Subtle Facial Skin Color Changes Enhance the Human Likeness of Artificial Agents: Insights from Pulse-Wave-Derived Modulation

Recent studies have shown that implementing explicit social cues, such as gaze, facial expressions, and gestures, in artificial agents can improve impressions of these agents. However, humans may also use implicit physiological cues, such as facial coloration and cardiac information, in social perception. The present study examined whether subtle facial skin color changes derived from pulse-wave signals enhance the perceived human likeness of artificial agents and whether this effect depends on the type of agent, the temporal characteristics of the signal, or individual differences in interoceptive sensibility. Participants observed morphed face stimuli created from artificial agents and human faces and judged whether each stimulus appeared human-like or robot-like. In Experiment 1, skin color changes based on human-derived pulse-wave signals enhanced perceived human likeness for a highly human-like agent, but not for a less human-like agent. In Experiment 2, perceived human likeness was enhanced not only by pulse-wave-derived facial skin color changes but also by sinusoidal color changes matched to the pulse-wave signals in mean amplitude and number of peaks. Interoceptive sensibility did not significantly moderate the effect of facial skin color changes on perceived human likeness. These findings suggest that periodic facial skin color changes with physiologically plausible temporal characteristics, rather than temporal dynamics specific to pulse-wave signals, may serve as cues that enhance the perceived human likeness of artificial agents.