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Biology 202, Spring 2005
Second Web Papers
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Seeing With Our Brains


Amanda Davis

It's become clear to me that humans' primary sight organ is our brain. Our retina receives light being reflected from the world around us and transmits information to the brain, but it's up to the brain to interpret that information so we can see. Different parts of the brain see different aspects of the world. There is no "one picture" in the brain. Different kinds of blindness illustrate this. A person with color blindness, which is not due to retinal damage, may have damage to one area of the brain and a person with face blindness would have damage to a different area of the brain. To understand how these different types of blindness affect one's world, one must understand how the brain acts as a sight organ. Additionally, knowing how to see is not innate, one must learn how to decipher the visual world.

How could a man who has seen color all his life suddenly lose all color vision if there was no damage to his retinas? A man named Jonathon I. became achromatically sighted at the age of sixty-five (1). Mr. I. still had all of his cones and they were still transmitting signals to his brain (1). Why then, did he not perceive color? It is because he suffered brain damage (1). He was in a car accident, but it was not clear whether the accident had caused the damage or a minor stroke had caused the damage and the accident (1). An area of Mr. I's brain known as V4 had been damaged (1). The V4 area receives signals from another area termed V1 which responds to wavelength, but not to color (1). Mr. I. could indeed discriminate wavelength he was shown a color in white light, and then filtered through short-, medium-, and long-wavelength light (1). What he could not discriminate in the white light, he could when it was filtered through different wavelength light (1). But because of the damage, his brain could not translate those signals into color (1). He reported his world as being distorted, even dirty (1). It was not like a color television, which he actually found pleasant (1). This is because he was receiving the information from his cones, which is relayed to V1, then to V4 (1). But Mr. I. was receiving the raw data from V1, which could be described as a "prechromatic sensation" (1). Mr. I. was a painter, and for about a year after the accident, he reported that he still "knew" which colors were right and what was beautiful (1). But after that he became unsure, he had less of a concern with color, and he no longer mourned its loss (1). This is probably because without the input, he forgot color all together; he no longer understood it (1).

Mr. I's experience shows that color is created by the brain. Wavelength is a part of reality, color is not. To think that my brain, as I look outside and see all the colors of the world is almost instantaneously interpreting the wavelengths being reflected from all objects as color is a completely new idea. I had previously known that in the dark I see in shades of grey, but I had thought that I just could not see the true color of objects in darkened environments. For example, if I was in my kitchen without the lights on at night and looked at an apple, I knew it was red even though it looked grey. I thought I knew that in reality it was really red; I just could not perceive its redness in the dark. Now I know that the wavelength the apple reflects in the darkened room changes, thus its "true" color also changes, and my perception of its color also changes.

Far different from colorblindness, there is face-blindness, in which the face is unrecognizable. Recognizing people by their faces is something I imagine most people take for granted, I certainly do. The face does not stand out as a separate unit from the body as normally sighted individuals see it. I was surprised to learn that visual information of faces is sent to the left temporal lobe, while the visual patterns of the rest of the human body are sent to the right side of the brain (2). These messages are split and sent to the different parts of the brain by a "traffic cop" of sorts (2). All incoming sensory goes through the thalamus, so that is the "traffic cop." If the thalamus could send the "face signals" to the same area on the right side of the brain where the rest of the visual patterns for a human go, a face-blind person could be "cured" somewhat (2). The only problem with this is that faces would be as important as hands, shoulders or arms to recognition (2). A face-blind person would, however be able to "see" faces (2). There are several sources of face-blindness (2). One can be born face-blind, or face-blindness can come from damage to the area of the brain that recognizes faces (2). Those born face-blind develop other ways to recognize those around them (2). They learn to recognize people they've seen many times by other visual signals (2). Those who become face-blind cannot recognize any faces, even those of people they've seen frequently, like family members (2).

One thing that is not clear on Bill Choisser's face-blind website is how a face-blind person actually sees a face. Understandably, a face-blind individual would not be able to describe how s/he sees faces in terms a normally sighted person would understand because they have different experiences from birth. I imagine, from what Choisser did describe that faces might look something like a blur.

