Task difficulty is an important factor in the acquisition of a novel motor skill. When presented with challenging tasks, participants may control task difficulty by deviating from mandated instructions to allow success within a self-selected bandwidth. To investigate the levels of task difficulty at which such deviations may occur, the current study used an on-screen target interception task which gradually increased in difficulty by lowering the size of the intercepting racquet. Measures of intrinsic motivation and cognitive effort were collected to examine the underlying psychological factors. Increases in difficulty provoked a tactical approach from participants where they did not attempt to intercept all targets as instructed. This behaviour was not disclosed when participants were given the opportunity to do so; potential reasons for this are discussed. Increases in task difficulty saw a lowering of intrinsic motivation, but a concurrent rise in cognitive effort, suggesting that task engagement was high despite lowering intrinsic motivation. The results demonstrate that expected experimental results are not necessarily arrived at by the expected means, and that methods of measurement and analysis should account for actual participant behaviour rather than that which is instructed, presumed, or predicted by whichever model or theory is under scrutiny.
This cross-sectional study aimed to investigate relationship between postural control and cervical joint position sense error (CJPSE) in children with spastic diplegic cerebral palsy (CP). Thirty-eight children with spastic diplegic CP (Gross Motor Function Classification System levels I-III), aged 5-12 years (mean age 7.94 ± 2.87), participated in study. CJPSE was evaluated using Cervical Range of Motion (CROM) device in flexion, extension, right/left rotation, and right/left lateral flexion directions. Postural control was assessed with Trunk Control Measurement Scale (TCMS), and gross motor function was measured by Gross Motor Function Measure-66 (GMFM-66). Correlations between variables were analyzed using Spearman's rank correlation test. Cervical joint position error was negatively correlated with postural control for flexion (r= -0.533, p = 0.001), extension (r= -0.413, p = 0.011), left rotation (r= -0.702, p < 0.001), and lateral flexion (r= -0.660/-0.736, p < 0.001), while right rotation showed small positive correlation (r = 0.350, p = 0.034). Strongest relationships appeared in dynamic sitting subscale of TCMS. Gross motor function was inversely associated with CJPSE error in flexion, left rotation, and lateral flexion movements, particularly in GMFM-C and GMFM-E dimensions. Impaired CJPSE is closely linked to lower postural control and gross motor performance in children with spastic diplegic CP. Incorporating CJPSE evaluation into rehabilitation may enhance functional outcomes.
Many motor skills in daily activities require hand-eye coordination, the performance of which can be measured by using speed or accuracy. Juggling provides a useful model for studying changes in speed and accuracy during skill acquisition. Seventy-four participants practiced 3-ball cascade juggling for 12 min each day for 18 days. On each day, we recorded the number of catches and the duration of each trial by the end of practice. Performance was evaluated using the number of catches and trial duration, from which accuracy was quantified as the probability of successfully catching a tennis ball and speed was quantified as juggling frequency. Over 18 days, participants improved accuracy from 0.67 to 0.91 in a decelerating pattern. Males were 16% more accurate than females on each day of practice. After adjusting for hand size, both genders showed similar accuracy. Juggling speed increased from 1.2 to 2.3 Hz, with no significant gender differences in 15 out of 18 days. These findings provide a probabilistic framework for characterizing skill acquisition in continuous motor tasks with cyclic and repetitive movement patterns and may help identify sensory and motor deficits in the upper extremities.
The aim of the current study was to determine the efficacy of unilateral conditioning exercises on post activation performance enhancement (PAPE) during a bilateral task, with particular reference to leg dominance. Over three days, 22 young adult male and female subjects were tested on unilateral and bilateral leg power and balance measurements, examined for footedness using a footedness questionnaire, and performed left and right reactive lateral leaps before and after unilateral conditioning exercise treatments. Response time of the step leg and leap distance from the push-off leg were evaluated with repeated measures ANOVA and ANCOVA with a p-level of .05. Results revealed no effects attributable to ipsilateral or contralateral PAPE effects and no differences in left versus right leaping distance or response time. However, when footedness (right, mixed) effects were examined, differences in performance consequent to conditioning exercises were found. Mixed footed subjects responded slower and leaped further on posttests following CE, but these results were not based on which leg was conditioned. Mixed footers, and not right footers, may have adopted a leaping strategy following conditioning strategies. These findings question the usefulness of unidimensional assessments of leg dominance and laterality in evaluating characteristics of sport and exercise performance.
