Developed stereoscopic vision helps in extrasensory perception. Stereoscopic vision and methods of its research. Color vision: what is it and what are the violations

The ability to see the world in volume gives a person binocular vision. With its violations, visual acuity worsens, problems arise with orientation in space. This happens for various reasons. Binocularity can be restored by hardware and surgical methods. The doctor also prescribes exercises for the eyes.

What is binocular vision and how does it work?

Binocular vision is vision with both eyes. It is also called stereoscopic and spatial, because it allows you to see in 3D projection. Thanks to this function, a person sees objects, recognizing their dimensions by width and height, shape, and the distance between them. Both eyes of a person receive one image each, which they transmit to the brain. It combines these images into one picture.

If there is no binocular vision, the brain will receive two different visual images that cannot be combined into one. As a result, diplopia occurs - double vision. This happens with anisometropia (a strong difference between the refraction of the right and left eyes), diseases of the lens, cornea and retina, damage to the nervous system, and for other reasons. Binocular vision is impossible if one eye is not involved in the process of visual perception, as is the case with strabismus.

The development of binocular vision begins in childhood. From the very first months, the prerequisites for its emergence and development begin to form. First, the child develops photosensitivity, color perception, and central vision. Over time, visual acuity improves, the field of vision expands. All this contributes to the formation of binocularity. This process is completed by about 12-14 years. Violations can occur at any age. A variety of factors can provoke them.

Causes of impaired binocular vision

The main reason for the lack of binocular vision is uncoordinated movements of the eyeballs. This occurs due to weakening of the eye muscles or damage to the oculomotor muscles. The eyes begin to look in different directions, the visual axis shifts, which leads to a deterioration in the visual functions of one eye. In some cases, there is a complete loss of vision by one of them. This pathology often occurs in childhood and manifests itself in strabismus, the most common form of binocular vision impairment.

There are other reasons for the loss of binocularity. In fact, there are a lot of them. Hemorrhages in the retina, cataracts, rupture of the retina cause a strong deterioration in the visual abilities of the eye, and one of the conditions for the existence of stereoscopic vision is the absence of pathologies of the retina and cornea.

Thus, the loss of binocular vision is caused by various pathologies of the body, in general, and the eyes, in particular. Any disease that adversely affects the health of the eyes and vision can become a factor that provokes violations of spatial perception.

Recovery of binocular vision

The restoration of binocularity begins with the treatment of the pathology that led to visual impairment. Only after eliminating the causes, you can return stereoscopic vision.

The most common pathology in which binocular vision is absent is strabismus. This ophthalmic disease is treated with the help of surgery, hardware methods and eye gymnastics. Surgical intervention is necessary only in extreme cases, when the eye is strongly displaced from its normal position and is not involved in the process of vision.

Recovery and training of binocular vision at home

Daily training of spatial vision is the key to its rapid recovery. There are various exercises that you can do on your own right at home. The simplest is the exercise with a sheet of paper.

leaf exercise

You will need a paper sheet on which you need to draw a vertical line 10 cm long and 1 cm wide with a felt-tip pen. Attach the sheet to the wall at eye level and move 1 meter away from it. Look at the line and tilt your head down a little, continuing to look at the line until it begins to double. Next time, take your head up, and then to the sides. It is necessary to perform such exercises three times a day for five minutes. A prerequisite for implementation is good lighting in the room.

This exercise is the simplest in terms of technique. There are other techniques related to focusing. They also contribute to the training and restoration of binocular vision.

Exercise "Workout"

Place some object (a sheet with an image) on the wall and move away from it at a distance of 2-3 meters. Next, you should clench your fist, but at the same time the index finger should be extended upwards. The hand is located at a distance of 40 cm from the face, and the tip of the index finger should be on the same visual axis as the object on the wall. Look at an object through your fingertip. It will immediately begin to split. After that, you need to move the focus from the wall to the finger. At this point, the visual object will begin to double. So you can train both eyes alternately. It is the weak eye that should be loaded more. The workout will take you about 3-5 minutes. It is advisable to perform it several times a day. Over time, you will notice that your visual acuity has improved.

Focusing exercise

It will require a colored object (any picture). First you need to look at the whole picture, then at its individual details (the image should be complex, multi-colored). Then an even smaller object is selected. So, if the object is a butterfly, then first you examine it as a whole, then outline its contour with your eyes, then examine the wing or its half. The last object to focus on it should be no more than 0.5 cm in size. This way you will gradually learn to focus faster and more accurately without straining your eyes.

Exercise "Stereogram"

The stereogram drawing can be downloaded from the Internet and printed. It is encrypted drawings in which you can see any figures. The stereogram should be located at a distance of 30-40 cm from the face. The gaze must be focused as if behind the image. After a while, the hidden picture will begin to appear. After this has happened, you need to increase the distance between the stereogram and the eyes, but at the same time try not to lose the found picture. The next actions are turning the head up and down and left and right while holding the seen image. It might not work the first time. However, over time, the eyes will get used to it and the visible object will be recognized from different angles. Stereograms are very useful for training binocularity, as well as for relieving tension from the visual apparatus. Especially such an exercise will be useful for people who work at a computer. Stereograms can not be printed out, but viewed directly from the monitor. It is only necessary to set its optimal brightness.

In addition to these exercises, you can perform general gymnastics for the eyes, which helps with fatigue and to improve visual acuity. There are also many such methods. Before performing them, consult an ophthalmologist.

A person with binocular (stereoscopic) vision can fully navigate in space. It is possible to distinguish objects and objects by shape even in the presence of monocular vision. However, it is possible to determine the distance between objects only with the formed stereoscopic perception. Any pathologies that lead to a violation of binocularity must be treated on time, especially if they occur in childhood, when vision is just being formed.

The binocular function formed in patients with concomitant strabismus in the process of orthooptic and diploptic treatment can be more or less perfect. The fusion of images of one and the second eye can occur only in one plane - this is planar binocular vision, determined on the color test, synoptophore and Bagolini's test.

A full-fledged binocular function is considered only in those cases when the fusion of images of both eyes is accompanied by the perception of depth, volume, stereoscopicity. This is the highest form of binocular function - stereoscopic vision.

The perception of depth, stereoscopicity arises in connection with the disparity of images on the retina of both eyes. The right and left eyes are at some distance from each other. The images of each point of the fixed object on the retina of one and the second eye are slightly shifted in the horizontal direction with respect to the central fovea. The consequence of this shift, disparity, is the feeling of depth, stereoscopicity.

The formation of a full-fledged stereoscopic vision, according to R. Sachsenweger (1956), is completed by the 8th year of a child's life.

R. Sachsenweger introduces the term "stereoamaurosis"- complete absence of stereoscopic vision (similar to the term "amaurosis" - complete blindness) and "stereoamblyopia" - functional inferiority of stereoscopic vision (similar to the term "amblyopia" - functional decrease in central vision).

The quality of deep vision is determined by the threshold. The maximum difference in depth that the subject is no longer able to feel is taken as the threshold of deep vision. The higher the threshold, the worse the depth vision. Thresholds of deep vision are not the same when examined with different instruments and at different distances. They are expressed in millimeters or arcseconds.

The appearance of strabismus in a child destroys his binocular and stereoscopic vision.

