Role of interpersonal tactile and visual interaction in modulating postural sway and enhancing stability.

Manual support and interpersonal interaction can enhance postural stability during upright standing, yet it remains unclear how tactile and visual interactions influence the temporal organization of postural control. We used a 2 × 2 factorial design manipulating interpersonal touch (Touch vs. No Touch) and partner visibility (Visible vs. Invisible) while participants stood quietly in pairs. Center-of-pressure velocity time series were analyzed using linear and nonlinear methods, including recurrence quantification analysis (RQA) and detrended fluctuation analysis (DFA). Both tactile interaction and partner visibility were associated with reduced sway magnitude, with no significant interaction between modalities. Nonlinear analyses revealed that tactile interaction was associated with reduced recurrence and lower DFA scaling exponents across timescales, indicating altered temporal organization. Visual coupling influenced recurrence measures and longer-timescale structure but did not significantly affect short-timescale scaling. These findings suggest that tactile and visual interactions contribute additively to sway reduction, yet are associated with distinct patterns of temporal organization in postural control.