The traditional polygraph or lie-detector-test as it is commonly known has been in existence for over a hundred years and in that time developments in both the technology itself and our understanding of it have been far and few between (read utterly non-existent). The traditional polygraph works in a very similar way to the traditional witch finding technique: tie them up, drop them in a river and if they live they are a probably a witch. Despite this a new breed of lie detector tests known as “Brain Finger Printing” is emerging that according to a number of experts could be even more unreliable than the status quo once it gets in to the hands of the police, the secret service, cranks and talk show hosts alike the world over.

emperor 300x279 Brain Fingerprinting, The Bastard Child of the PolygraphThe Theoretical Flaw

Essentially all forms of the original polygraph are an attempt to identify when either anxiety is present or when there is prior knowledge of information that would imply guilt through examining biological indicators. The former is a much less reliable indicator than the latter due to the fact that the tests in general invariably provoke anxiety. The main technique which is slightly more reliable involves presenting certain crime scenes to a suspect and then waiting for the “ahah” moment when their blood pressure rises when they are forced to attend to the target item that they are not supposed to know about. Sadly this method assumes two things: that the suspect isn’t just worried he’s been wrongly accused and that the suspect isn’t second guessing the interrogator and freaking out at the dodgiest or most likely sounding scenario.

What do the experts say?

In the largest review of polygraph testing to date, the National Academy of Sciences found that the accuracy of the polygraph was 80-90% when tested artificially. This leaves a hell of a large window for error if you consider that critically that means that when it comes down to it the polygraph will be wrong almost one in four times. The problem with this figure however is that we still have really no idea what we are measuring, it could be in response to anxiety, emotional salience, memory of an event or most likely a combination of the three. The problem being that all three of these factors conflict and none can be identified. The 2003 review of the scientific evidence by the US National Research Council effectively concluded that further investment in the polygraph is futile because of the “inherent ambiguity of the physiological measures”.

So why in that case is the industry experiencing a boom?

Polygraphs do have one value; they often are useful for frightening the victim in to giving a confession. They are also a very easy sell to the paranoid partner and nowadays more worryingly the prying employer.

I don’t know anything about polygraphs, and I don’t know how accurate they are, but I know they’ll scare the hell out of people.” Richard M. Nixon

So what is brain fingerprinting?

Brain Fingerprinting uses electrodes attached to the scalp (EEG) to attempt to define whether someone has experienced an event that would imply guilt. For example if the suspect gave a signal (known as the p-300) that suggests they recognised the scene of a robbery they were suspected of committing this would imply guilt. If the suspect did not recognise the scene it would imply innocence, much like real fingerprints left at a crime. This technology was used in America as long ago as 2000 by a defence council to free a convicted criminal, an interesting decision considering that it is far from impossible to suppress the P300 response.

fmri 218x300 Brain Fingerprinting, The Bastard Child of the Polygraph

The inevitable progression from polygraph to EEG has now lead some investigators to attempt to use a method of brain scanning (FMRI) to look for similar markers to see if certain memories are genuine. The main problem with this technique is that in many ways, when compared to the traditional polygraph the lines are even more blurred. It is very easy for an interrogator with or without bad intent and consciously or not to interpret a brain scan as indicative of guilt. This is of course the goal and the motive of the interrogator. In a stunning study published last year, scientists placed a dead salmon in an FMRI scanner and presented it with images of human faces. It was found to be recognising emotions. Even though it was dead, and a salmon.

“In fMRI, you have 160,000 darts, and so just by random chance, by the noise that’s inherent in the fMRI data, you’re going to have some of those darts hit a bull’s-eye by accident”  Craig Bennet

The benefit of a salmon is you can replay this test again and again and realise that your results are just down to blind luck. With a live, human suspect however you don’t really have that option. Now the same technology is being used by prosecutors to determine the freedom of our friends across the pond and according to some reports in places like Guantanamo. How many red herrings they hit upon we will never know.

red herring color Brain Fingerprinting, The Bastard Child of the Polygraph

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  • Jess

    Ugh, as a researcher who uses EEG and who works with colleagues who do lots of fMRI, I’m crying on the inside (maybe on the outside soon). A P300 isn’t necessarily a marker of recognition. The P300 can be a P3b or a P3a – roughly, the P3b is a marker of target recognition and a P3a is a marker of novelty detection (I assume any advocates of this sort of “brain fingerprinting” would be looking for a P3b). So if the suspect had any prior knowledge of the crime scene from interviews or whatever that could give them something that could be a target, they might display a P3b even if they’ve never seen that specific crime scene before (like if I say to my research participants “look at this stream of stimuli flashing up one after another and look for a big circle”, they’ll show a P3b the first time they see the big circle even though they’ve never seen it before and have only heard me describe it). If the innocent suspect knows the crime was committed with, say, a candlestick (for whismy’s sake), and they see a candlestick in a photo even if they’ve never seen that scene before – P300?

    As for the fMRI, yeah – change some thresholds and analysis methods and you can get whatever activation you want, really. It would take a large panel of fMRI experts to discuss what the appropriate threshold values were for analysis, and they would probably never reach consensus.


    • Neurobonkers

      Thanks for the feedback Jess, the work I’ve been involved with has focused on Beta rhythms (for brain computer interfacing) so I’m looking forward to getting in to the P300 a bit more. Theres certainly massive potential for it’s application in a brain computer interface. Most of the material in this piece was taken from a talk given by Professor Gina Rippon at the BACN conference last month, if the topic interests you and you happen to live near Bristol, Professor Rippon will be visiting in the new year to give a lecture on dodgey neuroscience claims / abuses.

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  • Debunker

    Brain Fingerprinting is made up crap. But not for the reasons this blogs mentions. The blog entry reveals an incredible level of ignorance about how polygraphs work and about the field in general.

    • Neurobonkers

      Care to elaborate?

  • rob isbister

    i took a polygraph lie detector test in NY with Daniel Ribacoff of He was a real professional! He tested me very fairly and i was cleared of the things I was accused of. There would have been no other way to clear my name otherwise. Polygraphs work! i highly recommend his indepth polygraphs if you need a lie detector test in nyc

    • Lewis Hughes

      My son took a test with Daniel Ribacoff too. http// My sone was accused of cheating in a college exam and was going to get expelled. Dan Ribacoff came to the university and testified before the borad about his lie detector test. My son was cleared! Thanks to Daniel Ribacoff of from saving my son’s future.

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