Inside Of A Dog Part 7

At first glance these prey-tracking eyes look much like ours: viscous spheres fitted in sockets. Our eyes are about the same size as dogs'. Despite the fact that dogs' heads vary so significantly in size (four Chihuahua heads would fit in a wolfhound's mouth-not that anyone would deign suggest verifying such a thing), eye size barely varies between breeds. Small dogs, like puppies and infants, have large eyes relative to the size of their heads.

But small differences between the eyes of humans and dogs immediately become apparent. First, our eyes are smack in the front of our face. We look forward, and images in the periphery fall away to darkness around our ears. While there is variation among dogs, most dogs' eyes are situated more laterally on their heads in the manner of other quadrupeds, allowing a panoramic view of the environment: 250270 degrees, as contrasted to humans' 180 degrees.

If we look a little closer, we discover another key difference. The superficial anatomy of our eyes gives us away: it shows where we're looking, how we're feeling, our level of attention. While dog and human eyes are similarly sized, our pupil size-the black center of the eye that lets light in-varies considerably when we are in a darkened room or are aroused or fearful (expanding to up to 9 millimeters wide) or in the bright sun or are highly relaxed (contracting to 1 millimeter). Dogs' pupils, by contrast, are relatively fixed at about 3 to 4 millimeters, regardless of the light or the dog's level of excitement. Our irises, the muscles that control pupil size, tend to be colored to contrast with the pupil, blue or brown or green. Not so in most dogs, whose eyes are often so monochromatically dark that they remind me of bottomless lakes, repository of all attributions of purity or desolation we might ascribe to them. And the human iris sits amidst the sclera-the white-of the eye, while many (but not all) dogs have very little sclera. The anatomical sum effect is that we can always see where another person is looking: the pupil and iris point the way, and the amount of sclera revealed underlines it. Without a prominent sclera or a distinct pupil, the eyes of a dog don't indicate the direction of their attention nearly as much.

Closer still, and we begin to see serious species differences. Dogs manage to gather more more light than we do. Once light enters the eye of a dog, it travels through the gel-like ma.s.s that holds nerve cells to the retina (we'll get to that in a moment), then through the retina to a triangle of tissue, which reflects it back. This light than we do. Once light enters the eye of a dog, it travels through the gel-like ma.s.s that holds nerve cells to the retina (we'll get to that in a moment), then through the retina to a triangle of tissue, which reflects it back. This tapetum tapetum lucidum, lucidum, in Latin "carpet of light," accounts for all the photographs you have of your dog with brilliant light s.h.i.+ning out where their eyes should be. Light entering the dog's eye hits the retina at least twice, resulting not in the redoubling of the image but in a redoubling of the light that makes images visible. This is part of the system enabling dogs to have such improved night and low-light vision. While we might make out a match being brightly struck in the distance on a dark night, the dog could detect the gentle flame on the lit candle. Arctic wolves spend a full half of the year living in utter darkness; if there is a flame on the horizon, they have the eyes to spot it. in Latin "carpet of light," accounts for all the photographs you have of your dog with brilliant light s.h.i.+ning out where their eyes should be. Light entering the dog's eye hits the retina at least twice, resulting not in the redoubling of the image but in a redoubling of the light that makes images visible. This is part of the system enabling dogs to have such improved night and low-light vision. While we might make out a match being brightly struck in the distance on a dark night, the dog could detect the gentle flame on the lit candle. Arctic wolves spend a full half of the year living in utter darkness; if there is a flame on the horizon, they have the eyes to spot it.

EYES OF THE BALL-HOLDER.

It is inside the eye-at that retina receiving light twice-that, one by one, characteristic habits of dogs can be traced to their anatomy. The retina, a sheet of cells on the back of the eyeball, translates light energy into electrical signals to our brains, which leads to our feeling that we've seen something. Much of what we see is given meaning only by our brains, of course-the retina just registers the light-but without the retina, we would experience only darkness. Even slight changes in the conformation of the retina can radically change vision.

There are two slight changes in the canine retinae: in the distribution of photoreceptor cells and in the speed with which they operate. The former leads to their ability to chase prey, retrieve a tossed tennis ball, to their indifference to most colors, and to their inability to see something right in front of their noses. The latter leads to their being uninterested in daytime soap operas left on for them when their owners are out of the house. We'll look at these in turn.

