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Chapter Four

Training with Vision

We’ve seen that equine acuity and focus are poor, but peripheral range and motion detection are excellent. Let’s round out our understanding with a few added aspects of equine eyesight: night vision, depth perception, visual capture, and color vision.

By nature, equestrians ride on the basis of human assumptions, imagining—if we ponder it at all—that the horse visualizes depth and color the same way we do. We also assume that other equine senses are subordinate to vision, as ours are. Because of misinformation concerning night vision and our own inexperience with it, we presume that horses see details in the dark with superhero sensitivity. The reality is quite different. Doubling down on these discrepancies between human and equine sight explains many common problems within the horse-and-human team.

Night Vision

Horses can see in the dark, right? So they have no trouble jumping at dusk or loading onto the trailer before dawn? Well, not so much! Take a look at your horse’s pupil sometime. See how much longer and larger it is than a human pupil? Large horizontal pupils take in more light across a wider range of visual angle. Having entered the eye, this luminosity filters toward the back of the eye, shining onto that patch of rods and cones that changes particles of light into neural impulses. Those impulses are then routed to areas of the brain that interpret their meaning.

Horses also have iridescent collagen fibers in an upper area of the eyeball called the tapetum (“TAP-uh-tum”). These fibers reflect light from the ground into the eyeball, allowing the horse to gather small amounts of illumination while moving in darkness. Human eyes have a similar mechanism, the choroid coat, but it is not as large or strong as the tapetum and cannot reflect light to an equivalent degree. In both species, the collagen fibers become visible when reflected in a camera flash or headlight. Ours appear to be red, but in horses, the eye-shine varies among green, yellow, or blue depending on a horse’s coat color and age.

With large pupils and a reflective tapetum, horses have a reasonable degree of night vision—enough to wander from hay bin to water trough in the dark and notice movements in the shrubs. It’s more acute than human night vision, which is about as effective as underwater breathing, but still not sharp enough to identify details, hop a cross-rail, or load into a trailer comfortably. The fact that a horse will try to complete these tasks in the dark is evidence of a willingness to obey, not proof of good nocturnal eyesight.

Dark Adaptation

The real rub with night vision comes when we realize that horses can make out shapes in dark conditions only after a long period of pupillary adaptation. This makes sense because equine vision developed when horses stood outside as dusk settled very slowly on the earth. But today, we expect them to enter dark barns and indoor arenas from bright sunlight.

Show riders often expect horses to move from sunlight into an indoor arena during performance. Top facilities use intense lights for illumination, but lesser locations tend to skimp. And at home, most winter riders work horses indoors, where footing is good but lighting is not. How do these changes affect equine performance?

Although all disciplines are affected, let’s consider jumping because it is so dependent on acute equine eyesight. Jumping horses have to judge the height and width of fences very quickly, often scanning distances on a short approach, adjusting stride length for takeoff, carrying riders who transmit countless cues, and coordinating their bodies to clear obstacles by only an inch or two. These are meticulous feats that would cause many human athletes to stumble.

Riders all over the world warm up hunters and jumpers in bright sun prior to competition. After a typical warm up, Twinkletoes’ pupils are constricted to the maximum degree to admit as little light as possible. The chemicals that transduce light into neural impulses are at their ebb. This combination of pupillary contraction and chemical paucity allows the horse to jump in bright sun without being blinded by the glare. High elevation, central latitudes, low humidity, pale arena sand, and white fences demand even greater adaptation.

Twinkletoes is jumping well in the warm-up when the gate steward calls him to the indoor show arena. His rider removes her sunglasses at the in-gate, instantly improving her indoor vision. Too bad Twink can’t shove his face into some military night goggles. Through the gate they go, galloping into the murk to leap over 8 or 12, sometimes 15, jumps that the horse can barely see. And oh, by the way, like all of us, Twink’s rider expects top-quality performance. But he hasn’t come close to the 45 minutes he needs to accommodate to indoor lighting. Typically, he’s had one minute, if that.

