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Research has shown that the kinematic characteristics of right-hand movements change when executed during both speech production and processing. Despite the variety of prehension and manual actions used to examine this relationship, the literature has yet to examine potential movement effects using an action with a distinct kinematic signature: the hand-to-mouth (grasp-to-eat) action. In this study, participants performed grasp-to-eat and grasp-to-place actions in (a) a quiet environment and (b) while processing speech. Results during the quiet condition replicated the previous findings; consistently smaller grasp-to-eat (compared to grasp-to-place), maximum grip apertures appeared only when using the right hand. Interestingly, in the listen condition, smaller maximum grip apertures in the grasp-to-eat movement appeared in both the right and left hands, despite the fact that participants were right-handed. This paper addresses these results in relation with similar behaviour observed in children, and discusses implications for functional lateralization and neural organization. [ABSTRACT FROM AUTHOR]

In a recent paper, Flament et al. (1999) studied the process of learning to flex the elbow faster. They concluded from their data that time-related parameters (e.g. movement time) changed faster during learning than magnitude-related parameters (e.g. peak velocity) and discussed this finding in terms of neural substrates responsible for the apparently different learning mechanisms. In this paper, I will argue that finding different time constants does not imply different learning mechanisms and will give a theoretical example of the development of parameters during learning to move faster. Despite the fact that only one learning process is modelled, various kinematic parameters show different time courses of learning. The differences the model predicts are comparable with the experimental results. [ABSTRACT FROM AUTHOR]

When using visual and proprioceptive information to plan a reach, it has been proposed that the brain combines these cues to estimate the object and/or limb's location. Specifically, according to the maximum-likelihood estimation (MLE) model, sensory inputs are combined such that more reliable inputs are assigned a greater weight (Ernst and Banks in Nature 415:429-433, ). In this paper, we examined if the brain is able to adjust which sensory cue it weights the most. Specifically, we asked if the brain changes how it weights sensory information when the availability of a visual cue is manipulated. Twelve healthy subjects reached to visual (V), proprioceptive (P), or visual + proprioceptive (VP) targets under different visual delay conditions (e.g., on V and VP trials, the visual target was available for the entire reach; it was removed with the go signal, or it was removed 1 s before the go signal). To establish which sensory cue subjects weighted the most, we compared endpoint positions achieved on V and P reaches to VP reaches. Results indicated that subjects combined visual and proprioceptive cues in accordance with the MLE model when reaching to VP targets. Moreover, subjects' reaching errors to visual targets increased with longer visual delays (particularly in the vertical direction). However, there was no change in reach variability with longer delays, and subjects did not reweight visual information as the availability of visual information was manipulated. Thus, a change in visual environment is not sufficient to cause the brain to reweight how it processes sensory information. [ABSTRACT FROM AUTHOR]

In point-to-point reaching movements, the trajectory of the fingertip along the horizontal plane is not completely straight but slightly curved sideward. The current paper examines whether this horizontal curvature is related to the height to which the finger is lifted. Previous research suggested that the height to which the hand is lifted might be a determinant of horizontal curvature. We asked participants to make point-to-point movements in three conditions: constrained movements (i.e., fingertip keeps contact with table top) over vertically curved surfaces that differed in height, constrained movements over a flat surface, and unconstrained movements (i.e., fingertip lifted from table top). In constrained movements, we found a strong relation between horizontal curvature and lifted height of the finger. Interestingly, for unconstrained movements, the relation between horizontal curvature and height to which the finger was lifted was weak. This demonstrates that the height to which the finger was lifted relates to horizontal curvature in some, but not in all conditions. This suggests that the height to which the hand is lifted should be included, in particular for constrained movements, when giving a full account of horizontal curvature in point-to-point movements. [ABSTRACT FROM AUTHOR]

