scholarly journals Quantifying exploration in reward-based motor learning

2019 ◽  
Author(s):  
Nina M. van Mastrigt ◽  
Jeroen B.J. Smeets ◽  
Katinka van der Kooij
Keyword(s):  
Experimental Data ◽  
Motor Learning ◽  
Weight Shift ◽  
Weight Shifting

AbstractExploration in reward-based motor learning is observable in experimental data as increased variability. In order to quantify exploration, we compare three methods for estimating other sources of variability: sensorimotor noise. We use a task in which participants could receive stochastic binary reward feedback following a target-directed weight shift. Participants first performed 6 baseline blocks without feedback, and next twenty blocks alternating with and without feedback. Variability was assessed based on trial-to-trial changes in movement endpoint. We estimated sensorimotor noise by the median squared trial-to-trial change in movement endpoint for trials in which no exploration is expected. We identified three types of such trials: trials in baseline blocks, trials in the blocks without feedback, and rewarded trials in the blocks with feedback. We estimated exploration by the median squared trial-to-trial change following non-rewarded trials minus sensorimotor noise. As expected, variability was larger following non-rewarded trials than following rewarded trials. This indicates that our reward-based weight-shifting task successfully induced exploration. Most importantly, our three estimates of sensorimotor noise differed: the estimate based on rewarded trials was significantly lower than the estimates based on the two types of trials without feedback. Consequently, the estimates of exploration also differed. We conclude that the quantification of exploration depends critically on the type of trials used to estimate sensorimotor noise. We recommend the use of variability following rewarded trials.

Enhanced error facilitates motor learning in weight shift and increases use of the paretic leg during walking at chronic stage after stroke

2021 ◽  
Author(s):  
Seoung Hoon Park ◽  
Chao-Jung Hsu ◽  
Weena Dee ◽  
Elliot J. Roth ◽  
William Z. Rymer ◽  
...  
Keyword(s):  
Motor Learning ◽  
Chronic Stage ◽  
Weight Shift

scholarly journals ‘Recoupling’ the attentional and motor control of preparatory postural adjustments to overcome Freezing of Gait in Parkinson’s

2020 ◽  
Author(s):  
Amy Maslivec ◽  
Anna Fielding ◽  
Mark Wilson ◽  
Meriel Norris ◽  
William Young
Keyword(s):  
Motor Control ◽  
Cognitive Deficits ◽  
Critical Evaluation ◽  
Freezing Of Gait ◽  
Baseline Condition ◽  
Verbal Instruction ◽  
Step Initiation ◽  
Weight Shift ◽  
Pronounced Reduction ◽  
Weight Shifting

Abstract Objectives: This study examined if people with Parkinson’s and freezing of gait pathology (FoG) could be trained to increase preparatory weight-shift amplitude, and facilitate step initiation during FoG. Methods: Thirty-five people with Parkinson’s and FoG attempted to initiate forward walking from a stationary position caused by a freeze (n=17, FoG-F) or voluntarily stop (n=18, FoG-NF) in a Baseline condition and two conditions where an increased weight-shift amplitude was trained via: i) explicit verbal instruction, and ii) implicit movement analogies. Results: At Baseline, weight-shift amplitudes were smaller during: i) unsuccessful, compared to successful step initiations (FoG-F group), and ii) successful step initiations in the FoG-F group compared to FoG-NF. Both Verbal and Analogy training resulted in significant increases in weight-shift amplitude in both groups, and a corresponding pronounced reduction in unsuccessful attempts to initiate stepping (FoG-F group). Conclusions: Hypometric preparatory weight-shifting is associated with failure to initiate forward stepping in people with Parkinson’s and FoG. However, impaired weight-shift characteristics are modifiable through conscious strategies. This current study provides a novel and critical evaluation of preparatory weight-shift amplitudes during FoG events. The intervention described represents an attractive ‘rescue’ strategy and should be further scrutinised regarding limitations posed by physical and cognitive deficits.

scholarly journals ‘Recoupling’ the attentional and motor control of preparatory postural adjustments to overcome Freezing of Gait in Parkinson’s

2020 ◽  
Author(s):  
Amy Maslivec ◽  
Anna Fielding ◽  
Mark Wilson ◽  
Meriel Norris ◽  
William Young
Keyword(s):  
Motor Control ◽  
Cognitive Deficits ◽  
Critical Evaluation ◽  
Freezing Of Gait ◽  
Baseline Condition ◽  
Verbal Instruction ◽  
Step Initiation ◽  
Weight Shift ◽  
Pronounced Reduction ◽  
Weight Shifting

