End-State Comfort Across the Lifespan: A Cross-Sectional Investigation of How Movement Context Influences Motor Planning in an Overturned Glass Task

Object Weight and Hand Dominance Impact Kinematics in a Functional Reach-to-Drink Task in School-Aged Children

This study evaluates the effects of object weight and hand dominance on the end-point kinematics of the hand-to-mouth (withdrawal) movement in a functional reach-to-drink task for typically developing school-aged children. Using 3D motion capture, speed (average velocity and peak velocity), straightness (ratio), and smoothness (number of velocity peaks and log dimensionless jerk) of hand movements were calculated for the withdrawal motion with three different bottle weights (empty, half-filled, and full). Average velocity (550.4 ± 142.0 versus 512.1 ± 145.6 mm/s) and peak velocity (916.3 ± 234 versus 842.7 ± 198.4 mm/s) were significantly higher with the empty versus half-filled bottle and with the non-dominant (average: 543.5 ± 145.2 mm/s; peak: 896.5 ± 207 mm/s) versus dominant (average: 525.2 ± 40.7 mm/s; peak: 864.2 ± 209.2 mm/s) hand. There were no differences in straightness or smoothness. These findings indicate that increasing weight in reach-to-drink task puts greater constraints on the task. The slower movements with the dominant hand might denote better precision control than the non-dominant hand. The quantitative motion capture results show average values for the kinematic variables for a functional reach-to-drink task in a typically developing population of school-aged children with changing weights of the bottles that are relevant to a real-life scenario. These results could inform the design of individualized therapeutic interventions to improve functional upper-extremity use in children with neurodevelopmental motor disorders.

The ontogeny of efficient second-order action planning: The developing interplay of controlled and habitual processes in goal-directed actions

The ability to act efficiently plays an important role in everyday human life. The current study investigated efficient motor planning in 2- to 14-year-old children and adults (N = 246) in two different object manipulation tasks that involved everyday objects (a cup and a spoon). Importantly, we manipulated whether or not the efficient controlled grasp was incongruent with the habitual use of the object. We assessed to what extent participants planned their grasping action in an anticipatory controlled manner or relied on the habitual use of an object. We found the ability of efficient movement planning to be correlated between the two conceptually different tasks. Furthermore, the interplay of controlled and habitual processes of action control showed different developmental patterns for the two tasks and does not indicate a simple linear developmental trend. Thus, this study expands our knowledge on the ontogeny of efficient motor planning and highlights the developmental dynamics of the interplay of controlled and habitual processes in goal-directed action control.

The effects of an object's height and weight on force calibration and kinematics when post-stroke and healthy individuals reach and grasp

Impairment in force regulation and motor control impedes the independence of individuals with stroke by limiting their ability to perform daily activities. There is, at present, incomplete information about how individuals with stroke regulate the application of force and control their movement when reaching, grasping, and lifting objects of different weights, located at different heights. In this study, we assess force regulation and kinematics when reaching, grasping, and lifting a cup of two different weights (empty and full), located at three different heights, in a total of 46 participants: 30 sub-acute stroke participants, and 16 healthy individuals. We found that the height of the reached target affects both force calibration and kinematics, while its weight affects only the force calibration when post-stroke and healthy individuals perform a reach-to-grasp task. There was no difference between the two groups in the mean and peak force values. The individuals with stroke had slower, jerkier, less efficient, and more variable movements compared to the control group. This difference was more pronounced with increasing stroke severity. With increasing stroke severity, post-stroke individuals demonstrated altered anticipation and preparation for lifting, which was evident for either cortical lesion side.

A robot goes to rehab: a novel gamified system for long-term stroke rehabilitation using a socially assistive robot-methodology and usability testing

Background

Socially assistive robots (SARs) have been proposed as a tool to help individuals who have had a stroke to perform their exercise during their rehabilitation process. Yet, to date, there are no data on the motivating benefit of SARs in a long-term interaction with post-stroke patients.

Methods

Here, we describe a robot-based gamified exercise platform, which we developed for long-term post-stroke rehabilitation. The platform uses the humanoid robot Pepper, and also has a computer-based configuration (with no robot). It includes seven gamified sets of exercises, which are based on functional tasks from the everyday life of the patients. The platform gives the patients instructions, as well as feedback on their performance, and can track their performance over time. We performed a long-term patient-usability study, where 24 post-stroke patients were randomly allocated to exercise with this platform—either with the robot or the computer configuration—over a 5–7 week period, 3 times per week, for a total of 306 sessions.

Results

The participants in both groups reported that this rehabilitation platform addressed their arm rehabilitation needs, and they expressed their desire to continue training with it even after the study ended. We found a trend for higher acceptance of the system by the participants in the robot group on all parameters; however, this difference was not significant. We found that system failures did not affect the long-term trust that users felt towards the system.

Conclusions

We demonstrated the usability of using this platform for a long-term rehabilitation with post-stroke patients in a clinical setting. We found high levels of acceptance of both platform configurations by patients following this interaction, with higher ratings given to the SAR configuration. We show that it is not the mere use of technology that increases the motivation of the person to practice, but rather it is the appreciation of the technology’s effectiveness and its perceived contribution to the rehabilitation process. In addition, we provide a list of guidelines that can be used when designing and implementing other technological tools for rehabilitation.

