How Horses See
by Evelyn B.
Hanggi, M.S., Ph.D.
(중요한것만 간단히 옮겼습니다)
Beginner, trainer, owner, lover, weekend rider, American, Canadian, European, Asian, Australian – these are the folks who come to the nonprofit Equine Research Foundation (ERF) in California . Determined to improve their relationships with horses, they seek knowledge about why horses behave as they do, how they think and learn, and how they perceive their world. 많은 사람들이 비영리단체 Equine Research Foundation(마필연구소)에 모입니다만 그들은 정작 말이 어떻게 배우고 생각하고, 왜 그렇게 행동하며 세상을 보는지 에 대해 잘 모릅니다.
Along with ambition, participants bring questions, conceptions and, often, misconceptions. “Many people may have years of horse experience,” says ERF program director Jerry Ingersoll, “yet they still do not fully understand what makes a horse tick. They groom, saddle, and ride as they’ve been taught but don’t often question the soundness of those teachings.”
And so, riders continue to steer their horses around puddles because, according to student volunteer and horse veteran Rebecca Grand on her first day at the ERF, “horses can’t tell how deep they are, at least that’s what my instructor said.” And people persist in pulling and pointing and pushing horses over jumps because of an idea that these animals lack perception of depth; in other words, that they have a tough time judging distance. When asked if any instructor ever spent time talking about equine vision, ERF participant Nancy Siddens replied “The only thing I remember being told was that since horses have eyes on the sides of their heads, they do not have binocular vision . . . I am assuming depth perception is not strong.”
Good with depth, trouble with depth; colourblind, not colourblind; sharp vision, blurry vision – which is it? Answers differ, depending on who is doing the talking. More often than not, the speaker is someone people trust and, therefore, do not question — the well-known clinician, the feared riding instructor, the respected old ranch hand. Unfortunately, some of these authorities base their comments on hearsay, on folklore, on myth.
말의 시력이 심도감각이 있는지, 색맹인지, 촛점이 명확한지도 모르면서 그냥 배운대로 묻지않고 따르는것은 오해를 일으킬수 있는 걱정스러운 일입니다.
Hearsay is a worry. Generally untested, most likely undocumented, it is the cause of much misunderstanding. How, then, does one distinguish fact from fiction? Simple really, just ask the experts. Today, scientific study into equine vision is at an all time high, with discoveries offering evidence that horses see a world not so far removed from ours. Here is what science tells us:
Field of View: Having eyes in the back of their heads, almost.
말의 시야: 마치 머리 뒤에 눈이 달린것과 같습니다.
양옆으로 놓여있기때문에 시야가 매우 넓고 머리를 들고 있을때는 거의 360도의 시야를 갖게됩니다. 맹수로부터 피하기 유리하죠. 그러나 또한 조금 앞쪽으로도 향하고 있어서 55도에서 65도 겹치는 부분이 있습니다. 거의 모든 부분을 볼수 있지만 사각지대는 바로 뒤와 이마와 수직되는곳과 코 바로 밑이지만 이것도 조금만 머리를 움직이면 다 볼수 있습니다.
Remember in school when your teacher, with her back to the class, always knew what everyone was up to? Seemed she had eyes in the back of her head. Or maybe she had eyes like a horse.
Horses have lateral eye placement, meaning their eyes are located on the sides of their heads. This gives them a much larger field of view compared to humans; in fact, when holding their heads level, they possess a nearly spherical field of vision. An advantage in detecting predators, many prey animals have this sort of eye placement. But horse eyes are also placed somewhat frontally, affording them binocular overlap ranging from 55 to 65 degrees.
With vision that extends almost a full horizontal circle, horses have no problem seeing what goes on around them. Blind areas exist only within a narrow region to the rear as well as a small area perpendicular to the forehead and directly below the nose. Even so, a tiny shift of the head suffices in bringing these areas into view.
Visual Acuity: on a clear day, can they see forever?
시각의 명확도
The ramp retina theory is passé. Long popular, even in veterinary textbooks, this concept sought to explain how the equine eye focuses. It was thought that objects at various distances were brought into focus by the horse raising or lowering its head so that images could fall onto different areas of the retina. Upon physical examination, however, scientists found little indication that the retina was ramped; on the contrary, they discovered that what small slope did exist slanted opposite to that which might have helped focusing.
말의 망막엔 눈 중심을 가로지르는 좁은 수평줄이 있는데 콘이라고 부르는 리셉터 세포로 가득차있습니다. 이것은 사람의 fovea와 같은 역할을 하며 이 밖으로 나가면 시각의 명확도는 떨어지는것이 사람과 같습니다.
More exactly, the horse’s retina contains a narrow horizontal streak across the center of the eye densely packed with receptor cells called cones. Providing an elongated band of acute vision over much of the lateral range, this visual streak probably serves the same purpose as the fovea in the human eye. Acuity drops off rapidly outside the fovea in humans as it does outside the streak in horses. Heads bouncing up and down, like a bobblehead dog in the rear window of a car, serves no advantage to horses in terms of keenness of vision.