Restoration of stereoscopic vision is carried out at the final stage of strabismus treatment, when planar binocular vision is already formed and normal fusional reserves are developed. When restoring deep vision in children with strabismus, T.P. Kashchenko (1973) noted the dependence of the results on the level of visual acuity of both eyes, the magnitude of the angle of strabismus and fusion ability. VA Khenkin (1986) additionally noted the dependence of depth vision thresholds on the timing of strabismus, the final visual acuity of the squinting eye, the difference in visual acuity of both eyes, and the magnitude of aniseikonia.

Deep, stereoscopic vision is better, the later the strabismus appeared, the higher the final visual acuity of both eyes, the better the fusion and the lower the degree of aniseikonia. With aniseikonia of 5%, deep perception is possible only in individual patients and its quality is very low.

It should be noted that it is possible to restore stereovision only in that part of children with concomitant strabismus, in whom it was formed to some extent before the onset of strabismus. With congenital and early developed strabismus, it is not possible to bring up stereoscopic vision.

There are special devices for diagnostics, formation and training of stereoscopic vision.

1) The classic device for evaluating real depth vision remains the device with three Howard-Dolman needles (Fig. 47).
It consists of a rod 50 cm long, on which three knitting needles are placed. Two of them are fixed on the sides of the rod, and the third, middle one, is movable. Horizontal slots are made for the eyes at one end of the rod. Between the eyes and the spokes, a diaphragm is installed in the form of a horizontal slit, which does not allow the patient to see the tops and bases of the spokes. The middle spoke moves back and forth.
The patient must determine whether it is in front of the two spokes or behind and, finally, install all three spokes in the frontal plane, catching the moment when the displaced spoke becomes equal to the fixed ones. This distance between the movable and fixed spokes determines the depth vision threshold.

R. Sachsenweger's monograph "Anomalies of stereoscopic vision in strabismus and their treatment" (1963) describes many devices used for the diagnosis and education of stereoscopic vision. Let's acquaint readers with some of them.

Rice. 47. A device with three spokes, a) with the diaphragm removed, b) with the diaphragm installed.

2) (Fig. 48) consists of a body 1, inside which two glass plates 3 and 4 are placed. They are illuminated by an electric bulb 2 placed behind them. Small round dots are pasted on both plates. On plate 3 they are arranged in no particular order, and on plate 4 they form the outline of a figure. When the plates stand directly one next to the other, the figure cannot be distinguished. As the distance between them increases, the figure, depending on the spatial threshold, begins to differ sooner or later.

Rice. 48 Parallax Visoscope

3) (Fig. 49) has drawers 1,2,3, equipped with light bulbs. The drawers can be moved forward and backward along the rails. In the front wall of the drawers there are slots into which any templates are inserted, as well as color and neutral filters.

The study is carried out in the dark, and the size of the light object, its brightness and color are often changed. The patient must determine which of the objects is closer and which is farther, set the objects in one frontal plane, space them evenly in depth, etc.

4) (fig.50). The basis of the device is a wire contour standing vertically in the middle plane, inside which the patient must hold a metal pencil without touching the wire. Touching the pencil to the wire leads to the circuit of the current and the sound of the buzzer. The patient's view is limited in such a way that he cannot view the wire frame from the side.

The difficulty of the task depends on the distance between the wires that form the contour. This distance can be changed using the set screw. The device develops deep vision acuity, as visual stimuli are combined with proprioceptive ones. Without deep visual acuity, for example, when using one eye, the exercise cannot be performed even after a long training session.

Rice. 50 Stereo buzzer

5) Binarimeter(Fig.51) is a new generation device that uses diploptics methods aimed at the formation of binocular and stereoscopic vision. In the binarimeter, spatial visual effects are formed that occur when identical images are duplicated on the basis of physiological doubling in free haploscopy without optics and division of visual fields.

Treatment on a binarimeter is carried out after the patient has achieved the ability to bifixation. The design of the device provides for the possibility of treatment not only with a symmetrical position of the eyes, but also with small deviations horizontally and vertically.

Fig.51. Binarimeter "Binar"

Exercises on the device activate sensory-motor interactions, contributing to the restoration of binocular and stereoscopic vision.
We used a binarimeter in combination with other methods for restoring binocular and stereoscopic vision in schoolchildren and adolescents, since treatment with it requires a certain amount of intelligence.

30-09-2011, 10:29

Description

The corpus callosum is a powerful bundle of myelinated fibers that connects the two hemispheres of the brain. Stereoscopic vision (stereopsis) is the ability to perceive the depth of space and assess the distance of objects from the eyes. These two things are not particularly closely related to each other, but it is known that a small part of the fibers of the corpus callosum still play some role in stereopsis. It turned out to be convenient to include both of these topics in one chapter, since when considering them, one and the same feature of the structure of the visual system will have to be taken into account, namely, that there are both crossed and uncrossed optic nerve fibers in the chiasm.

corpus callosum

The corpus callosum (in Latin corpus callosum) is the largest bundle of nerve fibers in the entire nervous system. According to a rough estimate, there are about 200 million axons in it. The true number of fibers is probably even higher, since the estimate given is based on conventional light microscopy, not electron microscopy.

This number is incomparable with the number of fibers in each optic nerve (1.5 million) and in the auditory nerve (32,000). The cross-sectional area of the corpus callosum is about 700 mm square, while that of the optic nerve does not exceed a few square millimeters. The corpus callosum, together with a thin bundle of fibers called anterior commissure, connects the two hemispheres of the brain (Fig. 98 and 99).

Term commissure means a collection of fibers connecting two homologous nerve structures located in the left and right halves of the brain or spinal cord. The corpus callosum is also sometimes called the greater commissure of the brain.

Until about 1950, the role of the corpus callosum was completely unknown. In rare cases, there is a congenital absence ( aplasia) corpus callosum. This formation can also be partially or completely cut during a neurosurgical operation, which is done intentionally - in some cases in the treatment of epilepsy (so that the convulsive discharge that occurs in one hemisphere of the brain cannot spread to the other hemisphere), in other cases in order to get from above to a deeply located tumor (if, for example, the tumor is located in the pituitary gland). According to the observations of neuropathologists and psychiatrists, after such operations, no mental disorders occur. Someone has even suggested (though hardly seriously) that the sole function of the corpus callosum is to hold the two hemispheres of the brain together. Until the 1950s, little was known about the details of the distribution of connections in the corpus callosum. It was obvious that the corpus callosum connected the two hemispheres, and on the basis of data obtained by rather crude neurophysiological methods, it was believed that in the striatal cortex, the fibers of the corpus callosum connected exactly symmetrical regions of the two hemispheres.

In 1955 Ronald Myers, a graduate student of psychologist Roger Sperry of the University of Chicago, conducted the first experiment that revealed some of the functions of this huge fibrous tract. Myers trained cats placed in a box with two screens placed side by side, onto which various images could be projected, such as a circle on one screen and a square on another. The cat was trained to put its nose on the screen with the image of a circle, and ignore the other - with the image of a square. Correct answers were reinforced with food, and cats were slightly punished for erroneous answers - a loud bell was turned on, and the cat was not rudely, but decisively pulled away from the screen. With this method, in several thousand repetitions, the cat can be brought to the level of reliable discrimination of figures. (Cats learn slowly; for example, pigeons need from several tens to several hundred repetitions to learn in a similar task, and a person can generally be taught immediately by giving him verbal instructions. This difference seems somewhat strange - after all, a cat has a brain many times larger, than dove.)

