Experimental Brain Research

Learning to reach with a visuomotor distortion has been shown to influence subsequent reaches with the same distortion and with a new distortion. Here, we examined whether learning to reach with a small 20{degrees} mirror reversed distortion leads to faster re-learning of the same distortion (i.e., demonstrates savings) and whether learning to reach with a mirror reversed distortion influences subsequent reaches with a 20{degrees} visuomotor rotation distortion. Thirty participants first learned to reach with the mirror reversed distortion. Following washout trials with aligned cursor feedback, 15 participants reached again with the mirror reversed distortion (MR-MR group), while the 15 other participants reached with a visuomotor rotation distortion (MR-VMR group). An additional twenty participants only reached with the visuomotor rotation distortion (VMR-only group). Implicit (unconscious) and explicit (conscious strategy) contributions to learning were assessed using the process dissociation procedure. Evidence of savings was evident in the MR-MR group, such that participants demonstrated reduced hand angles when re-introduced to the mirror reversed distortion. This savings was driven by explicit processes, consistent with the rapid retrieval of previously acquired task solutions. Additionally, learning to reach with the mirror reversed distortion interfered with learning to reach with the visuomotor rotation distortion, such that the MR-VMR group demonstrated increased reach variability and longer reaction times when reaching with the visuomotor rotation distortion compared to the VMR-only group. Reduced implicit contributions were also evident in the MR-VMR group compared to the VMR-only group. Together, results indicate that learning to reach with a mirror reversed distortion promotes savings and influences learning to reach with a visuomotor rotation distortion through engagement of explicit processes.

Cybersickness in virtual reality (VR) arises from conflicts between sensory signals, yet susceptibility varies considerably across individuals. Previous work in this cohort demonstrated that vestibulomotor responses during postural control are associated with cybersickness susceptibility. Here, we examined whether perceptual weighting of gravity, visual, and body cues used to estimate upright orientation is similarly associated with cybersickness and related to previously reported vestibulomotor measures. Thirty-eight healthy young adults (21 females, 17 males) completed a standing VR rollercoaster task while receiving continuous stochastic electrical vestibular stimulation (0-25 Hz, {+/-}4.5 mA). In the current analysis, perceptual cue weights were quantified before and after VR using the Oriented Character Recognition Task. Cybersickness was assessed using the Fast Motion Sickness Scale (FMS), and participants were classified as non-sick (FMS < 5), medium-sick (FMS [&ge;] 5), or high-sick (terminated the VR exposure early due to intolerance). Before VR, non-sick participants exhibited greater gravity weighting (36% vs. 25%) than high-sick participants, whereas high-sick participants showed a non-significant trend toward greater visual weighting (30% vs. 18%). Perceptual cue weights changed minimally following VR, and the magnitude of perceptual reweighting was not associated with sickness severity. Vestibulomotor measures were not correlated with perceptual gravity weighting, and postural sway during VR was not associated with visual weighting. These findings suggest that greater baseline perceptual gravity weighting, rather than short-term perceptual reweighting, is associated with reduced cybersickness susceptibility. The dissociation between perceptual and vestibulomotor measures suggests that orientation perception and postural control reflect partially distinct multisensory integration processes. New and NoteworthyThis study demonstrates that baseline perceptual gravity weighting is associated with susceptibility to cybersickness during virtual reality exposure with concurrent electrical vestibular stimulation. Greater reliance on gravity cues was associated with reduced susceptibility, whereas visual weighting showed a similar but non-significant trend and perceptual reweighting changed minimally following exposure. Perceptual measures were dissociable from vestibulomotor responses, suggesting that orientation perception and postural control reflect partially distinct multisensory integration processes.

