Sensorimotor performance asymmetries predict hand selection

Visual-perceptual features of augmentative and alternative communication displays affect efficiency of motor reaching by individuals with Down syndrome: a pilot study

Individuals with Down syndrome often have speech and language impairments that interfere with their ability to use speech to meet their full range of communication needs. Visual communication supports in the form of augmentative and alternative communication (AAC) are often a solution for individuals who require support to their own natural speech, including those with Down syndrome. Messages are produced via touch or reach to communication symbols presented on these AAC displays. While a line of past research has detailed the influence of AAC display design on the efficiency with which individuals with and without disabilities can find target symbols within an array, few studies have examined how different AAC displays might influence touch/reaching. Yet critical clinical implications arise if display design is resulting in inefficient (and fatiguing) motor/reaching behavior. This pilot study evaluated how visual-perceptual characteristics of AAC displays affected the efficiency and quality of reaches by six individuals with Down syndrome and six individuals without disabilities matched on age, gender, and hand preference.

Beyond Arm Capacity in Chronic Stroke: Evaluating Paretic Arm Non-Use Through Arm Efficiency-A Cross-Sectional Study

BACKGROUND

After a stroke, the use of the paretic arm is determined by its capacity (what it can or cannot do). When both arms have capacity to perform a task, the choice of which arm to use must be based on another criterion, probably by comparing the efficiency of each arm. Two numerical models account for this: the capacity model (the paretic arm is chosen in preference) and the efficiency model (the most efficient arm is chosen).

OBJECTIVE

To numerically determine whether capacity or efficiency best predict the use of the paretic arm in activities of daily living.

METHODS

We performed numerical simulations to predict paretic arm use with either the capacity model or the efficiency model. We used the Bayesian Information Criterion (BIC) to compare the adequacy of the 2 models in predicting clinical and accelerometric data collected from 30 patients with chronic stroke.

RESULTS

The efficiency model predicted arm use in activities of daily living better than the capacity model (BIC = -66.95 vs -5.89; root mean square error = 0.26 vs 0.72).

CONCLUSIONS

The study highlights the importance of considering efficiency when assessing paretic arm non-use. Assessing individuals' arm efficiency should help personalize rehabilitation strategies after stroke.

Gravity support from a robotic exoskeleton increases spontaneous use of the nondominant upper extremity during a choice reaching task

The objective was to determine whether gravity support for the left arm of right-handed participants would increase left arm use during a three-dimensional (3-D) reaching task in virtual reality. Twelve healthy control participants each completed 630 reaching movements broken into six blocks. The majority of targets were placed close to the midsagittal plane at three heights, and participants were free to use either limb when reaching for targets. The hand had to stay in the target for a prescribed dwell time before the target disappeared. For all reaching tasks within a block, the left arm gravity support was set to either 0% or 75% of full arm support. The blocks also varied in the dwell time (2, 4, or 6 s). The order of blocks was balanced across participants in terms of gravity support level and dwell time. Electromyogram (EMG) level in the left medial deltoid decreased with increasing gravity support (P < 0.001) and was higher for higher targets compared to lower targets (P < 0.001). The odds of using the left arm were 1.95 times higher with gravity support compared to no support (P < 0.001). With gravity support, we expected greater shifts toward the left arm in tasks that were more energetically demanding. This was not the case, as the increased use was evenly distributed across all target heights, and use decreased or remained unchanged with increasing dwell time. Results are discussed relative to current models of limb choice and the potential use of robotic gravity support to overcome learned nonuse in stroke patients.NEW & NOTEWORTHY We have shown that gravity support from a robotic exoskeleton increases use of the left arm of right-handed healthy participants. Prior work has shown similar results when movements of one arm are amplified in a virtual environment. The advantage of this approach is the potential to apply the intervention during functional task practice outside of the VR environment or during performance of actual activities of daily living (ADL).

Profiling the different types of laterality in high-performance male and female Gaelic footballers

When performing sporting tasks, individuals may use a single side for all tasks (consistently unilateral), both sides equally on each task (consistent bilateral), different sides for different tasks (mixed laterality) or opposing sides when performing tasks with hands versus feet (crossed laterality). Previous research has largely focused on analysing laterality within a single skill. This study used notational analysis to investigate laterality profiles across four skills (two with the hands: hand pass and hop; and two with the feet: kick pass and solo) within high-performance Gaelic Football players. Fifty females and 83 males completed sufficient trials on all four skills to be included. While the majority of players were unilateral, some players displayed a different laterality profile. No player was consistently bilateral for all four skills. Chi-squared tests of independence revealed minimal differences between males and females in levels of partial bilaterality, crossed laterality or mixed laterality. Left-sided male and female players were significantly less lateralized than their right-sided counterparts for all assessed skills. Overall, findings show that laterality is complex, idiosyncratic and non-binary. Recognizing the idiosyncratic nature of limb dominance has numerous applications for coaches involved in player development, opposition analysis and sport scientists involved in talent development.

A task-dependent analysis of closed vs. open and fine vs. gross motor skills in handedness

The traditional classifications of motor skills nature (open vs closed; fine vs gross) have not been considered in handedness investigations. Instead, previous research focused on comparing complex vs less complex motor behaviour, leaving a gap in the literature. We compared manual preference between different motor skill characteristics, namely: fine and closed (FC), gross and closed (GC) and gross and open (GO) tasks. The hand preference was assessed with the Global Lateral Preference Inventory in four hundred and forty participants (244 women) aged from 18 to 59 years old. By assessing the degree and direction of handedness in different motor skills, our results showed a stronger lateralization pattern for FC motor skills as compared to GC and GO, with GO also being less lateralized than GC. Our results expand those of previous investigations that used the motor skill complexity definitions by showing how handedness can also be modulated by the interaction between classic motor skills classifications. Future research should consider fine vs. gross and open vs. closed classifications when selecting tasks for analysis of asymmetries of preference.

Healthy adults favor stable left/right hand choices over performance at an unconstrained reach-to-grasp task

Reach-to-grasp actions are fundamental to the daily activities of human life, but few methods exist to assess individuals' reaching and grasping actions in unconstrained environments. The Block Building Task (BBT) provides an opportunity to directly observe and quantify these actions, including left/right hand choices. Here we sought to investigate the motor and non-motor causes of left/right hand choices, and optimize the design of the BBT, by manipulating motor and non-motor difficulty in the BBT's unconstrained reach-to-grasp task. We hypothesized that greater motor and non-motor (e.g. cognitive/perceptual) difficulty would drive increased usage of the dominant hand. To test this hypothesis, we modulated block size (large vs. small) to influence motor difficulty, and model complexity (10 vs. 5 blocks per model) to influence non-motor difficulty, in healthy adults (n = 57). Our data revealed that increased motor and non-motor difficulty led to lower task performance (slower task speed), but participants only increased use of their dominant hand only under the most difficult combination of conditions: in other words, participants allowed their performance to degrade before changing hand choices, even though participants were instructed only to optimize performance. These results demonstrate that hand choices during reach-to grasp actions are more stable than motor performance in healthy right-handed adults, but tasks with multifaceted difficulties can drive individuals to rely more on their dominant hand.

