bluuebunny/crossref_metadata_2025 huggingface dataset:
How Spreading the Forefeet Apart Influences Upright Standing Control
Authors: Rougier Patrice R.
Published: August 2016

Resultant center-of-pressure (CP) displacements result along mediolateral (ML) and anteroposterior (AP) axes from strategies mobilizing hips and ankles, respectively, and thus, should be largely influenced by the angles between the feet. To assess this relation and the effects of foot position on postural performance, 9 healthy young adults were tested. The main results, as the forefeet are spread farther apart (from 30° in endorotation to 120° in exorotation), indicate (1) a larger contribution of the estimated ankle mechanisms in the generation of the CP trajectories along the ML axis, (2) increased variances along the longitudinal axis of the feet, (3) a constant longitudinal pattern of the CP trajectories under each foot whose main axis displays a progressively increased angle with the inner borders of the feet, and (4) increased variances for CP displacements along both ML and AP axes. These data emphasize the importance of foot positioning in stance control, especially along the ML axis where spreading the forefeet apart progressively increases the contribution of the mechanisms mobilizing the ankles.
On the Use of Different Spatial Reference Frames for Movement Control
Authors: Bock Otmar , Worringham Charles , Dawson Sandi
Published: August 2016

Previous work has shown that amplitude and direction are two independently controlled parameters of aimed arm movements, and performance, therefore, suffers when they must be decomposed into Cartesian coordinates. We now compare decomposition into different coordinate systems. Subjects pointed at visual targets in 2-D with a cursor, using a two-axis joystick or two single-axis joysticks. In the latter case, joystick axes were aligned with the subjects’ body axes, were rotated by −45°, or were oblique (i.e., one axis was in an egocentric frame and the other was rotated by −45°). Cursor direction always corresponded to joystick direction. We found that compared with the two-axis joystick, responses with single-axis joysticks were slower and less accurate when the axes were oriented egocentrically; the deficit was even more pronounced when the axes were rotated and was most pronounced when they were oblique. This confirms that decomposition of motor commands is computationally demanding and documents that this demand is lowest for egocentric, higher for rotated, and highest for oblique coordinates. We conclude that most current vehicles use computationally demanding man–machine interfaces.
Differential Effects of the Rod-and-Frame Illusion on the Timing of Forearm Rotations
Authors: Lommertzen Janneke , van Zuijlen Alexander M.J. , Meulenbroek Ruud G.J. , van Lier Rob
Published: August 2016

The current study focused on the time course of the effects of the rod-and-frame illusion (RFI) on the kinematics of targeted forearm rotations. Participants were asked to reproduce perceived rod orientations by propelling a hand-held cylinder forward while rotating it to the target orientation. Rod and frame orientations were systematically varied, and cylinder rotations were normalized to time. Average realized cylinder orientations confirmed that when the frame orientation deviated from the vertical, a reproduction error occurred in the direction opposite to the direction of the frame tilt. In contrast, the perceived orientation of the stimulus rod was exaggerated relative to the vertical (i.e., reproduction errors were in the direction of the rod tilt). Furthermore, linear regression analyses for every normalized time sample showed that the rod and frame effects start simultaneously, but they reach their maximum effect at different points in time. We discuss the implications of our findings for current views on the effects of visual illusions on motor control.
Soleus H-Reflex Modulation During Stance Phase of Walking With Altered Arm Swing Patterns
Authors: Phadke Chetan P. , Klimstra Marc , Zehr E Paul. , Thompson Floyd J. , Behrman Andrea L.
Published: August 2016

The purpose of this study was to test the effect of arm swing on modulation of soleus H-reflexes amplitudes during walking. Fifteen subjects walked (1.07 m/s) on a treadmill in 4 arm swing conditions: 1-natural arm swing (control), 2-active restraint, 3-passive restraint, and 4-passive-assisted. Tibial nerve was electrically stimulated and soleus EMG was recorded. H-reflex amplitude was significantly greater during active than during passive restraint (p = .013). Remaining arm swing conditions were not significantly different. We detected a subtle effect of arm swing on soleus H-reflex amplitude. Descending regulation may serve as a gating mechanism to control the effect of arm movements on reflex pathways for leg muscles. This gating mechanism may be impaired postneural injury, potentially enhancing the modulation of peripheral sensory inputs on reflexes in leg muscles during walking. Future experiments to test additional conditions and evoking reflexes in more phases of walking are recommended.
Lyapunov Exponent and Surrogation Analysis of Patterns of Variability: Profiles in New Walkers With and Without Down Syndrome
Authors: Smith Beth A. , Stergiou Nick , Ulrich Beverly D.
Published: August 2016