Variability is an inherent feature of human force output, and its temporal structure provides insights into motor control. In young adults, this structure has been associated with efficient motor behavior. Conversely, aging-related physiological changes may constrain neuromuscular adaptability, leading to less effective response to perturbations. We tested this hypothesis using a perturbation-based paradigm that quantified the time required to return to baseline force following unexpected target shifts during an isometric grip task. Sixteen young and eighteen older adults performed steady contractions and sudden upward (30→45% maximum voluntary contraction; MVC) and downward (30→15% MVC) force perturbations. Force regularity and variability magnitude were assessed using Sample Entropy (SaEn) and standard deviation (SD) across contraction intensities ranging from 5% to 80% MVC. Older adults exhibited significantly longer adaptation times and greater force regularity than young adults, whereas SD did not differ between age groups. Across both groups, downward perturbations resulted in slower recovery than upward perturbations, indicating direction-specific constraints in force control. These findings demonstrate that aging prolongs adaptation to force perturbations and increases force output regularity, highlighting perturbation-based assessments as a sensitive approach for probing adaptive motor control. Force regularity may represent a more informative marker of aging-related changes in motor control than variability magnitude.
Anticipatory synergy adjustments (ASA) represent a feedforward mechanism by which the central nervous system transiently weakens postural synergies to enable rapid changes in performance variable, embodying the stability-agility tradeoff. This study investigated how temporal constraints and expertise modulate ASA onset time and magnitude during table tennis forehand strokes. Twenty male participants (10 skilled, 10 novice) performed 20 forehand trials in response to fast (5 m/s) and slow (1 m/s) visual stimuli in a coincidence anticipation timing task. Electromyography from 14 muscles and the center of pressure (COP) displacement were recorded. Synergy indices were computed using the uncontrolled manifold hypothesis. Results revealed that stimulus speed did not significantly affect ASA onset time (p = 0.519) or amplitude (p = 0.305). In contrast, skilled players exhibited significantly earlier ASA onset (p < 0.001) and larger magnitude (p = 0.002) than novices. Among skilled players, ASA features positively correlated with postural agility metrics (peak COP velocity and displacement) but not with timing errors. These findings indicate that ASA is shaped primarily by expertise rather than temporal task demands, reflecting refined neuromuscular control strategies that optimize the stability-agility tradeoff for rapid motor performance.
Classic ideomotor theory proposed that actions can be automatically triggered by internally evoked representations of action-related features. This study examined whether motor execution in ideomotor action is more closely linked to lexical-semantic labels or to perceptually based evaluative content. In Experiments 1 and 2, participants responded to the Korean words "short" and "long" by pressing left or right keys. Semantic labels alone did not modulate keypress response duration (RD). However, in Experiment 2, task-irrelevant auditory tones of varying durations produced a graded increase in RD. Experiment 3 tested whether this modulation reflected physical duration itself or the evaluative processes involved in distinguishing and categorizing stimulus durations. Participants categorized six auditory stimuli as "short" or "long," with categorization difficulty manipulated by varying the distance between boundary stimuli. RD increased gradually across stimulus durations, but this effect was not stronger in the easy condition despite the larger physical spacing between tones. In addition, RD showed a category-related increase beyond what could be explained by physical duration alone. Together, these findings suggest that motor execution is influenced less by lexical-semantic labels than by perceptually based evaluative and categorical processing, helping to clarify the level of mental content that serves as an ideomotor cue.
Previous research revealed that when actors select and complete only 1 of 2 movement options (Task-A OR Task-B), rational decision-makers choose the task with the maximum expected gain (MEG). The present study was designed to determine if actors choose to perform the task with the higher or lower MEG first when actors sequentially perform one task and then the other task (Task-A THEN Task-B). Participants were presented with 2 target-penalty configurations in which a target circle was partially overlapped by an equivalently-sized penalty circle. Configurations varied in the value of the penalty region and the amount of overlap (a spatial property related to the probability of the actor contacting the target and/or penalty regions) such that the configurations could have similar or different MEGs. Participants imagined sequentially performing aiming movements to both configurations, one after another, and indicated which of the two configurations they imagined aiming to first. Whenever the MEGs of the two options differed, most participants indicated that they would aim to the configuration with the higher MEG first more often than aiming to the configuration with the lower MEG first. When configurations had similar MEGs, most participants indicated that they would move first to the configuration with a larger exposed target region (greater probability of success) and higher penalty value, though some individual differences in strategies were noted. Overall, the data suggest that when presented with a sequential task, participants choose to perform the task with a higher potential gain before the task with the lower potential gain.
