Thermal imaging offers a promising hands-off approach to mass security screening.
We have developed a high-definition thermal-imaging technique that can detect attempted deceit by recording the thermal patterns from people's faces. This technique has an accuracy comparable to that of polygraph examination by experts and has potential for application in remote and rapid security screening, without the need for skilled staff or physical contact.
There is an urgent need to devise technologies that can be used for automated, high-throughput screening to identify individuals intending to perform acts of terrorism. At present, practicalities dictate that we rely on subjective assessment of responses to brief questions such as “Did you pack your own bags?” and “Why are you entering this facility?”
Although polygraph examinations, which have high precision when applied by experts1, are good at identifying liars, they are impracticable for mass screening because skilled operators are needed, subjects have to be attached to instrumentation for several minutes, data analysis is time-consuming and the interpretation of data is delayed.
We explored the possibility of using high-definition thermal imaging of the face for detecting deceit2 because it enables rapid automated analysis of changes in regional facial blood flow to be quantified3,4. We have shown previously2 that auditory startling is associated with a specific facial 'thermal signature', in which there is instantaneous warming around the eyes — probably as part of a fright/flight response mediated by the sympathetic nervous system5,6. Although the psychophysiology of startling differs from volitional deception, the nonspecificity of this facial thermal signature is reminiscent of the nonspecific variables monitored during a polygraph (respiration, pulse, relative blood pressure and electrodermal response). Were this thermal signature to accompany lying, independently of startling, it could be used for instantaneous lie detection without the subject even being aware of the test.
We therefore asked volunteers to commit a mock crime and then testify to their innocence under experimental conditions at the US Department of Defense Polygraph Institute (DoDPI; http://www.dodpi.army.mil)7. Twenty individuals were randomly assigned to stab a mannequin, rob it of $20 and then assert their innocence of the 'crime'. Control subjects had no knowledge of the crime or of the crime scene. The thermal imaging system correctly categorized 83% of these subjects (Fig. 1); three-quarters (6 of 8) of the guilty individuals were correctly identified as guilty and 90% (11 of 12) of the innocent individuals were correctly categorized as innocent. Traditional polygraphs, performed by experts at DoDPI on the same subjects, correctly categorized 70% of the subjects: 6 of 8 subjects were correctly identified as guilty and 8 of 12 were correctly identified as innocent. Under these experimental conditions, the accuracy of the thermal imaging system was comparable to that of the traditional polygraph.
High-definition thermal imaging of the face is therefore a promising technology that should allow psychological responses to be detected and analysed rapidly and without physical contact, in the absence of trained staff and in a variety of different situations.
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