Councils are facing questions about their use of lie detectors in attempts to catch benefits cheats over the phone. The idea is to listen out for subtle changes in the voice that might indicate that someone isn’t telling the truth about their circumstances.
But there are serious concerns about the technology being used and a chronic lack of evidence to support the claims made about it.
The UK government first tried out lie detection tools with offenders in 2004, despite findings from the US National Research Council that suggested research in this area had not “progressed over time in the manner of a typical scientific field”. In a 2003 assessment, the council warned that research into testing for deception using physiological monitors had failed to “strengthen its scientific underpinnings in any significant manner”.
The main problem is that both voice stress analysis software and the polygraph, which monitors blood pressure, are based on the assumption that liars are more behaviourally aroused than truth tellers because they are afraid of being caught. In reality, displays of arousal depend on many factors, not least the circumstances in which we tell a lie, the individual differences between people and how serious the lie is or the potential repercussions of being found out.
In fact, liars often fail to show an increase in arousal. This can be attributed to a number of causes. Liars do not necessarily experience a fear of being caught or may even be able to control their level of arousal during a test.
On the other hand, truth tellers may show increased arousal due to a fear of not being believed. In the case of the UK government’s attempts to bring in lie detection, this might mean a fear of losing benefits.
Lying or just stressed?
The voice stress analyser, or voice risk analyser, uses microphones attached to computers to detect and display readings for the intensity, frequency, pitch, harmonics and micro-tremors of the voice.
This is based on established theory, conducted via empirical research, that changes to the voice indicate stress or arousal. When we are aroused our muscles tense and tighten and, when this happens, these muscles vibrate at a higher frequency leading to an increase in pitch.
When voice stress analysis was first developed, it was hailed as an alternative to the polygraph because it is a non-invasive process and can even be conducted without the person being tested even knowing. Unfortunately, this is the only improvement on the polygraph. The only real difference between the two is that a different physiological response is being measured.
Both techniques suffer from methodological and theoretical problems, particularly if those conducting the test don’t spend time asking the examinee to lie and tell the truth in response to a series of control questions to test their responses first. Without this, there is no comparison between how an individual behaves when being truthful compared to when they lie.
They key point is that voice stress analysis offers a measure of stress or arousal and this is not the same as measuring deception. There is still an insignificant amount of data to link the signs of stress and negative emotion in the human voice with lying.
Despite disappointing results from numerous scientific studieson the validity of these systems, voice analysis continues to be popular and several manufacturers produce variations of voice analysis software, which are sold as user-friendly computer devices. There is no evidence to suggest that these programs work at a level any better than chance.
Even ignoring the lack of any empirical support for its application, voice stress analysis is an outdated tool. Recent advances in the area of deception detection acknowledge that you need to take a multi-channel approach, looking at both verbal and non-verbal behavioural cues while taking context into account.
This is one of the aims of on-going research being conducted within the Centre for Emotions, Credibility and Deception at the University of Central Lancashire. While technology, and in particular measures of real-time body motion and language use, undoubtedly have much to contribute to the field of deception detection, we need to ensure that the work is carried out in a rigorous manner, and is based on sound methodology and theory. Voice stress analysis is not.