We think we see the world clearly and in real time, but vision works differently. Why do we see objects

In the section on the question, what is the nature of color? Why do we see objects but not air? given by the author chevron the best answer is because the objects do not pass through a certain sector white color this gives them the color that we see, and the air lets through the entire spectrum of white, so we don’t see it

Answer from Alexey N. Skvortsov (SPbSPU)[guru]
Color is a _subjective_ perception of wavelength visible color(if you like - the energy of photons). So 680nm looks like deep red and 420nm looks like blue.
Let me also emphasize that this is subjective. For example, I am genetically colorblind and do not see the difference between what you call light lilac and light green.
Our eye sees only scattered (including - DIFFUSELY reflected) light. We do not see parallel light rays (so we do not see the surface of a pure mirror). Clean air scatters light very weakly (in the thickness of the atmosphere this becomes noticeable and looks like the blue color of the sky). For this reason, we do not see laser ray passing through the air. However, if you add a diffuser, for example, raise it, the beam will become visible.
The color of an object or substance appears when they absorb or scatter radiation in the optical range (400-700 nm) in different ways. Additionally: the substance that absorbs everything looks black; the substance that scatters everything looks white.

Answer from Kosovorotka[guru]
Objects we see only those that REFLECT light of a certain range. Accordingly, the air does NOT reflect light, therefore for us it is transparent.

Lines back wall eyeball and occupies 72% of its area inner surface. It is called RETINA. The retina is shaped like a plate about a quarter of a millimeter thick and consists of 10 layers.

By its origin, the retina is an advanced part of the brain: during the development of the embryo, the retina is formed from the eye bubbles, which are protrusions of the anterior wall of the primary brain bubble. The main of its layers is the layer of light sensitive cells - PHOTORECEPTORS. They are of two types: STICKS and CONES. They got such names due to their shape:

There are about 125-130 million rods in each eye. They are characterized high sensitivity to light and work in low light, that is, they are responsible for twilight vision. However, rods are not able to distinguish colors, and with their help we see in black and white. They contain visual pigment RHODOPSIN.

Rods are located throughout the retina, except for the very center, therefore, thanks to them, objects on the periphery of the visual field are detected.

There are much fewer cones than rods - about 6-7 million in the retina of each eye. The cones provide color vision, but they are 100 times less sensitive to light than rods. That's why color vision- daytime, and in the dark, when only sticks work, a person cannot distinguish colors. Cones are much better than rods at picking up fast movements.

The cone pigment to which we owe color vision is called IODOPSIN. Rods are "blue", "green", and "red", depending on the wavelength of light they preferentially absorb.

Cones are located mainly in the center of the retina, in the so-called YELLOW SPOT(also called MACULA). In this place, the thickness of the retina is minimal (0.05-0.08 mm) and all layers are absent, except for the layer of cones. The macula has yellow due to high content yellow pigment. yellow spot a person sees best: all light information that falls on this area of ​​\u200b\u200bthe retina is transmitted most fully and without distortion, with maximum clarity.

The human retina is arranged in an unusual way: it is, as it were, turned upside down. The layer of the retina with light-sensitive cells is not in front, on the side vitreous body, as one might expect, but behind, from the side of the choroid. To get to the rods and cones, light must first make its way through the other 9 layers of the retina.

between the retina and choroid there is a pigment layer containing a black pigment - melanin. This pigment absorbs light passing through the retina and prevents it from being reflected back, scattered inside the eye. In albinos - people with a congenital lack of melanin in all cells of the body - in high light, the light inside the eyeball is reflected in all directions by the surfaces of the retina. As a result, a single discrete spot of light that would normally excite only a few rods or cones is reflected everywhere and excites many receptors. Therefore, in albinos, visual acuity is rarely higher than 0.2-0.1 at a rate of 1.0.

Under the influence of light rays in the photoreceptors, a photochemical reaction occurs - the disintegration of visual pigments. As a result of this reaction, energy is released. This energy in the form of an electrical signal is transmitted to intermediate cells - BIPOLARS(they are also called interneurons or interneurons), and then on GANGLIONIC CELLS that generate nerve impulses and nerve fibers send them to the brain.

