Yesterday, as I was losing and trying to regain binocular vision, I was able to confirm and further develop some of my previous observations. I am not quite sure I was actually losing the ability to use both eyes; however, I was losing the feeling of 3d, the ability to track an object effortlessly, the extra-sensitivity to fine movement, and the very concept of focusing on an object and seeing everything else less clearly, as well as the new internal sensations that come with stereovision.
When I see with binocular vision, I see a tree or a streetstand, and I know that it goes directly upwards. I know and I feel. I notice if it goes 5 degrees away from the vertical. I am not talking about towers or very tall trees, just normal trees and streetlamps and stands with signs, things like that. Without binocular vision, I see a tree, I know it is up, but I do not feel it. I am trying to feel that a tree is a vertical, just as I had an hour or a few minutes ago, and I can't. I don't understand where to go to move up. I look a tree and I see it is slanted, and it feels very depressing. It feels like living in a world that is slanted, in a world without internal structure.
It may seem that I could just take a stone and throw it down, and see, if it flies parallel to the tree. First of all, what is "parallel"? The eye is spherical, after all, and vertical lines do not have to be "parallel" in any clear sense. This gets us to the second question: from which point should I drop the stone? If there is street tiling, you can imagine that I can pick a point on the ground in the same plane as the tree, then put a stone directly above it, drop it, see it fall, confirm that the tree is up. Right?
But where is directly above? This is the same as feeling that a tree is vertical. If the tree is slanted, there is no "directly above". Surely, it is possible to understand, where is directly above. A is directly above B if, when you drop a stone from A, it falls to B. However, this is not the same as feeling that A is directly above B, since this feeling involves visualizing a perfectly vertical line in space. In my experience, it is not possible to visualize a perfectly vertical line in space without binocular vision.
It may seem strange, since you can close one eye and still feel that a tree is vertical. In fact, one can close both eyes and still feel that the tree is vertical... but only with binocular vision, that is, only if both parts of the visual system are activated and working together. Maybe this feeling does not arise in the visual system, but then it arises in some other part of the brain that is very closely connected to the visual system, which is essentially the same thing.
For example, I am standing near a tree and I feel that it is slanted. I can then look at a flower near the tree. I can look at the leaves or at the petals, walking around, watching the optic flow, that is the sequence of different projections observed during the movement, and trying to feel that what I am seeing are but various projections of a three-dimensional object. As long as I start to feel it, I can look up and see crown of the tree directly above. If I the feeling is not strong enough, it is possible to then think "wait... but is it up? it just felt slanted" - and then it becomes slanted. It is actually better to not check if the trees are up or not, this only weakens the stereopsis, particularly because of the feeling of insecurity that arises from it, and the resulting lack of presence. It helps to actually feel that the crown of the tree is directly above, even if there is no tree. However, watching the optic flow is much more efficient, since the brain will be trying to reconstruct the three-dimensional feeling almost by itself. Furthermore, not trying to do anything helps a lot, but it is difficult to achieve. This is not exactly "presence", it is sufficient to not try to move the eyes and not try to observe things. It is essential to not try to observe things since the ways of looking at objects, going from one object to another, noticing objects on the periphery, are very different in 2d and in 3d, and correspond to different sets of habits, such as shifting the gaze as a laser beam, or as a shape morphing from one object into another, in 3d, as opposed to moving the gaze along a segment from point A to point B in 2d.
The implications for dance and other disciplines are quite profound. If you are standing on one leg and bending one knee, it is possible to go directly down, and then directly up, as the knee straightens. If you are bending from the hips to touch the floor with your hands or your fingers with the knees straight, it is possible to try to make the legs exactly vertical, or as vertical as possible, given the weight of the upper body. All this requires practice and neither the perceived direction nor the actual movement will be 100% precise, but this is not what I am talking about. Once again, without binocular vision there is no feeling of "UP", nor feeling of DOWN.