In previous studies we found that preadolescents with Down syndrome (DS) produce higher amounts of variability (Smith et al., 2007) and larger Lyapunov exponent (LyE) values (indicating more instability) during walking than their peers with typical development (TD) (Buzzi & Ulrich, 2004). Here we use nonlinear methods to examine the patterns that characterize gait variability as it emerges, in toddlers with TD and with DS, rather than after years of practice. We calculated Lyapunov exponent (LyE) values to assess stability of leg trajectories. We also tested the use of 3 algorithms for surrogation analysis to investigate mathematical periodicity of toddlers’ strides. Results show that toddlers’ LyE values were not different between groups or with practice and strides of both groups become more periodic with practice. The underlying control strategies are not different between groups at this point in developmental time, although control strategies do diverge between the groups by preadolescence.
Parameterized Estimation of Long-Range Correlation and Variance Components in Human Serial Interval Production
Authors: Diniz Ana , Barreiros João , Crato Nuno
Published: August 2016

Repetitive movements lead to isochronous serial interval production which exhibit inherent variability. The Wing-Kristofferson model offers a decomposition of the interresponse intervals in tapping tasks based on a cognitive component and on a motor component. We suggest a new theoretical and fully parametric approach to this model in which the cognitive component is modeled as a long-memory process and the motor component is treated as a white noise process, mutually independent. Under these assumptions, we obtained the autocorrelation function and the spectral density function. Furthermore, we propose an estimator based on the maximization of the frequency-domain representation of the likelihood function. Finally, we conducted a simulation study to assess the properties of this estimator and performed an experimental study involving tapping tasks with two target frequencies (1.250 Hz and 0.625 Hz).
Motor Synergies and the Equilibrium-Point Hypothesis
Authors: Latash Mark L.
Published: August 2016

The article offers a way to unite three recent developments in the field of motor control and coordination: (1) The notion of synergies is introduced based on the principle of motor abundance; (2) The uncontrolled manifold hypothesis is described as offering a computational framework to identify and quantify synergies; and (3) The equilibrium-point hypothesis is described for a single muscle, single joint, and multijoint systems. Merging these concepts into a single coherent scheme requires focusing on control variables rather than performance variables. The principle of minimal final action is formulated as the guiding principle within the referent configuration hypothesis. Motor actions are associated with setting two types of variables by a controller, those that ultimately define average performance patterns and those that define associated synergies. Predictions of the suggested scheme are reviewed, such as the phenomenon of anticipatory synergy adjustments, quick actions without changes in synergies, atypical synergies, and changes in synergies with practice. A few models are briefly reviewed.
Implicit Motor Learning in Patients with Parkinson’s and Alzheimer’s Disease: Differences in Learning Abilities?
Authors: van Tilborg Ilse A.D.A. , Hulstijn Wouter
Published: August 2016

Experimental studies show intact implicit motor learning in patients with Alzheimer’s disease (AD) but the results for patients with Parkinson’s disease (PD) are inconclusive. This study tests implicit sequence learning in AD and PD patients, and healthy controls, using the classical Serial Reaction Time Task (SRTT), and a somewhat similar Pattern Learning Task (PLT), which involves stylus movements in different directions, and which allows detailed movement analysis. As expected, the time measures showed less implicit motor learning in the PD patients relative to the other groups in both tasks, but their error percentages increased when the sequence changed from a fixed to a random order, which is indicative of implicit learning. The AD patients showed a reversed pattern of results. Arguably, errors and time measures may reflect the involvement of separate processes, e.g., spatial and motor components, which could be differently affected in AD and PD.
Assessment of the Propagation of Uncertainty on Link Segment Model Results
Authors: Ribeiro Daniel Cury , Loss Jefferson Fagundes
Published: August 2016

Link segment models are usually used to calculate proximal net reaction forces (PRF), as well as, proximal net moments (PNM). The correlation between electromyographic data and PNM is usually used to verify the model’s results. Nevertheless, this method permits only a qualitative verification of the obtained results. To assess model’s results in a quantitative perspective, another approach is needed. The aim of the current study was to assess the propagation of uncertainty on a link segment model results and identify the main sources of error on the quantification of PRF and PNM. One male performed five repetitions of different upper limb movements. An inverse dynamics approach associate with 3D link segment model was used to quantify PRF and PNM. The results of the model were evaluated by the use of Kleine and McClintock’s equation. The propagation of uncertainty for PRF reached, on average, 0.27 and for PNM, 0.97. The main cause of propagation of uncertainty was associated to the second time derivative calculations. Consequently, it is possible to suggest that the reduction of small distortions of center of mass acceleration will diminish the proximal net moment and proximal reaction force uncertainty values.
A Logarithmic Speed-Difficulty Trade-off in Speech Production
Authors: Latash Mark L. , Mikaelian Irina L.
Published: August 2016

We explored the relations between task difficulty and speech time in picture description tasks. Six native speakers of Mandarin Chinese (CH group) and six native speakers or Indo-European languages (IE group) produced quick and accurate verbal descriptions of pictures in a self-paced manner. The pictures always involved two objects, a plate and one of the three objects (a stick, a fork, or a knife) located and oriented differently with respect to the plate in different trials. An index of difficulty was assigned to each picture. CH group showed lower reaction time and much lower speech time. Speech time scaled linearly with the log-transformed index of difficulty in all subjects. The results suggest generality of Fitts’ law for movement and speech tasks, and possibly for other cognitive tasks as well. The differences between the CH and IE groups may be due to specific task features, differences in the grammatical rules of CH and IE languages, and possible use of tone for information transmission.
Modeling the Development of Pronunciation in Infant Speech Acquisition
Authors: Howard Ian S. , Messum Piers
Published: August 2016

