In a visual inverted pendulum balancing task avoiding impending falls gets harder as we age.

Younger adults (YA) and older adults (OA) used a joystick to stabilize an unstable visual inverted pendulum (VIP) with a fundamental frequency (.27 Hz) of half that of bipedal human sway. Their task was to keep the VIP upright and to avoid ± 60° "fall" boundaries.

Vibrotactile feedback as a countermeasure for spatial disorientation.

Spaceflight can make astronauts susceptible to spatial disorientation which is one of the leading causes of fatal aircraft accidents. In our experiment, blindfolded participants used a joystick to balance themselves while inside a multi-axis rotation device (MARS) in either the vertical or horizontal roll plane. On Day 1, in the vertical roll plane (Earth analog condition) participants could use gravitational cues and therefore had a good sense of their orientation.

Crash Prediction Using Deep Learning in a Disorienting Spaceflight Analog Balancing Task.

Were astronauts forced to land on the surface of Mars using manual control of their vehicle, they would not have familiar gravitational cues because Mars' gravity is only 0.38 g. They could become susceptible to spatial disorientation, potentially causing mission ending crashes.

The role of spatial acuity in a dynamic balancing task without gravitational cues.

In earlier studies, blindfolded participants used a joystick to orient themselves to the direction of balance in the horizontal roll plane while in a device programmed to behave like an inverted pendulum. In this spaceflight analog situation, position relevant gravitational cues are absent. Most participants show minimal learning, positional drifting, and failure of path integration.

The effect of hypergravity on upright balance and voluntary sway.

We compared voluntary oscillatory sway for eight subjects tested in 1.8- and 1- gravito-inertial force (GIF) levels of parabolic flight. Subjects performed voluntary forward-backward (FB) and lateral left-right (LR) swaying as the forces and moments under the soles of each foot were measured.

Multiple roles of active stiffness in upright balance and multidirectional sway.

Both passive and active mechanisms are necessary to explain small amplitude forward-backward (FB) voluntary swaying. Parallel and symmetric leg inverted pendulum models with stiffness control are a simple way to replicate FB swaying during quiet stance. However, it has been more difficult to model lateral left-right (LR) voluntary swaying involving the dual mechanisms of hip loading-unloading and ankle pressure distribution.

Characterizing Individual Differences in a Dynamic Stabilization Task Using Machine Learning.

: Being able to identify individual differences in skilled motor learning during disorienting conditions is important for spaceflight, military aviation, and rehabilitation.: Blindfolded subjects ( = 34) were strapped into a device that behaved like an inverted pendulum in the horizontal roll plane and were instructed to use a joystick to stabilize themselves across two experimental sessions on consecutive days. Subjects could not use gravitational cues to determine their angular position and many soon became spatially disoriented.

Velocity storage: its multiple roles.

Our research described in this article was motivated by the puzzling finding of the Skylab M131 experiments: head movements made while rotating that are nauseogenic and disorienting on Earth are innocuous in a weightless, 0- environment. We describe a series of parabolic flight experiments that directly addressed this puzzle and discovered the gravity-dependent responses to semicircular canal stimulation, consistent with the principles of velocity storage. We describe a line of research that started in a different direction, investigating dynamic balancing, but ended up pointing to the gravity dependence of angular velocity-to-position integration of semicircular canal signals.

Learning and long-term retention of dynamic self-stabilization skills.

In earlier studies, we had subjects use a joystick to balance themselves when seated in a device programmed to behave like an inverted pendulum. Subjects tested in a vertically oriented roll plane showed rapid learning for dynamically stabilizing themselves about the direction of balance when it corresponded with the direction of gravity. Subjects tested in a horizontally oriented roll plane, unlike the vertical roll plane subjects, did not have gravitational cues to determine their angular positions and showed minimal learning and persistent cyclical drifting.

Adaptation to Coriolis force perturbations of postural sway requires an asymmetric two-leg model.

In the companion paper (Bakshi A, DiZio P, Lackner JR. . In press, 2019), we reported how voluntary forward-backward sway in a rotating room generated medial-lateral Coriolis forces that initially deviated intended body sway paths.

Rapid adaptation to Coriolis force perturbations of voluntary body sway.

Studying adaptation to Coriolis perturbations of arm movements has advanced our understanding of motor control and learning. We have now applied this paradigm to two-dimensional postural sway. We measured how subjects ( = 8) standing at the center of a fully enclosed rotating room who made voluntary anterior-posterior swaying movements adapted to the Coriolis perturbations generated by their sway.

An Active Suspension System for Mitigating Motion Sickness and Enabling Reading in a Car.

Introduction: The advent of autonomous automobiles raises new challenges for maintaining passenger safety and comfort. The challenge addressed here is how to predict and mitigate motion sickness when passengers read in a moving vehicle.

Methods: We utilized a car equipped with a commercial active suspension system developed for attenuating the transmission of road surface fluctuations to passengers.

Learning dynamic control of body yaw orientation.

To investigate the role of gravitational cues in the learning of a dynamic balancing task, we placed blindfolded subjects in a device programmed with inverted pendulum dynamics about the yaw axis. Subjects used a joystick to try and maintain a stable orientation at the direction of balance during 20 100 s-long trials. They pressed a trigger button on the joystick to indicate whenever they felt at the direction of balance.

Gravitational and Somatosensory Influences on Control and Perception of Roll Balance.