The scenario described here is common. We allow it because we are not aware of the visual hardship for the horse. Most of us reprove mounts who balk at the in-gate, weave between fences, skirt the flower box, or refuse to jump. We assume that if we can see the course, they can, too. But imagine moving from a sunny parking lot into a darkened movie theater, then dashing around under a heavy backpack—hurdling seats, slipping on buttered popcorn, and dodging angry patrons. The fact that horses try to perform under such circumstances is a testament to their generosity.

Like humans, horses differ in individual visual abilities. One horse might require a little less than 45 minutes to adapt to dim light; another will require even more. Age plays a role, too. Older horses with healthy eyes take in less light than younger horses do. This age difference occurs in humans as well—in fact, the average person’s eyes take in 66% less light at age 60 than at age 20. No wonder the world can seem a little glum as we get older.

How can we help our horse’s eyes adapt before performing? No suggestion is ideal, but some will help. Allow your horse to walk in the shade before entering an indoor arena. Stand at the gate for a few minutes while the preceding team competes. When possible, schedule a jumping performance right after a flat class, giving your horse 15 minutes of adaptation time prior to starting over fences. Remember that a jumping round, no matter how easy it looks, is a complicated and unnatural coup for a horse. He can’t just phone it in.

The best solution is to require show organizers and facilities managers to brighten indoor arenas with strong artificial lighting. Exhibitors, trainers, boarders, and owners have the power to make such requests as a group, especially when safety is at stake. Veterinary schools and organizations can help the cause by publicizing the need for strong indoor lighting. Professional associations like the United States Equestrian Federation (USEF) and Fédération Equestre Internationale (FEI) should revoke horse show ratings when a venue’s lighting is not up to snuff.

As a show participant, suggest that officials cordon off a small strip of the indoor as a wait-and-walk area for horses about to perform. Ask that they open doors to illuminate the area inside. Be sure they have turned on all the lights—this sounds so elementary, but many show riders and trainers have experienced events at which the managers powered up only half of the indoor arena’s lights. When all else fails, scratch—and tell the event organizers why. Your horse’s long-term welfare and your own are more important than three minutes spent hopping around in Aladdin’s cave.

Horses need to see their surroundings, whether leaping 7-foot walls or just chillin’ in the barn. Those who can’t see well compensate by using other senses to a greater degree. This can yield new kerfuffles, as when the horse begins to listen to a dark indoor arena so closely that he spooks at the sound of two air molecules colliding.

Depth Perception

Eyes admit physical views, but it takes a brain to compute visual distance. When staring straight ahead, humans take in two views of a given sight—one from each eye. To see this for yourself, hold your finger in front of your nose at arm’s length. Close one eye and line your finger up with something vertical in the distance—a door frame or a fence post, whatever. Now open that eye and close the other. Your finger will appear to jump back and forth as you alternate eyes. Those are the two views that your right and left eyes send to your brain. The brain calculates the difference between them, and as if by magic, you become aware of depth. Using this automatic computation, you can look at a field of horses and note that the cute roan is farther from you than the pretty paint.

Human depth perception is extremely precise because our eyes are so close together. They are also yoked, moving in concert with each other for precise tracking. With this design, the average person can distinguish ¹⁄8 of an inch in depth from a distance of 16½ feet. In other words, if you were standing one long stride away from the takeoff to a double-rail vertical, your brain could tell you whether one of the rails was set ¹⁄8-inch behind the other one. That’s depth perception on steroids!

By contrast, the smallest amount of depth a horse can detect when standing the same distance away from something is 9 inches. Human stereoacuity is 72 times sharper than that (fig. 4.1).

Horses’ ability to see depth is limited because their eyes are set so far apart. From most angles, horses cannot get a left-eye and right-eye view of the same object in one glance. We hominids can see an outstretched finger with both eyes simultaneously. But even in a rearing position, Twinkletoes would have to be a contortionist to get his hoof in front of both eyes at the same time. As prey animals, horses are built for peripheral motion detection at the expense of depth perception. As predators, we’re built in reverse.

4.1 With two eyes from a stride away, the equine brain can sense a minimum of only 9 inches in depth from front to back. In contrast, the human brain can sense 1/8 inch in depth from front to back. We perceive differences in depth that the horse cannot see.