Pronunciation is an important part of speech acquisition, but little attention has been given to the mechanism or mechanisms by which it develops. Speech sound qualities, for example, have just been assumed to develop by simple imitation. In most accounts this is then assumed to be by acoustic matching, with the infant comparing his output to that of his caregiver. There are theoretical and empirical problems with both of these assumptions, and we present a computational model—Elija—that does not learn to pronounce speech sounds this way. Elija starts by exploring the sound making capabilities of his vocal apparatus. Then he uses the natural responses he gets from a caregiver to learn equivalence relations between his vocal actions and his caregiver’s speech. We show that Elija progresses from a babbling stage to learning the names of objects. This demonstrates the viability of a non-imitative mechanism in learning to pronounce.
Differences in Descending Control of External Oblique and Latissimus Dorsi Muscles in Humans: A Preliminary Study
Authors: Wightman Francesca , Delves Suzanne , Alexander Caroline M. , Strutton Paul H.
Published: August 2016

Descending bilateral control of external oblique (EO) and latissimus dorsi (LD) was investigated using transcranial magnetic stimulation. Contralateral (CL) motor evoked potential (MEP) thresholds were lower and latencies were shorter than for ipsilateral (IL) MEPs. Hotspots for EO were symmetrical; this was not the case for LD. The volumes of drive to the left and right muscles were not different. The laterality index was not different between the left and right muscles. The average index for the EO muscles was closer to zero than that for LD, suggesting a stronger IL drive to EO. The symmetry of drive to each muscle did not differ; however, the symmetry of drive varies within a subject for different muscles and between subjects for the same muscle. The findings may be useful in understanding a number of clinical conditions relating to the trunk and also for predicting the outcome of rehabilitative strategies.
Effects of Extensive Practice on Bradykinesia in Parkinson’s Disease: Improvement, Retention and Transfer
Authors: Smiley-Oyen Ann L. , Hall Sonja A. , Lowry Kristin A. , Kerr John P.
Published: August 2016

We investigated the effects of extensive practice of rapid aiming on bradykinesia and, more specifically, generation of peak velocity, in discrete rapid aiming and in transfer to reach-to-grasp. Twenty-one participants (seven young adults, seven older adults, and seven adults with mild to moderate Parkinson’s disease (PD) while on medication) engaged in eight practice periods per week for three weeks (> 700 trials), with changes in performance measured weekly. Retention was measured weekly for three weeks postpractice. Movement time decreased with one week of practice, primarily due to a decrease in time-to-peak velocity. With practice and after retention, the PD group generated peak velocity as consistently as both neurologically healthy groups, but remained more variable in time-to-peak velocity. Transfer was observed in the neurologically healthy groups, but not in the PD group. We concluded that short-term practice (one week in our paradigm) is sufficient for decreasing movement time, but more extensive practice is needed to improve consistency of rapid aiming performance for people with mild to moderate PD.
Biomechanical Analysis of Postural Strategies over the First Two Months Following Anterior Cruciate Ligament Reconstruction
Authors: Rougier P.R. , Berger S. , Barral S. , Rachet O.
Published: August 2016

To assess the postural strategies developed over the first 2 months following surgery by ACL patients during rehabilitation and highlight the sensory-motor impairment recovery, 21 patients were measured at three timeframes. Three two-legged standing conditions were assessed: with the eyes open, with the eyes closed either wearing or not wearing a knee orthosis. The results indicate that the weight-bearing asymmetry, initially observed (i.e., 56–44% of body-weight), disappeared progressively during rehabilitation (51–49%). The comparison of the plantar center-of-pressure displacements under both sound and operated legs demonstrated noticeable differences that also tended to decrease but without reaching a matched behavior during the last measures. These effects were seen in both eyes open and eyes closed conditions with the greatest effects in the latter condition. Wearing a knee orthosis inferred no particular changes in the postural control behaviors. These data could be used as benchmarks for highlighting the effects on undisturbed postural control of various surgery techniques and/or rehabilitation protocols.
Rambling and Trembling in Response to Body Loading
Authors: Tahayori Behdad , Riley Zachary A. , Mahmoudian Armaghan , Koceja David M. , Hong Siang Lee
Published: August 2016

