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, 9 (4), e93892
eCollection

Limb Dominance Results From Asymmetries in Predictive and Impedance Control Mechanisms

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Limb Dominance Results From Asymmetries in Predictive and Impedance Control Mechanisms

Vivek Yadav et al. PLoS One.

Abstract

Handedness is a pronounced feature of human motor behavior, yet the underlying neural mechanisms remain unclear. We hypothesize that motor lateralization results from asymmetries in predictive control of task dynamics and in control of limb impedance. To test this hypothesis, we present an experiment with two different force field environments, a field with a predictable magnitude that varies with the square of velocity, and a field with a less predictable magnitude that varies linearly with velocity. These fields were designed to be compatible with controllers that are specialized in predicting limb and task dynamics, and modulating position and velocity dependent impedance, respectively. Because the velocity square field does not change the form of the equations of motion for the reaching arm, we reasoned that a forward dynamic-type controller should perform well in this field, while control of linear damping and stiffness terms should be less effective. In contrast, the unpredictable linear field should be most compatible with impedance control, but incompatible with predictive dynamics control. We measured steady state final position accuracy and 3 trajectory features during exposure to these fields: Mean squared jerk, Straightness, and Movement time. Our results confirmed that each arm made straighter, smoother, and quicker movements in its compatible field. Both arms showed similar final position accuracies, which were achieved using more extensive corrective sub-movements when either arm performed in its incompatible field. Finally, each arm showed limited adaptation to its incompatible field. Analysis of the dependence of trajectory errors on field magnitude suggested that dominant arm adaptation occurred by prediction of the mean field, thus exploiting predictive mechanisms for adaptation to the unpredictable field. Overall, our results support the hypothesis that motor lateralization reflects asymmetries in specific motor control mechanisms associated with predictive control of limb and task dynamics, and modulation of limb impedance.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Experimental apparatus.
Figure 2
Figure 2. Hand paths in the consistent and inconsistent fields for the dominant and non-dominant arms during initial and final phases of adaptation.
The non-dominant arms' hand paths are flipped about the y-axis such that left of the center is medial and the right is lateral for both the dominant and non-dominant arms.
Figure 3
Figure 3. Final position error for the dominant and non-dominant in consistent and inconsistent fields.
Figure 4
Figure 4. Normalized time after first submovement for the dominant and non-dominant arms in the consistent and inconsistent fields.
The asterisks on top of standard error bars indicate the phases where the interlimb differences were significant in post-hoc tests. The circles indicate the phases beyond which there was no significant difference between the final phase and individual phases.
Figure 5
Figure 5. Mean squared jerk for the dominant and non-dominant arms in the consistent and inconsistent fields.
The asterisks on top of standard error bars indicate the phases where the interlimb differences were significant in post-hoc tests. The circles indicate the phases beyond which there was no significant difference between the final phase and individual phases.
Figure 6
Figure 6. Linearity deviation for the dominant and non-dominant arms in the Consistent and Inconsistent fields.
The asterisks on top of standard error bars indicate the phases where the interlimb differences were significant in post-hoc tests. The circles indicate the phases beyond which there was no significant difference between the final phase and individual phases.
Figure 7
Figure 7. Duration for the dominant and non-dominant arms in the consistent and inconsistent fields.
The asterisks on top of standard error bars indicate the phases where the interlimb differences were significant in post-hoc tests. The circles indicate the phases beyond which there was no significant difference between the final phase and individual phases.
Figure 8
Figure 8. Performance measures for the dominant (shaded-square) and non-dominant (dark-diamond) arms in unpredictable field for different field strengths.

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