Neural correlates of bilateral proprioception and adaptation with training

Bilateral proprioception includes the ability to sense the position and motion of one hand relative to the other, without looking. This sensory ability allows us to perform daily activities seamlessly, and its impairment is observed in various neurological disorders such as cerebral palsy and stroke. It can undergo experience-dependent plasticity, as seen in trained piano players. If its neural correlates were better understood, it would provide a useful assay and target for neurorehabilitation for people with impaired proprioception. We designed a non-invasive electroencephalography-based paradigm to assess the neural features relevant to proprioception, especially focusing on bilateral proprioception, i.e., assessing the limb distance from the body with the other limb. We compared it with a movement-only task, with and without the visibility of the target hand. Additionally, we explored proprioceptive accuracy during the tasks. We tested eleven Controls and nine Skilled musicians to assess whether sensorimotor event-related spectral perturbations in μ (8-12Hz) and low-β (12-18Hz) rhythms differ in people with musical instrument training, which intrinsically involves a bilateral proprioceptive component, or when new sensor modalities are added to the task. The Skilled group showed significantly reduced μ and low-β suppression in bilateral tasks compared to movement-only, a significative difference relative to Controls. This may be explained by reduced top-down control due to intensive training, despite this, proprioceptive errors were not smaller for this group. Target visibility significantly reduced proprioceptive error in Controls, while no change was observed in the Skilled group. During visual tasks, Controls exhibited significant μ and low-β power reversals, with significant differences relative to proprioceptive-only tasks compared to the Skilled group-possibly due to reduced uncertainty and top-down control. These results provide support for sensorimotor μ and low-β suppression as potential neuromarkers for assessing proprioceptive ability. The identification of these features is significant as they could be used to quantify altered proprioceptive neural processing in skill and movement disorders. This in turn can be useful as an assay for pre and post sensory-motor intervention research.

Roles of Handedness and Hemispheric Lateralization: Implications for Rehabilitation of the Central and Peripheral Nervous Systems: A Rapid Review

IMPORTANCE

Handedness and motor asymmetry are important features of occupational performance. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence.

OBJECTIVE

To review the basic neural mechanisms behind handedness and their implications for central and peripheral nervous system injury.

DATA SOURCES

Relevant published literature obtained via MEDLINE.

FINDINGS

Handedness, along with performance asymmetries observed between the dominant and nondominant hands, may be due to hemispheric specializations for motor control. These specializations contribute to predictable motor control deficits that are dependent on which hemisphere or limb has been affected. Clinical practice recommendations for occupational therapists and other rehabilitation specialists are presented.

CONCLUSIONS AND RELEVANCE

It is vital that occupational therapists and other rehabilitation specialists consider handedness and hemispheric lateralization during evaluation and treatment. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence. Plain-Language Summary: The goal of this narrative review is to increase clinicians' understanding of the basic neural mechanisms related to handedness (the tendency to select one hand over the other for specific tasks) and their implications for central and peripheral nervous system injury and rehabilitation. An enhanced understanding of these mechanisms may allow clinicians to better tailor neurorehabilitation interventions to address motor deficits and promote functional independence.

Bilateral Transfer of a Visuomotor Task in Different Workspace Configurations

Bilateral transfer occurs when a learned behavior transfers from one (group of) effectors(s) to another. Researchers investigating bilateral transfer of a visuomotor adaptation task between limbs used across workspaces have observed divergent results. This study assessed whether bilateral transfer of a visuomotor adaptation task changes with workspace configuration manipulation. Ninety-six right-handed young adults were assigned to one of three workspace locations, i.e., ipsilateral, contralateral, and central. Within each workspace were two retention groups (RRR/LLL) and two bilateral transfer groups (RLR/LRL). Performance before and after training was collected to determine direct and after-effects. We observed an asymmetric transfer of pathlength (left to right) but no ensuing after-effect. However, the transfer of movement time and normalized jerk was symmetric in the contralateral workspace. These findings showed differences in the pattern of bilateral transfer asymmetry in the different workspace configurations, which was parameter specific.

Healthy adults favor stable left/right hand choices over performance at an unconstrained reach-to-grasp task

Reach-to-grasp actions are fundamental to the daily activities of human life, but few methods exist to assess individuals' reaching and grasping actions in unconstrained environments. The Block Building Task (BBT) provides an opportunity to directly observe and quantify these actions, including left/right hand choices. Here we sought to investigate the motor and non-motor causes of left/right hand choices, and optimize the design of the BBT, by manipulating motor and non-motor difficulty in the BBT's unconstrained reach-to-grasp task We hypothesized that greater motor and non-motor (e.g. cognitive/perceptual) difficulty would drive increased usage of the dominant hand. To test this hypothesis, we modulated block size (large vs. small) to influence motor difficulty, and model complexity (10 vs. 5 blocks per model) to influence non-motor difficulty, in healthy adults (n=57). We hypothesized that healthy adults with high non-dominant hand performance in a precision drawing task should be more likely to use their non-dominant hand in the BBT. Our data revealed that increased motor and non-motor difficulty led to lower task performance (slower speed), but participants only increased use of their dominant hand only under the most difficult combination of conditions: in other words, participants allowed their performance to degrade before changing hand choices, even though participants were instructed only to optimize performance. These results demonstrate that hand choices during reach-to grasp actions are more stable than motor performance in healthy right-handed adults, but tasks with multifaceted difficulties can drive individuals to rely more on their dominant hand.

Statements and Declarations

Dr. Philip and Washington University in St. Louis have a licensing agreement with PlatformSTL to commercialize the iPad app used in this study.

Does the Degree and/or Direction of Handedness in Children With Developmental Coordination Disorder Influence Motor and Cognitive Performance? A Pilot Study

Research has shown that nonright-handedness in children with developmental coordination disorder (DCD) is associated with poorer motor and cognitive performance. This study investigated the influence of degree and direction of handedness on performance using the Home Handedness Questionnaire, the Hit-the-Dot test, the Movement Assessment Battery for Children, and the digital Trail-Making Test. Eighteen children with DCD and 21 typically developing children aged 8–12 years participated in this study. The distribution of degree and direction of handedness in the group of DCD children were not different from that found in the typically developing group. In the Hit-the-Dot test, typically developing children significantly performed better than children with DCD, no matter which hand was dominant or to which degree. A significant inconsistent-handed advantage in the subdomain balance was found for children with DCD. Inconsistent handedness also seems to be an advantage for children with DCD on the digital Trail-Making Test performance. The relationship between the subcategories of the Movement Assessment Battery for Children and the digital Trail-Making Test part B is stronger for consistent than for inconsistent handedness. Our findings suggest that children with DCD and inconsistent handedness might benefit from greater crosstalk across hemispheres. In addition, these predispositions can be reinforced or discouraged throughout development and via occupational therapy.

