The Computerized Voice Stress Analyzer (CVSA)
Throughout history man has tried to identify a single, unique physiological responses that would only be present when a person lied. In the 1970’s a phenomenon known as a vocal micro tremor was identified and seemed to be only present in a person’s voice during periods of high stress. Before any serious research could be conducted, entrepreneurs seized the opportunity to manufacture a lie-detector that would require practically no training to use and could even be used surreptitiously. The device was called the psychological stress evaluator (PSE) and law enforcement agencies reported that the PSE greatly increased their confession rates during interrogation. The reputation of the successful use of the device soon spread and police departments across the country purchased the machine and sent investigators to a short seminar to learn how to use it effectively during an interrogation.
The scientific community, however, recognized the distinction between utility and validity. Utility is a measure of usefulness. A device may be considered useful because it is less expensive or faster than other alternatives, or creates a higher incident of desired results. Validity, on the other hand, is established when (1) the device measures what it purports to measure i.e., is accurate and, (2) the results can be reproduced with consistency i.e., is reliable. Validity studies conducted on the PSE by independent researches found that the presence or absence of a micro tremor had little correlation to whether or not a person was telling the truth. Essentially, the PSE represented nothing more than a psychological prop to elicit confessions. Manufacturers were probably correct in their claim that investigators were eliciting more confessions and faster confessions with the use of the PSE. However, any claim of the PSE’s validly to detect deception were impossible to support. By the 1980’s a number of states had passed legislation prohibiting the use of the PSE and courts suppressed confessions that were extracted through the use of the PSE, correctly citing psychological coercion.
In response to these setbacks, manufacturers re-tooled their factory and came up with the Computerized Voice Stress Analyzer (CVSA), claiming that it represented completely new technology. The criteria for detecting deception, however, was still centered around the micro tremor. What they did come up with was a more powerful confession inducer. Rather than the investigator simply telling the suspect that his PSE charts indicated deception, with the CVSA the investigator could actually show the suspect a printout of the computer’s analysis of his micro tremors and purported deception. While we advocate the limited use of trickery and deceit in an effort to learn the truth, investigators must appreciate that legally these efforts cannot shock the conscience of the community.
Repackaging flawed technology obviously will not change the underlying validity of the technology. It may, however, increase the liability risks. We have reviewed a number of video-taped interrogations of homicide suspects who ultimately confessed to the crimes they were questioned about. The repeated reference to CVSA results during these interrogations, along with exaggerated claims of its validity, clearly contribute to the involuntariness of the suspects’ confessions. One suspect went so far as to say, “Even though I don’t remember killing (the victim) your test shows that I did so I must have.”
The following is a summary of some of the studies that have been conducted on the CVSA:
An analysis of Voice Responses for the Detection of Deception, 1994. Victor L. Cestaro and Andre B. Dollins
Results: “Results of the analyses suggest that no single human voice measures, as collected and analyzed in this study, can reliably discriminate between truthful and deceptive responses.”
A Comparison between Decision Accuracy Rates Obtained Using the Polygraph Instrumentation and the Computer Voice Stress Analyzer (CVSA) in the Absence of Jeopardy, 1995. Victor L. Cestro Department of Defense Polygraph Institute.
Results: “The decision accuracy utilizing the traditional polygraph and its procedures was significantly higher than that of the CVSA approach.”
A Comparison of Accuracy Rates Between Detection of Deception Examinations Using the Polygraph and the Computer Voice Stress Analyzer in a Mock Crime Scenario, 1996. Victor Cestaro, Department of Defense Polygraph Institute.
Results: “The data analysis indicate that within the test paradigm used in this study, neither the polygraph nor the CVSA test chart evaluators were able to reliably differentiate between truthful responses and deception at levels greater than chance.”
Effectiveness of Detection of Deception Examinations Using the Computer Voice Stress Analyzer (CVSA), 1998. Michael Janniro and Victor Cestaro.
Results: “In summary, although there is evidence to support the basic electrical theory of operation of the CVSA, the instrument failed to function in a manner that would allow examiners to discriminate between truthful and deceptive test subjects.”
The average accuracy rate of the CVSA in these studies was 38.7%.