|MadSci Network: Neuroscience|
You have posed an interesting series of questions about the visual system. I'll try my best to give you some of the basics and then to point you in some other directions where you might discover some interesting things yourself. To start with, the visual system is quite complex and can't be addressed adequately in a brief forum like this one. However, despite its complexities, we (perhaps) know more about the visual system than about any of the other senses. This is due, in part, to the fact that a large portion of the human brain is devoted to the processing of visual information. Indeed, humans are predominantly visually oriented creatures (as are most mammals) and this no doubt played a large role in our evolution -- but that's getting into a whole other area. As to your first question, the color of paper most certainly does effect the ability to read. Here is a real world example that might be of interest to you since you may have recently acquired your driver's license (or may be sitting for the exam in the near future). You probably have noticed that important road signs are frequently BLACK print on a YELLOW background. This isn't a subtle attempt to get you to cheer for the Pittsburgh Steelers, but it is an effective use of science. Our eyes respond best to the color yellow (it may have something to do with evolving on a planet surrounding a yellow star). Thus, yellow things are easily and quickly noticed (like a school bus!). Dark print on a lighter background produces a great deal of contrast between the print and the background, and thus makes it easier to detect. Likewise, the converse (light print on a dark background) is also true. Most signs that people want you to read are light on dark, or dark on light. It is just easier on the eyes that way. When you change colors to ones with less contrast, distinguishing the letters can be more difficult and reading could be slowed (although I could not find a specific study that addressed this specific question). Think about trying to read something printed in red on a blue background. Pretty difficult, no?! Sometimes this lack of contrast is used for a reason. Chris Carter, the writer/director of TV's X-Files, often likes to keep the scripts for the series (and last summer's movie) a secret. So how does he prevent leaks or unauthorized photocopies from being distributed? He makes sure the scripts are printed in red ink on pink paper. It's readable (although not as easy to read as black text on white paper), but doesn't have enough contrast to be photocopied. As to the rest of your question (what does the brain do when reading...), that is too much information for me to summarize here (books and books and books!). In brief, visual information enters your eye and travels along the optic nerve towards the back of your head (occipital cortex). The primary visual cortex starts to process the information and from here it goes to other areas of your brain (such as the visual association cortex in the parietal lobe) for additional "processing" and interpretation. One thing to keep in mind is that the different areas of the brain have evolved to process very specific types of visual information. Some neurons process motion information, others work mainly with perceiving colors, forms or textures. Up to this point in the visual system, we share most of these abilities with other mammals (you can test the color or movement vision of cats or monkeys in much the same as humans). However, when it comes to reading, humans are unique. Moreover, reading involves a great deal of cognitive learning and development (often studied in psychology) that is (obviously) only able to be studied in humans. Distinguishing boundaries of objects (such as letters on a page, or a dog walking in the snow) deals with a process called lateral inhibition. In plain terms, lateral inhibition is when the activity of one neuron is reduced by a neighboring neuron that has been excited. This helps us perceive, among other things, boundaries. It also helps create some interesting visual illusions. The page below has some good ones you might want to check out. TRICKS OF THE EYE, WISDOM OF THE BRAIN (http://serendip.brynmawr.edu/bb/latinhib.html) Other visual phenomena, which may be of interest to you are blindsight (the ability of a seemingly blind persons to touch or grab objects that they report they can not see) or perhaps some of the various visual deficits (visual agnosia, simultanagnosia). You can find out more information on these in textbooks or by doing a MEDLINE search. Try using the Pub-Med (www.ncbi.nlm.nih.gov/PubMed/index.html) or Grateful Med (igm.nlm.nih.gov/) web sites. For a general overview of the visual system, I'd recommend looking at a basic biopsychology textbook. They usually have a good overview chapter(s) on the subject of the visual system. Two that have helped me through the years are: Neil R. Carlson's Physiology of Behavior, (Allyn & Bacon Publishers) or James W. Kalat's Biological Psychology (Brooks/Cole Publishers) (I looked at both before I wrote this answer) Also, Oliver Sacks, M.D. has written a number of good books on some of his more interesting neurological patients (Two of his more popular books are The man who mistook his wife for a hat, and, An anthropologist on Mars) that I would encourage you to examine.
Try the links in the MadSci Library for more information on Neuroscience.