Animals in Translation (7 page)

 

You could make up the same kind of list for any animal, although it would be different for each one. Bats have sonar and dogs don't, so the list of common distractions for bats is going to have some sonar distracters on it, while the dog's distracter list won't. But any list of common distractions for an animal would be highly, highly detailed, exactly like this one.

T
HE
D
IFFERENCE
B
ETWEEN
A
NIMAL
V
ISION AND
H
UMAN
V
ISION

Although I created this list for cattle and hogs, you can use this list to predict trouble spots for any other animal if you think about what these eighteen distracters have in common.

First of all, fourteen out of the eighteen distracters are visual, and I wouldn't be surprised to find a ratio like that for most animals. But
to predict
what kind
of visual object will distract or frighten an animal, you have to know more about what animal vision is like.

It's pretty different from ours. For instance, you always hear that dogs “don't see well,” which is true as far as it goes. Dogs don't have very good visual acuity, which is the ability to see the tiny details of what you're looking at clearly and crisply. People with 20/20 vision have excellent visual acuity, and a lot of animals don't. That means that most animals aren't going to be frightened by tiny objects, simply because they can't see them well.

A typical dog has a visual acuity of 20/75, which means that a dog has to stand twenty feet away to clearly see an object a person with normal vision sees well standing seventy-five feet away. The dog has to get much closer to the object than we do. This isn't due to nearsightedness but to the fact that dogs have fewer cones in their retinas than people do. Everyone probably remembers from biology class that cones handle color and daytime vision, and rods handle nighttime vision. Basically dogs have traded good visual acuity for good nighttime vision. A dog doesn't see
any
objects as sharply as a person does, including an object that's right under his nose. That's why it's so hard for dogs to see a piece of kibble you've dropped on the floor for them to eat. If they didn't watch it fall, most dogs can't see it lying on a mottle-colored tile floor (though some can).

There's also a lot of variation in visual acuity among the different breeds of dogs, as well as among individuals of a breed. One study found that 53 percent of German shepherds and 64 percent of Rottweilers were nearsighted. You might wonder whether being nearsighted matters to a dog since everything it sees is fuzzy to start out with, but tests show that it does. A nearsighted dog has much worse visual acuity than a normal-sighted dog. Interestingly, although German shepherds tend to be nearsighted, only 15 percent of the Shepherds in a demanding program for guide dogs were myopic.
²
Probably the nearsighted dogs were flunking out of the program without the trainers' knowing why.

Another huge difference between animals and people is that most animals have panoramic vision. The eyes of prey animals like horses, sheep, and cows are set so far apart that they can literally see behind their heads. That's why some hansom cab horses wear blinkers; they
can see everything going on behind them, and they get distracted. Most racehorses
don't
wear blinkers for the same reason: their trainers want them to know exactly where the horses behind them are, and how fast they're moving.

Prey animals don't have perfect 360-degree vision, although they come close. There's one small blind spot directly behind a cow or horse that you have to be careful not to sneak up to. The animal can't tell what you are, and he might get scared and lash out and kick you. Prey animals also have a small blind spot directly in front of their heads because their eyes are set so far to the sides.

Even though their eyes are so far apart, prey animals
do
have depth perception, though it seems to be different from ours. We use
binocular vision,
which means each eye is seeing the same thing from a slightly different angle. When our brains combine the angles, we get our sense of depth.

Prey animals' eyes are so far apart that a lot of researchers have assumed their left eye was seeing something completely different from the right eye, so they couldn't have binocular vision. But they've tested this in sheep, and sheep do have at least
some
binocular vision. We know this because sheep can see the cliff in
visual cliff
experiments. In the original visual cliff studies the experimenters put a baby on top of a table covered in a sheet of glass thick enough to crawl on. Directly underneath the glass there was a checkered surface that, midway across the table, suddenly dropped off way below the glass surface. It was a
visual
cliff, not a real one, so the baby couldn't actually fall over the edge if he crawled out over the drop-off. Very young babies will refuse to crawl over the cliff even if their mothers stand on the opposite side of the table and call them. They can see the cliff, and they instinctively know it's dangerous. It turns out that sheep won't walk over the cliff, either, which means they have to be seeing the difference in depth. (On the other hand, sheep don't appear to have depth perception while they're moving, only when they stand still.)

You've probably seen bulls in bullfights lower their heads before they charge the matador. Border collies do the exact same thing when they're herding sheep. They lower their heads below their shoulders and stare at the sheep. They do this because their retinas
are different from ours. The human retina has a fovea, which is a round spot in the back of the eye where you get your best vision. Domestic animals and fast animals who live on the open plains like antelopes and gazelles have a
visual streak
instead of a fovea. The visual streak is a straight line across the back of the retina. When you see an animal lower its head to look at something, it's probably getting the image lined up on its visual streak. Most experts think the streak helps animals scan the horizon.

Researchers have also found that of the meat-eating animals that have been tested so far, the two fastest animals—the cheetah and the greyhound—also have the most highly developed visual streaks. Their visual streaks are dense with photoreceptors, giving them extra-acute vision. To test visual acuity you can use a bar code design. The more acute your vision, the tinier a bar code you can look at, from a greater distance, and still see the stripes as separate rather than as a gray square. Animals with super-acute vision can also see separate grains of sand on the beach.

S
EEING
C
OLOR AND
C
ONTRAST

A third area where animals and people diverge is in the ability to see color and contrast. At least ten of the eighteen distracters are high-contrast images, like a shiny reflection on metal, or a sparkling reflection in a puddle. Several of the other visual distracters, such as a white Styrofoam or plastic coffee cup on the floor or a piece of clothing hanging over a fence, involve contrast, too. I have some photographs of high-contrast distracters on my Web site. One is a picture of a white coffee cup on a brown floor; another is a pair of bright yellow boots against a gray floor and railing.

