Occlusion

Occlusion

Occlusion Zones: Integral with Binocular Vision

The six retinal-section boundaries K, G, VL, VR, and the two monocular boundaries in SSSRD, depict the fundamental framework structure of the single image. Inside this framework, many variations occur in order to accommodate such a versatile visual system. The retinal-sections vary dramatically due to occlusion, camouflage, brightness, and completeness. A decrease in dominance in a retinal-section in one eye is matched with the dominance of a corresponding suppressed area in the other eye. Using occlusion zones, the retinal-section structure can be examined in a more comprehensive way, where the fundamental sectional structure can also be a much more complex sectional entity.

The consensus of contemporary vision science holds that binocular rivalry occurs when the eyes are presented with two somewhat conflicting images. The images seem to compete with each other. Sometimes they appear to blend but more often, they alternate back and forth between the two eyes. The underlying reason why one image is chosen over another is unknown and the mechanism as to how it occurs is still under debate. In 1928, Diaz-Caneja published a paper concerning binocular rivalry. Being in French, his paper was virtually hidden from a much wider research community. His paper received little attention until its recent rediscovery by Logothetis (1998). His findings back then are similar to findings of recent cotemporary researchers.

Diaz-Caneja proposed that each half of a good form generates synchronised oscillations in the visual system. This synchronisation enables the two halves of the form to be perceived as a whole, despite being presented to opposite eyes. Bose (1926-27) believed binocular rivalry revealed perpetual alterations between the two eyes. Diaz-Caneja along with Helmholtz (1867-1962) and Roelofs (1921), noticed that parts of the stimuli were visible, suggesting that the alterations cannot be as simple as between the two eyes. Diaz-Caneja’s findings are similar to recent findings by KoVacs et al (1996) using homogenous kinds of stereograms. Porta (1593) took the view of suppression, suggesting that we see through one eye at a time. Detour (1763) suggested the failure of dichotic images to combine could only be the result of not seeing with both eyes simultaneously, which repudiates the well-known theory of fusion. 

Wheatstone (1838) discovered that contours at slightly different horizontal positions in the two eyes would combine and produce an illusion of depth. This caused him to reject the suppression theory in favour of the fusion theory, and he suggested that binocular rivalry only occurred when fusion broke down. Breese (1899-1909) discovered ongoing alteration when optically superimposing a red and a green grating, and then holding his eyes still.

What is the cause of binocular rivalry? Is Helmholtz right in attributing it to attention? Is Hering (1874-1964) right in attributing its cause to simple inhibition at low levels of the visual system? Is Wheatstone right by attributing it to a break down in fusion? This debate has gone on for hundreds of years. There is one finding where most agree on, and that is where binocular alteration occurs in some form. The question that baffles me is what is to be learned by trying to understand this term “binocular rivalry”, particularly in the context of deliberately presenting opposing stimuli separately to each eye. This is simply a direct interference with the natural function of the eyes. Our visual system has evolved to perceive three-dimensional space binocularly, and it is an extremely rare occurrence where each eye is presented with a conflicting image to that of the other eye, but alterations between the two eyes constantly occur.

Most findings do suggest that there are alterations between the two eyes. SSSRD proves that there are also alterations of separate, retinal-section monocular areas of the two eyes. Binocular alteration using natural observations and occlusion is very easily proved. For example, a subject with a long-sighted and a short-sighted eye, assuming he or she is retaining binocular vision, can read small print with unquestionable clarity at close range, yet the print would be just a blur to the other eye. In the same way, print on a distance sign is viewed with clarity with the long-sighted eye and it is just a blur with the other eye. If the image of the two eyes resulted in the average of the two eyes, then the average would result in an inability to read the near small print or the distant sign. Instead, the small print and at close range is viewed only with the clarity of the shortsighted eye and the distant sign is viewed only with the clarity of the long-sighted eye.

The reason why this occurs is clear; the eyes alternate in order to see the most informed image possible. In order to achieve this, one eye is suppressed while the other remains dominant and vice-versa. SSSRD explains how this instant alteration occurs. Bose gave us an insight into how it occurs back in 1926. His studies on electrical responses of the retina in a fish revealed that the maximum electrical responses of one eye corresponded with the minimum electrical responses of the other eye. SSSRD proves that the electrical responses of dominant monocular areas of one eye, synchronising with electrical responses of suppressed monocular areas of the other eye, and varying degrees of synchronisation between the two eyes creates binocular rivalry. Breese performed this experiment in reverse. He optically superimposed a red grating and an orthogonal green grating. What he saw was perceptual alterations, which he named monocular rivalry.

How can the electrical responses of the long-sighted eye instantly suppress and the synchronised electrical responses of the shortsighted eye remains dominant and active when viewing close up, and vice-versa for the long-sighted eye. The electrical responses have to be directly stimulated by the visual sensation in the optic array. Our vision evolved to see the clearest, most informed image at all times. This could not occur if the image was not the sensation that created the monocular electrical responses in the retina. The physiological structure of vision obviously synchronises with the sensory awareness of three-dimensional space. There is no possible way of understanding a complex and sensitive system without being able to study it with absolutely no interference to its normal function. Using methods such as viewing separate images in a stereoscope, in an effort to try to understand it, has been a futile exercise. Studying stereograms could possibly assist us in studying the binocular single vision, if the visual system was based only on retinal correspondence and fusion, but it is not, and as a result, progress in vision science has been hampered for the last two hundred years.