Relevant factors for arm choice in reaching movement: a scoping review

[Purpose] Arm choice is an unconscious action selection performed in daily life. Even if hemiparetic stroke patients can use their paretic arm, they compensate for their movements with their non-paretic arm, leading to decreased function of their paretic arm. Therefore, we need to encourage stroke patients to actively use their paretic arm. For this purpose, it is imperative to understand the process of selection of the left or right hand by patients. Here, we conducted a scoping review to summarize the findings of previous studies on factors and brain regions related to choice of arm. [Methods] We used PubMed/Medline, EBSCO, and the Cochrane Library to obtain research literature according to the PRISMA Extension for Scoping Reviews guidelines. [Results] Twenty-five of the 81 articles obtained from the search met the defined criteria. Cost, success, and dominance were investigated as relevant factors for arm choice. We also extracted articles examining the relationship between the posterior parietal and premotor cortex activity and arm choice. [Conclusion] From these results, we considered ways to facilitate the use of the paretic arm, such as the use of virtual reality systems or exoskeletal robots to modulate the reaching cost and success rates, or non-invasive brain stimulation methods to modulate brain activity.

Reaction time asymmetries provide insight into mechanisms underlying dominant and non-dominant hand selection

Handedness is often thought of as a hand "preference" for specific tasks or components of bimanual tasks. Nevertheless, hand selection decisions depend on many factors beyond hand dominance. While these decisions are likely influenced by which hand might show performance advantages for the particular task and conditions, there also appears to be a bias toward the dominant hand, regardless of performance advantage. This study examined the impact of hand selection decisions and workspace location on reaction time and movement quality. Twenty-six neurologically intact participants performed targeted reaching across the horizontal workspace in a 2D virtual reality environment, and we compared reaction time across two groups: those selecting which hand to use on a trial-by-trial basis (termed the choice group) and those performing the task with a preassigned hand (the no-choice group). Along with reaction time, we also compared reach performance for each group across two ipsilateral workspaces: medial and lateral. We observed a significant difference in reaction time between the hands in the choice group, regardless of workspace. In contrast, both hands showed shorter but similar reaction times and differences between the lateral and medial workspaces in the no-choice group. We conclude that the shorter reaction times of the dominant hand under choice conditions may be due to dominant hand bias in the selection process that is not dependent upon interlimb performance differences.

Assessing corticospinal excitability and reaching hand choice during whole-body motion

Behavioral studies have shown that humans account for inertial acceleration in their decisions of hand choice when reaching during body motion. Physiologically, it is unclear at what stage of movement preparation information about body motion is integrated in the process of hand selection. Here, we addressed this question by applying transcranial magnetic stimulation over left motor cortex (M1) of human participants who performed a preferential reach task while they were sinusoidally translated on a linear motion platform. If M1 only represents a read-out of the final hand choice, we expect the body motion not to affect the motor-evoked potential (MEP) amplitude. If body motion biases the hand selection process prior to target onset, we expect corticospinal excitability to be influenced by the phase of the motion, with larger MEP amplitudes for phases that show a bias to using the right hand. Behavioral results replicate our earlier findings of a sinusoidal modulation of hand choice bias with motion phase. MEP amplitudes also show a sinusoidal modulation with motion phase, suggesting that body motion influences corticospinal excitability which may ultimately reflect changes of hand preference. The modulation being present prior to target onset suggests that competition between hands is represented throughout the corticospinal tract. Its phase relationship with the motion profile indicates that other processes after target onset take up time until the hand selection process has been completely resolved, and the reach is initiated.

Early life experience sets hard limits on motor learning as evidenced from artificial arm use

The study of artificial arms provides a unique opportunity to address long-standing questions on sensorimotor plasticity and development. Learning to use an artificial arm arguably depends on fundamental building blocks of body representation and would therefore be impacted by early life experience. We tested artificial arm motor-control in two adult populations with upper-limb deficiencies: a congenital group—individuals who were born with a partial arm, and an acquired group—who lost their arm following amputation in adulthood. Brain plasticity research teaches us that the earlier we train to acquire new skills (or use a new technology) the better we benefit from this practice as adults. Instead, we found that although the congenital group started using an artificial arm as toddlers, they produced increased error noise and directional errors when reaching to visual targets, relative to the acquired group who performed similarly to controls. However, the earlier an individual with a congenital limb difference was fitted with an artificial arm, the better their motor control was. Since we found no group differences when reaching without visual feedback, we suggest that the ability to perform efficient visual-based corrective movements is highly dependent on either biological or artificial arm experience at a very young age. Subsequently, opportunities for sensorimotor plasticity become more limited.

Hand pose selection in a bimanual fine-manipulation task

Many daily tasks involve the collaboration of both hands. Humans dexterously adjust hand poses and modulate the forces exerted by fingers in response to task demands. Hand pose selection has been intensively studied in unimanual tasks, but little work has investigated bimanual tasks. This work examines hand poses selection in a bimanual high-precision-screwing task taken from watchmaking. Twenty right-handed subjects dismounted a screw on the watch face with a screwdriver in two conditions. Results showed that although subjects used similar hand poses across steps within the same experimental conditions, the hand poses differed significantly in the two conditions. In the free-base condition, subjects needed to stabilize the watch face on the table. The role distribution across hands was strongly influenced by hand dominance: the dominant hand manipulated the tool, whereas the nondominant hand controlled the additional degrees of freedom that might impair performance. In contrast, in the fixed-base condition, the watch face was stationary. Subjects used both hands even though single hand would have been sufficient. Importantly, hand poses decoupled the control of task-demanded force and torque across hands through virtual fingers that grouped multiple fingers into functional units. This preference for bimanual over unimanual control strategy could be an effort to reduce variability caused by mechanical couplings and to alleviate intrinsic sensorimotor processing burdens. To afford analysis of this variety of observations, a novel graphical matrix-based representation of the distribution of hand pose combinations was developed. Atypical hand poses that are not documented in extant hand taxonomies are also included.NEW & NOTEWORTHY We study hand poses selection in bimanual fine motor skills. To understand how roles and control variables are distributed across the hands and fingers, we compared two conditions when unscrewing a screw from a watch face. When the watch face needed positioning, role distribution was strongly influenced by hand dominance; when the watch face was stationary, a variety of hand pose combinations emerged. Control of independent task demands is distributed either across hands or across distinct groups of fingers.

