Frequency dependence of the action-perception cycle for postural control in a moving visual environment: relative phase dynamics

Contains fulltext : 103984.pdf (publisher's version ) (Open Access

Postural Coordination Dynamics in Standing Humans

Human stance requires the coordination of multiple joints. This article examines the dynamics of postural coordination modes involving the torso and legs in the control of stance and stance-related activities. Based on data obtained in various experiments using the same postural tracking task, we provide evidence that postural modes (i) emerge out of the coalescence of multiple constraints, (ii) exhibit persistence and changes that are characteristic of self-organized systems, (iii) are modulated by the actors intention, and (iv) can be learned by modifying the intrinsic dynamics of the postural system. Similarities between postural phase transitions in humans or non-biological phenomena suggest the existence of general and common principles governing pattern formation and flexibility in complex systems, and circumscribe the generality of neurophysiologically-based theories of postural behavior. Postural Coordination Dynamics in Standing Humans One of the major problems facing movement scientists is how humans and other animals coordinate the multitude of degrees of freedom of their bodies, constraining them to act as a single unit in accomplishing behavioral tasks. Standing, walking, reaching, or hitting a moving object are prosaic examples in which successful performance is based upon, and severely constrained by, a set of neuro

Effects of visual motion consistent or inconsistent with gravity on postural sway

Vision plays an important role in postural control, and visual perception of the gravity-defined vertical helps maintaining upright stance. In addition, the influence of the gravity field on objects' motion is known to provide a reference for motor and non-motor behavior. However, the role of dynamic visual cues related to gravity in the control of postural balance has been little investigated. In order to understand whether visual cues about gravitational acceleration are relevant for postural control, we assessed the relation between postural sway and visual motion congruent or incongruent with gravity acceleration. Postural sway of 44 healthy volunteers was recorded by means of force platforms while they watched virtual targets moving in different directions and with different accelerations. Small but significant differences emerged in sway parameters with respect to the characteristics of target motion. Namely, for vertically accelerated targets, gravitational motion (GM) was associated with smaller oscillations of the center of pressure than anti-GM. The present findings support the hypothesis that not only static, but also dynamic visual cues about direction and magnitude of the gravitational field are relevant for balance control during upright stance