The study investigated the effects of ten 20-minute sessions of neurofunctional motor training combined with anodal transcranial direct current stimulation (tDCS) over the primary motor cortex or cerebellum on motor skills in autistic children. A randomized, sham-controlled, double-blind clinical trial was conducted with 30 autistic children five to seven years of age. The two-week intervention (10 sessions) consisted of either sham tDCS or active tDCS (1 mA) over the primary motor cortex or cerebellum during 20 min of neurofunctional motor training (treadmill training and task-oriented circuit). Assessments were performed before as well as one, four, and eight weeks after the interventions. The primary outcome was gross and fine motor skills. The secondary outcomes were mobility, functional balance, and motor evoked potential. Analysis of variance revealed no significant difference when considering the time*group interaction (F(1.8) = 0.6, p = 0.726) for gross and fine motor skills. No significant differences were found in the secondary outcomes of mobility (F(1.8) = 1.1, p = 0.331) and functional balance (F(1.8) = 1.5, p = 0.226). In contrast, the amplitude of the motor evoked potential was significantly increased in the group that received active tDCS over the primary motor cortex compared to active tDCS over the cerebellum and sham stimulation. Ten sessions of anodal tDCS over the primary motor cortex and cerebellum during neurofunctional motor training were not effective at improving gross and fine motor skills in autistic children.
Properties like the weight and length of wielded objects can be judged without vision. Previous studies have investigated perceptual information, like the moment of inertia, specifying such object properties by wielding with one hand. The current study extends this work by investigating how blindfolded participants bimanually heft and wield objects to perceive the weight or length. Participants were presented with rods, with weights attached either symmetrically on both sides of the center, or asymmetrically. The magnitude of weights attached and their position on the rod were also manipulated. Blindfolded participants were asked to either judge the weight or length of a set of rods, after they actively wielded each rod. Participants' muscle activity and exploratory movements were tracked. We investigated whether the temporal pattern of movements and muscle activity differed, depending on their intention to perceive rod weight or length. As expected, participants wielded the rods differently, depending on whether they were judging the weight or length. Additionally, weight distribution, the magnitude, and the position on the rod where the weights were attached, affected perceived heaviness. Surprisingly, none of these factors affected the perceived length of the rod, indicating the availability of perceptual information other than the moment of inertia.
Stroke is a leading cause of long-term sensorimotor disability, with upper limb deficits often persisting into the chronic stage. For many patients with stroke, the active muscle control zone, i.e., the angular range of typical muscle activation patterns, is reduced, leading to abnormal patterns and spasticity. When the displayed angle in a virtual environment is smaller than the actual angle, participants may implicitly perceive that their arm remains within the control zone. This discrepancy between visual and proprioceptive information may promote visuo-proprioceptive recalibration and sensorimotor adaptation. The current study included two preliminary investigations, one with healthy participants and one with participants with stroke, each divided into two groups (offset, control). Twenty-one healthy participants underwent a 30-min training session, after which they were tested with the actual elbow angle. Twelve hospitalized individuals with sub-acute stroke underwent three 30-min training sessions over one week. In both studies motion duration of participants who trained with an offset differed from motion of controls who trained with actual feedback. However, Fugl-Meyer Assessment upper limb scores in participants with stroke increased similarly for both groups. Additional testing is required to examine whether the method may be a potential direction for individualized impairment-based intervention.
Reactive turning requires considerable cognitive resources and precise motor control to maintain dynamic balance. Increased cognitive load can impair motor performance and alter turning behavior. This study examined how cognitive load and cue timing influence reactive turning strategies and postural control timing. Nineteen healthy young adults performed 90° contralateral and ipsilateral reactive turns while walking and completing a flanker task under varying cue timings and conflict conditions. Turning strategies and temporal parameters (head/pelvis rotation and center of mass deceleration times) were analyzed using linear mixed models; sensitivity analyses additionally adjusted for turning strategy. Under conflict, participants maintained near-perfect directional accuracy; however, temporal parameters were significantly delayed. These delays persisted after accounting for strategy switching, suggesting that cognitive interference influenced the temporal organization of reactive turning. Turning strategy selection was primarily associated with cue timing, with no significant effect of cognitive conflict. Furthermore, when temporal constraints limited the feasibility of a prompt second-step turn, contralateral turns shifted toward a mechanically stable third-step reorganization, whereas ipsilateral turns relied on a less stable alternative. Overall, these findings suggest that cognitive load modulates the temporal coordination of postural control during reactive turning without altering the selected turning strategy.