Various studies have suggested that postural sway is controlled by at least two subsystems. Rambling-Trembling analysis is a widely accepted methodology to dissociate the signals generated by these two hypothetical subsystems. The core assumption of this method is based on the equilibrium point hypothesis which suggests that the central nervous system preserves upright standing by transiently shifting the center of pressure (COP) from one equilibrium point to another. The trajectory generated by this shifting is referred to as rambling and its difference from the original COP signal is referred to as trembling. In this study we showed that these two components of COP are differentially affected when standing with external loads. Using Detrended Fluctuation analysis, we compared the pattern of these two signals in different configurations of body loading. Our findings suggest that by applying an external load, the dynamics of the trembling component is altered independently of the area of postural sway and also independently of the rambling component. The dynamics of rambling changed only during the backloading condition in which the postural sway area also substantially increased. It can be suggested that during loaded standing, the trembling mechanism (which is suggested to be activated by peripheral mechanisms and reflexes) is altered without affecting the central influence on the shifts of the equilibrium point.
Smooth Pursuit Eye Movement Adaptation in High Level Gymnasts
Authors: von Lassberg Christoph , Beykirch Karl , Campos Jennifer L. , Krug Jürgen
Published: August 2016

This study investigated long-term adaptations of smooth pursuit eye movement characteristics in high-level gymnasts and compared these responses to those of nonathletes. Gymnasts were selected because of their exceptional ability to spatially orient during fast, multiaxial whole body rotations. Participants were tested with standardized and supra-maximal sinusoidal smooth pursuit measurements. The results showed significantly higher gain values in top-level gymnasts, followed by young federal team gymnasts, followed by the nonathlete control group. By testing participants over the course of three years and also after periods of abstinence from training, changes to patterns of smooth pursuit over time are revealed. These results have interesting implications for understanding the characteristics of eye-movements in expert populations as well as understanding the general principles that underlie oculomotor adaptation.
Effect of Fatigue on Grip Force Control During Object Manipulation in Carpal Tunnel Syndrome
Authors: Mattos Daniela JS , Domenech Susana Cristina , Junior Noé Gomes Borges , Santos Marcio José
Published: August 2016

Eight subjects with carpal tunnel syndrome (CTS) (47.13 ± 7.83 years) and 8 matched controls (46.29 ± 7.27 years) manipulated a test object fitted with an accelerometer and force sensor, both before and after hand muscle fatigue. Grip force and object acceleration were recorded and used to calculate grip force control variables that included Grip Force Peak, Safety Margin, and Time to Grip Force Peak. Individuals with CTS exhibited a higher Safety Margin (p = .010) and longer Time to Peak of Grip Force (p = .012) than healthy controls during object manipulation. Once fatigued, both groups significantly decreased their grip force to perform the task (Grip Force Peak; p = .017 and Safety Margin; p < .001). Nevertheless, individuals with CTS maintained an unnecessarily high safety margin. Our results suggest that CTS can adversely affect how the central nervous system regulates grip force, which might aggravate the inflammatory process and exacerbate the symptoms of this disease.
Development of Temporal and Spatial Bimanual Coordination During Childhood
Authors: de Boer Betteco J. , Peper C. (Lieke) E. , Beek Peter J.
Published: August 2016

Developmental changes in bimanual coordination were examined in four age groups: 6/7, 10/11, 14/15 years, and young adults. Temporal coupling was assessed through the stabilizing contributions of interlimb interactions related to planning, error correction, and reflexes during rhythmic wrist movements, by comparing various unimanual and bimanual tasks involving passive and active movements. Spatial coupling was assessed via bimanual line-circle drawing. With increasing age, temporal stability improved. Relative contributions of planning and reflex interactions to the achieved stability did not change, whereas error correction improved. In-phase and antiphase coordination developed at similar rates; implications of this result were discussed in terms of mirror-activity inhibition. Overall spatial drawing performance (circularity, variability, smoothness) improved with age, and spatial interference was smaller in adults than children. Whereas temporal coupling increased from 6/7 years to adulthood, spatial coupling changed mainly after 14/15 years. This difference in the development of temporal and spatial coupling corresponds to the anterior-posterior direction of corpus callosum myelination as reported in the literature.
The Structure of Somatosensory information for Human Postural Control
Authors: Jeka John J. , Ribeiro Pedro , Oie Kelvin , Lackner James R.
Published: August 2016

The goal of the present study was to determine the properties of the somatosensory stimulus that alter its temporal coupling to body sway. Six standing subjects were tested while touching a metal plate positioned either directly in front of or lateral to the subject. In each condition, the plate moved 4 mm at 0.2 Hz in either the medial-lateral (ML) or anterior-posterior direction (AP). The results showed that coupling between body sway and touch plate movement was strongest when the touch plate moved in a direction along the longitudinal axis of the arm. Coupling strength was weaker when the touch plate moved perpendicular to the longitudinal axis of the arm. The results consistently show that a radial expansion stimulus was more effective than a lamellar-type stimulus at the fingertip. Moreover, somatosensory information from a surface is interpreted in terms of the orientation of the contact limb and the potential degrees of freedom available through its movement.
Stability of Rhythmic Finger Movements in Children with a Developmental Coordination Disorder
Authors: Volman M.J.M. , Geuze Reint H.
Published: August 2016

