There are many kinds of human feelings, such as touch, taste and smell. We can feel an object by touching its shape, tasting its taste and smelling its smell. Vision is an extremely complex and important feeling, and more than 80% of the external information people feel comes from vision.
The formation of vision needs a complete vision analyzer, including eyeball and occipital lobe of cerebral cortex, and the visual pathway system between them. Due to the characteristics of light, human eyes will have quite complex reactions to the stimulation of light, and light has many functions. When people look at things, the image of the object passes through the pupil and lens and falls on the retina. Stimulated by light, the optic nerve cells in the retina convert light signals into bioelectric signals, which are transmitted to the brain through the nervous system, and then form vision according to extremely complicated processes such as human experience, memory, analysis, judgment and recognition, and form concepts such as the shape and color of objects in the brain.
Human eyes can not only distinguish the shape, brightness and color of objects, but also produce more visual functions (eye muscle activity, etc.) with the cooperation of visual analyzer and motion analyzer. ). At the same time, each function influences and complements each other in time and space, making the vision more exquisite and perfect. Therefore, vision is a multifunctional name, and what we often say is only one of its contents. The generalized visual function should be composed of four successive stages: visual perception, quantum absorption, specific space-time composition and the consistency of psychology and nerves.
What is illusion?
Illusion refers to people's incorrect feelings or perceptions of external things. The most common is optical illusion. The reasons for illusion are not only the influence of the characteristics of objective stimulus itself, but also the physiological and psychological reasons of observers. Its mechanism is not fully understood. Physiological reasons are related to the structure and characteristics of our sensory organs; Psychological reasons are related to our living conditions and experiences.
Here are some typical optical illusion diagrams.
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The illusion of vertical and horizontal lines in the diagram (1): The vertical line is overestimated and seems to be longer than the horizontal line.
Figure (2)a, two horizontal lines of equal length, it seems that the upper one is shorter. B, the two arcs are congruent, and it seems that the lower one is wider and shorter.
Figure (3)a, B, and parallel lines are affected by the intersecting lines, which seem to change direction and are uneven.
In Figure (4)a, the two circles in the middle are equal and influenced by the background. B, the two circles are equal in size and look different in size. C the small circles and squares in the big circle seem to be distorted by the background.
In real life, people often perceive and adapt to the objective world in the process of constantly correcting mistakes. The ability to distinguish the characteristics of external stimuli (information) is an important means for us to know the world and acquire knowledge. At the same time, we should constantly correct wrong reflections. This is very important in life, work and study. For example, people who have lost their hearing will become difficult to understand over time, because they can't hear their own voice (language), can't get feedback and correction, and even lead to the loss of language. Therefore, constantly correcting the wrong feedback of the senses can improve our understanding level. External things are diverse and ever-changing, and the relationship between them is complicated. However, people's reflection on external things in their minds only holds external things conditionally and approximately, and their understanding of things has personal limitations. But dialectical materialism holds that objective things are knowable and people's understanding of the objective world is endless. As far as illusion (perception of objective things) is concerned, there are many illusions caused by phenomena based on our physiological basis, except "a cup of bow and a snake shadow", "grass is full of soldiers" and "the wind shakes the flower shadow, and it is suspected that it is a jade person". For example, in our vision, when the image of an object falls on the blind spot of the retina, we will have the illusion of "turning a blind eye". (See the picture above) For another example, when watching a movie, the movements of the characters on the screen are jumping, and the images (pictures) are alternately bright and dark, but in our view, the movements of the characters are continuous, with no changes in light and dark. This takes advantage of the visual retention of the eyes. Movie pictures change at a speed of 24 frames per second, so that "jumping" pictures are regarded as continuous actions (the discontinuity of actions is imperceptible), and at the same time, because the eyes can keep the light effect acting on them for a certain period of time, people see not a series of flashing pictures, but stable pictures.
In addition, we know that in color perception, each color has its corresponding complementary color (if the complementary color is mixed with the color wheel, it will turn gray, only brightness and achromatic color). Red and green are a pair of complementary colors, so are yellow and blue, and other colors have their own complementary colors. Black and white also complement each other. If complementary colors are presented on the same screen at the same time, they will be particularly bright. If the surroundings are full of stimuli of one color, the "neutral space" without stimuli will have the feeling of complementary colors, thus creating the illusion of "making something out of nothing". The most common fact is that the moon (colorless) that appears in the blue sky will appear yellow. Car drivers have this experience when driving at night. Walking on the road of high-pressure mercury lamp lighting (blue-purple light source), their car lights (incandescent lamps) are orange; While walking on the road illuminated by sodium lamp (yellow light source), your car light is blue. This example shows that feelings and perceptions can be changed by background conditions. This difference cannot be regarded as an illusion. The above is the illusion caused by physiological phenomena.
In the picture, due to the influence of light and shade and shadow, we get the perception of protrusion or depression. The bright part of the object in the same picture is at the top and the shadow part is at the bottom. It seems that this object is protruding. Turn this picture upside down and you will have a sense of concavity. This is caused by our long life experience. In life, the light source (sunlight) is always above, which naturally forms the bright part of the above protrusion and the shadow below. Concave things, in turn, are no exception. Therefore, reversing the same picture will get the opposite image perception. Without more reference objects, when one of two objects is moving, we often regard one of them as moving. For example, in Yun Zheyue, the moon can be regarded as moving behind the clouds, and the clouds can also be regarded as moving in front of the moon. For example, in a darkroom, a box with a small square in the center is presented on the curtain facing the subject by slide show. When the square is moved left and right, the subject feels that the square is moving. This is because people's general experience is that moving objects always move in a large static environment, and this connection is quite firm, so this illusion will be produced. We all have this experience. When we are on the train, we always feel that our train is moving when we look at the coming train through the window. This is because when taking a bus, because the running of the bus forms the perception of the movement of foreign objects, this experience is firmly imprinted in the mind, so the movement of the adjacent trains in the train is always considered as the train in which it is located is moving without thinking. However, due to the lack of vibration and propulsion, you will soon realize that your train is not moving forward.
In some cases, the perception we get is not consistent with the facts, because this perception is formed under the influence of specific conditions, not an illusion. If the chopsticks are inserted obliquely into the water cup, it seems that the chopsticks are not straight, and the parts in the water are staggered downwards. This is caused by the refraction phenomenon that the part inserted into water enters a medium different from air. It is normal and reasonable to regard chopsticks as twists and turns. Another example is a mirage, convex mirrors and mirrors on cars. These phantom or deformed images cannot be regarded as hallucinations.
Our understanding of illusion enables us to get rid of it in observation without thinking it is correct. Illusion plays an active role in art, technology and military affairs. For example, moving scenery is used in film production to cause the operation of vehicles, simulation devices for training drivers such as cars, planes and space navigation, various military camouflage, clothes design according to shape, color matching and so on. It has something to do with illusion.
In a word, there are both physiological and psychological reasons for the illusion. We should prevent cognitive errors caused by illusions, but we can also use illusions to serve us.