In the current experiment, we compared reported perceptual awareness of the visuomotor rotation to motor awareness of changes in reaches established using the process dissociation procedure and drawing task following visuomotor adaptation to a large (50 degrees; R50 group) or a small (30 degrees; R30 group) cursor rotation. Results revealed that perceptual and motor awareness did not differ in magnitude for the R50 group and were significantly correlated. In contrast, while the R30 group perceptually reported being aware of the visuomotor rotation, motor awareness was significantly less and responses were not significantly correlated across tasks. Overall, results suggest that perceptual and motor tasks assess different processes underlying visuomotor adaptation to a small cursor rotation, such that perceptual awareness of the visuomotor rotation is not reflected in reaching performance on tasks assessing motor awareness.

In mirror reversed (MR) learning, the magnitude and direction of the visuomotor distortion varies with target location. To date, implicit (i.e., unconscious) processes have not been implicated in learning to reach with an MR distortion, even when the distortion is small in magnitude. Across two experiments, we examined whether explicit processes (i.e., motor and perceptual awareness of reaching strategies) are engaged when learning to reach with a small (20{degrees}) MR distortion and whether this learning generalizes to novel targets. Learning to reach with an MR distortion was compared to learning to reach with a small visuomotor rotation (VR), in which cursor feedback was rotated 20{degrees} relative to hand motion at each target. Participants in the MR group engaged both motor and perceptual awareness and learning to reach with the MR distortion generalized to novel targets. Participants in the VR group also learned to reach with the VR distortion but they did not engage either motor or perceptual awareness and there was no evidence of generalization. Reaction times were longer for the MR group compared to the VR group, consistent with engagement of explicit processes. Together, these findings suggest that learning to reach with an MR distortion is supported by motor and perceptual awareness that generalize to novel targets.

Heart rate (HR) deceleration occurs following movement error and has been interpreted as an autonomic response to adverse behavioral outcomes. However, movement errors not only represent adverse movement outcomes but may also violate expectations. The present study employed a reaching movement paradigm using a robotic manipulandum in male and female human participants to dissociate the contributions of movement outcome and expectation violation to HR responses. We confirmed that HR deceleration occurred following visuomotor perturbations that induce movement errors, consistent with previous studies. However, when contextual cues predicted upcoming movement outcomes, HR deceleration emerged during movement preparation rather than following movement error, suggesting the involvement of expectation in HR responses. Moreover, across varying levels of expectation for different movement outcomes, HR deceleration was associated with unexpected movement outcomes rather than with the negative valence of movement outcomes. By altering target width to permit successful movements despite visuomotor rotations, we further found that HR deceleration was more strongly associated with task error than with sensory prediction error. Together, these findings indicate that HR responses during movement are more closely associated with violations of movement expectation than with movement error itself. These findings provide a new perspective on autonomic responses during sensorimotor processing and suggest that HR may serve as a physiological marker of expectation-related processing during movement.

Background: Paretic-arm nonuse and trunk compensation after stroke are often interpreted as impairment or learned behavior but may also reflect task-dependent optimization. We previously showed that gravitational shoulder effort and force reserve shape these behaviors. Here, we tested whether endpoint precision is an additional constraint. Methods: Twenty-two individuals with stroke and 22 matched controls performed a seated Proximal Arm Nonuse reaching task toward small (2 cm) and large (12 cm) targets. Stroke participants were tested at normal arm weight and with the paretic arm mechanically lightened; controls were tested at normal arm weight and while holding a dumbbell corresponding to 85% of maximal voluntary shoulder force. Results: In stroke participants, trunk compensation was 15% lower for the large target than for the small target, independently of arm weight condition (F(1,13)=8.166, p=.013, pes=.39). Target size did not significantly affect trunk compensation in controls or anterior deltoid activation in either group. In stroke participants, movement time was 24% longer for the small target than for the large target (F(1,13)=8.533, p=.012, pes=.40). In controls, the small target increased movement time only when the arm was weighted (F(1,18)=14.9, p=.001, pes=.45), not at normal arm weight (F(1,18)=0.158, p=.695, pes=.01). Conclusions: Endpoint precision altered reaching after stroke partly independently of gravitational shoulder effort. Trunk compensation after stroke was therefore modulated by task demands rather than fixed by impairment, a pattern consistent with, although not a direct demonstration of, an optimal-control account. Rehabilitation should evaluate compensation by its functional role and the cost of suppressing it, not only by its deviation from typical kinematics, and should treat target size as an adjustable parameter of the task. Clinical Trial: NCT04747587. https://clinicaltrials.gov/study/NCT04747587