Abstract Objectives This study examined if people with Parkinson’s and freezing of gait pathology (FoG) could be trained to increase preparatory weight-shift amplitude, and facilitate step initiation during FoG. Methods Thirty-five people with Parkinson’s and FoG attempted to initiate forward stepping either during a FoG event (n = 17, FoG-F) or following a voluntary stop (n = 18, FoG-NF) in a Baseline condition and two conditions where an increased weight-shift amplitude was trained via: i) Explicit verbal instruction, and ii) Implicit movement analogies. Results At Baseline, weight-shift amplitudes were smaller during: i) unsuccessful, compared to successful step initiations (FoG-F group), and ii) successful step initiations in the FoG-F group compared to FoG-NF. Both Verbal and Analogy training resulted in significant increases in weight-shift amplitude in both groups, and a corresponding pronounced reduction in unsuccessful attempts to initiate stepping (FoG-F group). Conclusions Hypometric preparatory weight-shifting is associated with failure to initiate forward stepping in people with Parkinson’s and FoG. However, impaired weight-shift characteristics are modifiable through conscious strategies. This current study provides a novel and critical evaluation of preparatory weight-shift amplitudes during FoG events. The intervention described represents an attractive ‘rescue’ strategy and should be further scrutinised regarding limitations posed by physical and cognitive deficits.

scholarly journals Which Aspects of Postural Control Differentiate between Patients with Parkinson’s Disease with and without Freezing of Gait?

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Griet Vervoort ◽  
Evelien Nackaerts ◽  
Farshid Mohammadi ◽  
Elke Heremans ◽  
Sabine Verschueren ◽  
...  
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Postural Control ◽  
Freezing Of Gait ◽  
Sensory Information ◽  
Response Strength ◽  
Dynamic Posturography ◽  
Directional Control ◽  
Weight Shift ◽  
Weight Shifting

This exploratory study aimed to identify which aspects of postural control are able to distinguish between subgroups of patients with Parkinson’s disease (PD) and controls. Balance was tested using static and dynamic posturography. Freezers (n=9), nonfreezers (n=10), and controls (n=10) stood on a movable force platform and performed 3 randomly assigned tests: (1) sensory organization test (SOT) to evaluate the effective use of sensory information, (2) motor control test (MCT) to assess automatic postural reactions in response to platform perturbations, and (3) rhythmic weight shift test (RWS) to evaluate the ability to voluntarily move the center of gravity (COG) mediolaterally and anterior-posteriorly (AP). The respective outcome measures were equilibrium and postural strategy scores, response strength and amplitude of weight shift. Patients were in the “on” phase of the medication cycle. In general, freezers performed similarly on SOT and MCT compared to nonfreezers. Freezers showed an intact postural strategy during sensory manipulations and an appropriate response to external perturbations. However, during voluntary weight shifting, freezers showed poorer directional control compared to nonfreezers and controls. This suggests that freezers have adequate automatic postural control and sensory integration abilities in quiet stance, but show specific directional control deficits when weight shifting is voluntary.

scholarly journals ‘Recoupling’ the attentional and motor control of preparatory postural adjustments to overcome Freezing of Gait in Parkinson’s

2020 ◽  
Author(s):  
Amy Maslivec ◽  
Anna Fielding ◽  
Mark Wilson ◽  
Meriel Norris ◽  
William Young
Keyword(s):  
Motor Control ◽  
Cognitive Deficits ◽  
Critical Evaluation ◽  
Freezing Of Gait ◽  
Verbal Instruction ◽  
Step Initiation ◽  
Weight Shift ◽  
Baseline Weight ◽  
Pronounced Reduction ◽  
Weight Shifting

Abstract Objectives This study examined if people with Parkinson’s and freezing of gait pathology (FoG) could be trained to increase preparatory weight-shift amplitude, and facilitate step initiation during FoG. Methods Thirty-five people with Parkinson’s and FoG attempted to initiate forward stepping either during a FoG event (n=17, FoG-F) or following a voluntary stop (n=18, FoG-NF) in a Baseline condition and two conditions where an increased weight-shift amplitude was trained via: i) Explicit verbal instruction, and ii) Implicit movement analogies. Results At Baseline , weight-shift amplitudes were smaller during: i) unsuccessful, compared to successful step initiations (FoG-F group), and ii) successful step initiations in the FoG-F group compared to FoG-NF. Both Verbal and Analogy training resulted in significant increases in weight-shift amplitude in both groups, and a corresponding pronounced reduction in unsuccessful attempts to initiate stepping (FoG-F group). Conclusions Hypometric preparatory weight-shifting is associated with failure to initiate forward stepping in people with Parkinson’s and FoG. However, impaired weight-shift characteristics are modifiable through conscious strategies. This current study provides a novel and critical evaluation of preparatory weight-shift amplitudes during FoG events. The intervention described represents an attractive ‘rescue’ strategy and should be further scrutinised regarding limitations posed by physical and cognitive deficits.

scholarly journals ‘Recoupling’ the attentional and motor control of preparatory postural adjustments to overcome freezing of gait in Parkinson’s