In the companion paper utilizing a quantitative model of optimal motor coordination (Part I, Rand and Shimansky, in Exp Brain Res 225:55-73, ), we examined coordination between X and Y movement directions (XYC) during reaching movements performed under three prescribed speeds, two movement amplitudes, and two target sizes. The obtained results indicated that the central nervous system (CNS) utilizes a two-phase strategy, where the initial and the final phases correspond to lower and higher precision of information processing, respectively, for controlling goal-directed reach-type movements to optimize the total cost of task performance including the cost of neural computations. The present study investigates how two different well-known concepts used for describing movement performance relate to the concepts of optimal XYC and two-phase control strategy. First, it is examined to what extent XYC is equivalent to movement trajectory straightness. The data analysis results show that the variability, the movement trajectory's deviation from the straight line, increases with an increase in prescribed movement speed. In contrast, the dependence of XYC strength on movement speed is opposite (in total agreement with an assumption of task performance optimality), suggesting that XYC is a feature of much higher level of generality than trajectory straightness. Second, it is tested how well the ballistic and the corrective components described in the traditional concept of two-component model of movement performance match with the initial and the final phase of the two-phase control strategy, respectively. In fast reaching movements, the percentage of trials with secondary corrective submovement was smaller under larger-target shorter-distance conditions. In slower reaching movements, meaningful parsing was impossible due to massive fluctuations in the kinematic profile throughout the movement. Thus, the parsing points determined by the conventional submovement analysis did not consistently reflect separation between the ballistic and error-corrective components. In contrast to the traditional concept of two-component movement performance, the concept of two-phase control strategy is applicable to a wide variety of experimental conditions. [ABSTRACT FROM AUTHOR]

A quantitative model of optimal transport-aperture coordination (TAC) during reach-to-grasp movements has been developed in our previous studies. The utilization of that model for data analysis allowed, for the first time, to examine the phase dependence of the precision demand specified by the CNS for neurocomputational information processing during an ongoing movement. It was shown that the CNS utilizes a two-phase strategy for movement control. That strategy consists of reducing the precision demand for neural computations during the initial phase, which decreases the cost of information processing at the expense of lower extent of control optimality. To successfully grasp the target object, the CNS increases precision demand during the final phase, resulting in higher extent of control optimality. In the present study, we generalized the model of optimal TAC to a model of optimal coordination between X and Y components of point-to-point planar movements (XYC). We investigated whether the CNS uses the two-phase control strategy for controlling those movements, and how the strategy parameters depend on the prescribed movement speed, movement amplitude and the size of the target area. The results indeed revealed a substantial similarity between the CNS's regulation of TAC and XYC. First, the variability of XYC within individual trials was minimal, meaning that execution noise during the movement was insignificant. Second, the inter-trial variability of XYC was considerable during the majority of the movement time, meaning that the precision demand for information processing was lowered, which is characteristic for the initial phase. That variability significantly decreased, indicating higher extent of control optimality, during the shorter final movement phase. The final phase was the longest (shortest) under the most (least) challenging combination of speed and accuracy requirements, fully consistent with the concept of the two-phase control strategy. This paper further discussed the relationship between motor variability and XYC variability. [ABSTRACT FROM AUTHOR]

Step length, cadence and joint flexion all increase in response to increases in gradient and walking speed. However, the tuning strategy leading to these changes has not been elucidated. One characteristic of joint variation that occurs during walking is the close relationship among the joints. This property reduces the number of degrees of freedom and seems to be a key issue in discussing the tuning strategy. This correlation has been analyzed for the lower limbs, but the relation between the trunk and lower body is generally ignored. Two questions about posture during walking are discussed in this paper: (1) whether there is a low-dimensional restriction that determines walking posture, which depends not just on the lower limbs but on the whole body, including the trunk and (2) whether some simple rules appear in different walking conditions. To investigate the correlation, singular value decomposition was applied to a measured walking pattern. This showed that the whole movement can be described by a closed loop on a two-dimensional plane in joint space. Furthermore, by investigating the effect of the walking condition on the decomposed patterns, the position and the tilt of the constraint plane was found to change significantly, while the loop pattern on the constraint plane was shown to be robust. This result indicates that humans select only certain kinematic characteristics for adapting to various walking conditions. [ABSTRACT FROM AUTHOR]

