Gravito-inertial ambiguity resolved through head stabilization

Farkhatdinov, Ildar; Michalska, H.; Berthoz, Alain; Hayward, Vincent

doi:10.1098/rspa.2018.0010

Cited by 7 publications

(8 citation statements)

References 69 publications

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“…This is clearly shown by the large head displacements when subjects read a text fixed to, and moving with, the support base. Contrary to traditional interpretations, our results suggest that head stabilization may be revoked by the CNS as a mechanism to ensure a reliable reference for inertial guidance for postural control (80, 81), when necessary for accurate performance of a concurrent visual task. This finding is in line with the conclusion of pioneer investigations, performed under different balance conditions, showing that a supra-postural task influences postural control in an adaptive manner (26, 42, 82).…”

Section: Resultscontrasting

confidence: 94%

Vision Does Not Necessarily Stabilize the Head in Space During Continuous Postural Perturbations

2019

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Vision favors head stabilization in space during perturbations of standing balance. This is particularly obvious under conditions of continuous predictable perturbations as during sinusoidal antero-posterior (A-P) translations of the supporting platform. We tested here the hypothesis that under this condition the head can instead undergo large A-P oscillations, when a precision visual task is concurrently performed. We compared the head oscillations across four conditions while standing on a continuously translating platform. Eyes open (EO, no visual task), EO while reading a text fixed to the moving platform (EO-TP), EO while reading a text fixed to earth-ground (EO-TG), eyes-closed (EC). The platform translated at 0.2 and 0.6 Hz. Participants were young adult subjects, who received no particular instruction except reading the text aloud when required. Markers fixed on head, platform and text-sheet were captured by an optoelectronic device. We found that head oscillations were larger with EC than under all EO conditions. The oscillations were the least with EO and EO-TG, and intermediate with EO-TP. This was true under both low and high translation frequency, in spite of broadly smaller head oscillations at high frequency, common to all visual conditions. The distance between the head and the text was quite constant with EO-TP but fluctuated with EO-TG. The basic whole-body coordination features were moderately similar under all conditions, as assessed by the head-platform correlation coefficients and time lags. It appears that vision does not produce head stabilization in space when a concurrent visual task requiring focusing on a reading-text moving with the platform is performed. Contrary to traditional views centered on the stabilizing effect of vision under both static and dynamic conditions, the results show that head stabilization, normally ensuring a reference for inertial guidance for body balance, can be revoked by the CNS to allow performance of a non-postural task. This novel paradigm can shift long-standing views on the effect of vision on equilibrium control and be considered a potential exercise treatment for enhancing the multisensory integration process in people with balance problems.

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Section: Resultscontrasting

confidence: 94%

Vision Does Not Necessarily Stabilize the Head in Space During Continuous Postural Perturbations

2019

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“…The present work addressed this issue through modeling the sensor's and the head's dynamics with closed loop head stabilization controller and observer. The result presented here complements recent developments in the field [22,23,24,25] by demonstrating that head stabilization significantly improves the quality of verticality estimation. This result has many applications in the control of humanoid robots, rovers, drones, as well as human mobility assistance robots [26,27].…”

Section: Discussionsupporting

confidence: 74%

Idiothetic Verticality Estimation Through Head Stabilization Strategy

Farkhatdinov

Michalska

Berthoz

et al. 2019

IEEE Robot. Autom. Lett.

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The knowledge of the gravitational vertical is fundamental for the autonomous control of humanoids and other freemoving robotic systems such as rovers and drones. This article deals with the hypothesis that the so-called 'head stabilization strategy' observed in humans and animals facilitates the estimation of the true vertical from inertial sensing only. This problem is difficult because inertial measurements respond to a combination of gravity and fictitious forces that are hard to disentangle. From simulations and experiments, we found that the angular stabilization of a platform bearing inertial sensors enables the application of the separation principle. This principle, which permits one to design estimators and controllers independently from each other, typically applies to linear systems, but rarely to nonlinear systems. We found empirically that, given inertial measurements, the angular regulation of a platform results in a system that is stable and robust and which provides true vertical estimates as a byproduct of the feedback. We conclude that angularly stabilized inertial measurement platforms could liberate robots from ground-based measurements for postural control, locomotion, and other functions, leading to a true idiothetic sensing modality, that is, not based on any external reference but the gravity field. Index Terms-Biologically-Inspired Robots; Biomimetics; Sensor-based Control I. INTRODUCTION F OR humans, as for other living creatures, it is substantial to know the spatial orientation of our body with respect to the external world. Most of our sensory systems can contribute to this task. Interestingly, visual, auditory, tactile, proprioceptive, or olfactory sensory inputs can be easily put out of action, but the vestibular inputs are always available, even in the absence of gravity [1]. In artificial systems, robots in particular, inertial measurement units (IMUs) often play the role of a 'robotic vestibular system'. These IMUs sense the movements of the robot and provide its control system Manuscript

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“…Under a balance challenging condition (HF), the system for posture control likely disengages the command to the pelvis from that to the head in order to maintain the equilibrium while letting the head assist the visual task. Such process also underpins the EC condition, where the estimate of the gravitational vertical and head acceleration is driven by proprioception and vestibular input [ 73 – 75 ]. Probably, the variable pelvis control across participants is an indication of the attempt to draw a new strategy under unfamiliar challenging conditions.…”

Section: Discussionmentioning

confidence: 99%

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

2020

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When humans are administered continuous and predictable perturbations of stance, an adaptation period precedes the steady state of balancing behaviour. Little information is available on the modulation of adaptation by vision and perturbation frequency. Moreover, performance of supra-postural tasks may modulate adaptation in as yet unidentified ways. Our purpose was to identify differences in adaptation associated to distinct visual tasks and perturbation frequencies. Twenty non-disabled adult volunteers stood on a platform translating 10 cm in antero-posterior (AP) direction at low (LF, 0.18 Hz) and high frequency (HF, 0.56 Hz) with eyes open (EO) and closed (EC). Additional conditions were reading a text fixed to platform (EO-TP) and reading a text stationary on ground (EO-TG). Peak-to-peak (PP) displacement amplitude and AP position of head and pelvis markers were computed for each of 27 continuous perturbation cycles. The time constant and extent of head and pelvis adaptation and the cross-correlation coefficients between head and pelvis were compared across visual conditions and frequencies. Head and pelvis mean positions in space varied little across conditions and perturbation cycles but the mean head PP displacements changed over time. On average, at LF, the PP displacement of the head and pelvis increased progressively. Adaptation was rapid or ineffective with EO, but slower with EO-TG, EO-TP, EC. At HF, the head PP displacement amplitude decreased progressively with fast adaptation rates, while the pelvis adaptation was not apparent. The results show that visual tasks can modulate the adaptation rate, highlight the effect of the perturbation frequency on adaptation and provide evidence of priority assigned to pelvis stabilization over visual tasks at HF. The effects of perturbation frequency and optic flow and their interaction with other sensory inputs and cognitive tasks on the adaptation strategies should be investigated in impaired individuals and considered in the design of rehabilitation protocols.

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Gravito-inertial ambiguity resolved through head stabilization

Cited by 7 publications

References 69 publications

Vision Does Not Necessarily Stabilize the Head in Space During Continuous Postural Perturbations

Vision Does Not Necessarily Stabilize the Head in Space During Continuous Postural Perturbations

Idiothetic Verticality Estimation Through Head Stabilization Strategy

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

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