Asany one with any long term experience with horses will tell you, the right side doesn't seem to know what the left side is doing. Horse behavior scientists will go so far as to say the right side of the brain doesn't communicate with the left side. If that is the case, is it any wonder why sometimes we feel as though we are dealing with two different horses under the same saddle?
One of the most direct pathways to the horse's brain is through his eyes. Understanding how a horse sees is paramount to understanding how he behaves, and the left-side, right side communication problems can be directly tied into a horse's eye sight. Horses have "monocular vision" as opposed to human "binocular vision." As all of us know, human eyes focus together, forming one picture. Horses' eyes, however, work independently. Each eye sees a different picture, and only with concentrated effort, focusing strait ahead and to a distance, can a horse focus both eyes on the same picture. So, under normal conditions a horse is faced with two separate and distinct vision stimuli. This is akin to standing in a major appliance store and watching two different TVs, tuned to different programs, at the same time. Even with our superior human intelligence, it is not easy, if not impossible, to follow both programs. We tend to pay more attention to one of them until something in the other catches our attention. Horses deal with this situation as a normal fact of their existence.
Horses are not born naturally favoring one eye over the other. They will pay attention to which ever "picture" is the most engaging. Yet, after only a short time associating with people, most horses become definitely "left-eyed." Why? Our traditions of handling horses from the left side consistently make that side of the horse more interesting. He gets used to activity on the left side as a matter of course, and becomes very comfortable focusing on his left "picture" as a matter of habit. Why we have the left side tradition is not important. It is lost to some ancient history where some king some place passed down a decree that unified and simplified his mounted knights. It never had anything to do with what works best for the horse. However, the results of this old and accepted tradition does have a lot to do with the horse and his behavior.
From the time a colt is halter broke, his halter is buckled on the left. He is led from the left side. Since humans, as well as horses form habits easily, we tend to begin our grooming sessions from the left side, and generally, without noticing, we often spend more time brushing the left side. Our bridle buckles and saddle cinches are on the left side. We mount from the left. Horses become very conditioned to all of this activity and they become very comfortable watching the world through their left eye - in essence, becoming "left-eyed". When lounged for the first time, a horse will usually work well to the left, as he is very comfortable seeing his handler on his left side. However, when you try to go to the right for the first time, the horse is disconcerted and uncomfortable. Often they will spin and face their trainer or try to turn around. They are not refusing to work, they are simply trying to restore the comfort and security of seeing the activity at the center of the lounging circle through their left eye. If you tie a horse facing a solid wall, such as the broad side of a horse trailer, he will often flatten his body against the wall so that his right eye is looking at the wall, his left at the world beyond. If you pass an unusual, non moving object on a trail that just happens to lie on your right side, chances are the horse won't notice it. Yet, turn around and come back down the same trail, pass the same object and he may spook. The object didn't change or move. The horse just saw it for the first time. When something does catch your horse's attention and he spooks, his reaction can very well be determined by what side the spooky item is on. If the fright comes from the right side, the horse is very likely to spin, putting the scary thing on his left side so that he may more comfortably see what it is. If the spook comes from his left side, he is more likely to jump away from it, spooking sideways rather than
spinning. Often, in the show ring, a rider will notice that a young horse prefers to work one way of the ring better than the other. If the arena walls are not high enough to block the horse's view of the audience, he will be most unhappy working clockwise, with his left eye constantly confronted with the confusion and movement in the grandstands. Since ignorance is bliss, working the other direction, a horse can comfortably focus to the inside of the arena at the other horses and the judge standing quietly in the middle. Only major movement from the grandstand will cause him to change his focus to his right eye. If he can't spin to get his comfortable side toward the arena wall, he will stop, back up, or try to come away from the rail. It is amazing to some riders why, after a good go the first way of the ring, or up a trail, that the spooks happen going the other way! The sad part is, so many riders assume that since the horse passed the frightening object once without a spook or worked the first way of the ring without a freak, that any subsequent behavior is the horse misbehaving, not truly being frightened. After all, he passed the thing once already and didn't spook! The horse is punished for his fear, which tends to confirm to the horse that the he had a good reason to be afraid.
The best solution to the problem is to not create left-eyed horses from the start. Horses are not born expecting to be handled exclusively from the left side, and they should not be. An attentive trainer will be mindful of his own left sided habits and be careful to handle the young horse equally from both sides. Not falling into a pattern of leading from the left or starting a grooming session from the left side is mandatory for making a balanced horse. If you already have a left eyed horse, patiently begin the process of changing your behavior to right sided handling, all the while understanding that converting a left eyed horse to one that is comfortable with activity viewed with either eye can be just as difficult as persuading a left handed human to become ambidextrous!