The principal goal of our study is to gain an insight into the coordinative structure of a complex body movement. As a first step, this paper describes the activity of multiple skeletal muscles associated with the drawing-like movements that resemble the Jeté, performed by skilled ballet dancers. The EMG activity of 18 muscles of the trunk, pelvis, and both legs was recorded when dancers standing on the left leg moved the toe of the right leg forward and backward along a straight line. A major finding is that the EMG activity of all right muscles, despite their functional and anatomical diversity, was minimised not only at the initial, vertical position but also in the reversal phase of movement when the moving leg was maximally deviated from the vertical position. In other words, the activity was minimal when torques of the weights of limb segments were minimal as well as when these torques were maximal. In contrast, in the static task when the maximally deviated leg position was maintained, there was substantial tonic activation of leg muscles, an activity that was necessary to balance these torques. The result is consistent with the hypothesis that movements of the body result from centrally induced changes in the muscle recruitment thresholds influencing the referent configuration of the body. The existence of minima in the overall EMG activity of skeletal muscles is not the only prediction of the referent configuration hypothesis. An immediate consequence of the hypothesis is that, in movements of the limb, the EMG patterns should be a direction-dependent phenomenon known as “directional tuning” of muscles. In combination with the principle of minimal interaction of neuromuscular system, the referent configuration hypothesis offers a dynamic approach to the problems of how control levels may guide multi-muscle and multi-joint systems without redundancy problems. [ABSTRACT FROM AUTHOR]

Watt et al. (Exp Brain Res, 2000, 135:411-416) suggested that a reduced field of view causes objects to appear closer than their physical distance. This suggestion is based on the observation that individuals terminated open-loop prehension prematurely when pretending to grasp a paper rectangle initially viewed through a reduced field of view. We tested Watt et al.’s suggestion in an open-loop pointing task. In experiment 1, 21 participants pointed at targets in three locations (20, 30 and 40 cm relative to the starting position) in three viewing conditions (full, 16° and 4° field of view). No difference in accuracy was found between conditions but the reduced field of view led to an increase in end-point variability across trials. We interpret these results as indicating that a reduced field of view decreases precision but does not necessarily affect object localisation. In experiment 2, we asked participants to reach-and-grasp a real object under the same three open-loop viewing conditions but without vision following movement onset. The experimental design ensured that haptic feedback was available, which could be used to calibrate reaching movements. We found that the reduced field of view caused no changes in grasp but we observed changes in the transport kinematics consistent with increased variability in the perceptual estimate of target location. Notably there were no changes in the spatial path (expected from movements to a closer location). In experiment 3, we repeated the Watt et al. design but removed vision and forced participants to rely on memory. In this condition we found the same undershoots as described by Watt et al. We conclude that a reduced field of view is neither necessary nor sufficient for underestimation and suggest that a reduced field of view decreases precision. This can cause participants to undershoot and/or alter the movement kinematics but we argue that such findings cannot be ascribed unambiguously to perceptual underestimation as they may reflect strategic alterations in behaviour. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to review the kinematics and dynamics of the vestibulo-ocular reflex (VOR) in three dimensions. We give a brief, didactic tutorial on vectors and matrices and their importance as representational schemes for describing the kinematics and dynamics of the angular and linear accelerations that activate the vestibular system. We show how the vectors associated with angular and linear head accelerations are transformed by the peripheral and central vestibular systems to drive the oculomotor system to produce eye movements in three-dimensional space. We also review critical questions and controversies related to the compensatory and orientation behavior of the VOR. One such question is how the central vestibular system distinguishes tilts of the head, which generate interaural linear acceleration from translations along the interaural axis. Another question is how the velocity-position integrator is implemented centrally. The review has been placed in the context of a model that explains the behavior of the VOR in three dimensions. Model processes have been related to peripheral and central neural behavior in order to gain insight into the nature of the three-dimensional organization and the controversial questions that are addressed. [ABSTRACT FROM AUTHOR]

Object-based visual attention is observed when the benefit of attending to one element in a display extends to other elements that are part of the same perceptual object. Apperceptive agnosia is an object identification deficit in which spatial attention is preserved but object-based attention is impaired. Some debate exists regarding the extent to which the object-based impairment can be attributed to perceptual mechanisms that are specifically involved in grouping and segmentation of a scene, as opposed to early sensory processes. In the present paper we show that random visual noise is sufficient to eliminate the object benefit, a result inconsistent with the view that grouping mechanisms are responsible for the effect. The results have implications for an understanding of apperceptive agnosia, and for an understanding of object-based attention more generally. [ABSTRACT FROM AUTHOR]

