End Posture Research Articles

Anticipation (second-order motor planning) is stored in memory - processing of grasp postures in a priming paradigm.

The end-state comfort effect (ESC) describes the tendency to grasp an object with an initial uncomfortable grasp posture in order to achieve a comfortable end posture. The ESC is an example for anticipative processes in manual action. ESC planning is investigated in many studies where this effect is measured in the context of motor observation and motion capture. However, there is little evidence if the anticipative link between different action states, especially between initial grasp postures and comfortable end postures, is represented in memory. The aim of the present study was to investigate whether the perception of a grasp posture holding a bar leads to the activation of action-related representations of grasping actions. For this purpose, a priming paradigm was used in which prime images were shown depicting either a comfortable (overhand grip) or uncomfortable (underhand grip) grasp posture holding a two-colored bar. The subsequently shown target images represented either a comfortable (thumb-up) or uncomfortable (thumb-down) final grasp posture of this grasping action. Due to the different grasp postures in the prime and target, prime-target pairs represented different types of action sequences. Furthermore, physically possible, and physically impossible actions were presented. Participants were asked to react to the top color of the bar shown in the target-picture, whereby the shown grasp posture was irrelevant for this decision. Results showed that reaction times did not differ after presentation of an overhand grip to target pictures showing comfortable or uncomfortable final grasp postures. In contrast, after presentation of an underhand grip in the prime, reactions to target pictures with final comfortable grasp postures were faster compared to target pictures with uncomfortable grasp postures. The effect was only found for the physically possible action. The findings suggest that the perception of the underhand grip leads to cognitive pre-activation of a final action state. The present study suggests that the association between an initial uncomfortable underhand grip and its action effect, in form of a final action state that is consistent with the ESC, is represented in memory. Such motor representation might be important for the anticipation and control of goal-directed grasping.

Dexterous obstacle-avoidance motion control of Rope Driven Snake Manipulator based on the bionic path following

The RDSM (Rope Driven Snake Manipulator) is a hyper-redundant robot operating in narrow and confined environments, such as aerospace, nuclear industry and etc. Inspired from the bionic following motion, an obstacle-avoidance control method of the RDSM in uncharted environments is proposed without the information of global obstacles. First, the kinematic model of a 17-DOF RDSM is established considering the mapping among the joint angle, rope length and end posture. Then, the motion path and inverse kinematic iterative algorithm of the RDSM in multi-obstacle environments is deduced using the piecewise Bézier curves. The motion control method of the RDSM is designed based on the model reference adaptive control, guaranteeing the joint error and end posture error asymptotically stable. Finally, the proposed obstacle avoidance method is verified with the simulation and experiment. As the result shown, the RDSM avoids obstacles on a path with a minimum curvature radius of 1/8 arm length, and the motion control precision of the end posture is within ±2.5mm/±0.5∘.

Neural network-based robot nonlinear output feedback control method

In order to improve the accuracy of robot terminal pose tracking and the anti-interference performance of robot nonlinear motion path control, a nonlinear output feedback control method based on neural network is proposed. Construct the coordinate transformation matrix of the connecting rod, calculate the linear and angular velocity of the nonlinear motion of the robot, then calculate the sum of the kinetic energy of each connecting rod of the robot, and establish the motion equation of the robot. The structure of BP neural network is analyzed, and the motion equation is solved by BP neural network. Finally, a Fractional Order PID controller is designed and BP neural network is constructed to control the nonlinear motion equation of the robot to complete the output feedback control of the robot. The experimental results show that the end attitude tracking error of this method is the smallest, and it best fits the actual nonlinear trajectory of the robot. It shows that this method can accurately track the end posture of the robot, and can still effectively control the trajectory of the robot in the interference environment.

Eliciting End-State Comfort Planning in Children With and Without Developmental Coordination Disorder Using a Hammer Task: A Pilot Study.

The end-state comfort (ESC) effect refers to the consistent tendency of healthy adults to end their movements in a comfortable end posture. In children with and without developmental coordination disorder (DCD), the results of studies focusing on ESC planning have been inconclusive, which is likely to be due to differences in task constraints. The present pilot study focused on the question whether children with and without DCD were able to change their planning strategy and were more likely to plan for ESC when demanded by complex object manipulations at the end of a task. To this end, we examined ESC planning in 18 children with and without DCD (aged 5–11years) using the previously used sword-task and the newly developed hammer-task. In the sword-task, children had to insert a sword in a wooden block, which could be relatively easily completed with an uncomfortable end-posture. In the hammer-task, children had to strike down a nail in a wooden pounding bench, which required additional force and speed demands, making it relatively difficult to complete the movement with an uncomfortable end-posture. In line with our hypothesis, the results demonstrated that children with and without DCD were more likely to plan for ESC on the hammer-task compared with the sword-task. Thus, while children with and without DCD show inconsistent ESC planning on many previously used tasks, the present pilot study shows that many of them are able to take into account the end-state of their movements if demanded by task constraints.

