Age and Not the Preferred Limb Influences the Kinematic Structure of Pointing Movements

In goal-directed movements, effective open-loop control reduces the need for feedback-based corrective submovements. The purpose of this study was to determine the influence of hand preference and aging on submovements during single- and two-joint pointing movements. A total of 12 young and 12 older right-handed participants performed pointing movements that involved either elbow extension or a combination of elbow extension and horizontal shoulder flexion with their right and left arms to a target. Kinematics were used to separate the movements into their primary and secondary submovements. The older adults exhibited slower movements, used secondary submovements more often, and produced relatively shorter primary submovements. However, there were no interlimb differences for either age group or for the single- and two-joint movements. These findings indicate that open-loop control is similar between arms but compromised in older compared to younger adults.

Effects of Local Gravity Compensation on Motor Control During Altered Environmental Gravity

Our sensorimotor control is well adapted to normogravity environment encountered on Earth and any change in gravity significantly disturbs our movement. In order to produce appropriate motor commands for aimed arm movements such as pointing or reaching, environmental changes have to be taken into account. This adaptation is crucial when performing successful movements during microgravity and hypergravity conditions. To mitigate the effects of changing gravitational levels, such as the changed movement duration and decreased accuracy, we explored the possible beneficial effects of gravity compensation on movement. Local gravity compensation was achieved using a motorized robotic device capable of applying precise forces to the subject’s wrist that generated a normogravity equivalent torque at the shoulder joint during periods of microgravity and hypergravity. The efficiency of the local gravity compensation was assessed with an experiment in which participants performed a series of pointing movements toward the target on a screen during a parabolic flight. We compared movement duration, accuracy, movement trajectory, and muscle activations of movements during periods of microgravity and hypergravity with conditions when local gravity compensation was provided. The use of local gravity compensation at the arm mitigated the changes in movement duration, accuracy, and muscle activity. Our results suggest that the use of such an assistive device helps with movements during unfamiliar environmental gravity.

Effects of pointing movements on visuospatial working memory in a joint-action condition: Evidence from eye movements

Previous studies showed that (a) performing pointing movements towards to-be-remembered locations enhanced their later recognition, and (b) in a joint-action condition, experimenter-performed pointing movements benefited memory to the same extent as self-performed movements. The present study replicated these findings and additionally recorded participants’ fixations towards studied arrays. Each trial involved the presentation of two consecutive spatial arrays, where each item occupied a different spatial location. The item locations of one array were encoded by mere visual observation (the no-move array), whereas the locations of the other array were encoded by observation plus pointing movements (the move array). Critically, in Experiment 1, participants took turns with the experimenter in pointing towards the move arrays (joint-action condition), while in Experiment 2 pointing was performed only by the experimenter (passive condition). The results showed that the locations of move arrays were recognized better than the locations of no-move arrays in Experiment 1, but not in Experiment 2. The pattern of eye-fixations was in line with behavioral findings, indicating that in Experiment 1, fixations to the locations of move arrays were higher in number and longer in duration than fixations to the locations of no-move arrays, irrespective of the agent who performed the movements. In contrast, no differences emerged in Experiment 2. We propose that, in the joint-action condition, self- and other-performed pointing movements are coded at the same representational level and their functional equivalency is reflected in a similar pattern of eye-fixations.

A Kinematic Evaluation of Linear and Parabolic Pointing in Virtual Reality

We present the results of a study investigating the influence of task and effector constraints on the kinematics of pointing movements performed in immersive virtual environments. We compared the effect of target width, as a task constraint, to the effect of movement distance, as an effector constraint, in terms of overall effect on movement time in a pointing task. We also compared a linear ray-cast pointing technique to a parabolic pointing technique to understand how interaction style may be understood in the context of task and effector constraints. The effect of target width as an information constraint on pointing performance was amplified in VR. Pointing technique acted as an effector constraint, with linear ray-cast pointing resulting in faster performance than parabolic pointers.

