Intra‐dyadic Similarity as an Index of Reciprocal Co‐representation in the Joint Simon Task

Joint action—the coordination of one's actions with others—is fundamental to social interaction. The joint Simon task has been widely used to study this process, revealing the joint Simon effect (JSE): faster responses on spatially compatible than incompatible trials, even though each actor performs a go/no‐go task. Although the JSE is often interpreted as evidence for shared task representation, similar effects have been observed in nonsocial contexts, raising questions about its underlying mechanisms. To distinguish JSEs arising from reciprocal interaction from those driven by one‐sided processes, we examined intra‐dyadic correlations in JSE magnitude as a potential marker of reciprocal co‐representation. Across two experiments, we tested whether two socio‐cognitive factors—the sense of power (high vs. low) and self‐construal (interdependent vs. independent)—modulate this alignment. While overall JSE magnitude did not differ across conditions, significant intra‐dyadic correlations emerged in the low‐power and interdependent conditions—contexts supposedly associated with greater social attunement. These findings suggest that intra‐dyadic JSE alignment may reflect reciprocal consideration between co‐actors and that this alignment is shaped by social factors.