Intermittency in the Control of Continuous Force Production

2000 ◽  
Vol 84 (4) ◽  
pp. 1708-1718 ◽  
Author(s):  
Andrew B. Slifkin ◽  
David E. Vaillancourt ◽  
Karl M. Newell
Keyword(s):  
Visual Feedback ◽  
Visual Information ◽  
Spectral Power ◽  
Force Production ◽  
Motor Output ◽  
Force Variability ◽  
Force Output ◽  
Feedback Information ◽  
Information Processes ◽  
Feedback Frequency

The purpose of the current investigation was to examine the influence of intermittency in visual information processes on intermittency in the control continuous force production. Adult human participants were required to maintain force at, and minimize variability around, a force target over an extended duration (15 s), while the intermittency of on-line visual feedback presentation was varied across conditions. This was accomplished by varying the frequency of successive force-feedback deliveries presented on a video display. As a function of a 128-fold increase in feedback frequency (0.2 to 25.6 Hz), performance quality improved according to hyperbolic functions (e.g., force variability decayed), reaching asymptotic values near the 6.4-Hz feedback frequency level. Thus, the briefest interval over which visual information could be integrated and used to correct errors in motor output was approximately 150 ms. The observed reductions in force variability were correlated with parallel declines in spectral power at about 1 Hz in the frequency profile of force output. In contrast, power at higher frequencies in the force output spectrum were uncorrelated with increases in feedback frequency. Thus, there was a considerable lag between the generation of motor output corrections (1 Hz) and the processing of visual feedback information (6.4 Hz). To reconcile these differences in visual and motor processing times, we proposed a model where error information is accumulated by visual information processes at a maximum frequency of 6.4 per second, and the motor system generates a correction on the basis of the accumulated information at the end of each 1-s interval.

scholarly journals Intermittent Visuomotor Processing in the Human Cerebellum, Parietal Cortex, and Premotor Cortex

2006 ◽  
Vol 95 (2) ◽  
pp. 922-931 ◽  
Author(s):  
David E. Vaillancourt ◽  
Mary A. Mayka ◽  
Daniel M. Corcos
Keyword(s):  
Parietal Cortex ◽  
Visual Feedback ◽  
Visual Information ◽  
Grip Force ◽  
Premotor Cortex ◽  
Force Variability ◽  
Neural Activation ◽  
Control Force ◽  
Force Condition ◽  
Visuomotor Processing

The cerebellum, parietal cortex, and premotor cortex are integral to visuomotor processing. The parameters of visual information that modulate their role in visuomotor control are less clear. From motor psychophysics, the relation between the frequency of visual feedback and force variability has been identified as nonlinear. Thus we hypothesized that visual feedback frequency will differentially modulate the neural activation in the cerebellum, parietal cortex, and premotor cortex related to visuomotor processing. We used functional magnetic resonance imaging at 3 Tesla to examine visually guided grip force control under frequent and infrequent visual feedback conditions. Control conditions with intermittent visual feedback alone and a control force condition without visual feedback were examined. As expected, force variability was reduced in the frequent compared with the infrequent condition. Three novel findings were identified. First, infrequent (0.4 Hz) visual feedback did not result in visuomotor activation in lateral cerebellum (lobule VI/Crus I), whereas frequent (25 Hz) intermittent visual feedback did. This is in contrast to the anterior intermediate cerebellum (lobule V/VI), which was consistently active across all force conditions compared with rest. Second, confirming previous observations, the parietal and premotor cortices were active during grip force with frequent visual feedback. The novel finding was that the parietal and premotor cortex were also active during grip force with infrequent visual feedback. Third, right inferior parietal lobule, dorsal premotor cortex, and ventral premotor cortex had greater activation in the frequent compared with the infrequent grip force condition. These findings demonstrate that the frequency of visual information reduces motor error and differentially modulates the neural activation related to visuomotor processing in the cerebellum, parietal cortex, and premotor cortex.

