The Hacker's Encyclopedia 1998

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% %% %% ========================== %% %% Meet and Beat the Lie Detector %% %% ========================== %% %% %% %% Stolen from the book %% %% BIG SECRETS! %% %% by: William Poundstone %% %% %% %% Typed By %% %% --==**>>THE RELFEX<<**==-- %% %% [Member: Omnipotent, Inc.] %% %% %% %% 80-col for Countlegger 8 and %% %% various typo. corrections by %% %% Count Lazlo Hollifeld-Nibble %% %% %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% The polygraph test was invented by William Moulton Marston, who was, strangely enough, also the creator of the "Wonder Woman" comic strip (under the name Charles Moulton). The standard polygraph records only three distinct vital signs. A blood-pressure cuff on the upper arm measures changes in blood pressure. Wires attached to the fingers measure changes in electrical resistance of the skin due to sweating. Rubber straps around the torso measure the breathing rate. This information is displayed as four squiggles on a moving strip of graph paper. Whether or not you believe a polygraph provides useful information (most psychologists have their doubts), there is a good chance you'll be asked to take a polygraph test. The vast majority of lie-detector tests are administered for employee screening--"Have you been using the WATS like for personal calls?" and so forth--not for police work. In 'A Tremor In the Blood: Uses and Abuses of the Lie Detector' (New York: McGraw-Hill, 1981), polygraph critic David Thoreson Lykken estimates that as many as one million polygraph examinations are performed on Americans each year. In criminal cases however, even the manifestly innocent may be asked to take a polygraph test. All Yakima County, Washington, rape victims are required to take the test; refusal means the case will not be prosecuted. At best, all the polygraph can indicate is a heightened emotional reaction to a question. It cannot specify what kind of an emotional reaction. Polygraphers try to design question formats so guilt-induced nervousness will be the only emotional invoked and so the subject's reaction to relevant questions can be compared to other, "control" questions. THE LIE CONTROL TEST -------------------- This is the question format used in most police investigations. It usually starts with a card trick devised by two pioneer polygraphers, John E. Reid and F. E. Inbau. The polygrapher hooks the subject to the polygraph and takes out a deck of cards. The polygrapher tells the subject that he must "calibrate" the polygraph with a simple test. He fans the deck and asks the subject to select a card. The subject is told to look at the card but not to show it or mention its name. The polygrapher tells the subject to answer "no" to every question asked about the card. "Is it a black card?" the polygrapher asks. "Is it a high card?" and so on. After each "no" the polygrapher scrutinizes the tracings and fiddles with the dials. If the no answer is incorrect, the polygrapher disagrees. The field is soon narrowed to one card--and it is the correct card. Needless to say, the polygrapher uses a trick deck. The point is to foster confidence in the machine. After identifying the card, the polygrapher comments that the subject's reactions are particularly easy to read and segues into the interrogation. Three types of questions are used in a lie-control test. The entire list is read to the subject well in advance of the test. The start of a typical interrogation might run like this: 1. Is your name Sarah Elkins? 2. Is Paris the capital of France? 3. Have you ever failed to report more than $50 of tip, gambling or gift income on a single year's tax return? 4. Is this apple red? 5. Do you have any idea why the cash reciepts for the last quarter are about $22,000 in error? 6. Is there something important that you did not mention on your job application? 7. Have you ever been embezzling from the company? The first question is always irrelevant to the matter being investigated. It has to be because many subjects get nervous on the first question no matter what. Other irrelevant questions are asked throughout the interrogation (questions 2 and 4 in the sample list). If the subject gives any thought to these questions, he assumes that they are control questions to provide a yardstick for evaluating responses to the relevant questions. Actually, the irrelevant questions are there to give the subject's vital signs time to return to normal. They aren't the control questions. Questions 5 and 7 in the list above are relevant questions--the only questions the examiner is really interested in. The relevant questions are asked in several different wordings during the test. Questions 3 and 6 are control questions. In the pretest discussion of the questions, the polygrapher explains that it is helpful to throw in a few "general honesty" questions. Whoever committed the serious crime, the spiel goes, probably comitted less serious crimes in the past. Hence the inclusion of questions about tax cheating, lying on the job applications, stealing as a child, etc. The polygrapher affects the attitude that it would be damaging indeed to admit any such indiscretions. Frequently this scares the subject into admitting minor crimes. In that case, the plygrapher frowns and