Looking to Deceive: Voluntary Gaze Control Reduces the Discriminative Power of Eye-Movement-Based Concealed Information Testing.

The Concealed Information Test (CIT) detects whether an individual recognizes crime-relevant information, and eye tracking has been proposed as a non-invasive method for detecting this recognition. It remains unclear, however, whether individuals who are motivated to conceal their knowledge can voluntarily control their gaze and thereby undermine the test's validity. We developed a novel free-viewing, parallel-presentation eye-movement-based CIT and administered it to 75 participants randomly assigned to three groups: Innocent, Informed Innocent, and Guilty. For each participant, twelve eye-tracking measures were calculated as differential (crime-relevant minus control) scores and analyzed using four supervised classifiers under a participant-wise, leave-two-out cross-validation, with accuracy reported at both the trial and participant levels. Cumulative dwell- and duration-based measures, together with glance and fixation counts, carried most of the discriminative signal. The classifiers demonstrated high accuracy when distinguishing between the naive and knowledgeable but non-concealing individuals, as well as between knowledgeable non-concealing individuals and culpable individuals. However, classification performance fell to chance-level probability when distinguishing naive and culpable individuals. Thus, participants who were motivated to avoid detection markedly reduced their distinctive eye-movement signature with voluntary gaze control, becoming indistinguishable from truly naive individuals. We discuss methodological implications for designing eye-movement-based CITs that exhibit greater resilience against voluntary gaze modulation.