The Mind of Your Horse

Last revised April 17, 2017.

His mind is in there.1

The brains of mammals are very similar, and differ in degree rather than kind.

The human desire to believe that we are the most intelligent species has led to a number of comparisons of brains. Brain size must matter, but our brains are smaller than those of the elephant or whale. Some researchers find pleasure in noting that some parts of our brain are much bigger than the same parts in other animals. For instance, our friend Cowboy Bob reports that “the brain cavity of a horse is filled with a lot more than what we usually think of as the “brain.” Although the space would, in fact, hold a small grapefruit, the cerebral hemisphere — or “thinking” portion of the brain cavity is a lot smaller.2

If horses could talk, though, they might point out that the brain cavity of their skulls is about the size of ours, and that lots of preprocessing happens between the nostrils and the brain, and between the eyes and the brain. If we compare head size of Mr. Horse and Mr. Man, Mr. Horse does just fine.

But you don’t have to take an opinion on this matter to find the rest of this chapter interesting.

What does your horse know about you?

If you are sitting in the woods and are approached by a deer or fox, they’ll come a lot closer if you hold still, remain quiet, and put one hand over your eyes (you can watch them through spread fingers.) This shape-shifting seems to put them at ease, but makes me wonder what a deer or fox actually reacts to. Do I scare them, or is it just my eyes, my movement, my sound? I consider these things inherent parts of me, not easily disembodied. Do they comprehend me as I comprehend myself, or am I some collection of components, some scary, some not so?

Before you laugh at what I’m going to tell you about my horse, let me tell you about my awakening with butterflies. I had always thought of caterpillars and adult butterflies as different beasts, disconnected from each other, with no carryover of memory, personality, or anything else. But it turns out that an adult moth or butterfly can remember important things it learned as a caterpillar.3 Before I learned about this memory carry over, it seemed as if one beast was actually two: first the caterpillar, and then the butterfly.

When I first rode my horse, I often pondered an odd question: is he clear that the thing on his back is me? Or does he think that one beast is actually two? I wondered this partly because the experience of standing next to a horse, hugging and stroking and talking to him is so very different than the experience of sitting on top of him. From the ground, my horse could stretch his neck for a scratch, and drop his lip and close his eyes when it felt so good. From the saddle, he just ambled along as requested. He might have once worked on a merry-go-round. How could I prove he knew that his best human friend was up there? How could I prove that he knew it was me, and not a sack of potatoes with my voice? Does he know my smell, my weight, my eye color, my hair length? Does he know that the one on top is the one who likes to stand next to him and laugh at his jokes? My suspicion was not that he thought I was someone else, but rather that the continuity was unimportant to him.

If you went out riding on Bob, and when you finished your ride you found you were on Fred, you’d be puzzled. But if your horse went out with Bob on his back, would he be surprised if Fred dismounted?

I am certain that my horse views me differently than you do. You know me by my written words. He does not yet read. If we were to meet, you would know me by my facial appearance. My horse may be able to identify me by my face in a lineup, but he places more confidence in his identification from my smell. And if I showed up at the barn with three arms, or with one, I honestly don’t think he’d be a bit troubled.

Confidence in Constancy

Humans are confident that when a person stands, they are the same person as when they are sitting. That when they put on a snowsuit, that they are the same person as when they wear a bathing suit. But small children are often scared by Halloween masks, and I suspect that children must come to learn about the intransitivity of individuals. Our adult notions of the individual are flawed: We are amazed when we learn that a butterfly has food preferences that it developed as a caterpillar, or that a turtle has a migration route that it learned in the egg, or that the experiences of a tadpole affect his behavior as an adult frog.

Animals give us evidence that they know us, until they give evidence that they don’t. Sit quietly in a chair near your bird feeder, and hold still. Birds will return to the feeders, and seem to be very tame. Now stand up. They’ll all disappear. You think: “Didn’t you know I was here when I was sitting? Do you think I will now harm you?” They think: “What’s this!?” Some warthogs I once met in Zimbabwe on a golf course grazed comfortably as I approached. When I sat down on the ground to minimize my disturbance, they panicked and ran. Apparently they had the same reaction to my sitting as the birds have to my standing.

As I write, I am surrounded with a flock of cockatiels, who spend their lives at near-liberty (wings are not clipped, and they are free to fly in the office when I’m here, in their aviary when I’m not.) They are very, very tame. One is on my knee right now, and others are sitting on perches around my desk. Some will come into the shower with me, and can manage to stay on my shoulder or head as I get dressed. But if I put on a baseball cap, even if I do it slowly, they all freak out and fly as far away as they can get. I don’t know if the bill above my eyes makes them think my head is on upside down (this happens often when I get dressed quickly), or just what triggers their flight, but they make it clear that they don’t understand what has happened to me, and don’t trust me with a hat the way they trust me with no hat. So their understanding of human attire is not the same as ours.

Interviewing the Horse

We cannot know how any species views another. Does a horse consider that our legs are the equivalent of his legs, or that our nose must do the sort of thing that his nose does?

