Most likely the brain implement is working against/with a persons consciousness. This "information extraction" device you talk about, would need to work against

Most likely the brain implement is working against/with a persons consciousness. This "information extraction" device you talk about, would need to work against/with the sub-consciousness, otherwise you can just think "WALL WALL WALL WALL WALL" and the device would only be able to extract that. Not to say that this device was probably trained on the person a lot before they could reach that accuracy. A "information extraction" device would have to be trained on it's victim first, but why would they play along with the training? Maybe I'm wrong, but I think most people have control over what they consciously think, at least it works like that for me.