Go get the ball!

Some of the most important things for humans to see are any other humans situated within a few feet of their face. Our eyes face forward, and our retinae have foveae: foveae: central areas with an extra abundance of photoreceptors. Having so many cells in the center of the retina means that we are very good at seeing things right in front of us in high detail, great focus, and strong color. Perfect for identifying that blob of color and form coming at you as your boyfriend or your mortal enemy. central areas with an extra abundance of photoreceptors. Having so many cells in the center of the retina means that we are very good at seeing things right in front of us in high detail, great focus, and strong color. Perfect for identifying that blob of color and form coming at you as your boyfriend or your mortal enemy.

Only primates have foveae. By contrast, dogs have what is called an area area centralis: centralis: a broad central region with fewer receptors than a fovea, but more than in peripheral parts of the eye. Things directly in front of a dog's face are visible to him, but they are not quite as sharply in focus as they would be for us. The lens of the eye, which adjusts its curvature to focus light onto the retina, doesn't accommodate to nearby sources of light. In fact, dogs might overlook small things right in front of their nose (within ten to fifteen inches), because they have fewer retinal cells committed to receiving light from that part of the visual world. You need no longer puzzle at your dog's inability to find the toy that he is nearly stepping on: he's not got the vision to take note of it until he takes a step back. a broad central region with fewer receptors than a fovea, but more than in peripheral parts of the eye. Things directly in front of a dog's face are visible to him, but they are not quite as sharply in focus as they would be for us. The lens of the eye, which adjusts its curvature to focus light onto the retina, doesn't accommodate to nearby sources of light. In fact, dogs might overlook small things right in front of their nose (within ten to fifteen inches), because they have fewer retinal cells committed to receiving light from that part of the visual world. You need no longer puzzle at your dog's inability to find the toy that he is nearly stepping on: he's not got the vision to take note of it until he takes a step back.

Breeds of dogs differ so much in their retinae that they see the world differently. The area centralis is most p.r.o.nounced in those breeds with short noses. Pugs, for instance, have very strong areas centralis-almost fovea-like. But they lack a "visual streak," which dogs with long noses (and wolves) have. In Afghans and retrievers, for instance, the area centralis is less p.r.o.nounced, and the photoreceptors of the retina are more dense along a horizontal band spanning the middle of the eye. The shorter the nose, the less visual streak; the longer the nose, the more visual streak. Dogs with the visual streaks have better panoramic, high-quality vision, and much more peripheral vision than humans. Dogs with the p.r.o.nounced area centralis have better focus in front of their faces.

In a small but significant way, this difference explains some breed-based behavioral tendencies. Pugs are not typically so-called "ball dogs" but long-nosed Labrador retrievers are. Not because of their long noses per se. In addition to their ability to put their millions of olfactory cells to good use, Labradors are visually equipped to notice, say, a tennis ball traveling across the horizon, without having to s.h.i.+ft their gaze. For a short-nosed dog (as for all humans of any nose length), a ball tossed to the side just disappears into the periphery if they don't follow it with their head. Instead pugs are probably better at bringing close objects into focus-say, the faces of their owners on whose laps they sit. Some researchers speculate that this relatively blinkered vision makes them more attentive to our expressions, and seem more companionable.

Go get the green ball!

Dogs are not color-blind, as is popularly believed. But color plays a much less important role for them than it does for humans, and their retinae are why. Humans have three kinds of cones, the photoreceptors responsible for our perception of details and of colors: each fires to red, blue, or green wavelengths. Dogs have only two: one is sensitive to blue and the other to greenish-yellow. And they have fewer of even those two than humans do. So dogs experience a color most strongly when it is in the range of blue or green. Ah, but a well-scrubbed backyard pool must seem radiant to a dog.

As a result of this difference in cone cells, any light that looks to us like yellow, red, or orange simply doesn't look the same way to a dog. Consequently, they seem perfectly oblivious when you ask them to bring back grapefruits from the store and grow irritated when they bring back tangerines. Still, orange, red, and yellow objects might still look different to them: the colors have different brightnesses. Red may be seen by them as a faint green; yellow a stronger one. If they seem to be able to discriminate red and yellow, they are noticing a difference in the amount amount of light these colors reflect toward them. of light these colors reflect toward them.

