Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds

The speed of voluntary movements is determined by the conflicting needs of maximizing accuracy and minimizing mechanical effort. Dynamic perturbations, e.g., force fields, may be used to manipulate movements in order to investigate these mechanisms. Here, we focus on how the presence of position- an...

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Main Authors:	Summa, Susanna, Casadio, Maura, Sanguineti, Vittorio
Format:	Online
Language:	English
Published:	Frontiers Media S.A. 2016
Online Access:	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126124/

id	pubmed-5126124
recordtype	oai_dc
spelling	pubmed-51261242016-12-13 Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds Summa, Susanna Casadio, Maura Sanguineti, Vittorio Neuroscience The speed of voluntary movements is determined by the conflicting needs of maximizing accuracy and minimizing mechanical effort. Dynamic perturbations, e.g., force fields, may be used to manipulate movements in order to investigate these mechanisms. Here, we focus on how the presence of position- and velocity-dependent force fields affects the relation between speed and accuracy during hand reaching movements. Participants were instructed to perform reaching movements under visual control in two directions, corresponding to either low or high arm inertia. The subjects were required to maintain four different movement durations (very slow, slow, fast, very fast). The experimental protocol included three phases: (i) familiarization—the robot generated no force; (ii) force field—the robot generated a force; and (iii) after-effect—again, no force. Participants were randomly assigned to four groups, depending on the type of force that was applied during the “force field” phase. The robot was programmed to generate position-dependent forces—with positive (K+) or negative stiffness (K−)—or velocity-dependent forces, with either positive (B+) or negative viscosity (B−). We focused on path curvature, smoothness, and endpoint error; in the latter we distinguished between bias and variability components. Movements in the high-inertia direction are smoother and less curved; smoothness also increases with movement speed. Endpoint bias and variability are greater in, respectively, the high and low inertia directions. A robust dependence on movement speed was only observed in the longitudinal components of both bias and variability. The strongest and more consistent effects of perturbation were observed with negative viscosity (B−), which resulted in increased variability during force field adaptation and in a reduction of the endpoint bias, which was retained in the subsequent after-effect phase. These findings confirm that training with negative viscosity produces lasting effects in movement accuracy at all speeds. Frontiers Media S.A. 2016-11-29 /pmc/articles/PMC5126124/ /pubmed/27965559 http://dx.doi.org/10.3389/fnhum.2016.00609 Text en Copyright © 2016 Summa, Casadio and Sanguineti. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
repository_type	Open Access Journal
institution_category	Foreign Institution
institution	US National Center for Biotechnology Information
building	NCBI PubMed
collection	Online Access
language	English
format	Online
author	Summa, Susanna Casadio, Maura Sanguineti, Vittorio
spellingShingle	Summa, Susanna Casadio, Maura Sanguineti, Vittorio Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds
author_facet	Summa, Susanna Casadio, Maura Sanguineti, Vittorio
author_sort	Summa, Susanna
title	Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds
title_short	Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds
title_full	Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds
title_fullStr	Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds
title_full_unstemmed	Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds
title_sort	effect of position- and velocity-dependent forces on reaching movements at different speeds
description	The speed of voluntary movements is determined by the conflicting needs of maximizing accuracy and minimizing mechanical effort. Dynamic perturbations, e.g., force fields, may be used to manipulate movements in order to investigate these mechanisms. Here, we focus on how the presence of position- and velocity-dependent force fields affects the relation between speed and accuracy during hand reaching movements. Participants were instructed to perform reaching movements under visual control in two directions, corresponding to either low or high arm inertia. The subjects were required to maintain four different movement durations (very slow, slow, fast, very fast). The experimental protocol included three phases: (i) familiarization—the robot generated no force; (ii) force field—the robot generated a force; and (iii) after-effect—again, no force. Participants were randomly assigned to four groups, depending on the type of force that was applied during the “force field” phase. The robot was programmed to generate position-dependent forces—with positive (K+) or negative stiffness (K−)—or velocity-dependent forces, with either positive (B+) or negative viscosity (B−). We focused on path curvature, smoothness, and endpoint error; in the latter we distinguished between bias and variability components. Movements in the high-inertia direction are smoother and less curved; smoothness also increases with movement speed. Endpoint bias and variability are greater in, respectively, the high and low inertia directions. A robust dependence on movement speed was only observed in the longitudinal components of both bias and variability. The strongest and more consistent effects of perturbation were observed with negative viscosity (B−), which resulted in increased variability during force field adaptation and in a reduction of the endpoint bias, which was retained in the subsequent after-effect phase. These findings confirm that training with negative viscosity produces lasting effects in movement accuracy at all speeds.
publisher	Frontiers Media S.A.
publishDate	2016
url	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126124/
_version_	1613743945567698944

Effect of Position- and Velocity-Dependent Forces on Reaching Movements at Different Speeds

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