How is visual information processed in the brain to perceive the outside world?

Our eyes take in external information, such as the color, texture, and size of objects, and transmit it to the brain, where it is processed by the visual nerves, which play an important role in how we perceive and judge the outside world. This process allows us to have a clear picture of our surroundings and react appropriately.

 

Through our eyes, we can obtain extrinsic information about objects that are within the perceptual range of our eyes, such as their color, texture, thickness, and size. By recognizing these objective, external characteristics of the objects around us, we get cues that allow us to make the right judgments and reactions to the situations we are in.
We call this sensation vision, and the sensory organ that receives a set of external information about objects in our field of perception is the eye. Vision is by far the most primary and instinctive of the five senses, gathering the information we need to perceive the outside world and make comprehensive judgments about it. We are bombarded with visual information on a daily basis, so let’s take a look at how the brain processes the visual information we receive through our eyes.
A camera is modeled after the human eye, and it has a similar structure to the human eye. When you take a photo, light from a light source and reflected by an object passes through the lens of the camera, refracted, and captured on film in a dark box inside the camera. The lens of the camera is the lens of our eye, and the choroid and retina correspond to the dark box and film inside the camera, respectively. The thickness of the lens is controlled by the contraction and relaxation of a muscle called the ciliary body, which determines how much light is refracted depending on the distance, and the refracted light is deposited on the retina. The refracted light passes through the lens and is projected onto a film called the retina.

 

 

So how does this projected image get to the brain? The retina is composed of several layers of cells, and the flow of information travels along the cell layers. Visual information from the retina travels through three layers of cells: photoreceptor cells, dipolar cells, and ganglion cells to the optic nerve. There are two types of photoreceptor cells: rods and cones. Cones perceive light and dark, while rods perceive colors based on three primary colors: red, green, and blue. Many photoreceptor cells cluster together to form a receptive field. This receptive field corresponds one-to-one with each cell in the dipolar cell layer that lies outside the photoreceptor cell layer. The aggregation of photoreceptor cells, called the receptive field, is circular and divided into two zones: a center and a periphery. Whether a dipolar cell is active or not depends on which photoreceptor cell in which zone generates the action potential. The bipolar cells, each with its own receptive field, are connected horizontally by horizontal cells, which secrete inhibitory neurotransmitters to sharpen the outer image from the receptive field. Outside of the bipolar cells, the last layer of cells in the retina are ganglion cells. Like bipolar cells, ganglion cells have a circular receptive field, with a center and a periphery. Just as bipolar cells have a circular receptive field composed of photoreceptor cells, ganglion cells have a receptive field composed of a bundle of bipolar cells. There are three types of ganglion cells: W cells, X cells, and Y cells. Depending on the type, the receptive field associated with each ganglion cell determines the visual information it receives. X cells receive input from cone cells, which are responsible for determining the color of external objects. Y cells are responsible for focusing the image based on the motion of the object, and have a relatively wider receptive field than X cells. The function of W cells is still unknown, and they are the smallest of the three types of ganglion cells. The amacrine cells that connect the ganglion cells horizontally maintain the ganglion cells’ light sensitivity to changes in background light levels. After passing through these three layers of cells, visual information is transmitted to the brain via the visual nerves.
The brain is a collection of nerve cells. How does the brain process the information we receive through our eyes? The visual nerve is the bridge between the eyes and the brain. The visual nerve is one of the 12 pairs of cranial nerves that extend from the brain and connect to the left and right eyeballs. What’s unique about this nerve is that it’s a cross between the left and right nerves. That’s why the information received by each eye is transmitted to the brain in the opposite direction. The crossed visual information stays in the thalamus. The thalamus is called the control tower of the senses because it’s where all sensations, except smell, pass through before being sent to the cerebrum and then to the cortex of that sense. Each sense is sent to a separate area of the thalamus, and in the case of vision, it travels through a place called the lateral geniculate nucleus to the primary visual cortex. Like the retina, the lateral geniculate nucleus is made up of several layers of cells, each of which processes different types of visual information. The visual cortex, which is responsible for vision in the brain, crosses the thalamus and receives information from the left and right eyeballs. The primary visual cortex is located in the occipital lobe, which is organized in longitudinal sections. Information from a single ganglion cell is relayed to millions of neurons that make up the visual cortex, which recognizes different combinations of information such as light direction and wavelength, position, and motion. There are seven levels of the visual cortex, and once visual information reaches the primary visual cortex, it travels through different pathways depending on the type of information. For example, color travels through the fourth visual cortex to the temporal lobe, while motion and spatial information travels through the fifth visual cortex to the right parietal lobe. Once the visual information reaches the areas of the brain where it is finally processed, we are able to fully analyze the image on the retina and perceive the unfolding world as if we were watching a scene from a movie.
The physical reality in front of us is transmitted to the brain, where it is converted into electrochemical signals, and we are able to see the world according to these signals. In our daily lives, we take in the scenery around us so naturally, but the world unfolds through a constant process of signaling between our eyes and brain. The information we receive from our eyes passes through hundreds of millions of neurons before we subconsciously recognize it. The sophistication and complexity of this process is one of the true mysteries of the human body.
This process of visual information processing is directly related to our survival. For example, in the wild, visual information enables immediate survival responses in situations such as avoiding predators or finding food. Visual information also plays an important role in modern society. Whether it’s driving a car, communicating with people through facial expressions and body language, or navigating a new environment, we constantly use visual information to make decisions and adjust our behavior. This shows that the ability to process and interpret visual information is an important component of human intelligence and adaptability.
Furthermore, advances in modern technology have enabled new visual experiences such as virtual reality and augmented reality. These technologies utilize our ability to process visual information, blurring the boundaries between the real and the virtual, and providing new forms of learning, entertainment, and therapy. In the future, visual information processing technologies will be further developed to improve our quality of life.
Therefore, the collection and processing of visual information is not just a physiological process, but an important mechanism for expanding human experience and knowledge. Understanding and utilizing these processes is essential not only for personal growth, but also for the development of society as a whole. Visual information allows us to make better decisions, gain deeper understanding, and have richer experiences.