Subtle gaze and pupil dynamics: Detecting concealed familiar faces with moving serial visual presentation

A major limitation of the standard concealed information test (CIT) is its susceptibility to countermeasures. Rapid serial visual presentation (RSVP) can improve resilience against countermeasures, and pupil dilation has been shown to indicate concealed information in RSVP-based CITs. Here, we introduce a novel variation of the RSVP-based CIT that may further improve individual detection and potentially offer the same resilience against countermeasures. We combined serial visual stimulus presentation with movements either towards the left or right, to capitalize on (pursuit) eye movements, in addition to pupil size, for detecting concealed information (familiar faces). In both experiments that we conducted, either a target face, a familiar face (the participant’s parent’s face), or one of two control faces appeared in these streams. In Experiment 1, participants maintained their fixation at a central fixation dot, only deviating their gaze to follow the target face in response. In Experiment 2, participants were allowed to move their eyes freely and respond using a keyboard. Results indicated that participants’ eye movement did not provide valuable information for concealed familiar face detection, but pupil dilation exhibited a noticeable increase when familiar faces appeared, in comparison to control faces. Based on the difference in pupil dilation rate, we achieved an individual detection rate of 55.2% in Exp. 1 and 33.3% in Exp. 2 – a substantial improvement from the 22.6% in the standard RSVP-based CIT. In conclusion, moving serial visual presentation (MSVP), combined with eye movement suppression, offers a promising method for detecting concealed information.