The information from the external environment, in infinite number, is limited by the sensitivity of our sensory sensors such as those of vision, hearing, olfaction or tactile perception.
This limited information allows our brain to process it quickly in order to send us back a mental image that corresponds to a more or less correct perception of reality. Thus, among all the data captured by our senses, only a part can be processed at the conscious level.
This data filtering is also determined by attention and motivation. When we focus on a specific task (reading, listening, thinking, etc.), other data in the environment that does not concern this task are ignored.
Our eyes, which are a heritage of selection, cannot be mistaken because the light information limited to a precise spectrum is physically real. This information captured by the photoreceptors of our eyes, is only the reflection of photons on objects in our environment. Like a mirror our eyes are faithful to the luminous information which forms a concrete image on the retina. Then this information will trigger chemical reactions on the photoreceptors (cones and rods). Then the message will be transcoded into nerve impulses (transduction) via the bipolar neurons and then the ganglionic neurons.
The axons of these neurons (optic nerve) join the visual cortex located at the back of the occipital lobe of the brain. This is where the visual information (image) disappears completely to be reconstructed into chemical signals (neurotransmitters) of an electrical nature. This information will be processed globally with the other sensory signals to bring out an integrated multisensory representation of the environment. The selection chose this mode of operation so that we can interact effectively with the world around us.
From this window open to the outside, our brain will select, decode, integrate and interpret the characteristic events of the colored three-dimensional scene (visual stimulus).
Thus, what we call "vision" is only a cerebral interpretation of electrical signals dependent on our mental patterns. Indeed, the same image can be interpreted differently by different individuals because they have not had the same experiences at the same times in their lives.
We do not see with our eyes but with our brain!
According to the psychologists of perception, this interpretation goes through several stages (sensory, perceptual and cognitive).
The sensory stage allows us to feel, thanks to our specialized receptor cells, a very large number of light, auditory, odorous and tactile information coming from the environment.
The perceptual stage allows our brain to select part of sensory data such as shapes, colors and movements.
The cognitive stage will assign a coherent meaning to the information. This concept will be created based on our prior knowledge, in other words, our learning. For example, when we look at the thousands of randomly scattered stars in the night sky, we mainly notice those that form asterisms (remarkable figures drawn by stars) that we call constellations (Big Dipper, Aries, Taurus, Gemini, etc.) . Our brain immediately detects geometric shapes (lines, circles, squares, rectangles). These figures will give meaning to our environment because they will help us to locate ourselves in space. Throughout life, the brain learns to see through neurobiological mechanisms (perception, motor skills, language, memory, reasoning, emotion, etc.).
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Image: The "Checker shadow illusion of Adelson" was published by Edward H. Adelson in 1995.
On this chessboard, squares A and B have exactly the same color. This incredible illusion can be checked by clicking on the image.
This illusion of the same color illustrates the cognitive stage well. From a precise image of reality, our brain provides us with a coherent result, corresponding to our knowledge. He interprets the colors, shapes and movements of objects and then modifies or completes the missing elements if necessary to give things a certain coherence. In other words, he wants to see the sensible world as an intelligible world as he conceives it, as he has understood it, as he has been taught. Since birth, seeing is knowledge and our brain is blind until it has learned to see.
Credit: Edward H. Adelson Professor of Vision Science