To react or not to react? Intrinsic stochasticity of human control in virtual stick balancing

Understanding how humans control unstable systems is central to many research problems, with applications ranging from quiet standing to aircraft landing. Increasingly, much evidence appears in favour of event-driven control hypothesis: human operators only start actively controlling the system when the discrepancy between the current and desired system states becomes large enough. The event-driven models based on the concept of threshold can explain many features of the experimentally observed dynamics. However, much still remains unclear about the dynamics of human-controlled systems, which likely indicates that humans use more intricate control mechanisms. This paper argues that control activation in humans may be not threshold-driven, but instead intrinsically stochastic, noise-driven. Specifically, we suggest that control activation stems from stochastic interplay between the operator's need to keep the controlled system near the goal state, on the one hand, and the tendency to postpone interrupting the system dynamics, on the other hand. We propose a model capturing this interplay and show that it matches the experimental data on human balancing of virtual overdamped stick. Our results illuminate that the noise-driven activation mechanism plays a crucial role at least in the considered task, and, hypothetically, in a broad range of human-controlled processes.

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How a plantar pressure-based, tongue-placed tactile biofeedback modifies postural control mechanisms during quiet standing

Experimental Brain Research ◽

10.1007/s00221-007-0953-9 ◽

2007 ◽

Vol 181 (4) ◽

pp. 547-554 ◽

Cited By ~ 13

Author(s):

Nicolas Vuillerme ◽

Nicolas Pinsault ◽

Olivier Chenu ◽

Matthieu Boisgontier ◽

Jacques Demongeot ◽

...

Keyword(s):

Postural Control ◽

Plantar Pressure ◽

Quiet Standing ◽

Control Mechanisms

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IDENTIFICATION OF DYNAMIC PATTERNS OF BODY SWAY DURING QUIET STANDING: IS IT A NONLINEAR PROCESS?

International Journal of Bifurcation and Chaos ◽

10.1142/s0218127410026472 ◽

2010 ◽

Vol 20 (04) ◽

pp. 1269-1278 ◽

Cited By ~ 7

Author(s):

HAMED GHOMASHCHI ◽

ALI ESTEKI ◽

JULIEN CLINTON SPROTT ◽

ALI MOTIE NASRABADI

Keyword(s):

Time Series ◽

Postural Control ◽

Correlation Dimension ◽

Postural Sway ◽

Convincing Evidence ◽

Temporal Organization ◽

Quiet Standing ◽

Body Sway ◽

Linear Measure ◽

Control Mechanisms

During quiet standing, the human body continuously moves about an upright posture in an erratic fashion. Many researchers characterize postural fluctuations as a stochastic process while some others suggest chaotic dynamics for postural sway. In this study, first we examined these assumptions using principles of chaos theory in normal healthy and in patients with deteriorated postural control mechanisms. Next, we compared the ability of a nonlinear dynamics quantifier correlation dimension to that of a linear measure standard deviation to describe variability of healthy and deteriorated postural control mechanisms during quiet standing. Our findings did not provide convincing evidence for existence of low dimensional chaos within normal and abnormal sway dynamics but support the notion that postural fluctuations time series are distinguishable from these generated by a random process. The results indicated that although linear variability measures discriminated well between groups, they did not provide any information about the structure of postural fluctuations. Calculated correlation dimension as a complexity measure which describes spatio temporal organization of time series may be useful in this regard.

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Evidence accumulation account of human operators’ decisions in intermittent control during inverted pendulum balancing

10.31234/osf.io/5yf9d ◽

2018 ◽

Author(s):

Arkady Zgonnikov ◽

Gustav Markkula

Keyword(s):