Study of Equilibrium Sense Improvement Displaying Visual Information

2008 ◽  
Vol 381-382 ◽  
pp. 369-372
Author(s):  
Gi Beum Kim ◽  
S.H. Jeong ◽  
Woo Suk Chong ◽  
H.S. Kang ◽  
S.J. Kim ◽  
...  
Keyword(s):  
Young People ◽  
Visual Feedback ◽  
Postural Balance ◽  
Visual Information ◽  
Muscular Strength ◽  
Center Of Pressure ◽  
Vestibular Function ◽  
Feedback Information ◽  
Weight Shift ◽  
Repeated Training

The effectiveness of the visual feedback to improve ability with the sense and muscular strength of human in our bicycle system was quantitatively verified in our study. Experiments were performed to find the factors related to the training of equilibrium sense. The subjects consisted of young and the aged and the group of young people was compared against the group of the aged. We investigated three different training modes, non-visual feedback (NVF), visual feedback of the weight (VFW), and visual feedback of the center of pressure (VFC) and measured the riding time and speed, the weight shift, and the center of pressure (COP) for twenties and seventies. The results showed that the running capability of the young and the aged became much better after repeated training. In addition, it was found out that the ability to control postural balance and the capability of equilibrium sense were improved with the presentation of the visual feedback information. These results will be effective in the diagnosis of equilibrium sense and vestibular function with the aged.

MODELING THE CONTROL OF ISOMETRIC FORCE PRODUCTION WITH PIECE-WISE LINEAR, STOCHASTIC MAPS OF MULTIPLE TIME-SCALES

2003 ◽  
Vol 03 (01) ◽  
pp. L23-L29 ◽  
Author(s):  
GOTTFRIED MAYER-KRESS ◽  
KATHERINE M. DEUTSCH ◽  
KARL M. NEWELL
Keyword(s):  
Time Scales ◽  
Isometric Force ◽  
Force Production ◽  
Human Movement ◽  
Multiple Time Scales ◽  
Force Variability ◽  
Multiple Time ◽  
Force Level ◽  
Force Output ◽  
Isometric Force Production

In human movement, the large number of system degrees of freedom at different levels of analysis of the system, joints, muscles, motor units, cells etc, naturally affords complexity and adaptability in action. It also leads to variability in movement and its outcome, even in intentional efforts to reproduce the same movement or action goal. An example is continuous isometric force output to a constant force level where the amount and structure of force variability changes with information available, force level and individual differences. In this paper we model the control of isometric force production with piece-wise linear stochastic maps of multiple time scales. At the core of our model is a piecewise linear function, depending on three parameters that can be estimated from the observed data that is perturbed by additive Gaussian noise at a given level. The result of the stochastic forcing is that outside of a threshold interval the system behaves like a discrete Ornstein-Uhlenbeck process and inside it performs a Brownian motion. The model is shown to simulate the basic findings of the structure of human force variability that decreasing variability is correlated with increased dynamical complexity as measured with the "Approximate Entropy (ApEn)" statistic.

scholarly journals Complexity of force output during static exercise in individuals with Down syndrome

2009 ◽  
Vol 106 (4) ◽  
pp. 1227-1233 ◽  
Author(s):  
Kevin S. Heffernan ◽  
Jacob J. Sosnoff ◽  
Edward Ofori ◽  
Sae Young Jae ◽  
Tracy Baynard ◽  
...  
Keyword(s):  
Down Syndrome ◽  
Spectral Power ◽  
Temporal Structure ◽  
Voluntary Contraction ◽  
Premature Aging ◽  
Force Variability ◽  
Force Output ◽  
Isometric Handgrip ◽  
Similar Time ◽  
Output Variability

Force variability is greater in individuals with Down syndrome (DS) compared with persons without DS and is similar to that seen with normal aging. The purpose of this study was to examine the structure (in both time and frequency domains) of force output variability in persons with DS to determine whether deficits in force control are similar between individuals with DS and older adults. An isometric handgrip task at a constant force (30% of maximal voluntary contraction) was completed by individuals with DS ( n = 29, age 26 yr), and healthy young ( n = 26, age 27 yr) and older ( n = 33, age 70 yr) individuals. Mean, standard deviation (SD), and coefficient of variation (CV) were used to analyze the magnitude of force output variability. Spectral analysis and approximate entropy (ApEn) were used to analyze the structure of force output variability. Mean force output for DS was lower than in young controls ( P < 0.05) but no different from old controls. Individuals with DS had greater SD and CV than young and old controls ( P < 0.05). The DS group had a significantly greater proportion of spectral power within the 0-to 4-Hz bandwidth than the young and older controls ( P < 0.05). The DS group had significantly lower ApEn values than the young controls ( P < 0.05), but there were no differences in ApEn between the DS group and the old controls ( P > 0.05). In conclusion, young persons with DS demonstrate enhanced temporal structure and greater amplitude of low-frequency oscillations in the force output signal than age-matched non-DS peers. Interestingly, young persons with DS and older persons without DS have similar time-dependent structure of force output variability. This would suggest a possible link between premature aging and less complex force output in persons with DS.