The present study aimed to directly replicate the seminal findings of Decety et al. (1989), while also extending the original work with a larger sample size and additional statistical analyses. Thirty healthy adults completed both imagined and executed walking tasks over distances of 5, 10, and 15 meters. Participants also completed the Movement Imagery Questionnaire 3 (MIQ 3). Temporal correspondence between imagined and executed walking was assessed using repeated-measures ANOVA, correlation analyses, Bayesian equivalence tests, and Bland Altman analyses. Walking duration increased significantly with distance, while no significant differences were observed between imagined and executed walking times. Bayesian equivalence tests provided evidence supporting temporal equivalence between the two modalities, and Bland Altman analyses indicated good agreement with minimal systematic bias. Strong positive correlations were found between imagined and executed durations at all distances. MIQ-3 scores were not significantly associated with differences between imagined and executed walking durations. Overall, the findings successfully replicate and extend the original results reported by Decety et al. (1989), providing additional evidence supporting temporal equivalence between motor imagery and movement execution. By combining a larger sample size with contemporary statistical approaches, the present study strengthens support for the principle of functional equivalence for highly automated and cyclic movements.

Abstract Background: Reward can influence both the selection and execution of goal-directed actions. Healthy ageing is associated with changes in reward processing, raising the possibility that reward effects on motor control may be reduced in older adults. Objective: This study examined how monetary reward affects action execution and action selection during reaching movements and whether these effects differ between younger and older adults. Methods: 28 younger adults and 28 older adults performed a reward-based reaching task. Behaviourally non-distracted trials were used to assess action execution, whereas distractor-containing trials were used to assess action selection. Outcomes included maximum velocity, movement time, endpoint error, reaction time, and selection accuracy. Results: Reward increased maximum velocity and reduced movement time in both age groups without increasing error. These reward-related changes in movement vigour were larger in younger adults. During action selection, reward shortened reaction time but reduced selection accuracy in both groups, indicating faster but less accurate responses. The reward-related changes in reaction time and selection accuracy did not differ significantly between age groups. Conclusion: Ageing did not produce a uniform reduction in reward responsiveness. Instead, ageing attenuated reward-driven movement invigoration, while reward-related changes in action-selection behaviour were similar across age groups. These findings may inform the design of reward-based interventions that promote movement vigour without encouraging speed at the expense of accurate action selection.

Standing balance relies on the continuous detection of body motion across a wide range of amplitudes and frequencies. According to Weber's law, sensory discrimination should degrade in proportion to stimulus amplitude, yet vestibular self-motion perception deviates from this prediction. Whether this deviation extends to the vestibular control of posture remains unknown. To test this hypothesis, we delivered amplitude-increasing electrical vestibular stimulation (EVS, 0-2 mA) at four frequencies (0.1, 0.2, 0.5, and 1 Hz) to 10 healthy young adults, and quantified balance discrimination thresholds (DTs) from the gain and inter-trial variability of the lateral ground reaction force, using signal detection theory. Balance control DTs increased sublinearly with EVS amplitude at all frequencies, deviating from Weber's law. Both balance-correcting response gain and variability accounted for this deviation: gain decreased more slowly than the strictly inverse relationship that would have alone produced strict adherence to Weber's law, while variability exhibited an initial increase followed by saturation at higher EVS amplitudes, a signal-dependent structure necessary to reproduce the observed DT pattern. EVS frequency modulated the shape of this deviation but affected neither overall DT nor the signal-to-noise ratio of the balance-correcting response, which instead remained similar across frequencies. This study revealed a particular property of postural control discrimination by extending the psychophysical and neural deviations from Weber's law previously reported for vestibular perception. Overall, these results provide a better understanding of the balance control discrimination process and provide potential additional assessment criteria for vestibular impairments.

