Dynamic primitives in constrained action: systematic changes in the zero-force trajectory

Hermus, James; Doeringer, Joseph; Sternad, Dagmar; Hogan, Neville

doi:10.1152/jn.00082.2023

“…A kinematic constraint provides an intermediate stage between unconstrained (free) motion and interaction with complex dynamics. Circularly constrained motion, such as crank-turning, has been less widely studied 42 – 44 , despite being ubiquitous in everyday manipulation (e.g., turning a steering wheel or opening a door). In fact, opening a door was reported to be the most common activity of daily living 26 .…”

Section: Methodsmentioning

confidence: 99%

Brownian processes in human motor control support descending neural velocity commands

Tessari,

Hermus,

Sugimoto-Dimitrova

et al. 2024

Sci Rep

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The motor neuroscience literature suggests that the central nervous system may encode some motor commands in terms of velocity. In this work, we tackle the question: what consequences would velocity commands produce at the behavioral level? Considering the ubiquitous presence of noise in the neuromusculoskeletal system, we predict that velocity commands affected by stationary noise would produce “random walks”, also known as Brownian processes, in position. Brownian motions are distinctively characterized by a linearly growing variance and a power spectral density that declines in inverse proportion to frequency. This work first shows that these Brownian processes are indeed observed in unbounded motion tasks e.g., rotating a crank. We further predict that such growing variance would still be present, but bounded, in tasks requiring a constant posture e.g., maintaining a static hand position or quietly standing. This hypothesis was also confirmed by experimental observations. A series of descriptive models are investigated to justify the observed behavior. Interestingly, one of the models capable of accounting for all the experimental results must feature forward-path velocity commands corrupted by stationary noise. The results of this work provide behavioral support for the hypothesis that humans plan the motion components of their actions in terms of velocity.

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“…A kinematic constraint provides an intermediate stage between unconstrained (free) motion and interaction with complex dynamics. Circularly constrained motion, such as crank-turning, has been less widely studied (Hermus et al 2023; Ohta et al 2004; Russell and Hogan 1989), despite being ubiquitous in everyday manipulation (e.g., turning a steering wheel or opening a door). In fact, opening a door was reported to be the most common activity of daily living (Petrich et al 2022).…”

Section: Methodsmentioning

confidence: 99%

Behavioral Consequences of Velocity Commands: Brownian Processes in Human Motor Tasks

Tessari,

Hermus,

Sugimoto-Dimitrova

et al. 2023

Preprint

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Human postural control exhibits stochastic behavior resembling a random walk, which implies unbounded growth of position variance. Here we show that unbounded position variance is indeed observed in a common task, turning a crank. In postural tasks, intermittent control has been proposed to limit position variance. We further show that when position variance is unbounded, it displays a distinctive signature of underlying Brownian motion, a low-frequency power spectrum that declines at -20 dB/decade but exhibits flattening in bounded tasks. Remarkably, a descriptive model of a control system competent to account for all of these data must feature a forward-path velocity command corrupted by stationary noise. This provides independent behavioral support for the theory that the brain encodes motion commands in terms of velocity.

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“…A kinematic constraint provides an intermediate stage between unconstrained (free) motion and interaction with complex dynamics. Circularly constrained motion, such as crank-turning, has been less widely studied [46]- [48], despite being ubiquitous in everyday manipulation (e.g., turning a steering wheel or opening a door). In fact, opening a door was reported to be the most common activity of daily living [26].…”

Section: Methodsmentioning

confidence: 99%

Behavioral Consequences of Velocity Commands: Brownian Processes in Human Motor Tasks

Tessari,

Hermus,

Sugimoto-Dimitrova

et al. 2023

Preprint

Self Cite

0

View full text Add to dashboard Cite

The motor neuroscience literature suggests that the central nervous system may encode some motor commands in terms of velocity. In this work, we tackle the question: what consequences would velocity commands produce at the behavioral level? Considering the ubiquitous presence of noise in the neuromusculoskeletal system, we predict that velocity commands affected by stationary noise would produce “random walks”, also known as Brownian processes, in position. Brownian motions are distinctively characterized by a linearly growing variance and a power spectral density that declines in inverse proportion to frequency. This work first shows that these Brownian processes are indeed observed in unbounded motion tasks e.g., rotating a crank. We further predict that such growing variance would still be present, but bounded, in tasks requiring a constant posture e.g., maintaining a static hand position or quietly standing. This hypothesis was also confirmed by experimental observations. A series of descriptive models are investigated to justify the observed behavior. Interestingly, one of the models capable of accounting for all the experimental results must feature forward-path velocity commands corrupted by stationary noise. The results of this work provide behavioral support for the hypothesis that humans plan the motion components of their actions in terms of velocity.

show abstract

Dynamic primitives in constrained action: systematic changes in the zero-force trajectory

Cited by 3 publications

References 88 publications

Brownian processes in human motor control support descending neural velocity commands

Brownian processes in human motor control support descending neural velocity commands

Behavioral Consequences of Velocity Commands: Brownian Processes in Human Motor Tasks

Behavioral Consequences of Velocity Commands: Brownian Processes in Human Motor Tasks

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