Effects of speeds and force fields on submovements during circular manual tracking in humans

Abstract

Complex limb movements exhibit segmentation into submovements characterized as bell-shaped speed pulses. Submovements have been implicated in both feedback and feedforward control, reflecting an intermittent error-correction process. This study examines submovements occurring during a circular manual tracking task in humans, focusing on the amplitude-duration scaling of submovements and the properties of this scaling across changes in movement speed and external force load. The task consisted of intercepting and tracking a circularly moving target using a two-jointed, robotic arm that allowed external force fields to be imposed during tracking. Different speed levels and different levels of three types of force field were examined. Submovements were defined as fluctuations in the speed profile. The properties of the amplitude-duration ratio of the speed pulses were examined in relation to target speed and external force fields. The results show that the amplitude and duration of the submovements scale linearly in human manual tracking. The slope of the scaling was independently influenced by both target speed and external force fields. A common element in the increase in the scaling slope was increased tracking errors. Control experiments using passive movements and power spectral analysis showed that the submovements were not artifacts of the mechanical/acquisition system or the imposed force field. These results are consistent with the concept of stereotypy in which movements are constructed of scaled versions of a single prototype. Furthermore, the results support the hypothesis that submovements are integral to an error detection and correction control process.

Intermittency of slow arm movements increases in distal direction

“…Although there is strong evidence for the existence of submovements in the literature [3], [10], [11], we report here that submovements as generated by a central planner are not necessarily responsible for the intermittency of movements. Our results are in agreement with those reported by Nagasaki [8] and Wann et al [9], although we do not explicitly propose a change in muscular properties as the source of movement intermittency.…”

“…After completing the four phases, the screen went blank for a very short period, and then the next trial began with the hold phase. The visual interface design was adapted from Pasalar et al [10] where they analyzed the changes in the submovement properties for varying tracking speeds and force fields with a planar manipulandum.…”

Fatigue-induced changes of impedance and performance in target tracking

“…Both higher target frequencies and smaller targets resulted in an increase of SP gain as a result of an increase in SP amplitude. Similarly, Pasalar et al (2005) reported that SP gain increases for larger external perturbing force fields in circular drawing. All those increases may be interpreted as a result of a feedback controlled (relative) error correction mechanism.…”

Individual Premotor Drive Pulses, Not Time-Varying Synergies, Are the Units of Adjustment for Limb Trajectories Constructed in Spinal Cord

“…Kinematic strokes of specific features have been proposed as high-level or kinematic planning primitives (Viviani and Terzuolo, 1982;Hogan, 1984;Flash and Hogan, 1985;Sanger, 2000;Schaal et al, 2003;Sosnik et al, 2004;Flash and Hochner, 2005). Unit strokes or unimodal kinematic primitives, identified at the trajectory level, are used to examine adjustments and tracking (Burdet and Milner, 1998;Novak et al, 2002;Roitman et al, 2004;Fishbach et al, 2005Fishbach et al, , 2007, motor learning (Sosnik et al, 2004;Pasalar et al, 2005), and recovery of function (Doeringer and Hogan 1998;Krebs et al, 1999;Rohrer et al, 2004).…”