Because most horses don’t talk, we need to devise some basic techniques for determining what a horse knows. Turns out, researchers have this covered. Here are ways to get a horse to talk:

  • Observation. Watching horses is one of the best ways to learn about them. In this book, I count on observation for most of my conclusions in the section on Behavior. Scientists do a more careful job of observation, often videotaping behavior then scoring it and tabulating their findings. For instance, Rubenstein and Hack observe4 that “of a sample of 310 male-male interactions involving 21 stallions during one breeding season, dominance was determined solely by an approach in 53% of the contests.” You may not have access to 21 stallions, but your eyes and ears will serve you well as an observer of what is on hand. Just remember that your horse may not always perfectly represent his species.
  • Preferential looking. If something surprises us, we attend to it. We may turn our heads to look in the direction of an unexpected sound, reach toward an unfamiliar object, or if we are a horse, turn our ears to better hear this unexpected thing. We look when our expectations are violated, and this reveals what we expected, what we know. Psychologists have devised preferential looking methods as tools for studying the cognition of human infants5. Preferential looking can also be used when we want to know what a horse knows: if we present something that surprises him (i.e., is not familiar, not known), and he turns his ears or head toward it, he has revealed something.
  • Comparative biology. Once we know that something is true in one species, we can wonder whether it is true in another. So, for instance, an animal’s call can carry information about species (guenons),6 sex (gibbons)7, kinship (guinea pigs, fur seals, pigs, hens, cows, sheep, and whales)8, emotional state (squirrel monkeys)9, hierarchical status (baboons)10, social bonding (parakeets11 and Campbell’s monkeys)12 or individual identity (Guenons, Geese, Penguins, Dolphins, Elephants, Indigo Buntings, Ovenbirds, White-throated Sparrows, Wood Larks, Ground Squirrels, Marmots, Coatis, deer, dogs, sheep, and European Robins).13 Can a horse’s whinny or other sound convey such information? It’s worth a look!

Recognizing Himself

A study of self-recognition in ants placed a blue dot on the ant’s face, provided a mirror, and watched what happened. Ants with blue dots would move slowly in front of the mirror, shake their antennae, and touch the mirror. They might retreat and re-approach the mirror. Some would groom themselves. But young ants, ants with brown dots on their face (matching their face’s color), or blue dots on the backs of their heads didn’t do this cleaning. Ants with blue dots could have acted aggressively toward their mirror image, the way other ants in the colony acted toward them. But by engaging in cleaning and grooming rather than acting aggressively to their mirror image, the ants showed the researchers that they had recognized themselves.14 The mirror self-recognition test has been used to establish whether an animal has a theory of mind — the ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires, intentions, and perspectives that are different from one’s own.15

Self-recognition as established with a mirror test is not restricted to ants and humans. In one study, pigs given a mirror appeared to look at their image. After 5 hours with the mirror, they were shown a familiar food bowl, visible in the mirror but hidden behind a solid barrier. Seven out of eight pigs found the food bowl in 23 seconds, on average, by going away from the mirror and around the barrier. The authors conclude: “To use information from a mirror and find a food bowl, each pig must have observed features of its surroundings, remembered these and its own actions, deduced relationships among observed and remembered features and acted accordingly. This ability indicates assessment awareness in pigs.16

If ants and pigs can recognize themselves or their environment in a mirror, can horses do this? I have not found research directly on this point. But I can tell you that whenever my mule Bud gets into the arena with its mirrors, he walks right over to one and studies himself. And as I reflect on him (using my theory of mind), I am certain that he has a theory of mind too.

Recognizing Others

All animals prefer to avoid fighting, and dominance rank reduces the need for fighting, if such rank can be recognized in advance. When two stallions approach each other, they typically begin by sniffing each other’s faces, genitals, and feces. This sniffing is followed by vocalizing. After such signaling, stallions may push or rub, and sometimes escalate to biting, kicking, and rearing. In one study, 79% of encounters between stallions ended after sniffing and vocalizing.17 That is, something about the smell or sound of fury was enough to convince one horse that the other had higher rank and should be deferred to. This study included an experiment in which recorded squeals and dung samples were presented to horses, to assess their reactions.

  • Recognizing dominance. The squeal of a dominant stallion is longer and lower than that of a subordinate. Recorded sounds of other stallions were played through a loud speaker to each stallion, and his reactions observed. The study found that “stallions, regardless of their own dominance status, kept their heads elevated for almost twice as long when they heard the call of a subordinate and they were much more likely to approach the squeal if it came from a low-ranking male.” This study also found that stallions had the same reaction to the squeals of those they met regularly and those they had never met. So stallions can distinguish low and high ranking males from their sound, but were not using sound to identify familiarity.18
  • Recognizing familiarity. In a dung sample test, researchers collected dung from known stallions and transplanted it to the test site. They found that stallions examined the scent of dung of unfamiliar stallions for twice as long as that from familiar stallions. So the stallions could tell which others were familiar, but did so from scent, rather than sound. But in other studies,19 where the speaker was placed behind the horse and played a familiar or unfamiliar whinny, horses turned their heads much more when they heard an unfamiliar whinny. Combining these two studies, I think it likely that a horse can recognize a familiar or strange horse both by sound and scent.
  • Recognizing kin. As many humans have learned, cousins don’t make the make the best marital partners if reproduction will be involved. Animals that disperse from their family before mating solve the problem of messy genetics by lowering the odds: once gone, any amorous encounters are not likely to be between close relatives. But if a female or her father does not leave the herd prior to her puberty, or a male or his mother does not leave prior to his puberty, then inbreeding might occur. In humans, it is sometimes suggested that childhood familiarity with each other may interfere with a desire to mate with each other.20 An important study of feral horses living in Nevada found that in the 24 copulations that were observed, there were none between a female and her father — or, if she had changed bands, with her stepfather. About their findings, the authors conclude that “first, they demonstrate that young females emigrated from bands in which they grew up, regardless of whether or not resident stallions were true fathers. Second, they show that the inbred mating occurred later in life and not when daughters reached puberty. Third, they show that natural situations occur in which individuals are born or grow up in groups where they are treated as kin although they have only associated with the members of the group and are not related genetically to them.21” Kinship recognition works for young mares and stallions, but may be nothing more than recognizing familiarity.
  • Recognizing individuals. Horses recognize each other individually. The strongest proof of this is the interactions between mother and foal. Most mares reject suckling foals other than their own. Mares separated from their foals shortly after birth will reject them when reunited a few days later. These rejections may be based on unfamiliar scent. When a foal is separated from his mom because he has fallen asleep, young foals may first approach some other mare before finding mom, whereas older foals can find mom directly upon awakening.22 This suggests that foals learn to recognize their mothers from a distance by sight. This recognition of individuals is long-lasting. One study found that young stallions could distinguish their dams in a large herd after a one year absence23, though another study suggested that this recognition of formerly familiar horses did not extend to 18 months.24

