Blindsight

At Not Exactly Rocket Science is a video of a man navigating a hallway filled with obstacles, even though he's completely blind--he has zero conscious awareness of visual perception and his visual cortex shows no activity when given visual tasks (most of which he fails), but he does have an ability known as blindsight. He became blind as a result of strokes which caused damage to the occipital lobe of his brain, including his visual cortex. Yet his eyes still function and there is still some visual processing occurring without rising to the level of conscious awareness. He can perform a number of visual tasks with perfect accuracy, even though his conscious perception is that he is simply guessing.

(Hat tip to Dan Noland for the link.)