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

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.

Decisions in motion: passive body acceleration modulates hand choice

“…Biomechanical cost estimation. We computed the biomechanical costs for the forthcoming-, constant-, and zero-acceleration hypotheses on the basis of a planar two-link arm model (for details see Bakker et al 2015). We imposed the assumed acceleration profiles on the shoulders of the arm model to compute the required shoulder and elbow torques to follow a minimum-jerk trajectory (Flash and Hogan 1985) from the start to the target position in body-centered coordinates.…”

Vestibular contributions to high-level sensorimotor functions

“…arm-reaching movements with passively-induced whole-body motion (Bakker et al, 2015). Experimentally, we observed a stable in-phase relationship when reaches are made between targets that are aligned parallel to the body motion.…”

Gait Compensation Strategies to Expected and Unexpected Yielding Terrain

“…De ning a general rule of motor control for walking on even terrain is challenging due to the numerous equivalent solutions arising from the extensive degrees of freedom encompassing dynamic, kinematic, and informational body properties. Indeed, it is necessary to establish stable body segment phase relationships through body torque and impedance control to achieve action goals 5 . Furthermore, the integration of vestibular signals with visual, muscular, and underfoot pressure information plays a crucial role in determining individual perceptual strategies [6][7][8][9] .…”