Each cone is connected via a bipolar cell to one ganglion cell. But the rod signals going to the ganglion cells undergo the so-called convergence: several rods are connected to one bipolar cell, it sums up their signals and transmits them to one ganglion cell. Convergence allows increasing the light sensitivity of the eye, as well as the sensitivity of peripheral vision to movements, while in the case of cones, the absence of summation allows increasing visual acuity, but the sensitivity of "cone" vision is reduced.

Through the optic nerve, information about the image from the retina enters the brain and is processed there, in such a way that we see final picture the surrounding world.

Read more: brain visual system(visual analyzer)

Structure visual apparatus human
1 - retina,
2 - non-crossed fibers optic nerve,
3 - crossed fibers of the optic nerve,
4 - optic tract,
5 - outer cranked body,
6 - visual radiance,
7 - visual cortex
8 - oculomotor nerve
9 - superior tubercles of the quadrigemina

In humans and higher apes, half of the fibers of each optic nerve of the right and left sides intersect (the so-called optic chiasm, or CHIASMA). In the chiasm, only those fibers that transmit a signal from the inner half of the retina of the eye cross over. And this means that the vision of the left half of the image of each eye is directed to left hemisphere, and the vision of the right half of each eye - to the right!

After passing through the chiasm, the fibers of each optic nerve form the optic tract. The optic tracts run along the base of the brain and reach the subcortical visual centers- outdoor cranked bodies. The processes of nerve cells located in these centers form visual radiance, which forms most white matter temporal lobe brain, as well as the parietal and occipital lobes.

Ultimately, all visual information is transmitted in the form nerve impulses to the brain, its highest authority - the cortex, where the formation of a visual image takes place.

The visual cortex is located - imagine! - in occipital lobe brain.

At present, much is already known about the mechanisms of the visual system, but we must honestly admit that modern science does not yet fully know how the brain copes with the complex task of converting the electrical signals of the retina into the visual scene as we perceive it - with all the complexity of shapes, depth, movement and color. But the study of this issue does not stand still, and, hopefully, science in the future will unravel all the secrets of the visual analyzer and be able to use them in practice - in medicine, cybernetics and other areas.

Educational video:
The structure and operation of the visual analyzer

Ecology of life: Fix your gaze on a line of text and do not move your eyes. At the same time, try to switch your attention to the line below. Then one more. And further. After half a minute, you will feel that your eyes seem to have clouded over: only a few words on which your eyes are focused are clearly visible, and everything else is blurry. In fact, this is how we see the world. Is always. And at the same time we think that we see everything crystal clear.

Fix your gaze on the line of text and do not move your eyes. At the same time, try to switch your attention to the line below. Then one more. And further. After half a minute, you will feel that your eyes seem to have clouded over: only a few words on which your eyes are focused are clearly visible, and everything else is blurry. In fact, this is how we see the world. Is always. And at the same time we think that we see everything crystal clear.

We have a small, small point on the retina, in which there are enough sensitive cells - rods and cones - so that everything can be seen normally. This point is called the "central fovea". The fovea provides a viewing angle of about three degrees - in practice, this corresponds to the size of the nail thumb on an outstretched hand.

On the rest of the surface of the retina, there are much fewer sensitive cells - enough to distinguish the vague outlines of objects, but no more. There is a hole in the retina that does not see anything at all - the "blind spot", the point where the nerve connects to the eye. You don't notice it, of course. If this is not enough, then let me remind you that you also blink, that is, turn off your vision every few seconds. Which you don't pay attention to either. Although now you are paying. And it bothers you.

How do we even see anything? The answer seems to be obvious: we move our eyes very quickly, on average three to four times per second. These sharp synchronous eye movements are called "saccades". By the way, we don’t usually notice them either, which is good: as you may have guessed, vision does not work during a saccade. But with the help of saccades, we constantly change the picture in the fovea - and as a result, we cover the entire field of view.

Peace through a straw

But if you think about it, this explanation is no good. Take a cocktail straw in your fist, put it to your eye and try to watch a movie like that - I'm not talking about going out for a walk. How is it normal to see? This is your three degree view. Move the straw as much as you like - normal vision will not work.

In general, the question is not trivial. How is it that we see everything if we see nothing? There are several options. First: we still do not see anything - we just have the feeling that we see everything. To check whether this impression is misleading, we shift our eyes so that the fovea is directed exactly at the point we are testing.

