Polygraph Test

The Central Bureau of Investigation (CBI) is planning to conduct a Polygraph test on Sandip Ghosh, the former principal of RG Kar Medical College and Hospital.

• CBI already has the permission from a local court to conduct a polygraph test on the  prime accused, Sanjoy Roy.

About Polygraph Test

• A polygraph test or a  ‘lie-detector test’ is a psychological diagnostic test tool used by crime agencies to investigate a case.
• Techniques to Perform: A polygraph examiner measures the subjects physiological responses by a three- or four-channel polygraph machine that records responses on a moving chart. 
  • The examination duration may vary between one to three hours
• Assessment: The polygraph examiner obtains a subject’s responses to a carefully structured set of questions and based on which the assessment of truthfulness or deception is done.
• Pre test Interview: Often a pretest interview is also conducted before a polygraph examination to induce anxiety in subjects with deceptive tendencies and inform them of their legal rights.
• Legal provision:
  • Article 20(3): The Right against Self Incrimination gives accused the right to not consent to any such test. Also the confessions from the test cannot be submitted as evidence in the court. 
    • But any subsequent revelation in the case, which is a result of such a confession, is admissible, as laid down in a 2010 Selvi & Ors vs State of Karnataka & Anr’ Supreme Court Judgement.
• Types of Physiological Response Measured:Three types of physiological responses are measured during a polygraph test
  • The Rate and Depth of Respiration: A medical device called Pneumographs is strapped around the chest and the abdomen to measure respiration.
  • Cardiovascular Activity: A blood pressure cuff (sphygmomanometer) is placed around the bicep to measure a subject’s cardiovascular.
  • Electrodermal Response: Electrodermal Response (EDR) also known as galvanic skin response (GSR) measures perspiration levels using electrodes attached to the fingertips.

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