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Seminar Report Lie Detector

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8/12/2019 90354868 Lie Detector



PSYCHO PHYSIOLOGICAL CREDIBILITY

ASSESSMENT

INTRODUCTION

Lies are part of human life! People often tell lies to deceiveothers. many of us have heard about “lie detector “,some where seen in movies orread it in fiction stories. Does anything of this sort really e ist "f yes, does it reallydetect lies #es it does. $he first thing that comes to our mind is how an instrumentwith some electronic components can read out our mind. $hough science andtechnology are growing at the speed of light, has it reached a stage where it can

read mind %ot e actly! &ut it can approach to that stage by monitoring the physiological reaction by plotting graphs.

WHAT IT IS

Polygraph, a multigraph of physiological reaction. Lie detectoror polygraph as it is technically called is an instrument that monitors the

physiological reaction. "t can detect only deceptive behavior of human mapped tolies. $he underlying factor of this concept is a person is sub'ected to stress whiletrying to decieve.&iomedical technology is used to bring out this deception. Lyingis a sort of defense mechanism used by human to avoid trouble but when it is aserious crime li(e murder, spying on a country, it is necessary to bring out the truth.in such a case polygraph provide a helping hand to the law.

PRINCIPLE APPLIED

)hen someone decieves, sometimes we are able to guess byhis*her reactions whether they are deceiving or not. &ut most of the times we areunable to predict this. $his principle of guessing is more widely used with thegrowing technologies to monitor the physiological reactions. "t monitors theinvoluntary change that occurs in the body when the person is under stress.

&iomedical instruments are used to monitor those physiological reactions.$hey are+

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TAKING THE TEST:

$his test challenges the mind of the most stoical person. ll thee5uipments are attached to the sub'ect6s body. polygraph e am is along processthat can be divided up in to severalStages.

7. PR-$-S$8. "%$-S$9. P/S$ $-S$

:orensic psychophysiologist, a trained e aminer e amines the sub'ect ;pretest< .he5uestions the sub'ect ;intest< and loo( for fluctuations in the graphs produced ;post=test< to find the amount of deception.

PRETEST:

$his consists of an interview between the e aminer and the e aminee, wherethe two individuals get to learn about each other. $his may last about one hour.During this the e aminer gets the e aminee6s side of the story concerning theevents under investigation.while the sub'ect is sitting there answering 5uestions, thee aminer also profiles the e aminee. $he e aminer sees how the sub'ect respondsto 5uestions and processes information. $he e aminer designs 5uestions that arespecific to the issue under investigation. $he physiological reactions that aremonitored are heart rate , heart sound,respiratory rate,galvanic s(in resistance.

HEART RATE AS A FACTOR IN DETECTION OF DECEPTION + %ormally a heart beats >8 times per minute. &ut while

decieving, the sub'ect is under stress, hence the rate of heart beat increases. $hat isthe fre5uency of heart rate increases. $his involuntary response going in a person6s body is detected by forensic psychophysiologist.hence by monitoring heart beat onecan detect deception. "n heart rate there are two parameters monitored.

7. &ioelectric signals produced by heart muscle cells.8. Sound produced by the heart.

WHAT ARE BIOELECTRIC SIGNALS?

0ertain types of cells inside the body, such as nerve andmuscle cells are encased in semi permeable membrane that permits some substance

to pass through the membrane and bloc( the others. Surrounding the cells are bodyfluids. $hese are conductive solutions containing ions. $he principle ions aresodium, potassium and chloride. $he cell membrane readily permits potassium andchloride ions and bloc( sodium ions. Since a balance is re5uired between inside andoutside of the cell, both according to concentration and electric charge, the inabilityof sodium to penetrate the membrane results in two condition.


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Seminar Report Lie Detector 7. $he concentration of sodium ions inside the cell becomes much lower than

the fluid outside. Since sodium ions are positive, they would ma(e theoutside of the cell more positive.

8. $o balance electric charge, additional potassium ions which are also positiveenter the cell, ma(ing the concentration higher inside than outside.

