SCIENCE & TECHNOLOGY
 

Detecting lies through polygraph
S.S. Verma
T
ELLING a lie by a criminal becomes a serious problem for the law-enforcement authorities. In that case, we always hear about the use of lie detector tests to people under trials and thus, curiosity arises to know about the working principle of a lie detector. These instruments do not, as their nickname suggests, detect lies.

NEW PRODUCTS & DISCOVERIES
A spin through Space-Time
A
satellite designed to test one of the more twisted predictions of Albert Einstein's general theory of relativity is finally at its launch site after 40 years of preparation. The probe will look for evidence of a gravitational effect known as frame dragging. Just as a dipper drags honey along as it twirls in a honey jar, any spinning body in space, including Earth, ought to drag some space-time along with it.

  • Safer future for rail travel

UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL

Why are the planets around the sun in elliptical paths: why are they not all circular?



Top









 

Detecting lies through polygraph
S.S. Verma

Fig. 1: Analog polygraph
Fig. 1: Analog polygraph

TELLING a lie by a criminal becomes a serious problem for the law-enforcement authorities. In that case, we always hear about the use of lie detector tests to people under trials and thus, curiosity arises to know about the working principle of a lie detector. These instruments do not, as their nickname suggests, detect lies. Polygraphs, commonly called ďlie detectors,Ē are instruments that monitor a personís physiological reactions to variety of questions by the examiners. They can only detect whether deceptive behaviour is being displayed.

A polygraph instrument is basically a combination of medical devices that are used to monitor changes occurring in the body. As a person is questioned about a certain event or incident, the examiner looks to see how the personís heart rate, blood pressure, respiratory rate and electro-dermal activity (sweatiness, in this case of the fingers) change in comparison to normal levels. Fluctuations may indicate that a person is being deceptive, but exam results are open to interpretation by the examiner.

Polygraph exams are most often associated with criminal investigations, but there are other instances in which they are used. In future, one may be subjected to a polygraph exam before being hired for a job. Polygraph examinations are designed to look for significant involuntary responses going on in a personís body when that person is subjected to stress, such as the stress associated with deception. The exams are not able to specifically detect if a person is lying, according to polygrapher Dr Bob Lee, former executive director of operations at Axciton Systems (USA), a manufacturer of polygraph instruments. But there are certain physiological responses that most of us undergo when attempting to deceive another person. By asking questions about a particular issue under investigation and examining a subjectís physiological reactions to those questions, a polygraph examiner can determine if deceptive behaviour is being demonstrated.

Digital polygraph
Fig. 2: Digital polygraph

The polygraph instrument has undergone a dramatic change in the last decade. For many years, polygraphs were those instruments with little needles scribbling lines on a single strip of scrolling paper. These are called analog polygraphs (Figure 1). Today, most polygraph tests are administered with digital equipment (Figure 2). The scrolling paper has been replaced with sophisticated algorithms and computer monitors. While sitting down in the chair for a polygraph exam (Figure 3), several tubes and wires are connected to the body in specific locations to monitor physiological activities.

Deceptive behaviour is supposed to trigger certain physiological changes that can be detected by a polygraph and a trained examiner, who is called a forensic psychophysiologist (FP). This examiner is looking for the amount of fluctuation in certain physiological activities. Hereís a list of physiological activities that are monitored by the polygraph and how they are monitored.


Fig. 3

Respiratory rate: Two pneumographs, rubber tubes filled with air, are placed around the test subjectís chest and abdomen. When the chest or abdominal muscles expand, the air inside the tubes is displaced. In an analog polygraph, the displaced air acts on a bellows, an accordion-like device that contract when the tubes expand. This bellows is attached to a mechanical arm, which is connected to an ink-filled pen that makes marks on the scrolling paper when the subject takes a breath. A digital polygraph also uses the pneumographs, but employs transducers to convert the energy of the displaced air into electronic signals.

Blood pressure/heart rate: A blood-pressure cuff is placed around the subjectís upper arm. Tubing runs from the cuff to the polygraph. As blood pumps through the arm it makes sound; the changes in pressure caused by the sound displace the air in the tubes, which are connected to a bellows, which moves the pen. Again, in digital polygraphs, these signals are converted into electrical signals by transducers.

Galvanic skin resistance (GSR): This is also called electro-dermal activity, and is basically a measure of the sweat on the fingertips. The fingertips are one of the most porous areas on the body and so are a good place to look for sweat. The idea is that we sweat more when we are placed under stress. Fingerplates, called galvanometers, are attached to two of the subjectís fingers. These plates measure the skinís ability to conduct electricity. When the skin is hydrated (as with sweat), it conducts electricity much more easily than when it is dry.

Some polygraphs also record arm and leg movements. As the examiner asks questions, signals from the sensors connected to the body are recorded on a single strip of moving paper.