For horses in disciplines like dressage, reining, or pleasure, depth perception is not so critical. But consider cutting, barrel racing, or jumping. A horse needs to know how far away relevant objects are and how fast those distances are changing as he moves. A horse can improve depth perception by raising his head, dropping his withers, or lifting his nose, but this often complicates his task. In cutting, for instance, horses need to keep their eyes down on the cow and their heads low to make quick turns. In jumping, they need impulsion from their hindquarters to power off the ground and abdominal tuck to lift their legs. The physics of such movements require horses to maintain a round back for core strength, which often precludes the position of a high head.

The distinction between hunters and jumpers is also important here. Top jumpers are judged by the clearance and speed of their rounds over high, wide fences—fences that are often approached off sharp turns from short distances. Such horses are often selected as jumpers because their necks are set high on the withers, with head position proportionately higher. Those without that conformation are encouraged to approach jumps with their heads raised. If you watch a jumper approaching a fence, you’ll see his head lift in the last stride or two. This natural form provides both eyes with a brief view of the jump, so that the equine brain can determine its height and width. But the view is indeed brief—fractions of a second—and it’s late.

Occasionally, we hear that jumpers are aided in depth perception by wagging their heads back and forth on approach, to allow each eye a view of the jump. This suggestion does not hold up in terms of brain science. To compute distance, the brain requires a simultaneous view of the object with both eyes. Wiggling the head back and forth only interferes with centering the horse. It probably also prevents him from concentrating on other cues from the rider that are much more important.

Depth perception is easier for hunters. These horses are judged on the quiet beauty of their jumping form and are taught to maintain a long frame with hindquarters engaged, necks arched long, heads low, and faces nearer the vertical to form a strong topline. This position can be preserved over fences because hunters are given a long approach with which to see relatively low jumps without raising their heads. Good hunter riders encourage horses to look at a fence while rounding a distant corner. This supplies the horse with a better side view, a longer front view, and more time for the two eyes to send images of the jump to the brain. It’s still a good idea, of course, to allow any jumping horse some freedom in moving his head to improve his view.

In terms of width, only about half the area visible to two human eyes at the same time is visible to a horse’s two eyes at the same time (fig. 4.2). Stand about 30 feet back from an arena fence. Roughly 5 feet of that fence is clear and sharp to both of your eyes as you hold them still. From the same position, only half of that—about 2½ feet—is clear to both the horse’s eyes. And it is only that small portion visible to both eyes for which a brain can calculate depth by stereoacuity.

4.2 With two eyes focused straight ahead, the horse sees only half the width of the human view.

When you’re aiming a horse toward a fence, center him on the narrow middle portion that he can see with both eyes. Many early jumping errors occur when a rider does not steer the horse to the center of a jump. These problems are frequently blamed on the horse—he ran out, he refused, he chipped, he jumped in bad form. Well, that’s not because he’s a bad horse; it’s because the rider didn’t let him see the fence!

Visual Capture

Vision is our strongest human sense—it hogs more neural real estate than any other sensory system, filling almost one-third of the human brain. With such clout, it can override other senses, a neural ability known as visual capture.

Visual capture is responsible for the fact that ventriloquists can fool us. We believe that speech is emanating from a dummy’s mouth, even when the human speaker is standing right there. The visual movement of the fake mouth captures our attention and links it to the spoken words. Magicians use visual capture to hide actions of their hands in plain sight. Moviegoers gesture toward an actor’s mouth on the screen when asked where the sound is coming from—even when theater speakers are placed at the back or sides of the house.

Because we rely so heavily on sight, we suppose our horses do, too. Yet we’ve seen that many aspects of equine vision are worse than ours. The horse compensates for his visual weaknesses with good hearing and a fantastic sense of smell. We help him by encouraging reliance on these stronger senses. The next time your horse skitters away from a safe spot, think about what he might hear or smell that is imperceptible to you. In his world, it’s not all about vision.

Color Vision

Harley was a six-year-old red dun Quarter Horse who knew how to be led and longed. Nothing else. An adult horse who knows so little is not the safest animal. (Let me make a plea to backyard horse owners everywhere: Hire a trainer when the horse is young and small!) I was holding this overgrown baby in an indoor arena one day when snow slid off the roof. Many horses shy from this, but most don’t try to jump in my lap. Harley jumped a foot high and a couple feet forward off all four hooves and landed on the arch of my left foot.

