The polygraph is said to be accurate but not full proof according to the lie detector test London UK agencies. The polygraph uses a blood pressure device to measure the blood pressure and a pnuemograph attached to the chest of to check the changes in the respiration and breathing patterns. Electrodes are also attached to the finger tips to check the conductivity of the person. If there are any unusual changes in the various autonomous system and rise in the blood pressure or breathing, it shows that the person is hiding something. It is a psychological assumption that the people show an increase in fear and anxiety in certain pressure questions compared to that of relatively easy questions.
Historically speaking, William Moulton Marston, an alumni of Harvard law school did an project where he designed a machine that indicated strong positive correlation between systolic blood pressure and lying. Marston then lobbied for its use in courts and carefully placed himself in history as “the father of polygraph”. After him Dr. John Augustus Larson from the University of California designed a device which measured a person’s blood pressure and breathing. This machine was then used by the Berkeley police department. Larson’s design was more developed by his protégé Leonard Keeler by making it portable and added the galvanic skin response. This device was then acquired by the FBI and has been dubbed as the modern polygraph.
The polygraph recently has come under a lot of criticism as the results are said to be not reliable. Studies have shown that many introverts are immune to the tests as they don’t show any major change in the data. Further there have been proof that the device can be cheated on by the use of sedatives that keep the heart beat and the blood pressure in a low controlled level. Trained professionals can even con the tests by being very vague about their answers and answering only in positive and negative responses. These people are trained to keep their emotions in check by breathing in a monotonous way and by keeping calm. So the polygraph doesn’t show any radical change in the reading so the lies of the trained professional go un noticed.
Many a times innocent people come under the heat of the situation and show a huge spike in the readings as they can’t control their emotions. They start being imaginative and think about everything that could be happening to them. This leads to an innocent person getting caught as guilty and a wrong person getting prosecuted.
So the polygraph test has come under a lot of criticism lately and therefore many new methods are being worked upon that can work as a lie detector and is most reliable. One of these tests is the voice error analysis which shows changes in the pitch, frequency and tremors. Scientifically speaking if a person is lying there is a complete unconscious change in the characteristics of the sound of the person and therefore this test could be much more reliable.