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Exp Brain Res (2009) 192:293298 DOI 10.1007/s00221-008-1615-2
RESEARCH NOTE
Interaction of Wnger enslaving and error compensation in multiple Wnger force production
Joel R. Martin Mark L. Latash Vladimir M. Zatsiorsky
Received: 18 August 2008 / Accepted: 8 October 2008 / Published online: 5 November 2008 Springer-Verlag 2008
Abstract Previous studies have documented two patterns of Wnger interaction during multi-Wnger pressing tasks, enslaving and error compensation, which do not agree with each other. Enslaving is characterized by positive correlation between instructed (master) and non-instructed (slave) Wnger(s) while error compensation can be described as a pattern of negative correlation between master and slave Wngers. We hypothesize that pattern of Wnger interaction, enslaving or compensation depends on the initial force level and the magnitude of the targeted force change. Subjects were instructed to press with four Wngers (I index, M middle, R ring, and L little) from a speciWed initial force to target forces following a ramp target line. Forceforce relations between master and each of three slave Wngers were analyzed during the ramp phase of trials by calculating correlation coeYcients within each masterslave pair and then two-factor ANOVA was performed to determine eVect of initial force and force increase on the correlation coeYcients. It was found that, as initial force increased, the value of the correlation coeYcient decreased and in some cases became negative, i.e. the enslaving transformed into error compensation. Force increase magnitude had a smaller eVect on the correlation coeYcients. The observations support the hypothesis that the pattern of inter-Wnger interactionenslaving or compensation depends on the initial force level and, to a smaller degree, on
the targeted magnitude of the force increase. They suggest that the controller views tasks with higher steady-state forces and smaller force changes as implying a requirement to avoid large changes in the total force.
Keywords Fingers Force Enslaving
Error compensation Synergy
Introduction
When a person produces force at the Wngertips, two patterns of force production emerge. One pattern of force interaction, between Wngers of a hand, is called enslaving. Enslaving occurs when the Wngers not explicitly involved in a pressing task (slave Wngers) produce force when a Wnger from the same hand produces force by instruction (master Wnger) (Kilbreath and Gandevia 1994; Leijnse 1997; Li et al. 1998; Zatsiorsky et...