fragments of sight to connect a train and its whistle. In other words, sensory connections are made with logic, reason, and neural connections unique to each species.
A dog assembles sensory information more directly and holistically. Your dog instantly and naturally reads your moods, intentions, pending actions, and other meaningful (to a dog) behaviors better than any other animal including humans and chimpanzees. The processing centers in a dog's brain connect to integrate emotions, memories, sight, smell, etc. into a single coherent understanding of your state of mind and its context. You hear that dogs live "in the moment". This likely is true. But that does not mean a dog has no history or can't learn from life's experiences. The past is embedded in the dog's brain as it pertains to the present. I doubt we as humans can ever really understand how profound an effect this has on how a dog sees the world. I don't try other than to recognize that the present context is what matters to a dog with it's past integrated into the "now" in ways we cannot truly understand.
Context is particularly critical to a dog's understanding and behavior. One woman writes that her dog learned to find her husband. "Go find Jim" would trigger a search through the house ending at Jim. She then transferred the command to anticipating Jim's arrival from work. The command would send the dog to the front window eagerly watching for Jim. One day, the dog and Jim were in the same room. "Go find Jim" sent the dog running to the window in eager anticipation of - well, something exciting that only a dog can understand.