title: Learning dynamic control of body roll orientation.
abstract: Our objective was to examine how the control of orientation is learned in a task involving dynamically balancing about an unstable equilibrium point, the gravitational vertical, in the absence of leg reflexes and muscle stiffness. Subjects (n = 10) used a joystick to set themselves to the gravitational vertical while seated in a multi-axis rotation system (MARS) device programmed with inverted pendulum dynamics. The MARS is driven by powerful servomotors and can faithfully follow joystick commands up to 2.5 Hz with a 30-ms latency. To make the task extremely difficult, the pendulum constant was set to 600°/s(2). Each subject participated in five blocks of four trials, with a trial ending after a cumulative 100 s of balancing, excluding reset times when a subject lost control. To characterize performance and learning, we used metrics derived from joystick movements, phase portraits (joystick deflections vs MARS position and MARS velocity vs angular position), and stabilogram diffusion functions. We found that as subjects improved their balancing performance, they did so by making fewer destabilizing joystick movements and reducing the number and duration of joystick commands. The control strategy they acquired involved making more persistent short-term joystick movements, waiting longer before making changes to ongoing motion, and only intervening intermittently.
authors.affiliation: Ashton Graybiel Spatial Orientation Laboratory, MS 033, Brandeis University, Waltham, MA, 02245-9110, USA. somde@brandeis.edu.|Volen Center for Complex Systems, Brandeis University, Waltham, MA, 02245-9110, USA. somde@brandeis.edu.
authors.forename: Vivekanand Pandey
authors.initials: VP
authors.lastname: Vimal
authors.affiliation: Ashton Graybiel Spatial Orientation Laboratory, MS 033, Brandeis University, Waltham, MA, 02245-9110, USA.|Volen Center for Complex Systems, Brandeis University, Waltham, MA, 02245-9110, USA.|Department of Psychology, Brandeis University, Waltham, MA, 02245-9110, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Lackner
authors.affiliation: Ashton Graybiel Spatial Orientation Laboratory, MS 033, Brandeis University, Waltham, MA, 02245-9110, USA.|Volen Center for Complex Systems, Brandeis University, Waltham, MA, 02245-9110, USA.|Department of Psychology, Brandeis University, Waltham, MA, 02245-9110, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: DiZio
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology*; D008297:Male; D009949:Orientation / Q000502:physiology*; D010865:Pilot Projects; D004856:Postural Balance / Q000502:physiology*; D012399:Rotation; D055815:Young Adult
keywords: Dynamic balancing; Gravitational vertical; Orientation; Phase portraits; Stabilogram diffusion function; Vehicle control; Vestibular system