Recent research demonstrates that horses don’t merely respond to each other because they are familiar, but that they also recognize each other individually. In one interesting study that defines a testing paradigm for this question, horses in a stall watched (and probably smelled) a colleague walk past them and out of sight. Around the corner, a loudspeaker played the whinny of that horse, or played the whinny of a different horse they knew. The horse in the stall looked more quickly, and looked longer, when the incongruent whinny — from a different horse — was played. This greater attention indicates they were surprised, knew which horses made which whinnies, and could identify other horses by sight, sound, and probably smell.25

But of course we knew that. We know that individuals of other species recognize other individuals of their species.26 For example, hooded warblers can remember their specific neighbors from the previous breeding season even after overwintering in the tropics.27 King penguins can find their chick from among thousands of chicks, after months of separation.28 Paper wasps can identify each other, using facial recognition the way we do.29 And so a horse, just as social an animal as a warbler, penguin, or wasp, must be adept at recognizing others. A horse must be able to recognize other horses as individuals if we are going to have hierarchies in family groups, stallions attached to harems (and vice versa), or friendships.

But what we weren’t expecting here has to do with lateralization. A recent study30 has found that while horses are good at matching a voice with a familiar person, horses are better at this when the person is standing on their right, rather than on their left. Individual recognition works best from their right side, meaning the left side of their brain is specialized for this task. More support for “right is right” — the horse’s right side is the right place to be.

Do Clothes Make the Horseman?

Does the talent for individual recognition extend to other species? Do horses recognize humans individually? The question would seem preposterous to horse lovers, but Paul Guillaume has written “It is very unlikely that many animals possess an innate scheme corresponding to the human form. What is observed, thus, reflects knowledge acquired from a global perception whose main details, a priori, may be whatever; it is consequently not surprising that, in the recognition of a familiar person, clothes, for example, may play a greater role than the person’s face or voice. Grzimek has conducted experiments with horses that would only submit to being saddled or bridled by a person they were used to. In general, the experiments show that a change of clothes sufficed to prevent recognition; other studies show that, by wearing a familiar person’s clothes or approaching a horse that has just been bridled by a familiar, a stranger may be taken for that person.31

These are surprising conclusions. I am sure your horse knows who you are. I’m sure he isn’t unfaithful to you, just because someone else has borrowed your barn coat. You don’t find your horse behaving oddly when you change your clothes. But your horse has many possible clues that you are you: your smell, the way you walk, your arrival time, the sound of your voice.

Fortunately, some modern research, using a better scientific procedure than Grzimek reported in 1942, has come to different conclusions. Proops and McComb (2012) used a “preferential looking” paradigm to determine whether horses could match a specific familiar person with the correct familiar voice. Their findings: yes they can. Your horse knows that your voice is your voice. From the number of different handlers in this study, the researchers conclude that “horses use this recognition strategy [matching sight and sound of a person] naturally to identify numerous individual people in their day-to-day lives.32

An interesting study of sheep has found that they can recognize fifty different sheep from their faces alone, after a two year absence.33 Sheep, like people, have evolved temporal and frontal lobes for helping identify others from their faces, and are attracted to both sheep and people with familiar faces. Such capabilities have not yet been studied in horses.

What’s That on your Shoe?

On a trail ride, your horse will likely encounter something left behind by another horse. If it is fresh, he may want to bend down and take a good sniff. If you are coming back to the barn, and he comes upon his own feces, he doesn’t bend over. This tells me that he can identify his feces from a reasonable distance, and knows that the pile up ahead is his without needing to pause or bend down. By that simple act, your horse proves that he has some ability to recognize individuals from their feces. And considerable ability to smell and recognize poop from a great distance.

If your horse is to spend time smelling feces, what can we infer about what he is thinking? It turns out that horses pay most attention to the feces of horses from which they have received the most aggressive behavior.34 While we don’t know what they are thinking, because they are giving preferential attention to some of the individuals in their herd, we can be certain that individual recognition extends to the smell of feces: a horse will know another horse by his sight, his whinny, his smell, and the smell of his feces. Pretty clever! Does this mean that your horse smells like his feces? I don’t know, but I doubt it. I think a horse builds up a composite of another horse, adding to it bit by bit: what they look like, what they sound like, what they smell like, and what their poop smells like.