When the non-dominant arm dominates: the effects of visual information and task experience on speed-accuracy advantages

Speed accuracy trade-off, the inverse relationship between movement speed and task accuracy, is a ubiquitous feature of skilled motor performance. Many previous studies have focused on the dominant arm, unimanual performance in both simple tasks, such as target reaching, and complex tasks, such as overarm throwing. However, while handedness is a prominent feature of human motor performance, the effect of limb dominance on speed-accuracy relationships is not well-understood. Based on previous research, we hypothesize that dominant arm skilled performance should depend on visual information and prior task experience, and that the non-dominant arm should show greater skill when no visual information nor prior task information is available. Forty right-handed young adults reached to 32 randomly presented targets across a virtual reality workspace with either the left or the right arm. Half of the participants received no visual feedback about hand position throughout each reach. Sensory information and task experience were lowest during the first cycle of exposure (32 reaches) in the no-vision condition, in which visual information about motion was not available. Under this condition, we found that the left arm group showed greater skill, measured in terms of position error normalized to speed, and by error variability. However, as task experience and sensory information increased, the right arm group showed substantial improvements in speed-accuracy relations, while the left arm group maintained, but did not improve, speed-accuracy relations throughout the task. These differences in performance between dominant and non-dominant arm groups during the separate stages of the task are consistent with complimentary models of lateralization, which propose different proficiencies of each hemisphere for different features of control. Our results are incompatible with global dominance models of handedness that propose dominant arm advantages under all performance conditions.

Transcranial direct current stimulation of the posterior parietal cortex biases human hand choice

Hand choices—deciding which hand to use to reach for targets—represent continuous, daily, unconscious decisions. The posterior parietal cortex (PPC) contralateral to the selected hand is activated during a hand-choice task, and disruption of left PPC activity with a single-pulse transcranial magnetic stimulation prior to the execution of the motion suppresses the choice to use the right hand but not vice versa. These findings imply the involvement of either bilateral or left PPC in hand choice. To determine whether the effects of PPC’s activity are essential and/or symmetrical in hand choice, we increased or decreased PPC excitability in 16 healthy participants using transcranial direct current stimulation (tDCS; 10 min, 2 mA, 5 × 7 cm) and examined its online and residual effects on hand-choice probability and reaction time. After the right PPC was stimulated with an anode and the left PPC with a cathode, the probability of left-hand choice significantly increased and reaction time significantly decreased. However, no significant changes were observed with the stimulation of the right PPC with a cathode and the left PPC with an anode. These findings, thus, reveal the asymmetry of PPC-mediated regulation in hand choice.

Perceived effort affects choice of limb and reaction time of movements

The decision regarding which arm to use to perform a task reflects a complex process that can be influenced by many factors, including effort requirements of acquiring the goal. In this study, we considered a virtual reality environment in which people reached to a visual target in three-dimensional space. To vary the cost of reaching, we altered the visual feedback associated with motion of one arm but not the other. This altered the extent of motion that was required to reach, thus changing the effort required to acquire the goal. We then measured how that change in effort affected the decision regarding which arm to use, as well as the preparation time for the movement that ensued. As expected, with increased visual amplification of one arm (reduced effort to reach the goal), subjects increased the probability of choosing that arm. Surprisingly, however, the reaction times to start these movements were also reduced: despite constancy of the visual representation of the target, reaction times were shorter for movements with less effort. Thus, as the perceived effort associated with accomplishing a goal was reduced for a given limb, the decision-making process was biased toward use of that limb. Furthermore, movements that were perceived to be less effortful were performed with shorter reaction times. These results suggest that visual amplification can alter the perceived effort associated with using a limb, thus increasing frequency of use. This may provide a useful method to increase use of a limb during rehabilitation.NEW & NOTEWORTHY We report that visual amplification may serve as an effective means to alter the perceived effort associated with use of a limb. This method may provide an effective tool with which use of the affected limb can be encouraged noninvasively after neurological injury.

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.

Are the Predictions of the Dynamic Dominance Model of Laterality Applicable to Children?

According to the dynamic dominance model, the left cerebral hemisphere is specialized for the control of intersegmental dynamics and the right hemisphere for impedance control. Our aim was to test predictions from the dynamic dominance model in children by comparing performance between the right (preferred) and left hands in aiming. Three groups were compared: 4-7, 8-11, and 18-38 years old. Results showed higher movement linearity in the performance with the right hand in all age groups (P < .01), while initial directional error and endpoint accuracy were equivalent between hands. These results provided partial support for the dynamic dominance model.

The probability of choosing both hands depends on an interaction between motor capacity and limb-specific control in chronic stroke

A goal of rehabilitation after stroke is to promote pre-stroke levels of arm use for every day, frequently bimanual, functional activities. We reasoned that, after a stroke, the choice to use one or both hands for bimanual tasks might depend not only on residual motor capacity, but also the specialized demands imposed by the task on the paretic hand. To capture spontaneous, task-specific choices, we covertly observed 50 pre-stroke right-handed chronic stroke survivors (25 each of left, LHD, and right-hemisphere damage, RHD) and 11 age-similar control adults and recorded their hand use strategies for two pairs of bimanual tasks with distinct demands: one with greater precision requirements (photo-album tasks), and another with greater stabilization requirements (letter-envelope tasks). The primary outcome was the choice to use one or both hands. Logistic regression was used to test the two hypotheses that the probability of choosing a bimanual strategy would be greater in those with less severe motor impairment and also in those with LHD. When collapsed across the four tasks, we found support for these hypotheses. Notably, however, the influence of these factors on bimanual choice varied based on task demands. For the photo-album pair, the probability of a bimanual strategy was greater for those with LHD compared to RHD, regardless of the degree of motor impairment. For the letter-envelope pair, we found a significant interaction between impairment and side of lesion in determining the likelihood of choosing both hands. Therefore, the manner in which side of lesion moderates the effect of impairment on hand use depends on the task.

Interlimb differences in coordination of rapid wrist/forearm movements

We have previously proposed a model of motor lateralization that attributes specialization for predictive control of intersegmental coordination to the dominant hemisphere/limb system, and control of limb impedance to the non-dominant system. This hypothesis was developed based on visually targeted discrete reaching movement made predominantly with the shoulder and elbow joints. The purpose of this experiment was to determine whether dominant arm advantages for multi-degree of freedom coordination also occur during continuous distal movements of the wrist that do not involve visual guidance. In other words, are the advantages of the dominant arm restricted to controlling intersegmental coordination during discrete visually targeted reaching movements, or are they more generally related to coordination of multiple degrees of freedom at other joints, regardless of whether the movements are discrete or invoke visual guidance? Eight right-handed participants were instructed to perform alternating wrist ulnar/radial deviation movements at two instructed speeds, slow and fast, with the dominant or the non-dominant arm, and were instructed not to rotate the forearm (pronation/supination) or move the wrist up and down (flexion/extension). This was explained by slowly and passively moving the wrist in each plane during the instructions. Because all the muscles that cross the wrist have moment arms with respect to more than one axis of rotation, intermuscular coordination is required to prevent motion about non-instructed axes of rotation. We included two conditions, a very slow condition, as a control condition, to demonstrate understanding of the task, and an as-fast-as-possible condition to challenge predictive aspect of control, which we hypothesize are specialized to the dominant controller. Our results indicated that during as-fast-as-possible conditions the non-dominant arm incorporated significantly more non-instructed motion, which resulted in greater circumduction at the non-dominant than the dominant wrist. These findings extend the dynamic dominance hypothesis, indicating that the dominant hemisphere-arm system is specialized for predictive control of multiple degrees of freedom, even in movements of the distal arm and made in the absence of visual guidance.