My studies display that the visual system is based on separate sectional monocular inputs from both eyes. These inputs have a fundamental processing structure, but they are also influenced by the sensory sensations in the optic array. We cannot learn anything about such a sophisticated system that took millions of years to evolve in natural surroundings and three-dimensional space, by trying to study it in unnatural, artificial ways. As a direct consequence, stereoscopes, and other artificial means of studying the binocular single image, and our hang-ups on correspondence and fusion, very little has been discovered over the last few hundred years about how our eyes actually perceive the world. All we have produced from those years of exhausting studies are an abundance of fanciful theories.

SSSRD is integral with the cortex eye and creates a logical, proven structural design as to how this is achieved. In analyzing the image in three-dimensional depth, the fixated point can be on any plane, but the three-dimensional image has a depth disparity created by the perceived movement of disparate object images, nearer than and farther than the fixated point, created from the function of the cortex eye.

There is never competition between the two eyes, regardless of whether there is so called ‘binocular rivalry, alteration, occlusion, or ‘camouflage’ occurring. Why the term ‘binocular rivalry’ is used to describe this phenomenon, I do not understand. The retinal-section structure of each eye is so precise that no encroachment of one eye on the other occurs unless the dominant area of one eye cannot see an object clearly, or for example, cannot see it at all due to occlusion. The other eye will then view the object. It will encroach and occupy the area occluded on that dominant area, so that the object or surface can be viewed in the single image. This is not rivalry in any sense of the word; this is coordination between the two eyes. Therefore, instead of binocular rivalry, I refer to this phenomenon as ‘binocular coordination’. The visual system could not work if the two eyes did not fully coordinate and problems in vision occur when there is a break down in this coordination.

SSSRD combined with occlusion and the way the cortex eye functions, provides proof not theory, as to how the visual system works. The proof provides a very complex visual system that operates in a complete coordinating system, as opposed to a visual system that over the years each conventional theoretical explanation leads to another theoretical explanation as to how the problems of the first explanation may be solved, the most significant of these problems of course being the correspondence problem. There are many reasons why binocular coordination occurs, but what is the mechanism? SSSRD provides us with the fundamentals of this mechanism. The main reason why binocular coordination occurs is integral with the evolution of the visual system. That is to create the clearest most informed image at all times and above all to retain stability in visual perception and visual direction at the same time.

When we understand SSSRD, we know that the fundamental framework of binocular single vision consists of six separate monocular-retinal-sections, three of each eye. It is the simultaneous dominance of these areas during fixation that creates the binocular single image. In order for this to occur, the other six corresponding retinal areas are suppressed. However, in binocular coordination, a more complex process of sectional suppression and dominance occurs. The monocular-sections are not always evenly balanced in the cortex eye. Any of the dominant monocular areas can increase or decrease dominance; the increase or decrease is matched by the increase or decrease of suppression or dominance in the other eye. This can result in total dominance of one eye, and total suppression of the other eye and, in an instant, alteration of complete dominance of the suppressed eye to complete suppression of the other eye, which is binocular alteration.

This occurrence is frequent, as described in long and short sightedness. In most cases however, binocular coordination occurs in a much more intricate and complex way, where a section of a dominant area of one eye is suppressed to that eye due to occlusion. The area that becomes dominant in exactly the same area in the corresponding, suppressed section of the other eye. As we will observe in occlusion, this area, which becomes dominant in the corresponding dominant sectional area, moves with the visual axis of that eye. It moves in an opposite direction, with the rotation of the cortex eye, to that of all other targets in the same dominant sectional area it is now located in. Bose showed how a type of this phenomenon of ‘suppression and dominance’ occurred, through electrical responses of the retina in binocular alteration, where the maximum sensitivity of one retina coincides with the minimum of the other. In SSSRD, the suppression of any retinal-section coincides with the dominance of a corresponding retinal-section in the other eye.

Our vision has evolved in such a way that we see everything that is visible to either eye. In order to achieve this in binocular single vision, the structure of all the dominant retinal-sections is constantly changing. These changes occur with suppression of one part of a dominant retinal-section in the binocular image, which is replaced with a corresponding, dominant suppressed area of the other eye. One of ways of proving this phenomenon is through natural observation of occlusion zones in three-dimensional space. Practically the entire structure of the visual process can be examined using occlusion in this way.

The Da Vinci factor

Five hundred years ago, when Leonardo Da Vinci first illustrated occlusion zones, the significance of his discovery was never built upon and was soon stifled with the advent of correspondence and fusion, and almost buried with the introduction of Wheatstone’s invention, the stereoscope. The era of natural observation was over and with it the possibility of discovering the monocular aspect of BSV. Da Vinci showed that when viewing an object, parts of the background along the vertical edges of the object were visible to one eye and not to the other. The monocular aspect of his observations was not thought to be very significant at that time. His observations were most likely based on curiosity because this was an era before the advent of theories on retinal correspondence or fusion, or any other theory regarding the structure of binocular single vision. He was simply an individual that was above any type of social conditioning and like all geniuses, observed nature in isolation and in a complete and objective manner.