Long-latency stretch reflex and corticospinal excitability in the tibialis anterior muscle (TA) are facilitated when balance is threatened, even without background TA activity, suggesting supraspinal modulation as preparatory tuning for ankle stabilization. However, it remains unclear whether such tuning is evident at the spinal level and specific to the TA among lower-limb muscles. We therefore examined the effects of height-induced postural threat on multi-segmental monosynaptic spinal reflexes (MMR) in lower-limb muscles during quiet standing. Seventeen healthy young males performed 90-s standing tasks under three postural threat conditions, created by combining real and virtual reality (VR) heights: (1) Low-threat (real ground & VR ground), (2) Medium-threat (real table & VR ground), and (3) High-threat (real table & VR bridge). During each condition, transcutaneous spinal cord stimulation (tSCS) was applied to the lumbar spine to elicit MMR in lower-limb muscles. Electromyograms (EMG) were recorded from six muscles of the right leg: vastus medialis (VM), biceps femoris (BF), TA, soleus (SOL), medial (MG), and lateral gastrocnemius (LG). MMR excitability was quantified as peak-to-peak EMG amplitude. Fear ratings and electrodermal activity were higher in High-threat than Low-threat (all p < 0.05), confirming successful threat induction. Peak-to-peak EMG amplitude in the TA was significantly higher in High-threat than Low-threat (17.1% increase, p = 0.0393), whereas background TA activity remained absent across conditions. These results indicate that TA has unique function to facilitate spinal excitability as a preparatory tuning for ankle stabilization. Key pointsO_LIPrevious studies have shown the supraspinal facilitation of the tibialis anterior muscle without background muscle activation as a preparatory tuning for ankle stabilization. C_LIO_LITo test the hypothesis that such tuning is also evident at the spinal level and specific to the tibialis anterior muscle, this study examined whether height-induced postural threat modulates multi-segmental monosynaptic reflex excitability in lower-limb muscles using transcutaneous spinal cord stimulation. C_LIO_LIElectrodermal activity and fear ratings increased under height-induced postural threat, confirming the successful induction of postural threat. C_LIO_LIUnder height-induced postural threat, the multi-segmental monosynaptic reflex was selectively facilitated in the tibialis anterior muscle, while its background activity remained absent. C_LIO_LIOur findings demonstrate selective facilitation of spinal excitability in the tibialis anterior muscle, which may serve as preparatory tuning for ankle stabilization under threat to balance. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=147 SRC="FIGDIR/small/742625v1_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@ca21f3org.highwire.dtl.DTLVardef@7b1679org.highwire.dtl.DTLVardef@1007191org.highwire.dtl.DTLVardef@1ff88a_HPS_FORMAT_FIGEXP M_FIG C_FIG Abstract figure legendWhen balance is threatened, corticospinal excitability and long-latency stretch reflex in the tibialis anterior muscle (TA) are facilitated even in the absence of background TA activity, suggesting supraspinal preparatory tuning for ankle stabilization. This study tested the hypothesis that such facilitation is also expressed at the spinal level and is specific to the TA. Participants completed 90-s quiet standing trials under three different height-induced postural threat conditions. During each trial, transcutaneous spinal cord stimulation was delivered over the lumbar spine to elicit multi-segmental monosynaptic reflexes (MMR) in multiple lower-limb muscles. High-threat condition increased fear ratings and electrodermal activity, indicating successful threat induction. Moreover, MMR excitability was selectively increased in the TA under High-threat condition despite the absence of background TA activity. These findings suggest that spinal facilitation is selectively expressed in the TA and may reflect preparatory tuning for ankle stabilization under threat to balance.

