In a new study, researchers have developed a new test that could help police to determine when criminals or witnesses are lying about their knowledge of a person’s identity.
The research was conducted by a team from the University of Stirling.
Police officers routinely use photographs of faces to establish key identities in crimes. Some witnesses are honest—but many are hostile and intentionally conceal knowledge of known identities.
For example, criminal networks—such as terrorist groups—might deny knowledge to protect one another, or a victim might be too afraid to identify their attacker.
In the study, the team examined whether liars could hide their reaction when shown a photograph of a familiar face—and found that they could not.
The team tracked people’s eye movements when they denied knowledge of someone they knew.
Instead of looking for signs of lying directly, the team looked for markers of recognition in patterns of eye fixations—such as how individuals looked at a photograph of someone they recognized; compared to someone they did not.
The main aim was to determine if liars could conceal recognition by following instructions to look at every familiar and unfamiliar face with the same sequence of eye fixations—in short, they could not.
The researchers used a process known as the concealed information test (CIT), in which participants’ eye movements are tracked while viewing photographs of familiar and unfamiliar faces on a computer screen.
In each test, participants denied knowledge of one familiar identity while correctly rejecting genuinely unfamiliar faces, by pressing a button and saying ‘no’.
The team found that most liars could not fully conceal markers of face recognition—either spontaneously, or during explicit strategies to look at every face with the same sequence of eye movements.
Moreover, these explicit attempts uncovered more instances of concealment than spontaneous attempts to hide knowledge.
The team explains that the harder that individuals tried to conceal knowledge, the more markers of recognition there were.
These results suggest that it is difficult to conceal multiple markers of recognition at the same time.
The CIT is currently used in the field practice in Japan to uncover guilty knowledge about a crime, which only the culprit would know, such as a murder weapon.
The lead author of the study is Dr. Ailsa Millen, Research Fellow in Psychology at Stirling.
The study is published in Principles and Implications.
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