The stability of single and bimanual (i.e., in-phase and antiphase) rhythmic finger movements was studied in 24 children with a developmental coordination disorder (DCD) and 24 matched controls from a dynamic pattern perspective. Stability was assessed by applying perturbations and measuring the time the system needed to return to its initial stability (i.e., the relaxation time). In addition, fluctuations of the patterns were measured. For antiphase coordination patterns, the frequency at which loss of stability occurred was also determined. Children with DCD displayed less stable single and bimanual rhythmic coordination patterns than control children. Further, within the DCD group, 9 children were identified as having particularly poor bimanual coordination stability. Individual differences suggested that variability of individual limb oscillations might have contributed to this poorer interlimb coordination stability. Findings were discussed in relation to a previous study on DCD in which the Wing-Kristofferson timekeeper model was applied.
Learning Transfer from Flexion to Extension Movements: Importance of the Final Position
Authors: Ilic Dusko B. , Mirkov Dragan M. , Jaric Slobodan
Published: August 2016

Nine subjects (experimental group) were tested on rapid elbow flexion and extension movements performed in the same final position, before and after extensive practice of the movements. Nine additional subjects (control group) were also tested, but without any practice between the tests. Comparison of the pretest and posttest results suggested that the experimental group decreased their variable error (i.e., standard deviation of the final movement position) in both practiced (elbow flexion) and nonpracticed (elbow extension) movements. The control group, however, did not improve in either of tested movements. The experimental group demonstrated lower variable error in the nonpracticed elbow extensions than the control group, while the same difference for practiced elbow flexion movements was slightly below the level of significance. The results support the importance of the final position in programming of rapid, self-terminated movements; however, they do not rule out the role of other kinetic and kinematic variables (such as movement distance).
Relative Coordination Reconsidered: A Stochastic Account
Authors: Collins David R. , Park Hyeongsaeng , Turvey Michael T.
Published: August 2016

Von Holst (1939/1973) parsed intersegmental coordination into relative and absolute to distinguish moderate and extreme forms. Kelso and DeGuzman (1992) discussed an interpretation of relative coordination in terms of the chaotic phenomenon of intermittency. The data of concern (DeGuzman & Kelso, 1991) do not, however, exclude a stochastic interpretation, which is detailed here following earlier suggestions. The key difference is modeling relative coordination by stochastic variability about weak attractors rather than by deterministic variability about remnants of attractors (”ghost attractors”). The intermittency interpretation is not robust in the presence of noise and, therefore, is not well disposed to account for uncertainty in detailing a model of behavioral data or its parameters. In contrast, the stochastic interpretation is based upon an approximation of unknown underlying processes in the form of Gaussian white noise. A stochastic method for estimating model parameters from a stationary probability distribution and a mean first passage time is illustrated using experimental and simulated data.
Facilitation of a Hand Muscle Response to Stimulation of the Motor Cortex Preceding a Simple Reaction Task
Authors: Davey Nick J. , Rawlinson Steve R. , Maskill David W. , Ellaway Peter H.
Published: August 2016

Transcranial magnetic stimulation (TMS) of the motor cortex was used to produce compound motor evoked potentials (cMEPs) in the first dorsal interosseus (FDI) muscle. The size of cMEPs was measured as an index of corticospinal excitability before and after initiation of a simple reaction task (SRT). The SRT, consisting of an abduction of the right index finger against a vertical support in response to a 1 kHz cueing tone, was performed in 6 healthy male subjects. cMEPs were facilitated when timed to occur just before the fastest simple reaction time (fSRT). When the cMEP was placed 15.5 ± 1.5 ms before the fSRT, its amplitude increased to 176 ± 36% of the control response seen in the relaxed state (no SRTs). Facilitation of the cMEP increased to 382 ± 43% of the control when it was placed 11.9 ± 1.5 ms after the fSRT. The facilitation of cMEP responses prior to the SRT is discussed with particular reference to the premovement potential that may be recorded over the cortex prior to a voluntary movement.
Instant Equilibrium Point and Its Migration in Standing Tasks: Rambling and Trembling Components of the Stabilogram
Authors: Zatsiorsky Vladimir M. , Duarte Marcos
Published: August 2016

A method of decomposing stabilograms into two components, termed rambling and trembling, was developed. The rambling component reveals the motion of a moving reference point with respect to which the body's equilibrium is instantantly maintained. The trembling component reflects body oscillation around the reference point trajectory. The concepts of instant equilibrium point (IEP) and discrete IEP trajectory are introduced. The rambling trajectory was computed by interpolating the discrete IEP trajectory with cubic spline functions. The trembling trajectory is found as a difference between the approximated rambling trajectory and the COP trajectory. Instant values of the trembling trajectory are negatively correlated with the values of the horizontal ground reaction force at a zero time lag. It suggests that trembling is strongly influenced by a restoring force proportional to the magnitude of COP deviation from the rambling trajectory and acts without a time delay. An increment in relative COP position per unit of the restoring force, in mm/N, was on average 1.4 ± 0.4. The contribution of rambling and trembling components in the stabilogram was ascertained. The rambling variability is approximately three times larger than the trembling variability.
Retaining the Equilibrium Point Hypothesis as an Abstract Description of the Neuromuscular System
Authors: Tresilian James R.
Published: August 2016