There is nothing surprising in the fact that Myers' cats learned to solve this problem just as well in the case when one eye of the animal was covered with a mask. It is also not surprising that if training in such a task as choosing a triangle or a square was carried out with only one eye open - the left one, and when checking the left eye was closed and the right eye was opened, then the accuracy of discrimination remained the same. This does not surprise us, because we ourselves can easily solve a similar problem. The ease of solving such problems is understandable, given the anatomy of the visual system. Each hemisphere receives input from both eyes. As we said in the article, most of the cells in field 17 also have inputs from both eyes. Myers created a more interesting situation by making a longitudinal transection of the chiasma in the midline. Thus, he cut the criss-crossing fibers and kept the non-crossing fibers intact (this operation requires a certain skill from the surgeon). As a result of such a transection, the left eye of the animal turned out to be connected only to the left hemisphere, and the right eye - only to the right.

Experiment Idea was to train the cat using the left eye, and on the "exam" to address the stimulus to the right eye. If the cat can solve the problem correctly, then this will mean that the necessary information is transmitted from the left hemisphere to the right along the only known path - through the corpus callosum. So Myers cut the chiasm lengthwise, trained the cat with one eye open, and then made a test by opening the other eye and closing the first. Under these conditions, the cats still successfully solved the problem. Finally, Myers repeated the experiment on animals in which both the chiasm and the corpus callosum had previously been cut. This time the cats did not solve the problem. Thus, Myers empirically established that the corpus callosum does indeed perform some function (although one could hardly think that it exists only so that individual people or animals with a cut optic chiasm can perform certain tasks using one eye after learning using another).

Study of the physiology of the corpus callosum

One of the first neurophysiological studies in this area was carried out a few years after the experiments of Myers by D. Witteridge, who was then working in Edinburgh. Whitteridge reasoned that there was little point in having bundles of nerve fibers connecting homologous mirror-symmetrical sections of fields 17. Indeed, there is no reason for a nerve cell in the left hemisphere associated with some points in the right half of the visual field , connected to a cell in the right hemisphere associated with a symmetrical section of the left half of the visual field. To test his assumptions, Whitteridge cut the optic tract on the right side of the brain behind the chiasm and thereby blocked the input signals from entering the right occipital lobe; but this, of course, did not exclude the transmission of signals there from the left occipital lobe through the corpus callosum (Fig. 100).

Then Whitteridge began to turn on the light stimulus and record electrical activity from the surface of the cortex with a metal electrode. He did get answers in his experience, but they only appeared at the inner border of field 17, i.e., in the area receiving input signals from a long, narrow vertical strip in the middle of the field of view: when stimulated with small spots of light, answers appeared only when the light flashed on or near the vertical midline. If the cortex of the opposite hemisphere was cooled, thereby temporarily suppressing its function, the responses stopped; cooling of the corpus callosum also led to this. Then it became clear that the corpus callosum cannot connect the entire field 17 of the left hemisphere with the entire field 17 of the right hemisphere, but only connects small areas of these fields, where there are projections of a vertical line in the middle of the field of view.

A similar result could be expected based on a number of anatomical data. Only one section of field 17, very close to the border with field 18, sends axons through the corpus callosum to the other hemisphere, and most of them seem to terminate in field 18 near the border with field 17. If we assume that the inputs to cortex from the NKT exactly correspond to the contralateral parts of the visual field (namely, the left hemisphere is displayed in the cortex of the right hemisphere, and the right - in the cortex of the left), then the presence of connections between the hemispheres through the corpus callosum should eventually lead to the fact that each hemisphere will receive signals from areas slightly larger than half of the field of view. In other words, due to connections through the corpus callosum, there will be an overlap of the hemifields projected into the two hemispheres. This is exactly what we found. With the help of two electrodes inserted into the cortical region at the border of fields 17 and 18 in each of the hemispheres, we were often able to register the activity of cells whose receptive fields mutually overlapped by several angular degrees.

T. Wiesel and I soon made microelectrode leads directly from that zone of the corpus callosum (in its most posterior part) where there are fibers associated with the visual system. We found that almost all the fibers that we could activate with visual stimuli responded in exactly the same way as ordinary field 17 neurons, i.e., exhibited the properties of both simple and complex cells, selectively sensitive to the orientation of the stimulus and usually responding to stimulate both eyes. In all these cases, the receptive fields were located very close to the middle vertical below or above (or at the level of) the fixation point, as shown in Fig. 101.

Perhaps the most elegant neurophysiological demonstration of the role of the corpus callosum was the work of J. Berlucchi and J. Rizzolatti from Pisa, performed in 1968. By cutting the optic chiasm along the midline, they recorded responses in field 17 near the border with field 18, looking for those cells that could be activated binocularly. It is clear that any binocular cell in this area in the right hemisphere must receive input signals both directly from the right eye (through the LNT) and from the left eye and left hemisphere through the corpus callosum. As it turned out, the receptive field of each binocular cell captured the middle vertical of the retina, and that part of it that belongs to the left half of the visual field delivered information from the right eye, and the one that goes into the right half - from the left eye. Other cell properties studied in this experiment, including orientational selectivity, were found to be identical (Fig. 102).

The results obtained clearly showed that the corpus callosum connects cells to each other in such a way that their receptive fields can go both to the right and to the left of the middle vertical. Thus, it seems to stick together the two halves of the image of the surrounding world. To better imagine this, suppose that initially the cortex of our brain was formed as a whole, not divided into two hemispheres. In this case, field 17 would have the form of one continuous layer onto which the entire visual field would be mapped. Then neighboring cells, in order to realize such properties as, for example, sensitivity to movement and orientational selectivity, would, of course, have to have a complex system of mutual connections. Now imagine that the "constructor" (be it a god, or, say, natural selection) decided that it was impossible to leave it like that - from now on, half of all cells should form one hemisphere, and the other half - the other hemisphere.

What then needs to be done with the whole multitude of intercellular connections, if the two sets of cells must now move away from each other?

Apparently, one can simply stretch these connections, forming part of the corpus callosum from them. In order to eliminate the delay in the transmission of signals along such a long path (about 12-15 centimeters in a person), it is necessary to increase the transmission rate by providing the fibers with a myelin sheath. Of course, in fact, nothing like this happened in the process of evolution; long before the cortex arose, the brain already had two separate hemispheres.

The experiment of Berlucca and Rizzolatti, in my opinion, provided one of the most striking confirmations of the amazing specificity of neural connections. The cell shown in fig. 108 (near the tip of the electrode), and probably a million other similar cells connected through the corpus callosum, acquire their orientational selectivity both through local connections with neighboring cells and through connections through the corpus callosum from the other hemisphere from cells with such the same orientational sensitivity and a similar arrangement of receptive fields (this also applies to other properties of cells, such as directional specificity, the ability to respond to the ends of lines, as well as complexity).

Each of the cells in the visual cortex that have connections through the corpus callosum must receive input from cells in the other hemisphere with exactly the same properties. We know many facts pointing to the selectivity of compounds in the nervous system, but I think that this example is the most striking and convincing.

