PF
P.A. Forbes
info
Please Note
<p>This page displays the records of the person named above and is not linked to a unique person identifier. This record may need to be merged to a profile.</p>
2 records found
1
The vestibular system plays a central role in maintaining upright balance by encoding head motion and integrating this information with visual and somatosensory cues. When the relationship between self-motion and vestibular input becomes unreliable, the central nervous system (CNS) adapts to preserve postural stability. Previous studies demonstrated that adaptation occurs when altered vestibular input remains coherently linked to head movement; however, it remains unclear whether recalibration persists when this motion--afference relationship is degraded by non-coherent noise (\cite{Heroux2015, Chen2020}).
This report investigates vestibular recalibration under two forms of galvanic vestibular stimulation: a coherent, head-coupled stimulus derived from a validated motion-to-current conversion model, and the same stimulus combined with high-amplitude non-coherent noise. Fourteen participants completed standing-balance trials assessing baseline sway, externally replayed vestibular perturbations, and short-term learning during a brief eyes-open calibration period. Postural stability was quantified using T1 lateral displacement, and adaptation was assessed by comparing sway variability before and after calibration.
Under coherent stimulation, participants exhibited clear recalibration: sway variability increased immediately after stimulation onset but decreased during calibration, returning toward baseline levels. In contrast, non-coherent stimulation produced substantially greater sway and reduced adaptive improvement, indicating that noise limits the CNS’s ability to reinterpret vestibular input. Nonetheless, some recalibration was still observed, although highly variable across individuals. Additional findings revealed transient post-stimulation after-effects and modest order-dependent influences, though these did not reach statistical significance.
Overall, the results indicate that vestibular recalibration depends critically on the coherence and reliability of motion-linked vestibular input. When the motion–afference mapping is degraded by an external noise source, the CNS down-weights vestibular cues and exhibits limited adaptive learning. ...
This report investigates vestibular recalibration under two forms of galvanic vestibular stimulation: a coherent, head-coupled stimulus derived from a validated motion-to-current conversion model, and the same stimulus combined with high-amplitude non-coherent noise. Fourteen participants completed standing-balance trials assessing baseline sway, externally replayed vestibular perturbations, and short-term learning during a brief eyes-open calibration period. Postural stability was quantified using T1 lateral displacement, and adaptation was assessed by comparing sway variability before and after calibration.
Under coherent stimulation, participants exhibited clear recalibration: sway variability increased immediately after stimulation onset but decreased during calibration, returning toward baseline levels. In contrast, non-coherent stimulation produced substantially greater sway and reduced adaptive improvement, indicating that noise limits the CNS’s ability to reinterpret vestibular input. Nonetheless, some recalibration was still observed, although highly variable across individuals. Additional findings revealed transient post-stimulation after-effects and modest order-dependent influences, though these did not reach statistical significance.
Overall, the results indicate that vestibular recalibration depends critically on the coherence and reliability of motion-linked vestibular input. When the motion–afference mapping is degraded by an external noise source, the CNS down-weights vestibular cues and exhibits limited adaptive learning. ...
The vestibular system plays a central role in maintaining upright balance by encoding head motion and integrating this information with visual and somatosensory cues. When the relationship between self-motion and vestibular input becomes unreliable, the central nervous system (CNS) adapts to preserve postural stability. Previous studies demonstrated that adaptation occurs when altered vestibular input remains coherently linked to head movement; however, it remains unclear whether recalibration persists when this motion--afference relationship is degraded by non-coherent noise (\cite{Heroux2015, Chen2020}).
This report investigates vestibular recalibration under two forms of galvanic vestibular stimulation: a coherent, head-coupled stimulus derived from a validated motion-to-current conversion model, and the same stimulus combined with high-amplitude non-coherent noise. Fourteen participants completed standing-balance trials assessing baseline sway, externally replayed vestibular perturbations, and short-term learning during a brief eyes-open calibration period. Postural stability was quantified using T1 lateral displacement, and adaptation was assessed by comparing sway variability before and after calibration.
Under coherent stimulation, participants exhibited clear recalibration: sway variability increased immediately after stimulation onset but decreased during calibration, returning toward baseline levels. In contrast, non-coherent stimulation produced substantially greater sway and reduced adaptive improvement, indicating that noise limits the CNS’s ability to reinterpret vestibular input. Nonetheless, some recalibration was still observed, although highly variable across individuals. Additional findings revealed transient post-stimulation after-effects and modest order-dependent influences, though these did not reach statistical significance.