Effects of arm weight and target height on hand selection: A low-cost virtual reality paradigm

We evaluated the ability of a virtual reality (VR) system to reliably detect the reaching frequency midline position of a user; the distinguishing plane between free-choice use of the left and right hand. The paradigm utilized the Leap Motion Hand Tracker along with a custom script written in C# and was realized through a Unity3D application. Stimuli appeared in random locations on the computer screen and required the participant to reach with the hand of their choice to contact them with a virtually coupled hand inside the virtual space. We investigated the effects of two manipulations of effort on the free-choice reaching of either the left or right hand. We varied the height of target positions and applied an additional weight to the non-dominant, left hand. We observed main effects of height and weight on reaching frequency midline positions across the group. We found increased use of the dominant hand as stimuli height increased, as well as a significant increase in overall use of the dominant, right hand when a weighted-glove was worn by the non-dominant, left hand. Our results are in line with previously published research on hand selection from similar paradigms, supporting the use of our VR paradigm in future experiments and applications.

Transformation of vestibular signals for the decisions of hand choice during whole body motion

In daily life, we frequently reach toward objects while our body is in motion. We have recently shown that body accelerations influence the decision of which hand to use for the reach, possibly by modulating the body-centered computations of the expected reach costs. However, head orientation relative to the body was not manipulated, and hence it remains unclear whether vestibular signals contribute in their head-based sensory frame or in a transformed body-centered reference frame to these cost calculations. To test this, subjects performed a preferential reaching task to targets at various directions while they were sinusoidally translated along the lateral body axis, with their head either aligned with the body (straight ahead) or rotated 18° to the left. As a measure of hand preference, we determined the target direction that resulted in equiprobable right/left-hand choices. Results show that head orientation affects this balanced target angle when the body is stationary but does not further modulate hand preference when the body is in motion. Furthermore, reaction and movement times were larger for reaches to the balanced target angle, resembling a competitive selection process, and were modulated by head orientation when the body was stationary. During body translation, reaction and movement times depended on the phase of the motion, but this phase-dependent modulation had no interaction with head orientation. We conclude that the brain transforms vestibular signals to body-centered coordinates at the early stage of reach planning, when the decision of hand choice is computed. NEW & NOTEWORTHY The brain takes inertial acceleration into account in computing the anticipated biomechanical costs that guide hand selection during whole body motion. Whereas these costs are defined in a body-centered, muscle-based reference frame, the otoliths detect the inertial acceleration in head-centered coordinates. By systematically manipulating head position relative to the body, we show that the brain transforms otolith signals into body-centered coordinates at an early stage of reach planning, i.e., before the decision of hand choice is computed.

Increased Perceptual and Motor Performance of the Arms of Elite Water Polo Players

Background

It has been stated that long-term participation in sport training can influence the motor asymmetry of the arms with a decreased interlimb difference. However, whether this pattern is observable in different sports and with different variables, like perceptual performance, still needs to be tested. Therefore, we investigated if long-term sports participation might modify the motor and perceptual performance asymmetries of arms in water polo players. It was hypothesized that water polo players would perform with less interlimb asymmetry in comparison to nonathletes.

Methods

Right-handed water polo players and nonathletes were tested on motor performance for both arms during a reaching task. Thirteen water polo players and thirteen nonathletes performed reaching movements under two experimental conditions: (a) right arm and (b) left arm. Velocity, accuracy, hand path deviation from linearity, and reaction time were calculated for each trial and for both arms. The potential interlimb differences in movement performance could be assessed by testing.

Results

Consistent with the hypothesis, our findings showed that water polo players displayed substantially less asymmetry in the performance of accuracy and reaction time.

Conclusions

These findings suggest that performance asymmetries of arms can be altered via intense long-term practice.

Effects of Fencing Training on Motor Performance and Asymmetry Vary With Handedness

Previous studies showed that motor asymmetries are reduced in left-handers and after a long-term fencing training in right-handers. Interestingly, left-handed athletes are substantially over-represented in elite fencing. These findings have been speculatively explained by imbalance in experience of fighting opposite handedness opponents resulted from skewed distribution of handedness, i.e. lefties encounter more righties than righties encounter lefties. Whereas these assumptions could be accurate, the underlying mechanisms remain ambiguous. In this study, we investigated effects of fencing training on motor performance and asymmetry with respect to handedness. We compared fencing performance of left- and right-handed fencers in both training and combat conditions. In the combat condition, left-handers won seven out of twelve matches consisted of twelve bouts each. They also showed a significantly longer hit detection time, a measure indicating better quality of fencing attack. In the training condition, left-handed fencers completed fencing board tests significantly faster than right-handers. These findings provide additional factor of superior motor performance to be considered when interpreting over-representation of lefties in elite fencing. Furthermore, our left-handers were less lateralized, which could explain that superior motor performance. This idea is consistent with previous findings of reduced asymmetry in right-handed fencers when comparing to non-athletes.

Motor Lateralization May Be Influenced by Long-Term Piano Playing Practice

Motor lateralization is viewed as anatomical or functional asymmetry of the two sides of the body. Functional motor asymmetry can be influenced by musical practice. This study explored whether piano playing experience modulates motor asymmetry and leads to an altered pattern of hand selection, reflecting an altered handedness. We asked two groups of right-handed participants-piano players and non-piano players-to reach targets in their frontal space with both arms, and we tested the motor performance of each arm on this task and then on an arm preference test. As musical practice can decrease motor asymmetry between arms, we hypothesized that participants with piano playing experience would display less interlimb asymmetry and that this, in turn, would change their arm preference pattern, compared with participants without piano playing experience. We found support for both hypotheses, and we conclude that arm selection (preference) is not biologically fixed, but, rather, can be modulated through long-term piano playing.