Background: Detecting environmental regularities is a sophisticated cognitive skill, but its neural basis remains unclear. We tested whether corticospinal excitability tracks stimulus predictability, prediction errors, and task progression while the participants played the Goalkeeper Game. Methods: Sixteen right-handed males (24.4 +/- 6.8 years) saved penalty kicks using index, middle, or ring fingers (left, center, right). Kick sequences were generated by a context tree model, in which contexts represent the minimum recent history required to predict the next event. Participants completed 1,200 trials (6 blocks x 200 trials each). Transcranial magnetic stimulation (TMS) delivered 400 ms before the go signal elicited motor evoked potentials (MEPs) in the first dorsal interosseous (FDI) and flexor digitorum superficialis (FDS) muscles during blocks 2, 4, and 6. Contexts were classified as unpredictable (1, 10) or predictable (2, 20, 00); prediction errors were defined for non-deterministic transitions after context 1. Log-MEPs were analyzed using mixed-effects models. Results: In FDI, a Predictability x Previous-Error x Block interaction emerged (F(2,8997)=6.89, p=.001), confined to the final block. Predictability increased MEP amplitudes after successful transitions (+6.3%; p=0.006) but decreased MEP amplitudes after failed transitions (-7.0%; p=0.007). For FDS, unpredictable trials elicited larger MEPs (+7.2%; p=0.002), and MEPs increased from block 2 to 6 (+16.8%; p=0.003). Conclusions: FDS MEP responses were broadly associated with uncertainty and task progression, whereas FDI MEP responses showed context-specific, error-dependent modulation after extended exposure, suggesting fine-grained predictive coding in goal-executing effectors.

Preventing object slippage requires the central nervous system to control and coordinate the muscle groups while adapting to the variations in the slip characteristics. Our study investigates how slip characteristics, such as slip direction, slip distance, and slip speed, affect the modulation of muscle synergies as a manifestation of object slippage. Our results reveal that there are shared synergies existing in the upward and downward slip emulation, and that these shared synergies are dependent on slip characteristics. However, there were no specific synergies found to exist in the upward and downward slip conditions. Our results also indicate the existence of combined synergies, as the motor modules in the upward slip direction were found to have shared synergies with multiple motor modules in the downward slip direction. We also observed that the number of shared synergies varied depending on the slip distance and slip speed. Together, these findings suggest that the CNS flexibly reconfigures a limited set of muscle synergies to accommodate varying slip dynamics, balancing control stability with adaptability.

Motor imagery and overt action are proposed to share common planning mechanisms while relying on distinct processes during movement performance. To investigate how repetition affects physical and imagined movements, participants physically or mentally drew paths while avoiding barriers. The barrier orientations were either repeated or different across consecutive trials, and the modality (execution or imagery) of the trials either changed or remained the same for two consecutive trials. Reaction time and movement time were analysed as measures of movement planning and task performance, respectively. Imagined movements produced longer reaction times and movement times than physical movements. Repetition of orientation reduced reaction times in both physical and imagined trials, indicating that trajectory repetition facilitated movement preparation. In contrast, previous trial type influenced reaction times only for physical movements, which were only initiated faster when preceded by another physical trial. Different effects emerged for movement time. Physical movements were faster when the same trajectory was repeated no matter the previous trial type, whereas imagined movements were unaffected by orientation and instead showed shorter durations when preceded by another imagined trial. The findings indicate that physical and imagined movements rely on more similar trajectory representations during the planning stage, but diverge during task performance. While physical movements appear to benefit from the persistence of previously generated movement trajectories, imagined trials seems more influenced by modality-specific cognitive processes. These results provide behavioural support for the Motor-Cognitive model and contribute to understanding how movement repetition influences overt and imagined actions.

Body ownership over an artificial body can alter perceptual and autonomic responses, but its influence on online postural control remains less understood. We investigated whether ownership-related body-avatar correspondence modulates postural responses to an unexpected change in avatar posture. Thirty-six healthy male participants were randomly assigned to an Embodiment condition, in which body-avatar correspondence was maintained, or a Disruption condition, in which the avatar's arm temporarily moved independently of the participant before the critical event. During a standing virtual-reality session with synchronous visuotactile stimulation, the avatar unexpectedly leaned forward. We introduced Avatar-Induced Postural Response (AIPR), an event-related index of anterior-posterior center-of-pressure displacement following the avatar's movement. Ownership-related questionnaire ratings were higher in the Embodiment condition, whereas self-location-related ratings did not differ between conditions. AIPR was greater in the Embodiment condition and was greater than zero only in this condition. AIPR was also positively correlated with skin conductance responses in the Embodiment condition, but was not associated with questionnaire ratings. These findings suggest that an unexpected change in avatar posture can influence the participant's own postural regulation when ownership-related body-avatar correspondence is maintained. AIPR may provide a complementary behavioral index of a postural-control component of avatar embodiment not fully reflected in explicit subjective reports.

