According to MIT neuroscientist Mriganka Sur, half of the human brain is devoted to vision. Why? I'm no neuroscientist, but I imagine that there are two reasons: First, vision is extremely valuable: humans use it constantly, and for an endless variety of tasks, from reading to navigation to creating all manner of objects. Second, vision is a hard problem, considering all of the things that we're able to discern visually--under widely varying and often very challenging conditions, such as glare and low light.