Explain what an illusion is and its application in life.

The brain analyzes the object information received by the eyes and analyzes four main types of data; namely, the space, color, properties and dynamics of the object. With this information, we can identify foreign objects and respond promptly and appropriately. When there is light, human eyes can distinguish the brightness and darkness of the object itself. With the contrast between light and dark in an object, the eyes can create visual spatial depth and see the three-dimensionality of the object. At the same time, the eyes can distinguish shapes, helping us to identify the form of objects. In addition, the human eye can see colors, which is called color or color vision. These four visual abilities are used in an integrated manner and serve as the source for us to explore and identify external data and establish visual perception. The position of objects In addition to identifying the characteristics of objects, the eyes also need to know the position of objects and changes in their movements, so that they can drive other parts of the body to make corresponding movements. In understanding the distance or depth between oneself and the outside world, human perception can extract hints about space from the data obtained from the field of vision, thereby knowing the distance between oneself and various objects. The retina is the core of vision. It is a flat film, and the object image obtained is flat and lacks a three-dimensional sense. Therefore, perception needs to organize other information to achieve deep perception. Human eyeballs are gifted with the instinct to distinguish three-dimensional depth and distance, because humans look at each other with their eyes. At the same time, we can recognize the distance between the object and us through the size of the image formed by the external object in the business scope, as well as the state of arrangement or expression. Information about distance can even be obtained through shape and color. Structure of the Eyeball (Anatomy of Human Eye) Vision refers to the visual organ, the eye (or eyeball), which receives and aggregates light to obtain the image of the object, and then transmits the received information back to the brain for analysis as a thought and reflection of action. To perceive changes in the external environment, we must rely on the cooperation of our eyes and brain to obtain information from the outside world. The receptor of the human visual system is the eyeball. The operation of the eyeball is like a camera, and the process can be divided into two parts: light gathering and light sensing. The optical structure of the eyeball is completely wrapped in a layer of film (Selear). This film is like the black box of the camera and is divided into two sections: front and back. The anterior segment of the eyeball is the part where light is collected and is composed of the cornea, pupil, lens and vitreous body. Their function is to adjust and aggregate the incident light from the outside. Light first passes through the cornea, a transparent membrane, and passes through the pupil and crystalline lens, where it bends and converges at the back of the eyeball. The pupil is an opening that can transmit light and can adjust the size of its circumference in response to the intensity of light. When in darkness, the diameter of the pupil expands to allow in more light. When there is sufficient light, the diameter of the pupil will shrink so that the amount of light entering the eye is not too strong. With the cooperation of the pupil and the lens, the eyeball can receive different light sources, strong, weak, far and near. There are ciliary muscles (Ciliary Muscles) in the eyeball. Its stretching effect can deform the crystalline lens, thus adjusting the diopter so that light can be focused on the retina to form an image. When light comes from close objects, the crystal becomes more rounded and has a larger diopter. When light comes from farther away objects, the lens becomes flatter and has less diopter power. To ensure that the light level entering the eyeball can form the highest quality image under different illuminances. Image Perception The back part of the eye is the light-sensitive part. The posterior segment contains the retina, which is composed of two types of photoreceptor cells. These two types of cells are called rod cells and cone cells because of their shape. Their function is to focus the light produced by the crystal. It becomes an electrical signal and is sent to the brain by the nerve cells. The light from the outside is converted into electrical signals by nerve cells in the eyeball, and then transmitted to the brain. After the brain receives electrical signals, it will trigger a series of thinking activities and make appropriate actions or reactions. The nerves on the retina converge and connect to a point in the brain. Since there are no light receptors, the brain cannot perceive the image focused there, hence the name blind spot. The relationship between the retina, yellow spots, and blind spots. The principle of color vision (Colour Vision). There are three different cone cells in the eye, which are sensitive to red, green, and blue wavelengths of light. When light waves of different wavelengths enter the eye and are projected on the retina, At this time, the brain perceives the color of the scene by analyzing the information input by each cone cell. Color Sensitivity Normal human eyes can distinguish about seven million different colors. Different areas of the human eye have different sensitivities to color. The center of the eye is very sensitive to color and movement, but the color sensitivity of the edges of the eye is poor. Among different colors, people are more sensitive to red, green and yellow than blue. This characteristic has a great impact on visual communication. Many graphical interfaces use blue as the background color so that the eye can focus on the more eye-catching foreground. When blue is juxtaposed with other colors in a design, such as the French national chess game, the area of ??blue is often slightly enlarged so that it appears to be the same size as the other colors. Light source: Our perception of the color of an object comes from reflections on the surface of the object. The light from the light source, so the object itself and the light source are equally important to our perception. If the light source lacks certain wavelength components, the color of the object we see will also lack the corresponding color.

In order to emphasize the red color of fresh meat, meat vendors will install special-colored fluorescent tubes on the meat cabinets and often use red backgrounds in the display space. The human eye has a very high ability to distinguish two adjacent vertically similar colors. In the light color range, the sensitivity of the naked eye is especially better than that of instruments. Another characteristic of human color perception is its adaptability to color shift. This property allows us to reduce the effects of color shifts of the light source. Visual illusions You can easily be fooled by your visual system. We often think that we can see everything in our field of vision with equal clarity, but if our eyes remain still for a short period of time, we will find out that this is wrong. Only when you are close to the center of your gaze can you see the details of an object. The further you deviate from the center of vision, the worse your ability to distinguish details. When you reach the outermost periphery of your field of vision, it is even difficult to distinguish objects. The reason why this is not obvious in daily life is because it is easy for us to keep moving our eyes, giving us the illusion that objects everywhere are equally clear. In addition, there are many patterns that can create optical illusions for the eyes, such as the Kanisha triangle, which creates an "illusion contour" for the eyes. Any kind of visual information our eyes provide us is often ambiguous, providing insufficient information on its own to allow us to give a definitive interpretation of objects in the real world. In fact, there are often several plausible alternative explanations. But it is worth noting that there can only be one explanation at a time, and there will not be a strange situation where several explanations are mixed. Different interpretations of visual images are examples of what is known in mathematics as "ill-posed problems." There are multiple possible solutions to any ill-posed problem, and they are all equally reasonable without any additional information. In order to get a true solution, you need to use what are called "constraints" in mathematics. The visual system must develop inherent assumptions about how best to interpret the input information. The reason why there is no uncertainty when we usually see things is because the brain combines the information provided by many salient features of the visual scene, such as shape, color, movement, etc., and makes a proposal after comprehensively considering all these different visual clues. the most reasonable explanation. Seeing is a construction process. The brain does not passively record the visual information entering the eyes, but actively seeks to interpret this information. A prominent example is the "filling" process, such as the filling phenomenon associated with blind spots. Blind spots occur because the optic nerve fibers that connect the eye to the brain need to leave the eye at a certain point, so there are no photoreceptors in a small area of ??the retina. But despite the blind spots, there are no obvious holes in our field of vision. This shows that the brain is trying to fill in what should be in the blind spot with accurate guesses. As the saying goes, "Seeing is believing." According to common understanding, it means that when you see something, you should believe that it actually exists. However, Crick gave a completely different explanation: What you see does not necessarily exist, but your brain thinks it exists. In many cases, it does correspond to the properties of the visual world, but in other cases, blind "belief" can lead to errors. Seeing is an active construction process, and your brain can make the best interpretation based on previous experience and the limited and vague information provided by your eyes. The reason why psychologists are keen on studying optical illusions is because some functional defects in the visual system can provide some useful clues to how the system is organized. For many people, it is difficult to accept that what we see is only a symbolic interpretation of the world.