To imagine what this might be like, consider the time of day when our color system breaks down: in the dusk right before night. If you're outside in a park, in your yard, or anywhere nature lives, take a look around you. You might notice the wash of exuberant green leaves above you subtly dulling to a more una.s.suming hue. You can still see the ground underfoot, but details-the distinctness of blades of gra.s.s, the layers of petals-are reduced. Depth of field squashes somewhat. I tend to stumble more than usual on protuberant gray rocks that blend with the earth. The reason for this loss of visual information is anatomical. Cones, cl.u.s.tered toward the center of the retina, are not sensitive to low light, so they don't fire as often at dusk or night. As a result, our brains get signals from fewer cells detecting colors. And the near world flattens out a little: we can still see that there is color, and we still detect lights and darks, but the richness of colors has fallen away; colors are grainier, less detailed. So it might be for dogs, even at noontime.

As they do not experience a great range of distinct colors, dogs rarely show color preferences. Your clas.h.i.+ng choice of red leash and blue collar affects your dog not at all. But a deeply saturated color may get more attention from a dog, as will an object placed in a background of contrasting colors. It may be meaningful that your dog attacks and pops all the blue or red balloons left over after the birthday party winds down: they are most distinct among a sea of pastels.

Go get the green bouncing ball ... on the TV!

Dogs make up for their dearth of cones with a battery of rods, the other kind of photoreceptor in the retina. Rods fire most in low-light situations and at changes in light densities, which is seen as motion. In human eyes, rods cl.u.s.ter at the periphery, helping us notice something moving out of the corner of our vision, or when the cones slow their firing at dusk or night. The density of rods in dogs' eyes varies, but they have as much as three times as many rods as we do. You can make that ball your dog is not seeing directly in front of him magically appear by giving it a little shove. Acuity greatly improves for close objects when they are bouncing.

All these differences in the dog's perception, experience, and behavior result from some small changes in the distribution of cells on the back of the canine eyeball. And there is another small change that results in a large difference-potentially more far-reaching than a change in focal area or color vision. In all mammalian eyes, rods and cones make electrical activity out of light waves by means of a change in the pigment in the cells. The change takes time-a very small amount of time. But in that time, a cell processing light from the world cannot receive more light to process. The rate at which the cells do this leads to what is called the "flicker-fusion" rate: the number of snapshots of the world that the eyes take in every second.

For the most part, we experience the world as smoothly unfolding, not as a series of sixty still images every second, which is our flicker-fusion rate. Given the pace at which events that matter to us happen, this is usually plenty fast. A closing door can be grabbed before it slams; a handshake received before it is withdrawn in annoyance. To create a simulacrum of reality, films-literally "moving pictures"-must exceed our flicker-fusion rate only slightly. If they do, we do not notice that they are just a series of static pictures projected in sequence. But we will will notice if an old-fas.h.i.+oned (pre-digital) film reel slows down in the projector. While ordinarily the images are being shown to us faster than we can process them, when it slows we see the film flickering, with dark gaps between the frames. notice if an old-fas.h.i.+oned (pre-digital) film reel slows down in the projector. While ordinarily the images are being shown to us faster than we can process them, when it slows we see the film flickering, with dark gaps between the frames.

Similarly, fluorescent lights are so annoying because they operate too close to the human flicker-fusion rate. The electrical devices used to regulate the current in the light function right at sixty cycles per second, which those of us with slightly faster flicker-fusion rates can thus see as a flicker (and hear as a buzz). All indoor lights fluorescently flicker to houseflies, with extremely different eyes than ours.