2020 ◽  
Vol 17 (1) ◽  
Author(s):  
Amy Maslivec ◽  
Anna Fielding ◽  
Mark Wilson ◽  
Meriel Norris ◽  
William Young
Keyword(s):  
Motor Control ◽  
Cognitive Deficits ◽  
Critical Evaluation ◽  
Freezing Of Gait ◽  
Baseline Condition ◽  
Verbal Instruction ◽  
Step Initiation ◽  
Weight Shift ◽  
Pronounced Reduction ◽  
Weight Shifting

Abstract Objectives This study examined if people with Parkinson’s and freezing of gait pathology (FoG) could be trained to increase preparatory weight-shift amplitude, and facilitate step initiation during FoG. Methods Thirty-five people with Parkinson’s and FoG attempted to initiate forward walking from a stationary position caused by a freeze (n = 17, FoG-F) or voluntarily stop (n = 18, FoG-NF) in a Baseline condition and two conditions where an increased weight-shift amplitude was trained via: (i) explicit verbal instruction, and (ii) implicit movement analogies. Results At Baseline, weight-shift amplitudes were smaller during: (i) unsuccessful, compared to successful step initiations (FoG-F group), and (ii) successful step initiations in the FoG-F group compared to FoG-NF. Both Verbal and Analogy training resulted in significant increases in weight-shift amplitude in both groups, and a corresponding pronounced reduction in unsuccessful attempts to initiate stepping (FoG-F group). Conclusions Hypometric preparatory weight-shifting is associated with failure to initiate forward stepping in people with Parkinson’s and FoG. However, impaired weight-shift characteristics are modifiable through conscious strategies. This current study provides a novel and critical evaluation of preparatory weight-shift amplitudes during FoG events. The intervention described represents an attractive ‘rescue’ strategy and should be further scrutinised regarding limitations posed by physical and cognitive deficits.

Impaired Weight-Shift Amplitude in People with Parkinson’s Disease with Freezing of Gait

2021 ◽  
pp. 1-14
Author(s):  
Bauke Wybren Dijkstra ◽  
Moran Gilat ◽  
L. Eduardo Cofré Lizama ◽  
Martina Mancini ◽  
Bruno Bergmans ◽  
...  
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Balance Control ◽  
Dynamic Balance ◽  
Center Of Mass ◽  
Freezing Of Gait ◽  
Dopaminergic Medication ◽  
Weight Shift ◽  
Future Work ◽  
Weight Shifting

Background: People with Parkinson’s disease and freezing of gait (FOG; freezers) suffer from pronounced postural instability. However, the relationship between these phenomena remains unclear and has mostly been tested in paradigms requiring step generation. Objective: To determine if freezing-related dynamic balance deficits are present during a task without stepping and determine the influence of dopaminergic medication on dynamic balance control. Methods: Twenty-two freezers, 16 non-freezers, and 20 healthy age-matched controls performed mediolateral weight-shifts at increasing frequencies when following a visual target projected on a screen (MELBA task). The amplitude and phase shift differences between center of mass and target motion were measured. Balance scores (Mini-BESTest), 360° turning speed and the freezing ratio were also measured. Subjects with Parkinson’s disease were tested ON and partial OFF (overnight withdrawal) dopaminergic medication. Results: Freezers had comparable turning speed and balance scores to non-freezers and took more levodopa. Freezers produced hypokinetic weight-shift amplitudes throughout the MELBA task compared to non-freezers (p = 0.002), which were already present at task onset (p < 0.001). Freezers also displayed an earlier weight-shift breakdown than controls when OFF-medication (p = 0.008). Medication improved mediolateral weight-shifting in freezers and non-freezers. Freezers decreased their freezing ratio in response to medication. Conclusion: Hypokinetic weight-shifting proved a marked postural control deficit in freezers, while balance scores and turning speed were similar to non-freezers. Both weight-shift amplitudes and the freezing ratio were responsive to medication in freezers, suggesting axial motor vigor is levodopa-responsive. Future work needs to test whether weight-shifting and freezing severity can be further ameliorated through training.

Microdiffraction Patterns of Small Metallic Particles II; Theoretical Analysis

1982 ◽  
Vol 40 ◽  
pp. 668-669
Author(s):  
A. Gómez ◽  
P. Schabes-Retchkiman ◽  
M. José-Yacamán ◽  
T. Ocaña
Keyword(s):  
Experimental Data ◽  
Electron Diffraction ◽  
Theoretical Analysis ◽  
Size Range ◽  
Dynamical Theory ◽  
Metallic Particles ◽  
Splitting Effect

The splitting effect that is observed in microdiffraction pat-terns of small metallic particles in the size range 50-500 Å can be understood using the dynamical theory of electron diffraction for the case of a crystal containing a finite wedge. For the experimental data we refer to part I of this work in these proceedings.

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