What adaptation is observed with increasing brightness. Mechanisms of light perception. Visual adaptation. (dark and light). Factors that increase light sensitivity during adaptation
To distinguish colors, their brightness is crucial. The eye's adjustment to different brightness levels is called adaptation. There are light and dark adaptations.
Light adaptation means a decrease in the eye's sensitivity to light in high light conditions. During light adaptation, the cone apparatus of the retina functions. Practically, light adaptation occurs in 1–4 minutes. The total light adaptation time is 20-30 minutes.
Dark adaptation- This is an increase in the sensitivity of the eye to light in low light conditions. During dark adaptation, the rod apparatus of the retina functions.
At brightnesses from 10-3 to 1 cd/m2, rods and cones work together. This is the so called twilight vision.
Color adaptation involves a change in color characteristics under the influence of chromatic adaptation. This term refers to a decrease in the sensitivity of the eye to color when observing it for a more or less long time.
4.3. Patterns of color induction
Color induction is a change in the characteristics of a color under the influence of observing another color, or, more simply, the mutual influence of colors. Color induction is the desire of the eye for unity and integrity, for the closure of the color circle, which in turn serves as a sure sign of a person’s desire to merge with the world in all its integrity.
At negative Induction, the characteristics of two mutually inducing colors change in the opposite direction.
At positive Induction, the characteristics of colors come closer together, they are “trimmed” and leveled.
Simultaneous induction is observed in any color composition when comparing different color spots.
Consistent induction can be observed in a simple experiment. If you put a colored square (20x20 mm) on a white background and fix your gaze on it for half a minute, then on the white background we will see a color contrasting with the color of the coloring (square).
Chromatic induction is a change in the color of any spot on a chromatic background in comparison with the color of the same spot on a white background.
Luminance induction. With a large contrast in brightness, the phenomenon of chromatic induction is significantly weakened. The smaller the difference in brightness between two colors, the more the perception of these colors is affected by their hue.
Basic patterns of negative color induction.
The degree of induction staining is influenced by the following: factors.
Distance between spots. The smaller the distance between the spots, the greater the contrast. This explains the phenomenon of edge contrast - an apparent change in color towards the edge of the spot.
Contour clarity. A sharp outline increases luminance contrast and reduces chromatic contrast.
The ratio of brightness of color spots. The closer the brightness values of the spots, the stronger the chromatic induction. Conversely, an increase in luminance contrast leads to a decrease in chromatic contrast.
Spot area ratio. The larger the area of one spot relative to the area of the other, the stronger its inductive effect.
Saturation of the spot. The saturation of a spot is proportional to its inductive effect.
Observation time. When the spots are fixed for a long time, the contrast decreases and may even disappear completely. Induction is best perceived with a quick glance.
The area of the retina that detects color spots. The peripheral areas of the retina are more sensitive to induction than the central one. Therefore, color relationships are more accurately assessed if you look slightly away from the place of their contact.
In practice, the problem often arises weakening or eliminating induction staining. This can be achieved in the following ways:
by mixing the background color into the spot color;
outlining the spot with a clear dark outline;
generalizing the silhouette of spots, reducing their perimeter;
mutual removal of stains in space.
Negative induction can be caused by the following reasons:
local adaptation– a decrease in the sensitivity of the retinal area to the fixed color, as a result of which the color that is observed after the first one seems to lose the ability to intensely excite the corresponding center;
autoinduction, i.e., the ability of the organ of vision, in response to irritation by any color, to produce the opposite color.
Color induction is the cause of many phenomena united by the general term “contrasts”. In scientific terminology, contrast generally means any difference, but at the same time the concept of measure is introduced. Contrast and induction are not the same thing, since contrast is a measure of induction.
Luminance Contrast characterized by the ratio of the difference in brightness of spots to greater brightness. Brightness contrast can be high, medium or low.
Saturation Contrast characterized by the ratio of the difference in saturation values to greater saturation . The contrast in paint saturation can be large, medium or small.