Dogs also have a higher flicker-fusion rate than humans do: seventy or even eighty cycles per second. This provides an indication why dogs have not taken up a particular foible of persons: our constant gawking at the television screen. Like film, the image on your (non-digital) TV is really a sequence of still shots sent quickly enough to fool our eyes into seeing a continuous stream. But it's not fast enough for dog vision. They see the individual frames and the dark s.p.a.ce between them too, as though stroboscopically. This-and the lack of concurrent odors wafting out of the television-might explain why most dogs cannot be planted in front of the television to engage them. It doesn't look real.*

One could say that dogs see the world faster than we do, but what they really do is see just a bit more more world in every second. We marvel at dogs' seemingly magical skill at catching a Frisbee on the fly, or following a rapidly bouncing ball. Their Frisbee-catching procedure, as has been doc.u.mented with microvideo recording and trajectory a.n.a.lysis, turns out to match nicely the navigational strategy naturally used by baseball outfielders to line themselves up with the arc of an incoming ball. Excepting a few phenomenal outfielders, dogs actually see the Frisbee's, or the ball's, new location a fraction of a second before we do. Our eyes are internally blinking in those milliseconds that a flung Frisbee is moving along its course toward our heads. world in every second. We marvel at dogs' seemingly magical skill at catching a Frisbee on the fly, or following a rapidly bouncing ball. Their Frisbee-catching procedure, as has been doc.u.mented with microvideo recording and trajectory a.n.a.lysis, turns out to match nicely the navigational strategy naturally used by baseball outfielders to line themselves up with the arc of an incoming ball. Excepting a few phenomenal outfielders, dogs actually see the Frisbee's, or the ball's, new location a fraction of a second before we do. Our eyes are internally blinking in those milliseconds that a flung Frisbee is moving along its course toward our heads.

Neuroscientists have identified an unusual brain disorder in some humans called "akinetopsia." These akinetopsics have a kind of motion blindness: they have difficulty integrating a sequence of images into the normal perception of motion. A person with akinetopsia may begin pouring a cup of tea and then not register a change until many images later, by which time the cup is overflowing. As non-brain-damaged persons are to akinetopsics, dogs are to us: they see the interstices between our moments. We must always seem a little slow. Our responses to the world are a split second behind the dogs'.

VISUAL UMWELT.

With age, Pump suddenly became reluctant to enter the elevator, perhaps not seeing it well in the darkness after being outside. I encourage her, or jump in myself first, or throw something light-colored on the elevator floor for her to see. Finally, every time, she rallies and leaps in, as though crossing a great creva.s.se, brave girl.

So dogs can see some of the same things we do, but they don't see in the way that we do. The very construction of their visual capacity explains a broad swath of dog behavior. First, with a wide visual field, they see what is around them well, but what is right in front of them less well. Their own paws are probably not in terrific focus to dogs. What wonder then how little they use their paws, relative to our reliance on the end of our forelimbs, to manipulate the world. A small change in vision leads to less reaching, grabbing, and handling.

Similarly, dogs can bring our faces into focus, but detect eyes less well. This means they will catch your full facial expression better than a meaningful glare, and they will follow a point or a turn better than a surrept.i.tious glance out of the corner of the eye. Their vision complements their other senses. While they can locate a sound in s.p.a.ce only roughly, their hearing is good enough for them to turn their eyes in the right direction, so they can search further visually ... and then examine closely by nose.

For instance, dogs recognize us by our smells-but they also clearly look at us. What are they seeing? If your smell is not available-you are downwind or you're covered in perfume-they can use visual cues exclusively. They will hesitate if they hear your voice calling them, but it is not your face atop the approaching person, or your particular walk, or your mouth moving to call their name. Recent research confirmed this by examining dogs' behavior when they heard their owner's voice or a stranger's voice, accompanied by either a picture of the owner's face (on a large monitor) or of a stranger's face. The dogs looked longer at the incongruous faces: the owner's face, when paired with a stranger's voice, and the stranger's face, when it appeared with the owner's voice. If it were just that the dog preferred the owner's face, they would have always gazed at that face the longest. Instead they looked longest when there was something surprising: a mismatch.

The physical elements of vision define and circ.u.mscribe what the dog experiences. There is a further element of that experience: the role vision plays in the hierarchy of senses. For visual creatures like humans, there is particular delight when we encounter something through one of our non-visual senses first. To arrive outside my apartment door and smell something wonderful-to open the door and hear the sounds of sizzling in pots, the clank of silverware; to be instructed to taste a forkful of the pot's contents with my eyes closed-renders a familiar experience new. I only come forth to verify the scene with my eyes: my boyfriend in front of me with dinner in messy preparation around him.