Motor sequence learning (MSL) involves transitioning from reactive, stimulus-led control to predictive, automated execution. While expertise is traditionally quantified by speed and accuracy, the underlying organizational shifts in fractal movement variability remain poorly understood. We propose the Readiness-Efficiency hypothesis: expertise emerges through a functional coupling of high preparatory complexity and reduced execution complexity. Participants (n = 22) performed a whole-body Dance Discrete Sequence Production task while Center of Mass (CoM) kinematics were recorded. Hurst exponents (H) quantified fractal complexity across ten blocks of practice and transfer. As learning progressed, preparatory dynamics shifted toward higher complexity (Hprep↑), reflecting structured readiness, while execution dynamics shifted toward reduced complexity (Hexec↓), reflecting automated efficiency. Crucially, a three-way interaction revealed that the fastest response times were achieved specifically when high preparatory readiness was coupled with reduced execution complexity. This coupling collapsed upon transfer to novel sequences, indicating task-specificity. State-space analysis confirmed the Readiness-Efficiency configuration acts as a functional attractor, with the probability of occupying this state increasing five-fold through practice. These findings demonstrate that expertise is characterized by dynamic flexibility - the capacity to dissociate and pair control regimes to meet phase-specific demands - providing a mechanistic framework for profiling skill acquisition.
Engaging in a cognitive dual-task while standing relies on the allocation of available cognitive resources. Automatic postural control is engaged while distracted; however, the use of automatic mechanisms and modulation of this automaticity based on the level of cognitive load has not been thoroughly explored. This study aims to determine whether the level of cognitive task difficulty influences automatic postural control and the magnitude of postural sway during quiet stance. Twenty-six healthy young adults (22.2 ± 2.2 years) completed twelve upright stance trials consisting of quiet standing without distraction and five arithmetic cognitive task conditions (add by 3 and subtract by 3, 7, 3.3, 7.7) while standing upright with eyes open or closed. Automaticity was assessed using sample entropy of center of pressure (COP). Magnitude and variability of COP excursions were quantified using 95% confidence ellipse area and root mean square, respectively. In general, engaging in a cognitive dual-task led to an increase in sample entropy and reduced COP variability, but these did not change as a function of cognitive task difficulty. Manipulating the availability of visual input had a variable effect across outcome measures. Young healthy adults use automatic control mechanisms to remain stable regardless of the level of cognitive load.
We examined how concussion impacts sensorimotor memories used to adapt goal-directed reaches to unpredictable hand-held loads. Recently concussed individuals underwent computerized cognition testing and a robotic test of sensorimotor adaptation as soon as possible after injury, on return to activity, and after three months. Control subjects were tested at similar intervals. During robotic testing, subjects moved a robot handle repeatedly between two targets; the handle resisted movement with spring-like forces that changed unpredictably between trials, allowing us to model how performance memories contribute to trial-by-trial adaptation. Because symptom severity varied markedly at Session 1, we bisected the concussed cohort based on initial reaction time. Although Session 1 data revealed abnormally high limb compliance estimates in more severely concussed individuals relative to controls, we did not find group differences in how memories contribute to adaptation in any session. However, control group models revealed a practice effect affecting memory model coefficients; this may have masked concussion's initial effects on how memories contribute to adaptation. Although a practice effect and a heterogeneous concussed cohort preclude strong conclusions, our study demonstrates feasibility of the robotic assessment and indicates procedural improvements that may increase its sensitivity and specificity to concussion-related changes in how memories contribute to adaptation.
Excessive visual reliance for postural control may increase injury risk, yet its extent in dancers remains unclear. In this study, we examined whether dancers exhibit greater dependence on visual input during single-leg balance compared to non-dancers using traditional center-of-pressure (COP) and time-to-boundary (TTB) metrics. Forty-eight participants (24 dancers and 24 non-dancers) performed three 10-second single-leg balance trials on a force plate under eyes open (EO) and eyes closed (EC) conditions. Eleven COP and six TTB parameters quantified postural control, with visual reliance defined as the percent reduction in balance performance upon visual input removal. Independent t-tests showed that dancers displayed significantly higher visual reliance in five of the COP parameters (p = 0.022 to 0.037, average 21.6% increase) and three of the TTB metrics (p = 0.014 to 0.047, average 7.3% increase) compared to non-dancers. Effect size analyses confirmed moderate group differences with non-overlapping confidence intervals. These findings indicate that dancers depend more on visual cues for postural control during single-leg balance. The combined use of COP and TTB assessments offers a comprehensive evaluation of visual reliance, highlighting the need for targeted interventions to mitigate potential injury risks in dancers.
