The researchers found that the neurons do two important things. They sense where the cursor is, and they predict where it will be in the future, based on visual cues and feedback from the muscular system as they manipulate the joystick.
So the part of the brain that plans the movement of the cursor also directs the movement and can change the course if clues suggest something is wrong.
In a real sense, that's exactly what A-Rod does standing at home plate. He predicts where the ball will be. He doesn't just react to what his vision is telling him because he doesn't have time. And if something doesn't look right, he can check his swing even if he doesn't know exactly where the ball is.
He has to do that, because the human brain doesn't work as fast as we like to believe.
All this may be a little disconcerting to athletes who think their responses are lightning quick. So here's a game to show just how delayed the response can be.
Hold the end of a dollar bill by your thumb and forefinger, and let it hang toward the floor. Tell a friend to place his or her thumb and forefinger, about two inches apart, on each side of the bottom edge of the bill. See if your friend can catch the bill with his or her fingers, without moving his or her hand, after you release it.
If you lose your buck, sign your friend up for the All-Stars.
Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.