Patterns of muscle coactivation provide a window into mechanisms of limb stabilization. In the present paper we have examined muscle coactivation in single-joint elbow and single-joint shoulder movements and explored its relationship to movement velocity and amplitude, as well as phasic muscle activation patterns. Movements were produced at several speeds and different amplitudes, and muscle activity and movement kinematics were recorded. Tonic levels of electromyographic (EMG) activity following movement provided a measure of muscle cocontraction. It was found that coactivation following movement increased with maximum joint velocity at each of two amplitudes. Phasic EMG activity in agonist and antagonist muscles showed a similar correlation that was observable even during the first 30 ms of muscle activation. All subjects but one showed statistically significant correlations on a trial-by-trial basis between tonic and phasic activity levels, including the phasic activity measure taken at the initiation of movement. Our findings provide direct evidence that muscle coactivation varies with movement velocity. The data also suggest that cocontraction is linked in a simple manner to phasic muscle activity. The similarity in the patterns of tonic and phasic activation suggests that the nervous system may use a simple strategy to adjust coactivation and presumably limb impedance in association with changes in movement speed. Moreover, since the pattern of tonic activity varies with the first 30 ms of phasic activity, the control of cocontraction may be established prior to movement onset. [ABSTRACT FROM AUTHOR]

The purpose was to determine the impact of transcutaneous electrical nerve stimulation (TENS) on measures of walking kinematics and standing balance of healthy older adults who were stratified into two groups based on differences in the distance walked during the 6-min test of walking endurance. Regression models were developed to explain the variance in the 6-min distance and to assess the predictive power of balance metrics to categorize the 26 older adults (72 ± 5.4 yrs) as either slow or fast walkers. Walking kinematics were measured during 6- and 2-min walk tests that were performed with and without the concurrent application of TENS to the hip flexor and ankle dorsiflexor muscles. Participants walked briskly during the 6-min test and at a preferred pace during the 2-min test. The supplementary sensory stimulation provided by TENS did not alter the power of the models to explain the variance in the Baseline 6-min distance: Baseline, R2 = 0.85; TENS, R2 = 0.83. In contrast, TENS improved the explanatory power of the data obtained during the 2-min walk to account for the variance in the Baseline 6-min distance: no TENS, R2 = 0.40; TENS, R2 = 0.64. Logistic regression models based on force-plate and kinematic data obtained during the balance tasks were able to discriminate between the two groups with excellent certainty. The impact of TENS was greatest when older adults walked at a preferred speed but not when they walked at a brisk pace or performed tests of standing balance. [ABSTRACT FROM AUTHOR]

Learning of a motor task, such as making accurate goal-directed movements, is associated with a number of changes in limb kinematics and in the EMG activity that produces the movement. Some of these changes include increases in movement velocity, improvements in end-point accuracy, and the development of a biphasic/triphasic EMG pattern for fast movements. One question that has remained unanswered is whether the time course of the learning-related changes in movement parameters is similar for all parameters. The present paper focuses on this question and presents evidence that different parameters evolve with a specific temporal order. Neurologically normal subjects were trained to make horizontal, planar movements of the elbow that were both fast and accurate. The performance of the subjects was monitored over the course of 400 movements made during experiments lasting approximately 1.5 h. We measured time-related parameters (duration of acceleration, duration of deceleration, and movement duration) and amplitude-related parameters (peak acceleration, peak deceleration, peak velocity), as well as movement distance. In addition, each subject’s reaction time and EMG activity was monitored. We found that reaction time was the parameter that changed the fastest and that reached a steady baseline earliest. Time-related parameters decreased at a somewhat slower rate and plateaued next. Amplitude-related parameters were slowest in reaching steady-state values. In subjects making the fastest movements, a triphasic EMG patterns was observed to develop. Our findings reveal that movement parameters change with different time courses during the process of motor learning. The results are discussed in terms of the neural substrates that may be responsible for the differences in this aspect of motor learning and skill acquisition. [ABSTRACT FROM AUTHOR]