Pointing in depth is shaped by a natural grasping distance prior

Vision in depth is distorted. A similar distortion can be observed for pointing to visual targets in depth. It has been suggested that pointing errors in depth reflect the visual distortion. However, much research has suggested that in case visual information is not rich enough, the sensorimotor system involves prior knowledge to optimally plan movement trajectories. Here, we show that pointing in depth is guided by a prior that biases movements toward the natural grasping distance at which object manipulation is usually performed. To dissociate whether pointing is guided by distorted vision only or whether it takes into account a natural grasping distance prior, we adapted pointing movements. Participants received visual feedback about the success of their pointing once the movement was finished. We distorted the feedback to signal either that pointing was not far enough or in separate sessions that pointing was too far. Participants adapted to this artificial error by either extending or shortening their pointing movements. The generalization of pointing adaptation revealed a bias in movement planning that is inconsistent with pointing being guided only by distorted vision but with the involvement of knowledge about the natural grasping distance. Adaptation was strongest for pointing movements to a middle position that corresponds to the natural grassing distance and it was weakest for movements leading away from it. It has been demonstrated that pointing adaptation in depth changes visual perception (Volcic et al., 2013). We also wondered how effects of pointing adaptation on visual space would generalize in depth.

Arm choice post-stroke is habitual rather than optimal in right-, but not in left-paretic individuals

In non-disabled individuals, arm choice in pointing movements depends on expected biomechanical effort, expected success, and a handedness bias. Following a stroke, is arm choice re-optimized to account for the decreased motor performance, or does it follow a pre-injury habitual pattern? Because premorbidly right-handed individuals with left hemiparesis generally use their affected arm less than those with right hemiparesis, we hypothesized that arm choice follows a more habitual pattern in right- than in left-hemiparetic individuals. Participants with mild to moderate chronic stroke who were right-handed before stroke performed pointing movements in both free- and forced-choice blocks, both under a no-time constraint condition and under a fast-time constraint condition designed to promote habitual choice. Mixed-effects models of arm choice revealed that expected effort and side of stroke predicted choices overall. However, expected success predicted choice in left-, but not of right-hemiparetic individuals. Furthermore, while left-hemiparetic individuals tended to avoid unsuccessful movements in the fast condition by selecting their non-paretic arm, right-hemiparetic individuals persevered in choosing their more affected arm. In addition, reaction times decreased in left-hemiparetic individuals between the no-time and the fast condition but showed no changes in right-hemiparetic individuals. Finally, arm choice in the no-time condition correlated with a clinical measure of spontaneous arm use for right-, but not for left-hemiparetic individuals. Our results thus show that, in premorbidly right-handed individuals with mild to moderate chronic stroke, arm choice is habitual in right-hemiparetic individuals, but shows a greater degree of optimality by taking account expected success in left-hemiparetic individuals.

Analisis Gerak Pointing Pada Olahraga Petanque

This study aimed to analyze pointing movement skill of Semarang Petanque athlete. This study was descriptive quantitative design which described systematically facts and characteristics of pointing movement by Semarang Petaque Athlete. The pointing movements as data were descriptive. This analysis used descriptive statistic which measured frequency. This data was taken from Biomechanics aspect of 3 pointing movements of Petaque by 8 men and women players of Semarang city. They were; (1) holding a boule, (2) foot position, and (3) throwing the boule. The measurement was carried out by two national coaches and one international coach of Petaque. The result shows that; 1) the average value of holding a boule is 4.4 or 88% of percentage which categorized as very good, 2) the average value of foot position is 4.6 or 92% of percentage which categorized as very good, and 3) the average value of throwing a boule is 3.72 or 74.4% of percentage which categorized as good. Overall movements point out good category with 88% of percentage.

Synergies reciprocally relate end-effector and joint-angles in rhythmic pointing movements

During rhythmic pointing movements, degrees of freedom (DOF) in the human action system—such as joint-angles in the arm—are assumed to covary to stabilise end-effector movement, e.g. index finger. In this paper, it is suggested that the end-effector movement and the coordination of DOF are reciprocally related in synergies that link DOF so as to produce the end-effector movement. The coordination of DOF in synergies and the relation between end-effector movement and DOF coordination received little attention, though essential to understand the principles of synergy formation. Therefore, the current study assessed how the end-effector movement related to the coordination of joint-angles during rhythmic pointing across target widths and distances. Results demonstrated that joint-angles were linked in different synergies when end-effector movements differed across conditions. Furthermore, in every condition, three joint-angles (shoulder plane of elevation, shoulder inward-outward rotation, elbow flexion-extension) largely drove the end-effector, and all joint-angles contributed to covariation that stabilised the end-effector. Together, results demonstrated synergies that produced the end-effector movement, constrained joint-angles so that they covaried to stabilise the end-effector, and differed when end-effector movement differed. Hence, end-effector and joint-angles were reciprocally related in synergies—indicating that the action system was organised as a complex dynamical system.