Does the horse see fairly clearly at distance? Well, yes. In fact, if you are even moderately nearsighted, chances are your horse sees better than you! Whereas normal human vision is 20/20, horses are rated at 20/30. In comparison, cats come in at 20/75, rats at 20/300.
말은 멀리서도 명확하게 봅니다. 명확도를 보자면 사람이 20/20, 말이 20/30, 고양이는 20/75, 쥐가 20/300 입니다.
Colour Vision: Looking at the world through rose-colored glasses?
콘은 다기능적이죠. 섬세한 내용도, 색상도 제어합니다. 우리는 네가지 주된색과 그에 따른 다양한 색을 봅니다. 여러가지 다른 주장이 있습니다만, 말은 색을 잘 못 보는 사람과 같답니다. 몇가지 색은 보는것 같고 그에.따라 각각의 다른 반응을 하지만 색을 보는것에 대한 정확히 일치하는 연구결과가 없습니다.
Cones are multifunctional. They control fineness of detail but they also control colour when more than one type of cone exists. Humans with normal colour vision are trichromats: we see four main hues – red, green, blue, and yellow, as well as many subtle variations.
The topic of equine colour vision has raged controversial for years. Backyard owners swear their horses prefer buckets and blankets based on colour; top trainers sell books proclaiming horses are colourblind. Yet, when asked how they know, most people cannot support their statements, falling back on the adage “Well, so and so said so.” Enter again the researcher. Equine vision expert Dr. Brian Timney, of the University of Western ontario , explains that horses are like humans with colour deficiencies. For example, humans with red-green colour vision defects have only two hues (blue and yellow) rather than four. Such dichromats do not see intermediate hues, seeing instead white or gray or a faded form of the two colours.
What colours, then, do horses see? “Horses have little difficulty in discriminating red or blue from gray. With respect to green and yellow, the results are mixed,” says Timney. His findings are similar to those from earlier studies but other researchers’ results differ. Exact answers have proven elusive in colour vision research because of the difficulty in designing experiments with adequate controls (such as for brightness). Nonetheless, we can reasonably say that horses do see some colours and may react positively or negatively to them.
Scotopic Vision: It was a dark and stormy night.
어두운곳에서의 시각
사람보다는 어둠속에서 잘 보겠지만 이부분에 관한 연구가 적습니다. 말은 어두운곳에서 잘 보게하는 리셉터가 있지만 이건 또한 빛이 반사되어 산재되므로 구별능력을 감소시키기 때문에 밤에도 장애물을 피해서 움직이며 풀을 뜯는 말의 행동으로 볼때 어둔곳에서도 잘 보는것으로 판단되어 집니다.
And your horse probably saw more than you did. But scientific research into equine night vision remains sparse. What there is of it is based on anatomical and physiological factors, not behavioral. What we do know is that the equine retina has many more rod receptors than cones, about 9:1. These receptors are responsible for vision in dim light. The eye also contains a tapetum lucidum (the reason eyes of nocturnal animals shine in the dark), which reflects light and enhances the light-gathering properties of the rods. All this indicates good night vision but there may be a hitch. The tapetum lucidum, while increasing sensitivity to dim light, may also, because of light scattering, reduce visual discrimination. Nonetheless, horses are active during the night, grazing, moving about, avoiding obstacles. This gives us a behavioral clue that their scotopic vision is decent.
Depth Perception: Are puddles the terrestrial equivalent of celestial black holes?
심도 인지능력
Think about it. How can an animal gallop full speed over uneven ground, screech to a halt mere inches from a fence, easily clear high hurdles, step over rocks and logs, or nudge a friend gently, with inadequate depth perception? Put that way, it sounds rather silly, does it not? Yet, no small number of horse people (even equine professionals) persist in their beliefs that horses do not possess this visual ability.
This notion stems from the idea that because horses have laterally placed eyes, they have no binocular vision, hence, no depth perception. This is wrong. Firstly, horses do have substantial overlap in their fields of view and secondly, some depth perception exists even when only one eye is used.
말은 심도를 인지할수 없다고 생각들하는데 이것은 잘못된 생각입니다.
말은 한 눈으로도 심도를 감식할 능력이 있습니다. 웅덩이를 피하는건 아마 발이 젖는게 싫어서일지도 모릅니다.^^
Let us look once more at the scientific evidence. In one study, horses were tested for recognition of depth in pictures using the famous visual illusion, the Ponzo Effect. “The sense of depth is conveyed by a flat image when lines that appear as separate at the edge of the picture converge near the center,” explains Timney. Horses had to choose between a photograph showing strong depth cues – converging railroad tracks – and a photograph that lacked obvious cues. Overwhelmingly, the horses went for the railroad tracks. “Not only could they recognize depth in pictures,” Timney says, “but they also must be susceptible to the same kinds of visual illusions that we perceive.”