Introduction: Blindfolded subjects used a joystick to orient themselves to the direction of balance in a device programmed to exhibit inverted pendulum behavior in the roll plane; they indicated with a trigger press when they were at that location. Our goal was to determine how otolith and somatosensory information about the gravitational vertical influenced the ability to locate the direction of balance.

Methods: The subjects (N = 12) were tested in each of three orientations of the body roll plane: vertical (Upright), 45° back (45_Degree), and 90° back (Supine), which provided progressively less salient otolith and somatosensory information about roll orientation with regard to the direction of gravity.

Learning dynamic balancing in the roll plane with and without gravitational cues.

We determined the relative contributions of gravity-dependent positional cues and motion cues to the learning of roll balance control. We hypothesized that gravity-dependent otolith and somatosensory shear forces related to body orientation would yield better initial performance, more rapid learning, and better retention. Blindfolded subjects rode in a device programmed to roll with inverted pendulum dynamics in a vertical (UPRIGHT) or horizontal plane (SUPINE), and used a joystick to align themselves with the direction of balance.

The influence of sleep deprivation and oscillating motion on sleepiness, motion sickness, and cognitive and motor performance.

Our goal was to determine how sleep deprivation, nauseogenic motion, and a combination of motion and sleep deprivation affect cognitive vigilance, visual-spatial perception, motor learning and retention, and balance. We exposed four groups of subjects to different combinations of normal 8h sleep or 4h sleep for two nights combined with testing under stationary conditions or during 0.28Hz horizontal linear oscillation.

Learning dynamic control of body roll orientation.

Our objective was to examine how the control of orientation is learned in a task involving dynamically balancing about an unstable equilibrium point, the gravitational vertical, in the absence of leg reflexes and muscle stiffness. Subjects (n = 10) used a joystick to set themselves to the gravitational vertical while seated in a multi-axis rotation system (MARS) device programmed with inverted pendulum dynamics. The MARS is driven by powerful servomotors and can faithfully follow joystick commands up to 2.

Direction of balance and perception of the upright are perceptually dissociable.

We examined whether the direction of balance rather than an otolith reference determines the perceived upright. Participants seated in a device that rotated around the roll axis used a joystick to control its motion. The direction of balance of the device, the location where it would not be accelerated to either side, could be offset from the gravitational vertical, a technique introduced by Riccio, Martin, and Stoffregen (J Exp Psychol Hum Percept Perform 18: 624-644, 1992).

Parkinsonian gait ameliorated with a moving handrail, not with a banister.

Objective: To determine whether haptic (touch and proprioception) cues from touching a moving handrail while walking can ameliorate the gait symptoms of Parkinson disease (PD), such as slowness and small stride length.

Design: Nonrandomized, controlled before-after trial.

Setting: Physical therapy clinic.

Statistical analysis of quiet stance sway in 2-D.

Subjects exposed to a rotating environment that perturbs their postural sway show adaptive changes in their voluntary spatially directed postural motion to restore accurate movement paths but do not exhibit any obvious learning during passive stance. We have found, however, that a variable known to characterize the degree of stochasticity in quiet stance can also reveal subtle learning phenomena in passive stance. We extended Chow and Collins (Phys Rev E 52(1):909-912, 1995) one-dimensional pinned-polymer model (PPM) to two dimensions (2-D) and then evaluated the model's ability to make analytical predictions for 2-D quiet stance.

Adaptation to Coriolis perturbations of voluntary body sway transfers to preprogrammed fall-recovery behavior.

In a rotating environment, goal-oriented voluntary movements are initially disrupted in trajectory and endpoint, due to movement-contingent Coriolis forces, but accuracy is regained with additional movements. We studied whether adaptation acquired in a voluntary, goal-oriented postural swaying task performed during constant-velocity counterclockwise rotation (10 RPM) carries over to recovery from falling induced using a hold and release (H&R) paradigm. In H&R, standing subjects actively resist a force applied to their chest, which when suddenly released results in a forward fall and activation of an automatic postural correction.

Experimental measure of arm stiffness during single reaching movements with a time-frequency analysis.

We tested an innovative method to estimate joint stiffness and damping during multijoint unfettered arm movements. The technique employs impulsive perturbations and a time-frequency analysis to estimate the arm's mechanical properties along a reaching trajectory. Each single impulsive perturbation provides a continuous estimation on a single-reach basis, making our method ideal to investigate motor adaptation in the presence of force fields and to study the control of movement in impaired individuals with limited kinematic repeatability.

Immediate compensation for variations in self-generated Coriolis torques related to body dynamics and carried objects.

We have previously shown that the Coriolis torques that result when an arm movement is performed during torso rotation do not affect movement trajectory. Our purpose in the present study was to examine whether torso motion-induced Coriolis and other interaction torques are counteracted during a turn and reach (T&R) movement when the effective mass of the hand is augmented, and whether the dominant arm has an advantage in coordinating intersegmental dynamics as predicted by the dynamic dominance hypothesis (Sainburg RL. Exp Brain Res 142: 241-258, 2002).

Measuring multi-joint stiffness during single movements: numerical validation of a novel time-frequency approach.

This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis.

Comparative analysis of methods for estimating arm segment parameters and joint torques from inverse dynamics.

A common problem in the analyses of upper limb unfettered reaching movements is the estimation of joint torques using inverse dynamics. The inaccuracy in the estimation of joint torques can be caused by the inaccuracy in the acquisition of kinematic variables, body segment parameters (BSPs), and approximation in the biomechanical models. The effect of uncertainty in the estimation of body segment parameters can be especially important in the analysis of movements with high acceleration.