Development of motor planning in children: Disentangling elements of the planning process

Second-order motor planning of grasping movements is usually measured using tasks that focus on the relative (dis)comfort of end posture of the arm and hand regardless of the objective outcome of performance. This may underestimate the ability for forward planning in young children. In the current study, we aimed to examine the developmental mechanisms of motor planning in children using a task that necessitates second-order motor planning for its successful completion. We tested 311 children (aged 5–12 years) who were instructed to grasp and rotate a hexagonal knob over 60°, 120°, 180°, or 240°. The 180° and 240° rotation conditions necessitated adjustment of the preferred start grip for successful task completion. We examined successful or unsuccessful task completion, reaction time (RT), and movement time (MT) as a function of task demands (i.e., rotation angle) and age. Results showed that most children of all ages were able to successfully complete the task in the 180° rotation condition. In the most demanding 240° rotation condition, many children had difficulty in completing the task, but successful task completion increased with age. Time course analysis showed increased RT and MT with increasing task demands. Furthermore, whereas RT decreased with age for each rotation angle, MT remained stable with the exception of an increase in MT for the most demanding rotation condition. Together, these results exemplify that children aged 5–12 years are indeed able to engage in forward planning. With development, second-order motor planning proficiency increases, especially for more demanding movements, and the process becomes more efficient.

Trajectory planning of tokamak flexible in-vessel inspection robot

Tokamak flexible in-vessel inspection robot is mainly designed to carry a camera for close observation of the first wall of the vacuum vessel, which is essential for the maintenance of the future tokamak reactor without breaking the working condition of the vacuum vessel. A tokamak flexible in-vessel inspection robot is designed. In order to improve efficiency of the remote maintenance, it is necessary to design a corresponding trajectory planning algorithm to complete the automatic full coverage scanning of the complex tokamak cavity. Two different trajectory planning methods, RS (rough scanning) and FS (fine scanning), according to different demands of the task, are used to ensure the full coverage of the first wall scanning. To quickly locate the damage position, the first trajectory planning method is targeted for quick and wide-ranging scan of the tokamak D-shaped section, and the second one is for careful observation. Furthermore, both of the two different trajectory planning methods can ensure the full coverage of the first wall scanning with an optimal end posture. The method is tested on a simulated platform of EAST (Experimental Advanced Superconducting Tokamak) with the flexible in-vessel inspection robot, and the results show the effectiveness of the proposed algorithm.

Movement Induces the Use of External Spatial Coordinates for Tactile Localization in Congenitally Blind Humans.

To localize touch, the brain integrates spatial information coded in anatomically based and external spatial reference frames. Sighted humans, by default, use both reference frames in tactile localization. In contrast, congenitally blind individuals have been reported to rely exclusively on anatomical coordinates, suggesting a crucial role of the visual system for tactile spatial processing. We tested whether the use of external spatial information in touch can, alternatively, be induced by a movement context. Sighted and congenitally blind humans performed a tactile temporal order judgment task that indexes the use of external coordinates for tactile localization, while they executed bimanual arm movements with uncrossed and crossed start and end postures. In the sighted, start posture and planned end posture of the arm movement modulated tactile localization for stimuli presented before and during movement, indicating automatic, external recoding of touch. Contrary to previous findings, tactile localization of congenitally blind participants, too, was affected by external coordinates, though only for stimuli presented before movement start. Furthermore, only the movement's start posture, but not the planned end posture affected blind individuals' tactile performance. Thus, integration of external coordinates in touch is established without vision, though more selectively than when vision has developed normally, and possibly restricted to movement contexts. The lack of modulation by the planned posture in congenitally blind participants suggests that external coordinates in this group are not mediated by motor efference copy. Instead the task-related frequent posture changes, that is, movement consequences rather than planning, appear to have induced their use of external coordinates.

Research on Yinma Palletizing Robot Motion Feasibility Based on MATLAB-Robotics Toolbox

To realize the working requirements of silver Horse Companys palletizing robot. Firstly, MATLAB software was used to establish mathematical model of the robot, and it calculated the robot workspace and generated workspace figures; it can also verify whether the predetermined grip and place points satisfy a predetermined workspace. Based on this analysis inverse kinematic of the robot, each joint angle from gripping position to place position was calculated. Polynomial interpolation method is applied to calculate the each joint trajectory; Finally, Robotics Toolbox is used to simulate the robot kinematics, and get the trajectory of the robot terminate executive body; each joint position, velocity trajectory can ensure no sudden change occurs in joint angular. In this paper, robot inverse kinematics completed robot end actuator position and posture transformation from the Cartesian space to the joint space. In order to make the joint space path planning possible, this will greatly simplify the calculation. And the joint space and Cartesian coordinate space does not exist a continuous relation, thus eliminating the singularity problem.