The axons discussed above cells of the visual cortex make up only a small proportion of all fibers of the corpus callosum. In the somatosensory cortex, experiments were carried out using axon transport, similar to those described in previous chapters with the injection of a radioactive amino acid into the eye. Their results show that the corpus callosum similarly binds those areas of the cortex that are activated by skin and articular receptors located near the midline of the body on the trunk and head, but does not bind the cortical projections of the extremities.

Each area of the cortex is connected to several or even many other areas of the cortex of the same hemisphere. For example, the primary visual cortex is connected to area 18 (visual area 2), to the medial temporal area (MT area), to visual area 4, and to one or two other areas. Many areas of the cortex also have connections with several areas of the other hemisphere through the corpus callosum, and in some cases through the anterior commissure.

Therefore, we can consider these commissural connections simply as a special kind of cortico-cortical connections. It is easy to see that this is evidenced by such a simple example: if I tell you that my left hand feels cold or that I saw something on the left, then I formulate words using my cortical speech zones located in the left hemisphere (said, maybe be, and not entirely true, since I'm left-handed); information coming from the left half of the visual field or from the left hand is transmitted to my right hemisphere; then the appropriate signals must be transmitted through the corpus callosum to the speech cortex of the other hemisphere so that I can say something about my sensations. In a series of works begun in the early 1960s, R. Sperry (now working at the California Institute of Technology) and his colleagues showed that a person with a cut corpus callosum (for the treatment of epilepsy) loses the ability to talk about those events, information about which enters the right hemisphere. Working with such subjects has become a valuable source of new information about the various functions of the cortex, including thinking and consciousness. The first articles about this appeared in Brain magazine; they are extremely interesting, and anyone who has read a real book can easily understand them.

stereoscopic vision

The distance estimation mechanism based on the comparison of two retinal images is so reliable that many people (unless they are psychologists and visual physiologists) are not even aware of its existence. To see the importance of this mechanism, try driving a car or bicycle, playing tennis, or skiing with one eye closed for a few minutes. Stereoscopes have gone out of fashion and you can only find them in antique shops. However, most readers have watched stereoscopic films (where the viewer has to wear special glasses). The principle of operation of both a stereoscope and stereoscopic glasses is based on the use of the stereopsis mechanism.

Images on the retinas are two-dimensional while we see the world in three dimensions. It is obvious that the ability to determine the distance to objects is important for both humans and animals. Similarly, perceiving the three-dimensional shape of objects means judging relative depth. Consider, as a simple example, a round object. If it is oblique with respect to the line of sight, its image on the retinas will be elliptical, but usually we easily perceive such an object as round. This requires the ability to perceive depth.

A person has many mechanisms for estimating depth. Some of them are so obvious that they hardly deserve mention. However, I will mention them. If the approximate size of an object is known, for example in the case of objects such as a person, a tree or a cat, then we can estimate the distance to it (although there is a risk of making a mistake if we encounter a dwarf, bonsai or lion). If one object is located in front of the other and partially obscures it, then we perceive the front object as being closer. If we take a projection of parallel lines, for example, railroad tracks going into the distance, then in the projection they will converge. This is an example of perspective - a very effective measure of depth.

The convex section of the wall appears lighter in its upper part if the light source is located higher (usually the light sources are at the top), and the recess in its surface, if it is illuminated from above, appears darker in the upper part. If the light source is placed below, then the bulge will look like a recess, and the recess will look like a bulge. An important sign of remoteness is motion parallax - the apparent relative displacement of near and more distant objects if the observer moves his head left and right or up and down. If some solid object is rotated, even at a small angle, then its three-dimensional shape is immediately revealed. If we focus the lens of our eye on a nearby object, then the more distant object will be out of focus; thus, by changing the shape of the lens, i.e., by changing the accommodation of the eye, we are able to estimate the distance of objects.

If you change the relative direction of the axes of both eyes, bringing them together or spreading(performing convergence or divergence), then two images of an object can be brought together and held in this position. Thus, by controlling either the lens or the position of the eyes, one can estimate the distance of an object. The designs of a number of rangefinders are based on these principles. With the exception of convergence and divergence, all other distance measures listed so far are monocular. The most important depth perception mechanism, stereopsis, depends on the sharing of two eyes.

When viewing any three-dimensional scene, the two eyes form slightly different images on the retina. You can easily be convinced of this if you look straight ahead and quickly move your head from side to side by about 10 cm or quickly close one eye or the other in turn. If you have a flat object in front of you, you won't notice much of a difference. However, if the scene includes objects at different distances from you, you will notice significant changes in the picture. During stereopsis, the brain compares images of the same scene on two retinas and estimates relative depth with great accuracy.

Suppose now that Q is another point in space, which seems to the observer located at the same depth as P. Let Qlh Qr be the images of the point Q on the retinas of the left and right eyes. In this case, the points QL and QR are called the corresponding points of the two retinas. It is obvious that two points coinciding with the central pits of the retinas will be corresponding. From geometrical considerations it is also clear that the point Q ", estimated by the observer as located closer than Q, will give two projections on the retinas - and Q" R - at non-corresponding points located farther apart than if these the points were corresponding (this situation is depicted on the right side of the figure). In the same way, if we consider a point located farther from the observer, then it turns out that its projections on the retinas will be located closer to each other than the corresponding points.

What has been said above about the corresponding points is partly definitions and partly assertions following from geometrical considerations. When considering this issue, the psychophysiology of perception is also taken into account, since the observer subjectively evaluates whether the object is located further or closer to the point P. Let's introduce one more definition. All points which, like point Q (and, of course, point P), are perceived as equidistant, lie on a horopter - a surface passing through points P and Q, the shape of which differs from both a plane and a sphere and depends on our ability estimate distance, i.e. from our brain. The distances from the fovea F to the projections of the Q point (QL and QR) are close, but not equal. If they were always equal, then the line of intersection of the horopter with the horizontal plane would be a circle.

Suppose now that we are fixing a certain point in space with our eyes and that in this space there are two point sources of light that give a projection on each retina in the form of a point of light, and these points are not corresponding: the distance between them is somewhat greater than between the corresponding points . Any such deviation from the position of the corresponding points we will call disparity. If this deviation in the horizontal direction does not exceed 2° (0.6 mm on the retina), and vertically does not exceed a few minutes of arc, then we will visually perceive a single point in space located closer than the one we fix. If the distances between the projections of a point are no more, but less than between the corresponding points, then this point will seem to be located farther than the fixation point. Finally, if the vertical deviation exceeds a few arc minutes, or the horizontal deviation is greater than 2°, then we will see two separate points, which may appear to be further or closer to the fixation point. These experimental results illustrate the basic principle of stereo perception, first formulated in 1838 by Sir C. Wheatstone (who also invented the device known in electrical engineering as the "Wheatstone bridge").

It seems almost unbelievable that before this discovery, no one seemed to have realized that the presence of subtle differences in the images projected on the retinas of the two eyes can lead to a distinct impression of depth. This stereo effect demonstrated in a few minutes by any person who can arbitrarily reduce or separate the axes of his eyes, or by someone who has a pencil, a piece of paper and several small mirrors or prisms. It is not clear how Euclid, Archimedes and Newton missed this discovery. In his article, Wheatstone notes that Leonardo da Vinci came very close to discovering this principle. Leonardo pointed out that a ball located in front of a spatial scene is seen differently by each eye - with the left eye we see its left side a little further, and with the right eye - the right. Wheatstone further notes that if Leonardo had chosen a cube instead of a sphere, he would certainly have noticed that its projections are different for different eyes. After that, he might, like Wheatstone, be interested in what would happen if two similar images were specifically projected onto the retinas of two eyes.