scholarly journals Sources of Signal-Dependent Noise During Isometric Force Production

2002 ◽  
Vol 88 (3) ◽  
pp. 1533-1544 ◽  
Author(s):  
Kelvin E. Jones ◽  
Antonia F. de C. Hamilton ◽  
Daniel M. Wolpert
Keyword(s):  
Motor Unit ◽  
Isometric Force ◽  
Force Production ◽  
Motor Command ◽  
Force Variability ◽  
Isometric Contractions ◽  
Linear Scaling ◽  
Force Output ◽  
Extensor Pollicis Longus ◽  
Isometric Force Production

It has been proposed that the invariant kinematics observed during goal-directed movements result from reducing the consequences of signal-dependent noise (SDN) on motor output. The purpose of this study was to investigate the presence of SDN during isometric force production and determine how central and peripheral components contribute to this feature of motor control. Peripheral and central components were distinguished experimentally by comparing voluntary contractions to those elicited by electrical stimulation of the extensor pollicis longus muscle. To determine other factors of motor-unit physiology that may contribute to SDN, a model was constructed and its output compared with the empirical data. SDN was evident in voluntary isometric contractions as a linear scaling of force variability (SD) with respect to the mean force level. However, during electrically stimulated contractions to the same force levels, the variability remained constant over the same range of mean forces. When the subjects were asked to combine voluntary with stimulation-induced contractions, the linear scaling relationship between the SD and mean force returned. The modeling results highlight that much of the basic physiological organization of the motor-unit pool, such as range of twitch amplitudes and range of recruitment thresholds, biases force output to exhibit linearly scaled SDN. This is in contrast to the square root scaling of variability with mean force present in any individual motor-unit of the pool. Orderly recruitment by twitch amplitude was a necessary condition for producing linearly scaled SDN. Surprisingly, the scaling of SDN was independent of the variability of motoneuron firing and therefore by inference, independent of presynaptic noise in the motor command. We conclude that the linear scaling of SDN during voluntary isometric contractions is a natural by-product of the organization of the motor-unit pool that does not depend on signal-dependent noise in the motor command. Synaptic noise in the motor command and common drive, which give rise to the variability and synchronization of motoneuron spiking, determine the magnitude of the force variability at a given level of mean force output.

scholarly journals Role of post-trial visual feedback on unintentional force drift during isometric finger force production tasks

2019 ◽  
Author(s):  
S Balamurugan ◽  
Dhanush Rachaveti ◽  
Varadhan SKM
Keyword(s):  
Visual Feedback ◽  
Visual Information ◽  
Force Production ◽  
Finger Force ◽  
Visual Occlusion ◽  
Referent Configuration ◽  
Central Controller ◽  
Post Trial ◽  
Lower Magnitude ◽  
The Right

AbstractForce produced during an isometric finger force production task tends to drift towards a lower magnitude when visual information is occluded. This phenomenon of drift in force without one’s awareness is called unintentional drift. The present study used epilogue, a particular case of post-trial visual feedback, and compared the unintentional drift for two conditions, i.e., with and without the epilogue. For this purpose, fourteen healthy participants were recruited for the experiments and were instructed to produce fingertip forces using four fingers of the right hand with the target line at 15% MVC. A trial lasted for sixteen seconds, where for the initial eight seconds, there is visual feedback followed by the visual occlusion period. The results showed a significant reduction in unintentional drift for the condition involving epilogue when compared to no epilogue. This reduction in drift is due to the shift in the referent configuration parameter by the phenomenon of RC back coupling. Further, we also claim that there might be a distribution of λs or RCs, based on the history of tuning of the control parameter by the central controller. This distribution of λs selected by the central controller in a redundant environment based on the epilogue resulted in a reduction of unintentional drift.

scholarly journals Visual information processing in older adults: reaction time and motor unit pool modulation

