'Voice stress' technology supplements polygraph

PHILADELPHIA -- Police want to know if a suspect is lying, but the polygraph test comes back inconclusive.

What's an exasperated interrogator to do?

Increasingly, law enforcement agencies are using a technology that measures "voice stress" -- small frequency modulations in the human voice that supposedly occur whenever someone is lying.

Some police officials swear by the Computer Voice Stress Analyzer -- a laptop computer, software and microphone package that promises to catch deception.

Proponents call it just as reliable as a polygraph but more portable, less intrusive and easier to use. Additionally, law enforcement in some states can surreptitiously record a suspect's voice, then run the tape through the analyzer.

The industry hopes to get a boost from the new federal aviation safety law, enacted in the wake of the Sept. 11 attacks. A provision of the law calls for the use of "voice stress analysis, biometrics or other technologies" to prevent terrorists from boarding airplanes.

But how well does it work? Studies suggest that voice stress analysis is no better than chance at detecting deception. It is banned in several states and, like the polygraph, it is not admissible in any court of law.

"There is no scientific evidence to validate it," said Victor Cestaro, a retired biological psychologist who conducted research on voice stress for the U.S. Department of Defense Polygraph Institute.

Nevertheless, the National Institute for Truth Verification, the West Palm Beach, Fla., company that makes the market-leading Computer Voice Stress Analyzer, says it has sold the devices to 1,100 law enforcement agencies across the country.

The cost: more than $11,000 for the analyzer and a six-day training course.

Detective Al Elverson and his colleagues in the Upper Merion Township Police Department in suburban Philadelphia say they have used the Computer Voice Stress Analyzer to nab suspects for child abuse, employee theft, stolen credit cards and other crimes.

Research into voice analysis began in the late 1950s when scientists identified a "physiological tremor" -- tiny, involuntary oscillations in a muscle produced during times of stress. In the early 1970s, three retired military officers invented the first voice analyzer, the Psychological Stress Evaluator, based on the research.

Voice analyzers function on the same "fight-or-flight" principles as the polygraph, a technology little changed since its invention more than 80 years ago.

But voice stress analysis has plenty of critics.

Chief among them is the American Polygraph Association, which led a campaign against the technique two decades ago and again in 1998. The group says no independent research exists to validate voice stress analysis.

Ten states ban law enforcement agencies from using voice stress analysis.