An important physiological fact is that the sensation of depth (i.e., the ability to “directly” see whether this or that object is located further or closer to the fixation point) occurs when two retinal images are slightly shifted relative to each other in the horizontal direction - moved apart or vice versa , are close together (unless this offset is greater than about 2° and the vertical offset is close to zero). This, of course, corresponds to geometric relationships: if an object is located closer or farther with respect to a certain distance reference point, then its projections on the retinas will be moved apart or brought closer horizontally, while there will be no significant vertical displacement of images.

This is the basis of the action of the stereoscope invented by Wheatstone. The stereoscope was so popular for about half a century that almost every home had one. The same principle underlies the stereo movies that we now watch using special polaroid glasses for this. In the original design of the stereoscope, the observer viewed two images placed in a box using two mirrors that were positioned so that each eye saw only one image. Prisms and focusing lenses are now often used for convenience. The two images are identical in every way, except for small horizontal offsets, which give the impression of depth. Anyone can produce a photograph suitable for use in a stereoscope by selecting a fixed object (or scene), taking a picture, then moving the camera 5 centimeters to the right or left and taking a second picture.

Not everyone has the ability to perceive depth with a stereoscope. You can easily check your stereopsis yourself if you use the stereopairs shown in Fig. 105 and 106.

If you have a stereoscope, you can make copies of the stereo pairs shown here and paste them into the stereoscope. You can also place a thin piece of cardboard perpendicularly between two images from the same stereopair and try to look at your image with each eye, setting the eyes parallel, as if you were looking into the distance. You can also learn to move your eyes in and out with your finger, placing it between the eyes and the stereo pair and moving it forward or backward until the images merge, after which (this is the most difficult) you can examine the merged image, trying not to split it into two. If you succeed, then the apparent depth relationships will be the opposite of those perceived when using a stereoscope.

Even if you fail to repeat the experience with depth perception Whether it's because you don't have a stereoscope, or because you can't arbitrarily move the axes of your eyes in and out, you can still get the gist of the matter, although you won't enjoy the stereo effect.

In the upper stereopair in Fig. 105 in two square frames there is a small circle, one of which is shifted slightly to the left of the center, and the other is slightly to the right. If you consider this stereopair with two eyes, using a stereoscope or another method of image alignment, you will see a circle not in the plane of the sheet, but in front of it at a distance of about 2.5 cm. If you also consider the lower stereopair in fig. 105, the circle will be visible behind the sheet plane. You perceive the position of the circle in this way because exactly the same information is received on the retinas of your eyes as if the circle were actually in front of or behind the plane of the frame.

In 1960 Bela Yulesh from Bell Telephone Laboratories, came up with a very useful and elegant technique for demonstrating the stereo effect. The image shown in fig. 107, at first glance, seems to be a homogeneous random mosaic of small triangles.

So it is, except that in the central part there is a hidden triangle of a larger size. If you look at this image with two pieces of colored cellophane placed in front of your eyes - red in front of one eye and green in front of the other, then you should see a triangle in the center protruding forward from the plane of the sheet, as in the previous case with a small circle on stereopairs . (You may have to watch for a minute or so the first time, until the stereo effect occurs.) If you swap the pieces of cellophane, a depth inversion will occur. The value of these Yulesh stereo pairs lies in the fact that if your stereo perception is disturbed, then you will not see a triangle in front of or behind the surrounding background.

Summing up, we can say that our ability to perceive the stereo effect depends on five conditions:

1. There are many indirect signs of depth - partial obscuration of some objects by others, motion parallax, object rotation, relative dimensions, shadow casting, perspective. However, stereopsis is the most powerful mechanism.

2. If we fix a point in space with our eyes, then the projections of this point fall into the central pits of both retinas. Any point judged to be at the same distance from the eyes as the fixation point forms two projections at the corresponding points on the retinas.

3. The stereo effect is determined by a simple geometric fact - if an object is closer than the fixation point, then its two projections on the retinas are farther apart than the corresponding points.

4. The main conclusion based on the results of experiments with the subjects is as follows: an object whose projections on the retinas of the right and left eyes fall on the corresponding points is perceived as located at the same distance from the eyes as the point of fixation; if the projections of this object are moved apart in comparison with the corresponding points, the object seems to be located closer to the fixation point; if, on the contrary, they are close, the object seems to be located further than the fixation point.

5. With a horizontal projection shift of more than 2° or a vertical shift of more than a few minutes of arc, doubling occurs.

Physiology of stereoscopic vision

If we want to know what are the brain mechanisms of stereopsis, then the easiest way to start is with the question: are there neurons whose responses are specifically determined by the relative horizontal displacement of images on the retinas of the two eyes? Let us first see how the cells of the lower levels of the visual system respond when both eyes are stimulated simultaneously. We must start with neurons in field 17 or higher, since the retinal ganglion cells are clearly monocular, and the cells of the lateral geniculate body, in which inputs from the right and left eyes are distributed in different layers, can also be considered monocular - they respond to stimulation of either one eye or the other, but not both at the same time. In field 17, approximately half of the neurons are binocular cells that respond to stimulation from both eyes.

Upon careful testing, it turns out that the responses of these cells, apparently, depend little on the relative position of the stimulus projections on the retinas of the two eyes. Consider a typical complex cell that responds with a continuous discharge to the movement of a stimulus strip through its receptive field in one or the other eye. With simultaneous stimulation of both eyes, the frequency of discharges of this cell is higher than with stimulation of one eye, but usually for the response of such a cell it is immaterial whether at some point the projections of the stimulus hit exactly the same areas of the two receptive fields.

The best response is recorded when these projections enter and exit the respective receptive fields of the two eyes at approximately the same time; however, it is not so important which of the projections is slightly ahead of the other. On fig. 108 shows a characteristic curve of response (eg, total number of impulses in response per passage of a stimulus through the receptive field) versus difference in stimulus position on both retinas. This curve is very close to a horizontal straight line, from which it is clear that the relative position of the stimuli on the two retinas is not very significant.

A cell of this type will respond well to a line of proper orientation, regardless of its distance - the distance to the line may be greater than, equal to, or less than the distance to the point fixed by the eye.

Compared to this cell, the neurons whose responses are shown in Fig. 109 and 110 are very sensitive to the relative position of the two stimuli on the two retinas, i.e., sensitive to depth.

The first neuron (Fig. 109) responds best if the stimuli hit exactly the corresponding areas of the two retinas. The amount of horizontal misalignment of stimuli (i.e., disparity), at which the cell already stops responding, is a certain fraction of the width of its receptive field. Therefore, the cell responds if and only if the object is approximately the same distance from the eyes as the point of fixation. The second neuron (Fig. 110) responds only when the object is located further than the fixation point. There are also cells that respond only when the stimulus is closer than this point. When the degree of disparity changes, neurons of the last two types, called distant cells and near cells, very sharply change the intensity of their responses at the point of zero disparity or close to it. Neurons of all three types (cells, tuned to disparity) were found in field 17 monkeys.