The contemporary definition of an occlusion zone refers to what is “next to the vertical edge of an opaque object seen by both eyes lies a region of a far surface that is visible only to one eye” (Howard and Rogers, 2002). From personal experience in the art of painting, I believe Da Vinci’s studies of monocular occlusion zones were sparked when painting a canvas where the subject, whether a model or a building, was positioned to the side and the rear of the canvas. A man with such sophisticated attention to detail must have noticed that while viewing the canvas, the subject of his painting at the back and on the side was viewed only with one eye. The opaque object (the canvas) is creating a monocular occlusion zone.

Monocular occlusion zones have been largely ignored in theories on stereopsis. Gillam and Borsting (1988) showed how monocular occlusion zones enhanced the impression of depth. Anderson and Nakayama (1994) revisited the role of monocular occlusion in perceiving depth in stereograms. Anderson and Charowhas (1999) developed a model of how monocular occlusion could be used as a supplementary cue to depth. Most previous and even recent studies of monocular occlusion have been in the area of depth, but we cannot understand the function of occlusion zones without understanding the fundamental structure of the visual system. In SSSRD and the cortex eye, monocular occlusion plays a very significant role in understanding the fundamental structures of the binocular single image.

Using natural observation, the fundamentals of binocular coordination and all its variations can be observed in the basic structure of the visual system. One of the classical definitions, of a monocular occlusion being an object more distant than the binocular target and being viewed by only one eye, is over simplified. This is a limited explanation for a monocular occlusion zone and is not the way it becomes a supplementary cue to depth in the absence of disparity, which is the conventional view held. An occlusion zone can occur in any area of the visual field nearer and further the fixation point. Many occlusion zones can even occur in all the retinal-sections simultaneously and each zone creates another retinal-section sub-area. All retinal-sections, including targets in occlusion zones, are governed by the rotation of the visual axes in the cortex eye, and because of this, disparity movements between targets occur and depth is created.

A sectional area in SSSRD becomes dominated by the monocular view of the other eye, creates the cue to depth, and in doing so creates an additional sub-sectional area. Small occlusion zones greatly enhance depth while large occlusion zones, which are as large or larger than any one of the retinal-sections, cause deterioration in depth. This phenomenon will become more apparent and is illustrated in the following figures, which show how occlusion zones play such a major role in our perception of space and how the two eyes coordinate to produce the clearest, most informed image at all times. 

Figure 4.1: Target occluded in section B.

In figure 4.1A, ‘F’ is the fixation point. Target 1 is in section B1 and would be viewed ‘D1’ distance left of ‘F’ in the cortex eye, but the target is located in an area in section B1 that is occluded to the monocular view of the left eye. Therefore, when ‘F’ is focused on, the target is not viewed by the left eye, but is now viewed by the right eye. Instead of being viewed ‘D1’ distance left of ‘F’, it is now viewed ‘C’ distance left of ‘F’ by the right eye, in section B1, which is not a dominant retinal-section of the right eye.

In figure 4.1A, the occluded area in B1 becomes a dominant area in a corresponding suppressed area in the right eye. Figure 4.1B illustrates the occluded target 1 in the cortex eye. The occlusion is still viewed ‘O’ distance left of ‘F’, having moved ½ ‘D’ distance with the rotation of the visual axis of the left eye. However, target 1 has moved ½ ‘D’ distance in the opposite direction with the rotation of the visual axis of the right eye, Note that target 1 is viewed ‘C’ distance left of ‘F’ but is not occluded after the function of the cortex eye. This proves that the occluded area is precisely assembled as an additional sub-retinal-section with all the dominant retinal-sections, before the rotation of the visual axes occur in the cortex eye. When the occlusion is removed, the target is viewed at its normal location ‘D1’ distance left of ‘F’, at its depth location relative to VL. Only the left eye can be occluded from section B1: the occlusion zone creates an automatic suppression of that area but also creates simultaneous retinal dominance in the corresponding suppressed area of the right eye. Likewise, the right eye can only be occluded from section A: the occlusion zone creates an automatic suppression of that area but also creates simultaneous retinal dominance in the corresponding suppressed area of the right eye. 

Figure 4.2: Target occluded in section A. 

In figure 4.2A, ‘F’ is the fixation point. Target 2 is in section A and would be viewed ‘D1’ distance right of ‘F’ in the cortex eye, but the target is located in an area in section A that is occluded to the monocular view of the right eye. Consequently, when ‘F’ is focused on, the target is not viewed by the right eye, but by the left eye. Instead of being viewed ‘D1’ distance right of ‘F’, it is now viewed ‘C’ distance right of ‘F’ in section A (which is not a dominant retinal-section area) by the left eye. The occluded area in section A is now a dominant area in a corresponding suppressed area in the left eye.