Does Observation of Postural Imbalance Induce a Postural Reaction?

Abstract

BackgroundSeveral studies bring evidence that action observation elicits contagious responses during social interactions. However automatic imitative tendencies are generally inhibited and it remains unclear in which conditions mere action observation triggers motor behaviours. In this study, we addressed the question of contagious postural responses when observing human imbalance.Methodology/Principal FindingsWe recorded participants' body sway while they observed a fixation cross (control condition), an upright point-light display of a gymnast balancing on a rope, and the same point-light display presented upside down. Our results showed that, when the upright stimulus was displayed prior to the inverted one, centre of pressure area and antero-posterior path length were significantly greater in the upright condition compared to the control and upside down conditions.Conclusions/SignificanceThese results demonstrate a contagious postural reaction suggesting a partial inefficiency of inhibitory processes. Further, kinematic information was sufficient to trigger this reaction. The difference recorded between the upright and upside down conditions indicates that the contagion effect was dependent on the integration of gravity constraints by body kinematics. Interestingly, the postural response was sensitive to habituation, and seemed to disappear when the observer was previously shown an inverted display. The motor contagion recorded here is consistent with previous work showing vegetative output during observation of an effortful movement and could indicate that lower level control facilitates contagion effects.

Effects of different unstable supports on EMG activity and balance

“…Our findings are consistent with the idea that equilibrium in unstable surfaces is modulated by ecological strategies along the anteroposterior axis and by biomechanics and stabilisation strategies. In the literature, it is well established [33] that standing postural control in humans is direction-dependent, and that goal oriented actions (for instance, reaching or locomotion) are mainly along the anteroposterior axis, and primarily involves muscles from the anteroposterior plane [30,31]. This direction dependence results from several biomechanical factors that characterise human posture [30].…”

Common coding and dynamic interactions between observed, imagined, and experienced motor and somatosensory activity

“…When an observed action is incongruent with motor planning it can slow down the motor response (e.g. Brass 2000), perturb the path of movement in space (Kilner et al 2003), or increase the observer's body-sway (Tia et al 2011). Similarly, movements can alter the perception of discrepant actions.…”

Measuring Human-Robot Interaction Through Motor Resonance

“…Another example of automatic imitation of the observed movement comes from Tia et al's [93] study on postural reaction during postural imbalance observation. Participants looked at upright point-light display (i.e., an impoverished display composed of moving dots obtained by placing small light sources to the major joints of the human body used for the first time by Johansson [94]) of a gymnast balancing on a rope in an instable manner, causing a larger center of pressure (CoP) area.…”