The machine makes it possible to type messages onto a computer screen by mentally controlling the movement of a cursor. A user must wear a cap containing electrodes that measure electrical activity inside the brain, known as an electroencephalogram (EEG) signal, and imagine moving their left or right arm in order to manoeuvre the cursor around.|link|
So we can’t read your intentions directly off your brain, but we can indirectly figure out where you imagine moving your arms. So the subjects must actually think about moving their arms, and not the cursor, in order to get the cursor to move. I wonder if this process can become transparent, the way we use our mouse and keyboard now; or if making the motor commands explicit in consciousness will wind up limiting the use of these sorts of tools beyond anything practical.