Lie detector Test

Lie detector Test
The first modern “lie detector” – Polygraph test was developed by John A. Larson, a medical student at the University of California in the USA, in collaboration with a police officer. It is called a polygraph because it is capable of recording blood pressure, pulse and respiration continuously and simultaneously.The police first used the polygraph as an interrogation device in 1924.

It is considered that physiological phenomenon such as blood pressure, pulse and respiration  are affected by a person’s emotional condition. These phenomenon are not generally under voluntary control.

A pneumograph tube is fastened around the subject’s chest. A blood pressure cuff is strapped around his arm. The operator puts questions to the the subject, changes in the physiological phenomenon are recorded on a moving graph paper as in an ECG machine. A long questionnaire is prepared in which loaded questions are mingled with a large number of innocuous questions.

Experts then analyze the data and correlate the subject’s response to specific questions. Then the experts decide on which questions the subject had lied and where he was truthful.

Though in use for almost for 80 years, the polygraph test’s reliability is not accepted universally. The results are not always judicially acceptable.