Some experts say that lie detector might have some vague use in increasing the psychological stress of a subject under interrogation, but galvanic skin response and heart rate have little to do with the process of lying. Thus, it is acknowledged that a habitual liar can fool a polygraph machine and examiner. But, lie detectors equipped with newfangled nuclear magnetic-resonance brain scans are expected to become more accurate devices.

Furthermore, forget the elevated pulses, sweaty palms, and respiration changes scrutinised by conventional lie detector tests. Thereís a more direct and, in theory at least, accurate way to measure deceit: track the flow of blood where the lie is born. Lying requires an extra bit of thought, which pulls more blood into a swath of the brain just beneath the forehead. These flows can be tracked optically. Biophysicist Britton Chance ó who 60 years ago was part of the wartime research team that developed radar at MITís Radiation Laboratory ó is pioneering technology that can literally see a lie as it is spoken. He believes the method is better than conventional tests because the flows canít be suppressed and are less likely to have been caused by the stress of test taking.Top

 

NEW PRODUCTS & DISCOVERIES
A spin through Space-Time

Stacked inside Gravity Probe B's insulated tank of liquid helium, seen between the solar panels in this photo, are four gyroscopes and a telescope that can peer through the top hatch
Stacked inside Gravity Probe B's insulated tank of liquid helium, seen between the solar panels in this photo, are four gyroscopes and a telescope that can peer through the top hatch

A satellite designed to test one of the more twisted predictions of Albert Einstein's general theory of relativity is finally at its launch site after 40 years of preparation. The probe will look for evidence of a gravitational effect known as frame dragging. Just as a dipper drags honey along as it twirls in a honey jar, any spinning body in space, including Earth, ought to drag some space-time along with it. That was Einstein's prediction, anyway. The effect has never been convincingly observed.

That's partly because Earth's tweaking of space should barely register on even the most sensitive instruments. Yet the effects of frame dragging may prove enormous in deep space where spinning, ultradense concentrations of mass known as supermassive black holes may torque space-time vigorously enough to create the enormously powerful jets of matter and energy known as quasars.

Many relativity experts are enthusiastic about the prospects for Gravity Probe B (GP-B), as the spacecraft is known. Gathering hard evidence that "space is not the fixed fabric we think of" would be a "stunning achievement," says Clifford M. Will of Washington University in St. Louis, a gravitational physicist who served on a NASA-convened review panel that endorsed the mission's science goals last spring. He adds, "It's the kind of result that will be written in physics textbooks for years to come."

Safer future for rail travel

A tiny electronic device which could prevent rail disasters will be showcased by scientists who created it less than a mile from where the railway revolution began.

Microlog, a highly advanced miniature data logger, weighs less than 10 grammes and boasts a four megabyte memory, a powerful 16 byte microprocessor and satellite and mobile phone technology packed into one third of the size of a matchbox.

It has been developed by a father and son team at the University of Newcastle upon Tyne's Stephenson Centre, a new venture inspired by the 19th Century entrepreneur, Robert Stephenson, who built the Rocket locomotive in a nearby Newcastle factory with his father, George.

Tests on the device are due to start shortly on the GNER east coast main line, a route which Stephenson was involved in developing almost two centuries ago.
Top

 

UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL

Why are the planets around the sun in elliptical paths: why are they not all circular?

PROF YASH PALThe general solution of equations of motion gives elliptical orbits. A circle is a specific example of an ellipse when the major and minor axes of the ellipse are equal. When we launch satellites around the earth and want them to have circular orbits we follow the following procedure:

The satellite is first put in an elliptical orbit with its highest point close to the distance at which a circular orbit is desired. This point in the orbit is called the apogee. The satellite goes around the earth, passing quite close to the earth during the perigee. After accurately determining the parameters of the orbit the satellite is given a measure of push by firing rockets when it reaches the apogee next. This helps to circularise the orbit. The process may have to be repeated to achieve the exact orbit desired.

What is acid rain? How does it occur?

Acid rain occurs when the water coming down is slightly acidic. The reason for this is the emissions of gases like sulfur dioxide and nitrous oxide that arise in intense industrial activity. These gases combine with water and convert the rainwater into dilute sulfuric and nitric acid. Such rain can devastate forests and make the lakes sterile. Lately there has been much stress on controlling such emissions.

Why does black surface attract heat?

A surface appears black if it absorbs all visible radiation falling on it. Absorption of this energy heats up the black surface to a temperature such that the emitted energy is equal to the energy received. What applies to visible radiation is generally applicable to the infrared region of the spectrum even though one can design surfaces that have some degree of selective absorption.

You can, of course, turn around and ask me to tell you what it is in a surface that makes it black. I can give a facetious reply: just paint it black. You can stump me again by asking why is black paint black. I am sure the answer lies in the energy levels of the pigments used, which would imply that all blacks are not equally black.

HOME PAGE
Top