And we think: well, it’s still visible! And on the left (eyes zipper to the left), and on the right (eyes zipper to the right). It's like with a refrigerator: based on our own feelings then the light is always on.

The second option: we see not an image coming from the retina, but a completely different one - the one that the brain builds for us. That is, the brain crawls back and forth like a straw, diligently composes a single picture from this - and now we already perceive it as the surrounding reality. In other words, we see not with our eyes, but with the cerebral cortex.

Both options agree on one thing: the only way to see something - move your eyes. But there is one problem. Experiments show that we distinguish objects at a phenomenal speed - faster than the oculomotor muscles have time to react. And we ourselves do not understand this. It seems to us that we have already shifted our eyes and saw the object clearly - although in fact we are only going to do this. It turns out that the brain does not just analyze the picture received with the help of vision - it also predicts it.

Unbearably dark stripes

German psychologists Arvid Herwig and Werner Schneider conducted an experiment: they fixed their heads on volunteers and recorded their eye movements with special cameras. Subjects stared at the blank center of the screen. On the side - in the lateral field of view - a striped circle was displayed on the screen, to which the volunteers immediately turned their gaze.

Here psychologists did a tricky trick. During a saccade, vision does not work - a person becomes blind for a few milliseconds. The cameras caught that the subject began to move his eyes towards the circle, and at that moment the computer replaced the striped circle with another, which differed from the first number of stripes. The participants in the experiment did not notice the change.

It turned out the following: peripheral vision volunteers were shown a circle with three stripes, and in a focused or central strip, for example, there were four.

In this way, volunteers were trained to associate a vague (lateral) image of one figure with a clear (central) image of another figure. The operation was repeated 240 times within half an hour.

After training, the exam began. The head and gaze were again fixed, and a striped circle was again drawn in the lateral field of view. But now, as soon as the volunteer began to move his eyes, the circle disappeared. A second later, a new circle appeared on the screen with a random number of stripes.

The participants in the experiment were asked to use the keys to adjust the number of stripes so that they got the figure that they had just seen with peripheral vision.

Volunteers from the control group, who were shown the same figures in lateral and central vision at the training stage, determined the “degree of striping” quite accurately. But those who were taught the wrong association saw the figure differently. If during training the number of stripes was increased, then at the examination stage, the subjects recognized three-striped circles as four-stripes. If they reduced it, then the circles seemed to them two-lane.

The illusion of sight and the illusion of the world

What does this mean? Our brains, it turns out, are constantly learning to associate appearance object in peripheral vision with how this object looks when we look at it. And further uses these associations for predictions. This explains the phenomenon of our visual perception: we recognize objects even before we, strictly speaking, see them, because our brain analyzes a blurry picture and remembers, based on previous experience, how this picture looks after focusing. He does it so fast that we get the impression clear vision. This feeling is an illusion.

It is also surprising how effectively the brain learns to make such predictions: just half an hour of mismatched pictures in the lateral and central vision was enough for the volunteers to begin to see incorrectly. Considering that in real life we move our eyes hundreds of thousands of times a day, imagine the terabytes of video from the retina the brain shovels every time you walk down the street or watch a movie.

It's not even about vision as such - it's just the most vivid illustration of how we perceive the world.

It seems to us that we are sitting in a transparent spacesuit and sucking in the surrounding reality. In fact, we do not interact directly with her at all. What seems to us to be an imprint of the world around us, is actually built by the brain virtual reality, which is issued to consciousness at face value.

This will be of interest to you:

It takes about 80 milliseconds for the brain to process information and build a more or less complete picture from the processed material. Those 80 milliseconds are the delay between reality and our perception of that reality.

We always live in the past - more precisely, in a fairy tale about the past, told to us nerve cells. We are all sure of the veracity of this fairy tale - this is also a property of our brain, and there is no getting away from it. But if each of us at least occasionally remembered these 80 milliseconds of self-deception, then the world, it seems to me, would be a little kinder. published

Candidate of Chemical Sciences O. BELOKONEVA.

Science and life // Illustrations

Science and life // Illustrations

Science and life // Illustrations

Imagine that you are standing in a sunlit meadow. How many bright colors are around: green grass, yellow dandelions, red strawberries, lilac-blue bells! But the world is bright and colorful only during the day, at dusk all objects become equally gray, and at night they are completely invisible. It is the light that allows you to see the world in all its colorful splendor.