If you do yoga, you probably know that "cat-cow stretch". A common instruction is "shoulders directly above the wrists". I have always used two things to check if I was following this instruction. First, it is possible to look if the arms are perpendicular to the floor, which can be learned by experience. Second, it is possible to feel proprioceptively the various muscles in the arm and those connecting the arms to the shoulder girdle, and to feel if all these muscles are in balance. This second one is a very good compensation for many purposes. It also works for balancing on one leg, but only to a degree, and even when it works quite well, it takes a lot of constant attention with specific control of various muscle groups. On the other hand, with binocular vision, there is a direct perception of "UP". In cat-cow stretch it suffices to merely place the shoulders directly above the wrists, and no further action is necessary. The center of gravity can be perceived as exactly above the area that the foot is standing on. More importantly, it is possible to visualize, or intend, that the center of gravity be directly above the area that the leg is standing on, and just this intent already coordinates all those various muscle groups, sometimes better, sometimes less, depending on the experience and other things, but all this takes considerably less attention. It is similar to learning a foreign language and using associations to memorize words. You may create a short sentence for every word you are trying to learn that helps you to memorize the meaning. However, this does not allow you to process language on the fly. It simply takes too much mental work to recall this association for every word. You want to perceive the words of a foreign language directly.
Even more profoundly, there are no diagonal directions without binocular vision. There are really only four clear directions: forward, backward, left, and right, just like the arrows on the computer keyboard. You can get a hint of what's wrong with the diagonals, if you recall that "up" goes diagonally as well. As far as dance goes, there is no direct perception of croisé, écarté, or effacé. It can be inferred quite well, but only approximately. I do not feel it right it, because I do have binocular vision at the moment, and had for most of the day yesterday except for several hours when it was disappearing and occasionally coming back for a few seconds. However, once again: the point is not how well the directions can be inferred, but how direct is this experience, and how much mental concentration it requires.
As it should be already clear, without binocular vision there is no sense of gravity. I realized recently that "dropping my shoulders" means that they are moving down, closer to the ground. Now I also understand how the shoulder can get wider, as I learned from Alexander technique: they can move a little bit back, if the tendency is to contract forward, and this allows them to move more to the sides, making the surface of the body flatter. Without binocular vision it is possible to feel that the shoulders move a little back, to the sides, get wider, but I couldn't understand, why it was happening.
When I see with binocular vision, I see a tree or a streetstand, and I know that it goes directly upwards. I know and I feel. I notice if it goes 5 degrees away from the vertical. I am not talking about towers or very tall trees, just normal trees and streetlamps and stands with signs, things like that. Without binocular vision, I see a tree, I know it is up, but I do not feel it. I am trying to feel that a tree is a vertical, just as I had an hour or a few minutes ago, and I can't. I don't understand where to go to move up. I look a tree and I see it is slanted, and it feels very depressing. It feels like living in a world that is slanted, in a world without internal structure.
It may seem that I could just take a stone and throw it down, and see, if it flies parallel to the tree. First of all, what is "parallel"? The eye is spherical, after all, and vertical lines do not have to be "parallel" in any clear sense. This gets us to the second question: from which point should I drop the stone? If there is street tiling, you can imagine that I can pick a point on the ground in the same plane as the tree, then put a stone directly above it, drop it, see it fall, confirm that the tree is up. Right?
But where is directly above? This is the same as feeling that a tree is vertical. If the tree is slanted, there is no "directly above". Surely, it is possible to understand, where is directly above. A is directly above B if, when you drop a stone from A, it falls to B. However, this is not the same as feeling that A is directly above B, since this feeling involves visualizing a perfectly vertical line in space. In my experience, it is not possible to visualize a perfectly vertical line in space without binocular vision.
It may seem strange, since you can close one eye and still feel that a tree is vertical. In fact, one can close both eyes and still feel that the tree is vertical... but only with binocular vision, that is, only if both parts of the visual system are activated and working together. Maybe this feeling does not arise in the visual system, but then it arises in some other part of the brain that is very closely connected to the visual system, which is essentially the same thing.
