TWO millivolts is not much. But it is enough to show that someone has seen something even before he knows he has seen it himself. The two millivolts in question are those associated with P300, a fleeting electrical signal produced by a human brain which has just recognised an object it has been seeking. Crucially, this signal is detectable by electrodes in contact with a person’s scalp before he is consciously aware of having recognised anything.
That observation is of great interest to DARPA, the Defence Advanced Research Projects Agency, one of America’s military-research establishments. DARPA’s Neurotechnology for Intelligence Analysts programme is dedicated to exploiting it in the search for things like rocket launchers and roadside bombs in drone and satellite imagery. To that end it has been paying groups of researchers to look into ways of using P300 to cut human consciousness out of the loop in such searches.