In the last two decades, new scanning technology has given us a
better idea of what is happening in the brain as we process
visual information. One of the discoveries that has come out of
these new data is the realization that that visual processing
divides into two streams, which end up in very different parts
of the brain. According to Dr. Margaret Stratford Livingston,
Professor of neurobiology at Harvard University, the visual
brain processes tonal information separately from color
information. (Addendum: I changed the image thanks to a
different way of processing them--Thanks, Nick! The image on the
left has only luminance, but the one on the right has color
information with luminance removed.) The two streams originate
in the retina, which begins some low-level processing. The
information pathways route back to the optical cortex at the
back of the brain. Although there is some crossover and
interaction, the two streams are largely kept separate, from the
level of the retina all the way to the higher-le