Why Not Voice Stress Analysis?

Voice stress analysis

Voice stress analysis (VSA) was developed in the 1970’s by three American army personnel. These men were first tasked with enabling voice identification of intercepted radio communications. The premise is that something known as the physiological microtremor will change due to the fight or flight response. These changes were supposed to be noticeable in graphic representations of a subject’s answers.

It was first accepted as a means of psychophysiological detection of deception however many studies since have concluded that it is unacceptable. One study even states that voice stress analysis yields results ‘no better than flipping a coin’. A simple google search for voice stress analysis will bring you conflicting results. Regardless, an extensive review of literature published by the National Research Council in 2003 regarding biofeedback polygraph and possible alternatives also concluded that there is ‘little to no scientific evidence for the use of voice based lie detection.

Voice stress analysis

More reasons why voice stress analysis may not work.

There are several issues with voice stress analysis apart from these results. The physiological microtremor is present in all mammals at normal frequencies of 8-12Hz. The initial studies by Lippold saw that under physiological stress it is reduced to 4-6Hz. No microphone available to the consumer is capable of picking up these frequencies. Most microphones available only have frequency ranges of 100Hz – 10kHz. Even the better ones do not go below 20Hz. Therefore these microphones are not collecting the correct frequencies to even display the physiological microtremor within an answer’s representation.

Also, the only physiological reactions being recorded are at the moment of the subject’s answer which is a maximum of one second. Although a physiological response is generally initiated within milliseconds of a perceived threat they are different for each individual and can last for up to 15 seconds. Thus voice stress analysis is taking only a tiny portion of the response (if any) to be analysed, as opposed to traditional polygraph which is continuously measuring. This can lead to serious errors.

The three largest associations; the American polygraph association (APA), the European polygraph association (EPA) and the Israeli computerised polygraph association (ICPA) all do NOT condone Voice Stress Analysis (VSA) in any form.

Standard voice stress analysis display

There are also programs available for VSA aka Voice Stress Detection (VSD), claiming autonomous scoring. These have been thoroughly tested by our institute and proven faulty. A single recording of one answer was played repeatedly directly into the system and the values returned differed each and every time. Definitely not what one would expect.

All in all, voice stress analysis still has potential despite it’s flaws but a lot more research and development needs to be done before it can be truly accepted as a justifiable detection of deception technique. You would definitely be better off undertaking one of our online polygraph examiner courses in order to join the field of deception detection.