The λ version of the equilibrium point (EP) hypothesis for motor control is examined in light of recent criticisms of its various instantiations. Four important assumptions that have formed the basis for recent criticism are analyzed: First, the assumption that intact muscles possess invariant force-length characteristics (ICs). Second, that these ICs are of the same form in agonist-antagonist pairs. Third, that muscle control is monoparametric and that the control parameter, λ, can be given a neurophysiological interpretation. Fourth, that reflex loop time delays and the known, asymmetric, nonlinear mechanical properties of muscles can be ignored. Mechanical and neurophysiological investigations of the neuromuscular system suggests that none of these assumptions is likely to be correct. This has been taken to mean that the EP hypothesis is oversimplified and a new approach is needed. It is argued that such an approach can be provided without rejecting the EP hypothesis, rather to regard it as an input-output description of muscle and associated segmental circuits. The operation of the segmental circuitry can be interpreted as having the function, at least in part, of compensating for a variety of nonlinearities and asymmetries such that the overall system implements the λ-EP model equations.
What Does EMC Tell Us about Muscle Function?
Authors: Gielen Stan C.A.M.
Published: August 2016

EMG recordings are frequently used to obtain a better understanding in the coordination of movements. However, EMG activity is made up by the weighted summation of activity of many motor units with different contractile properties. Recent studies have revealed that different motor units contribute to muscle force in different motor tasks. The flexible recruitment of motor units with various contractile properties allows a flexible tuning of muscle properties, but also complicates the interpretation of EMG activity.
Influence of lntermittency and Synergy on Grasping
Authors: Neilson Peter D.
Published: August 2016

This commentary firstly supports Smeets and Brenner in their choice of a kinematic trajectory, submitting that the challenge posed by the rival torque-change formulation is resolved by consideration of intermittency in human movement control. Second, it examines the choice of optimization criterion for trajectory planning, arguing in favor of minimum acceleration rather than minimum jerk. Third, using the notion of optimized trajectories in task-dependent coordinate space together with synergy generation, it suggests a formulation that reduces the processing load entailed in Smeets and Brenner's proposal of individual trajectories for each digit.
Coordination of One- and Two-Joint Muscles during Voluntary Movement: Theoretical and Experimental Considerations
Authors: Herzog Walter , Ait-Haddou Rachid
Published: August 2016

The target article by Dr. Prilutsky is based on three incorrectly derived mathematical rules concerning force-sharing among synergistic muscles associated with a cost function that minimizes the sum of the cubed muscle stresses. Since these derived rules govern all aspects of Dr. Prilutsky's discussion and conclusion and form the basis for his proposed theory of coordination between one-and two-joint muscles, most of what is said in the target article is confusing or misleading at best or factually wrong at worst. The aim of our commentary is to sort right from wrong in Dr. Prilutsky's article within space limitations that do not allow for detailed descriptions of mathematical proofs and explicit discussions of the relevant experimental literature.
Rambling and Trembling in Quiet Standing
Authors: Zatsiorsky Vladimir M. , Duarte Marcos
Published: August 2016

The goal of this study was to explore the rambling-trembling decomposition in quiet standing. The center of pressure (COP) and the horizontal ground reaction force (Fhor) were registered in healthy subjects standing in an upright bipedal posture on a force platform. The COP positions at the instants when Fhor = 0 were identified (instant equilibrium points, IEP) for the anterior-posterior direction, then the COP time series, were partitioned into its components using 2 different techniques, rambling-trembling decomposition and gravity line decomposition. The two decomposition techniques provided very similar results. An unexpectedly large correlation between the trembling trajectory and the difference between COP and gravity line was found, r = 0.91 (range, 0.83 < r < 0.98). The correlation implies that the GL moves from an IEP to the subsequent IEP along a smooth trajectory that can be predicted by the spline approximation. A substantial negative cross-correlation at a zero time lag was observed between the trembling and the Fhor, -0.90 < r < -0.75. For the rambling trajectory, the coefficients of correlation with Fhor were low, -0.33 < r < -0.05. The data support the hypothesis that during quiet standing the body sways for two reasons: the migration of the reference point (rambling) and the deviation away from that point (trembling).
Parameter Precuing and Motor Preparation
Authors: Anson J. Greg , Hyland Brian l. , Kötter Rolf , Wickens Jeffery R.
Published: August 2016

A movement task was used to investigate the effects of precued variables on reaction time. The task involved rapid rotation of a hand-held manipulandum to target locations and required either pronation or supination of the forearm through short or long extent. The effects on reaction time of precues signalling target direction, extent, or a combination of direction and extent, were measured. The longest reaction times occurred when no information about direction or extent was provided in the precue (all parameters uncertain). Complete prior specification of target position produced the shortest reaction times. Specification of direction when extent was uncertain produced a significantly larger reduction in reaction time than specification of extent when direction was uncertain. Prior specification of extent also produced a small but significant reduction in reaction time relative to the condition in which direction and extent were specified in a mutually conditional manner. The results are discussed in relation to parameter precuing and motor programming, in which the direction is programmed by the pre-selection of neurons representing the muscles to be used in the task while programming of extent is represented by their level of activity during task performance.
EEC Correlates of Wrist Kinematics as Revealed by Averaging Techniques and Morlet Wavelet Transforms
Authors: Slobounov Semyon , Simon Robert , Tutwiler Richard , Rearick Matthew
Published: August 2016

