title: Perceptual and motor learning underlies human stick-balancing skill.
abstract: We investigated the acquisition of skill in balancing a stick (52 cm, 34 g) on the fingertip in nine participants using three-dimensional motion analysis. After 3.5 h of practice over 6 wk, the participants could more consistently balance the stick for longer durations with greatly reduced magnitude and speed of stick and finger movements. Irrespective of level of skill, the balanced stick behaved like a normal noninverted pendulum oscillating under greater-than-gravity torque with simple harmonic motion about a virtual pivot located at the radius of gyration above the center of mass. The control input parameter was the magnitude ratio between the torque applied on the stick by the participant and the torque due to gravity. The participants utilized only a narrow range of this parameter, which did not change with practice, to rotate the stick like a linear mass-spring system. With increased skill, the stick therefore maintained the same period of oscillation but showed marked reductions in magnitude of both oscillation and horizontal translation. Better balancing was associated with 1) more accurate visual localization of the stick and proprioceptive localization of the finger and 2) reduced cross-coupling errors between finger and stick movements in orthogonal directions; i.e., finger movements in the anteroposterior plane became less coupled with stick tip movements in the mediolateral plane, and vice versa. Development of this fine motor skill therefore depended on perceptual and motor learning to provide improved estimation of sensorimotor state and precision of motor commands to an unchanging internal model of the rotational dynamics.
authors.affiliation: School of Exercise Science, Australian Catholic University, Strathfield, New South Wales, Australia; Discipline of Exercise and Sport Science, The University of Sydney, New South Wales, Australia.
authors.forename: Kwee-Yum
authors.initials: KY
authors.lastname: Lee
authors.affiliation: School of Human Movement Studies, Charles Sturt University, Bathurst, New South Wales, Australia; and Discipline of Exercise and Sport Science, The University of Sydney, New South Wales, Australia nodwyer@csu.edu.au.
authors.forename: Nicholas
authors.initials: N
authors.lastname: O'Dwyer
authors.affiliation: Discipline of Exercise and Sport Science, The University of Sydney, New South Wales, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Halaki
authors.affiliation: Discipline of Exercise and Sport Science, The University of Sydney, New South Wales, Australia.
authors.forename: Richard
authors.initials: R
authors.lastname: Smith
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005385:Fingers; D006801:Humans; D007858:Learning; D008297:Male; D009048:Motor Skills; D010507:Periodicity; D011434:Proprioception; D012399:Rotation; D055815:Young Adult
keywords: depth perception; gravitational dynamics; kinesthesis; perception-action coupling; pole balancing