An increasing number of studies have suggested that interpersonal emotion regulation plays a key role in maintaining and improving mental health, strengthening emotional connections between individuals, and promoting the development of healthy interpersonal relationships. Therefore, it is of great importance to enhance the effectiveness of interpersonal emotion regulation. However, previous research has given limited attention to how contextual factors influence its effectiveness. Notably, past studies have typically manipulated the context and emotional events through participants' imagination, meaning the regulator often participates in the emotion regulation process as a "bystander." For example, the regulator was made aware of the target’s negative emotions through the presentation of images, text, or by asking the participant to recall specific events. Although the regulator in this "bystander" scenario receives emotional information from the target, the absence of direct experience may result in a less accurate understanding of the other person's emotions. In contrast, when the regulator and the target experience negative emotions together—that is, when they "co-suffer"—the regulator can access the most direct and accurate emotional information from the target. This can potentially enhance the effectiveness of emotion regulation.

To investigate this issue, the present study used an innovative, high ecological validity interpersonal emotion regulation task to examine the impact of the regulator's situation on interpersonal emotion regulation. A 2 (electrical stimulation probability: low probability - safe/high probability - dangerous) × 2 (regulator’s situation: bystander/co-sufferer) within-subjects design was used. Negative emotions (anxiety, panic) were induced through real electrical stimulation, and the presentation method of the stimulation was manipulated to create two conditions for the regulator: "bystander" (not receiving stimulation) and "co-sufferer" (receiving the stimulation along with the target).To explore the impact of contextual factors on interpersonal emotion regulation with greater ecological validity, we manipulated the probability of electrical stimulation to simulate relatively safe and dangerous situations, with the safe condition set as the baseline. Participants were paired for the experiment. Before the formal experiment began, both participants first assessed their pain thresholds for the electrical stimulation, then learned the definitions and practiced two emotion regulation strategies: distraction and reappraisal. Next, participants drew lots to determine their roles, with one acting as the regulator and the other as the target. Roles remained fixed throughout the experiment. The task was divided into two blocks, corresponding to the "bystander" and "co-sufferer" conditions. In both conditions, the regulator's task was to reduce the negative emotions of the target caused by the anticipation of the impending electrical stimulation.

Our results showed that the co-sufferer condition did not improve the regulation effect as expected. In contrast, when the regulator acted as a bystander, their empathy accuracy was higher, and the interpersonal emotion regulation effect was better.

This study is the first to examine the impact of the regulator’s situation on interpersonal emotion regulation, offering a new theoretical perspective to enrich its process model. While the goal of interpersonal emotion regulation is to improve the emotional state of the target, the regulator's own emotional state is also continuously influenced throughout the process, impacting the implementation and effectiveness of regulation. This study suggests that the process model of interpersonal emotion regulation should include modules for the regulator to manage their own emotions. To improve the effectiveness of interpersonal emotion regulation and benefit both parties, it is crucial to enhance our understanding of the cognitive and neural mechanisms underlying the regulator's role. Additionally, from both the regulator's and the target 's perspectives, efforts should be made to ensure that the regulator's emotional regulation of both the other person and themselves mutually reinforce each other during the process. Based on the findings of this study, we recommend that, when providing emotional regulation assistance, the regulator should carefully assess their own situational characteristics, embodying the principle, "Maintain your kindness in poverty, lend a helping hand in prosperity."