How does a person see?
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Human sight is a very complex multi-levelprocess of image processing of surrounding objects, giving the chance to receive the information on their form, size, color and an arrangement. Vision should be viewed from the point of view of optics, physiology and psychology. Therefore, in a nutshell to explain how a person sees, it is hardly possible. Let us consider this process in detail.
Optical nature of human sight
The main optical organs of the visual systemhuman being are the eyes that the photoreceptors in them perceive rays of light reflected from various objects. This happens in the following way: getting into the eye through the pupil, the rays are refracted in the lens and fall on the retina, which lined the fundus. It is in the retina that there are special cells that are capable of perceiving light. Getting to them, light photons cause a number of chemical changes in the receptors, thereby creating nerve impulses that are transmitted to the brain through the optic nerves. In the visual center, which is located in the cerebral cortex, the received encoded information is deciphered, processed, as a result of this process, and the image that we see is formed.
As the person sees: the physiological point of view
- The lens is located opposite the pupil insideeyeball and is a small biconvex biological lens in which the rays of light are refracted. In a healthy person, the lens is very elastic and can change its refractive power by as much as 14 diopters. This allows a person to equally clearly see those items that are literally under his nose, and those that are removed a long distance. The minimum distance at which we can well consider an object is approximately equal to five centimeters, and the maximum is strongly dependent on the amount of light emitted by the object. Scientists say that the figure of a person can be discerned at a distance of three kilometers, and the flame of a burning candle can be seen as much as seven kilometers. Sometimes it happens that the lens loses its ability to accommodation and can not properly focus the image on the retina of the eye. If the image focus is behind the retina, the person is diagnosed with hyperopia, and if the near-retina is short-sightedness. Now these defects are easily corrected with the help of glasses or contact lenses.
- The retina covers approximately 70% of the totalthe area of the inner surface of the eyeball. It is in it are all the light-sensitive cells, divided into cones and rods. The rods are responsible for the operation of the night vision mechanism. With the help of them, a person can see in the half-darkness, but the image that they provide is devoid of color and resembles a picture on the screen of a black and white TV. The cones are active with more intensive lighting and are responsible for day vision, which allows us to see the color of all objects .;
How a person sees the world in color
There are three kinds of cones in the retina -receptors of color, as sensitive as possible to the red, blue and green portions of the spectrum, respectively. The correspondence of cones to these three basic colors provides a person the ability to recognize thousands of different shades of color. If, however, in the retina, due to a lack of a certain type of rods, a problem arises with the perception of one of the base colors, a person has a lack of vision called color blindness. He does not see a certain group of shades, and they all seem to him gray. Now, when we told about how a person sees, it's time to talk about the basic properties of his vision.
Basic properties of human sight
In addition to color, a person is also able to see the volumespace. This is achieved through the effect of merging the image when looking at the subject with two eyes. Such vision is scientifically called binocular.
The ability of the human eye to recognizedifferent degrees of brightness of light radiation are called light sensations. The maximum sensitivity of the eye to light is achieved after a long adaptation to darkness. It is believed that a long look at the red light can increase the light sensitivity of the eyes for a while.
The ability of different people to see a differentthe number of parts of the same object from the same distance is called visual acuity. Visual acuity is mainly determined genetically and depends on the person's age, the width of his pupil, the elasticity of the lens and the number and size of the cones located in the retina of the eye.