Timney next investigated the role of binocular vision in the perception of depth with the use of random-dot stereograms – pairs of pictures that look like flat patterns of random dots when viewed normally. However, when these pictures are tinted and viewed through red and green filters (remember those weird 3D glasses at the movies?), a shape emerges to individuals with stereoscopic capability. Amazingly, when horses wore red and green goggles, they behaved as if they, too, saw depth in such pictures. “Apparently, horses have many of the same depth-detecting skills that we have,” Timney says. “They have true stereoscopic vision, despite having lateral eyes.”
Why do horses avoid puddles? Perhaps they simply do not want to get their feet wet.
Interocular Transfer: Seeing eye to eye.
일반적인 개념과는 달리 말은 한쪽 눈으로 본것을 다른 눈으로도 인식합니다.
One of the purposes of the Equine Research Foundation is to test the validity of myths in the horse world. one heard time and again involved the idea that horses cannot recognize with one eye objects they had previously seen only with the other eye (such as when returning from a trail ride). Hence, they spook. Reasoning along the lines of the two sides of the brain not being connected, thus, no transfer of information, was thrashed about by layperson and veterinarian alike.
This would make the horse rather bizarre because all placental mammals have a corpus callosum, the structure in the brain connecting both hemispheres. But the presence of this structure alone is not enough to prove transfer, just as the presence of cones does not necessarily confirm colour vision. To find out for sure, the ERF ran a series of interocular transfer tests using several different figures. Horses were trained to select one of a pair of black shapes (say, a circle instead of a rectangle) with one eye blindfolded. once they reliably chose the circle – a learning task that could take hundreds of repetitions – the blindfold was switched to the other eye. The horses chose the circle immediately, clearly demonstrating that they recognized the object previously only seen with the other eye.
Mental Rotation: A mailbox is a mailbox is a mailbox. Or is it?
말은 한쪽눈으로 본것을 다른 눈으로도 인지하지만 같은 물건이 각도가 다른곳에서 보거나 각도가 다르도록 놓을때 같은 물체로 인지를 하기도 하고 경우에따라 그렇지 않은 실험결과가 있습니다. 그러므로 말에게 충분한 시간을 주어 사물을 관찰하게 하고 자세히 보게하면 기억하고 인식할것입니다.
Dispelling one myth does not the story end, however. Yes, the interocular transfer study demonstrated that eye-to-eye communication was not a problem. Nevertheless, horses still spook at things they apparently have seen before. So, same question, different explanation.
Enter theory #2: horses spook under such circumstances because they do not recognize that an object is the same when seen from a different angle. A mailbox, for example, exhibits certain features when approached from the front. But viewed from the side, it may look entirely different to a horse. This not so far-fetched possibility was what our summer participants helped investigate during part of their learning vacation at the Equine Research Foundation. After raiding toy stores in search of ideal test items, we trained horses to always choose one of two objects (several pairs were tested with all the mandatory controls), presented with the front facing to the left. Next, we rotated the objects — front to right, front facing horse but upside down, front straight up with bottom to horse, any and all orientations. And we wondered. Would the horses still select the same object? Could they turn it over (or sideways) in their minds?
Although not yet quite finished, this study has shown some remarkable results. Notably, horses are not perfect at recognizing rotated objects. Some rotations are simple; others prove perplexing. But overall, it appears that horses are pretty good at identifying rotated objects, once learning has occurred. And therein, I think, lies the key to this conundrum. Horses need to be given time to consider their surroundings, to look at details, to understand, to learn enough so things can later be remembered and compared. Granted that, they do all right.
Re: View
말은 우리가 보는것 보다는 색감이 덜하고, 흐릿하게 보지만 훨씬 넓은 시야를 갖고 있습니다. 기능이 같고도 다릅니다.
The horse’s visual world is a little different from ours – a little less colourful, a little bit blurry, but oh so much broader and useful around the clock. The horse’s eyes look quite different from ours but function quite similarly – with good depth perception, eye-to-eye transfer, and rotation ability. We are alike but also different because of what is important to us as a species. As owners, as trainers, as handlers, as caretakers, we must consider this if we desire to excel with horses.
Contact information: The Equine Research Foundation offers learning and riding vacations and internships. Participants are actively involved in the research projects and, through hands-on experience, learn bonding and training methods based on equine cognition, natural horsemanship, and positive reinforcement. Participants also enjoy riding on the beaches, through the redwoods and vineyard, and in the arena. For information, call (831) 662-9577, visit www.equineresearch.org, or write to Equine Research Foundation, P.O. Box 1900 , Aptos , California 95001 USA .
Evelyn B. Hanggi, M.S., Ph.D., is an equine cognitive behaviorist and the president and cofounder of the nonprofit Equine Research Foundation in California . Horses have always been part of her life and, since 1992, after almost a decade of studying seals and sea lions, she has been dedicated to the study and teaching of equine cognition, behavior, training, care and welfare.
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