Monday, January 30, 2012

How Horses See

The February 2007 edition of "Perfect Horse" has a fascinating article "Eye Openers" by Tracey Emslie about recent research on how horses perceive the world. Did you know that horses have the largest eyes of any land mammal? I recommend that you check out this article in your local library or bookstore. I have summarized some of the key points below. Most of the results are from the studies of Dr. Evelyn Hanggi, president of the Equine Research Foundation. The research has some interesting implications for people who train or ride horses. It helps explain why that sign post/drain pipe/car was not a problem on the ride out when it was in shadow but was a problem when it was glinting in full sunlight on the ride back.
Horses can see almost 360 degrees around but have small blind spots in front of their noses, just behind their tails, and probably low on their backs. By shifting their heads slightly, they can see even those spots. Horses can see using monocular vision (view different things out of each eye) like a chameleon or binocular (both eyes work together to focus on the same view) like a human. Using monocular vision, the horse can focus on both on the horse behind him and the trail in front—all at the same time! Just think how many scary things the horse can see that way.
This monocular versus binocular vision has probably contributed to the myth that horses need to see things with both eyes before they really process it. However, experiments have shown that a horse can learn to select a symbol with one eye blindfolded and will immediately transfer that learning when the other eye is blindfolded. So information is processed between the two eyes.
Then there is the situation "The horse passes the mail box on the way down the trail but spooks at seeing the mail box when coming home. The horse must not be able to recognize the mail box from a different angle." Horses can recognize different objects when they are rotated through most, but not all, angles. Horses are sensitive to changes in "lighting, contrast, and shadows" so perhaps the horse does not recognize the mailbox due to these differences.
The horse's eyes are set slightly to the front of the head with a 55- to 65-degree overlap in eyesight. From a binocular point of view, the horse has fairly accurate depth perception but needs to raise or lower her head to adjust the depth perception. When riding, you need to give your horse enough rein to move her head when she needs the additional depth perception required to herd cattle or maneuver through tight situations.
This finding has a profound implication when riding "on the bit." After watching two dressage horses collide without seeming to see each other, Dr. Alison Harmon did some studies on the horse retina. "She found that the forward portion of a horse's sight runs approximately down his nose, with the blind spot being roughly the width of the horse's body in front of him as well as slightly above the level of his eyes. If a horse is ridden `on the bit' with hisforehead vertical to the ground, or overflexed and `behind the bit; with his nose pointed toward his chest, he only sees the dirt beneath his nose. The peripheral vision is still showing what is to the side, but he is working blind in regard to anything smack dab in front of him" (p. 35-36). In disciplines like dressage that encourage this type of headset, the horse has to really trust his rider since the horse effectively has blinders on.
Here are some other bits (no pun intended) of horse sight trivia:
  • The horse is a little nearsighted with 20/30 vision.
  • A horse can see fairly well at night 
  • It can adjust to differences in brightness and darkness fairly quickly but is impacted more by "situational differences."
  • Horses can see color but have trouble distinguishing between red and green.
  • "Color vision deficiencies do not make objects invisible" (p. 37).
I hope that you enjoyed reading about some of these perceptual differences as much as I did. Researchers have a lot more to learn about how the horse sees the world. Does anyone have any stories illustrating these differences? Does everyone agree with the research? As a new rider, I am curious about this.
Source: Emslie, T. (2007, February). Eye openers. Perfect Horse, 12, 2, pp. 33-37.

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