Remapping of touch in the blind for current, but not for planned postures

Crossing effects in temporal order judgment (TOJ) have been interpreted to indicate remapping of touch from somatotopic into external spatial coordinates. Such crossing effects have been reported to be absent in the congenitally blind, presumably indicating that they do not, by default, remap touch (e.g., Röder et al., 2004). Here, we devised a TOJ task in which participants, trial by trial, took on an uncrossed or crossed start posture and executed a cued movement with both arms into an uncrossed or crossed end posture. When stimulated during movement planning (i.e., before movement execution into the end posture), sighted participants’ performance was affected both by start posture (i.e., the posture during stimulation) as well as end posture (i.e., the currently planned posture). In contrast, blind participants showed a crossing effect for the start posture, but no effect of end posture. Thus, the blind do seem to remap touch when hand posture must be explicitly coded to perform the task such as when planning hand movements. However, whereas the sighted relate touch not only to current, but also to planned future postures, the blind seem to restrict remapping to current posture.

Semantics in the motor system: motor-cortical beta oscillations reflect semantic knowledge of end-postures for object use

In the present EEG study we investigated whether semantic knowledge for object use is represented in motor-related brain areas. Subjects were required to perform actions with everyday objects and to maintain either a meaningful or a meaningless end posture with the object. Analysis of the EEG data focused on the beta-frequency band, as previous studies have indicated that the maintenance of a posture is reflected in stronger beta-oscillations. Time frequency analysis indicated that the execution of actions resulting in a meaningless compared to a meaningful end posture was accompanied by a stronger beta-desynchronization towards the end of the movement and a stronger subsequent beta-rebound after posture-onset. The effect in the beta-frequency band was localized to premotor, parietal and medial frontal areas and could not be attributed to differences in timing or movement complexity between meaningful and meaningless actions. Together these findings directly show that the motor system is differentially activated during the execution and maintenance of semantically correct or incorrect end postures. This suggests that semantic object knowledge is indeed represented in motor-related brain areas, organized around specific end postures associated with the use of objects.

The effect of the “rod-and-frame” illusion on grip planning in a sequential object manipulation task

We investigated the effect of visual context (i.e., a visual illusion) on the planning of a sequential object manipulation task. Participants (n = 13) had to grasp a rod embedded in a “rod-and-frame” illusion and insert the rod-end into a tight hole in a pre-defined way. The grip type (defined by start posture, either pronated or supinated; and end posture, either comfortable or uncomfortable) used to grasp the rod was registered as a macroscopic variable of motor planning. Different rod orientations forced the participants to switch between grip types. As expected, most participants switched between pronated and supinated start postures, such that they ended the movement with a comfortable end posture. As it has been argued that planning is dependent on visual context information, we hypothesized that the visual illusion would affect the specific rod orientation at which participants would switch into a different grip type. This hypothesis was confirmed. More specifically, the illusion affected the critical spatial information that is used for action planning. Collectively, these findings are the first to show an effect of an illusion on motor planning in a sequential object manipulation task.

Mapping Implied Body Actions in the Human Motor System

The human visual system is highly tuned to perceive actual motion as well as to extrapolate dynamic information from static pictures of objects or creatures captured in the middle of motion. Processing of implied motion activates higher-order visual areas that are also involved in processing biological motion. Imagery and observation of actual movements performed by others engenders selective activation of motor and premotor areas that are part of a mirror-neuron system matching action observation and execution. By using single-pulse transcranial magnetic stimulation, we found that the mere observation of static snapshots of hands suggesting a pincer grip action induced an increase in corticospinal excitability as compared with observation of resting, relaxed hands, or hands suggesting a completed action. This facilitatory effect was specific for the muscle that would be activated during actual execution of the observed action. We found no changes in responsiveness of the tested muscles during observation of nonbiological entities with (e.g., waterfalls) or without (e.g., icefalls) implied motion. Thus, extrapolation of motion information concerning human actions induced a selective activation of the motor system. This indicates that overlapping motor regions are engaged in the visual analysis of physical and implied body actions. The absence of motor evoked potential modulation during observation of end posture stimuli may indicate that the observation-execution matching system is preferentially activated by implied, ongoing but not yet completed actions.