Tactile imagery has attracted growing fundamental and clinical interest. Previous studies often investigated neural and functional similarities between imagined and actual touch. Several functional aspects of touch, such as differences between active and passive touch, between different haptic features during active touch or sensitivity of different body parts for passive touch, have also been explored in tactile imagery. Furthermore, considerable individual differences in the ability to engage in tactile imagery have been observed. However, several important aspects, involving different imagery components and a wide variety of touch qualities remain to be explored within a single comprehensive study. The current study therefore aims to provide a wide-ranging assessment of tactile imagery in terms of imagery processing components (vividness, maintenance, transformation), type of touch (active versus passive) and touch qualities (object properties for active touch, different tactile sensations across body sites for passive touch). We developed a comprehensive questionnaire containing 72 items to assess tactile imagery ability. 136 healthy participants were asked to imagine different touch types and rate imagery vividness and their ability to maintain and transform each sensation on 5-point Likert-scales. Active touch varied by object (plastic bottle, modeling clay, sponge) and property (temperature, weight, texture, resistance). Passive touch varied by body site (lip, shin, sole of the foot, lower back) and sensation (stroking, vibration, pinching). Overall, participants were able to perform tactile imagery: the vast majority reported at least some imagery across touch types. Individual variability was substantial: scores bridged both ends of the scale. Active tactile imagery differed significantly between objects, depending on tactile property. Object-property pairs with particularly strong imagery were bottle-temperature, bottle-weight and sponge-texture, whereas bottle-resistance elicited weaker imagery, as did temperature and weight for both sponge and clay. Passive tactile imagery was significantly stronger for body sites with higher receptor density (i.e. lip and foot). Imagery of stroking was significantly weaker than vibration and pinching. Active and passive imagery showed a strong, positive correlation, though some participants had relatively strong active imagery, but weaker passive imagery, or vice versa. Our findings confirm that tactile imagery ability varies across individuals and touch types, underlining the importance of a comprehensive imagery ability assessment tool specific to the tactile domain.

Targeted stepping requires coordinating limb transport, preparatory postural adjustments, and accurate foot placement while maintaining balance under competing speed and accuracy demands. Although Fitts' law robustly describes speed-accuracy trade-offs (SATs) in upper-limb movements, its applicability to whole-body stepping remains unclear due to additional postural and visuomotor constraints. This study investigates how instructional emphasis and spatial demands modulate SAT regulation and pre-step postural dynamics during stepping. Twenty-four healthy young adults will perform a multidirectional stepping task across two directions (0 degrees and 45 degrees) and two distances (45% and 80% of leg length) under three instruction conditions: Fast, Accurate, and Fast & Accurate. Kinematic and force-plate data will quantify movement time, foot-placement error, and pre-step center-of-pressure dynamics. We hypothesize that instructional emphasis and increased postural demands will systematically alter stepping strategies and produce deviations from classical Fitts-type scaling, particularly during diagonal stepping.

