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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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Related in: MedlinePlus

Single trial data one representative subject in the parallel condition.(Top) Finger kinematics in body-centered coordinates (blue). Sled motion in world-centered coordinates (brown) for in-phase entrainment (left) and anti-phase entrainment (right). (Bottom) Relative phase between finger and sled movement for in-phase (left) and anti-phase (right). The grey area on each plot represents the first 16 cycles, during which timing of hand motion was guided by a metronome.
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pone.0146231.g003: Single trial data one representative subject in the parallel condition.(Top) Finger kinematics in body-centered coordinates (blue). Sled motion in world-centered coordinates (brown) for in-phase entrainment (left) and anti-phase entrainment (right). (Bottom) Relative phase between finger and sled movement for in-phase (left) and anti-phase (right). The grey area on each plot represents the first 16 cycles, during which timing of hand motion was guided by a metronome.

Mentions: Fig 3 shows the position of the finger and the body as a function of time for one representative subject in the parallel condition, for both the in-phase and anti-phase entrainment. Note that the finger motion is represented in body coordinates. The body moved sinusoidally at a frequency of 0.83 Hz and 15cm amplitude (as shown in brown in Fig 3). Hand motion, shown in blue, was guided by a metronome for the first 16 cycles, either in-phase or anti-phase with the body motion. When the metronome was turned off, the entrained hand motion continued during the first cycles in both conditions. The in-phase relationship appeared stable throughout the block, while the anti-phase relationship drifted and showed several transitions to an in-phase relation. We analyzed the number of phase transitions per condition. In the parallel condition, subjects made phase transitions in 13% (σ = 4%) of the in-phase blocks and in 26% (σ = 7%) of the anti-phase blocks. In the orthogonal condition, phase transitions were visible in 27% (σ = 6%) of the in-phase blocks and in 32% (σ = 6%) of the anti-phase blocks. In the following paragraphs, we will focus on this entrainment-dependent drift.


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

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

Single trial data one representative subject in the parallel condition.(Top) Finger kinematics in body-centered coordinates (blue). Sled motion in world-centered coordinates (brown) for in-phase entrainment (left) and anti-phase entrainment (right). (Bottom) Relative phase between finger and sled movement for in-phase (left) and anti-phase (right). The grey area on each plot represents the first 16 cycles, during which timing of hand motion was guided by a metronome.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0146231.g003: Single trial data one representative subject in the parallel condition.(Top) Finger kinematics in body-centered coordinates (blue). Sled motion in world-centered coordinates (brown) for in-phase entrainment (left) and anti-phase entrainment (right). (Bottom) Relative phase between finger and sled movement for in-phase (left) and anti-phase (right). The grey area on each plot represents the first 16 cycles, during which timing of hand motion was guided by a metronome.
Mentions: Fig 3 shows the position of the finger and the body as a function of time for one representative subject in the parallel condition, for both the in-phase and anti-phase entrainment. Note that the finger motion is represented in body coordinates. The body moved sinusoidally at a frequency of 0.83 Hz and 15cm amplitude (as shown in brown in Fig 3). Hand motion, shown in blue, was guided by a metronome for the first 16 cycles, either in-phase or anti-phase with the body motion. When the metronome was turned off, the entrained hand motion continued during the first cycles in both conditions. The in-phase relationship appeared stable throughout the block, while the anti-phase relationship drifted and showed several transitions to an in-phase relation. We analyzed the number of phase transitions per condition. In the parallel condition, subjects made phase transitions in 13% (σ = 4%) of the in-phase blocks and in 26% (σ = 7%) of the anti-phase blocks. In the orthogonal condition, phase transitions were visible in 27% (σ = 6%) of the in-phase blocks and in 32% (σ = 6%) of the anti-phase blocks. In the following paragraphs, we will focus on this entrainment-dependent drift.

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