No one has yet created an infallible tool to spot a liar. It's only possible to measure a person's emotions and then determine whether these are consistent with the person being truthful. That's the idea behind the polygraph, which measures increases in sweating, heart rate and breathing rate that are associated with heightened emotion. New technology that analyzes faces may improve on this classic "lie detector" by revealing not only the presence of emotion but also the type of emotion. For example, a man who is asked "Did you kill your wife?" during a polygraph test might "fail" because he felt either anger or disgust — emotions that cause similar physical reactions but have different implications for innocence or guilt. A facial analysis, on the other hand, might distinguish between anger and disgust, providing police with a valuable insight.

Polygraph tests are not normally admissible in courts of law in the United States, but they are often used when both sides agree in advance, such as for workplace security clearances. Unfortunately, innocent people sometimes fail the tests, and automatic facial measurement systems are not yet ready to take their place.

Comprehensive systems are still at least 5 to 10 years away, and they will need to be tested extensively before they can even be considered for use in the legal system, the workplace or elsewhere.

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Reprinted from the HHMI Bulletin,
May 2001, pages 12-17.
©2001 Howard Hughes Medical Institute