Snap Circuits Science: Lie Detector Or "Voodoo Psychology"
    By Steve Schuler | August 23rd 2013 12:07 PM | 19 comments | Print | E-mail | Track Comments
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    In my previous article, you learned how to use the 555 test circuit as a cable tester. It can also be used to test whether different materials conduct or don’t conduct electricity such as plastic, glass, cloth, wood, a coin from your pocket, a house key, aluminum foil, or any number of materials from around the house. You can also use it to see how well you conduct electricity to demonstrate one of the measurements, skin conductance, of a polygraph, or lie detector.

    In the demonstration video I touch the snaps together to get a base line tone. Next I hold the snaps on the red and black Jumper Wires between my fingertips to demonstrate that your skin does indeed conduct electricity. The variation in the tone you hear is me squeezing the snaps and relaxing thus increasing the surface area between my skin and the snaps, and when I relax reducing the surface area. In the final part of the demonstration I dip my fingers in tap water (contained in the 50ml beaker) and hold the snaps to demonstrate how moisture on your skin increases conductivity (or reduces resistivity).

    The idea is when your are lying you are afraid of being caught and this causes a physiological response (skin conductance response). Your sweat glands increase their secretion increasing the moisture of your skin which is detected by the lie detector (sweat contains electrolytes). 

    Here’s an interesting story I came across the other day and it does seem that sometimes truth is stranger than fiction. I'm not sure if the story is true but several newspapers and websites are covering it so, maybe it really is a thing, but I’m still withholding provisional assent just in case it is a joke.

    According to the story:

    “Federal agents, as part of an Obama administration crackdown on security violators and leakers, have launched a criminal investigation of instructors who claim they can teach job applicants how to pass lie-detector tests.

    The criminal inquiry, which has not been acknowledged publicly, is aimed at discouraging criminals and spies from infiltrating the U.S. government by using so-called polygraph-beating techniques, which are said to include controlled breathing, muscle tensing, tongue biting and mental arithmetic.”

    My first impression, and probably yours too, was that a just-out-of-law-school-just-passed-the-bar-hasn't-yet-set-foot-in-a-courtroom public defender could get this case thrown out of court on account of the First Amendment. The story says, however, that, “instructors may be prosecuted if they know their students plan to lie about crimes during federal polygraphs.”

    This, to me, is where the story really gets interesting. I, of course, defer to practitioners of Law and by all means do feel free to post your professional opinion regarding this matter in the comments section below. I think we can set aside the case of Mr. Chad Dixon (a Hoosier, by the way, but I haven’t seen any reference in the Indianapolis Star regarding his case as of this writing) who plead guilty to “obstructing an agency proceeding and wire fraud.” But how do the Feds plan on prosecuting Mr. Williams?

    Here’s Mr. Williams’ website:

    The problem for the prosecution is quite simple: Defense can easily demonstrate that there is no scientific basis for detecting deception using a polygraph. First, take a look at National Academies of Sciences (NAS) press release regarding polygraphy, and then take a look at our own Gerhard Adam’s article. And finally, for numerous resources regarding polygraphy issues visit this website.


    Prosecution could bring in expert witnesses from the American Polygraph Association, psychologists, etc. but their testimony will not stand up to scrutiny because, “polygraph testing now rests on weak scientific underpinnings despite nearly a century of study…and much of the available evidence for judging its validity lacks scientific rigor,” according to NAS.

    Though there are some additional sensors that can be connected to the machine, a polygraph usually measures four metrics: respiration, pulse, blood pressure, and skin conductivity. Tubes of corrugated rubber are strapped to your chest to measure your breathing, a blood pressure cuff is wrapped around your arm to measure blood pressure and heart rate, and electrodes are strapped to your fingers to measure skin conductivity. Polygraphers believe that they can detect deception, by reading the squiggly lines that measure your physiological changes (respiration, pulse, blood pressure, and skin conductivity) when you are lying. You’re more likely, however, to be stressed about being electrocuted by all the doodads attached your body than you are being caught telling a lie (which might be read by the polygrapher that you’re lying when you’re actually telling the truth--a false positive)

    A polygraph machine does not give the polygrapher magical powers to tell when you’re lying. It is nothing more than the power of suggestion. That is, people are more likely to confess to some sort of wrongdoing based on the false belief that the polygrapher can detect whether or not a person is lying by looking a the squiggly lines the machine produces when, in fact, he or she cannot. There is absolutely no reason to be intimidated by a polygrapher. Think of it this way: it takes twice as long to pass Barber College than the nine and a half weeks it takes to become a certified polygrapher. You’re not intimidated by the person who does your hair are you?


    dude, i'm TERRIFIED by the guy who cuts my hair. all those blades whirling around near my ears.... and now that i know he's twice as well-trained as a polygrapher, he's all the more intimidating.

