Written by: Antonia J.Z. Henderson, Equine Psychologist
When considering any equine or human sensory ability, we need to ask what that sense was evolved to do.
The concept of umwelt, from the German word meaning “surrounding world,” refers to one’s species-specific perception of reality, and is relevant when considering a horse’s sensory world. Organisms create and shape their own umwelt, guided by their unique evolutionary histories. Entrenched as we are within our own umwelt, our ability to step into an equine reality is limited. Carol Saslow, an equine behaviourist, comments:
“We are prone to attribute behavioral shortcomings or peculiarities [of our animals] to “lack of intelligence” and “deficient obedience” on the one hand or to animal extrasensory perception (‘ESP’) on the other. But often the best explanation is a mismatch of Umwelts (Saslow, 2001, p. 210).
I: What do horses see? A close-up look at equine vision
A graphic example of these mismatching umwelts is the overwhelming emphasis on equine vision in the small literature on equine senses. Vision, so critical to us, may not be the most important sense in a horse’s umwelt. Horses have different visual abilities than we do – abilities that have come to be because they were evolutionarily advantageous. But evolutionary change is slow, and many of the horse’s boogeyman-detecting abilities mare not adaptive in a predator-free environment, where a nonreactive attitude to change is expected and demanded.
Seeing all the way around
Horses’ laterally-placed eyes give them an almost 360- degree perspective, with blind spots directly in front of the nose and behind the tail. A common eye placement for prey animals, this extensive peripheral range offers the advantage of detecting predators easily, but comes at the expense of restricted overlap between the two eyes. Contrary to the myth that horses have no depth perception, their visual fields overlap by approximately 55-60 degrees. Furthermore, research indicates that even with one eye covered, horses use the same depth perception cues that we do (distant objects are smaller, near objects overlap further objects, parallel lines converge as they move further away, etc.).
Rods and Cones:
Night vision trumps visual detail Horses are equipped with an abundance of photoreceptors called rods, a lower ratio of ganglion cells to photoreceptors, and a unique tapetum (a reflecting layer of cells) at the back of the retina. All of these structures increase sensitivity to light, but come with a corresponding compromise in acuity. Contrastingly, we have a greater abundance of cones, specialized for colour vision and high definition visual acuity, but which need high light conditions to function effectively.
The ground level view
Recent colour discrimination tasks by equine behaviourist Carol Hall indicated that horses were able to distinguish colours and shapes more accurately when the cards were placed at ground level. The horse’s superior vision from this head-on-the- ground perspective is so foreign to our “eye-level” umwelt that all the highly-educated equine researchers previous to Hall never considered it. When thinking about how a prey animal who spends 18 hours a day grazing might best see their world, one wonders why not.
Are horses colour-blind?
Human eyes, with trichromatic vision, include three different kinds of cones, each containing a different photopigment, allowing us to see the full range of the colour spectrum. Research on horses’ colour vision has suffered from small sample sizes (horses are not as conveniently stored or trained as lab rats), and results have been inconsistent. However, the general consensus is that horses are dichromatic. Similar to colour-blind people, they perform well for blue and red stimuli, but have more difficulty with green or yellow discrimination.
In summary, horses have a much wider visual perspective than we do, but at the expense of visual clarity. They see best in low light, and when their heads are close to the ground, conditions that are not often afforded to a horse under saddle. Add to this that the horse is evolutionarily programmed to get the hell out of Dodge if anything suspect enters his visual field and it is a wonder that horses are not depositing us in the dirt a great deal more often than they do. A horse’s rapid response to movement in their wide visual field makes good evolutionary sense for an animal that needs to detect and flee predators. It is not particularly welcome when the horse is under saddle, and tends to persist, often regardless of the horse’s level of training.
With a better understanding of the horse’s visual umwelt, we can adjust our training and expectations accordingly. For example, we can ameliorate much of the horse’s “when in doubt, flee” response by allowing him time to adapt to new visual stimuli. Since horses’ daytime visual acuity is not ideal, objects that seem non-threatening to us may be much more suspect to a horse. Allowing the horse ample time and the freedom to lower his head for a clear view of a feared object will enhance our training progress. I cringe when seeing horses reluctant to load on a trailer lower their heads to investigate the ramp, only to have their heads jerked upwards and be told to pay attention. This is precisely what the horse was trying to do!
II: Smelling in Stereo:
The fact that smell is big for horses is clear when looking at their physiological structures for smelling. The horse’s brain has extremely large olfactory bulbs with a large convoluted surface allowing for a huge number of receptor cells. They also possess a vomeronasal organ, an olfactory structure all but vestigial in humans. Horse’s nostrils are designed to take in large numbers mof molecules, and with the nostrils’ orientation on either side of the horse’s face, horses are able to smell in stereo! Horses – unlike us, who gain most information through our eyes – can learn about others long after the originator of those olfactory clues is gone. Whereas we recognize one another by seeing each other’s face, horses may be learning a veritable treatise about another individual by smelling his or her manure. Scent markers are the equine Facebook.
