But the speed of the typists' keystrokes revealed something else. After hitting the wrong key, a typist’s fingers slowed down for the next keystroke, even if the researchers sneakily fixed the error so that the typist didn't notice it. In these cases, a typist wasn't explicitly aware of the mistake, but the brain's motor signal changed nevertheless.
Logan says that this change in timing reflects a kind of automatic assessment of performance. "The body is doing one thing and the mind is doing another," he says. "What we found was that the fingers knew the truth."
This makes sense to me because I sometimes type with my eyes closed, and I've definitely noticed myself correcting typos without ever having seen them.
Update: Apparently it's not faked. Details here, including recipes.