Horse Brain, Human Brain. Janet Jones
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(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: