AFRL-R 00-102
AFRL Study Finds Voice Analysis Accurately Detects Stress
ROME, N.Y., Oct. 23, 2000 - Law enforcement personnel may soon have an efficient and unobtrusive – even covert - method to determine deception during investigations.
A three-year study by Air Force Research Laboratory (AFRL) Information Directorate engineers has concluded that several features of voice stress analysis are effective for detecting when a person is answering questions under stress. Funded by the National Institute of Justice (NIJ), the research investigated the ability to detect and classify stress in an individual's voice and evaluated the effectiveness of commercially available voice stress analyzers. AFRL is interested in voice stress to improve the performance of voice recognition technologies. NIJ's interest in voice stress is for police investigation. "We concluded that several features in an individual’s speech pattern are different under stress," said Darren M. Haddad, program manager in the directorate’s Information and Intelligence Exploitation Division. "However, there is insufficient evidence at this time to say that voice stress analyzers detect deception. There are numerous forms of stress, ranging from deception to anger and fear." The goal of the study was to determine the scientific value and utility of existing voice stress analysis technology for law enforcement applications. Voice stress analyzers have been marketed commercially to law enforcement agencies for more than a decade. The systems are advertised as being cheaper, easier to use, and less constrained in their operation than polygraph machines that must be physically attached to the speaker's body. A person does not even have to know the voice stress analysis system is being used, as the technology is claimed to be effective on telephone speech or tape recordings. "We looked at different types of features and how those features could detect stress," said Haddad. "The more voice features you use, the more accurate your results. We also looked at what type of recording media should be used: which ones performed the best and which ones gave corrupt results." "The Department of Defense Polygraph Institute provided us with tapes of investigations from two murder cases where the suspects eventually confessed and were found guilty," said Haddad. "Using voice stress analyzers provided by two vendors, both machines were accurate on 45 out of 45 instances." AFRL engineers will now propose a follow-on effort to investigate methods that differentiate deception stress from other types of stress. The research, in conjunction with the NIJ’s Northeast Law Enforcement and Corrections Technology Center at Rome, will also involve the Department of Defense Polygraph Institute and Walter Reed Army Medical Center.