Sharp contrasts are also a problem when you're trying to move an animal toward an area that's either too dark or too light. We already talked about the cattle that wouldn't go into the squeeze chute building because it was too dark, but cattle will also refuse to walk directly into an area that is too bright. Strong changes in light are so distracting to cattle that you can't have direct sources of lighting, like an unshaded lantern or lightbulb, at the mouth of an alley. They won't walk toward it. You want overhead lighting with
no shadows, like the light outdoors on a bright but cloudy day. Sometimes you can get that effect with skylights made out of white translucent plastic.

Slowly rotating fan blades are also a high-contrast stimulus, because animals see contrast differently from the way we do. If the fan is turned on and is rotating so fast you can't see the blades, there's no problem. But when a fan blade is turning slowly it creates a flicker, and that flicker is a much higher contrast image for an animal than it is for us.

Animals see more intense contrasts of light and dark because their night vision is so much better than ours. Good night vision involves excellent vision for contrasts and relatively poor color vision. I first learned about animals' incredible contrast vision back when I was taking black-and-white pictures of the cattle chutes. There'd be a shadow on the ground that even I wouldn't see until I got the pictures developed. The reason I could see it only in my photographs is that contrast is much sharper when you take away color. Shadows are so much clearer in black and white that during World War II the Allies recruited people who were completely color-blind—not just red-green color-blind, but people who didn't see any color at all—to interpret reconnaissance and spy photos. They could spot things like netting draped over a tank to camouflage it that were invisible to people whose color vision was normal.

Animals seem to see sharp contrast on the floor as a false visual cliff; they act as if they think the dark spots are deeper than the lighter spots. That's why
cattle guards
work on roads. A cattle guard is a pit dug across a road, covered with metal bars. A car can drive over it and a cow
could
walk over it if it tried, but it won't because it sees the two-foot drop-off between the bars.

To a cow the contrast is so sharp the drop-off probably looks like a bottomless pit. In
An Anthropologist on Mars
Oliver Sacks has an essay about an artist who lost his color vision in a car crash. After that it was hard for him to drive, because tree shadows on the road looked like pits his car could fall into. Without color vision, he saw contrasts between light and dark as contrasts in depth.
³
Since cows have much poorer color vision than normal people do and mainly see colors in the yellow-green range, they may see light-dark con
trasts as contrasts in depth in an analogous fashion to Dr. Sacks's color-blind artist.

Whatever the reason, cows act like Dr. Sacks's color-blind artist. Cattle guards are expensive to build, so a lot of times the Department of Transportation just uses a standard line-painting machine (that's the machine they use to paint the center line on highways) to paint batches of bright white lines across the highway going in the same direction as a crosswalk. It's a poor man's cattle guard.

When the cattle aren't highly motivated to cross the road, a grouping of twenty white lines painted six inches apart will make them stay put, because the contrast scares them. If the cattle are highly motivated, it's a different story. If you've got mama on one side and baby on the other, painted lines won't work. Or if cattle are starving, they'll cross the lines to get to better grazing on the other side of the road. But under normal circumstances, painted lines work just fine.

You need to know something about animals' color vision to predict what visual stimuli they'll experience as high-contrast. The breakdown is pretty simple: birds can see four different basic colors (ultraviolet, blue, green, and red), people and some primates see three (blue, green, and red), and most of the rest of the mammals see just two (blue and green). With
dichromatic,
or two-color,
vision
the colors animals see best are a yellowish green (the color of a safety vest) and bluish purple (which is close to the purple of a purple iris). That means that yellow is the high-contrast color for almost all animals. Anything yellow will really pop out at them, so you have to be careful about yellow raincoats, boots, and machinery.
⁴

T
HE
R
EAL
P
ROBLEM
I
S
N
OVELTY

Any sharp contrast between light and dark will draw the attention of a dichromatic animal, either distracting or scaring him. If he's a big animal who you're trying to move from Point A to Point B, a sharp contrast in light and dark will stop him in his tracks.

However, not all high contrast will scare an animal, only high-contrast visual stimuli
that are novel and unexpected.
If dairy cattle are used to seeing bright yellow raincoats slung over gates every day
when they enter the milking parlor there'd be no problem. It's the animal who's seeing a bright yellow raincoat slung over a gate for the first time at a slaughter plant or feedlot who's going to balk. Novelty is the key.

The anti-backup gates used in many cattle alleys have the same problem: the cattle have never seen them before, so they don't want to go through them. Novelty is a huge problem for all animals, all autistic people, all children—and just about all normal grown-ups, too, though normal adults can handle novelty better than animals, autistic people, or kids. Fear of the unknown is universal. If you've never seen something before, you can't make a judgment about it; you don't know if it's good or bad, dangerous or safe. And your brain always wants to make that judgment; that's how the brain works. Researchers have found that even nonsense syllables spark positive and negative emotions; to your brain, there's no such thing as neutral. So if you can't tell what something is, you get anxious trying to decide whether it's good or bad.

Any
novel object or image in a cow's visual field will get her worried, and if you happen to be trying to move her in the direction of the novel object or image, forget it.

It's different when you don't try to force things. On its own, an animal will always investigate a novel stimulus, even though new things are scary. I learned that back when I was writing stories and taking photographs for
Arizona Farmer Ranchman Magazine.
I noticed that if you just left a pile of camera equipment alone in the middle of the field, all the cows would come up to it and investigate. But if you walked toward them
carrying
the same equipment, they'd take off. Motion was a problem, so if I just stood there holding the equipment, the cows would come to me.