Stallions have been shown to differentiate the sex35 and familiarity36 of the source of feces. But puddles are different than piles: horses may not be able to determine the sex of donors37 or the oestrus stage38 of female donors from urine — unless the horses are familiar. Horses can discriminate between the sexes from urine samples of familiar horses.39

Horses also spend more time sniffing the feces of horses they are not very familiar with. And they don’t have an interest in sniffing the feces of other animals, such as sheep. So something in the poop is coded for “horse”, and your horse knows this.

Horses learn quickly about scents: after only two presentations of another horse’s urine, feces, or body odors, a horse has memorized the scent.40

Sex Differences

In a study cited earlier, mares were significantly better at recognizing individual handlers than geldings.41 Another study has found that mares seem to be better than geldings at gauging the attentional state of humans.42 We know that mares form close social bonds in wild herds, and that in the wild, horse society is matriarchal.


We now know quite a bit about the memory of the horse. Since horses still don’t speak, experiments will often use a horse’s willingness to approach an object, or efforts to avoid an object, as a sign of what it remembers.

Early experience with humans can leave horses with positive memories of humans (as revealed by approach and contact), or negative memories (as revealed by avoidance). In one fascinating study,43 forty one foals and their moms were divided into two groups. In the experimental group, mares were softly brushed and fed by hand for 15 minutes a day for the first five days of the foal’s life, in addition to routine procedures from caretakers. In the control group, only the routine procedures were provided. Experimental foals remained, at all ages, closer to the experimenter and initiated more physical contact with the experimenter than the control foals. Avoidance and flight responses of the experimental foals were considerably reduced when the experimenter approached, and accepted saddle pads on their backs more easily and quickly than control foals. And the handling of mares had effects that lasted at least until the foals were one year old, and generalized from experimenter to unfamiliar humans. These are huge and lasting effects on foals for only 75 minutes of positive contact with their mother.

From their experience with familiar humans, horses generalize to unfamiliar people44. With one caretaker, horses may come to be particularly friendly to unknown humans, and with another caretaker, horses may become aggressive toward strangers.

Horses also generalize from their experience with objects associated with various memories of humans. In one study, horses were presented with a bucket (an object they previously associated with food), a traffic cone (unknown, no likely associations), and a white shirt (like that used by the veterinarian). Horses were more reluctant to approach the white shirt than the bucket or cone, and showed visual responses comparable to those observed for fear-inducing objects.45

Growing evidence shows that training conditions have an impact on all of a horse’s daily life46. A study of more than 700 horses showed that the type of work influenced emotionality and tendencies to present abnormal behavior outside work.47

What Does Your Horse Know About Where He Lives?

Mental Maps

Birds and mammals — and probably all animals — seem to develop and use mental maps of the area where they live. A swallow learns its home range by moving about it after it hatches. After migrating thousands of miles, it returns to its home. This feat is made possible by a magnetic compass, a celestial compass, a circannual48 clock, and an inherited mean migratory direction.49 Once all of these mechanisms have guided the bird to her original neighborhood, her mental map of the place takes over, and she can fly to the branch of the tree where she was born.

Horses are no less remarkable than birds. While horses don’t migrate, they can take you home in the middle of the night. They can do this both by following the trail you took when you left the barn, or by going cross country, making a beeline for the barn.

Horses and humans appear to maintain a mental map that resembles a physical map, or at least can function as if we are reading or drawing a physical map. Such mapping involves place cells in the brain that record an experience of a location, and the geographic relation between that place and other nearby places. If you think about your favorite trail ride, you don’t remember every detail of every foot along the path. You remember the intersections, the water crossings, and other distinctive places. You can construct in your imagination which place comes next, as you imagine your trail ride.

Without a mental map, we would spend our last days lost in the woods. Your horse doesn’t need such a map the way we do, because he has an incredible nose, and could likely find his way home if he were blindfolded at each turn.

But your horse does have a mental map of his area because he has such strong place memories, and has expectations for what the next place will look like. You’ve probably been riding him when something you passed every day was suddenly changed. Your horse ambles along until he spots this change, and Wow! My horse, at least, might apply full brakes. He takes in the new look of the place, memorizes it, and can then continue.

My horse’s ability to remember small details of a place far exceeds my own, and I am always astounded when he freezes because a tire is now lying at the side of a road he has traveled many times when there was no tire. Such an ability, in horse or human, seems to involve place cells, which store information on a specific place. “Place” here is some very small area — perhaps inches in diameter if you are a mouse, or feet in diameter if you are a horse. A place cell in the hippocampus fires whenever the owner of that hippocampus reaches the place field (the spot that this place cell is in charge of remembering). How a route is constructed in a cognitive map seems to involve linking specific place cells in sequence. If a location is remembered, it can trigger one, two, or many place cells. When it triggers two cells, it is because we are moving from one remembered location to another.

Spatial firing patterns of 8 place cells recorded from a layer in the hippocampus of a rat. The rat ran back and forth along an elevated track, stopping at each end to eat a small food reward. Dots indicate positions where action potentials were recorded, with color indicating which neuron emitted that action potential. There is overlap in the area remembered by the place cells, so that in some spots, two place nerves are firing.50

Place cells likely store multiple kinds of information about a place. In a human, they likely store mostly what we see. In a mouse, spending much of its life in the dark, they may focus on smells. In a horse, they likely store both visual and olfactory information.

