This Electronics Seminar Topic deals with the following:
Psycho Physiological Credibility Assessment
INTRODUCTION
Lies are part of human life! People often tell lies to deceive others. many of us have heard about “lie detector “,some where seen in movies or read it in fiction stories. Does anything of this sort really exist? If yes, does it really detect lies? Yes it does. The first thing that comes to our mind is how an instrument with some electronic components can read out our mind. Though science and technology are growing at the speed of light, has it reached a stage where it can read mind? Not exactly! But it can approach to that stage by monitoring the physiological reaction by plotting graphs.
WHAT IT IS
Polygraph, a multigraph of physiological reaction. Lie detector or polygraph as it is technically called is an instrument that monitors the physiological reaction. It can detect only deceptive behavior of human mapped to lies. The underlying factor of this concept is a person is subjected to stress while trying to decieve.Biomedical technology is used to bring out this deception. Lying is a sort of defense mechanism used by human to avoid trouble but when it is a serious crime like 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
When someone decieves, sometimes we are able to guess by his/her reactions whether they are deceiving or not. But most of the times we are unable to predict this. This principle of guessing is more widely used with the growing technologies to monitor the physiological reactions. It monitors the involuntary change that occurs in the body when the person is under stress. Biomedical instruments are used to monitor those physiological reactions. They are:
- HEART RATE
- RESPIRATORY RATE
- ELECTRO DERMAL ACTIVITY
- CHANGE IN BLOOD PRESSURE
TAKING THE TEST:
This test challenges the mind of the most stoical person. All the equipments are attached to the subject’s body. A polygraph exam is along process that can be divided up in to several Stages.
1. PRETEST
2. INTEST
3. POST TEST
Forensic psychophysiologist, a trained examiner examines the subject (pretest) .he questions the subject (intest) and look for fluctuations in the graphs produced (post-test) to find the amount of deception.
PRETEST:
This consists of an interview between the examiner and the examinee, where the two individuals get to learn about each other. This may last about one hour. During this the examiner gets the examinee’s side of the story concerning the events under investigation.while the subject is sitting there answering questions, the examiner also profiles the examinee. The examiner sees how the subject responds to questions and processes information. The examiner designs questions that are specific to the issue under investigation. The physiological reactions that are monitored are heart rate , heart sound,respiratory rate,galvanic skin resistance.
HEART RATE AS A FACTOR IN DETECTION OF DECEPTION:
Normally a heart beats 72 times per minute. But while deceiving, the subject is under stress, hence the rate of heart beat increases. That is the frequency of heart rate increases. This involuntary response going in a person’s body is detected by forensic psycho physiologist.hence by monitoring heart beat one can detect deception. In heart rate there are two parameters monitored.
1. Bioelectric signals produced by heart muscle cells.
2. Sound produced by the heart.
WHAT ARE BIOELECTRIC SIGNALS?
Certain types of cells inside the body, such as nerve and muscle cells are encased in semi permeable membrane that permits some substance to pass through the membrane and block the others. Surrounding the cells are body fluids. These are conductive solutions containing ions. The principle ions are sodium, potassium and chloride. The cell membrane readily permits potassium and chloride ions and block sodium ions. Since a balance is required between inside and outside of the cell, both according to concentration and electric charge, the inability of sodium to penetrate the membrane results in two condition.
1. The concentration of sodium ions inside the cell becomes much lower than the fluid outside. Since sodium ions are positive, they would make the outside of the cell more positive.
2. To balance electric charge, additional potassium ions which are also positive enter the cell, making the concentration higher inside than outside.
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