It is not yet entirely clear how often they occur there, whether they are located in certain layers of the cortex, and whether they are in certain spatial relationships to the columns of eye dominance. These cells are highly sensitive to the object's distance from the eyes, which is encoded as the relative position of the corresponding stimuli on the two retinas. Another feature of these cells is that they do not respond to stimulation of only one eye, or they respond, but very weakly. All these cells share the property of orientational selectivity; as far as we know, they are similar to the usual complex cells of the upper layers of the cortex, but they have an additional property - sensitivity to depth. In addition, these cells respond well to moving stimuli and sometimes to the ends of lines.

J. Poggio of Johns Hopkins School of Medicine recorded the responses of such cells in field 17 of an awake monkey with electrodes implanted, which had previously been trained to fix the gaze of a certain object. In anesthetized monkeys, such cells were also detected in the cortex, but they were rare in field 17 and very often in field 18. I would be extremely surprised if it turned out that animals and humans can stereoscopically estimate the distances to objects using only the three described above cell types - tuned to zero disparity, "near" and "far". I would rather expect to find a complete set of cells for all possible depths. In awake monkeys, Poggio also encountered narrowly tuned cells that responded best not to zero disparity, but to small deviations from it; Apparently, the cortex may contain specific neurons for all levels of disparity. Although we still don't know exactly how the brain "reconstructs" a scene involving many objects at different distances (whatever we mean by "reconstruction"), cells like those described above are probably involved in the first stages of this process.

Some problems associated with stereoscopic vision

During the study of stereopsis psychophysicists are faced with a number of problems. It turned out that the processing of some binocular stimuli occurs in the visual system in completely incomprehensible ways. I could give many examples of this kind, but I will confine myself to two.

On the example of stereopairs shown in Fig. 105, we have seen that moving two identical images (in this case circles) towards each other results in a feeling of greater proximity, and moving away from each other leads to a feeling of greater distance. Suppose now that we are doing both of these operations simultaneously, for which we place two circles in each frame, located next to each other (Fig. 111).

Obviously, considering such stereo pairs could lead to the perception of two circles - one closer and the other farther than the plane of fixation. However, we can assume another option: we will see just two circles lying side by side in the plane of fixation. The fact is that these two spatial situations correspond to the same images on the retinas. In fact, this pair of stimuli can be perceived only as two circles in the plane of fixation, which can be easily seen if the square frames in Fig. 2 are merged by any means. 111.

In the same way, we can imagine a situation where we consider two strings of characters x, say, six characters in a string. When viewed through a stereoscope, one can in principle perceive any of a number of possible configurations, depending on which x sign from the left chain merges with a certain x sign in the right chain. In fact, if we consider such a stereopair through a stereoscope (or in another way that creates a stereo effect), we will always see six x signs in the fixation plane. We still don't know how the brain resolves this ambiguity and chooses the simplest of all possible combinations. Because of this kind of ambiguity, it is difficult even to imagine how we manage to perceive a three-dimensional scene, which includes many branches of different sizes, located at different distances from us. True, physiological data suggest that the task may not be so difficult, since different branches are likely to have different orientations, and we already know that the cells involved in stereopsis are always orientation-selective.

The second example of the unpredictability of binocular effects, related to stereopsis is the so-called struggle of the visual fields, which we also mention in the section on strabismus (chap. 9). If very different images are created on the retinas of the right and left eyes, then often one of them ceases to be perceived. If you look with your left eye at a grid of vertical lines and with your right eye at a grid of horizontal lines (Fig. 112; you can use a stereoscope or convergence of the eyes), then one would expect that you would see a grid of intersecting lines.

However, in reality it is almost impossible to see both sets of lines at the same time. Either one or the other is visible, and each of them is only for a few seconds, after which it disappears and another appears. Sometimes you can also see, as it were, a mosaic of these two images, in which separate homogeneous areas will move, merge or separate, and the orientation of the lines in them will change (see Fig. 112, below). For some reason, the nervous system cannot perceive such different stimuli at the same time in the same part of the visual field, and it suppresses the processing of one of them.

Word " suppress we use here simply as another description of the same phenomenon: in fact, we do not know how such suppression occurs and at what level of the central nervous system it occurs. It seems to me that the mosaic nature of the perceived image in the struggle of visual fields suggests that the "decision making" in this process occurs at a fairly early stage in the processing of visual information, perhaps in field 17 or 18. (I am glad that I do not need to defend this assumption .)

The phenomenon of visual field struggle means that in cases where the visual system cannot combine the images on the two retinas (into a flat picture if the images are the same, or into a three-dimensional scene if there is only slight horizontal disparity), it simply rejects one of the images - either completely when, for example, we look through a microscope with the other eye open, either partially or temporarily, as in the example above. Attention plays a significant role in the microscope situation, but the neural mechanisms underlying this shift in attention are also unknown.

You can observe another example of the struggle of visual fields if you simply look at some multi-color scene or picture through glasses with red and green filters. The impressions of different observers in this case can be very different, but most people (including myself) note transitions from a general reddish tone to greenish and back, but without the yellow color that results from the usual mixing of red light with green.

stereo blindness

If a person is blind in one eye, then it is obvious that he will not have stereoscopic vision. However, it is also absent in a certain proportion of people whose vision is otherwise normal. Surprisingly, the proportion of such people is not too small. So, if we show stereopairs like those shown in Fig. 105 and 106 to a hundred student subjects (using polaroids and polarized light), it usually turns out that four or five of them cannot achieve the stereo effect.

Often this surprises them themselves, since in everyday conditions they do not experience any inconvenience. The latter may seem strange to anyone who, for the sake of experiment, tried to drive a car with one eye closed. Apparently, the absence of stereopsis is quite well compensated by the use of other depth cues, such as motion parallax, perspective, partial occlusion of some objects by others, etc. In Chapter 9, we will consider cases of congenital strabismus, when the eyes work inconsistently for a long time. This can lead to disruption of connections in the cortex that provide binocular interaction, and as a result, to the loss of stereopsis. Strabismus is not uncommon, and even a mild degree, which may go unnoticed, is probably the cause of stereoblindness in some cases. In other cases, a violation of stereopsis, like color blindness, may be hereditary.

Since this chapter has dealt with both the corpus callosum and stereoscopic vision, I will take the opportunity to say something about the connection between the two. Try asking yourself the question: what kind of stereopsis disturbances can be expected in a person with a cut corpus callosum? The answer to this question is clear from the diagram shown in Fig. 113.

If a person fixes point P with his gaze, then the projections of point Q, located closer to the eyes within the acute angle of the FPF, - QL and QR - will be in the left and right eyes on opposite sides of the fovea. Accordingly, the Ql projection transmits information to the left hemisphere, and the Qr projection - to the right hemisphere. In order to see that the Q point is closer than P (i.e., to get a stereo effect), you need to combine the information of the left and right hemispheres. But the only way to do this is to relay information along the corpus callosum. If the path through the corpus callosum is destroyed, the person will be stereoblind in the area shaded in the figure. In 1970, D. Mitchell and K. Blakemore from the University of California at Berkeley investigated stereoscopic vision in one person with a cut corpus callosum and obtained exactly the result predicted above.

