Horse Brain, Human Brain. Janet Jones

side or another, above, below, or from some angle in front of you. Horses seem to be likely candidates for localization genius: They have large cupped ears with a turning radius of 180 degrees front to back and about 90 degrees top to side. Sixteen muscles per ear are devoted to flicking all that cartilage around quickly and accurately. These movements operate independently, so one ear can be pointed toward the front, for example, and the other toward the back. Fur protects equine ears from insect bites, cold, foreign objects, dirt, and rain, so they can function well.

      In addition, equine ears are set far apart, which increases the time difference in the arrival of a sound as it approaches the horse’s head. This is a key feature for good localization. Physically, a sound is a wave of air molecules that strikes the eardrum. Suppose the wave is coming toward the left side of the head. This sound will arrive in the left ear before it arrives in the right. The greater the distance between ears, the greater the difference in arrival time. This tiny interval tells the brain that the sound is coming from the left. The horse—or human—then knows to turn to the left and look for more information or run toward the right to escape potential harm.

      All these advantages should produce excellent sound localization in the horse. Humans, after all, have meager little ears set close to the head. We have three weakling vestigial muscles connected to our ears that are only good for party tricks in those rare funsters who can wiggle their ears. A human’s head is narrower than most horses’, though the placement of our ears down the sides of the head increases the time difference of sound arrival to the two ears. Still, with all the advantages a horse has, plus the evolutionary pressure to survive by sound localization, we would expect horses to excel.

      Yet, research does not bear out this suspicion. Humans can locate the origin of a sound within less than 1 degree of precision; elephants 1 to 2 degrees; cats 5 degrees. Horses? Their precision ranges from 22 to 30 degrees, depending on the type of noise that is studied (figs. 5.2 A & B). That’s like a D minus! If a lion is sneaking through the meadow, a horse needs to identify the lion’s location with greater precision than a 30-degree angle of “maybes.”

      Why would horses have such weak ability to hear the origin of a sound? I’ll speculate with two guesses. First, when this kind of anomaly occurs in science, we check the research methods. Sometimes the sample sizes are too small—we can’t generalize across 60 million horses worldwide on the basis of one or two individuals. Often the method of gathering data is weak or confounded by other variables. Subjects, especially horses, don’t always cooperate with the process. Research flaws are part of science—with something as complicated as a brain, nobody fashions the perfect experimental design every time. We replicate and revise studies to overcome such problems.

      5.2 A The human brain identifies a sound’s location with less than one degree of error.

      5.2 B The equine brain identifies a sound’s location with 22 to 30 degrees of error.

      But the second guess is this: maybe horses don’t need excellent sound localization because they have other ways of protecting themselves. The horse’s excellent peripheral vision for along the horizon might render sound localization moot. His outstanding sense of smell is also working to locate a threat. Remember Aspen the Bear Hunter? She didn’t need to hear the location of the bear in the bushes—she could smell him from much farther away (see p. 23).

      Noise

      People design equestrian facilities in all sorts of interesting ways. Which way should the wash racks face? Where should the grooming areas be? How much of the world should horses see from their stalls? Should the barn be tightly closed for warmth or wide open for air? And so on, ad nauseam. Many choices depend on our assumptions about how horses experience the human world.

      For several years, I trained at a barn where the owners believed random noises were an aid to schooling. Located next to their indoor arena was the shop where paint sprayers were blown out with high pressure air hoses, snow plows were sledge-hammered, and power saws were blasted through plastic fence posts at unexpected moments. Horses and riders working in the indoor could not see out, so we had no visual warning of these impending explosions. At times it was dangerous, especially for beginning riders with insecure seats or horses who were green or anxious. The layout was “grumpifying,” to say the least.

      One would imagine that the shop had been located near the indoor by accident. But no. It was a conscious decision, intended to help the horses “get used to unexpected noises.” This way, the rationale went, they would be calmer at horse shows. Hmmm. The equine brain doesn’t work like that. Although some level of desensitization is necessary with young horses, plunking a tender filly into a flaming bowl of frightening distractions is not the way to go about it.

      Environments marked by loud, unexpected, and unfamiliar noises cause horses much distress. Even consistent unpleasant noises bother horses, like wind or idling diesel engines. Wind makes things flap around, and engines mask sounds that might be important to a prey animal. Decades of research prove that constant noise is not good for human ears, minds, or emotions, either. Animals—and humans—cannot relax in such settings, and without the security of relaxation, true learning is impaired. Within days of moving to a quieter barn, my training horses were much easier to handle at home and at shows.

      “Say What?”

      Horses have powerful pitch perception, but why? Why does a horse need to analyze sound frequencies across a 10-octave range? The rustling grasses of a predator’s approach don’t vary by that much. The answer lies in the horse’s position as a social animal. To survive, he must be able to hear and interpret the vocalizations of herd mates.

      Horses communicate with each other all the time. Much of this communication is hidden from humans—not because our four-legged friends are keeping secrets, but because most of us don’t notice the subtle ways that animals reach out to each other. And when we do notice a movement or vocalization, we often fail to understand what it means.

      Let’s reflect on a simple whinny. It averages 1.5 seconds in length and can be heard half a mile away. It’s produced in three phases—a high-frequency introduction, a rhythmic collection of medium frequencies in the middle, and a lower-frequency waffle near the end. Many of these frequencies sound simultaneously, like a musical chord, but some waver in and out. Minute variations in these parameters convey meaning to the equine brain.

      Compared to neutral, a fearful whinny is higher in fundamental pitch, and the highest frequencies within it are produced at stronger intensities. A greeting whinny is much lower in pitch, and there is greater range and more time in the wavering or vibrato between tones. A separation whinny cuts off early in the ending phase. And so on, through the whinnies that mean, “Good to see you,” “Why won’t that mare come over here?” “Feed me now,” or “Help, the barn’s on fire!” Horses might produce 10 million variations of whinny, and each variation will have different physical characteristics from the next.

      The brain of a listening horse analyzes all these components instantly and automatically. Cells in the horse’s inner ear encode the varied frequencies within each whinny; cells in the auditory cortex calculate the differences and mark the timing. The brain’s association areas apply meaning: “Oh, that’s Mirror. She’s worried about something.” We hear the whinny and, if we are observant, we notice the response. But all of the complicated neural work is hidden, so we assume the analysis is easy. Or magical. It’s not. There’s a lot going on inside your horse’s forehead.

      In addition to gradations of emotion and meaning, each horse’s whinny is also unique—it’s a signature. Reno’s fearful whinny, for example, differs in its physical composition from Dee Sea’s fearful whinny. So, in addition to decoding what a whinny means, a listening horse also knows without sight who produced it. Knowing who’s sounding off provides even more information, because horses differ in their sensitivity just like humans do. The fearful whinny of a horse who’s generally laid back is a stronger warning than the fearful whinny of a horse who’s got the willies