Beelines are an entirely different approach to navigation. When a bee finds a great bunch of flowers, he does not need to retrace the route he took to get there. He can fly straight back to the hive. Ants can make beelines, too.51 A human navigating home from the flowers would likely not be able to fly, and might find scrambling through brush unpleasant, so would need to take a path similar to the one already taken. But a horse in open country should be able to either follow a cognitive map or take a beeline back to the barn.

A beeline to the barn could come about by the phenomenon of dead reckoning, or path integration. With dead reckoning, we constantly update our sense of the distance and direction of some place, without regard to the route we have taken. Animals like bees, ants, and horses don’t need to travel thousands of miles, like birds, so can have a somewhat simpler system for navigation. Since they don’t travel day and night, bees, ants, and horses likely use a skylight compass: as they travel, they collect information on distance traveled and direction traveled, and update a “mean home vector”.52 We can’t prove this explanation (yet), but no other explanation of dead reckoning seems more plausible.

Dead reckoning must be used by sea turtles returning to the beach where they were born, knowing the general direction to travel and the exact latitude of their destination. In the ocean, it would be difficult for a sea turtle to navigate very far using place memory. But for a horse returning from a long hike in the woods on his own, some combination of dead reckoning and a mental map using place cells is likely the trick. On an open plain, the route home is likely guided more by dead reckoning than it is when coming home through an Eastern woods. The skylight compass will work better when there is a view of the sky, and place memory will be preferable when the alternative to following the original path is to scramble through the brush.

And what’s your horse doing walking back to the barn on his own?

Math and Reasoning

Counting and Comparing

If you happen to have a basket of apples, and two containers, try putting one apple in a container with your horse watching. He’ll head for that container and have his apple. On another day, try putting one apple in one container, and two apples in an adjacent container. If he’s seen you do that, he’ll head to the container with two apples. You can try this with two apples in one, and three in the other. So your smart horse is able to hold a memory of “how many” for these two containers, and choose the larger of them.53

But your smart horse has his shortcomings. He may not be able to choose as well when the containers hold 4 apples and 6 apples.54

The thinking in this aspect of counting is that your horse is showing you his Approximate Number System (ANS). Many animals can determine which is more, when looking at small numbers or certain ratios of more and less. An ANS seems to operate in mosquito fish, guppies, pigeons, capuchin monkeys, chimpanzees, rats, raccoons, mallard ducks, bottlenose dolphins, African Grey parrots, crows, salamanders, dogs, horses, and more.55 Horses do about as well as very young children. In one study, college students did about as well as guppies in the numerical comparison test, and it seems likely that the ANS evolved a very long time ago, and is part of the brain power of most animals.

Traditional mathematics probably requires language and the ability to express a number as a word or symbol. Speakers of Mundurukú (an Amazonian language), have no words for numbers beyond 5. They are not able to do exact arithmetic with numbers larger than 4 or 5, but can compare and add large approximate numbers.56 An ANS gives all the children a place in the choir, and language moves them to the front row. Until your horse learns to talk, he’ll need to make do with an ANS.

In humans, the ANS improves with age, so that adults are better able than children to say which is more when larger quantities are involved. Training extends the numerical abilities of guppies,57 and likely could do the same for your horse.

Brain Function

Left Brain, Right Brain

In birds and mammals, the two sides of the brain have somewhat different functions. Hemispheric lateralization gives one side or the other dominance in certain kinds of processing.

The left side of the brain receives most of its input from the right side of the body (and vice versa) for vision and hearing. The left side of the brain receives most of its input from the left side of the body (and vice versa) for smell, taste and touch. Consider these differences in functioning:

Left Hemisphere Right Hemisphere
Processes positive emotions, such as pleasure from eating Processes negative emotions such as fear, aggression
Specialized for approach Specialized for attack or avoidance
Produces vocal communications. Recognizes species-specific vocalizations. Processes vocal communications of modulated frequency, transmitting information about the identity of the emitter, whether a threat is present, and details about the threat.58
Categorizes stimuli, controls responses that require choices, inhibits responses until decisions have been made.59 Specialized for quick reactions to novel stimuli. Neophobia lives here.
Handles input from right eye, right ear, left nostril. Handles input from left eye, left ear, right nostril.
In humans, specialized for speech and language, processing information by analyzing stimuli as discrete items with reference to temporal arrangement, including speech, syntax, naming, reading, writing, perception of stimulus duration and temporal order, oral movements, verbal learning and memory.60 In humans, specialized for nonverbal skills, for processing information of an integrative temporal aspect, such as perception of faces, melodies, color, spatial position, emotional tone, intonation patterns, and singing and regulation of alertness and meaning61.

When an animal encounters a predator, many species react faster when it is first seen in their left visual field.62 Remember that the left eye directs most of its input to the right hemisphere.

The lateralization of brain function appears to occur in all vertebrates. The right hemisphere seems to be in charge of escape responses throughout vertebrates,63 suggesting that lateralization evolved a very long time ago. In many species, such as parrots,64 toads,65 and primates66, lateralization is revealed in side biases and limb preferences. Your horse likely grazes most often with his left leg in front of his right.67 One study68 reports that horses use their right ear (processed by the left hemisphere) significantly more at the sound of a whinny by a familiar horse, and use their left ear (processed by the right hemisphere) significantly more when they hear a whinny from an unfamiliar horse.