Decision Making ◽

Inverted Pendulum ◽

Experimental Studies ◽

Intermittent Control ◽

Accumulation Process ◽

Activation Patterns ◽

Control Error ◽

Evidence Accumulation ◽

Human Operators ◽

Control Activation

Human operators often employ intermittent, discontinuous control strategies in a variety of tasks. A typical intermittent controller monitors control error and generates corrective action when the deviation of the controlled system from the desired state becomes too large to ignore. Most contemporary models of human intermittent control employ simple, threshold-based trigger mechanism to model the process of control activation. However, recent experimental studies demonstrate that the control activation patterns produced by human operators do not support threshold-based models, and provide evidence for more complex activation mechanisms. In this paper, we investigate whether intermittent control activation in humans can be modeled as a decision-making process. We utilize an established drift-diffusion model, which treats decision making as an evidence accumulation process, and study it in simple numerical simulations. We demonstrate that this model robustly replicates the control activation patterns (distributions of control error at movement onset) produced by human operators in previously conducted experiments on virtual inverted pendulum balancing. Our results provide support to the hypothesis that intermittent control activation in human operators can be treated as an evidence accumulation process.

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Novel σ B regulation modules of Gram-positive bacteria involve the use of complex hybrid histidine kinases

Microbiology ◽

10.1099/mic.0.045740-0 ◽

2011 ◽

Vol 157 (1) ◽

pp. 3-12 ◽

Cited By ~ 24

Author(s):

Mark de Been ◽

Christof Francke ◽

Roland J. Siezen ◽

Tjakko Abee

Keyword(s):

Sigma Factor ◽

Current Knowledge ◽

Bacterial Species ◽

Fine Tuning ◽

Activation Mechanism ◽

Future Research ◽

Control Mechanisms ◽

Gram Positive ◽

Gram Positive Bacteria ◽

Genome Context

A common bacterial strategy to cope with stressful conditions is the activation of alternative sigma factors that control specific regulons enabling targeted responses. In the human pathogen Bacillus cereus, activation of the major stress-responsive sigma factor σ B is controlled by a signalling route that involves the multi-sensor hybrid histidine kinase RsbK. RsbK-type kinases are not restricted to the B. cereus group, but occur in a wide variety of other bacterial species, including members of the the low-GC Gram-positive genera Geobacillus and Paenibacillus as well as the high-GC actinobacteria. Genome context and protein sequence analyses of 118 RsbK homologues revealed extreme variability in N-terminal sensory as well as C-terminal regulatory domains and suggested that RsbK-type kinases are subject to complex fine-tuning systems, including sensitization and desensitization via methylation and demethylation within the helical domain preceding the H-box. The RsbK-mediated stress-responsive sigma factor activation mechanism that has evolved in B. cereus and the other species differs markedly from the extensively studied and highly conserved RsbRST-mediated σ B activation route found in Bacillus subtilis and other low-GC Gram-positive bacteria. Implications for future research on sigma factor control mechanisms are presented and current knowledge gaps are briefly discussed.

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MULTIFRACTAL SPECTRA AS A MEASURE OF COMPLEXITY IN HUMAN POSTURE

Fractals ◽

10.1142/s0218348x02001130 ◽

2002 ◽

Vol 10 (01) ◽

pp. 103-116 ◽

Cited By ~ 130

Author(s):

YU SHIMIZU ◽

STEFAN THURNER ◽

KLAUS EHRENBERGER

Keyword(s):

Visual Cues ◽

Functional Form ◽

Balance Control ◽

Multifractal Spectrum ◽

Quiet Standing ◽

Control Mechanisms ◽

Tactile Information ◽

Human Posture ◽

Multifractal Spectra ◽

Complex Control System

Human posture is the result of a complex control system. The joint output of several physiological — most likely nonlinearly interacting — processes leads to constant correctional movements which enable humans to stand upright. These correctional body movements reflect features of the underlying control mechanisms and have recently been shown to be multifractal processes. We analyze the movements of healthy quiet standing persons by means of wavelet-based multifractal spectra. We show that the functional form of these spectra depends on the mode of balance control. We compare the findings from a group of healthy persons to a group of patients suffering from balance disorders. As the main result we find that if balance control inputs, such as visual cues or tactile information are reduced, the dominant fractal exponent becomes smaller and the range of fractal exponents strongly narrows. We suggest to use a set of multifractal spectrum parameters as a "measure of complexity."

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