For example, I am standing near a tree and I feel that it is slanted. I can then look at a flower near the tree. I can look at the leaves or at the petals, walking around, watching the optic flow, that is the sequence of different projections observed during the movement, and trying to feel that what I am seeing are but various projections of a three-dimensional object. As long as I start to feel it, I can look up and see crown of the tree directly above. If I the feeling is not strong enough, it is possible to then think "wait... but is it up? it just felt slanted" - and then it becomes slanted. It is actually better to not check if the trees are up or not, this only weakens the stereopsis, particularly because of the feeling of insecurity that arises from it, and the resulting lack of presence. It helps to actually feel that the crown of the tree is directly above, even if there is no tree. However, watching the optic flow is much more efficient, since the brain will be trying to reconstruct the three-dimensional feeling almost by itself. Furthermore, not trying to do anything helps a lot, but it is difficult to achieve. This is not exactly "presence", it is sufficient to not try to move the eyes and not try to observe things. It is essential to not try to observe things since the ways of looking at objects, going from one object to another, noticing objects on the periphery, are very different in 2d and in 3d, and correspond to different sets of habits, such as shifting the gaze as a laser beam, or as a shape morphing from one object into another, in 3d, as opposed to moving the gaze along a segment from point A to point B in 2d.
The implications for dance and other disciplines are quite profound. If you are standing on one leg and bending one knee, it is possible to go directly down, and then directly up, as the knee straightens. If you are bending from the hips to touch the floor with your hands or your fingers with the knees straight, it is possible to try to make the legs exactly vertical, or as vertical as possible, given the weight of the upper body. All this requires practice and neither the perceived direction nor the actual movement will be 100% precise, but this is not what I am talking about. Once again, without binocular vision there is no feeling of "UP", nor feeling of DOWN.
If you do yoga, you probably know that "cat-cow stretch". A common instruction is "shoulders directly above the wrists". I have always used two things to check if I was following this instruction. First, it is possible to look if the arms are perpendicular to the floor, which can be learned by experience. Second, it is possible to feel proprioceptively the various muscles in the arm and those connecting the arms to the shoulder girdle, and to feel if all these muscles are in balance. This second one is a very good compensation for many purposes. It also works for balancing on one leg, but only to a degree, and even when it works quite well, it takes a lot of constant attention with specific control of various muscle groups. On the other hand, with binocular vision, there is a direct perception of "UP". In cat-cow stretch it suffices to merely place the shoulders directly above the wrists, and no further action is necessary. The center of gravity can be perceived as exactly above the area that the foot is standing on. More importantly, it is possible to visualize, or intend, that the center of gravity be directly above the area that the leg is standing on, and just this intent already coordinates all those various muscle groups, sometimes better, sometimes less, depending on the experience and other things, but all this takes considerably less attention. It is similar to learning a foreign language and using associations to memorize words. You may create a short sentence for every word you are trying to learn that helps you to memorize the meaning. However, this does not allow you to process language on the fly. It simply takes too much mental work to recall this association for every word. You want to perceive the words of a foreign language directly.
Even more profoundly, there are no diagonal directions without binocular vision. There are really only four clear directions: forward, backward, left, and right, just like the arrows on the computer keyboard. You can get a hint of what's wrong with the diagonals, if you recall that "up" goes diagonally as well. As far as dance goes, there is no direct perception of croisé, écarté, or effacé. It can be inferred quite well, but only approximately. I do not feel it right it, because I do have binocular vision at the moment, and had for most of the day yesterday except for several hours when it was disappearing and occasionally coming back for a few seconds. However, once again: the point is not how well the directions can be inferred, but how direct is this experience, and how much mental concentration it requires.
As it should be already clear, without binocular vision there is no sense of gravity. I realized recently that "dropping my shoulders" means that they are moving down, closer to the ground. Now I also understand how the shoulder can get wider, as I learned from Alexander technique: they can move a little bit back, if the tendency is to contract forward, and this allows them to move more to the sides, making the surface of the body flatter. Without binocular vision it is possible to feel that the shoulders move a little back, to the sides, get wider, but I couldn't understand, why it was happening.
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