Abstract
Humans are social beings and when working in pairs, there is a tendency for intentional or unintentional synchronization of movements (Schmidt & O'Brien, 1997). This represents an example of "joint action" behavior where individuals coordinate movements to act as a multidimensional dynamical system described by the coupled oscillator model (Haken, Kelso & Bunz, 1985). The purpose of this study is to explore the social phenomenon of joint action during unconscious, rhythmic movements such as postural sway. Based on research examining human mimicry (Wang et al., 2011) and inter-primate gaze (Mosher et al., 2014), we hypothesize that the spontaneous synchronization of sway is facilitated by eye contact, a powerful form of non-verbal communication involved in understanding movement and intention. Additionally, we suggest that haptic feedback will serve to further stabilize postural entrainment. Sixteen participants (20.56 ± 1.37 years) formed eight sex-matched pairs and performed 45-second static balance tests on force platforms. There were four conditions with differing visual and haptic cues: fixate gaze on wall, fixate on the back of partner's head, direct partner eye contact, and eye contact with hand holding. Centre of pressure signals were cross-correlated to examine the degree of between-person synchronization as a function of time delay. Results show significantly (p < .05) stronger correlation while maintaining eye-contact in comparison to fixating on a wall and fixating their respective gazes on the back of their partners' head. These findings suggest that engagement of visual attention through eye contact, as opposed to the simple presence of another person, encourages interpersonal synchronization of postural sway.