    Gerhard Adam
    I suppose it's not too bad if you don't care how your hair looks. :)
    Mundus vult decipi
    Gerhard Adam
    There is absolutely no reason to be intimidated by a polygrapher.
    Actually on a more serious note, the problem is how readily polygrapher's are believed and how often they are such zealous advocates of their own questionable interpretations.
    Mundus vult decipi
    Gerhard in your story ( you mention the green river killer being allowed to go free for another 17 years for passing a polygraph. Polygraphs have allowed the dangerous to go free, but the greater concern is using it to screen government employees who are entrusted with our national secrets.

    Aldrich Ames who was an normal criminal (not a psychopath) was able to pass the polygraph five times and was one of the worst spies in American history--second only to Robert Hanson. Ames was advised by his KGB handler to remain calm during his polygraphs. Foreign intelligence services know that polygraphs are useless and if they need to risk personnel to gather HUMINT those operatives will easily be able to pass a polygraph. If all that's standing between foreign intelligence operatives and access to, I dunno, Sandia National Laboratories, is a person, well, who my barber is better educated than, seems to me like a national security issue.

    Here's some more resources from the Federation of American Scientists:

    Also take a moment to see how polygrahy can be abused:

    Gerhard Adam
    Yes, but more importantly I don't believe our intelligence services are so naive as to not have similar training regarding the polygraph. Of course, this leaves open the question of why anyone believes in their accuracy if everyone that they are intended to target at this level knows they don't work.
    So what we are left with is the mythology in law enforcement [whom I suspect also knows they don't work] but insists on using them as an intimidation tool to elicit confessions.
    Mundus vult decipi
    Hence the need for public education about polygraphy. There's no reason to waste any more tax money and private contractor funds on polygraph machines and polygraphers. Polygraph results are not admissible in court, but if criminals are dumb enough to believe a polygraph works and fess up to their crimes--maybe that's not necessarily a bad thing.
    Gerhard Adam
    That could be acceptable if it weren't for the number of innocent people that become tainted by such testing. You can be assured that with greater public education, the criminals will know enough to refuse to take one. It's the innocent and naive that believe that "telling the truth" will help them and they don't realize how readily the deck can be stacked against them.
    Mundus vult decipi
    "It's the innocent and naive that believe that "telling the truth" will help them and they don't realize how readily the deck can be stacked against them." True. Ok--just wishful thinking that criminals would be dumb and confess.
    Also, with public education about polygraphy people who work as bank tellers or retail will no longer have to be subjected to the indignity of polygraph examinations.
    Gerhard Adam
    Again, the difficulty isn't with the public, but rather with those institutions that insist on it as a condition of employment. I'm sure many people are afraid of polygraphs precisely because they don't trust them, but what can anyone do if the organization you work for insists on it?

    What we need is for the courts to rule that they are not a legitimate tool for employers to use.
    Mundus vult decipi
    For some reason I thought courts had ruled that polygraphs were not allowed as condition of employment in the private sector (someone who practices law would know better than I). Although I think they can be used for bank tellers or retail when money has been stolen (again, someone who practices law would know better than I). The only time I know when a polygraph is required is for government or private contractors for government to get a security clearance.
    Gerhard Adam
    It appears you are correct.
    Mundus vult decipi
    I didn't get one when I got my Secret clearance, I think they give those out as door prizes, I did however get one from one of the 3 letter security agencies that eliminated their having to fill out paperwork every time I needed to go on site. This was 30 years ago though, so I'm sure things are different now.
    Never is a long time.
    I never had one for my clearance either. Even then people didn't trust them (except lawyers - and daytime television reality shows), but they did contact a lot of people so they weren't just rubber-stamping them.
    The best I can ascertain is that polygraphs are used for SCI (sensitive compartmented information) and SAP (special access programs).

    Here's the link to FAS project on Government Secrecy: Through research, advocacy, and public education, the FAS Project on Government Secrecy works to challenge excessive government secrecy and to promote public oversight

    Under this theory can you be charged with attempted murder for pushing pins in a voodoo doll?

    I'm not sure which resource you are referencing (sounds like hyperbole a critic of polygraphy might use). There is no theory of polygraphy. Polygraphy is not science.  
    I should have been clearer, there was an element of tongue in cheek in my response.

    But since polygraphy is largely BS, it would seem that any techniques to avoid it could not be considered 'helping criminals' . Otherwise one can be charged like the (presumably) absurd charge in my original post.

    This can get weird. A couple of years ago there was a hubbub about a preacher who seemed to suggest praying for the death of the president (some people considered that an assassination threat). Given the track record of prayer, that does not seem like a credible threat. And if a death did occur, it would seem that the deity would be the one responsible not the one doing the praying.

    Precisely what I was wondering about in the article: "how to the Feds plan on prosecuting Mr. Williams?"