Distinct effects of empathy on self-other processing revealed by different behavioral and EEG indices.

The self-prioritization effect refers to the tendency for individuals to perceive self-related stimuli more accurately than other-related stimuli. We leveraged this phenomenon to investigate the mechanisms underlying empathy. According to the self-other merging hypothesis, empathy broadens self-representation to encompass others, predicting a reduced self-prioritization effect. In contrast, the self-other distinction hypothesis posits that empathy heightens the differentiation between self and other, predicting an increased self-prioritization effect. To test these competing hypotheses, we employed a perceptual task combined with electroencephalogram (EEG) recordings, and analyzed the data by using signal detection theory. Fifty-two participants aged 19 to 33 years were randomly assigned to either a high-empathy or low-empathy group. Participants listened to an interview and were instructed to either empathize with or remain neutral toward the interviewee. Subsequently, they completed a shape-label matching task using geometrical shapes associated with the self, the interviewer, and the interviewee. The self-prioritization effect was measured by performance differences between self-related and other-related stimuli. Different performance indices provided support for each hypothesis. Specifically, the patterns observed in the sensitivity index (d') and the lateral positive component (LPC) of the event-related potential supported the self-other distinction hypothesis at the perceptual and attentional levels. In contrast, the patterns in the response bias index (c) and reaction time supported the self-other merging hypothesis at the response level. These findings suggest that empathy influences self-representation in distinct ways across different levels of processing.