Much of what has been attributed to a horse’s psychic abilities may be more parsimoniously explained by a keen sense of smell. We have all heard the claim from terrorized first-time trail riders, “That horse knew I was afraid and so he bolted for the barn.” Angry, anxious, or emotionally volatile humans produce sweat-gland excretions that may send olfactory messages to horses, triggering emotional responses in them as well. From the horse’s perspective, if the rider is afraid, the safest place is probably back at the barn, and the sooner the better! Similarly, owners often exclaim over their horse’s sixth sense because of his propensity to get agitated before the vet is even in sight. In all likelihood the horses’ superior olfactory abilities are at the source of his ESP, and through previously learned associations he knows that this particular smell is the harbinger of unpleasant events.
Simply noting that horses are living in a rich olfactory world quite unlike our own places us within the horse’s umwelt. Although this world is largely inaccessible to our inept noses, we can still be cognizant that quite possibly our horse does know something that we do not.
Horses’ auditory capabilities cover a broad range far exceeding ours in the higher frequencies. Their large, funnel-shaped and upright ears can tilt, turn, and twist independently, and are infinitely more adept at catching and localizing sound waves than our small, flat, immovable ears tucked close against our head. Despite their broad frequency range, horses’ ability to localize brief, high-frequency sounds is limited. If a sound is prolonged, they can use their mobile ears to locate the source. Brief sounds, such as the snap of a branch or the snort of another horse, are not easily localized and are likely to trigger a flight response. Much of horse’s spookiness about seemingly invisible monsters may be attributed to his ability to hear sounds that we cannot, without always knowing their source.
The implications for training are to allow horses the commodity that is always in short supply in our human umwelts – time. If our horse suddenly stops and swivels his ears and his head, chances are he heard something that we did not. We will have far greater success if we offer the horse sufficient time to localize the sound than by driving him to focus on the task we have in mind.
As the image of the recalcitrant school horse with a rider mercilessly thumping the horse’s sides would belie, horses can react to pressures too light for a human to feel. Researchers using instruments for measuring human tactile sensitivity found that horses’ sides, specifically the area that comes in contact with the human leg, were more sensitive than human fingertips. Rather, it is the inadvertent delivery of conflicting aids that results in the apparent insensitivity of the dulled school horse. Horses who have been labeled “dead-sided” may simply have been denied the opportunity to react to a consistent, meaningful, and light aid. Contrastingly, highly-trained horses who appear to read their riders’ intentions before an aid is administered may more likely be responding to the rider’s inadvertent subtle muscle tensions or weight shifts that habitually precede the aid.
Since our human umwelt is so intrinsically a part of who we are, it is challenging to embrace the equine Umwelt and experience the world through a horse’s eyes – or, more accurately, through his ears, nose, or skin. Good science will give us more information about what a horse sees, hears, smells, or feels. But this knowledge is of limited use on its own. The greater challenge is to use this knowledge to step inside the horse’s umwelt, to get it “from the horse’s mouth” and allow that perspective to permeate and become the guiding force of our training.
The Twitch Myth
Twitching (the practice of pinching the horse’s upper lip with a twisted loop of chain or rope for aversive procedures) is often considered cruel, effective only because the pain of the twitch deflects the horse’s attention away from the procedure at hand. To the contrary, used appropriately, the twitch is a humane restraint that applies pressure to a mass of nerve endings in the end of the nose, inducing a release of endogenous opiates or endorphins. The anesthetic action of the endorphins results in the horse not feeling the pain of the twitch or the invasive procedure. Equine behaviourist Sue McDonnell describes three phases of a twitched horse.
During the “Distraction” phase, the first 3-5 minutes, the endorphin release has not yet been activated and the twitch has no analgesic (pain-killing) effect. During the “Analgesia” phase the horse becomes heavy and relaxed, the eyes appear glazed, and the lower lip droops. This phase, where aversive interventions can be practiced, lasts for about 10-15 minutes, after which the endorphin output falls rapidly and the horse enters the “Blow” phase, so named because of the horse’s volatile and explosive behaviour. To ensure successful and non-traumatic twitch use, McDonnell recommends the following:
• Twitch use should be limited to relatively short and mildly aversive procedures. Clipping the inside of a horse’s ear while using a twitch is appropriate; a full body clip courts disaster.
• The twitch should be applied 3-5 minutes before the procedure begins, allowing sufficient time for the analgesic to take effect.
• The twitch should be removed well before the rapid endorphin decline so as to avoid the explosive and dangerous “Blow” phase.
• Horses should be habituated to the twitch, without an accompanying aversive procedure, to familiarize them with non-traumatic twitch use, and to learn each horse’s progression through the phases.
• Contrary to the notion that the twitch will be more humane if not applied too tightly, the twitch needs to be sufficiently snug so as not to fall off and so that the analgesic effect is triggered. If the horse is not showing the heavy-headed, glassy look characteristic of the Analgesic phase, the twitch may be too loose to be effective.
• Twitch use should always be positively reinforced with a food reward once the twitch is removed.
Horses that have always been correctly twitched do not become “wise” to the twitch, and do not mount a barrage of defensive behaviours. For horses that fear twitch use (because of a history of incorrect usage), repeated positive exposure without an intervening aversive procedure, in several brief sessions, and followed by positive reinforcement can be rehabilitative.