The study explores the connection between interoception (the perception of one's internal physiological state) and social cognition. While previous research suggests a link between interoception, emotional awareness, self-consciousness, empathy, and mentalizing, the underlying mechanisms remain unclear. This study proposes a more nuanced understanding by examining the role of interoception in two key aspects of social cognition: the self-other boundary (the degree of overlap in processing self and others) and sensitivity to social cues. The researchers hypothesize that higher interoceptive accuracy will be associated with both a greater degree of self-other overlap and increased sensitivity to social cues, specifically eye contact.

Existing literature indicates a relationship between interoception and social cognitive abilities, often explained through a syllogism: interoception correlates with self-awareness, self-awareness correlates with understanding others, therefore interoception correlates with understanding others. However, this is considered an oversimplification. The self-other boundary is examined through embodied reactions like spontaneous facial mimicry (SFM), with studies showing inconsistent results regarding the correlation between interoceptive sensitivity and this boundary. Similarly, the relationship between interoception and sensitivity to social cues lacks direct evidence, though Quattrocki and Friston suggested that social cues increase the brain's weighting of interoceptive processing, facilitating socio-affective inference and learning. The current study uses spontaneous facial mimicry as a task-independent measure to assess the self-other boundary and eye contact effect as a measure of sensitivity to social cues.

Eighty Japanese participants (45 males) with no history of psychiatric or neurological conditions participated. The study involved three parts: a heartbeat counting task (to measure IAc), a spontaneous facial mimicry (SFM) task involving video clips of models with either direct or averted gaze (to measure self-other boundary and social cue sensitivity), and a self-report questionnaire (alexithymia). The heartbeat counting task involved four trials of varying durations (25, 35, 45, and 100 s), with participants silently counting their perceived heartbeats while an electrocardiogram monitored their actual heartbeats. Interoceptive accuracy was calculated using a standard formula. The SFM task used video clips of models displaying happy expressions with either direct or averted gaze. Two trained coders, using the Facial Action Coding System (FACS), assessed the frequency of SFM (lip-corner pull) in participants. The eye contact effect was calculated as the difference in SFM frequency between direct and averted gaze conditions. Statistical analyses included paired t-tests, Spearman rank correlation analyses (with Bonferroni correction), Welch's t-tests, and two-way ANOVA.

The mean IAc score was 67.95 (SD = 19.43). A paired t-test showed significantly higher SFM frequency in the direct gaze condition (p < 0.001, r = 0.45). Crucially, a positive correlation was found between IAc and SFM frequency only in the direct gaze condition (p < 0.001, 95% CI [0.40, 0.71]). Furthermore, a significant positive correlation existed between IAc and the eye contact effect on SFM (p < 0.001, 95% CI [0.43, 0.73]). These correlations were consistent across both male and female participant groups, suggesting robustness of the findings. There was no significant difference in IAc between genders (p = 0.079). Two-way ANOVA showed a significant main effect of condition on SFM (p < 0.001), but no significant gender effect or interaction (p = 0.912, p = 0.251).

The results indicate that interoceptive accuracy is significantly related to sensitivity to social cues, as evidenced by the positive correlation between IAc and the eye contact effect on SFM. This suggests that individuals with higher interoceptive awareness are more responsive to the socially significant information conveyed by direct gaze. The findings regarding the self-other boundary are less clear, with a positive correlation between IAc and SFM only present in the direct gaze condition. This suggests a potential interaction between interoception and contextual factors influencing the self-other boundary. The study notes alternative interpretations, including that SFM might reflect general emotional response or the strength of embodied simulation triggered by eye contact. Future studies using various social cues and neural-physiological measures are needed to further clarify the complex interplay between interoception and social cognition.

This study provides evidence for a relationship between interoceptive accuracy and sensitivity to social cues, particularly the impact of eye contact on spontaneous facial mimicry. Future research should explore the moderating role of context on the self-other boundary and investigate these relationships using diverse social cues and neurophysiological measures, such as electrodermal activity and heartbeat-evoked neural responses, to disentangle arousal and attentional factors.

The study's limitations include the use of a specific measure of interoception and facial mimicry. The sample was limited to Japanese participants and may not generalize to other cultures. The study’s interpretation of SFM as solely reflecting self-other boundary or social cue sensitivity is a simplification, as alternative interpretations exist. The cross-sectional design prevents causal inferences.