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Chapter Five

“Did You Hear That?”

Reno, a blood bay off-the-track Thoroughbred, stood in the cross-ties one afternoon while his owner’s toddler went inside for a nap. A nursery monitor in the barn allowed the mother to hear the two-year-old in his crib while she worked. The horse was accustomed to baby and monitor, so he paid no attention to the noises of adult speech and the movement of blankets and pillows as the baby was put to bed. But a few minutes later, when the baby began babbling, Reno came to military attention. He lifted his head and peered around the corner, ears nailed to the monitor.

“Ba-ba-ba-ba-ba, na-na-na-na, muh-muh-muh-muh,” the baby repeated one syllable after another. Reno pushed his nose forward and jiggled the cross-ties; he seemed to bob his head in time with the repetition. Out of curiosity, I led him to the baby monitor to see what he would do. He approached eagerly, showing no fear, and sniffed every corner of it. He cocked his head from one side to another, listening. He did not want to turn away, even though the baby’s babbling continued for perhaps 15 minutes. Reno was spellbound.

Loudness

To explain equine hearing, it helps to distinguish between loudness, pitch, and localization. The easiest to describe is loudness. The volume of a sound is measured in decibels (dB). By convention, 0 dB represents the softest sound that human ears are capable of sensing. It’s the tiniest tick in a soundproof room of dead silence—a tick that can be detected only by that rare 18-year-old who’s never gone to a rock concert or cranked up her earbuds. Even the most sensitive horse will not hear that sound.

According to the best available data, the softest sound an average horse can hear occurs at 7 dB. That’s the volume of a person breathing quietly. In general, then, the same noise seems a little quieter to a horse than to a person. Horses hear us speak to them but at slightly lower volumes than we believe we have used. On one hand, we might be surprised that horses do not perceive hushed noises as well as humans do…after all, spooky horses certainly seem to have bionic hearing out on the trail! On the other hand, we have to give them credit for hearing something as quiet as an easy breath.

Pitch

Within the volumes that people and horses can detect, a second aspect of sound is pitch. Pitch refers to the range of low to high frequencies that corresponds to musical notes from low bass to high soprano. Horses can hear pitches from about 55 to 33,500 Hertz (Hz). That’s similar to the 10-octave range (20 to 20,000 Hz) humans can sense. By comparison, Indian elephants hear lower pitches, and wild mice sense tones up in super-squeak territory (fig. 5.1).

5.1 Pitch ranges of various animals in young adulthood, with a piano range included for comparison. Horses hear pitches slightly higher than human range, but fail to notice pitches that we experience as very low.

Equine ears miss about an octave and a half of the lowest bass notes we can hear, those between 20 and 55 Hz. However, horses can pick up many of these low frequency sounds through vibrations in their teeth and jawbones while grazing. Their hooves also transmit low vibrations. Ears aren’t everything!

At the high end of the sound spectrum, equine ears surpass ours by half an octave (from 20,000 to 33,500 Hz). Horses can hear the ultrasonic squeal of a bat or dolphin, the silent dog whistle, and the noise that insect and rodent repelling machines produce—all inaudible to humans. Although researchers have found no difference in hearing sensitivity between male and female horses, males do pay more attention to sound. This heightened reaction probably occurs because it is the male horse’s job to warn mares and youngsters of danger.

Hearing Over Time

Equine hearing declines with age just as human hearing does. By the time a horse is 20 years old, he’s usually experiencing mild to moderate hearing loss. Humans decline much faster in proportion to our life span, with higher frequencies generally inaudible by age 30. A controversial anti-loitering system called the “Mosquito” is used in many countries to disperse young people from public areas that are prone to vandalism. The frequency of the noise it makes (17,400 Hz) is too high for older adults to perceive, but young people won’t hang around in such an annoying environment. Nor will horses!

You know how your mount sometimes stops dead and goes taut to listen to something that you keep telling him “isn’t there?” I’m only the messenger, but uh…if it’s high frequency, it probably is there. Our ears just can’t hear it. An older rider on a younger horse is at a particular disadvantage in terms of being unable to hear high frequencies as well as the horse does. Often the horse freezes in place to reduce ambient noise—a squeaking saddle, hooves striking the ground, the soft jangle of a bit. Grazing horses stop chewing when they hear a quiet noise—that’s because the grinding of their jaws interferes with their ears’ ability to transmit sound signals to the brain.

Aside from their physical range of hearing, horses have evolved to pay much greater attention to small noises than humans do. Although the two of you are often capable of hearing the same sounds, you might heed the voice inside your head—your plans and thoughts and worries—more than the crackling of a dry twig.

Interpreting Sounds

All sensory organs—eyes, ears, noses, tongues, skin—pick up patterns in the external world, transform them into neural impulses, and send them to the brain for interpretation. Tiny differences in loudness and pitch are critical to comprehending human speech, tonal emotion, music, environmental noises, and animal vocalizations. A horse or human who can’t discriminate sounds well is going to have some trouble communicating.

So, once a horse’s ears pick up a sound wave and send it to that squashed grapefruit called his brain, what happens there? All sorts of things. We often study those processes by considering what happens when the brain isn’t doing its job. Humans with good ears but damage to the auditory cortex often experience auditory agnosia (“ag-NO-zhuh”). The sounds come in, but they don’t make sense. Patients report that sounds—often voices—are too loud, unpleasant, blurred, crackling, echoing, sometimes painful. They’re not sure whether a sound is real, but they usually don’t realize that anything is wrong with their brains. Instead, these patients complain that the noises themselves are to blame for the misperception.

Intact human and equine brains order sounds, allowing some tones to fade into the background and others to come forward. They become accustomed to typical sounds and use atypical ones as warning signals. They associate learned sounds with sights, smells, touches, knowledge, or experiences. What horse, for example, does not link the sound of the feed truck or bucket with the time of day?