Trial registration: This trial is registered in the NIH ClinicalTrials.gov database. Registration number NCT03651063, registration date 21.08.2018. https://clinicaltrials.gov/ct2/show/NCT03651063.

The influence of object size on second-order planning in an overturned cup task

For children, second-order planning in object manipulation, as demonstrated by the end-state comfort (ESC) effect, is constrained by numerous factors. As a step towards delineating the influence of object size, children (ages 6-10, n = 113) and adults (ages 18-25, n = 17) performed an overturned cup task with 8 cup sizes (4.7-8.4 cm diameter). Contrary to the hypothesis, cup size did not predict the overall proportion of trials with ESC. An increase in age and hand length did result in more ESC. Subsequent analyses with children, which focused on each cup size, revealed an increase in the ratio of hand size to cup size resulted in an increase in ESC with the 4.7, 5.2, 6.2, and 6.7 cm cups, age was a significant predictor with 4.7, 5.2, and 6.2 cm cups, and the interaction was significant for the 6.2 cm cup. No other significant results emerged. Together, findings offer preliminary support for the notion that object size does constrain children's motor planning skills to a certain degree (i.e., with large cups); however, further inquiry is warranted to elucidate the link between object size and hand size in children's performance of tasks requiring second-order planning.

Preferential Reaching and End-State Comfort: How Task Demands Influence Motor Planning

Various factors (e.g., hand preference, object properties) constrain reach-to-grasp in hemispace. With object use, end-state comfort (ESC) has been shown to supersede the preferential use of one hand at the midline. To assess how location, size, and orientation of objects (dowel, mallet, cup) influence preferred-hand use and ESC (N = 50; M_age = 20.83), three preferential reaching tasks were implemented. Object location influenced hand selection in all tasks, along with size (cups) and orientation (mallets). Object location and orientation influenced ESC, but only with dowels and mallets. When oriented away from the preferred hand in hemispace, there was a higher occurrence of non-preferred hand use to facilitate ESC. Overall, findings add to understanding of ESC and preferential reaching with varying task demands.

Age-group differences in beginning-state comfort reveal an increase in motor planning capabilities

Objects can be grasped in different ways to ensure a movement plan is aligned with the intended action. The current study assessed grasp posture in joint action object manipulation in children (ages 6–11, n = 68), young adults ( n = 21), and older adults ( n = 23). Participants performed two actions (pickup and pass; pickup and pass for use) within two movement contexts (using a dowel as if it were the actual object; actual object use), using two objects (glass and hammer) that differed in use-dependent experience. Beginning-state comfort (prioritizing a comfortable initial hand posture for an object recipient) was assessed. Taken together, findings support the notion that the ability to anticipate the intended action, and thus consider an action partner in one’s action plan, increases with age. With age and use-dependent experience, it can be argued that there is a shift from stimulus-driven, familiar responses, to considering affordances and task demands. Together, findings add to our understanding of changes in motor planning capabilities across the life span.

End-state comfort meets pre-crastination

Research on motor planning has revealed two seemingly contradictory phenomena. One is the end-state comfort effect, the tendency to grasp objects in physically awkward ways for the sake of comfortable or easy-to-control final postures (Rosenbaum et al., Attention and Performance XIII: Motor representation and control, Lawrence Erlbaum Associates, Hillsdale, New Jersey, 1990). The other is pre-crastination, the tendency to hasten the completion of tasks even at the expense of extra physical effort (Rosenbaum et al., Psychol Sci 25:1487-1496, 2014). End-state comfort seems to reflect emphasis on final states, whereas pre-crastination seems to reflect emphasis on initial states. How can both effects exist? We sought to resolve this seeming conflict by noting, first, that the effects have been tested in different contexts. End-state comfort has been tested with grasping, whereas pre-crastination has been tested with walking plus grasping. Second, both effects may reflect planning that aids aiming, as already demonstrated for end-state comfort but not yet tested for pre-crastination. We tested the two effects in a single walk-and-grasp task and found that demands on aiming influenced both effects, although precrastination was not fully influenced by changes in the demands of aiming. We conclude that end-state comfort and precrastination are both aiming-related, but that precrastination also reflects a desire to hasten early task completion.

Sex differences in the end-state comfort effect in pre-adolescent children

There has been recent interest in the developmental trajectory of the end-state comfort effect (ESCE) in young children. However, potential sex differences have yet to be examined in the overturned glass task. We examined the ESCE using this task in a large sample (N=232) of typically-developing elementary school children (111 girls, 121 boys) in grades 1-5 (approximately 7-11years old). We sought to determine whether there were similarities or differences in performance between boys and girls. Children picked up an overturned drinking glass from a table, turned the glass upright, and then poured water into it from a measuring cup. Three trials were performed, and the use of an initial awkward thumb-down grip to pick up the glass was taken as evidence for the ESCE. There were non-significant main effects for sex and grade, but a significant interaction between factors. Boys increased in sensitivity to end-state comfort across the five grades while girls showed a decrease from grades 1-3, followed by an increase between grades 3 and 5. Taken together, the results indicate the presence of adult-like motor planning for the overturned glass task by the 4th grade (i.e., age 10), but also suggest the presence of a motor reorganization in girls, at around the 2nd or 3rd grade (i.e., 8 or 9years of age).