The second question, closely related to the first, is what kind of stereopsis disorder will occur if the optic chiasm is cut along the midline (which R. Myers did on cats). The result here will be in a certain sense the opposite. From fig. 114 it should be clear that in this case each eye will become blind in relation to stimuli falling on the nasal region of the retina, i.e., coming from the temporal part of the visual field.

Therefore, there will be no stereopsis in the area of space, colored lighter, where it is normally present. The lateral zones outside this area are generally accessible to only one eye, so there is no stereopsis here even under normal conditions, and after transection of the chiasm they will be zones of blindness (in the figure this is shown in a darker color). In the area behind the point of fixation, where the temporal parts of the visual fields overlap, now invisible, blindness will also set in.

However, in the area closer to the point of fixation, the remaining half-fields of both eyes overlap, so stereopsis should be preserved here, unless the corpus callosum is damaged. K. Blakemore nevertheless found a patient with a complete cutting of the chiasm along the midline (this patient, as a child, received a fracture of the skull while riding a bicycle, which, apparently, led to a longitudinal rupture of the chiasm). When tested, he was found to have exactly the combination of visual defects that we have just hypothetically described.

Article from the book: .

The book by the famous American neurophysiologist, Nobel Prize winner, summarizes modern ideas about how the neural structures of the visual system, including the cerebral cortex, are arranged and how they process visual information. With a high scientific level of presentation, the book is written in a simple, clear language, beautifully illustrated. It can serve as a textbook on the physiology of vision and visual perception.

For students of biological and medical universities, neurophysiologists, ophthalmologists, psychologists, specialists in computer technology and artificial intelligence.

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The images on the retinas are two-dimensional, yet we see the world in three dimensions. It is obvious that the ability to determine the distance to objects is important for both humans and animals. Similarly, perceiving the three-dimensional shape of objects means judging relative depth. Consider, as a simple example, a round object. If it is oblique with respect to the line of sight, its image on the retinas will be elliptical, but usually we easily perceive such an object as round. This requires the ability to perceive depth.

A person has many mechanisms for estimating depth. Some of them are so obvious that they hardly deserve mention. However, I will mention them. If the approximate size of an object is known, for example in the case of objects such as a person, a tree or a cat, then we can estimate the distance to it (although there is a risk of making a mistake if we encounter a dwarf, bonsai or lion). If one object is located in front of the other and partially obscures it, then we perceive the front object as being closer. If we take a projection of parallel lines, for example, railroad tracks going into the distance, then in the projection they will converge. This is an example of perspective - a very effective measure of depth. The convex section of the wall appears lighter in its upper part if the light source is located higher (usually the light sources are at the top), and the recess in its surface, if it is illuminated from above, appears darker in the upper part. If the light source is placed below, then the bulge will look like a recess, and the recess will look like a bulge. An important indicator of distance is motion parallax- the apparent relative displacement of near and more distant objects if the observer moves his head left and right or up and down. If some solid object is rotated, even at a small angle, then its three-dimensional shape is immediately revealed. If we focus the lens of our eye on a nearby object, then the more distant object will be out of focus; thus, changing the shape of the lens, i.e. by changing the accommodation of the eye (see Chapters 2 and 6), we are able to estimate the distance of objects. If you change the relative direction of the axes of both eyes, bringing them together or spreading them (carrying out convergence or divergence), then you can bring together two images of an object and keep them in this position. Thus, by controlling either the lens or the position of the eyes, one can estimate the distance of an object. The designs of a number of rangefinders are based on these principles. With the exception of convergence and divergence, all other distance measures listed so far are monocular. The most important depth perception mechanism, stereopsis, depends on the sharing of two eyes. When viewing any three-dimensional scene, the two eyes form slightly different images on the retina. You can easily be convinced of this if you look straight ahead and quickly move your head from side to side by about 10 cm or quickly close one eye or the other in turn. If you have a flat object in front of you, you won't notice much of a difference. However, if the scene includes objects at different distances from you, you will notice significant changes in the picture. During stereopsis, the brain compares images of the same scene on two retinas and estimates relative depth with great accuracy.

Suppose the observer fixes a certain point P with his gaze. This statement is equivalent to saying: the eyes are directed in such a way that the images of the point are in the central pits of both eyes (F in Fig. 103). Suppose now that Q is another point in space that appears to the observer to be located at the same depth as P. Let Q L and Q R be the images of point Q on the retinas of the left and right eyes. In this case, the points Q L and Q R are called corresponding points two retinas. It is obvious that two points coinciding with the central pits of the retinas will be corresponding. It is also clear from geometrical considerations that the point Q", estimated by the observer as located closer than Q, will give two projections on the retinas - Q "L and Q" R - at non-corresponding points located farther apart than in the case if these points were corresponding (this situation is depicted on the right side of the figure.) In the same way, if we consider a point located farther from the observer, then it turns out that its projections on the retinas will be located closer to each other than the corresponding points. what is said above about the corresponding points are partly definitions, and partly statements arising from geometric considerations.When considering this issue, the psychophysiology of perception is also taken into account, since the observer subjectively evaluates whether an object is located further or closer to the point P. Let us introduce another definition.All points , which, like point Q (and, of course, point P), are perceived as equidistant, lie on horoptera- a surface passing through the points P and Q, the shape of which differs from both a plane and a sphere and depends on our ability to estimate the distance, i.e. from our brain. The distances from the fovea F to the projections of the Q point (Q L and Q R) are close, but not equal. If they were always equal, then the line of intersection of the horopter with the horizontal plane would be a circle.

Rice. 103. Left: if the observer looks at point P, then two of its images (projections) fall on the central pits of two eyes (point F). Q - point, which, according to the observer, is at the same distance from him as P. In this case, we say that two projections of the Q point (Q L and Q R) fall into the corresponding points of the retinas. (A surface composed of all points Q that appear to be at the same distance from the observer, the same as point P, is called a horopter passing through point P). On right: if the point Q "is closer to the observer than Q, then its projections on the retinas (Q" L and Q "R) will be further apart horizontally than if they were at the corresponding points. If the point Q" was further, then the projections Q "L" and Q "R would have been shifted horizontally closer to each other.

Suppose now that we are fixing a certain point in space with our eyes and that in this space there are two point sources of light that give a projection on each retina in the form of a point of light, and these points are not corresponding: the distance between them is several more, than between corresponding points. Any such deviation from the position of the corresponding points we will call disparity. If this deviation in the horizontal direction does not exceed 2° (0.6 mm on the retina), and vertically does not exceed a few minutes of arc, then we will visually perceive a single point in space located closer than the one we fix. If the distances between the projections of the point are not greater, but less, than between the corresponding points, then this point will appear to be located farther than the fixation point. Finally, if the vertical deviation exceeds a few arc minutes, or the horizontal deviation is greater than 2°, then we will see two separate points, which may appear to be further or closer to the fixation point. These experimental results illustrate the basic principle of stereo perception, first formulated in 1838 by Sir C. Wheatstone (who also invented the device known in electrical engineering as the "Wheatstone bridge").

