Written by Howard Hill - quote taken from Hunting the Hard way... not the whole chapter but the parts pertinent to this conversation.
"This brings us to the most important point in field or hunting archery; namely, aiming. I believe the question I am asked most often is: How do you aim when you are shooting at game? I use the same method of aiming all the time, and I call it split-vision or secondary aiming. It is also sometimes referred to as the indirect method of aiming. To anyone wishing to learn the split-vision or secondary-aiming method in shooting a bow, here are practical directions to follow: Select any given object to represent the target to be hit, and focus your eye on that object. Using the right hand, closed except for the index finger, bring that finger into your field of vision. At first it will be difficult to keep from shifting your direct vision away from the original or primary object, but after some practice it will be easy to hold fast with your direct vision on the original object, looking at it primarily, while secondarily you will be able to point your finger at any other object inside the scope of your vision, without looking directly at either the finger or whatever secondary object you have selected. Keep both eyes open at all times. As soon as the eyes have become accustomed to seeing in this manner, you are ready to begin using the split-vision method of aiming an arrow. You merely have to substitute your arrow for your index finger, using only the tip end of the arrow when it is at full draw to aim with. As a practical illustration of this method, suppose there were a basketball fastened to the side of a bare wall. Around that basketball suppose there were a baseball, a tennis ball, and a ping-pong ball also fastened to the wall. Suppose you choose the basketball as the target to be hit. Take your object, looking at it primarily, while secondarily you will be able to point your finger at any other object inside the scope of your vision, without looking directly at either the finger or whatever secondary object you have selected. Keep both eyes open at all times. As soon as the eyes have become accustomed to seeing in this manner, you are ready to begin using the split-vision method of aiming an arrow. You merely have to substitute your arrow for your index finger, using only the tip end of the arrow when it is at full draw to aim with. As a practical illustration of this method, suppose there were a basketball fastened to the side of a bare wall. Around that basketball suppose there were a baseball, a tennis ball, and a ping-pong ball also fastened to the wall. Suppose you choose the basketball as the target to be hit. Take your shooting stance and look directly at the ball with both eyes. While concentrating on the basketball with both your brain and your vision, draw your arrow its full length and bring the tip of it up into your field of vision. Point the tip of the arrow at the baseball and loose. With another arrow do the same thing as before, except that this time you point the tip of the arrow at the tennis ball and shoot. Then with a third arrow repeat the performance as before, except to point the arrow head at the ping-pong ball and let go. When you are able to do this without letting your eyes shift from the basketball, you are using the secondary or split-vision method of aiming which I employ at all times. If, however, you allow your eyes to shift away from the basketball to the point of the arrow and back again to the ball, you have not yet trained your eyes enough to use this method of aiming. At first it will seem impossible to aim in the manner directed, but after a few hours of practice, it will be easy to do. In order to use this method of aiming in the field when hunting, suppose a deer were standing broadside to you at thirty yards. The object to be hit, naturally, would be the deer; the spot on the deer to be hit would of course be the heart. Look directly at the spot on the deer just back of the fore shoulder where the heart is located. Focus your eyes and mind on that particular spot, and draw your arrow. When the point of your arrow comes into your field of vision, aim the point at an imaginary spot ten to twelve inches below the spot on the deer you intend to hit, and loose. If you have selected the proper imaginary spot at which to point your arrow, you will hit the deer in the heart; naturally, if you have failed in your calculation you will not do so. After a little practice, however, you will be amazed at the ease with which you will be able to select the imaginary aiming point. If an archer uses this method and misses, it is easy to make a hit with the next arrow, because he only has to compensate for his mistake by shifting his imaginary aiming point right or left, up or down the same distance by which his arrow has missed the spot he was trying to hit on the first shot. After this correction, the second arrow is bound to hit the mark, provided, of course, the two arrows fly alike. If one does not use the method I have described, but aims purely instinctively, seeing nothing but the object to be hit, then he has no way of compensating on his second arrow, and so is likely to go on getting a series of misses, only because he has been forced to shoot all his arrows without having anything concrete to help him compensate for his mistakes. I have used this split-vision method of aiming in hunting for many years and have found it much faster and more accurate than either the sight Method, the instinctive, or any other type of aiming. When one has mastered this method of aiming, it can be used as well on running game or flying birds as on still targets. The one fault that defeats the efforts of many archers when using the method I advocate is that they allow their eyes to shift away from the target to the point of the arrow and back to the target again. If the archer allows himself to do this, he may just as well forget this type of aiming; it will not work that way. Anyone who desires to use this method must realize the importance of understanding it thoroughly, and must be willing to spend enough time to train both the eyes and the mind to perform rightly. Naturally, the imaginary aiming point at thirty yards with a 50-pound bow is nowhere near the same place as it is with a 75-pound bow. I think a fellow will become so acquainted after practice with the various bows and ranges that after one or two shots he will be able to shoot the 5o-pound bow almost as accurately as the 75-pound. A good field archer should be able after a very few shots to shoot almost any weight bow and arrow fairly accurately up to thirty-five or forty yards, provided of course the bows and arrows match. It isn't possible to be so dogmatic about this indirect method of aiming as it is to explain a direct point-of-aim, or sight, but it is possible to perfect it to a degree where one can hit fairly small objects pretty regularly up to fifty or sixty yards. Of course, it is hard on a man who has been shooting by the target method and who decides he wants to hunt with the bow, to have to learn a new method entirely, like the one I have outlined. It would be grand to use a point-of-aim or a sight for hunting if the archer had all the time he needed to establish his sight or point-of-aim, or if he knew to the inch how far distant the creature he wanted to hit was from him. But most game animals are funny that way - they just won't stand and let a fellow get lined up. The first shot is the one that should count, and by practicing shooting at various distances and from different angles with different types of backgrounds and foregrounds, one will soon become able to judge within a few feet how far away an animal is and almost instantly to know where his own imaginary aiming point should be. This judgment can be accomplished so quickly that by the time the two hands are in shooting position and the bow drawn, one will have already estimated the distance, picked out the desired spot on the animal to hit, located his imaginary aiming point, and be entirely ready to shoot. At first it will seem like a tremendous task, but it will become easier as one goes along, and soon the hunter will be enthusiastic about the results he is obtaining. It was not before I had tried point-of-aim shooting and sights of various and sundry types that I adopted this cheek-draw method of drawing and the secondary or indirect-aiming method. I am sure that in my case, at least, there's no other method yet devised that would serve me so well. There are many more aspects of this kind of aiming that could be discussed. However, most of the essentials have been set forth. Therefore, if one will understand these as they are written here, the points covered are sufficient for success."
