Mark Changizi is proposing a new origin of vision and how we see. It moves the emphasis from food to socializing. He proposes that vision provides us with six super powers: telepathy, x-ray vision, future vision, and spirit reading. Cool, huh? Ok, they are really a bit more mundane than that, especially since we use them on a regular basis.
In more ordinary terms, we have telepathy from our ability to read each other. Our color vision has its greatest response range around the areas of our skin involving blood flow. We can tell the oxygenation levels and blood volume by subtle changes in skin color. These changes correspond to health and basic brain activity.
We have x-ray vision by virtue of our binocular vision. When we have a leafy environment close to us, our brain combines two images from our eyes and is able to remove the leaves from our view. He argues that animals from leavy environments are more likely to have forward-facing eyes, and that animals larger than the size of leaves and grasses are also more likely to have forward-facing eyes.
In a similar vein he explains future vision and spirit reading. In all cases, you understand why this ability is special, and why it is also ordinary. He backs his theory up well with data and interesting trivial.
He also uses his theory to explain a variety of visual illusions. These are primarily related to our future vision. He makes very good arguments and demonstrates a number of different classes of illusion.
The book is fascinating and a very good read for anyone interested in vision, physiology, or psychology.