Weakened self-other boundaries during multisensory integration in men with body dysmorphic disorder symptoms

Disturbances in bodily self-perception, particularly self-face perception, characterize body dysmorphic disorder (BDD). However, the mechanisms underlying these disturbances and potential ways to modify them remain unclear. To address these gaps, we investigated whether alterations in self-face representation and underlying multisensory experiences-indexed via an enfacement illusion-are linked to symptoms of BDD or its subtype muscle dysmorphia (MD). We also explored whether experiencing the enfacement illusion can reduce face and body image disturbance. Sixty-two male participants (M = 22.6 years, SD = 3.5) completed synchronous (illusion inducing) and asynchronous (control) visuo-motor stimulation between their own face and an unfamiliar person's face. Results showed that elevated BDD symptoms predicted greater objective enfacement (shifts in self-face recognition thresholds during a self-other morphing task) and exclusively predicted subjective enfacement (self-reported shifts in face recognition), whereas MD symptoms were unrelated to enfacement susceptibility. Synchronous visuo-motor stimulation reduced head, body, and muscularity dissatisfaction across the sample, while asynchronous stimulation produced inconsistent effects on body image. BDD and MD symptom levels did not moderate most body image changes. These findings suggest that BDD may reflect abnormalities in the visual and multisensory integration processes underlying self-face representation, contributing to weakened self-other boundaries. These insights may advance understanding of bodily identity and social-cognitive difficulties in BDD. While enfacement-based interventions show modest therapeutic potential, future refinements are needed.