Voice Stress - Principle and Origins

Principle and Origins

VSA is based on the presence of infrasonic components of human voice not audible to observers, caused by a physiological phenomenon present in muscles called "microtremor". It was discovered in 1957 by British physiologist Olaf Lippold. Further investigation by other researchers explored the possibility of the presence of microtremor in the muscles controlling the voicebox (Larynx.) The experiment was made by attaching electrodes to the cricothyroid muscle and the posterior cricoarytenoid muscle and measuring EMG signals.

Detecting microtremor during sustained speech was not deemed possible because the EMG activity changed too rapidly. The experiment was therefore limited to measuring the presence of microtremor in the frequency range of 1 through 20 Hz in sustained vowel phonation, but yielded no positive results. It was concluded that "the electrical energy was randomly distributed throughout the spectrum." The conclusive research on microtremor in voice production has consequently been used to develop VSA technologies.

VSA technology is said to record psychophysiological stress responses that are present in human voice, when a person suffers psychological stress in response to a stimulus (question) and where the consequences of lying may be dire for the subject being 'tested'. In the Detection Of Deception (DOD) scenario, the voice-stress produced in response to a Relevant Question ("did you do it?") is referred to as psychological stress or 'deceptive stress'. No DOD technology can detect a lie or truth unequivocally. It is the fear of being exposed as lying to the question being posed that produces the 'high stress' voice signature, aka voice graph or voice tracing. The technique's accuracy remains debated. There are independent research studies that support the use of VSA as a reliable lie detection technology, whilst there are other studies that dispute its reliability. This is equally true for polygraph. The US NAS 2003 study on polygraph threw the polygraph industry into disarray when it reported that studies were unscientific and unreliable and that there was no promise of the technology improving.

The main difference in the method of operation between LVA and VSA is based on the analyzed frequencies ranges: while VSA focuses on the 8–14 Hz range which is recorded via an omni-directionalphone. LVA utilises components of the voice such as pitch and tone, which are conrollable by the user, also varying according to his/her emotions at time of utterance. Change of emotions produce unreliable results being not particularly relevant to DOD. .