Thermal Imaging

Accuracy as a Lie Detection Tool

In 2002, Ioannis Pavlidis and colleagues proposed thermal imaging as a lie detection tool in a brief communication in Nature. Departing from the assumption that liars experience anxiety about being caught, liars are expected to show a fight-or-flight reaction. This reaction is the response of the sympathetic nervous system to a stressful event, preparing the body to fight or flee, and is characterized by an increased blood flow to the brain and muscles. The increase in blood flow leads to a heightened body temperature, which can be picked up by a thermal imaging camera. Prior research indeed showed that a startle response elicited by an auditory noise is accompanied by heating of body temperature, particularly around the eyes. By focusing on thermal patterns around the eyes, Pavlidis and colleagues could correctly classify 75 [Page 887]percent of the liars and 90 percent of the truth-tellers in a mock crime study, when participants replied to the question “Have you stolen $20?”

The authors claimed that the thermal imaging technique has an accuracy comparable to that of the polygraph. Moreover, because thermal imaging can occur rapidly, without the need for skilled staff or physical contact, they argued that it could be used for instantaneous lie detection without the subject being aware. One apparent application they suggest would be mass airport screening, in which the thermal pattern of every passenger's face could be measured nonintrusively, thereby instantly identifying the wrongdoers among them. In an erratum, the authors later toned down their claims, stating it was premature to propose thermal imaging for large-scale truth screening.

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