It seems almost unbelievable that before this discovery, no one seemed to have realized that the presence of subtle differences in the images projected on the retinas of the two eyes can lead to a distinct impression of depth. Such a stereo effect can be demonstrated in a few minutes by any person who can arbitrarily reduce or separate the axes of his eyes, or by someone who has a pencil, a piece of paper and several small mirrors or prisms. It is not clear how Euclid, Archimedes and Newton missed this discovery. In his article, Wheatstone notes that Leonardo da Vinci came very close to discovering this principle. Leonardo pointed out that a ball located in front of a spatial scene is seen differently by each eye - with the left eye we see its left side a little further, and with the right eye - the right. Wheatstone further notes that if Leonardo had chosen a cube instead of a sphere, he would certainly have noticed that its projections are different for different eyes. After that, he might, like Wheatstone, be interested in what would happen if two similar images were specifically projected onto the retinas of two eyes.

An important physiological fact is that the sensation of depth (i.e. the ability to “directly” see, one or another object is located farther or closer to the fixation point) occurs when two retinal images are slightly shifted relative to each other in the horizontal direction - moved apart or, conversely, are close together (unless this displacement exceeds about 2°, and the vertical displacement is close to zero). This, of course, corresponds to geometric relationships: if an object is located closer or farther with respect to a certain distance reference point, then its projections on the retinas will be moved apart or brought closer horizontally, while there will be no significant vertical displacement of images.

Not everyone has the ability to perceive depth with a stereoscope. You can easily check your stereopsis yourself if you use the stereopairs shown in Fig. 105 and 106. If you have a stereoscope, you can make copies of the stereo pairs shown here and paste them into the stereoscope. You can also place a thin piece of cardboard perpendicularly between two images from the same stereopair and try to look at your image with each eye, setting the eyes parallel, as if you were looking into the distance. You can also learn to move your eyes in and out with your finger, placing it between the eyes and the stereo pair and moving it forward or backward until the images merge, after which (this is the most difficult) you can examine the merged image, trying not to split it into two. If you succeed, then the apparent depth relationships will be the opposite of those perceived when using a stereoscope.

Rice. 104. BUT. Wheatstone stereoscope. B. Diagram of Wheatstone's stereoscope, drawn up by himself. The observer sits in front of two mirrors (A and A"), placed at an angle of 40 ° to the direction of his gaze, and looks at two pictures combined in the field of view - E (with the right eye) and E" (with the left eye). In a simpler version created later, two pictures are placed side by side so that the distance between their centers is approximately equal to the distance between the eyes. The two prisms deflect the direction of gaze so that, with proper convergence, the left eye sees the left image and the right eye sees the right image. You yourself can try to do without a stereoscope by imagining that you are looking at a very distant object with eyes whose axes are set parallel to each other. Then the left eye will look at the left image, and the right eye will look at the right one.

Even if you fail to repeat the experience with depth perception - whether because you do not have a stereoscope, or because you cannot arbitrarily move the axes of the eyes together - you will still be able to understand the essence of the matter, although you will not get stereo enjoyment.

In the upper stereopair in Fig. 105 in two square frames there is a small circle, one of which is shifted slightly to the left of the center, and the other is slightly to the right. If you consider this stereopair with two eyes, using a stereoscope or another method of image alignment, you will see a circle not in the plane of the sheet, but in front of it at a distance of about 2.5 cm. If you also consider the lower stereopair in fig. 105, the circle will be visible behind the sheet plane. You perceive the position of the circle in this way because exactly the same information is received on the retinas of your eyes as if the circle really located in front of or behind the plane of the frame.

Rice. 105. If the upper stereo pair is inserted into the stereoscope, then the circle will look ahead of the frame plane. In the lower stereopair, it will be located behind the frame plane. (You can do this experiment without a stereoscope, by convergence or divergence of the eyes; convergence is easier for most people. To make things easier, you can take a piece of cardboard and place it between two images of a stereo pair. At first, this exercise may seem difficult and tedious to you; do not be zealous at first At the convergence of the eyes on the upper stereopair, the circle will be visible farther than the plane, and on the lower one - closer).

In 1960, Bela Jules of Bell Telephone Laboratories came up with a very useful and elegant technique for demonstrating the stereo effect. The image shown in fig. 107, at first glance, seems to be a homogeneous random mosaic of small triangles. So it is, except that in the central part there is a hidden triangle of a larger size. If you look at this image with two pieces of colored cellophane placed in front of your eyes - red in front of one eye and green in front of the other, then you should see a triangle in the center protruding forward from the plane of the sheet, as in the previous case with a small circle on stereopairs . (You may have to watch for a minute or so the first time, until the stereo effect occurs.) If you swap the pieces of cellophane, a depth inversion will occur. The value of these Yulesh stereo pairs lies in the fact that if your stereo perception is disturbed, then you will not see a triangle in front of or behind the surrounding background.

Rice. 106. Another stereo pair.

Summing up, we can say that our ability to perceive the stereo effect depends on five conditions:

5. With a horizontal projection shift of more than 2° or a vertical shift of more than a few minutes of arc, doubling occurs.

Rice. 107. In order to get this image called anaglyph, Bela Jules first built two systems of randomly placed small triangles; they differed only in that 1) one system had red triangles on a white background, while the other had green triangles on a white background; 2) within the large triangular zone (near the center of the figure), all green triangles are somewhat shifted to the left compared to the red ones. After that, the two systems are aligned, but with a slight shift so that the triangles themselves do not overlap. If the resulting image is viewed through a green cellophane filter, only red elements will be visible, and if through a red filter, only green elements will be visible. If you put a green filter in front of one eye and a red filter in front of the other, you will see a large triangle protruding about 1 cm in front of the page. If the filters are swapped, the triangle will be visible behind the page plane.

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3D VISION

3D VISION, the ability of the eyes to determine the position of objects in three-dimensional space. The RETINA creates a two-dimensional image, and the information about the depth of space is created in the brain. For this, such “depth indicators” as linear perspective, PARALLAX, and the relative size of objects serve. It also takes into account the fact that each eye sees the object a little differently.

Scientific and technical encyclopedic dictionary.

See what "VOLUME VISION" is in other dictionaries:

I Vision (visio, visus) is the physiological process of perceiving the size, shape and color of objects, as well as their relative position and distance between them; the source of visual perception is the light emitted or reflected from objects ... ... Medical Encyclopedia

I; cf. One of the five external senses, of which the eye is the organ; the ability to see. Organ of vision. Lose sight. Spoil, check h. Z. improved, worsened, recovered. Acute, good, bad, weak ◊ Field of view. one.… … encyclopedic Dictionary

vision- ▲ perception of the appearance, through, absorption, electromagnetic waves vision The body's perception of the appearance of objects by capturing light vibrations emanating from them. with a simple eye. anaglyph. stereoradiography. ... ...

VISION- the process of perception of external. of the world, which determines the idea of the size, shape, color of objects, their relative position and distance between them Organ 3. eye The human eye is endowed with the ability to perceive light waves in the range from 360 to ... ... Russian Pedagogical Encyclopedia

volumetric image- ▲ surround holography image. ↓ vision, sculpture ... Ideographic Dictionary of the Russian Language

binocular vision- (from lat. bini pair, two, oculus eyes) vision, in which both eyes take part, and the images they receive merge into one, corresponding to the object in question. B.z. provides volumetric (stereoscopic) perception of the observed ... ... Correctional pedagogy and special psychology. Dictionary

Primates- (order Primates) an extensive group of mammalian species (order), which systematically includes modern man and his evolutionary predecessors. In the vernacular of monkeys (which is not very true). The most important distinguishing ... ... Physical Anthropology. Illustrated explanatory dictionary.

Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasma, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia