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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.
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