Contribution of vision to postural behaviors during continuous support-surface translations

Abstract

During standing balance, kinematics of postural behaviors have been previously observed to change across visual conditions, perturbation amplitudes, or perturbation frequencies. However, experimental limitations only allowed for independent investigation of such parameters. Here, we adapted a pseudorandom ternary sequence (PRTS) perturbation previously used in rotational support-surface perturbations (Peterka 2002) to a translational paradigm, allowing us to concurrently examine the effects of vision, perturbation amplitude, and frequency on balance control. Additionally, the unpredictable PRTS perturbation eliminated effects of feedforward adaptations typical of responses to sinusoidal stimuli. The PRTS perturbation contained a wide spectral bandwidth (0.08-3.67 Hz) and was scaled to 4 different peak-to-peak amplitudes (3-24 cm). Root-mean-square (RMS) of hip displacement and velocity increased relative to RMS ankle displacement and velocity in the absence of vision across all subjects, especially at higher perturbation amplitudes. Gain and phase lag of CoM sway relative to the perturbation also increased with perturbation frequency; phase lag further increased when vision was absent. Together, our results suggest that visual input, perturbation amplitude, and perturbation frequency can concurrently and independently modulate postural strategies during standing balance. Moreover, each factor contributes to the difficulty of maintaining postural stability; increased difficulty evokes a greater reliance on hip motion. Finally, despite high degrees of joint angle variation across subjects, CoM measures were relatively similar across subjects, suggesting that the CoM is an important controlled variable for balance.

Adaptation of balancing behaviour during continuous perturbations of stance. Supra-postural visual tasks and platform translation frequency modulate adaptation rate

“…Rather, the minor displacements of the pelvis at HF compared to LF seems to represent a reference upon which the fine adjustments of head displacements occur. It has been noted already that minimization of the motion of the body’s centre of mass represents an important stabilization mechanism during continuous perturbations of stance [ 11 , 46 , 77 ]. Of course, these modest changes of the pelvis PP displacement across cycles could also affect the estimation of the time constants of the adaptation process.…”

“…During continuous and predictable perturbations, the appropriate balancing behaviour requires a fine coordination of body segments' motion. This undeniably depends on the visual condition, whereby the head tends to be stabilized in space ('head-fixed-in-space') with eyes-open (EO) and good visual acuity, and oscillates largely with poor visual acuity or with eyes-closed (EC) ('head riding the platform') [8][9][10][11][12]. Vision is an important factor for head stabilization, and its effect is independent of standing per se.…”

Higher Balance Task Demands are Associated with an Increase in Individual Alpha Peak Frequency

“…This suggests an important role of theta oscillations in somatosensory and/or vestibular information integration to maintain balance in the absence of visual information. In fact, electrode position CPz corresponds best to Brodman Area 5 (BA5) as a part of the posterior parietal cortex (PPC; Koessler et al, 2009 ) that is established to receive multimodal input from somatosensory, visual and vestibular systems ( Andersen et al, 1997 ) essential to maintain upright posture ( Mohapatra et al, 2012 ; Forbes et al, 2014 ; Joseph Jilk et al, 2014 ). During control of balance, the centro-parietal region may be involved in the integration of sensory afferents from the periphery subserving error detection and processing ( Sipp et al, 2013 ; Hülsdünker et al, 2015 ).…”

Changes in Posture Following a Single Session of Long-Duration Water Immersion

“…34 The 2 strategies are not mutually exclusive, but rather describe a continuum of possible postural control strategies. 34,35 Multiple mechanisms of change in balance strategy may be relevant when considering our results. Changes in hydrostatic pressure and buoyancy that occur during water immersion result in an underloading condition which effectively reduces the corrective torque required to maintain equilibrium.…”