The purpose of the present study was to make inferences about the sensorimotor mechanisms that result in the linear speed-accuracy tradeoff. Theoretical and empirical research have suggested that movements in Schmidt's task involve minimal online control. We tested this hypothesis with three types of trajectory analysis that could differentiate online control from impulse and limb-target regulation. Thirty participants made discrete pointing movements with goal movement times and amplitudes that ranged from 333 to 194 ms and 100 to 300 mm, respectively. Linear mixed-effects model analysis revealed a strong linear relationship between mean velocity and variable spatial error. Proportion of movement time after maximum velocity and the number of secondary submovements suggested that most conditions had minimal limb-target regulation. However, spatial variability throughout movement execution suggested that all conditions involved online control. This online control without limb-target regulation was likely the result of impulse regulation. We suggest that impulse regulation was used because it can modulate movement velocity without a large cost to temporal precision. This contributes to the primary and secondary goals of Schmidt's tasks, which are temporal precision and spatial accuracy. Future theoretical models of Schmidt's law should distinguish between online control from impulse and limb-target regulation.
This study aimed to investigate the effects of attentional focus (internal vs. external) and cognitive dual-tasking on gait variability in healthy adults. Walking, as a fundamental human motor pattern, is influenced by cognitive and attentional demands. Twenty healthy participants (10 men and 10 women) participated in this quasi-experimental within-subjects study. Participants completed four walking conditions: normal walking, walking with an internal focus, walking with an external focus, and walking while performing a cognitive dual-task (counting backward from 100). Kinematic data were recorded using a Vicon motion capture system and analyzed using Python. Key outcome measures included spatial-temporal gait parameters, local dynamic stability assessed via the Lyapunov exponent, and motor variability based on the uncontrolled manifold (UCM) framework. Repeated measures ANOVA and post hoc tests revealed that attentional focus and cognitive load significantly influenced walking patterns. Dual-tasking led to slower gait speed, increased step width, and a higher percentage of double support, alongside increased Lyapunov exponents and decreased UCM indices-indicating reduced gait stability and adaptability. Conversely, external focus improved most gait parameters. These findings highlight the critical role of attentional strategies in maintaining gait stability and suggest their relevance in motor control, learning, and rehabilitation programs.
We investigated the acute effects of moderate alcohol consumption on implicit and explicit motor learning in young adult male social drinkers. Two experiments used the Serial Reaction Time Task to test whether alcohol intake before practice (Experiment 1) or immediately after practice (Experiment 2) affects implicit and explicit motor learning. Participants (n = 160) were randomly assigned to eight subgroups defined by learning type (implicit vs. explicit), condition (alcohol vs. placebo), and experiment, with 20 participants per subgroup. Alcohol groups ingested vodka mixed with orange soda (Fanta®, 1:4; 0.4 g/kg ethanol), whereas placebo groups received orange soda sprayed with vodka. Explicit groups memorized the repeating sequence before practice and were informed when repeated-sequence blocks began; implicit groups practiced without declarative knowledge. Participants completed seven practice blocks and a one-week retention test. Performance was quantified by a Change Score (response time difference between repeated and pseudorandom sequences), and declarative knowledge by sequence identification/recognition. Alcohol intake did not affect performance improvements or retention whether consumed before or after practice, regardless of learning condition. We conclude that moderate alcohol consumption does not impair motor memory encoding or consolidation under implicit or explicit motor learning mechanisms.
Chronic exposure to manganese in occupational settings such as welding is known to accumulate in the basal ganglia and disrupt motor control. Although clinical symptoms emerge only after considerable neural damage, subtle motor deficits may exist in asymptomatic individuals. This study aimed to identify such subclinical motor alterations by examining multi-finger coordination in professional welders. Nine professional welders with more than 20 years of welding experience and ten age-matched healthy controls participated in the study. Participants performed three isometric finger force tasks: a maximal voluntary contraction task to assess maximal finger forces, a single-finger ramp task to evaluate finger enslaving, and a multi-finger quick pulse task to analyze motor synergies and anticipatory synergy adjustments (ASA). Surface electromyogram was recorded to quantify muscle co-contraction. Compared to controls, welders exhibited reduced motor synergy strength, delayed and decreased ASA, and increased antagonist muscle co-contraction. These findings suggest that long-term occupational welding exposure, which involves manganese as a major component, is associated with subtle but measurable alterations in motor coordination and neural control strategies, even in the absence of clinical symptoms. Multi-finger synergy analysis and co-contraction metrics may serve as sensitive markers for detecting early motor dysfunction in populations occupationally exposed to neurotoxic substances.