The ensuing injury interfered with my ability to use a stirrup, so a friend suggested mountain bike shoes with rigid soles that would support my foot. Off I hobbled to the cycling store, where the only inexpensive pair pulsed on the shelf in blazing yellow with a chartreuse afterglow. To accommodate the padding around my wrapped foot, they were also two sizes too big. They were probably visible from the surface of the moon. But riding is more important to me than style—a good thing, because I looked absurd wearing these shoes coupled with some old sunburned half-chaps.

On Day One of the new fashion, every horse at the ranch stared in surprise at my feet. They knew me well; some I’d ridden daily for years. They’d seen me wear a variety of neon shirts in an effort to liven up the atmosphere. But this was clearly a strong visual sight for them. All day, as soon as I mounted, every horse turned to my stirrups and sniffed each shoe carefully. We joked that the horses were embarrassed, but in reality we had proven a feature of equine color vision.

What colors do horses see best? Yep, you guessed it: bright yellow with a chartreuse tint, just like my shoes! Horses also pick up bright turquoise and teal hues well. Hang a few jackets on your arena fence someday. Notice how the horses are much more aware of the bright yellow rain jacket than they are of the equally flappable bright purple or flame red versions. A horse who needs to pick up his feet over fences can be reminded to do so with the simple use of some bright yellow or turquoise rails. A young horse who is just learning to negotiate ground poles will excel with other colors—he needs to see the poles without feeling provoked by them.

Remember the eye’s rod and cone cells from chapter 3 (p. 42)? Where rods sense movement in dim light, cones pick up detail and color. Horses have many rods and few cones; humans have the opposite. So, all colors visible to horses—even the bright yellows—are faded in comparison to human perception of color. Most critically, horses do not have any cones that pick up red and green. Because of this a horse (like a dog, squirrel, or pig) cannot distinguish between red and green—as journalist Wendy Williams has noted, a horse looking across a green pasture cannot see a stationary person dressed in bright red. Both pasture and person appear to be grey.

Saving Lives with Color

In 2018, British researchers demonstrated horses’ inability to see the bright red-orange poles used to mark the base of steeplechase jumps that they sail over at high speed. Against green grass, white poles were much more visible to the horses. Jockeys could see both colors equally well, so the choice didn’t matter to them. The British Racing Association now plans to change the color of steeplechase poles throughout the United Kingdom, increasing safety for thousands of animals and their riders. That’s brain science saving lives: in 2018 alone, 201 horses died on British steeplechase racecourses. Invisible ground lines likely played a role in some of those deaths.

Next time you need to mark off an area to keep horses from entering a reseeded portion of their pasture or a weekend construction job, throw away the fuschia survey tape. It’s salient to you, but invisible to your horse. Tie bright yellow tape around your temporary fence instead.

Seeing Equine Vision for Yourself

By exploring just a few important features of the brain, we can already see that equine vision differs dramatically from our own. An excellent 2016 video clip pulls a few of these differences together. (It’s online—see the Source Notes on p. 270 for the link.) In the video, a horse-and-human team is simply walking through a grassy meadow and forest to a barn. The view seen by each species is shown simultaneously at the top and bottom of the screen, so they’re easy to compare. In two minutes, you’ll get an idea of the vast changes caused by differences in range of vision, acuity, dark and light adaptation, and color vision.

All of us who work with horses need to think about the senseless difficulties we impose on our horses by assuming they see like we do. Let’s try seeing through their eyes for a change.

Time to Dark Adapt

Eyes adapt to light by contracting their pupils, and they adapt to darkness by expanding their pupils. Human eyes require about 25 minutes to adjust from bright sunlight to complete darkness. But equine eyes need 45 minutes, almost twice as long. So, upon entering a dim building from daylight, your horse will struggle with darkness long after your eyes have adapted. After adaptation, his eyes are 25,000 times more sensitive than they were at the beginning. Now he can see. Unfortunately, his 45-minute training session is about done by then.