The Truth Hurts: Scientists Question Voice-Based Lie Detection

By Ehrenberg, Rachel | Science News, July 3, 2010 | Go to article overview

The Truth Hurts: Scientists Question Voice-Based Lie Detection


Ehrenberg, Rachel, Science News


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Truster-Pro and the Vericator may sound like devices Wile E. Coyote would order from the Acme Co., but they are real technologies for detecting lies. Unlike the traditional polygraph, which zeroes in on factors such as pulse and breathing rate, these analyzers aim to assess veracity based solely on speech.

Police departments shell out thousands of dollars on such devices--known collectively as voice stress analyzers--in an attempt to tune in to vocal consequences of lying. Airports are considering versions for security screening purposes, and insurance companies may employ the polygraph alternatives to detect fraud.

But beyond their crime-fighting objective, these tools have something less noble in common with their predecessor: a poor track record in actually telling truth from deception.

Scientists evaluating Truster-Pro, the Vericator and newer analyzer models repeatedly report lackluster results. Now research finds that two of the most commonly used voice stress analyzers can discern lies from truth at roughly chance levels--no better than flipping a coin.

"Quite frankly, they're bogus. There's no scientific basis whatsoever for them," says John H.L. Hansen, head of the Center for Robust Speech Systems at the University of Texas at Dallas. "Law enforcement agencies--they're spending a lot of money on these things. It just doesn't make sense."

A lackluster alternative

Many agencies have been seeking alternatives to the polygraph, especially following a 2003 National Research Council report that concluded that the physiological responses measured, such as increased heart rate, can identify stress but not pinpoint deception. Champions of voice stress analyzers often cite this report among other criticisms of polygraphs as a reason to switch to voice-based lie detection. The National Institute for Truth Verification--a company based in West Palm Beach, Fla., that makes a widely used device called the Computer Voice Stress Analyzer--has a page on its website dedicated to denigrating this traditional lie detector, titled "Polygraph Failures Continue to Mount."

But the institute fails to mention the same report's conclusions about alternatives to the polygraph, including voice analyzers. Research offers "little or no scientific basis for the use of the computer voice stress analyzer or similar voice measurement instruments as an alternative to the polygraph for the detection of deception," the report noted.

As with the old lie detector, creators of voice analyzers usually avoid direct claims that the units detect deception, speech perception expert James Harnsberger said in April in Baltimore at a meeting of the Acoustical Society of America. Instead, the developers contend that physiological changes that occur when someone is lying trigger consistent, readable changes in voice. "There's an assumption that there's a direct mind-mouth link," said Harnsberger, of the University of Florida in Gainesville.

Speech does in fact change when a person is under stress, both in frequency and in the amount of time spent on segments of words, says Hansen. But, as with the polygraph, distinguishing stress related to deception from stress related to fatigue, anxiety or fear is not so easy.

"No one has identified an acoustic signature that is unique to deception," says Mitchell Sommers, director of the Speech and Hearing Laboratory at Washington University in St. Louis.

Two large studies, one conducted in a jail and another in a lab, suggest that the two most widely used voice stress analyzers haven't pinpointed such a signature, either.

One voice analyzer--Layered Voice Analysis, created by the Israel-based company Nemesysco--purports to use more than 8,000 algorithms to tune in to three states of mind: excitement, stress and cognitive dissonance (the psychological discomfort that comes with holding two conflicting views at once). …

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