title: Balancing with positive feedback: the case for discontinuous control.
abstract: Experimental observations indicate that positive feedback plays an important role for maintaining human balance in the upright position. This observation is used to motivate an investigation of a simple switch-like controller for postural sway in which corrective movements are made only when the vertical displacement angle exceeds a certain threshold. This mechanism is shown to be consistent with the experimentally observed variations in the two-point correlation for human postural sway. Analysis of first-passage times for this model suggests that this control strategy may slow escape by taking advantage of two intrinsic properties of a stochastic unstable first-order delay differential equation: (i) time delay and (ii) the possibility that the dynamics can be 'temporarily confined' near the origin.
authors.affiliation: W. M. Keck Science Center, The Claremont Colleges, Claremont, CA 91711, USA. jmilton@jsd.claremont.edu
authors.forename: John
authors.initials: J
authors.lastname: Milton
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Townsend
authors.forename: Meredith A
authors.initials: MA
authors.lastname: King
authors.forename: Toru
authors.initials: T
authors.lastname: Ohira
mesh_terms: D001835:Body Weight; D005246:Feedback / Q000502:physiology*; D006112:Gravitation; D006801:Humans; D007700:Kinetics; D009043:Motor Activity / Q000502:physiology*; D009068:Movement / Q000502:physiology; D011187:Posture / Q000502:physiology*; D011930:Reaction Time