Im sure you have all been waiting with baited breath for the following write up on the fascinating topic of equine vision. So, sit back, put on the reading glasses, for those of you that need em, and here we go: How well do horses see? Can they see colors, depth, motion and how well do they see in the dark? Just by looking, we notice that a horses eyes are located on either side of his head which is a big advantage for them as a prey animal as it offers a wide, circular view, meaning they can detect stalking animals sneaking up from behind. This panoramic vision is monocular (mono meaning one) which enables them to view their surroundings on both sides, with either eye. Their binocular vision (with both eyes) is directed down their nose and not straight ahead and the horse actually has a blind spot in front of its forehead. When a horse is grazing, his vision is directed at the ground in front of him and if he is relaxed, his monocular vision will be at work. Should he see something that warrants investigation, the horse will raise his head to bring the binocular vision into force. If the object was spotted in the horses side vision, he will turn and raise his head, or even whole body to look. horses large eye is an advantage as it enables him to detect the slightest motion which is why windy days make most horses uneasy...too many moving things! The horse moves its head in order to bring the object into its binocular field, which also gives better depth perception. This offers a better view, as while the horse has both monocular and binocular vision, he probably cant utilize both at the same time, hence he raises his head to switch to both (binocular) eyes. Say you are riding along, your horse nice and relaxed...he is probably using his monocular vision. Suddenly he spots an unusual object ahead and instantly raises his head and pricks his ears. This allows him to look down his nose and employ his binocular vision. If the object is on the ground, the horse will lower his head, again in order to look down his nose and use both eyes for a clear view. Another reason horses move their heads up and down is that their visual field is narrow so objects seen the clearest are the ones that fall within this narrow area–the horse tilts his head in order to get as much of an object as possible to cast an image onto the eye. So if a horse needs to look down his nose to see where he is going, what happens when he is on the bit as in showing or dressage? A horse who is flexed at the poll will have his head vertical (at right angles) to the ground and cannot see straight in front of him, only down his nose towards the ground. Recent research found this blind spot in front of the horse is about the width of his body and a horse on the bit must rely on the rider for direction as he is almost working blind! If you watch show jumpers negotiating a course, you will notice they lift their heads when approaching the fence to get a better idea of height and depth with their binocular vision. Try walking quickly towards a wall with one eye closed, then open both eyes and you will see that the view with both eyes gives you better depth perception. Horses were believed to have poor vision and be short sighted but they actually have very good binocular vision with a tendency towards long vision. Alison Harmon from the University of Western Australia, who has been involved in research on equine vision, relates a story of when she witnessed a nasty accident involving two dressage horses practicing a freestyle routine. They were cantering around the arena, on the bit, and collided head on...their vision was directed down their noses towards the ground so they simply didnt see each other How much detail can horses see? Using a method of placing rewards behind a trapdoor, a research team tested how much detail a horse could see by placing stripes on the door. The horse was trained to choose the striped door over the plain one for the food reward. They varied the thickness of the stripes until they were so fine, the horses could not distinguish the striped door from the grey. From the results, they discovered that horses see as well as we do...perhaps better! Using the Snellen scale to compare horse vision with our own, indicates that horses actually see well at a distance. The Snellen scale for humans is 20/20, meaning that a person can read the same line on an eye chart from 20 feet that the standard person reads from the same distance. Using this Snellen scale, horses rate 20/30 while as a matter of interest (and by comparison) a dog is 20/50, a cat 20/75 while rats rate 20/300. Horses are mostly day animals although they will continue to graze at night which suggests they do have some night vision. Horses eyes are sensitive to weak light, so they can see fairly well at dusk, but they dont have the ability to adjust their eyes to darkness quickly, which is why they may be one reason they often It was once commonly thought horses were color blind, but in fact they do have the ability to see some color. The eyes contain light-sensitive cells called rods and cones, and even these can be broken down into different types. Humans have three different types of cones which allows us to see all colors. Cats also have three types of cones but they are weak compared to ours so they can only see in pastel colors. To a cat, a green lawn appears as a whitish one. Dogs only have two types of cones and see color similar to a human who is red-green color blind. Horses have only two types of cones as well, so their ability to see color is also limited. Yet, for those of you Hunters and show jumpers out there, go right ahead and use the wild color of the jumps as an excuse when you need too! To learn how horses saw various colors, a research team had to find a way to test how horses could tell the difference between actual colors, rather than them just picking a color that appeared, say as just bright, For example, red looks bright, while blue looks dark. To do this, they asked the horse to select a color on a grey background that they could vary from light to dark. They discovered horses could always pick out red and blue regardless of what the background was like. However, horses would only reliably select yellow and green when these were brighter than the background. If the brightness of the colors was equal to the grey background, some horses couldnt pick these colors as easily. A few could tell the difference between green and yellow while others could not, so the results were not statistically relevant..
Posted on: Wed, 22 Oct 2014 04:56:25 +0000