The question regarding the invariant movement properties the central nervous system may organize to accomplish different motor task demands as reflected in EEG remains unsolved. Surprisingly, no systematic electrocortical research in humans has related movement preparation with different movement distance, although this area has been widely investigated in the field of motor control. This study examined whether the amplitude of discrete wrist movements influences the various EEG components both in time and frequency domains. Time-domain averaging techniques and Morlet wavelet transforms of EEG single trials were applied in order to extract three components [BP(0), Nl, and LPS] of movement related potentials (MRP) and to quantify changes in oscillatory activity of the movement-induced EEG waveforms accompanying 20, 40, and 60° unilateral wrist flexion movements. The experimental manipulations induced systematic changes in BP(0) and Nl amplitude along the midline (Fz, Cz, and Pz) with 20° movement showing the most negativity and 60° the least. The dominant energy within a 30-50 frequency cluster from bilateral precentral (C3, Cz, C4), frontal (F3, Fz, F4), and parietal (P3, Pz, P4) areas with maximum at vertex (Cz) also appeared to be sensitive to movement amplitude with the least power observed during 60° wrist flexion. This suggests that movement amplitude may be a controllable variable that is highly related with task-specific cortical activation primarily at frontocentral areas as reflected in EEG.
Low-Dimensional Control: Tonus (1963)
Authors: Meijer Onno G. , Kots Yakov M. , Edgerton V. Reggie
Published: August 2016

In 1963, an article on “Tonus” (tone), written by Nikolai A. Bernstein and Yakov M. Kots. appeared in the second edition of the Bols'aja Medicinskaja Enciclopedija [Grand Medical Encyclopedia]. The paper is now published for the first time in the English language, with Mark L. Latash as translator. In accordance with then contemporary neurophysiology and neuropsychology, the paper presented “tone” as a graded phenomenon (as opposed to all-or-none), serving to prepare the segmental level for phasic contractions. Influenced by Granit and Matthews, the authors proposed that the suprasegmental level controls the threshold and the slope of the stretch reflex. In their introduction to the present edition, the editors understand this proposal in the context of low-dimensional control, that is. control in terms of one or a few variables (as opposed to central commands specifying all the details). Selected episodes from the history of low dimensional control and its logical counterpart, spinal intelligence, are used to illustrate how difficult these ideas were to accept. As so often in new scientific developments, confusion was the rule, and in this respect the paper on “Tonus” is no exception. In the epilogue, Kots gives his personal memories of the context in which the paper was written. At the time, he was working on “equitonometry” (equitonometric), measuring tonic balance with gravity eliminated. Results of equitonometric research quite naturally led to the idea that suprasegmental centers control the threshold and the slope of me tonic stretch reflex. As Kots remembers, that was “no big deal.”
A New Method for Experimental Simulation of EMG Using Multi-Channel Independent Stimulation of Small Groups of Motor Units
Authors: Hulliger Manuel , Day Scott J. , Guimaraes Antonio , Herzog Walter , Zhang Yuan-Ting
Published: August 2016

The experimental simulation method was based upon the separate activation of up to 10 small groups of motor units (MU) in an acute nerve-muscle preparation. The investigator was able to precisely control and systematically alter the features of MU pool activation strategies. No implicit assumptions were made regarding MU properties. The purpose of this study was to evaluate the validity of this method. Three criteria were formulated and found to be satisfied: First, in the time domain, visual and audio displays of simulated EMG were indistinguishable from physiological EMG. Secondly, in the frequency domain, power spectra of simulated EMG revealed the typical features of EMG recorded during voluntary activation in the cat. Thirdly, the well-known mono-tonic relationship between EMG magnitude and force was readily reproduced, alüiough strictly linear relations were not found. In addition. the relationship between the pool's ensemble activation rate and EMG magnitude showed distinct gain compression, mostly attributable to signal cancellation.
Sensory Disturbances after Focal Extirpations of the Human “Motor” Cortex
Authors: Vilensky Joel A. , Gilman Sid
Published: August 2016

From the late 1800s until approximately the middle of the 20th century, neurosurgeons made discrete motor cortex lesions in humans in attempts to reduce or eliminate a variety of involuntary movements, resulting mainly from epilepsy. In some cases, the neurosurgeons tested and recorded their patients' ability to perform various movements and to perceive various types of sensory stimuli after the operation. Although these studies have been largely forgotten, they have an immense advantage over primate lesion studies for understanding the function of the motor cortex because the patients were able to attempt to perform complex movements upon request, and to describe their perceptions of cutaneous stimuli, including integrated sensations (e.g., recognition of objects by palpation alone). We provide here a table containing the results of these studies pertaining to sensory deficits. The most consistent and persistent sensory deficits reported relate to object recognition and position sense. This finding is in keeping with recent electrophysiological studies in primates. Our analysis suggests that the “motor” cortex serves important sensory functions; hence, the term sensorimotor cortex, remains appropriate for the primate precentral (and postcentral) cortex.
Comparison of the Relation between Timing and Force Control during Finger-Tapping Sequences by Pianists and Nonpianists
Authors: Inui Nobuyuki , Ichihara Takuya
Published: August 2016

