It's essentially the same idea, except that you elicit a particular brainwave signal only when recognizing something you've already seen. I believe India experimented with using it in murder trials a few years ago-- if the accused elicits a P300 upon seeing the actual murder weapon amongst a line-up of dozens of other weapons, they must know a priori how the murder took place and hence be guilty. Interesting times and there really are applications that could benefit from this kind of analysis.