The control of locomotion has been studied from various perspectives related to the tasks of pattern generation, equilibrium control or adaptation to the environment. The last of these locomotor components has received comparably less attention, specifically pertaining to anticipatory adjustments. Continuing the work which has been conducted on both humans and cats, the present paper explores the nature of the differences in anticipatory locomotor adjustments for obstacle avoidance versus the accommodation to level changes. Six subjects walked in six different environments including no obstructions, a simple obstacle, two different level changes (a platform and stairs), and a combination of an obstacle with each respective level change. Full dynamic analyses allowed comparison of muscle torques as well as muscle power generated and absorbed at the lower limb joints across conditions. It was found that the previously shown robust lower limb reorganization characterized by a knee flexor generation strategy was upheld in all conditions when the obstacle was present. Pure level changes involved an augmentation of the ongoing hip strategy inherent in normal level walking. In the compound environment of obstructed level changes, subjects chose to combine an augmentation of hip flexor power with a reorganization to active knee flexion. The results are discussed from the point of view of general principles of mechanical coordination and the exploitation of intersegmental dynamics for foot transport. [ABSTRACT FROM AUTHOR]

The focus of this paper is to examine the contributions of active and passive forces in the control of limb trajectory over obstacles during locomotion. Kintetic analyses of the swing phase of locomotion were carried out to determine the power profiles at various joints and to parcel the joint moments into moments due to muscle action, gravitational force and motion-dependent terms. The analyses revealed that toe elevation over the obstacles was achieved primarily by flexing at the hip, knee and ankle joint. Power analyses showed that translational energy applied at the hip joint and rotational energy applied at the knee joint were modulated as functions of obstacle height. This demonstrates that increased hip and ankle joint flexion are achieved not through active muscle action but rather through passive forces induced by translational action at the hip (representing contribution by the stance limb muscles) and rotational action at the knee joint. Parcelling the joint moment terms into various components clearly shows how the nervous system exploits intersegmental dynamics to simplify control of limb elevation over obstacles and minimize energy costs. [ABSTRACT FROM AUTHOR]

Some studies have demonstrated that Action Observation (AO) could help patients with aphasia to recover use of verbs. However, the role of kinematics in this effect has remained unknown. The main aim was to assess the effectiveness of a complementary intervention based on the observation of action kinematics in patients with aphasia. Seven aphasic patients (3 males, 4 females) aged between 55 and 88 years participated in the studies. All patients received a classical intervention and an additional, specific intervention based on action observation. This consisted in visualizing a static image or a point-light sequence representing a human action and in trying to name the verb representing the action. In each session, 57 actions were visualized: 19 represented by a static drawing, 19 by a non-focalized point-light sequence, i.e., a point-light display with all dots in white, and 19 by a focalized point-light sequence, i.e., a point-light display (PLD) with the dots corresponding to the main limbs in yellow. Before (pre-test) and after (post-test) the intervention, each patient performed the same denomination task, in which all actions were presented in photographs. The results showed a significant improvement in performance between pre and post-test, but only when the actions were presented in focalized and non-focalized point-light sequences during the intervention. The presentation of action kinematics seems crucial in the recovery of verbs in patients with aphasia. This should be considered by speech therapists in their interventions. [ABSTRACT FROM AUTHOR]

This study explored the relationship between single motor unit (MU) firing rates (FRs) and limb movement velocity during voluntary shortening contractions when accounting for the effects of time course variability between different kinematic comparisons. Single MU trains recorded by intramuscular electromyography in agonist muscles of the anconeus (n = 15 participants) and lateral head of the triceps brachii (n = 6) were measured during each voluntary shortening contraction. Elbow extension movements consisted of a targeted velocity occurring along the sagittal plane at 25, 50, 75 and 100% of maximum velocity. To account for the effect of differences in contraction time course between parameters, each MU potential was time locked throughout the shortening muscle contraction and linked with separated kinematic parameters of the elbow joint. Across targeted movement velocities, instantaneous FRs were significantly correlated with elbow extension rate of torque development (r = 0.45) and torque (r = 0.40), but FRs were not correlated with velocity (r = 0.03, p = n.s.). Instead, FRs had a weak indirect relationship with limb movement velocity and position assessed through multiple correlation of the stepwise kinematic progression. Results show that voluntary descending synaptic inputs correspond to a more direct relationship between agonist muscle FRs and torque during shortening contractions, but not velocity. Instead, FRs were indirectly correlated to preparing the magnitude of imminent movement velocity of the lagging limb through torque. [ABSTRACT FROM AUTHOR]

