Reply to comment

Before we returned from spring break and began looking at the sensory side of the nervous system and vision, I read a very interesting article called “Illusory Color & the Brain.” The article talk about how the role of color for most people seems to be to illustrate what we see in everyday life. However, color is merely a perception in the brain. In fact, when it comes down to it, while color does help us differentiate between objects, the part of the brain that deals movement and navigation is essentially color-blind. With this in mind, it seems that color has much less role in defining form and depth that one might have thought. But then there is the study of illusory colors – colors that the brain is “tricked” into seeing, much like we discussed in class. As has been mentioned, the basics of visual perception are that photons are absorbed by rods/cons in the retina, transmitting a signal through neurons to ganglion cells in the retina. Contrast – and thus the detection of edges - in our vision is created when ganglion cells fire maximally when their center is lighter (for an on ganglion) or darker (for an off ganglion) than its surroundings. This part of perception has little to do with color. However, in visual experiments researchers found that the visual cortex in the brain might respond to the direction of borders when color is involved. I couldn’t find a good image of it, but the example they used were two thin, jaggedy, red lines roughly shaped like the Italian peninsula. In on of them there was second, orange border on the inside of the shape, and on one an orange border on the outside. In the shape with the orange in the inside, the shape seemed to be a little elevated off the page and the color seems to spread throughout the empty space in the middle. The shape with the orange on the outside made the shape seem repressed into the page. Researches think that a possible explanation for this is that neurons respond to a certain type of contour when there is a lighter color against a darker color, or visa versa. They give a lot more examples of these visual illusion tricks, but seeing as that last one was hard to describe and probably made no sense you can find the article in the March 2007 issue of Scientific American. Basically, there is a separation in the brain between color and basic visual perception, but in both cases the brain can create illusions of things that aren’t really there, sometimes even combining the two.

http://www.scientificamericandigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=A2A84A32-2B35-221B-64B064E7B4B41259