Due to concentration imbalance of potassium ions, e5uilibrium is reached with a potential difference across the membrane, negative on the inside and positive on theoutside. $his membrane potential is called resting potential or bio electric potential.$his potential is negative since it is measured from inside to the body fluids. cellat resting potential is said to be polari?ed. )hen a cell membrane is e cited by the flow of ionic currentor by some form of e ternally applied energy, the membrane changes itscharacteristics and begins to allow some of the sodium ions to enter. $hesemovements of sodium ions into the cell constitute an ionic current flow. $his

process of disturbing the cell from its polari?ed state by the rushing in of sodium

ions is called depolari?ation. /nce the rushing in of sodium ions is stopped, the in lyingsodium ions are rushed out by an active process called sodium pump. $hus the cellagain becomes polari?ed. $his process of converting the cell from depolari?ed state

bac( to polari?ed state is called repolari?ation.

PHYSIOLOGICAL NATURE OF BIOELECTRIC SIGNAL

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P=wave atrial depolari?ation or contraction @.8A @[email protected];PR=interval<

R=wave;BRScomple <

repolari?ation of atria and depolari?ation ofventricles

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$=wave ventricular repolari?ation @[email protected] @.@[email protected];S$=interval<

4=wave repolari?ation of inter ventricular system @.7 @.8;$4=interval<

SOUNDS OF HEART


8/12/2019 90354868 Lie Detector


Seminar Report Lie Detector Listening to sound produced by organs and vessels is calledauscultation. normal heart beat produces two distinct sounds often described asElub=dubE.Lub:- it is a long and a dull sound caused by the closure of atrio=2entricular valves,which permits flow of blood from the atria into the ventricles but prevent in thereverse direction.Dub:- it is a short and sharp sound caused by the closure of semi lunar 2alves,which release blood into pulmonary and systemic circulatory systems. $here is sometimes a third heart sound especially in young adultswhich occurs from @[email protected] second after the second heart sound. $his is due to therush of blood from atria into the ventricles.

CORRELATION OF HEART SOUND WITH BIOELECTRIC SIGNALS:

$he first heart sound occurs at the time of BRS=comple . $he second heartsound occurs at the time of end of t=wave.

HEART RATE MONITORING .

$he bioelectric signals generated in the heart muscle cells areconverted to electric signals. lso the sound signals of the heart are converted toelectric signals and the graph of those signals is monitored.

TRANSDUCTION OF BIOELECTRIC SIGNALS.

BLOCK DIAGRAM:


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output

SURFACE ELECTRODES:

"t is employed to pic( up electrical signals. "t is a type of biopotential electrode. $hey use metal=electrolyte interface. $he interface ofmetallic ions in the solution with their associated metals results in an electric

potential which is called electrode or half=cell potential. $his potential acts asvoltage source. $his potential is the result of the difference in the diffusion rate ofion in and out of the metal. -5uilibrium is produced by the formation of the layer ofcharge at the interface. $his charge is a double layer, with the layer nearest to the

metal being on one polarity and the layer ne t of opposite polarity.

$his double layer acts as capacitor. $here is some lea(age potential. $his acts as a resistor which is in parallel with the capacitor. $here issome s(in resistance to the electrode. $his acts as series resistor to the parallelcircuit. $hese parameters form the electrical e5uivalent of the electrode interfacecircuit.

$he electrode measures the ionic potential at one point of the body. $he bioelectric potential is


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Seminar Report Lie Detector actually the ionic potential difference between two points of the body. ence toobtain bioelectric potential two electrodes are re5uired. $his combination of twoelectrodes acts as a transducer. $he two electrodes should be of same type to ensurethat we obtain the true bioelectric potential of the body.

ISOLATION AMPLIFIER

"t increases the input impedence.Low pass filter with carrier fre5uency 7@ ( ? toreduce the"nterference due to surgery. igh and over volt protection to withstand volt duringrefibrillation. %otch filter to eliminate interference due to line fre5uency.

TRANSDUCTION OF HEART SOUND SIGNALS +

BLOCK DIAGRAM:

CONDENSER MICROPHONE:

$he conversion of heart sound to electric signal can be doneusing a transducer called condensor microphone.there is two main categories.

7. air coupled microphone8. contact microphone

"n air coupled microphone, the movement of chest is transferred in air cushion and presents low mechanical impedance to the chest. &ut contact microphone is directlywww.seminarsonly.com

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Seminar Report Lie Detector coupled to the chest wall and presents higher impedance, high sensitivity, low noiseand light weight. 0ontact microphone is mostly preferred.

