Flexible or Hard-Wired?

On the back surface of each of your eyes, there is a scrawny, upside-down image with a hole in it, containing about two thirds of the scene in front of you. Over the first fraction of a second after light from the world reaches your eyes, this image is transformed by your brain into a single stable and richly detailed perception of the three-dimensional world. It is this perception that lets you hit a baseball, recognize your friends even at sunset, or upside down, and detect that someone is looking straight at you from across the room.

In spite of its enormous complexity, vision is one of the functions of the brain that modern neuroscientists understand best. We can describe, in astonishing detail, how patterns of light are transformed into electrical signals by photoreceptors in the eye, and how these electrical signals are transformed, reorganized and passed on, step by step, in...