2018 ◽  
Vol 120 (5) ◽  
pp. 2630-2639 ◽  
Author(s):  
MinHyuk Kwon ◽  
Evangelos A. Christou
Keyword(s):  
Older Adults ◽  
Information Processing ◽  
Reaction Time ◽  
Motor Unit ◽  
Visual Feedback ◽  
Force Control ◽  
Visual Information ◽  
Visual Information Processing ◽  
Force Variability ◽  
Premotor Time

Presently, there is no evidence that magnification of visual feedback has motor implications beyond impairments in force control during a visuomotor task. We hypothesized that magnification of visual feedback would increase visual information processing, alter the muscle activation, and exacerbate the response time in older adults. To test this hypothesis, we examined whether magnification of visual feedback during a reaction time task alters the premotor time and the motor unit pool activation of older adults. Participants responded as fast as possible to a visual stimulus while they maintained a steady ankle dorsiflexion force (15% maximum) either with low-gain or high-gain visual feedback of force. We quantified the following: 1) response time and its components (premotor and motor time), 2) force variability, and 3) motor unit pool activity of the tibialis anterior muscle. Older adults exhibited longer premotor time and greater force variability than young adults. Only in older adults, magnification of visual feedback lengthened the premotor time and exacerbated force variability. The slower premotor time in older adults with high-gain visual feedback was associated with increased force variability and an altered modulation of the motor unit pool. In conclusion, our findings provide novel evidence that magnification of visual feedback also exacerbates premotor time during a reaction time task in older adults, which is correlated with force variability and an altered modulation of motor unit pool. Thus these findings suggest that visual information processing deficiencies in older adults could result in force control and reaction time impairments. NEW & NOTEWORTHY It is unknown whether magnification of visual feedback has motor implications beyond impairments in force control for older adults. We examined whether it impairs reaction time and motor unit pool activation. The findings provide novel evidence that magnification of visual feedback exacerbates reaction time by lengthening premotor time, which implicates time for information processing in older adults, which is correlated with force variability and an altered modulation of motor unit pool.

scholarly journals Improvements in force variability and structure from vision- to memory-guided submaximal isometric knee extension in subacute stroke

2018 ◽  
Vol 124 (3) ◽  
pp. 592-603 ◽  
Author(s):  
John W. Chow ◽  
Dobrivoje S. Stokic
Keyword(s):  
Visual Feedback ◽  
Memory Retrieval ◽  
Spectral Power ◽  
Maximum Voluntary Contraction ◽  
Knee Extension ◽  
Force Variability ◽  
Median Frequency ◽  
Subacute Stroke ◽  
Isometric Knee Extension ◽  
Force Signal

We examined changes in variability, accuracy, frequency composition, and temporal regularity of force signal from vision-guided to memory-guided force-matching tasks in 17 subacute stroke and 17 age-matched healthy subjects. Subjects performed a unilateral isometric knee extension at 10, 30, and 50% of peak torque [maximum voluntary contraction (MVC)] for 10 s (3 trials each). Visual feedback was removed at the 5-s mark in the first two trials (feedback withdrawal), and 30 s after the second trial the subjects were asked to produce the target force without visual feedback (force recall). The coefficient of variation and constant error were used to quantify force variability and accuracy. Force structure was assessed by the median frequency, relative spectral power in the 0–3-Hz band, and sample entropy of the force signal. At 10% MVC, the force signal in subacute stroke subjects became steadier, more broadband, and temporally more irregular after the withdrawal of visual feedback, with progressively larger error at higher contraction levels. Also, the lack of modulation in the spectral frequency at higher force levels with visual feedback persisted in both the withdrawal and recall conditions. In terms of changes from the visual feedback condition, the feedback withdrawal produced a greater difference between the paretic, nonparetic, and control legs than the force recall. The overall results suggest improvements in force variability and structure from vision- to memory-guided force control in subacute stroke despite decreased accuracy. Different sensory-motor memory retrieval mechanisms seem to be involved in the feedback withdrawal and force recall conditions, which deserves further study. NEW & NOTEWORTHY We demonstrate that in the subacute phase of stroke, force signals during a low-level isometric knee extension become steadier, more broadband in spectral power, and more complex after removal of visual feedback. Larger force errors are produced when recalling target forces than immediately after withdrawing visual feedback. Although visual feedback offers better accuracy, it worsens force variability and structure in subacute stroke. The feedback withdrawal and force recall conditions seem to involve different memory retrieval mechanisms.

