In sighted people, the part of the brain that recognizes faces is linked to the brain's visual system. But in blind people it seems wired to circuits that process sound. Tina Zellmer/Ikon Images/Corbis hide caption

itoggle caption Tina Zellmer/Ikon Images/Corbis

This is a re-creation of a color plate from Interaction of Color, by Josef Albers. The two X's are are exactly the same — it's the different backgrounds that make them look like very different colors. Source: Josef Albers Interaction of Color hide caption

itoggle caption Source: Josef Albers Interaction of Color

One of the scariest parts of advanced macular degeneration can be losing the ability to read facial expressions. Maria Pavlova /iStockphoto hide caption

itoggle caption Maria Pavlova /iStockphoto