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Stability of Phase Relationships While Coordinating Arm Reaches with Whole Body Motion.

Bakker RS, Selen LP, Medendorp WP - PLoS ONE (2015)

Bottom Line: For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship.For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships.Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns.

View Article: PubMed Central - PubMed

Affiliation: Radboud University Nijmegen, Donders Centre for Cognition, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.

ABSTRACT
The human movement repertoire is characterized by the smooth coordination of several body parts, including arm movements and whole body motion. The neural control of this coordination is quite complex because the various body parts have their own kinematic and dynamic properties. Behavioral inferences about the neural solution to the coordination problem could be obtained by examining the emerging phase relationship and its stability. Here, we studied the phase relationships that characterize the coordination of arm-reaching movements with passively-induced whole-body motion. Participants were laterally translated using a vestibular chair that oscillated at a fixed frequency of 0.83 Hz. They were instructed to reach between two targets that were aligned either parallel or orthogonal to the whole body motion. During the first cycles of body motion, a metronome entrained either an in-phase or an anti-phase relationship between hand and body motion, which was released at later cycles to test phase stability. Results suggest that inertial forces play an important role when coordinating reaches with cyclic whole-body motion. For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship. When the latter was imposed, it readily transitioned or drifted back toward an in-phase relationship at cycles without metronomic entrainment. For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships. Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns. We discuss how predictive control and impedance control processes could be considered important mechanisms underlying the rhythmic coordination of arm reaches and body motion.

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Distribution of relative phase of all subjects in the Orthogonal condition.(Top) In-phase entrainment. (Middle) Anti-phase entrainment of selected subjects. (Bottom) Anti-phase entrainment of all subjects.
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pone.0146231.g005: Distribution of relative phase of all subjects in the Orthogonal condition.(Top) In-phase entrainment. (Middle) Anti-phase entrainment of selected subjects. (Bottom) Anti-phase entrainment of all subjects.

Mentions: Fig 5 shows the distributions of the relative phases in the orthogonal condition. In-phase hand motion, defined as reaches away from a rightward moving body, was fairly stable and within the required range (μ = 4.1°, σ = 19.4°) (Fig 5, top panel). However, the absence of the metronome resulted in a significant increase of the variance in early off (t2) t(9) = -2.68, p = 0.025) and late off periods (t3) (t(9) = -3.0, p = 0.02). The average phase did not drift away from the entrained phase.


Stability of Phase Relationships While Coordinating Arm Reaches with Whole Body Motion.

Bakker RS, Selen LP, Medendorp WP - PLoS ONE (2015)

Distribution of relative phase of all subjects in the Orthogonal condition.(Top) In-phase entrainment. (Middle) Anti-phase entrainment of selected subjects. (Bottom) Anti-phase entrainment of all subjects.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4697800&req=5

pone.0146231.g005: Distribution of relative phase of all subjects in the Orthogonal condition.(Top) In-phase entrainment. (Middle) Anti-phase entrainment of selected subjects. (Bottom) Anti-phase entrainment of all subjects.
Mentions: Fig 5 shows the distributions of the relative phases in the orthogonal condition. In-phase hand motion, defined as reaches away from a rightward moving body, was fairly stable and within the required range (μ = 4.1°, σ = 19.4°) (Fig 5, top panel). However, the absence of the metronome resulted in a significant increase of the variance in early off (t2) t(9) = -2.68, p = 0.025) and late off periods (t3) (t(9) = -3.0, p = 0.02). The average phase did not drift away from the entrained phase.

Bottom Line: For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship.For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships.Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns.

View Article: PubMed Central - PubMed

Affiliation: Radboud University Nijmegen, Donders Centre for Cognition, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.

ABSTRACT
The human movement repertoire is characterized by the smooth coordination of several body parts, including arm movements and whole body motion. The neural control of this coordination is quite complex because the various body parts have their own kinematic and dynamic properties. Behavioral inferences about the neural solution to the coordination problem could be obtained by examining the emerging phase relationship and its stability. Here, we studied the phase relationships that characterize the coordination of arm-reaching movements with passively-induced whole-body motion. Participants were laterally translated using a vestibular chair that oscillated at a fixed frequency of 0.83 Hz. They were instructed to reach between two targets that were aligned either parallel or orthogonal to the whole body motion. During the first cycles of body motion, a metronome entrained either an in-phase or an anti-phase relationship between hand and body motion, which was released at later cycles to test phase stability. Results suggest that inertial forces play an important role when coordinating reaches with cyclic whole-body motion. For parallel reaches, we found a stable in-phase and an unstable anti-phase relationship. When the latter was imposed, it readily transitioned or drifted back toward an in-phase relationship at cycles without metronomic entrainment. For orthogonal reaches, we did not find a clear difference in stability between in-phase and anti-phase relationships. Computer simulations further show that cost models that minimize energy expenditure (i.e. net torques) or endpoint variance of the reach cannot fully explain the observed coordination patterns. We discuss how predictive control and impedance control processes could be considered important mechanisms underlying the rhythmic coordination of arm reaches and body motion.

Show MeSH
Related in: MedlinePlus