Cognitive-perceptual load modulates hand selection in left-handers to a greater extent than in right-handers

Previous studies have proposed that selecting which hand to use for a reaching task appears to be modulated by a factor described as "task difficulty," defined by either the requirement for spatial precision or movement sequences. However, we previously reported that analysis of the movement costs associated with even simple movements plays a major role in hand selection. We further demonstrated, in right-handers, that cognitive-perceptual loading modulates hand selection by interfering with the analysis of such costs. It has been reported that left-handers tend to show less dominant hand bias in selecting which hand to use during reaching. We, therefore, hypothesized that hand selection would be less affected by cognitive-perceptual loading in left-handers than in right-handers. We employed a visual search task that presented different levels of difficulty (cognitive-perceptual load), as established in previous studies. Our findings indicate that left-handed participants tend to show greater modulation of hand selection by cognitive-perceptual loading than right-handers. Left-handers showed lower dominant hand reaction times than right-handers, and greater high-cost movements that reached to extremes of the contralateral workspace under the most difficult task conditions. We previously showed in this task that midline crossing has high-energy and time costs and that they occur more frequently under cognitively demanding conditions. The current study revealed that midline crossing was associated with the lowest reaction times, in both handedness groups. The fact that left-handers showed lower dominant hand reaction times, and a greater number of high-cost cross-midline reaches under the most cognitively demanding conditions suggests that these actions were erroneous.

Is Hand Selection Modulated by Cognitive-perceptual Load?

Previous studies proposed that selecting which hand to use for a reaching task appears to be modulated by a factor described as "task difficulty". However, what features of a task might contribute to greater or lesser "difficulty" in the context of hand selection decisions has yet to be determined. There has been evidence that biomechanical and kinematic factors such as movement smoothness and work can predict patterns of selection across the workspace, suggesting a role of predictive cost analysis in hand-selection. We hypothesize that this type of prediction for hand-selection should recruit substantial cognitive resources and thus should be influenced by cognitive-perceptual loading. We test this hypothesis by assessing the role of cognitive-perceptual loading on hand selection decisions, using a visual search task that presents different levels of difficulty (cognitive-perceptual load), as established in previous studies on overall response time and efficiency of visual search. Although the data are necessarily preliminary due to small sample size, our data suggested an influence of cognitive-perceptual load on hand selection, such that the dominant hand was selected more frequently as cognitive load increased. Interestingly, cognitive-perceptual loading also increased cross-midline reaches with both hands. Because crossing midline is more costly in terms of kinematic and kinetic factors, our findings suggest that cognitive processes are normally engaged to avoid costly actions, and that the choice not-to-cross midline requires cognitive resources.

Handedness and Reach-to-Place Kinematics in Adults: Left-Handers Are Not Reversed Right-Handers

The primary goal of this study was to examine the relations between limb control and handedness in adults. Participants were categorized as left or right handed for analyses using the Edinburgh Handedness Inventory. Three-dimensional recordings were made of each arm on two reach-to-place tasks: adults reached to a ball and placed it into the opening of a toy (fitting task), or reached to a Cheerio inside a cup, which they placed on a designated mark after each trial (cup task). We hypothesized that limb control and handedness were related, and we predicted that we would observe side differences favoring the dominant limb based on the dynamic dominance hypothesis of motor lateralization. Specifically, we predicted that the dominant limb would be straighter and smoother on both tasks compared with the nondominant limb (i.e., right arm in right-handers and left arm in left-handers). Our results only partially supported these predictions for right-handers, but not for left-handers. When differences between hands were observed, the right hand was favored regardless of handedness group. Our findings suggest that left-handers are not reversed right-handers when compared on interlimb kinematics for reach-to-place tasks, and reaffirm that task selection is critical when evaluating manual asymmetries.

Modulating Children’s Manual Preference Through Spontaneous Nondominant Hand Use

We evaluated the effect of repeated use of the nonpreferred hand on young children’s manual preference by positioning toys in the left hemifield in egocentric coordinates to induce right-handed 4–5-year-olds to use their left hands spontaneously. We induced motor activities in the laterally biased workspace by presenting tasks in a ludic context over different days, similar to their daily kindergarten experience. Preceding and following these lateralized experiences, the children were tested on a task requiring reaching, grasping, and inserting cards into a slot. In the 1-day retention assessment, we found that repeated use of the nonpreferred left hand in the previous phase led to increased use of the left hand to perform the probing task. Following 14 days of rest, the children with induced left-hand experiences used exclusively their left hands to manipulate the leftmost card positions. We propose that repeated use of the nonpreferred left hand leads to increased confidence to plan left-handed movements for subsequent tasks.

Interlimb differences in coordination of unsupported reaching movements

Previous research suggests that interlimb differences in coordination associated with handedness might result from specialized control mechanisms that are subserved by different cerebral hemispheres. Based largely on the results of horizontal plane reaching studies, we have proposed that the hemisphere contralateral to the dominant arm is specialized for predictive control of limb dynamics, while the non-dominant hemisphere is specialized for controlling limb impedance. The current study explores interlimb differences in control of 3-D unsupported reaching movements. While the task was presented in the horizontal plane, participant's arms were unsupported and free to move within a range of the vertical axis, which was redundant to the task plane. Results indicated significant dominant arm advantages for both initial direction accuracy and final position accuracy. The dominant arm showed greater excursion along a redundant axis that was perpendicular to the task, and parallel to gravitational forces. In contrast, the non-dominant arm better impeded motion out of the task-plane. Nevertheless, non-dominant arm task errors varied substantially more with shoulder rotation excursion than did dominant arm task errors. These findings suggest that the dominant arm controller was able to take advantage of the redundant degrees of freedom of the task, while non-dominant task errors appeared enslaved to motion along the redundant axis. These findings are consistent with a dominant controller that is specialized for intersegmental coordination, and a non-dominant controller that is specialized for impedance control. However, the findings are inconsistent with previously documented conclusions from planar tasks, in which non-dominant control leads to greater final position accuracy.

Decisions in motion: passive body acceleration modulates hand choice

In everyday life, we frequently have to decide which hand to use for a certain action. It has been suggested that for this decision the brain calculates expected costs based on action values, such as expected biomechanical costs, expected success rate, handedness, and skillfulness. Although these conclusions were based on experiments in stationary subjects, we often act while the body is in motion. We investigated how hand choice is affected by passive body motion, which directly affects the biomechanical costs of the arm movement due to its inertia. With the use of a linear motion platform, 12 right-handed subjects were sinusoidally translated (0.625 and 0.5 Hz). At 8 possible motion phases, they had to reach, using either their left or right hand, to a target presented at 1 of 11 possible locations. We predicted hand choice by calculating the expected biomechanical costs under different assumptions about the future acceleration involved in these computations, being the forthcoming acceleration during the reach, the instantaneous acceleration at target onset, or zero acceleration as if the body were stationary. Although hand choice was generally biased to use of the dominant hand, it also modulated sinusoidally with the motion, with the amplitude of the bias depending on the motion's peak acceleration. The phase of hand choice modulation was consistent with the cost model that took the instantaneous acceleration signal at target onset. This suggests that the brain relies on the bottom-up acceleration signals, and not on predictions about future accelerations, when deciding on hand choice during passive whole body motion.NEW & NOTEWORTHY Decisions of hand choice are a fundamental aspect of human behavior. Whereas these decisions are typically studied in stationary subjects, this study examines hand choice while subjects are in motion. We show that accelerations of the body, which differentially modulate the biomechanical costs of left and right hand movements, are also taken into account when deciding which hand to use for a reach, possibly based on bottom-up processing of the otolith signal.