Lateralization may have evolutionary advantages. Researchers69 studying the domestic chick suggest that “cerebral lateralization is associated with an enhanced ability to perform two tasks simultaneously: finding food and being vigilant for predators. This finding suggests that cerebral lateralization enhances brain efficiency in cognitive tasks that demand the simultaneous but different use of both hemispheres.” Horses are much like chicks in needing to go about their lives while monitoring for danger. In the horse, the left ear and left eye monitor for danger with the right hemisphere while the left nostril checks for tasty grazing with the left hemisphere. (Of course, if any of his senses detect danger, Mr. Horse will likely cease grazing and focus all senses on the source of concern.)

Considerable research on horses finds lateral biases in vision, hearing, smell, and emotional and motor operations.

When a dog meets an unfamiliar dominant dog, it would presumably handle the situation using his right hemisphere, which could cause him to wag his tail to the left; when a dog greets his owner, the tail would be handled by the left hemisphere, and would wag to the right. This, in fact, is what happens.70 And incredibly, a study has found that dogs looking at moving video images of other dogs exhibiting prevalent left- or right-asymmetric tail wagging showed higher cardiac activity and higher scores of anxious behavior when observing left- rather than right-biased tail wagging.71 So dogs can use a bias in tail wagging to infer the emotion of another dog, and are able to share the emotion. Dogs know about brain lateralization.

An interesting study by Austin and Rogers72 used an umbrella to scare horses. They stood five meters from a grazing horse, and suddenly popped the umbrella open. The person with the open umbrella continued walking toward the horse until it stopped moving away. The study found that horses that were approached from the left side moved farther away than those approached from the right. When the umbrella was popped open a second time, it didn’t matter which side it was popped open on if the horse had first seen it with his right eye — the horses tested seemed to habituate quickly to the umbrella when they learned about it with their right eye. But when the first umbrella presentation was to the left eye, then popped open a second time, horses on the second trial were more reactive when the second presentation was to the left eye. If you want to scare your horse, surprise it from the left. If you want your horse to be fearless, present the scary stuff to his right eye first.

And a surprising finding: horses did better matching a familiar person with a familiar voice when the person was standing on their right. When the horse’s owner was standing on their left side, the horse did not treat familiar and unfamiliar voices differently73! So horses are better at identifying people with their right eye than their left. Since the optic nerves cross in such a way that most of the processing of the right eye’s input is done by the left side of the brain, it is tempting to suggest that your bonding with your horse might be more efficient if you are standing so that he can see you with his right eye.

And another surprise: Turns out, horses and other animals have a marked preference for conspecifics to be situated on their left.74 This preference is likely to be defensive. But if you were to position yourself on the left, so that your horse is seeing you only with his left eye, and receiving a stronger scent and louder sound from his left nostril and left ear, then he will be processing you on his right side. And that means you are helping him worry about you, and to prepare to attack or flee from you, and monitor everything you say for possible threats.

With this logic, Sankey and colleagues write “Young or highly reactive horses would certainly learn faster and be more relaxed if first approached on their right side. Beginning their training by handling them on their most reactive side (i.e., left) may in some cases exacerbate their emotional reactivity.75

I want to stand next to my horse’s right side when possible, and help him squeeze every little bit of positive emotion from our time together. I want to stand on my horse’s right side when possible, to help him with his approach to me. If I’m going to train him, I want to stand on his right side, to help him think through the instructions and maybe tell me what he is thinking. And if I’m going to introduce him to some scary new obstacle on my obstacle course, I hope he can first see it with his right eye. Ultimately, your horse must be able to handle the scary stuff from either side, so you might want to introduce the scary stuff when it is on his right side. When he is relaxed with it, present it so he can see it with both eyes. Finally, you might giving him his toughest test by presenting it only to his left eye.

What about the tradition of walking on your horse’s left side when you lead him, and mount from his left side? Julie Goodnight tries to explain:

“First, because horses are very one-sided, that is, they only think on one side of their brain at a time (and it’s a very small brain), they can learn something on one side, and not know anything about that particular subject on the other side. So we have standardized the left side as the side the horse is trained for everything, from haltering to leading to mounting. Why the left side and not the right? You have to go back to ancient times when horses were used as war mounts. Soldiers carry their swords on the left side (to reach with their right hand) and so they could only mount from the left or they would sit on their sword.76

Mounting from the left is not universal. The cavalry of Alexander the Great, who rode bareback, pole vaulted aboard from the right using their battle spears. Samurai warriors wore their two swords tucked into their sash, are believed to have mounted from the right. Napoleon Bonaparte, who was left-handed and wore his sword on the right, apparently mounted from the right. And Native Americans who taught themselves to ride, boarded from the right.77 Mounting from the left seems to be rooted in European traditions, not science.

Unless you are carrying a sword on your left side,78 you’ll be better off if you lead and mount from his right side (or taught him to handle this from either side, as Xenophon recommended)79. Of course, the world is full of people who think their horse only thinks on one side of their brain at a time, and think that a horse won’t understand being lead or mounted from the wrong side. If you bought such a horse…

Feeling experimental? Consider this project: Buy a Guardian Mask80. Remove the eyecover from the right side. Leave the 95% sunshade in place on the left side. See how your horse does when meeting new people, encountering new scary stuff. Try the same experiences with a completely blocked view from the left side. Does blocking his view with his left eye help in calming him?