In this study, 26 young, 16 older adults ≤ 66a, and 22 older adults ≥ 67a were examined in a set of neuropsychological tests and the kinematics in two different activities of daily living (ADL) were assessed. Half of the participants performed the ADL in a natural speed, the other half as fast as possible. The performance in the Trail Making Task B revealed an increased slope after 67 years of age. When executed in a natural speed, ADL kinematics were comparable. When executed as fast as possible, almost all kinematic parameters showed significant group and speed differences and revealed group × speed interactions. Models of multiple linear regression predicting ADL trial durations showed similar strategies in the young and older adults < 67a. Factors were the general movement speed, the travelled path lengths, and the simultaneous use of both hands. In the older adults ≥ 67a, factors were the general movement speed, the travelled path length, and the activity level (during the task execution). A principal component analysis supported these findings by revealing two underlying components: movement strategy and age-dependent decline in primarily executive functions, where the ADL trial duration had comparable loadings on both components. These results in association with the accelerated decline in executive functions found in the oldest group suggest that deterioration of ADL with age is particularly caused by specific age-dependent changes in cognitive capacities. [ABSTRACT FROM AUTHOR]

The postural instability theory of motion sickness predicts that subjective symptoms of motion sickness will be preceded by unstable control of posture. In previous studies, this prediction has been confirmed with measures of the spatial magnitude and the temporal dynamics of postural activity. In the present study, we examine whether precursors of visually induced motion sickness might exist in postural time-to-contact, a measure of postural activity that is related to the risk of falling. Standing participants were exposed to oscillating visual motion stimuli in a standard laboratory protocol. Both before and during exposure to visual motion stimuli, we monitored the kinematics of the body’s center of pressure. We predicted that postural activity would differ between participants who reported motion sickness and those who did not, and that these differences would exist before participants experienced subjective symptoms of motion sickness. During exposure to visual motion stimuli, the multifractality of sway differed between the Well and Sick groups. Postural time-to-contact differed between the Well and Sick groups during exposure to visual motion stimuli, but also before exposure to any motion stimuli. The results provide a qualitatively new type of support for the postural instability theory of motion sickness. [ABSTRACT FROM AUTHOR]

We previously showed that proprioceptive sensory input from the hindlimbs to the anterior cerebellar cortex of the cat may not be simply organized with respect to a body map, but it may also be distributed to multiple discrete functional areas extending beyond classical body map boundaries. With passive hindlimb stepping movements, cerebellar activity was shown to relate to whole limb kinematics as does the activity of dorsal spinocerebellar tract (DSCT) neurons. For DSCT activity, whole limb kinematics provides a solid functional framework within which information about limb forces, such as those generated during active stepping, may also be embedded. In this study, we investigated this idea for the spinocerebellar cortex activity by examining the activity of cerebellar cortical neurons during both passive bipedal hindlimb stepping and active stepping on a treadmill. Our results showed a functional compartmentalization of cerebellar responses to hindlimb stepping movements depending on the two types of stepping and strong relationships between neural activities and limb axis kinematics during both. In fact, responses to passive and active stepping were generally different, but in both cases their waveforms were related strongly to the limb axis kinematics. That is, the different stepping conditions modified the kinematics representation without producing different components in the response waveforms. In sum, cerebellar activity was consistent with a global kinematics framework serving as a basis upon which detailed information about limb mechanics and/or about individual limb segments might be imposed. [ABSTRACT FROM AUTHOR]