Assessing the role of preknowledge in force compensation during a tracking task

Considerable research has been done looking at the asymmetries between the dominant and nondominant arms. However, one area that has received less attention is how information about a perturbation affects these upper limb asymmetries. Our study sought to determine whether foreknowledge of a perturbation can affect the compensation from each arm. In addition, we examined the differences in compensation for perturbations parallel with the line of action and perpendicular to it. Results showed that the nondominant arm was largely unaffected by the visual condition. The dominant arm showed a comparatively smaller improvement between visible and invisible forces.

Handedness and index finger movements performed on a small touchscreen

Many studies of right/left differences in motor performance related to handedness have employed tasks that use arm movements or combined arm and hand movements rather than movements of the fingers per se, the well-known exception being rhythmic finger tapping. We therefore explored four simple tasks performed on a small touchscreen with relatively isolated movements of the index finger. Each task revealed a different right/left performance asymmetry. In a step-tracking Target Task, left-handed subjects showed greater accuracy with the index finger of the dominant left hand than with the nondominant right hand. In a Center-Out Task, right-handed subjects produced trajectories with the nondominant left hand that had greater curvature than those produced with the dominant right hand. In a continuous Circle Tracking Task, slips of the nondominant left index finger showed higher jerk than slips of the dominant right index finger. And in a continuous Complex Tracking Task, the nondominant left index finger showed shorter time lags in tracking the relatively unpredictable target than the dominant right index finger. Our findings are broadly consistent with previous studies indicating left hemisphere specialization for dynamic control and predictable situations vs. right hemisphere specialization for impedance control and unpredictable situations, the specialized contributions of the two hemispheres being combined to different degrees in the right vs. left hands of right-handed vs. left-handed individuals.

The visual amplification of goal-oriented movements counteracts acquired non-use in hemiparetic stroke patients

BACKGROUND

Stroke-induced impairments result from both primary and secondary causes, i.e. damage to the brain and the acquired non-use of the impaired limbs. Indeed, stroke patients often under-utilize their paretic limb despite sufficient residual motor function. We hypothesize that acquired non-use can be overcome by reinforcement-based training strategies.

METHODS

Hemiparetic stroke patients (n = 20, 11 males, 9 right-sided hemiparesis) were asked to reach targets appearing in either the real world or in a virtual environment. Sessions were divided into 3 phases: baseline, intervention and washout. During the intervention the movement of the virtual representation of the patients' paretic limb was amplified towards the target.

RESULTS

We found that the probability of using the paretic limb during washout was significantly higher in comparison to baseline. Patients showed generalization of these results by displaying a more substantial workspace in real world task. These gains correlated with changes in effector selection patterns.

CONCLUSIONS

The amplification of the movement of the paretic limb in a virtual environment promotes the use of the paretic limb in stroke patients. Our findings indicate that reinforcement-based therapies may be an effective approach for counteracting learned non-use and may modulate motor performance in the real world.

Effort, success, and nonuse determine arm choice

How do humans choose one arm or the other to reach single targets in front of the body? Current theories of reward-driven decisionmaking predict that choice results from a comparison of "action values," which are the expected rewards for possible actions in a given state. In addition, current theories of motor control predict that in planning arm movements, humans minimize an expected motor cost that balances motor effort and endpoint accuracy. Here, we test the hypotheses that arm choice is determined by comparison of action values comprising expected effort and expected task success for each arm, as well as a handedness bias. Right-handed subjects, in either a large or small target condition, were first instructed to use each hand in turn to shoot through an array of targets and then to choose either hand to shoot through the same targets. Effort was estimated via inverse kinematics and dynamics. A mixed-effects logistic-regression analysis showed that, as predicted, both expected effort and expected success predicted choice, as did arm use in the preceding trial. Finally, individual parameter estimation showed that the handedness bias correlated with mean difference between right- and left-arm success, leading to overall lower use of the left arm. We discuss our results in light of arm nonuse in individuals' poststroke.

Proprioceptive bimanual test in intrinsic and extrinsic coordinates

Is there any difference between matching the position of the hands by asking the subjects to move them to the same spatial location or to mirror-symmetric locations with respect to the body midline? If the motion of the hands were planned in the extrinsic space, the mirror-symmetric task would imply an additional challenge, because we would need to flip the coordinates of the target on the other side of the workspace. Conversely, if the planning were done in intrinsic coordinates, in order to move both hands to the same spot in the workspace, we should compute different joint angles for each arm. Even if both representations were available to the subjects, the two tasks might lead to different results, providing some cue on the organization of the "body schema". In order to answer such questions, the middle fingertip of the non-dominant hand of a population of healthy subjects was passively moved by a manipulandum to 20 different target locations. Subjects matched these positions with the middle fingertip of their dominant hand. For most subjects, the matching accuracy was higher in the extrinsic modality both in terms of systematic error and variability, even for the target locations in which the configuration of the arms was the same for both modalities. This suggests that the matching performance of the subjects could be determined not only by proprioceptive information but also by the cognitive representation of the task: expressing the goal as reaching for the physical location of the hand in space is apparently more effective than requiring to match the proprioceptive representation of joint angles.

Modulation of manual preference induced by lateralized practice diffuses over distinct motor tasks: age-related effects

In this study we investigated the effect of use of the non-preferred left hand to practice different motor tasks on manual preference in children and adults. Manual preference was evaluated before, immediately after and 20 days following practice. Evaluation was made with tasks of distinct levels of complexity requiring reaching and manipulation of cards at different eccentricities in the workspace. Results showed that left hand use in adults induced increased preference of that hand at the central position when performing the simple task, while left hand use by the children induced increased preference of the left hand at the rightmost positions in the performance of the complex task. These effects were retained over the rest period following practice. Kinematic analysis showed that left hand use during practice did not lead to modification of intermanual performance asymmetry. These results indicate that modulation of manual preference was a consequence of higher frequency of use of the left hand during practice rather than of change in motor performance. Findings presented here support the conceptualization that confidence on successful performance when using a particular limb generates a bias in hand selection, which diffuses over distinct motor tasks.

Motor asymmetry in elite fencers

The authors previously reported that asymmetrical patterns of hand preference are updated and modified by present sensorimotor conditions. They examined whether participation in long-term training in the upper extremity sport fencing might modify arm selection and performance asymmetries. Eight fencers and eight nonfencers performed reaching movements under 3 experimental conditions: (a) nonchoice right, (b) nonchoice left, and (c) choice, either right or left arm as selected by subject. The nonchoice conditions allowed assessment of potential interlimb differences in movement performance, while the choice condition allowed assessment of the frequency and pattern of arm selection across subject groups. Our findings showed that the athlete group showed substantially greater symmetry in the performance and selection measures. These findings suggest that arm selection and performance asymmetries can be altered by intense long-term practice.