To examine the relation between timing and force control during finger tapping sequences by both pianists and nonpianists, participants lapped a force plate connected to strain gauges. A series of finger tapping tasks consisted of 16 combinations of pace (intertap interval: 180. 200, 400. or 800 ms) and peak force (50, 100. 200. or 400 g). Analysis showed that, although movement timing was independent of force control under low or medium pace conditions, there were strong interactions between the 2 parameters under high pace conditions. The results indicate that participants adapted the movement by switching from separately controlling these parameters in the slow and moderate movement to coupling them in the fast movement. While variations in intertap interval affected force production by nonpianists. they had little effect for pianists. The ratios of time-to-peak force to press duration increased linearly in pianists but varied irregularly in nonpianists, as the required force decreased. Thus, pianists regulate peak force by timing control of peak force to press duration, suggesting that training affects the relationship between the 2 parameters.
Three-Month-Old Infants Can Select Specific Leg Motor Solutions
Authors: Angulo-Kinzler Rosa M. , Ulrich Beverly , Thelen Esther
Published: August 2016

In this study we used a biofeedback system to evaluate the joint movements of 3-month-old infants in real-time. The computer was set to discriminate a specific leg position as the motor task infants had to discover to receive the reinforcement from a mobile. Two groups of infants were given two different tasks: (1) to cross 85° knee flexion in the flexion group, and (2) to cross 35° knee extension in extension group. The results from this experiment suggest that infants in both groups learned the task; however, they used different motor solutions. Infants in the flexion group demonstrated two distinctly different motor solutions to make the mobile move. One was movement-based and was characterized by an increase in kicking frequency, while the other was posture-based. In contrast, most infants in the extension group only used the movement-based solution to gain the reinforcements. Controlling the knee at the 35° extension positions seems to be more difficult than at the 85° flexion positions for 3-month-old infants. These results indicate that infants are capable of discovering narrowly defined leg motor solutions and that, depending on their individual characteristics and the task demands, they select different motor solutions.
The Effects of Intermittent Vision on Prehension under Binocular and Monocular Viewing
Authors: Bennett Simon J. , Elliott Digby , Weeks Daniel J. , Keil Damian
Published: August 2016

The aim of the present study was to examine the effects of intermittent binocular and monocular vision on the preparation and execution of the transport and grasp phases of prehension, and hence the temporal limit of binocular and monocular integration. Participants in two groups (speed or accuracy) performed prehensile movements of two amplitudes (20 and 40 cm) to either a large or small object (6 × 6 × 2 and 6 × 4 × 2 cm) under conditions of binocular and monocular viewing. The interval between visual samples was manipulated with liquid crystal goggles (continuous vision, 20on/60off, and 20on/120off ms). A kinematic analysis indicated that participants modified variables associated with the preparation and execution of prehension in the intermittent vision conditions when instructed to emphasize accuracy. Participants instructed to emphasize speed, modified variables associated with the preparation phase only. The impact of intermittent vision was similar under binocular and monocular viewing. Thus, for prehension, it appears that consecutive binocular or monocular samples need to occur less than 60 ms apart in order to be fully integrated for limb control.
Effects of Two Different Dynamic Environments on Force Adaptation: Exposure to a New Force but Not the Preceding Force Experience Accounts for Transition- and After-Effects
Authors: Kalenscher Tobias , Kalveram Karl-Theodor , Konczak Jürgen
Published: August 2016

This study investigated force adaptation in humans during goal-directed flexion forearm motion. The ability of the motor system to adapt to changes in internal or external forces is essential for the successful control of voluntary movement. In a first experiment, we examined how under- or overdamping differentially affected the length of the adaptation and the arm kinematics between force transitions. We found that transitions diverging from a null-force produced larger transition effects than transitions converging to a null force condition, indicating that re-adaptation was less error-prone. Whether the subjects had previously experienced underdamping or the null-force had no significant impact on the spatial trajectory after switching to overdamping. That is, prior force experience had no differential effect on the spatial transition kinematics. However, the transitions underdamping-to-overdamping and underdamping-to–null force did produce differently strong transition effects. These results indicate that exposure to the new force rather than previous force-field experience is responsible for transition- and after-effects. In a second experiment, we investigated whether learning was law-like—that is, whether it generalized to unvisited workspace. Subjects were tested in new, unvisited workspaces in the null-force condition after sufficient training in either force condition. The occurrence of transferred after-effects indicated that adaptation to both positive and negative damping was mediated by rule-based rather than exclusive associative processes.