I had a blind calculus professor in college. Blind. He used a teaching assistant to write his notes on the chalkboard. But my professor did all the math in his head. Watching him was beautiful and completely awe-inspiring. I thought of him this morning. En route to the laboratory, I listened to this new radio program, Invisibilia (which may very well be my replacement for Serial). The podcast I heard, "How to Become Batman", was about a blind man who uses echolocation to - quite literally - see. He makes a series of clicking sounds and listens to their echos as they bounce off objects around him. And he's able to construct projections of those objects in his mind. Their shapes, depths, movements. He's so good at it, he can ride a bike. So he, like my calculus professor, does not actually need his eyes to see.