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Dissociating Variability and Effort as Determinants of Coordination

When coordinating movements, the nervous system often has to decide how to distribute work across a number of redundant effectors. Here, we show that humans solve this problem by trying to minimize both the variability of motor output and the effort involved. In previous studies that investigated th...

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Detalles Bibliográficos
Autores principales: O'Sullivan, Ian, Burdet, Etienne, Diedrichsen, Jörn
Formato: Texto
Lenguaje:English
Publicado: Public Library of Science 2009
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2661023/
https://www.ncbi.nlm.nih.gov/pubmed/19360132
http://dx.doi.org/10.1371/journal.pcbi.1000345
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author O'Sullivan, Ian
Burdet, Etienne
Diedrichsen, Jörn
author_facet O'Sullivan, Ian
Burdet, Etienne
Diedrichsen, Jörn
author_sort O'Sullivan, Ian
collection PubMed
description When coordinating movements, the nervous system often has to decide how to distribute work across a number of redundant effectors. Here, we show that humans solve this problem by trying to minimize both the variability of motor output and the effort involved. In previous studies that investigated the temporal shape of movements, these two selective pressures, despite having very different theoretical implications, could not be distinguished; because noise in the motor system increases with the motor commands, minimization of effort or variability leads to very similar predictions. When multiple effectors with different noise and effort characteristics have to be combined, however, these two cost terms can be dissociated. Here, we measure the importance of variability and effort in coordination by studying how humans share force production between two fingers. To capture variability, we identified the coefficient of variation of the index and little fingers. For effort, we used the sum of squared forces and the sum of squared forces normalized by the maximum strength of each effector. These terms were then used to predict the optimal force distribution for a task in which participants had to produce a target total force of 4–16 N, by pressing onto two isometric transducers using different combinations of fingers. By comparing the predicted distribution across fingers to the actual distribution chosen by participants, we were able to estimate the relative importance of variability and effort of 1∶7, with the unnormalized effort being most important. Our results indicate that the nervous system uses multi-effector redundancy to minimize both the variability of the produced output and effort, although effort costs clearly outweighed variability costs.
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spelling pubmed-26610232009-04-10 Dissociating Variability and Effort as Determinants of Coordination O'Sullivan, Ian Burdet, Etienne Diedrichsen, Jörn PLoS Comput Biol Research Article When coordinating movements, the nervous system often has to decide how to distribute work across a number of redundant effectors. Here, we show that humans solve this problem by trying to minimize both the variability of motor output and the effort involved. In previous studies that investigated the temporal shape of movements, these two selective pressures, despite having very different theoretical implications, could not be distinguished; because noise in the motor system increases with the motor commands, minimization of effort or variability leads to very similar predictions. When multiple effectors with different noise and effort characteristics have to be combined, however, these two cost terms can be dissociated. Here, we measure the importance of variability and effort in coordination by studying how humans share force production between two fingers. To capture variability, we identified the coefficient of variation of the index and little fingers. For effort, we used the sum of squared forces and the sum of squared forces normalized by the maximum strength of each effector. These terms were then used to predict the optimal force distribution for a task in which participants had to produce a target total force of 4–16 N, by pressing onto two isometric transducers using different combinations of fingers. By comparing the predicted distribution across fingers to the actual distribution chosen by participants, we were able to estimate the relative importance of variability and effort of 1∶7, with the unnormalized effort being most important. Our results indicate that the nervous system uses multi-effector redundancy to minimize both the variability of the produced output and effort, although effort costs clearly outweighed variability costs. Public Library of Science 2009-04-10 /pmc/articles/PMC2661023/ /pubmed/19360132 http://dx.doi.org/10.1371/journal.pcbi.1000345 Text en O'Sullivan et al. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
spellingShingle Research Article
O'Sullivan, Ian
Burdet, Etienne
Diedrichsen, Jörn
Dissociating Variability and Effort as Determinants of Coordination
title Dissociating Variability and Effort as Determinants of Coordination
title_full Dissociating Variability and Effort as Determinants of Coordination
title_fullStr Dissociating Variability and Effort as Determinants of Coordination
title_full_unstemmed Dissociating Variability and Effort as Determinants of Coordination
title_short Dissociating Variability and Effort as Determinants of Coordination
title_sort dissociating variability and effort as determinants of coordination
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2661023/
https://www.ncbi.nlm.nih.gov/pubmed/19360132
http://dx.doi.org/10.1371/journal.pcbi.1000345
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