Producing unexpected emotional expressions in others reduces one's own agency.

The sense of agency (SoA), or the subjective feeling of causing and controlling action outcomes, is fundamental to how we engage with the world. In the present study, we investigated how SoA is influenced when individuals unintentionally elicit emotional expressions in others. In Experiment 1, participants freely selected actions that triggered either happy or sad facial expressions in the humanoid robot iCub. However, 20% of the time, when participants intended to elicit a happy expression, the robot unexpectedly displayed a sad one. Results showed reduced SoA when they accidentally made iCub display a sad expression. Experiment 2 replicated Experiment 1 with design adjustments to improve control. The results mirrored Experiment 1, with SoA again lower for unexpected sad expressions than for intentional ones. In Experiment 3, to determine whether the effect was due to the emotional content or simply outcome predictability, we replaced the expressions with emotionally neutral color changes on iCub's facial LED lights. The results showed no significant difference in SoA between accidental and intentional outcomes, suggesting that emotional content played a key role in Experiments 1 and 2. These findings highlight that SoA is specifically affected when emotional expressions occur as action outcomes, in ways that go beyond the role of outcome predictability.