The Movies in Our Eyes

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Vision was thought to be perceived by the eye and interpreted by the brain, but new experiments have shown that some processing of the incoming light occurs in the retina. The retina is a small transparent layer of cells only a third of a millimeter thick located on the outer layer of the interior part of the eyeball. It has been found that specialized groups of neurons, or
ganglions, process and send 12 different movie tracks to the brain. However, unlike film, which is a frame by frame representation of vision played faster than our brains can detect, our eyes transmit a constant stream of information as time advances. Each of 12 different ganglion types is responsible for the different movie tracks. The differing tracks each send specified information about a scene to the brain; some transmit only shadows or only highlights and another transmit a line-drawing of the image and still another responds only to movement.
In the retina, rod and cone cells absorb incoming light, convert it into neuronal activity, and connect to 10 different kinds of neurons called bipolar cells. These cells send the information into a region of the retina called the inner plexiform layer, consisting of 10 smaller layers or stratum, which acts as a relay station to the ganglion cell bodies. The signal is also modified or inhibited by yet another group of cells called amacrine cells, which help to coordinate the different movie tracks. "The interactions among bipolar and amacrine cells that are read out simultaneously by each set of ganglion cells make up the data we receive to interpret the visual world."
Scientists Frank Werblin and Botond Roska have been experimenting using a rabbit retina and a glass micropipette that acts as an electrode and can read the electrical signals made by the bipolar and amacrine cells. A small square of light is flashed at rabbit's eye lasting exactly one second. The results were very interesting. Electrical activity began slightly after the beginning of the flash and only lasted only one tenth of the full second the light was on. The scientists theorize that the particular ganglion type being studied specifically responds to change in light and not the sustained presence of light. Of the 7 ganglion types studied, an "...incredible diversity of activity occurs in response to a simple flashed square." The data received was input into a computer and extrapolated to analyze the movements of a talking face. The results showed further that each ganglion type extracts a "unique spacetime representation of the world..."

I picked this article because it dealt with the eyes and I have always marveled at the image God allows me to see everyday. As I expected, there is a large amount of information scientists don't know about how our eyes work, but it is amazing how complex the parts are that they do know about. It especially interested me how the different types of ganglions account for varying aspects of our vision. I wonder what it would look like to have only 11 types functioning?