The main source of light on Earth is the Sun, a huge hot ball, in the depths of which nuclear reactions are continuously going on. Part of the energy of these reactions the Sun sends us in the form of light.

What is light? Scientists have been arguing about this for centuries. Some believed that light is a stream of particles. Others conducted experiments from which it clearly followed: light behaves like a wave. Both turned out to be right. Light is electromagnetic radiation, which can be thought of as a traveling wave. A wave is created by fluctuations in electric and magnetic fields. The higher the oscillation frequency, the more energy the radiation carries. And at the same time, radiation can be considered as a stream of particles - photons. So far, it is more important for us that light is a wave, although in the end we will have to remember about photons as well.

The human eye (unfortunately, or maybe fortunately) is able to perceive electromagnetic radiation only in a very narrow wavelength range, from 380 to 740 nanometers. This visible light is emitted by the photosphere - a relatively thin (less than 300 km thick) shell of the Sun. If we decompose "white" sunlight by wavelengths, you get the visible spectrum - a rainbow well known to everyone, in which the waves different lengths perceived by us as different colors: from red (620-740 nm) to purple (380-450 nm). Radiation with a wavelength greater than 740 nm (infrared) and less than 380-400 nm (ultraviolet) for human eye invisible. The retina of the eye has special cages- receptors responsible for color perception. They have a conical shape, which is why they are called cones. A person has three types of cones: some perceive light best in the blue-violet region, others in yellow-green, and others in red.

What determines the color of the things around us? In order for our eye to see any object, it is necessary that the light first hit this object, and only then on the retina. We see objects because they reflect light, and this reflected light, passing through the pupil and lens, hits the retina. Light absorbed by an object cannot be seen by the eye. Soot, for example, absorbs almost all radiation and appears black to us. Snow, on the other hand, reflects almost all the light falling on it evenly and therefore appears white. And what happens if sunlight hits a blue-painted wall? Only blue rays will be reflected from it, and the rest will be absorbed. Therefore, we perceive the color of the wall as blue, because the absorbed rays simply do not have a chance to hit the retina.

Different objects, depending on what substance they are made of (or what paint they are painted with), absorb light in different ways. When we say: “The ball is red”, we mean that the light reflected from its surface affects only those receptors of the retina that are sensitive to red. And this means that the paint on the surface of the ball absorbs all light rays except red ones. The object itself has no color, the color occurs when electromagnetic waves of the visible range are reflected from it. If you were asked to guess what color the paper is in a sealed black envelope, you will not sin at all against the truth if you answer: “No!”. And if a red surface is illuminated with green light, it will appear black, because green light does not contain rays corresponding to red. Most often, a substance absorbs radiation in different parts visible spectrum. The chlorophyll molecule, for example, absorbs light in the red and blue regions, and the reflected waves give green color. Thanks to this, we can admire the greenery of forests and grasses.

Why do some substances absorb green light while others absorb red? This is determined by the structure of the molecules of which the substance is composed. The interaction of matter with light radiation occurs in such a way that at one time one molecule “swallows” only one portion of radiation, in other words, one quantum of light or a photon (this is where the idea of ​​light as a stream of particles came in handy!). The energy of a photon is directly related to the frequency of radiation (the higher the energy, the greater the frequency). After absorbing a photon, the molecule goes to a higher energy level. The energy of the molecule does not increase smoothly, but abruptly. Therefore, the molecule does not absorb any electromagnetic waves, but only those that suit it in terms of the size of the “portion”.

So it turns out that not a single object is painted by itself. Color arises from selective absorption by matter visible light. And since there are a great many substances capable of absorbing - both natural and created by chemists - in our world, the world under the Sun is colored with bright colors.

The oscillation frequency ν, the wavelength of light λ and the speed of light c are related by a simple formula:

The speed of light in vacuum is constant (300 million nm/s).

The wavelength of light is usually measured in nanometers.

1 nanometer (nm) is a unit of length equal to one billionth of a meter (10 -9 m).

There are one million nanometers in one millimeter.

The oscillation frequency is measured in hertz (Hz). 1 Hz is one oscillation per second.

