title: Does observation of postural imbalance induce a postural reaction?
abstract: BACKGROUND
  Several 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.
  
  
  RESULTS
  We 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
  These 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.
authors.affiliation: INSERM U887, Motricité et Plasticité, Université de Bourgogne, Dijon, France. banty.tia@u-bourgogne.fr
authors.forename: Banty
authors.initials: B
authors.lastname: Tia
authors.forename: Arnaud
authors.initials: A
authors.lastname: Saimpont
authors.forename: Christos
authors.initials: C
authors.lastname: Paizis
authors.forename: France
authors.initials: F
authors.lastname: Mourey
authors.forename: Luciano
authors.initials: L
authors.lastname: Fadiga
authors.forename: Thierry
authors.initials: T
authors.lastname: Pozzo
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D009068:Movement / Q000502:physiology; D010812:Physical Stimulation; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011312:Pressure; D055815:Young Adult