Contrast in color tone characterized by the size of the interval between colors in a 10-step circle. The contrast in color tone can be large, medium or small.
Big contrast:
high contrast in color tone with medium and high contrast in saturation and brightness;
medium contrast in hue with high contrast in saturation or brightness.
Medium Contrast:
average contrast in hue with average contrast in saturation or brightness;
low contrast in hue with high contrast in saturation or brightness.
Small contrast:
low contrast in color tone with medium and low contrast in saturation or brightness;
medium contrast in hue with low contrast in saturation or brightness;
high contrast in color tone with low contrast in saturation and brightness.
Polar contrast (diametrical) is formed when differences reach their extreme manifestations. Our senses function only through comparisons.
The sensitivity of the receptor cells of the eye is not constant, but depends on the illumination and the previous stimulus. Thus, after exposure to intense light, sensitivity sharply decreases, and in the dark it increases. The process of adaptation of vision is associated with the gradual “appearance” of objects when moving from a well-lit room to a dark one and, on the contrary, too bright light when returning to a lighted room. Vision adapts to light faster - within a few minutes. And dark adaptation occurs only after a few tens of minutes. This difference is partly explained by the fact that the sensitivity of the “daytime” cones changes faster (from 40 s to several minutes) than the “evening” rods (completely ends only after 40-50 minutes). At the same time, the rod system becomes much more sensitive than the cone system: in absolute darkness, the threshold of visual sensitivity reaches a level of 1-4 photons per second per photoreceptor. Under scotopic conditions, light stimuli are better distinguished not by the central fovea, but by the part surrounding it, where the density of rods is greatest. By the way, the difference in the speed of adaptation is quite understandable, since in natural nature the illumination decreases quite slowly after sunset.
The mechanisms of adaptation to changing illumination begin with the receptor and optical apparatus of the eye. The latter is associated with the reaction of the pupil: narrowing in the light and dilating in the dark. This mechanism is activated by the ANS. As a result, the number of receptors on which light rays fall changes: connecting rods in the twilight worsens visual acuity and slows down the time of dark adaptation.
In the receptor cells themselves, the processes of decreasing and increasing sensitivity are caused, on the one hand, by a change in the balance between the decaying and synthesized pigment (a certain role in this process belongs to pigment cells that supply the rods with vitamin A). On the other hand, with the participation of neural mechanisms, the sizes of receptor fields and switching from the cone to rod system are also regulated.
The involvement of receptor cells in the adaptation process can be easily verified by examining Fig. 6.30. If you first fix your eye on the right half of the picture and then move it to the left, then within a few seconds you will be able to see the negative of the right picture. Those areas of the retina that received rays from dark places become more sensitive than neighboring ones. This phenomenon is called in a consistent manner.
Rice. 6.30. A drawing that allows you to determine the gradual decomposition of the visual pigment: after looking at the black cross for 20-30 seconds, move your gaze to the nearby white field, where you can see a lighter cross.
A consistent image can also be colored. So, if you look at a colored object for a few seconds and then look at a white wall, you can see the same object, but painted in additional colors. Apparently, this is due to the fact that white color contains a complex of light rays of different wavelengths. And when the eye is exposed to rays of the same wavelength, even earlier, the sensitivity of the corresponding cones is reduced, and this color is, as it were, isolated from white.
The perception of color changes noticeably depending on external conditions. The same color is perceived differently in sunlight and in candlelight. However human vision adapts to the light source, which makes it possible to identify the light as the same in both cases - it happens color adaptation . With dark glasses, at first everything seems to be colored the color of the glasses, but this effect disappears after a while. Similar to taste, smell, hearing and other senses, the perception of color is also individual. People even differ from each other in their sensitivity to the range of visible light.
Adaptation of the eye to changing lighting conditions is called adaptation. There are dark and light adaptation.
