Biomedical Engineering Add-On

8/13/2019 Biomedical Engineering Add-On

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ADDITIONALTOPICS

BIOMEDICALENGINEERING


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The idea of using a polygraph for lie detection emerged at theend of the nineteenth century. Despite major technologicaladvances in the twentieth century, the polygraph has evolvedlittle since its invention. The polygraph works under the

assumption that lies can be detected by certain measurable physiological changes, a theory proposed more than 100 years ago. The three physiological vectors measured in polygraphs in the 1920s cardiovascular, respiratory and perspiratory activit ies are st il l measured by modern polygraphs. Although the polygraph is st il l widely used, crit icsquestion its accuracy because of the subjectivity involved inthe test. Recent technological breakthroughs have creatednew machines for lie detection.

LIE DETECTION: THE SCIENCE ANDDEVELOPMENT OF THE POLYGRAPH
http://illumin.usc.edu/index/article/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/index/article/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/index/article/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/index/article/43/lie-detection-the-science-and-development-of-the-polygraph/


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Of the three physiological signs recorded in modernpolygraphs, cardiovascular activity was the first sign to beassociated with lying. This association was first documented byan Italian criminologist named Lombroso in the late nineteenth

century. Lombroso noted an increase in a subject 's bloodpressure and heart rate when the subject was giving untruthfulanswers.

In the 1910s, some studies suggested that the ratio of inhalingand exhaling time during breathing changes when a person lies.

Using this theory along with Lombroso's findings, John Larson, amedical student working for the Berkeley Police Department,invented the first polygraph in 1921. This first polygraphsimultaneously traced a subject 's blood pressure and respiration.Under Larson's assumptions, irregularities in blood pressure andbreathing patterns would indicate lies.

DEVELOPMENT OF UNDERLYINGASSUMPTIONS IN MODERN POLYGRAPHS


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The third physiological channel used in modern polygraphs "skinresistance" was added later in the 1920s by Leonarde Keeler.Keeler assumed that a lying person would sweat more than atruthful person, which would decrease skinresistance due to a

higher concentration of negatively charged chloride ions on thesurface of the skin. By adding an extra metric for detecting lies,scientists had hoped to decrease the probability of errors in thepolygraph test. Since this addition, there have been no newunderlying assumptions introduced to improve the polygraph.

DEVELOPMENT OF UNDERLYINGASSUMPTIONS IN MODERN POLYGRAPHS


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Technological breakthroughs in past decades have improved theretrieval and analysis of data obtained from a subject during apolygraph. However, the fundamental assumptions behind thepolygraph and the parameters measured have not changed in

over eighty years. For example, in the 1970s and 80s, the analogpolygraph was used.

With advances in computer programming in the 1990s, mostmodern polygraphs are administered through computers. The

development of sophisticated software has allowed signals to bedisplayed on computer monitors, which allows examiners toidentify irregularities more efficiently.

RECENT POLYGR PH DESIGNS


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Despite its name, the lie detector, also known as the polygraph,is not capable of detecting lies. The device can only displaycertain physiological signs that are assumed to reflect thepsychological state of a liar. For example, the modern daypolygraph displays measurements of heart rate, blood pressure,respiration and perspiration in the figure.

THE MODERN POLYGR PH


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When a person lies or is asked a sensitive question, his or herheart may begin to race, raising the body's blood pressure. Thetest subject may also hold his or her breath, take in a deepbreath, or begin to sweat. These physiological irregularities aredetected by the polygraph and interpreted by the polygraphexaminer. It is the province of the examiner to decide whether ornot sudden changes in the data signify dishonesty. Theassumptions that lying will produce physiological changes andthat polygraph examiners will be able to interpret these signsaccurately have raised questions about the accuracy of thepolygraph.What if a test subject does not exhibit abnormal physiologicalsigns while lying? Can human errors occur in the polygraphinterpretation process? Indeed, polygraph testing is not an exactscience, and there is certainly margin for error in theinterpretation of the three metrics.


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Blood Pressure and Hear t Rate Data

Blood pressure and heart rate data are collected by an arm-encircling cuff placed on the upper arm. The cuff is filled withair and connected to the polygraph machine through air-filled

tubes. Changes in blood pressure modulates the air pressurein the cuff. These changes are recorded by the polygraphmachine and displayed on a computer screen. This data issimultaneously displayed with respiratory and perspiratorydata on a computer monitor, and all are interpreted by the

polygraph examiner.

MEASUREMENTS


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Respiratory Data

The respiration pattern of the subject is detected bytwo pneumograph, devices which record thoracic movements,or volume change during respiration. One of the pneumograph

tubes is strapped around the chest and the other is placedaround the abdomen. Each pneumograph has an air-filledrubber tube connected to the machine. When the subjectbreathes in and out, the air pressure inside the tubingchanges and is recorded by the polygraph machine.

MEASUREMENTS


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Perspiratory Data

The measurement of sweat, which is scientifically known as themeasurement of galvanic skin resistance, is conducted by a two-piece galvanometer attached to two of the subject 's fingertips.

The galvanometer works by sending a small electric current intothe skin from one of the fingerplates and records how muchcurrent was allowed to pass through on the other finge rplate. Dryskin is not a very good conductor of electricity. If a subjectperspires, however, the water and salt from the sweat reduces

the resistance of the skin. This decrease in resistance allows alarger amount of electric current to travel along the surface ofthe skin. Therefore, the amount of electric current recorded bythe galvanometer reflects the amount of sweat that wasproduced in the subject 's fingertips.

MEASUREMENTS


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There are new technologies that can be used for lie detection.One is the facial thermal imaging , a technology that mapsfacial blood flow . When a person lies, he or she oftenbecomes anxious and excessive blood flows to areas around

the eyes. This blood flow can be detected by a thermalimaging screener. Lasers have been developed to detectmuscular, circulatory, and other bodily changes assumed to beassociated with the anxiety of lying . Some computer programsclaim the ability to detect lies by analyzing the voice and toneof a spea ker.

NEW TECHNOLOGIES


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According to their inventors, "when a person lies, aninvoluntary interference of the nerves causes the vocal cordsto produce a distorted sound wave , namely a frequency levelwhich is different from the one produced by the same person

when telling the truth".

One company has even developed a lie-detecting keyboard,which is claimed to be able to detect lies when a person typesinto a computer by analyzing typing patterns, sensing

moisture in fingertips , recording body heat, and monitoringhow fast the finger s were moving when they hit the keyboard.

NEW TECHNOLOGIES


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The polygraph is a device that seeks to accurately and reliablydetect lies - an ability that humans have sought to developthroughout the centuries. However, due to its inherentlysubjective nature, the use of the polygraph is surrounded with

controversy. Regardless, the polygraph does serve as aninstructive tool for government authorities and lawenforcement agencies. With technological advancements,humans will be able to better correlate the psychological stateof lying with physiological responses.

CONCLUSION


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http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/

REFERENCES
http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/http://illumin.usc.edu/43/lie-detection-the-science-and-development-of-the-polygraph/

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Biomedical Engineering Add-On