Past studies using transcranial magnetic stimulation have shown larger motor-evoked potentials when people observe someone lifting a heavy object than when they observe someone lifting a light one. This means that observers may engage their own motor system in proportion to the perceived effort. However, the different responses during the observation of light and heavy objects may have been influenced by predictable trial sequences within blocked presentation, making it unclear whether corticospinal excitability reflects online processing of kinematics or is affected by top-down expectations. In this Registered Report, 57 right-handed participants passively observed videos of a precision grip and lift of heavy and light objects while receiving a single-pulse TMS to the left primary motor cortex during the lift phase of the movement. Motor-evoked potentials were recorded from the right first dorsal interosseous muscle. The study compared two main observation contexts: a predictable trial sequence in which repeated videos of the same lifts were presented in a blocked order, and an unpredictable one in which videos were presented semi-randomly and participants could rely only on kinematic cues to perceive the weight of the lifted object. In both conditions, the same videos of lifts of equivalent-looking heavy and light objects were used and only the order of presentation differed. Contrary to our predictions, in the blocked (predictable) condition, there was no significant difference in MEPs elicited by light and heavy lifts. In the unpredictable condition, participants showed greater corticospinal excitability during the observation of the light lifts compared to the heavy lifts. This suggests that in the absence of predictable information, the corticospinal system was sensitive to the observed kinematics, but contrary to previous findings, its excitability varied inversely with the object weight.

Feedforward control is impaired after stroke, but whether practice improves it in the chronic stage remains unclear. In fast single-joint movements, feedforward control scales initial acceleration to movement amplitude. Feedback-error-learning theory predicts that fast practice should promote recalibration. We tested whether speed-emphasized reach training improved this scaling in the more-affected arm. Thirty-six individuals with mild-to-moderate chronic stroke completed 2,080 reaches over four sessions emphasizing Speed (n = 17) or Accuracy (n = 19). At baseline, 3 days, and 1 month after training, participants performed single-joint elbow movements of three amplitudes without online visual feedback. The slope relating initial peak acceleration to target amplitude quantified feedforward scaling. At baseline, scaling was reduced on the more-affected side for extension and flexion. Speed training increased flexion scaling at 3 days, with 14 of 17 participants improving. The group-by-session interaction showed a greater increase after Speed than Accuracy training. Scaling declined by 1 month; no training-related changes occurred for extension. Peak acceleration occurred within 100 ms. Time to peak velocity, an index of pulse width, showed no group-specific training effect. Thus, speed-emphasized training produced a short-term improvement in early flexion acceleration scaling that transferred to an untrained single-joint task and was consistent with improved feedforward control. Transfer primarily reflected acceleration pulse-height rather than pulse-width modulation.

Serial dependence, whereby current perception is systematically biased toward the most recent sensory experience, has been demonstrated across multiple sensory modalities. However, whether serial dependence occurs during active haptic perception remains unknown. Moreover, because haptic perception of object geometry depends on hand movements for sensory acquisition (i.e., active touch), it remains unclear whether serial dependence, if any, originates from perceptual processing, movement, or both. Here, we investigated whether active haptic perception exhibits attractive serial dependence using a newly developed haptic device that let participants explore virtual slopes of different heights. Participants reported perceived slope heights, and we recorded their kinematics. Perceptual judgments were systematically attracted toward the most recently experienced slope, demonstrating serial dependence during active haptic perception. By contrast, none of the kinematic parameters exhibited corresponding serial dependence. These findings show that serial dependence extends to the somatosensory perceptual domain and suggest that the observed perceptual bias was not mediated by systematic changes in hand movements.

Pupillometry is commonly used to assess workload and fatigue, but its interpretation in applied, continuous-control tasks remains unclear because pupil responses are strongly shaped by task context and often lack a theory-guided interpretive basis. The Compensatory Control Model and Locus Coeruleus-Norepinephrine system offer complementary frameworks for interpreting pupil dynamics in relation to regulatory effort and engagement under sustained cognitive demand. We aimed to examine how tonic and phasic pupil dynamics reflect compensatory regulation following sustained cognitive demand, and how these dynamics relate to subsequent performance during continuous motor control. Participants completed two sessions consisting of a low- versus high- demand working-memory task followed by a joystick-based continuous motor-control task. Linear mixed-effects models tested demand effects on pupil dynamics and behavior and evaluated trial- level pupil-performance associations. Prior high demand produced small and specific changes in motor-control performance. Task-evoked pupil response showed effects of engagement dependent on prior demand and small associations with movement timing and accuracy. Our results show that pupil dynamics sensitively reflect sustained cognitive demand, but their trial-level predictive value for subsequent continuous motor performance is limited.