Horse wearing the Guardian Mask, with 95% sunlight blocking on both eyes.81

Motor Laterality

Motor laterality is sidedness or handedness in motor function. If you are right-handed, you prefer to open a door, hold a pencil, or dribble a basketball with your right hand. In humans who are right-handed, the right side is stronger and more coordinated. If you are a horse and right-sided, you prefer to gallop clockwise and jump or do your dressage moves on the right rein.

Motor laterality seems to be present in all of the animals studied, including humans, other primates, dogs, cats, rodents, whales, and horses.82

If you go off and read about laterality, remember that I’m talking about motor laterality here, not laterality in preferred nostril or eye or ear. The biases of first nostril use and first leg extended seem to be unrelated, suggesting that sensory and motor lateralization organize separately in the brain.83

Trotting. Researchers looked at gait symmetry in young horses at a trot. Horses trotted on a treadmill, and were recorded with high-speed cinematography. Films were analyzed with semi-automatic film-reading equipment. Asymmetry developed as the horses aged, so that it was pronounced by the age of 18 months. The researchers concluded that “the increasing asymmetries with age are interpreted as further manifestations of already existing asymmetries or laterality which may be influenced by physical activity and training.84

Galloping. Horses show sidedness in their choice of leading leg at a gallop. Researchers85 recorded Quarter Horse fillies at a gallop using high-speed movie cameras while running on a straightaway. Riders signaled for both leads an equal number of times, but horses preferred to lead with their left, choosing it twice as often as the right. On the left lead, stride lengths and velocities were greater than on the right. On the left lead, the right forelimb remained in contact with the ground longer than the left forelimb did when on the right lead. Reading between the lines: these horses were getting more power out of their right sides (on a left lead), as shown in stride lengths, velocities, and ground contact time. The authors suggest that “selecting the right fore limb as the trailing fore limb may have allowed horses to use it to withstand the greater stresses and caused them to preferentially gallop with the left fore limb leading.”

Grazing. If a horse “does the split”, reaching forward with one foreleg while holding the other back, the head is lowered toward the ground, making the grass handier. Many horses prefer to graze with their left foreleg forward beyond the right. In one study, 40% of horses grazed with left foot forward, 9% with right food forward, and the remainder showed no preference.86 In another study,87 49% of horses preferred to graze with left foreleg forward, 12% right, and the remainder showed no preference in grazing. the strength of preference increases with age. Below the age of 2, four times as many horses prefer to graze with left foreleg forward as right foreleg forward. But in those over 2 years, this ratio rises to 5:1. The gains in preference for grazing with left foreleg forward come mainly from the ambidextrous horses, who choose a preference as they age.

When the left leg is advanced and the horse is not moving forward, the right foreleg is supporting a bit more than half of the weight of their front ends, and over time becomes stronger. For those horses with no statistically significant preference for which leg leads in grazing, aging may gradually magnify an initially slight preference, by strengthening the side that is slightly preferred. Laterality favors one side or the other, and the favored side is likely to become better developed. This could explain why a side bias may also emerge with maturation in primates88.

Straining. One study89 used strain gauges glued to the surfaces of the front hooves to assess how turning affected strain. Turning strains were up to 43% higher for the non-lead foot. So if a horse normally leads with his left leg, the right leg is receiving more strain, an opportunity both for injury and muscle development. A preference for leading on one side could lead to better development of the other.

Consistency. If a horse shows a strong laterality with one behavior (such as leading with the left), will they show a strong laterality in other behaviors? Not necessarily. Things are not so simple. Researchers used four procedures to measure laterality: 1) favored foreleg to initiate forward movement; 2) obstacle avoidance within a passageway; 3) obstacle avoidance within the passageway while ridden; 4) assessment of motor preference while rolling. Here are the key results: in all measures, significantly more horses exhibited lateralized responses than equally balanced responses, but there was no significant difference between the numbers of horses that exhibited left versus right lateralized responses. Matching laterality preferences were seen comparing procedures 1 and 2, 1 and 3, 2 and 3, and between 3 and 4. Overall, female horses showed a significant right lateralized response, and males show a significant left preference90. So we can see some general laterality in some horses some of the time.

Individual horses are left-sided, right-sided, ambidextrous, or are any of these qualities much of the time in a given circumstance. But most prefer to gallop and graze leading with their left, putting a greater strain on the right. Long-term cyclic strain leads to greater muscle strength.91 So are they “left handed” or “handed”? If they were humans, who are strongest on the side of handedness, we’d call them right-handed, just like most of us.

Your horse. Are you a busy scientist? You can measure your horse’s laterality with pedometers attached to each of his front legs.92 A horse that puts his left foreleg forward to graze will likely move it farther in the course of the day than he’ll move the right.

Are you an observant tabulator? You can judge your horse’s laterality by watching him graze for 10 minutes. He may always lead with one foreleg or the other, or it may be a split decision — which might suggest he is well-balanced, equally strong on both sides, and therefore ambidextrous.

Or if you like to guess, you can make a quick guess about a horse’s laterality by looking at their whorls of facial hair. Horses that lead with their right leg when grazing are likely to have clockwise facial hair whorls, and those leading with their left are likely to have counterclockwise whorls.93 As for Longfellow’s little girl who had a little curl? We suspect she was not ambidextrous, but don’t know much else.

