title: Stabilization strategies for unstable dynamics.
abstract: The stabilization of the human standing posture was originally attributed to the stiffness of the ankle muscles but direct measurements of the ankle stiffness ruled out this hypothesis, leaving open the possibility for a feedback stabilization strategy driven by proprioceptive signals. This solution, however, could be implemented with two different kinds of control mechanisms, namely continuous or intermittent feedback. The debate is now settled and the latter solution seems to be the most plausible one. Moreover, stabilization of unstable dynamics is not limited to bipedal standing. Indeed many manipulation tasks can be described in the same framework and thus a very general protocol for addressing this kind of problems is the use of haptic virtual reality where instability is generated by some kind of divergent or saddle-like force field. Several studies demonstrated that human subjects can choose to adopt a stiffness or feedback strategy as a combination of biomechanical and task constraints and can learn to switch from one strategy to the other if it is feasible or to use one or the other is infeasible. Understanding such mechanisms is relevant, for example, for the design of novel ergonomic man-machine interfaces in difficult, unstable tasks.
authors.affiliation: Istituto Italiano di Tecnologia, Department of Robotics, Brain and Cognitive Sciences, Genoa, Italy. Electronic address: pietro.morasso@iit.it.
authors.forename: Pietro
authors.initials: P
authors.lastname: Morasso
authors.affiliation: University of Genoa, Department of Informatics, Bioengineering, Robotics and Systems Engineering, Genoa, Italy. Electronic address: maura.casadio@unige.it.
authors.forename: Maura
authors.initials: M
authors.lastname: Casadio
authors.affiliation: Istituto Italiano di Tecnologia, Department of Robotics, Brain and Cognitive Sciences, Genoa, Italy. Electronic address: dalia.desantis@iit.it.
authors.forename: Dalia
authors.initials: D
authors.lastname: De Santis
authors.affiliation: Department of Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Japan. Electronic address: taishin@bpe.es.osaka-u.ac.jp.
authors.forename: Taishin
authors.initials: T
authors.lastname: Nomura
authors.affiliation: Istituto Italiano di Tecnologia, Department of Robotics, Brain and Cognitive Sciences, Genoa, Italy. Electronic address: Francesco.rea@iit.it.
authors.forename: Francesco
authors.initials: F
authors.lastname: Rea
authors.affiliation: Istituto Italiano di Tecnologia, Department of Robotics, Brain and Cognitive Sciences, Genoa, Italy. Electronic address: jacopo.zenzeri@iit.it.
authors.forename: Jacopo
authors.initials: J
authors.lastname: Zenzeri
mesh_terms: D000818:Animals; D003198:Computer Simulation / Q000639:trends; D025461:Feedback, Physiological / Q000502:physiology*; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*
keywords: Control strategies; Intermittent feedback control; Motor cognition; Motor control; Stiffness control; Unstable tasks