Coming to something through the secondary senses first dis...o...b..bulates, then introduces a feeling of novelty to the ordinary. As dogs have their own hierarchy of senses, I imagine that they too might feel the mystery of coming at something by means other than their nose. This may explain both the difficulty dogs have in understanding some of our first requests to them (off the couch! I said to my new puppy, as she looked at me searchingly), and the pride they seem to take in learning a distinction from our visual world. I said to my new puppy, as she looked at me searchingly), and the pride they seem to take in learning a distinction from our visual world.

Though our visual worlds overlap, dogs attach different meanings to the objects seen. A Seeing Eye dog must be taught the umwelt of the human: the objects that are important to the blind person, not those of interest to the dog. Try yourself getting your dog to even acknowledge the existence of a sidewalk curb. What is a curb to a dog? With persistence, dogs can be taught, but most dogs simply do not see see a curb: it is not that the curb is invisible, but that it lacks any important meaning to them. The surface below their feet may be rough or soft, slippery or rocky, it may hold the scent of dogs or of men; but the distinction between the sidewalk and the street is a human distinction. A curb is but a slight variation in alt.i.tude of the hardened ma.s.s with which we cover the dirt, which only has a meaning to those who concern themselves with such concepts as a curb: it is not that the curb is invisible, but that it lacks any important meaning to them. The surface below their feet may be rough or soft, slippery or rocky, it may hold the scent of dogs or of men; but the distinction between the sidewalk and the street is a human distinction. A curb is but a slight variation in alt.i.tude of the hardened ma.s.s with which we cover the dirt, which only has a meaning to those who concern themselves with such concepts as roads, pedestrians, roads, pedestrians, and and traffic. traffic. The guide dog must learn the importance of the curb to his companion. He must learn the significance of a speeding car, a mailbox, other people approaching, a doork.n.o.b. And he will: he may begin to a.s.sociate the curb with the distinctive striping of a crosswalk, with the dark, smelly rain gutters that run along them, or with the change in brightness from the concrete to the asphalt. Dogs are much better at learning about things that are important to us in our visual world than we seem to be in understanding theirs. I still can't tell you why Pump became excited at the mere sight of a husky-shaped dog appearing around the corner. But after a dozen years I began to notice that she did. She, on the other hand, was quicker to recognize the importance I placed on certain objects-the distinction between the frayed sofa and my favored armchair with respect to her chance of sitting on it; the slippers whose fetching made me laugh versus the running shoes whose delivery made me scold. The guide dog must learn the importance of the curb to his companion. He must learn the significance of a speeding car, a mailbox, other people approaching, a doork.n.o.b. And he will: he may begin to a.s.sociate the curb with the distinctive striping of a crosswalk, with the dark, smelly rain gutters that run along them, or with the change in brightness from the concrete to the asphalt. Dogs are much better at learning about things that are important to us in our visual world than we seem to be in understanding theirs. I still can't tell you why Pump became excited at the mere sight of a husky-shaped dog appearing around the corner. But after a dozen years I began to notice that she did. She, on the other hand, was quicker to recognize the importance I placed on certain objects-the distinction between the frayed sofa and my favored armchair with respect to her chance of sitting on it; the slippers whose fetching made me laugh versus the running shoes whose delivery made me scold.

There is a final, unexpected facet of the visual experience of the dog: they see details that we cannot. The fact of dogs' relatively weak visual capacity turns out to be a boon to them. Since they are not trying to take in the whole world with their eyes alone, they may see details that we don't notice. Humans are gestalt lookers: every time we enter a room, we take it all in in broad strokes: if everything is more or less where we expect it to be ... yes ... we stop looking. We don't examine the scene for small, or even radical changes; we might miss a gaping hole in the wall. Don't believe it? At every moment of our lives we are not noticing a gaping hole: one in our visual field caused by the very construction of our eyes. The optic nerve, the neural route conveying information from the retinal cells to brain cells, tunnels right through the retina on its way back to the brain. Thus if we hold our eyes still, there is a part of the scene in front of us that is not captured on our retina-as there is no retina there to capture it. It's a blind spot.