Convergent models of handedness and brain lateralization

The pervasive nature of handedness across human history and cultures is a salient consequence of brain lateralization. This paper presents evidence that provides a structure for understanding the motor control processes that give rise to handedness. According to the Dynamic Dominance Model, the left hemisphere (in right handers) is proficient for processes that predict the effects of body and environmental dynamics, while the right hemisphere is proficient at impedance control processes that can minimize potential errors when faced with unexpected mechanical conditions, and can achieve accurate steady-state positions. This model can be viewed as a motor component for the paradigm of brain lateralization that has been proposed by Rogers et al. (MacNeilage et al., 2009) that is based upon evidence from a wide range of behaviors across many vertebrate species. Rogers proposed a left-hemisphere specialization for well-established patterns of behavior performed in familiar environmental conditions, and a right hemisphere specialization for responding to unforeseen environmental events. The dynamic dominance hypothesis provides a framework for understanding the biology of motor lateralization that is consistent with Roger's paradigm of brain lateralization.

Handedness can be explained by a serial hybrid control scheme

Our previous studies on healthy individuals and stroke patients led us to propose that the dominant and nondominant arms are specialized for distinct motor control processes. We hypothesize that the dominant arm is specialized for predictive control of limb dynamics, and the nondominant arm is specialized for impedance control. We previously introduced a hybrid control scheme to explain lateralization of single-joint elbow movements. In this paper we apply a similar computational framework to explore interlimb differences in multi-joint reaching movements: the movements of both arms are initiated using predictive control mechanisms, and terminated using impedance mechanisms. Four parameters characterize predictive mechanisms, four parameters characterize impedance mechanisms, and the ninth parameter describes the instant of switch between the two modes of control. Based on our hypothesis of motor lateralization, we predict an early switch to impedance control for the nondominant arm, but a late switch, near the end of motion, for the dominant arm. We fit our model to multi-joint reaching movements of each arm, made in the horizontal plane. Our results reveal that the more curved trajectories of the nondominant arm are characterized by an early switch to impedance mechanisms, in the initial phase of motion near peak velocity. In contrast, the trajectories of the dominant arm were best fit, when the switch to impedance mechanisms occurred late in the deceleration phase of motion. These results support a model of motor lateralization in which the dominant controller is specialized for predictive control of task dynamics, while the nondominant arm is specialized for impedance control mechanisms. For the first time, we are able to operationally define handedness expressed during multi-joint movements by applying a computational control model.

From specific training to global shift of manual preference in Kung Fu experts

Manual preference and intermanual performance asymmetry have been approached from a multidimensional and dynamic perspective. A point of interest from that approach is the role of lateralized motor experiences on handedness. In this study, intermanual performance asymmetry in sport-specific movements and manual preference in daily living tasks were compared between Kung Fu athletes and novices. Analysis of movement time in the performance of interlaterally symmetric and asymmetric movement patterns showed smaller intermanual performance asymmetry in experts. Analysis of manual preference using the Edinburgh Handedness Inventory indicated that experts presented predominantly weak or moderate strength of right hand preference. Novices, conversely, were found to have predominantly strong right hand preference. These results suggest that extensive bimanual training by experts leads to a global shift of manual preference, affecting hand selection in distinct tasks.

Limb dominance results from asymmetries in predictive and impedance control mechanisms

Handedness is a pronounced feature of human motor behavior, yet the underlying neural mechanisms remain unclear. We hypothesize that motor lateralization results from asymmetries in predictive control of task dynamics and in control of limb impedance. To test this hypothesis, we present an experiment with two different force field environments, a field with a predictable magnitude that varies with the square of velocity, and a field with a less predictable magnitude that varies linearly with velocity. These fields were designed to be compatible with controllers that are specialized in predicting limb and task dynamics, and modulating position and velocity dependent impedance, respectively. Because the velocity square field does not change the form of the equations of motion for the reaching arm, we reasoned that a forward dynamic-type controller should perform well in this field, while control of linear damping and stiffness terms should be less effective. In contrast, the unpredictable linear field should be most compatible with impedance control, but incompatible with predictive dynamics control. We measured steady state final position accuracy and 3 trajectory features during exposure to these fields: Mean squared jerk, Straightness, and Movement time. Our results confirmed that each arm made straighter, smoother, and quicker movements in its compatible field. Both arms showed similar final position accuracies, which were achieved using more extensive corrective sub-movements when either arm performed in its incompatible field. Finally, each arm showed limited adaptation to its incompatible field. Analysis of the dependence of trajectory errors on field magnitude suggested that dominant arm adaptation occurred by prediction of the mean field, thus exploiting predictive mechanisms for adaptation to the unpredictable field. Overall, our results support the hypothesis that motor lateralization reflects asymmetries in specific motor control mechanisms associated with predictive control of limb and task dynamics, and modulation of limb impedance.

Contralesional Arm Preference Depends on Hemisphere of Damage and Target Location in Unilateral Stroke Patients

Background Previous research has shown that during simulated activities of daily living, right-handed stroke patients use their contralesional arm more after left- than right-hemisphere stroke. These findings were attributed to a hand preference effect. However, these decisions about when to use the contralesional arm may be modulated by where in the work space the task is performed, a factor that could be used in physical rehabilitation to influence recovery by decreasing learned nonuse. Objective To examine how target location and side of stroke influences arm selection choices for simple reaching movements. Methods A total of 14 right-handed stroke patients (7 with left-hemisphere and 7 with right-hemisphere damage [RHD]), with similar degrees of hemiparesis (Fugl-Meyer motor score), and 16 right-handed controls participated in this experiment. In a pseudorandom fashion, 32 targets were presented throughout the reachable horizontal plane work space, and the participants were asked to select 1 hand to reach the target on each trial. Results The group with left-hemisphere damage chose their contralesional arm significantly more often than the group with RHD. Patients with RHD also chose their left (contralesional) arm significantly less often than the control group. However, these patterns of choice were most pronounced in the center of the workspace. Conclusion Both the side of hemisphere damage and work space location played a significant role in the choice of whether to use the contralesional arm for reaching. These findings have implications for structuring rehabilitation for unilateral stroke patients.

The shoulder and elbow joints and right and left sides demonstrate similar joint position sense

Proper orientation of the shoulder and elbow is necessary for accurate and precise positioning of the hand. The authors' goal was to compare these joints with an active joint position sense task, while also taking into account the effects of joint flexion angle and arm dominance. Fifteen healthy subjects were asked to replicate presented joint angles with a single degree of freedom active positioning protocol. There were no significant differences in angular joint position sense errors with respect to joint (shoulder vs. elbow) and side (left vs. right). However, when considering linear positioning, errors were lower for the elbow, due to a shorter lever arm. Also, as flexion angles increased toward 90°, there was a consistent pattern of lower errors for both joints.