Effect of motor planning on use of motor abundance

Abstract

This study examined the hypothesis that the degree to which motor redundancy is used to coordinate joint motions for reaching is influenced by motor planning and enhanced when the task requires greater movement flexibility. Subjects reached at arm's length to the same centrally placed target under conditions where the target location was either certain or uncertain, using a double-step paradigm. The hypothesis was evaluated by partitioning the across-trials variance of the joint configuration at each percent of the reach into a component corresponding to the use of different joint angle combinations to achieve an equivalent hand position (GEV) and a component leading to a variable hand position (NGEV). Pointer-tip movement variability along the path and variable targeting error did not differ between conditions. Larger overall joint variance was found for the uncertain target condition. Most of this increase was GEV, which was significantly higher in the uncertain condition for control of both movement extent and movement direction. In contrast, NGEV differed between the two conditions only for the control of movement extent early in the reach, suggesting that target uncertainty led to inter-trial timing variability along the movement path. The results suggest that more flexible patterns of joint coordination are used when the nervous system must plan reaching movements to an uncertain target direction.

Normal aging reduces motor synergies in manual pointing

“…In line with this reasoning, in a study manipulating accuracy constraints in manual pointing (Tseng et al, 2003) in young adults, participants used lower amounts of GEV when pointing to targets with higher indexes of difficulty. On the other hand, the ability for fast online movement corrections, which seems to be impaired in older adults (Sarlegna, 2006), was found to be related to the availability and use of motor abundance (de Freitas et al, 2007;Robertson and Miall, 1997). Potential interactions between a strategy of restraining motor abundance at the level biomechanical degrees of freedom and age-related changes in response flexibility at other behavioral levels remain to be investigated.…”

Stabilization of cat paw trajectory during locomotion

“…12), indicating the opposite strategy of stabilization of this performance variable. Note that human experiments have provided evidence for increased V UCM during movements to uncertain targets and practice in conditions of instability (de Freitas et al 2007;Freitas and Scholz 2009;Wu et al 2012). The differences in patterns of V UCM and V ORT for endpoint limb position between human movements and cat walking could reflect relatively high dynamic stability of quadrupedal locomotion (Farrell et al 2011;Farrell et al 2014).…”

Synergistic control of joint angle variability: Influence of target shape

“…Assuming the existence of an optimal controller, movement variability should exhibit a specific structure, with higher variability in task-irrelevant directions, and lower variability in task-relevant directions (Todorov, 2004;Todorov & Jordan, 2002). In recent years, the investigation of the structure of movement variability of the effector-system, with respect to hypothesized task variables, has become of increasing interest ( de Freitas, Scholz, & Stehman, 2007;Eggert et al, 2003;Gera et al, 2010;Müller & Sternad, 2004;Scholz, Danion, Latash, & Schöner, 2002;Scholz, Schöner, & Latash, 2000;Tseng, Scholz, & Galloway, 2009;Zhang, Scholz, Zatsiorsky, & Latash, 2008). In that context, the notion of a synergistic control of abundant degrees of freedom was introduced (Latash et al, 2007).…”