On the left: a horse with a clockwise facial hair whorl, one who is likely to lead with his right foreleg when grazing and be “left-handed”. In the center: a counter-clockwise whorl, on a horse likely to lead with his left. On the right: a horse with a radial facial hair whorl.94

I yearn for a book on horses, much like “How Monkeys See the World: Inside the Mind of Another Species”95 “Inside the Mind of a Horse” would be just as interesting, but we’ll need to do some more research before this topic can become book length.


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63 Lippolis, G., Bisazza, A., Rogers, L. J., & Vallortigara, G. (2002). Lateralisation of predator avoidance responses in three species of toads. Laterality, 7, 163 183.; Lippolis, G., Westman, W., McAllan, B. M., & Rogers, L. J. (2005). Lateralisation of escape responses in the stripe-faced dunnart, Sminthopsis macroura (Dasyuridae: Marsupialia). Laterality, 10 , 457 470.

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72 Austin, N. P., and L. J. Rogers. “Asymmetry of flight and escape turning responses in horses.” Laterality 12.5 (2007): 464-474.

73 Proops, Leanne, and Karen McComb. “Cross-modal individual recognition in domestic horses (Equus caballus) extends to familiar humans.” Proceedings of the Royal Society of London B: Biological Sciences 279.1741 (2012): 3131-3138.

74 Leblanc, Michel-Antoine. The Mind of the Horse. Harvard University Press, 2013., p. 97.

75 Sankey, C., Richard-Yris, M. A., Henry, S., Fureix, C., Nassur, F., & Hausberger, M. (2010). Reinforcement as a mediator of the perception of humans by horses (Equus caballus). Animal cognition, 13(5), 753-764.; Sankey, Carol, Marie-Annick Richard-Yris, Helene Leroy, Severine Henry, and Martine Hausberger. “Positive interactions lead to lasting positive memories in horses, Equus caballus.” Animal Behaviour 79, no. 4 (2010): 869-875.

76 Goodnight, Julie. “Why do we mount from the left?”

77 “Why cowboys get on the left side of a horse.”

78 Folk lore tells us that soldiers who were right handed needed to reach across and grab their swords from the left side. A sword on that side would possibly interfere with leading and mounting from the right.

79 Morgan, M. H. “Xenophon: The Art of Horsemanship.” JA Allen and Company Limited, London, UK (1993). Xenophon’s first draft was in 360 BCE.

80 Available from

81 Image source:

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83 McGreevy, P. D., and L. J. Rogers. “Motor and sensory laterality in thoroughbred horses.” Applied Animal Behaviour Science 92, no. 4 (2005): 337-352.

84 Drevemo, S., I. Fredricson, G. Hjerten, and D. McMiken. “Early development of gait asymmetries in trotting Standardbred colts.” Equine veterinary journal 19, no. 3 (1987): 189-191.

85 Deuel, N. R., and L. M. Lawrence. “Laterality in the gallop gait of horses.” Journal of biomechanics 20, no. 6 (1987): 645-649.

86 McGreevy, P.D., Rogers, L.J., 2005. Motor and sensory laterality in thoroughbred horses. Appl. Anim. Behav. Sci. 92, 337–352.; Murphy, J., Sutherland, A., Arkins, S., 2005. Idiosyncratic motor laterality in the horse. Appl. Anim. Behav. Sci. 91, 297–310.

87 P.D. McGreevy, L.J. Rogers / Applied Animal Behaviour Science 92 (2005) 337–352

88 Hook, M.A., Rogers, L.J., 2000. Development of hand preferences in marmosets (Callithrix jacchus) and effects of ageing. J. Comp. Psychol. 114, 263–271.; Ward, J.P., Milliken, G.W., Dodson, D.L., Stafford, D.K., Wallace, M., 1990. Handedness as a function of sex and age in a large population of lemur. J. Comp. Psychol. 104, 167–173.; Ward, J.P., Milliken, G.W., Dodson, D.L., Stafford, D.K., Wallace, M., 1990. Handedness as a function of sex and age in a large population of lemur. J. Comp. Psychol. 104, 167–173.

89 Summerley, H. L., J. J. Thomason, and W. W. Bignell. “Effect of rider and riding style on deformation of the front hoof wall in Warmblood horses.” Equine Veterinary Journal 30, no. S26 (1998): 81-85.

90 Murphy, J., A. Sutherland, and S. Arkins. “Idiosyncratic motor laterality in the horse.” Applied Animal Behaviour Science 91, no. 3 (2005): 297-310.

91 Kim, Byung-Soo, Janeta Nikolovski, Jeffrey Bonadio, and David J. Mooney. “Cyclic mechanical strain regulates the development of engineered smooth muscle tissue.” Nature biotechnology 17, no. 10 (1999): 979-983.

92 Warren-Smith, Amanda, and Paul McGreevy. “The use of pedometers to estimate motor laterality in grazing horses.” Journal of Veterinary Behavior: Clinical Applications and Research 5, no. 4 (2010): 177-179.

93 Summarized in Murphy, Jack, and Sean Arkins. “Facial hair whorls (trichoglyphs) and the incidence of motor laterality in the horse.” Behavioural Processes 79, no. 1 (2008): 7-12.

94 Image source: Murphy, Jack, and Sean Arkins. “Facial hair whorls (trichoglyphs) and the incidence of motor laterality in the horse.” Behavioural Processes 79, no. 1 (2008): 7-12.

95 Cheney, Dorothy L., and Robert M. Seyfarth. How monkeys see the world: Inside the mind of another species. University of Chicago Press, 1992.


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