We never notice this gaping hole in front of us because our imaginations fill in that spot with what we expect to be there. Our eyes dart back and forth constantly and unconsciously-movement called saccades saccades-to further complete the visual scene. We never experience the missing spot. In the same way, we also have a blind spot for those things that are slightly different-but close enough-to what we expect to see. As well-adapted visual creatures, our brains are equipped to find the sense in the visual information sent it, despite holes and incomplete information.

We are maybe too well adapted. Some of what we overlook, animals see. The celebrated autistic scientist Temple Grandin has demonstrated the reality of this with cows, for instance. Often cows being led along wending chutes into the slaughterhouse balk, kick, and refuse to proceed. As far as we know, this is not because they understand what will happen in the slaughterhouse. Instead there were small visual details that surprised or frightened them. The reflection of light in a puddle; an isolated yellow raincoat; a sudden shadow; a flag flapping in the breeze: seemingly insignificant details. We are certainly able to see these visual elements-but we do not notice them as cows do.

Dogs are closer to those cows than to us. Humans quickly label and categorize a scene. Walking to work along a Manhattan street, the typical commuter is perfectly oblivious to the world he is pa.s.sing. He notices neither beggars nor celebrities; startles neither to ambulances or parades; simply sidesteps a crowd gathered to gape at ... well, whatever it is crowds gape at: I rarely stop to see. On most mornings, the route is reduced to its landmarks; nothing else needs attending to. There is good reason to believe that this is not how dogs think. The walk to the park becomes familiar over time, but they don't stop looking. They are much more struck by what they actually see, the immediate details, than what they expect to see.

Given how dogs see, how do they apply their visual ability? Cleverly: they look at us. Once a dog has opened up his eyes to us, a remarkable thing happens. He starts gazing at us. Dogs see us, but the differences in their vision also seem to allow them to see things about us that even we do not see. Soon it seems they are looking straight into our minds.

Seen by a Dog

I am startled and a little fl.u.s.tered to look up from my work and see Pump watching me, her eyes trained on mine. There is a powerful pull to a dog who looks you in the eyes. I am on her radar: it feels that she is looking not just at me, but to-and into-me.

Look a dog in the eyes and you get the definite feeling that he is looking back. Dogs return our gaze. Their look is more than just setting eyes on us; they are looking at us in the same way that we look at them. The importance of the dog's gaze, when it is directed at our faces, is that gaze implies a frame of mind. It implies attention. A gazer is both paying attention to you and, possibly, paying attention to your own attention.

At its most basic level, attention attention is a process of bringing forward some aspects of all the stimuli bombarding an individual in a moment. Visual attention begins with is a process of bringing forward some aspects of all the stimuli bombarding an individual in a moment. Visual attention begins with looking; looking; auditory attention with auditory attention with hearing: hearing: both are possible for all animals with eyes and ears. Just having the sensory apparatuses isn't sufficient to do what we generally mean by both are possible for all animals with eyes and ears. Just having the sensory apparatuses isn't sufficient to do what we generally mean by paying attention, paying attention, though: considering what it is one has turned to look or hear. though: considering what it is one has turned to look or hear.

When invoked by psychologists, attention is treated not just as turning the head toward a stimulus, but as something else in addition: a state of mind that indicates interest, intent. In attending to someone else's head turns, one may be demonstrating an understanding of the psychological states of other people-a distinctively human skill. We attend to others' attention because it helps to predict what that someone other will do next, or what he can see and what he might know. One of the deficits that many people with autism have is an inability, or lack of inclination, to look at other people's eyes. As a result, they aren't instinctively able to understand when other people are paying attention-or how to manipulate others' attention.

The simple ability to focus on some things while ignoring others is crucial for any animal: objects one sees, smells, or hears may be more or less relevant for survival. Attend to those that are relevant; ignore the rest of the visual landscape or the confusion of sounds. Even with survival no longer our most pressing concern, humans are constantly trying to direct, divert, or attract attention. Some attention mechanism is required to do all the ordinary things of our days: to listen to someone talking to us, to plan a walking route to work, even to remember what one was thinking a moment ago.