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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Autores principales:	Ian O'Sullivan, Etienne Burdet, Jörn Diedrichsen
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2009
Materias:	Biology (General) QH301-705.5
Acceso en línea:	https://doaj.org/article/16460743cd6c47d98f20c392231f5cbc
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spelling	oai:doaj.org-article:16460743cd6c47d98f20c392231f5cbc2021-11-25T05:41:43ZDissociating variability and effort as determinants of coordination.1553-734X1553-735810.1371/journal.pcbi.1000345https://doaj.org/article/16460743cd6c47d98f20c392231f5cbc2009-04-01T00:00:00Zhttps://www.ncbi.nlm.nih.gov/pmc/articles/pmid/19360132/?tool=EBIhttps://doaj.org/toc/1553-734Xhttps://doaj.org/toc/1553-7358When 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.Ian O'SullivanEtienne BurdetJörn DiedrichsenPublic Library of Science (PLoS)articleBiology (General)QH301-705.5ENPLoS Computational Biology, Vol 5, Iss 4, p e1000345 (2009)
institution	DOAJ
collection	DOAJ
language	EN
topic	Biology (General) QH301-705.5
spellingShingle	Biology (General) QH301-705.5 Ian O'Sullivan Etienne Burdet Jörn Diedrichsen Dissociating variability and effort as determinants of coordination.
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.
format	article
author	Ian O'Sullivan Etienne Burdet Jörn Diedrichsen
author_facet	Ian O'Sullivan Etienne Burdet Jörn Diedrichsen
author_sort	Ian O'Sullivan
title	Dissociating variability and effort as determinants of coordination.
title_short	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_sort	dissociating variability and effort as determinants of coordination.
publisher	Public Library of Science (PLoS)
publishDate	2009
url	https://doaj.org/article/16460743cd6c47d98f20c392231f5cbc
work_keys_str_mv	AT ianosullivan dissociatingvariabilityandeffortasdeterminantsofcoordination AT etienneburdet dissociatingvariabilityandeffortasdeterminantsofcoordination AT jorndiedrichsen dissociatingvariabilityandeffortasdeterminantsofcoordination
_version_	1718414502423166976

Dissociating variability and effort as determinants of coordination.

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