Another type of selective blindness is motion blindness. This is the absence of the ability to see objects move through space (3). The human retina does not actually detect motion (3). The retina of a frog, however, responds only to movement (3). The more basal the animal, the smarter its retina is (3). The brains of humans and other primates take the job of deciphering the visual world (3). Motion is analyzed by a very specific neural pathway in humans (3). A normally sighted individual's brain gives the perception of motion even when there is none (3). An example of this is a movie, which is a series of still images strung together very quickly so our brain "sees" movement (3). A patient in Munich named Gisela Leibold is unable to make the fusion to see movement she sees life in a series of still images (3). A part of the visual cortex, called middle temporal area or V5, is not sensitive to color or form, but to movement (4). V5 is directly connected to V1 and both have a similar structure of cells that detect the direction of movement (4). V5 cells do not respond to form or color, but will detect a moving object more quickly if its background's color contrasts with its own color (5). An object moving in the opposite direction of its background will cause the V5 cells to fire more rapidly, and conversely, if the object is moving in the same direction, they will fire more slowly (5). Thus the V5 cells are very good at detecting movement especially if there is contrast in the surrounding environment of the moving object (5). Monkey's whose brains were being stimulated as if they were seeing "up" movement while they were being shown down movement on a screen simultaneously reported seeing only "up" movement (5). This shows that the brain gives the experience of "seeing," not the eyes.

The reverse of these previous conditions, but possibly not any less disabling, is the regaining of sight after forty-five years of almost-complete blindness. Blinded by a triple illness as a child, Virgil had been diagnosed with retinitis pigmentosa, which causes the retina to deteriorate (1). Virgil had thick cataracts also, which a doctor he met later in life thought might be the primary cause of his blindness (1). Virgil had surgery to have the cataracts removed, and he could see, kind of (1). He did not have retinitis pigmentosa, but he did have patchy areas on his retinas that were not functional, but his overall vision was about 20/80 (1). When the bandages were removed from the eye on which surgery was first performed, he could not make sense of what he saw (1). He saw light, movement and color as a blur (1). He realized what a face must be when he heard his surgeon say "Well?" because he knew voices came from faces (1). I wonder if the way Virgil saw faces initially is how face-blind people see them. Sacks does not write further on Virgil's perception of faces. Virgil could recognize letters because in the school for the blind he attended, they felt the alphabet, and even read words that were raised English letters (1). He translated this tactile knowledge to visual cues (1). From the moment we are born, we learn how to see our visual world and what different visual patterns mean. Virgil had no idea about distances because he had not had experience to learn that smaller objects are usually farther away(1). He found walking without his cane "scary" and "confusing" because he had an uncertain judgment of space and distance (1). He could not discriminate his dog from his cat unless he touched them (1). He saw a nose, or a paw, but could not put the different parts together to see a whole animal (1). Virgil had not had the visual experiences to teach him the basic rules sighted people take for granted for how we decipher the messages our retinas send out brain. Virgil enjoyed seeing movement and colors (1).

Seeing movement and color was something Virgil did not have to learn. His brain was wired, so to speak, to see those aspects of the world. This is an interesting contrast to those who were colorblind and motion-blind. It seems that the brain is wired to see different parts of the world in different ways. Recognition of faces goes to one area, the production of color to another, the experience of motion to yet another area of the brain. But one must learn how to see. Perhaps Virgil's experience, and the experience of normally sighted infants is like learning the techniques of drawing, such as overlapping gives the appearance that one object is in front of another, but in three dimensions. I know I can't see without eyes, or without functional retinas. But with functional retinas, damage to certain areas of the brain can affect vision profoundly. Our brains truly are our sight organ. Eyes are just light-receivers.


References

1) Sacks, Oliver. An Anthropologist on Mars. New York: Alfred A. Knopf, 1995. pg 141, 108152.

2)Face Blind by Bill Choisser, Chapter 3: Physical Causes of Face Blindness.

3)"How We See Things that Move: The Strange Symptoms of Blindness to Motion", Montgomery, Geoffrey. Howard Hughes Medical Institute.

4)"How We See Things that Move: A Hot Spot in the Brain's Motion Pathway", Montgomery, Geoffrey. Howard Hughes Medical Institute.

5) "How We See Things that Move: Integrating Information About Movement", Montgomery, Geoffrey. Howard Hughes Medical Institute.


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