What part of the brain is responsible for vision?

In this brief guide we are going to answer the question ‘’What part of the brain is responsible for vision?’’, We will explain how the brain processes images, the phases of the vision process and how vision diseases can affect cognition.

What part of the brain is responsible for vision?

The part of the brain responsible for vision is the occipital lobe. 

The brain has always been considered the great unknown and, as such, it has a great power of attraction. An element that never ceases to amaze scientists and seduces society in general.

There are about one million nerve fibers that connect the eye to the brain and more than 20 billion neurons that process visual information at high speed.

The human brain can process entire images that the eye sees for only 13 milliseconds. But how does this process occur?

What are the 4 phases of the vision process?

Although explained in this way it may seem simple, the truth is that the process that produces vision in humans is extremely complex. The visual stimuli collected by the eye have to reach the brain in perfect conditions, where they end up being transformed into images. In other words: the eye sees and the brain interprets what it sees.

This whole process takes place in the form of 4 distinct phases.

Perception

The first phase that explains how vision is produced is perception. In the first stage of the vision process, light enters the eye through a series of transparent organs: cornea, crystalline lens, aqueous humor and vitreous humor.

At this stage, the iris and pupil are responsible for regulating the amount of light entering the eye. If there is a lot of light, the pupil becomes smaller because we do not need more light, but if there is little, it dilates completely to try to capture as much light as possible. At this moment, the lens focuses on the near or distant object to adjust the image so that it is correctly focused on the retina.

Transformation

The second phase of the vision process is the transformation of light into nerve impulses. The image reaches the retina, which acts as a screen, and there the sensory cells are activated, which are fundamental to the vision process since they are the ones that transform light into nerve impulses (electrical impulses).

These light-sensitive cells are the rods and cones: the rods are responsible for peripheral vision and night vision, while the cones allow the human eye to have visual acuity and differentiate colors.

Transmission

The third phase explains how vision is produced in the transmission. That is the process of sending information from the eye to the brain. 

The nerve impulses created in the retina start their journey from the eye through the optic nerve to the brain, which is the organ in charge of interpreting the visual information that reaches it in the form of nerve impulses.

Interpretation

The last phase that explains how vision is produced is that of interpretation, which takes place in the brain. The brain is responsible for recognizing, processing and interpreting the impulses conducted by the optic nerve, converting them into images that make sense to us.

Specifically, this phenomenon occurs in an area of the brain called the lateral geniculate body, which is located in the occipital lobe. 

It should be noted that, as in traditional photographic cameras, the image formed on the retina is inverted, but we do not realize it thanks to the interpretative work of the brain, which is responsible for “turning it around” so that we can see it correctly.

Keys to understanding vision III: the brain

The process of vision consists of several parts, of which what we understand as seeing – that the eye captures the light reflected by objects – is only the beginning. Once this phase of perception is completed, the signal that is carried by the nervous system has to be decoded again.

The protagonist of this final part of the process responsible for vision is the brain, the real center of operations of our organism. The visual cortex is the cerebral area in charge of decoding perception and converting it into vision. These clues will help you to better understand what is going on inside the brain.

As we said before, vision does not end in the eye. In fact, the most complex part of the whole process begins precisely after the eye. At that moment, the image that has been captured by the retina is divided into fragments that follow different paths to the visual cortex.

Recent discoveries in the field of physiology have allowed us to know almost step by step how processing takes place. Once divided, the information is transferred simultaneously to several systems that divide up the processing of the different parts into which the image is decomposed.

John J. Ratey, a psychiatrist and professor at Harvard University, explains it very well in his book A user’s guide to the brain: “Information goes mainly along two separate routes: the HOW route of the parietal lobe and the WHAT route of the temporal lobe. Vision, like most brain functions, is partitioned – that is, to process it, it is sent to several brain regions; that fragmented information is somehow grouped back together and we SEE.”

Thus, it is different systems that are responsible for processing information about shape, color, movement and spatial organization (including location and distance), which together make up an image.

Each system is specialized and functions relatively independently of the others. This explains why some blind people cannot see colors, but can see movements, or why others show difficulties exclusively in the perception of the latter.

An organ in permanent evolution

In principle, the brain houses specific functions in each of its parts, and the processing of information perceived through the eye is located in the visual cortex, which in turn is located in the occipital cortex, i.e. at the back.

The brain, however, is an organ with a fascinating capacity for adaptation, and evidence has been found that the brain areas in which the functions of one sense organ develop can reinforce the functions of some other organ if the one that corresponds to them in principle suffers some damage or alteration.

This has been verified by means of studies carried out with positron magnetic resonance techniques, which show the brain areas that are functioning at any given moment. Thus we know, among other things, that when blind people read Braille, not only the areas normally associated with touch are activated in their brains, but also an extensive area linked to sight.

The brain and vision problems

As we can see, the functionality of vision and the functioning of the brain are interconnected. For this reason, some cognitive problems suffered by certain people can be treated if measures are taken to modify perception through the eyes.

For example, until recently it was not known that vision was related to the phenomenon of dyslexia, which affects many children. We now know that in some – but not all – of these cases, the difficulty in reading or writing can be solved with ophthalmological treatment or simply by using color-filtered glasses.

On the other hand, John J. Ratey, in the aforementioned book, tells us about the case of Rolf, a dyslexic psychotherapist who discovered that he felt especially comfortable wearing glasses with a yellow filter and began to wear them for everything. 

In fact, some people with dyslexia have trouble reading because they can’t anchor their eyes on the line and feel the letters move. With the different colored filters in Irlen glasses, it is possible to fix the gaze. Rolf succeeded with the yellow color.

Cases like these demonstrate that, although the eye is not solely responsible for what we see, it does have a very important involvement in vision. Understanding its use and its relationship with the brain in this exciting process allows ophthalmologists to find solutions to problems not necessarily linked to the functions of the eye.

Conclusion

There is an important number of diseases, either congenital or hereditary, as well as several refractive defects that prevent or hinder the perfect functioning of the vision process of the eye. Fortunately, most of them can be solved with optical means (glasses or contact lenses) or surgical procedures, such as refractive surgery.

In this sense, if you notice discomfort or difficulties in seeing correctly, the best advice you can follow is to go to the ophthalmologist for a check-up. In this way, any ocular problem can be diagnosed or ruled out and, if it is advisable, the most appropriate medical treatment can be started in each case.

References

Kandel RE, Schwarts J, Jessell TM. Principles of neural science. 3 ed. New York: Elsevier Science Publishing; 1991. Chapter 28. Phototransduction and information processing in the retina.

Lamme AFV, Roelfsema PR. The distinct modes of vision offered by feedforward and recurrent processing. Trends Neurosci. 2000;23:571-9.

Supèr H. Figure-ground activity in V1 and guidance of saccadic eye movements. J. Physiol. 2006;100:63-9. Supèr H. Working memory in the primary visual cortex. Arch. Neurol. 2003;60:809-12.

Potter, M.C., Wyble, B., Hagmann, C.E., & McCourt, E.S. (2014). Detecting meaning in RSVP at 13 ms per picture. Attention, Perception, and Psychophysics