Unmasking Deception: Examining Receivers' Emotional Responses with Automated Facial Expression Analysis in Veracity and Valence

Emotional mimicry, an unconscious nonverbal response, may reveal how people react to truthful versus deceptive communication. Mimicry typically increases when individuals seek connection but may be suppressed when deception reduces liking and affiliation. Emotional tone further shapes this process: positive expressions promote alignment, whereas negative ones can evoke scepticism or discomfort.This study examined how message truthfulness and emotional framing influence mimicry in receivers. Using Automated Facial Expression Analysis (AFEA) in a 2 × 2 within-subjects design, 33 participants viewed 16 video messages in which four speakers delivered truthful or deceptive stories with positive or negative valence. Facial expressions were recorded and analysed to quantify mimicry.Mimicry was significantly lower for deceptive than for truthful messages across both positive and negative content, consistent with expectations. The decrease was strongest for positively framed deceptions, indicating that deception disrupts alignment most when positivity would otherwise encourage connection. Negative messages elicited weaker mimicry overall, regardless of veracity, also in line with predictions. In contrast, presuppositions about deception and judgment type were unrelated to mimicry or veracity judgments, contrary to expectations.These findings suggest that mimicry is not a straightforward cue to deception but an indicator of affective attunement shaped by authenticity and emotional tone. Mimicry appears driven more by emotional than cognitive processes, offering insight into unconscious receiver responses. The use of AFEA underscores both the promise and the limitations of automated tools for studying dynamic interpersonal behavior.