Implicit Encoding of Social Perceptions: Modeling Eye-Gaze, Pupillary, and Neuronal Responses to Faces

Faces convey a wealth of social information, guiding human interactions and decisions. Using data-driven modeling, we identify facial features that influence physiological responses—including eye-gaze, pupillary, and neuronal activities—and demonstrate how these responses reflect underlying social judgments. First, fixation durations on the eye region increase for faces perceived as having negative and high-power traits (Preliminary Study, Study 1). Second, variations in pupil size represent both valence and power dimensions of social trait space (Preliminary Study, Study 1). Notably, in socially anxious individuals, pupillary reactions exhibited heightened sensitivity to valence perceptions, further supporting the involvement of high-level social information processing that was reflected in pupillary responses (Study 1). We also demonstrate the encoding of social perceptions in neuronal responses. The amygdala primarily encoded valence perceptions, with decreased neuronal activity when viewing the mouths of faces perceived as positive (e.g., competent, extraverted) (Study 2). The hippocampus, in contrast, showed a feature-invariant encoding of both the power and valence dimensions of social space, and was involved in modulating eye movement planning during face evaluations. (Study 2). These results reveal how face-based social perceptions are implicitly encoded in nondeliberate, immediate physiological reactions to social stimuli.