Dark adaptation occurs during the transition from high to low brightnesses. If the eye initially dealt with high brightness, then the cones worked, the rhodopsin in the rods faded, and the black pigment penetrated the retina, shielding the cones from light. If the brightness of visible surfaces suddenly decreases significantly, the pupil opening will first open wider, allowing more light to enter the eye. Then the black pigment will begin to leave the retina, rhodopsin will be restored, and only when there is enough of it, the rods will begin to function. Since cones are not at all sensitive to very weak brightness, at first the eye will not distinguish anything, and only gradually a new mechanism of vision comes into play. Only through 50-60 min Being in the dark, the sensitivity of the eye reaches its maximum value.
Light adaptation - this is the process of adaptation of the eye during the transition from low brightness to high brightness. In this case, the opposite series of phenomena occurs: the irritation of the rods due to the rapid decomposition of rhodopsin is extremely strong (they are “blind”), moreover, the cones, which are not yet protected by grains of black pigment, are irritated too much. Only after sufficient time has passed does the adaptation of the eye to new conditions end, the unpleasant feeling of blindness ceases and the eye acquires the full development of all visual functions. Light adaptation continues 8-10 min.
When lighting changes, the pupil can change in diameter from 2 before 8 mm, while its area and, accordingly, the luminous flux change in 16 times. The pupil contracts during 5 sec, and its full expansion is for 5 minutes.
So, adaptation is ensured by three phenomena:
· change in the diameter of the pupil opening;
· movement of black pigment in the layers of the retina;
· different reactions of rods and cones.
Optical illusions
Optical (visual ) illusions – these are typical cases of discrepancy between visual perception and the real properties of observed objects. These illusions are characteristic of normal vision, and therefore differ from hallucinations. In total, more than a hundred optical illusions are known, but there is no generally accepted classification of them, as well as convincing explanations for most illusions.
A ) When looking at stationary objects There are the following mechanisms for the emergence of illusions:
1) imperfection of the eye as an optical instrument -
· apparent radiant structure small bright sources;
· chromaticism lens (iridescent edges of objects), etc.
2) features of visual information processing at different stages of visual perception (in the eye, in the brain) –
· at the stage signal extraction a perceptual error arises from the background" optical illusion"(the use of protective coloring for camouflage in the animal world is based on optical illusion);
· at the next stage signal classification errors occur
- identifying figures(rice. A),
- estimating object parameters(brightness, shape, relative position, Fig. b);
· at the stage visual information processing errors occur
IN assessing the characteristics of objects such as areas, angles, color, lengths (for example, " arrows Muller - Liera , rice. A), i.e. geometric illusions,
- perspective distortion(rice. b),
- irradiation illusion, i.e. an apparent increase in the size of light objects compared to dark ones (Fig. V).
B ) At object movement the process of visual perception becomes more complicated and can lead to inadequate perception, so illusions can be combined into a group dynamic :
· if you observe a moving object for a long time and instantly stop observing, then the object seems moving in the opposite direction, or " waterfall effect ", open Aristotle(if you look at the waterfall and close your eyes, the stream “rises up”),
· if you look at a time-modulated flow of white light, then sense of color , For example, when rotating Benham disk , having black and white sectors,
· inertia of vision (i.e. the property of the eye to retain a visual impression of about 0.1 s) leads to all kinds stroboscopic effect and observation trace from a moving luminous source (the inertia of vision is the basis of cinema and television).
Vision hygiene
Vision - a physiological process that allows one to obtain an idea of the size, shape and color of objects, their relative position and the distance between them. Vision is possible only with normal functioning of the visual analyzer as a whole.
According to the teachings of I.P. Pavlov, the visual analyzer includes a peripheral paired organ of vision - the eye with its light-perceiving photoreceptors - rods and cones of the retina (Fig.), optic nerves, visual pathways, subcortical and cortical visual centers. The normal irritant of the rhenium organ is light. The rods and cones of the retina perceive light vibrations and convert their energy into nervous stimulation, which is transmitted through the optic nerve along the pathways to the visual center of the brain, where visual sensation occurs.