agrees to rewrite the question. Should the subject concede failing to report eighty dollars in gambling winnings, question 3 might be changes to "Have you ever failed to report more than a hundred dollars of tip, gambling, or gift income on a single years's tax return?" If necessary, several of the control questions may be reworded before the test--always so that the subject will be able to give the "honest" response. In reality, the whole point of each working question is to manufacture a lie. It is the secret working premise of polygraphers that everyone commits the minor transgressions that are the subject of the usual control questions. All the subject's denials on the control questions are assumed to be lies. The polygraph tracings during these "lies" establish a base line for interpreting the reaction to the relevant questions. The reason for rewriting some control questions is so a candid subject will no admit to minor crimes on the test. That would be telling the truth, and the polygrapher wants the subject to lie. The control questions are intentionally broad. Even if a question is reworded to exclude the confessed instance, it is assumed that any denial must be a lie. The rationale for the lie-control test goes like this: The honest subject will be worried about the control questions. He'll know that he has committted small transgressions or suspect that he must have, even if he can't remember them. So he'll be afraid that the machine will detect his deception on the "general honesty" questions (especially in view of its success with the card trick). That would be embarrassing at least, and it might throw suspicion on him for the larger crime. In contrast, the relevant questions should be less threating to the honest subject. He knows he didn't commit the crimes they refer to. The guilty person, on the other hand, should have far more to fear from the relevant questions. If the machine can detect lying on the relevant issue, it matters little that it might also implicate him in petty matters. By this hypothesis, an innocent person should have greater polygraphic response to the control questions than to the relevant questions. The guilty pattern is just the reverse: greater response to the relevant qustions. This, at any rate, is what polygraphers look for when the machine is switched on. THE RELEVANT-CONTROL TEST ------------------------- The relevant-control test is the type used for most employee screenings. Thus it is the most common type of examination. The interrogation consists only of irrelevant and relevant questions. As with the lie-control test, the first question and a few others are irrelevant. The relevant questions usually test workplace honesty: "Have you ever taken home office supplies for personal use?" "Have you ever clocked in for someone else?" The premise is that no one will lie about everything. So if a few of the relevant questions produce heightened responses, they are presumed to be the questions on which the subject is lying. Unfurtunately, there is no ambiguous way of deciding how much response is indicates a lie. Most psychologists agree that the relevant-control test is a poor test of deception. The Reid/Inbau card trick is eliminated from employee screenings: There is too great of a chance of coworkers comparing notes and discoverings that everyone picked the ace of spades. HOW TO BEAT THE LIE-DETECTOR ---------------------------- To the extent that the polygraph works at all, it works because people believe it does. Many criminals confess during polygraph examinations. Many employees are more honest for fear of periodic screenings. But a dummy polygraph that hummed and scribbled preprogrammed tracings would be no less effective in these instances. David Thoreson Lykken estimates that lie-control polygraph tests are about 70 percent accurate. (Remember, though, that choosing "heads" or "tails" of a flipped coin can be accurate 50 percent of the time.) Accuracy of 70 percent is not impressive, but it is high enough to talk meaningfully of beating a polygraph test. Just by having read this far, you stand a greater chance of beating a polygraph test. You won't be wowed by the card demonstration. You realize that the polygraph's powers are limited. There are two additional techniques for beating the polygraph. The more obvious is to learn how to repress physiologic responses to stressful questions. Some people are good at this one; others are not. Most people can get better by practicing with a polygraph. Of course, this training requires a polygraph, and polygraphs are expensive. The opposite approach is to pick out the control questions in the pretest discussion and exaggerate reactions to these questions during the test. When the control-question responses are greater than the relevant-question responses, the polygrapher must acquit the subject. Because breathing is one of the parameters measured, taking a deep breath and holding it will record as an abnormal response. Flexing the arm muscles under the cuff distorts the blood-pressure reading. But a suspicious polygrapher may spot either ruse. A more subtle method is to hide a tack in one shoe. Stepping on the tack during the control questions produces stress reactions with no outward signs of fidgeting. Biting the tounge forcefully also works. --William Poundstone