Police Using Voice Stress Analysis to Detect Lies
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.
Another company, Diogenes, sells a similar device called the Lantern for about $4,700, plus $950 for one week of training.
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.
When confronted with test results, a suspect often confesses, Elverson said.
"Some people obviously are still going to lie, but we've had good success with it so far," he said.
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.
William Endler, director of international operations for the National Institute for Truth Verification, believes polygraph examiners have a strong financial incentive for bashing voice stress analysis.
"In a lot of the departments we've gone into, after they see the ease of operation, the polygraph gets phased out. They are losing their revenue, so they are against it," said Endler, a former Syracuse, Ind., police chief.
Jim Kouri, vice president of the National Association of Chiefs of Police, begs to differ. Among law enforcement, the voice stress analyzer is "not as popular as the polygraph because it's not as reliable as the polygraph," he said.
Endler said 10 states ban law enforcement agencies from using voice stress analysis: Illinois, Oklahoma, Michigan, Texas, Vermont, Virginia, South Carolina, Kentucky, North Dakota and Oregon.
Detective Elverson still stands by it.
"You can't use it to arrest someone, but it helps the investigator know which way to go," he said. "Personally, I believe it works."