Duplicity Theory in Vision

        Duplicity theory is the theory that there are two systems of vision where one is controlled by the cones and the other the rods. Duplicity theory starts in the retina continues into the LGN and ends in the Visual Cortex. By learning about each system and functions within them we better understand how we process and understand both systems of vision.

        Starting in the Retina there are to receptors called the rods and the cones.  It is important to note that these are anatomically separate. The rods are located in the peripheral while he cones are located in the fovea. There are more rods than cones which explains why we are able to see more looking in no particular direction, but when focused on an object we are able to see it very clear and in detail. There are about 120 millions rods and there are 6 million cones which shows why our vision is more detailed and specific in the cones. The cones are also responsible for seeing color while the rods focus on black and white. The rods also do better in low illumination which contrast the cones which do better in high illumination. The importance here is that one is responsible for black and white where we can see things in our peripherals, but only movement not detail and the other is responsible for color and detail.

        The rods and the cones send the information they take in though the retina circuit which go through the bipolar, horizontal, ganglion, and amacrine cells. As the information moves through the cells it becomes more condensed. The information moves and reaches the parasol ganglion cells and the midget ganglion cells. The information from the cones gets sent to the midget ganglion cells and the information and the information from the rods gets sent to the parasol ganglion cells. Midget ganglion cells are small and do more divergence. 80% of them are in the optic nerve and are in the fovea which is why there is more focusing. This shows that there is a heavy focus on color and focusing on color. This differs from the parasol because there is more convergence and they are in the peripherals. There is also only 20% in the optic nerve and they are larger than the midget cells. There is less of a focus on black and white and this large difference is a large part of duplicity theory.  

        The optic nerve, where the parasol and midget cells are, connects to the lateral geniculate nucleus from the  optic chiasm to the optic tract. The midget cell's information gets organized in the LGN in layers 3, 4, 5, and 6 and is received by the parvocellular cells. These are small cells that are 1-color-opponent which process color and work by responding to opposing color pairs in a CSA way while the inside responds positively to one color in the color pair and negatively to the other color in the surrounding area. The magnocellular are CSA. The parasol cells send their information to the magnocellular cells in layers 1 and 2 of the LGN. This is responsible for black and white and it is center surround antagonistic. The importance here is that there is again a focus on color. There are double the amount of layers were color is processed (parvocellular) than there is for black and white (magnocellular).