An extremely important form of energy. Life on earth depends on the energy of sunlight. In addition, light is radiation that gives us visual sensations. laser radiation It is applied in many areas - from information transfer to steel cutting.

We see objects when the light from them reaches our eyes. These objects either emit light themselves, or reflect the light emitted by other objects, or pass it through themselves. We see, for example, the Sun and stars because they emit light. Most of the objects around us we see thanks to the light reflected by them. And some materials, such as stained-glass windows in cathedrals, reveal the richness of their colors by letting light pass through them.

Bright sunlight appears to us as pure white, that is, colorless. But here we are mistaken, since white light consists of many colors. They are visible when the rays of the sun illuminate the raindrops and we observe the rainbow. A multi-colored strip is also formed when sunlight is reflected from the beveled edge of the mirror or passes through a glass decoration or vessel. This band is called the light spectrum. It starts with a red color and, gradually changing, ends at the opposite end with purple.

Usually we do not take into account the weaker shades of color and therefore we consider the spectrum to consist of all seven color bands. The colors of the spectrum, called the seven colors of the rainbow, include red, orange, yellow, green, cyan, indigo, violet.

Prisms

In the 1760s, Isaac Newton experimented with light. To decompose light into its components and obtain a spectrum, he used a trihedral glass prism. The scientist discovered that by collecting the fragmented beam with the help of a second prism, you can again get white light. So he proved that white light is a mixture different colors.

The primary colors of light are red, green and blue. Their combination forms white light. Mixed in pairs, they form the colors yellow, blue, or purple. The pigment or primary colors of paints are purple, blue, yellow. Their combination is shown in the figure.

Light rays passing through a prism are refracted. But rays of different colors are refracted in varying degrees- red in the smallest, purple in the largest. That is why, passing through a prism, the white color is split into composite colors.

The refraction of light is called refraction, and the decomposition of white light into different colors is called dispersion. When raindrops scatter sunlight, a rainbow is formed.

Electromagnetic waves

The light spectrum is only part of a huge range of radiation, which is called the electromagnetic spectrum. It includes gamma, x-ray, ultraviolet, infrared (thermal) radiation and radio waves. All types of electromagnetic radiation propagate in the form of waves of electrical and magnetic oscillations at the speed of light - about 300,000 km / s. Electromagnetic waves differ mainly in their wavelength. It is determined by the frequency, that is, the speed with which these waves are formed. The higher the frequency, the closer they are to each other and the shorter the length of each of them. In the spectrum, light waves occupy a place between the infrared and ultraviolet regions.

The sun emits wide range electromagnetic radiation. The scale gives wavelengths in nanometers (one billionth of a meter) and larger units.

lenses

The image in cameras and optical instruments is obtained using lenses and the phenomenon of refraction of light rays in them. You may have noticed that in the lenses of cheap telescopes, for example, a colored border forms around the contours of the image. This happens because, like a prism, simple lens, made from a single piece of glass or plastic, refracts rays of different colors to different degrees. In higher quality devices, this defect is eliminated by using two lenses connected together. The first part of such a compound lens decomposes white light into different colors, and the second part combines them again, thus removing an unnecessary border.

Primary colors

As Newton showed, white candle can be obtained by mixing the seven colors of the rainbow. But this can be done even easier by mixing only three colors - red, green and blue. They are called the primary colors of light. We will get other colors by combining the main ones. So, for example, a mixture of red and green gives yellow.

A convex lens focuses parallel rays. Since white light is made up of more than one color, their rays are refracted to different degrees and focused at different distances from the lens. As a result, a colored border is formed around the contours of the image.

A lens made of two types of glass can be used to obtain images without a colored border. The first part of the lens refracts rays of different colors to varying degrees, causing them to diverge. The second collects them again, eliminating color distortions.

The fact that white light is made up of multiple colors explains why we see objects in one color or another. (For simplicity, let's assume that white light consists only of red, green, and blue.) We see an object white if it reflects all three components of white light, and black if it reflects none of them. But a red object illuminated by white light appears red because it reflects mostly the red component of white and absorbs most of the blue and green components. As a result, we see mostly red. Similarly, a blue object reflects blue rays while absorbing red and green ones. A green object reflects green rays, absorbing red and blue.

