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Nature writer Ed Yong has been in the press recently with editorials and essays about how animals perceive the world. His best-selling book, An Immense World (Random House, 2022), has been getting much praise. He writes very eloquently about the sensory “bubble” that every animal exists within. Our world is indeed immense and rich with scents, sounds of every decibel, and light ranging from infrared to ultraviolet and beyond. However, each animal is designed to only perceive the portion of this cacophony that they need to survive in the world. According to Jakob von Uexkull, an early 20th Century biologist, this narrow range of stimuli is what he called the Umwelt, each animal’s personal piece of the big reality. For example, the four types of color-sensing cells in a mockingbird’s eye allow them to see colors we humans cannot, and differentiate the feathers of a male mockingbird from a female. It allows a platypus to perceive electrical fields we have no use for. It allows your dog to smell the fine nuances of a squirrel’s path in the woods, or a whale to hear the songs of other whales across miles of ocean. And unfortunately, it lets a mosquito smell the carbon dioxide you expel so it can home in on a snack.
This got me thinking about a horse’s Umwelt. We know they see, hear, and feel differently from us, but how exactly? By better understanding how they perceive the world, our relationship with them improves. The horse’s particular sensory strengths have evolved over the millennium and are designed to keep this prey animal alive. Don’t forget that we humans are predators and our sensory needs are completely different.
Let’s start with the eyes. Placed on either side of a long head, a horse has only a very few small blind spots: directly in front of their forehead, under their jaw, above the poll, and directly behind them. When you approach a new horse, come towards him from an angle, not straight on, so that he can get a good look at you. Their excellent lateral vision encompasses about 350 degrees, compared to about 120 degrees for humans with our front-facing eyes. As prey animals, it is extremely important for them to see danger anywhere on the landscape and their eye placement makes that possible. To get an idea of what this might be like, imagine having your phone’s camera on Panorama view all the time. When you are riding, your human eyes might be only looking at the obstacle straight ahead of you, but your horse saw that guy way over to the left carrying a bucket over to the barn, and got a little distracted.
Take a look at your horse’s pupils. They are not round, but more like a horizontal rectangle. Horses only see with full clarity in a “streak of acuity.” It’s a limited oblong field and everything above, below, and on the sides is somewhat fuzzy. Their close-up vision is not good at all. When you are standing next to your horse loving him up, you are completely out of focus but he uses his whiskers and smell to identify you or that treat you are holding. Horse anatomy traded full clarity for a wider field of vision, which evolution favored for survival. That streak of acuity also perceives motion and brilliance to a greater degree than the human eye. A horse notices motion or something shiny that we don’t perceive and will move his head around to bring an object into focus. Another reason we often laugh at them for seeing “invisible” predators.
Many people believe horses have no binocular vision and therefore no depth perception, but this is not true. Their field of depth perception is limited to where both eyes can see together, and that is straight ahead at least six feet distant. Have you ever ridden up to a stream and your horse is hesitant to step in? It’s true that at this close proximity, it is hard for them to judge if it is deep or shallow, but watch them move their head around to optimize their sight, sniff the water to get an idea of what it is, and perhaps tentatively put a foot in. They are using all their resources to determine if it is safe to proceed. Similarly, a horse will quickly raise his head to check out a noise allowing his binocular vision to come into play. I’m sure you have all experienced this when out on a trail ride. Your horse is ambling along with his head in a relaxed position when he suddenly raises and turns his head in the direction of sound. They also want to raise their heads as they approach a jump. This brings the jump not only into their streak of acuity but also into their range of depth perception.
Horses are not exactly color blind but research indicates that they see in much more muted colors than we do. Their evolutionary journey took place in large grasslands bathed in greens and browns, not pink and red. Therefore, shades of red are very similar to green in their vision. Did you know there is a logic to which colors and patterns are painted on jumps to help horses perceive them better? Red and green fade together while blue and yellow are easier for them to distinguish. Light and dark patterns are also easier for them to see.
While horses lack the number of color-sensing cone photoreceptors in their eyes, they have superior rod-shaped receptors that work especially well in low light conditions. A ride at dusk is not a big deal for a horse. I remember hearing how my father-in-law as a young man in the 1930s would sneak over to the jump field at the Fairfield County Hunt Club at night to ride the course! Horses can see better in low light but their eyes adjust to the dark more slowly than human eyes. Entering a barn on a sunny day may seem like a black hole to your horse, as does a horse trailer. Once they adjust though, they will see better in a dark place than you or me.
In a future article, we’ll explore other aspects of horses’ Umwelt: hearing, touch, and taste, and how their natural world of perception is disturbed by human intervention.
Tracy Van Buskirk is a 37-year resident of Newtown and president of the Newtown Bridle Lands Association, at www.nblact.com, a nonprofit volunteer organization formed in 1978 to foster an interest in horseback riding as well as preserving, protecting and maintaining riding and hiking trails in the community. Horses have always been a part of her life. She owns a small bay quarter horse named Little Bear.
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NBLA Trail Notes — How Horses Experience The World, Part 1: Vision – The Newtown Bee
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