Inside of a Dog: What Dogs See, Smell, and Know (18 page)

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 A closing door can be grabbed before it slams; a handshake received before it is withdrawn in annoyance.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
notice if an old-fashioned (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 space 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
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 documented with microvideo recording and trajectory analysis, 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'.

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 crevasse, 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 surreptitious glance out of the corner of the eye. Their vision complements their other senses. While they can locate a sound in space 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 circumscribe 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 discombobulates, 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.

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
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 altitude of the hardened mass with which we cover the dirt, which only has a meaning to those who concern themselves with such concepts as
roads, pedestrians,
and
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 doorknob. And he will: he may begin to associate 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
—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 passing. 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.