The compound eyes of flies are made up of thousands of lenses. Each focuses light on only a few photosensitive cells, so that the fly cannot see all the details of the object. A flower, through the eyes of a fly, looks like a picture consisting of thousands of pieces.

WebProm banner network

If you mix colors different colors, then each will absorb (absorb) the various components of white light, the mixture will become darker. Thus, mixing paints is the opposite process of mixing color rays. To get a certain range of colors, you need to use a different set of primary colors. Primary colors used in painting are called primary pigment colors. This is the color magenta or "perfect red", blue and yellow are commonly (but incorrectly) referred to as red, blue and yellow. Black is added to increase the density of dark areas, and a rich mixture of all primary colors still reflects light to some extent. The result is dark brown instead of black.

Waves and particles

How light rays are formed and propagated has remained a complete mystery for centuries. And today this phenomenon is not fully investigated by scientists.

In the 17th century, Isaac Newton and others believed that light was made up of fast moving particles called corpuscles. Danish scientist Christian Huygens claimed that light is made up of waves.

In 1801, the English scientist Thomas Young made a series of experiments with the diffraction of light. This phenomenon consists in the fact that when passing through a very narrow slit, light scatters slightly, and does not spread in a straight line. Young explained diffraction as the propagation of light in the form of waves. And in the 60s of the XIX century, the Scottish scientist James Clark Maxwell suggested that electromagnetic energy propagates in waves, and that light is special kind this energy.

Mirage is optical illusion observed in hot deserts (top). When the sun heats up the earth, the air above it also heats up. When the temperature changes to different heights, the light in the air is refracted, as shown in the picture. To see the top of the tree, the observer has to look down, so the tree appears upside down. Sometimes the light falling from the sky looks like puddles spilled on the ground. Layers of cold air over the sea can cause the opposite phenomenon (below). Light reflected from a distant ship is refracted so that the ship appears to be floating in the sky.

However, by the beginning of the 20th century, the German scientist Max Planck proved in his works that radiation energy can exist only in the form of tiny bunches - quanta. This proof underlies Planck's quantum theory, for which he received in 1918 Nobel Prize in the field of physics A quantum of light radiation is a particle called a photon. When emitted or absorbed, light always behaves like a stream of photons.

Thus, sometimes light behaves like waves, sometimes like particles. Therefore, it is considered to have a dual nature. Scientists, when explaining observational data, can use either wave theory or particle theory.

Howliod fish emit bioluminescent light from abdominal organs (photophores). The fish adjusts their brightness to match the brightness of the light coming from the surface.

Light generation

Like electric current, light can be generated by other forms of energy. The sun generates light and other electromagnetic radiation through powerful fusion reactions that convert hydrogen into helium. When coal or wood is burned, the chemical energy of the fuel is converted into heat and light. Passing current through a thin filament in an electric light bulb gives the same result. The daylight lamp works on a different principle. A high voltage is applied to the ends of a tube filled with vapor (usually mercury) under high pressure. The vapor begins to glow, emitting ultraviolet radiation, which acts on the chemical coating inner walls tubes. The coating absorbs invisible ultraviolet radiation and emits light energy itself. This process of converting radiation is called fluorescence.

Phosphorescence is a phenomenon of the same kind, but the glow continues for quite a long time even after the removal of the radiation source. Luminous paint phosphoresces. After a short exposure to bright light, it glows for hours. Fluorescence and phosphorescence are forms of luminescence - the emission of light without the influence of heat.

bioluminescence

Some living organisms, including firefly beetles, certain types fish, fungi and bacteria, generate light in the way of bioluminescence. In this type of luminescence, the light source is the chemical energy produced by the oxidation of a substance called luciferin.

One of the most useful sources light is a laser. This word is made up of the first letters of the full term "light amplification by stimulated emission of radiation". In a laser tube, under the influence of electricity, photons are released from atoms. They come out of the tube as a narrow beam of light or some other form of electromagnetic radiation, depending on the substance used to produce the photons.

Breathtaking effects at rock concerts are obtained with the help of smoke generators. Its particles scatter the beams of spotlights, giving them a visible outline.

Unlike ordinary light, laser light is coherent. This means that the emitted light waves rise and fall together. The resulting light radiation is highly directional and high density energy has various areas applications, including stitching tissue in surgery, cutting steel, aiming missiles at targets, transmitting information.