Affordance theory and behavioural dynamics have been used as theoretical constructs to explain how individuals interact with the environment in order to avoid obstacles. Features of obstacle distance and multiple obstacle avoidance have been discussed in unique studies, yet the interactions of these environmental features have yet to be explored. The purpose of this study was to asses the effects of obstacle distance, relative to the goal, on aperture crossing strategies. Kinematics and gaze behaviours were assessed in a cohort of female young adults ( N = 24, 21.3 ± 1.4 years). Results identified that participants chose to navigate through gaps of 1.3× shoulder width or greater, regardless of obstacle distance. However, safety margin in the anterior-posterior direction was found to increase with increased obstacle distance, suggesting unique environmental affordances for each obstacle distance. Therefore, although decision making on whether to navigate through, or around, the aperture appears to be unaffected by obstacle location, specific environmental features result in unique kinematic behaviours. Such behaviours fit within, and add merit to, the tenets of both affordance theory and behavioural dynamics. [ABSTRACT FROM AUTHOR]

We exposed standing men and women to motion relative to the illuminated environment in a moving room. During room motion, we measured the kinematics of standing body sway. Participants were instructed to discontinue immediately if they experienced any symptoms of motion sickness, however mild. For this reason, our analysis of body sway included only movement before the onset of motion sickness. We analyzed the spatial magnitude of postural sway in terms of the positional variability and mean velocity of the center of pressure. We analyzed the multifractality of postural sway in terms of the width of the multifractal spectrum and the degree of multiplicativity of center of pressure positions. Results revealed that postural sway differed between participants who later reported motion sickness and those who did not, replicating previous effects. In a novel effect, postural responses to motion of the illuminated environment differed between women and men. In addition, we identified statistically significant interactions that involved both Sex and motion sickness status. Effects were observed separately in the spatial magnitude and multifractality of sway. The results were consistent with the postural instability theory of motion sickness (Riccio and Stoffregen in Ecol Psychol 3:195-240, 1991) and suggest that Sex differences in motion sickness may be related to Sex differences in the control and stabilization of bodily activity. [ABSTRACT FROM AUTHOR]

During intertemporal decisions, the preference for smaller, sooner reward over larger-delayed rewards (temporal discounting, TD) exhibits substantial inter-subject variability; however, it is currently unclear what are the mechanisms underlying this apparently idiosyncratic behavior. To answer this question, here we recorded and analyzed mouse movement kinematics during intertemporal choices in a large sample of participants ( N = 86). Results revealed a specific pattern of decision dynamics associated with the selection of 'immediate' versus 'delayed' response alternatives, which well discriminated between a 'discounter' versus a 'farsighted' behavior-thus representing a reliable behavioral marker of TD preferences. By fitting the Drift Diffusion Model to the data, we showed that differences between discounter and farsighted subjects could be explained in terms of different model parameterizations, corresponding to the use of different choice mechanisms in the two groups. While farsighted subjects were biased toward the 'delayed' option, discounter subjects were not correspondingly biased toward the 'immediate' option. Rather, as shown by the dynamics of evidence accumulation over time, their behavior was characterized by high choice uncertainty. [ABSTRACT FROM AUTHOR]

Action competency is defined as the ability of an individual to self-evaluate their own performance capabilities. The current experiment demonstrated that physical and observational training with a motor skill alters action competency ratings in a similar manner. Using a pre-test and post-test protocol, the results revealed that action competency is constrained prior to training by the intrinsic dynamics of relative phase ( ϕ), with in-phase ( ϕ = 0°) and anti-phase ( ϕ = 180°) patterns receiving higher competency ratings than other relative phase patterns. After 2 days of training, action competency ratings for two trained relative phase patterns, +60° and +120°, increased following physical practice or observational practice. A transfer test revealed that both physical performance ability and action competency ability transferred to the symmetry partners (−60° and −120°) of the two trained relative phase patterns following physical or observational training. The findings also revealed that relative motion direction acts as categorical information that helps to organize action production and facilitate action competency. The results are interpreted based on the coordination dynamics theory of perception-action coupling, and extend this theory by showing that visual perception, action production, and action competency are all constrained in a consistent manner by the dynamics of the order parameter relative phase. As a whole, the findings revealed that relative motion, relative phase, and possibly relative amplitude information are all distinct sources of information that contribute to the emergence of a kinematic understanding of action in the nervous system. [ABSTRACT FROM AUTHOR]