Thanks to their brains, horses are whiz kids at interpreting the whinnies, nickers, snorts, blows, groans, snores, and squeals of daily equine life. A horse can hear one whinny and know who’s calling, what mood he’s in, and what he wants. Horses whose owners arrive by car to feed them will nicker a greeting when that car arrives, yet ignore other cars. They know who’s who. Some ignore all transport rigs except their own, heading to the farthest corner of a pasture when the trailer arrives, as if to say, “No, thanks, I’d rather stay home.”

Stories abound: Have you heard about the retired circus horse who knew the command “high” as an instruction to rear? It worked all too well around his retirement barn when folks said, “Hi,” to each other. How about the American import who refused to canter on a longe until the English handler faked a strong American accent to pronounce the command, “Canter?” Once the horse understood the word, he picked up the gait.

Horses scope out a wide range of human emotion from tone of voice, and they respond to it well. A horse who knows to hold still while being tacked up, for example, might wiggle while the handler murmurs, “Oh, stop that,” or even voices a known command like, “Stand.” But the minute a respected handler says the same words in a sharp sudden tone, the horse reverts to good manners. Of course, he has learned the desired behavior in advance—unfortunately, we can’t just train a horse from scratch by speaking louder. If only!

Music

Normal human brains interpret certain pitch patterns as music. We take this ability for granted because it feels completely effortless and is common among almost all people. To comprehend music, though, our brains are working up a sweat. They have to analyze:

 Relationships between pitch, time, and volume

 Variations and consistencies in grouping and phrasing

 Patterns of rhythm and tempo

 Expectations based on memory

 Sensory illusions designed by the composer

 Emotion

This is complicated stuff.

I am often reminded of musical rhythm while riding—a horse who’s “behind the leg” is much like a singer behind the beat. And like music, the location of the rhythmic pocket changes with riding discipline: We teach Western Pleasure horses to work behind the leg, jumpers to work in front of it, and trail horses to stay on it.

Rarely, specific damage to the brain interferes with music perception. When listening to a song, people with amusia (“uh-MYOO-zhuh”) hear random disconnected tones. One patient, formerly a music composer and performer, described her post-injury perception as a collection of equal notes in which no one instrument or tone emerges as superior to the rest: “When I listen to an orchestra I hear 20 intense laser voices [each belonging to a separate instrument]. It is extremely difficult to integrate all these different voices into some entity that makes sense.”

An even tinier handful of people have congenital amusia, a lifelong disability in which their hearing is fine and their brains are normal in every other way. One described listening to a lilting lullaby like this: “If you were in my kitchen and threw all the pots and pans on the floor, that’s what I hear!”

We can infer that horses perceive music. It certainly has an effect on them that is different from the sound of kitchen pans landing on a floor. The equine brain is calmed by lyrical tunes without sudden changes in volume. Horses prefer Mozart to Beethoven, soft rock over techno, and country or folk more than heavy metal. Dissonant music agitates them, so it’s best to leave Stravinsky at home. Human brainwaves synchronize when a group of people listen to music together. Chances are that the same synchrony occurs among horses.

Despite the complexity of music perception, the horse’s brain makes sense of tonal patterns. How do we know this? Because his emotions change when listening to varied types of music. Even more intriguing, the same correspondences between music and emotion occur in a human as in a horse. A song that relaxes, invigorates, or annoys us is likely to have the same effect on our animals.

Winning with Music

A recent study explored the effects of music on Arabian racehorses. Thirty of them were housed in a barn where harmonious background music was played for five hours every afternoon. Forty of their peers were in a different barn at the same facility where there was no music. Conditions like feed, exercise, companionship, cleanliness, and handling were held constant. Within a month, the Arabians exposed to daily music developed significantly lower heart rates and won their races more often.

The positive effect lasted for three months. After that, the horses became accustomed to the music and its effect waned. But three months is long enough for a good trainer to change a smart aleck who becomes relaxed enough to learn. Once that foundation is set, the horse will remain trainable for the long term.

Where’s That Sound?

A third aspect of hearing is sound localization. Close your eyes and listen for a noise. (Have a friend hide a timer and set it to ring quietly in a few minutes, if necessary.) When you hear the noise, you know where it’s coming from—behind you, from one 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 most of the time.

Horses also cull information from a whinny even when they do not know the horse who produced it. From sound alone, they can identify an unfamiliar animal’s size, sex, and rank in the equine hierarchy. By contrast, humans can usually determine sex from the sound of a voice, but size is harder, and rank is not something we hear. After all, rank is less important to human survival than to equine survival.

Identifying Human Voices

Do horses identify a familiar human by her voice? Absolutely. Imagine two human friends whom your horse knows. Record their voices saying the same words. Now play the recordings while these two silent friends stand within the horse’s view. He will match the recorded voice to the person who owns it—looking immediately and for a longer period of time at the one whose recorded voice is played on a speaker. Incidentally, this type of cross-modal perception, in which vision and hearing are used in tandem, was once thought to be unique to humans. We now know that dogs and horses use it, too. Chances are that many species tap cross-modal perception. What’s remarkable is that we assumed they couldn’t.

For the full effect of the equine brain’s ability to decode what it hears, remember that we have considered only the whinny. Horses must also take into account the meanings of their neighbors’ nickers, squeals, groans, blows, and snorts. Their brains must analyze all the acoustic variations within those vocalizations, sort out which sound belongs to which horse, and figure out what it means in the context of the particular horse who produced it. Throw horses in a new setting where they don’t know anybody, and all this becomes a cacophony of confusing noise. And we wonder why they’re upset by change!