S1: Eye see through you! Eye tracking unmasks concealed face recognition despite countermeasures
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Description: Criminal associates such as terrorist members are likely to deny knowing members of their network when questioned by police. Eye tracking research suggests that lies about familiar faces can be detected by distinct markers of recognition (e.g. fewer fixations and longer fixation durations) across multiple eye fixation parameters. However, the effect of explicit eye movement strategies to concealed recognition on such markers has not been examined. Our aim was to assess the impact of fixed-sequence eye movement strategies (across the forehead, ears, eyes, nose, mouth and chin) on markers of familiar face recognition. Participants were assigned to one of two groups: (1) A standard guilty group who were simply instructed to conceal knowledge but with no specific instructions on how to do so, and (2) A countermeasures group who were instructed to look at every familiar and unfamiliar face the same way by executing a consistent sequence of fixations. Results: In the standard guilty group, lies about recognition of familiar faces showed longer average fixation durations and proportionately more viewing of the eye region than honest responses to genuinely unknown faces. In the countermeasures condition, familiar face recognition was detected by fewer fixations to the inner regions of the face, fewer interest areas of the face viewed and longer fixation durations. Longer fixation durations were a consistent marker of recognition across both conditions for most participants; differences were detectable from the first fixation. Conclusion: The results suggest that individuals can exert a degree of executive control over fixation patterns but that (1) the eyes are particularly attention grabbing for familiar faces, (2) the more viewers look around the face, the more they give themselves away, and (3) attempts to deploy the same fixation patterns to familiar and unfamiliar faces were unsuccessful. The results suggest that the best strategy for concealing recognition might be to keep the eyes fixated in the centre of the screen but, even then, recognition is apparent in longer fixation durations. We discuss potential optimal conditions for detecting concealed knowledge of faces.