"t consists of a diaphragm which acts as rotor and a bac( plate acts as stator of avariable capacitor. $he two electrodes are placed very close to each other. )hen aregulated dc voltage is supplied through a high a resistance across the electrodes, aconstant charge is maintainted.it is given by cF5*v.$he vibrations produced by thechest wall changes the position of diaphragm. $his results in change in voltage.

PHONOAMPLIFIER:

$he voltage produced in the condenser microphone is of theorder of millivolts.the preamplifier is used to amplify in the order ofvolts.phonoamplifier has two stages. :irst stage has an amplification of about 8@,second stage about [email protected] the total gain is 7@@@.0ontinuous variation of gain can

be achieved through 88 (ilo=ohms potentiometer.

FILTERS:

igh pass filter of gradual slope of attenuation is used. &and pass filters produce transients and mas(s the splitting of heart sounds. "n abnormalhearts additional heart sounds called murmurs. "n the case of murmurs wheregreater selectivity is re5uired, high pass filters with sharper slopes are re5uired.


8/12/2019 90354868 Lie Detector



RESPIRATORY RATE:

Pneumographs, rubber tubes filled with air are placed around thetest sub'ect6s chest and abdomen. )hen the chest or abdominal muscles e pand, theair inside the tubes is displaced. "n an analog polygraphs, the displayed air acts on a

bellows, an accordion li(e device that contracts when the tube e pands. digital polygraph also uses the pneumographs, but employs transducers to convert theenergy of the displayed air in to electronic signals.

ELECTRODERMAL ACTIVITY:

$his is also called as galvanic s(inresistance. $his is basically a measure of sweat on finger tipsas they are one of the most porous areas of the body. )esweat more when we are under stress. :inger plates calledgalvanometers are attached to the fingers of the sub'ect.$hese plates measures s(ins ability to conduct electricity.

)hen s(in is hydrated, it conducts electricity more easily than when it is dry.INTEST:

$his is the actual test. ere the e aminer as(s certain number of 5uestionsout of which only a few will be relevant to the issue or crime being investigated.$he others are “control 5uestionsE. control 5uestion is a very general 5uestion,such as “have you ever stolen anything in your life EGa type of 5uestion that is so

broadthat almost no one can honestly respond with aEnoE.if the person answers no, thee aminer gets an idea of the reaction that the e aminee demonstrates when beingdeceptive. )hile as(ing 5uestions he simultaneously monitors the physiologicalreactions which are plotted as graphs in the monitor.POSTTEST + $he e aminer analyses the data of physiological responses and ma(es adetermination regarding whether the person has been deceptive or not. "f there aresignificant fluctuations that show up in the results, this may signal that the sub'ect


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Seminar Report Lie Detector has been deceptive. -specially when a person displays different responses to a5uestion that was as(ed repeatedly.

MISINTERPRETATION OF RESULTS + $here are times when a polygraph e aminer misinterprets a person6s

reaction to a particular 5uestion. $he human factor of a polygraph e am and thesub'ective nature of the test are two reasons why polygraph e am results are seldomadmissible in court. ere are two ways that a response can be misinterpreted+

• : LS- P/S"$"2-+ $he response of a truthful person is found to be deceptive.

• : LS- %-3 $"2-+ $he response of a deceptive person is found to be truthful.

"f we loo( at laboratory=based studies, false positive errors occur morethan false=negative errors. 0ritics of polygraph e ams say that false=positive errors occur in realworld scenarios, which biases the system against the truthful person. $hese errorsare li(ely to occur if the e aminer has not prepared the e aminee properly or if thee aminer misreads the data following an e am.

APPLICATIONS:

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CONCLUSION:

merican polygraph association has certified that a polygraph is H@I toHJI truthful. $he outputs from the post=test are fed in to the computer, which usesan algorithm developed by applied physics lab of Kohannes op(ins 4niversity. "t6sall up to the e perience of the e aminers to line up the 5uestions and interpretingthe results. $he merican government now reali?es their mista(e of overseeing the

test and not sub'ecting Robert ansenn ;who was spying on merica for Russia< tothis assessment. fter this incident the merican government is (een in using thisin various fields. $hey want this to get upgraded to be 7@@I accurate. )ith such a

progress in this field why can6t an instrument read a person6s mind! #es, it will. "na very short span of time this field will spread widely all over the world.and oneday, very soon our country6s dream of “ satyameva jayate Ewill be fulfilled throughthis.


8/12/2019 90354868 Lie Detector




90354868 lie detector

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