Moderate similarity leads to empathic concern, but high similarity can also induce personal distress towards others' pain.

Empathic concern and personal distress are common vicarious emotional responses that arise when witnessing someone else's pain. However, the influence of perceived similarity on these responses remains unclear. In this study, we examined how perceived similarity with an injured target impacts vicarious emotional responses. A total of 87 participants watched a video of an athlete in pain preceded by a clip describing the athlete's trajectory, which indicated either high, moderate, or low similarity to the participants. Emotional self-reports, facial expressions, gaze behavior, and pupil diameter were measured as indicators of the participants' emotional responses. Participants in the moderate- and high-similarity groups exhibited greater empathic concern, as evidenced by their display of more sadness compared with those in the low-similarity group. Furthermore, those in the moderate-similarity group exhibited less avoidance by displaying reduced disgust, indicating lower personal distress compared with those in the low-similarity condition. Nevertheless, the high-similarity group displayed just as much disgust as the low-similarity group. These findings suggest that perceived similarity enhances empathic concern to others' suffering, but that high similarity can also lead to personal distress. Future studies on empathy should explore distinct vicarious states using multimodal measurements to further advance our understanding of these processes.