Overall, the results indicate that vestibular recalibration depends critically on the coherence and reliability of motion-linked vestibular input. When the motion–afference mapping is degraded by an external noise source, the CNS down-weights vestibular cues and exhibits limited adaptive learning.
This report investigates vestibular recalibration under two forms of galvanic vestibular stimulation: a coherent, head-coupled stimulus derived from a validated motion-to-current conversion model, and the same stimulus combined with high-amplitude non-coherent noise. Fourteen participants completed standing-balance trials assessing baseline sway, externally replayed vestibular perturbations, and short-term learning during a brief eyes-open calibration period. Postural stability was quantified using T1 lateral displacement, and adaptation was assessed by comparing sway variability before and after calibration.
Under coherent stimulation, participants exhibited clear recalibration: sway variability increased immediately after stimulation onset but decreased during calibration, returning toward baseline levels. In contrast, non-coherent stimulation produced substantially greater sway and reduced adaptive improvement, indicating that noise limits the CNS’s ability to reinterpret vestibular input. Nonetheless, some recalibration was still observed, although highly variable across individuals. Additional findings revealed transient post-stimulation after-effects and modest order-dependent influences, though these did not reach statistical significance.
Overall, the results indicate that vestibular recalibration depends critically on the coherence and reliability of motion-linked vestibular input. When the motion–afference mapping is degraded by an external noise source, the CNS down-weights vestibular cues and exhibits limited adaptive learning.
Reflexes and co-contraction are the two mechanisms used for effective limb control when humans face unexpected perturbations in their daily activities. When the environment has reduced stability margins, reflexes are tempered due to the oscillations caused by the neural time delay of the reflexive pathways. An explanation is that reflexes adapt to the dynamics of the environment and stability margins are the constraint. This view requires that humans assess stability margins, which could happen by detecting changes (i.e. oscillations) in the perturbation eliciting the reflexes. The perturbation perceived by the human is the actual perturbation filtered by the dynamics of the environment. Therefore, changes in the stability of the environment influence the perceived perturbation. The goal of this study is to determine whether reflex modulation is triggered by the environmental dynamics (i.e. damping and stability margins) or by the properties of the perturbation eliciting a reflexive response. An experiment was designed where participants were asked to minimize the displacements caused by continuous force perturbations applied to the hand while interacting with different environmental dynamics. Some of the perturbations were prefiltered to mimic the filtering effect of the environmental dynamics. Variations in the dynamics of the shoulder joint were quantified through the estimated arm admittance (i.e. displacements in response to force perturbations). The results show variations in the admittance between the perturbations mimicking the environment and the true environment at low frequencies (below 5Hz); and for different prior knowledge about the environmental dynamics (below 2Hz). These variations indicate that perturbations can be designed to mimic the environmental dynamics, and that perturbation properties and stability constraints cause changes in the motor behaviour.
...
Reflexes and co-contraction are the two mechanisms used for effective limb control when humans face unexpected perturbations in their daily activities. When the environment has reduced stability margins, reflexes are tempered due to the oscillations caused by the neural time delay of the reflexive pathways. An explanation is that reflexes adapt to the dynamics of the environment and stability margins are the constraint. This view requires that humans assess stability margins, which could happen by detecting changes (i.e. oscillations) in the perturbation eliciting the reflexes. The perturbation perceived by the human is the actual perturbation filtered by the dynamics of the environment. Therefore, changes in the stability of the environment influence the perceived perturbation. The goal of this study is to determine whether reflex modulation is triggered by the environmental dynamics (i.e. damping and stability margins) or by the properties of the perturbation eliciting a reflexive response. An experiment was designed where participants were asked to minimize the displacements caused by continuous force perturbations applied to the hand while interacting with different environmental dynamics. Some of the perturbations were prefiltered to mimic the filtering effect of the environmental dynamics. Variations in the dynamics of the shoulder joint were quantified through the estimated arm admittance (i.e. displacements in response to force perturbations). The results show variations in the admittance between the perturbations mimicking the environment and the true environment at low frequencies (below 5Hz); and for different prior knowledge about the environmental dynamics (below 2Hz). These variations indicate that perturbations can be designed to mimic the environmental dynamics, and that perturbation properties and stability constraints cause changes in the motor behaviour.