Partial tuning of motor cortex neurons to final posture in a free-moving paradigm

Motor cortex neurons in the monkey brain were tested with a diverse and naturalistic arm movement set. Over this global set of movements, the neurons showed a limited but significant degree of tuning to the multijoint posture attained by the arm at the end of each movement. Further supporting the hypothesis that the neurons are partially tuned to end posture, the postures preferred by the neurons significantly matched the postures evoked by electrical stimulation of the same cortical sites. However, much of the variance in neuronal activity remained unexplained even by the end-posture model, and thus other variables must have contributed to the response profile of the neurons. One possibility is that motor cortex neurons become tuned to the wide variety of movement parameters that are relevant to the animal's normal behavioral repertoire, and, therefore, any one parameter accounts for only a limited amount of neuronal variance.

Three-Dimensional Movement in Water of the Dolphin Robot (2nd Report, Control Between Two Postures by Combination Motion of Roll and Pitch)

The purpose of this study is to realize the three-dimensional maneuverability of high speed swimming animals such as dolphins by a biomimetic robot. In the preceding paper, a dolphin robot whose length is 1m was developed, and the loop-the-loop motion in the water was performed. In this paper, a reference trajectory from a start posture to an end posture was firstly planned as a combination motion of roll and pitch. Next, a simulation method to analyze the three-dimensional dynamics of the dolphin robot was developed, and the feedback control for roll, pitch and yaw was examined by the simulation. It was found that the proposed feedback control was sufficient for tracking the reference trajectory in the simulation. In addition, swimming experiments were conducted to examine the validity of the simulation method and the control algorithm. The control performance in the experiments was found to be satisfactory although the optimal feedback gain became somewhat different value from that in the simulation

End posture selection in manual positioning: evidence for feedforward modeling based on a movement choice method.

Although it is well known that the postures adopted at the ends of movements depend on where one starts and how one moves, it is not yet clear whether those differing end postures are selected before movements begin. Two experiments were designed to test the hypothesis that end postures for positioning movements are chosen before movements commence. The experiments were further designed to check whether movements are internally simulated before overt movements occur and end-postures are still being selected. To address these questions we used a movement choice method. Participants were presented with two possible end postures and were asked to choose between them by moving to the one that seemed easier to adopt. End-posture choices were affected by starting positions and also by the movements that would have to be made, as affected by having obstacles in the way. The results suggest that participants relied on feedforward modeling of prospective movements as they selected end postures prior to overt movement production. The fact that the movement choice method could confirm this suggests that the method holds considerable promise as a tool for investigating motor planning.

Constraints on grip selection in cerebral palsy. Minimising discomfort.

The present study examined whether movement characteristics of individuals with spastic hemiparesis could be accounted for by disorders in movement planning. Two experiments were performed that tested minimisation of postural discomfort and minimisation of movement costs as constraints on grip selection. In the 1st experiment, spastic subjects and controls had to pick up a bar and place it in one of 5 boxes with either the left or right side down. In addition, awkwardness ratings of the different postures were given. Minimisation of posture discomfort as constraint on grip selection was examined. In line with previous studies, grip selection for the control subjects was based on minimisation of end posture discomfort. For the unimpaired hand of the spastic subjects, no discrimination was made in discomfort ratings among the different postures. Accordingly, with this hand, subjects showed no preference for a particular grip type. The posture ratings for the impaired hand were more varied both within and between spastic subjects, and minimisation of discomfort at either the start or end could not completely account for the grips chosen. Rather, the results suggest that minimisation of total posture discomfort acted as a constraint on grip selection for this hand. In the 2nd experiment, minimisation of total movement costs as a constraint on grip selection was tested. Spastic subjects and a control group had to grasp a bar on a clockface and rotate one end to the top position, starting from 15 different starting positions. Again, the end-state comfort effect was demonstrated in the control group. For the impaired hand of the spastic subjects, minimisation of total movement costs as expressed by a reduction of the total amount of joint rotation was shown to account for the grips chosen. The lack of consistency in grip selection for the unimpaired hand at some starting positions seemed to stem from an unresolved conflict between minimisation of end posture discomfort and minimisation of total movement costs. The combined results of the two experiments suggest that grip planning in spastic hemiparetic subjects is not disturbed per se. Rather, different constraints are imposed during the grip selection process. If movements are difficult to execute (i.e. because the hand is impaired), grip planning proceeded by a minimisation of total movement costs by choosing a task solution that reduced the total amount of joint rotation.

Impairment of motor imagery in putamen lesions in humans

Patients with putamen or cortical lesions participated in a first- and third-person movement imagery task, each primarily engaging kinesthetic and visual imagery. The subjects were instructed to imagine themselves (first-person task) and a third party (third-person task) performing a sequence of three movements and to choose from a set of four photos the end posture resulting from the movements. The results demonstrated that, limb-specific imagery was impaired in both putamen and cortical lesions, in the first-, but not third-person task. Moreover, more than half of the errors made by cortical patients were with respect to the first movement, a finding consistent with motor cortex involvement in memory processes. Taken overall, the results provide evidence that the basal ganglia as well as cortical structures play an important role in the neural network mediating motor imagery.