scholarly journals Neurophysiological changes in the visuomotor network after practicing a motor task

2018 ◽  
Vol 120 (1) ◽  
pp. 239-249 ◽  
Author(s):  
James E. Gehringer ◽  
David J. Arpin ◽  
Elizabeth Heinrichs-Graham ◽  
Tony W. Wilson ◽  
Max J. Kurz
Keyword(s):  
Motor Learning ◽  
Motor Planning ◽  
Motor Task ◽  
Force Production ◽  
Oscillatory Activity ◽  
Matching Task ◽  
Force Output ◽  
Motor Action ◽  
Visuomotor Transformations ◽  
Target Matching

Although it is well appreciated that practicing a motor task updates the associated internal model, it is still unknown how the cortical oscillations linked with the motor action change with practice. The present study investigates the short-term changes (e.g., fast motor learning) in the α- and β-event-related desynchronizations (ERD) associated with the production of a motor action. To this end, we used magnetoencephalography to identify changes in the α- and β-ERD in healthy adults after participants practiced a novel isometric ankle plantarflexion target-matching task. After practicing, the participants matched the targets faster and had improved accuracy, faster force production, and a reduced amount of variability in the force output when trying to match the target. Parallel with the behavioral results, the strength of the β-ERD across the motor-planning and execution stages was reduced after practice in the sensorimotor and occipital cortexes. No pre/postpractice changes were found in the α-ERD during motor planning or execution. Together, these outcomes suggest that fast motor learning is associated with a decrease in β-ERD power. The decreased strength likely reflects a more refined motor plan, a reduction in neural resources needed to perform the task, and/or an enhancement of the processes that are involved in the visuomotor transformations that occur before the onset of the motor action. These results may augment the development of neurologically based practice strategies and/or lead to new practice strategies that increase motor learning. NEW & NOTEWORTHY We aimed to determine the effects of practice on the movement-related cortical oscillatory activity. Following practice, we found that the performance of the ankle plantarflexion target-matching task improved and the power of the β-oscillations decreased in the sensorimotor and occipital cortexes. These novel findings capture the β-oscillatory activity changes in the sensorimotor and occipital cortexes that are coupled with behavioral changes to demonstrate the effects of motor learning.

Effects of hypoxia and hypercapnia on geniohyoid contractility and endurance

1991 ◽  
Vol 71 (2) ◽  
pp. 709-715 ◽  
Author(s):  
R. J. Salmone ◽  
E. Van Lunteren
Keyword(s):  
Force Production ◽  
Upper Airway ◽  
Muscle Performance ◽  
Severe Hypoxia ◽  
Force Frequency ◽  
Force Output ◽  
Frequency Curve ◽  
Dilator Muscle ◽  
Index Ratio ◽  
Mild Hypoxia

Sleep apnea and other respiratory diseases produce hypoxemia and hypercapnia, factors that adversely affect skeletal muscle performance. To examine the effects of these chemical alterations on force production by an upper airway dilator muscle, the contractile and endurance characteristics of the geniohyoid muscle were examined in situ during severe hypoxia (arterial PO2 less than 40 Torr), mild hypoxia (PO2 45–65 Torr), and hypercapnia (PCO2 55–80 Torr) and compared with hyperoxic-normocapnic conditions in anesthetized cats. Muscles were studied at optimal length, and contractile force was assessed in response to supramaximal electrical stimulation of the hypoglossal nerve (n = 7 cats) or geniohyoid muscle (n = 2 cats). There were no significant changes in the twitch kinetics or force-frequency curve of the geniohyoid muscle during hypoxia or hypercapnia. However, the endurance of the geniohyoid, as reflected in the fatigue index (ratio of force at 2 min to initial force in response to 40-Hz stimulation at a duty cycle 0.33), was significantly reduced by severe hypoxia but not by hypercapnia or mild hypoxia. In addition, the downward shift in the force-frequency curve after the repetitive stimulation protocol was greater during hypoxia than hyperoxia, especially at higher frequencies. In conclusion, the ability of the geniohyoid muscle to maintain force output during high levels of activation is adversely affected by severe hypoxia but not mild hypoxia or hypercapnia. However, none of these chemical perturbations affected muscle contractility acutely.

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