Under the influence of light, visual pigments (rhodopsin and iodopsin) disintegrate in rods and cones. The rods function in low-intensity light, at dusk; the visual sensations obtained in this case are colorless. Cones function during the day and in bright light: their function determines the sensation of color. When transitioning from daylight to twilight, the maximum light sensitivity in the spectrum moves towards its short-wavelength part and red objects (poppy) appear black, blue objects (cornflower) appear very light (Purkinje phenomenon).
The human visual analyzer under normal conditions provides binocular vision, that is, vision with two eyes with a single visual perception. The main reflex mechanism of binocular vision is the image fusion reflex - the fusion reflex (fusion), which occurs with simultaneous stimulation of functionally unequal neural elements of the retina of both eyes. As a result, physiological double vision occurs of objects located closer or further than the fixed point. Physiological double vision helps to assess the distance of an object from the eyes and creates a feeling of relief, or stereoscopic vision.
When seeing with one eye (monocular vision), stereoscopic vision is impossible and depth perception is carried out by Ch. arr. thanks to secondary auxiliary signs of distance (apparent size of an object, linear and aerial perspective, blocking of some objects by others, accommodation of the eye, etc.).
In order for the visual function to be carried out for a sufficiently long time without fatigue, it is necessary to observe a number of hygienic conditions that facilitate 3. These conditions are combined into the concept<гигиена-зрения>. These include: good uniform illumination of the workplace with natural or artificial light, limitation of glare, sharp shadows, correct position of the body and head while working (without bending too much over a book), sufficient distance of the object from the eyes (on average 30-35 cm), short breaks every 40-45 minutes. work.
Natural daylight is considered the best lighting. In this case, you should avoid illuminating your eyes with direct sunlight, as they have a blinding effect. Artificial lighting is created using lamps with conventional electric or fluorescent lamps. To eliminate and limit the glare of light sources and reflective surfaces, the height of the suspension of lamps must be at least 2.8 m from the floor. Good lighting is especially important in school classrooms. Artificial illumination on desks and blackboards should be at least 150 lux [lux (lx) - unit of illumination] when illuminated by incandescent lamps and at least 300 lux when using fluorescent lighting. It is necessary to create sufficient illumination of the workplace at home: during the day you should work near the window, and in the evening with a 60 W table lamp covered with a lampshade. The lamp is placed to the left of the subject of work. Children with nearsightedness and farsightedness need appropriate glasses.
Various diseases of the eye, optic nerve and central nervous system lead to decreased vision and even blindness. Vision is affected by: impaired transparency of the cornea, lens, vitreous body, pathological changes in the retina, especially in the area of the macula, inflammatory and atrophic processes in the optic nerve, and diseases of the brain. In some cases, decreased vision is associated with occupational eye diseases. These include: cataracts caused by systematic exposure to radiant energy of significant intensity (X-rays, infrared rays); progressive myopia in conditions of constant visual strain during precise fine work; conjunctivitis and keratoconjunctivitis in persons in contact with hydrogen sulfide and dimethyl sulfate. To prevent these diseases, compliance with the rules of public and individual eye protection from harmful factors is of great importance.
Adaptation is the adaptation of the eye to changing lighting conditions. Provided by: changes in the diameter of the pupil opening, movement of black pigment in the layers of the retina, different reactions of rods and cones. The pupil can vary in diameter from 2 to 8 mm, while its area and, accordingly, the luminous flux change by 16 times. The pupil contracts in 5 seconds, and its full dilation occurs in 5 minutes.
Color adaptation
The perception of color can change depending on external lighting conditions, but human vision adapts to the light source. This allows the lights to be identified as the same. Different people have different eye sensitivity to each of the three colors.
Dark adaptation
Occurs during the transition from high to low brightnesses. If bright light initially entered the eye, the rods were blinded, the rhodopsin faded, and the black pigment penetrated the retina, blocking the cones from the light. If suddenly the brightness of the light decreases significantly, the pupil will first dilate. Then the black pigment will begin to leave the retina, rhodopsin will be restored, and when there is enough of it, the rods will begin to function. Since cones are not sensitive to low brightness, at first the eye will not distinguish anything until a new vision mechanism takes effect. The sensitivity of the eye reaches its maximum value after 50-60 minutes of being in the dark.
Light adaptation
The process of adaptation of the eye during the transition from low to high brightness. In this case, the rods are extremely irritated due to the rapid decomposition of rhodopsin, they are “blind”; and even the cones, not yet protected by grains of black pigment, are too irritated. Only after sufficient time has passed does the adaptation of the eye to new conditions end, the unpleasant feeling of blindness ceases and the eye acquires the full development of all visual functions. Light adaptation lasts 8-10 minutes.
Looking at objects with both eyes. When a person looks at an object with both eyes, he cannot perceive two identical objects. This is due to the fact that images from all objects during binocular vision fall on the corresponding, or identical, areas of the retina, as a result of which in a person’s imagination these two images merge into one
Binocular vision is of great importance in determining the distance to an object and its shape. Estimation of the size of an object is related to the size of its image on the retina and the distance of the object from the eye
Lack of binocular vision often leads to strabismus
Pupillary reflex
The eye's response to light (constriction of the pupil) is a reflex mechanism for limiting the amount of light reaching the retina. Normal pupil width is 1.5 – 8 mm
The degree of room illumination can change the width of the pupil by 30 times. When the pupil narrows, the flow of light decreases, spherical aberration disappears, which gives self-scattering circles on the retina. In low light, the pupil dilates, which improves vision. The pupillary reflex takes part in the adaptation of the eye
Adaptation
Adaptation of the eye to seeing objects in conditions of different intensities of room lighting
Light adaptation. When moving from a dark room to a light one, blinding occurs at first. Gradually, the eye adapts to light by reducing the sensitivity of the photoreceptors of the retina. Lasts 5 – 10 minutes.
Mechanisms of light adaptation:
Reduced sensitivity of photoreceptors to light
Narrowing of the receptor field due to the severing of connections between horizontal cells and bipolar cells
Rhodopsin decay (0.001 sec.)
Constriction of the pupil
Dark adaptation. When moving from a light room to a dark room, a person initially sees nothing. After some time, the sensitivity of the retinal photoreceptors increases, the outlines of objects appear, and then their details begin to be distinguished. lasts 40 – 80 minutes.
Dark adaptation processes:
Increases the sensitivity of photoreceptors to light by 80 times
Rhodopsin resynthesis (0.08 sec.)
Pupil dilation
Increase in the number of connections between rods and retinal neurons
Increase in receptive field area
Rice. 6.11. Dark and light adaptation of the eye
Color vision
The human eye perceives 7 primary colors and 2000 different shades. The mechanism of color perception is explained by different theories
Three-component theory of color perception(Lomonosov-Jung-Helmholtz theory of color perception) - suggests the existence in the retina of three types of photosensitive cones that respond to different lengths of light rays. This creates different color perception options.
the first type of cones reacts to long waves (610 - 950 µm) - sensation Red
the second type of cones - for medium waves (460 - 609 µm) - sensation Green colour
the third type of cones perceives short waves (300 - 459 microns) - sensation of blue color
The perception of other colors is determined by the interaction of these elements. Simultaneous excitation of the first and second types creates the sensation of yellow and orange colors, and the second and third give violet and bluish colors. Equal and simultaneous stimulation of three types of color-perceiving elements of the retina gives the sensation white, and inhibition forms them black color
The decomposition of light-sensitive substances found in cones causes irritation of nerve endings; the excitation that reaches the cerebral cortex is summed up, and a sensation of one uniform color arises
The complete loss of the ability to perceive colors is called anopia, while people see everything only in black and white
Color perception disorder – color blindness (color blindness) - Mostly men suffer - about 10% - lack of a certain gene on the X chromosome
There are 3 types of color vision disorders:
protanopia – lack of sensitivity to red color (have loss of perception of waves with a length of 490 microns)
deuteranopia – to green color (have a loss of perception of waves with a length of 500 microns)
tritanopia – to blue color (loss of perception of waves with a length of 470 and 580 microns)
Complete color blindness - monochromacy rare
Color vision testing is carried out using Rabkin tables
