Biology subjects

Tsay, J. S.

Publications and source records attributed to Tsay, J. S..

At least 19 recordsLinked to original sources

bioRxiv2026

Understanding Strategic Motor Learning as a Process of Hypothesis Testing

Multiple learning processes contribute to successful goal-directed actions under changing physiological states, biomechanical constraints, and environmental contexts. Among these, explicit strategies enable us to discover new movement patterns when existing ones no longer achieve the desired outcome. Yet, how strategies are discovered during motor learning remains unknown. To address this, we developed a novel behavioral paradigm that isolates strategy discovery in response to a range of visuomotor perturbations. This approach revealed that strategy discovery unfolds through an initial period of systematic exploration across multiple candidate strategies, followed by an 'aha' moment in which behavior converges on a stable solution. To account for these dynamics, we developed a computational model based on hypothesis testing in which learners generate and evaluate visuomotor rules to counteract the perturbation. This hypothesis testing model outperformed a range of alternative accounts, including gradual error reduction, win-stay lose-shift learning, and sudden one-shot insight. Together, these findings identify hypothesis testing as a computational mechanism by which humans discover new strategies during motor learning.

neuroscience↗

bioRxiv2026

Tracking the hidden dynamics of proprioception

Every movement unfolds with a simple question: Where is my body? The nervous system answers through proprioception - the sense of limb position (static position sense) and movement (dynamic proprioception). Although position sense has been well characterized, dynamic proprioception has remained difficult to isolate and measure. Here we introduce a continuous proprioceptive tracking paradigm, coupled with computational modelling, that captures dynamic proprioception in real time. We first establish that this approach is sensitive, reliable and efficient. Leveraging this method, we then show that dynamic proprioception provides faster and more faithful estimates of limb state than vision, dominates multisensory state estimation when vision is also available, and is not correlated with conventional measures of position sense. Together, these findings provide a new quantitative framework for characterizing dynamic proprioception in health and disease.

neuroscience↗

bioRxiv2026

Motor Learning and Transfer Are Symmetric Across Hands

Functional asymmetry between the cerebral hemispheres is a defining feature of the sensorimotor system, with the dominant hemisphere playing a central role in motor control. Whether motor learning is similarly lateralized, however, remains unresolved. To tackle this question, we combined a comprehensive meta-analysis (114 datasets) with a series of well-powered, preregistered experiments (N = 526) to test two core behavioral predictions of hemispheric lateralization in sensorimotor adaptation, a canonical form of motor learning: (1) adaptation is preferentially expressed in the dominant hand and (2) transfers asymmetrically between limbs. Across both approaches, we found that adaptation and interlimb transfer were strikingly symmetric. Together, these findings support a fundamental dissociation in the neural organization of skilled behavior: whereas motor control is lateralized to the dominant hemisphere, motor learning is supported by a neural architecture that functions symmetrically.

neuroscience↗

bioRxiv2026

Cervical spinal cord stimulation disrupts proprioception yet improves voluntary arm reaching

Whether proprioception is necessary for upper-limb motor control has been debated for decades. Classic studies in deafferented animals and humans suggested that proprioception may be dispensable for rapid, goal-directed movements. However, chronic sensory loss conflates the absence of proprioceptive input with years of compensatory adaptation. As a result, the field has lacked a strong causal test of proprioceptions contribution to motor control. Here, we leveraged a clinical trial of cervical spinal cord stimulation (SCS) in individuals with chronic post-stroke hemiparesis to study if electrical stimulation of sensory afferents causally perturbs proprioception and affects arm reaching. We found that turning SCS ON causally impaired proprioceptive perception and postural stabilization in response to force perturbations, and enhanced adaptation to visual errors during implicit learning. Yet visually and non-visually rapid, goal-directed reaching improved in smoothness, straightness and spatial accuracy. These findings provide strong causal evidence that proprioception is not required for rapid, goal-directed action, helping resolve a decades-long debate regarding its necessity for effective movement.

bioengineering↗

bioRxiv2025

Hypothesis Testing Governs an Efficiency-Flexibility Trade-off in Strategic Motor Learning

It remains unknown how people discover an effective movement strategy when the environment changes (e.g., when adapting to a new computer trackpad). We propose that strategic adaptation operates through hypothesis testing: learners generate candidate hypotheses, discard those inconsistent with feedback, and iteratively refine their actions through practice. A core prediction of this account is an efficiency-flexibility trade-off. In constrained environments, where few hypotheses are viable, learning slows as people eliminate competing hypotheses but supports broader generalization. In unconstrained environments, where many hypotheses are viable, learning accelerates as learners adopt one of many expedient hypotheses but yields poorer generalization. In two reaching experiments (N = 560), we varied the arrangement of target positions to manipulate how tightly the hypothesis space was constrained. As predicted, the constrained group learned more slowly but generalized more--an efficiency- flexibility trade-off that highlights hypothesis testing as a novel process governing human motor learning.

neuroscience↗

bioRxiv2025

Minimal Impact of Low Vision on Explicit Sensorimotor Adaptation

Rehabilitation from motor system dysfunction relies on learning deliberate motor corrections through practice and feedback. This is called explicit motor adaptation. One key source of feedback for this adaptation is the visual error signal between the intended movement and the achieved movement. As people age, both motor dysfunction and visual impairment become more common, potentially compromising the visual feedback signal. Previous work has shown that visual impairment can disrupt the implicit, automatic adjustments made by the sensorimotor system. But how visual impairment influences the explicit motor adaptation, a cornerstone of rehabilitation, remains unknown. To address this gap, we recruited individuals with low vision--defined as uncorrectable visual impairment resulting in functional vision loss--and age-matched controls to complete a visuomotor task designed to isolate two components of explicit motor adaptation: discovering a new deliberate sensorimotor strategy and recalling a previously learned one. Surprisingly, low vision had no measurable impact on either component. Despite reduced visual fidelity, individuals with low vision were as effective as controls in both discovering and retrieving successful explicit sensorimotor strategies. These results highlight potential mechanisms that can be leveraged in rehabilitation.

neuroscience↗

bioRxiv2025

Goal Uncertainty Attenuates Sensorimotor Adaptation

Implicit sensorimotor adaptation--the automatic correction of movement errors through feedback and practice--is driven by a perceptual prediction error, the mismatch between the perceived movement outcome and its intended goal. While perceptual uncertainty is known to attenuate adaptation, the impact of goal uncertainty on adaptation remains unknown. We employed a visuomotor adaptation task that isolates implicit adaptation (N = 180), manipulating goal uncertainty by varying how precisely the goals midpoint could be identified. Display format was varied independently to control for the objective size of visual features, and targets were hidden at movement onset, ensuring identical visual input at the moment the error was experienced. We found that goal uncertainty significantly attenuated implicit adaptation, independent of low-level visual and kinematic features. Together, these results demonstrate that a precise internal representation of the goal is essential for supporting implicit sensorimotor adaptation.

neuroscience↗

bioRxiv2025

Target configuration determines how and what we learn during sensorimotor adaptation

Motor adaptation--the process of correcting movement errors through feedback and practice--is a fundamental human capacity that keeps our actions well-calibrated amid changes in the environment and the body. However, how training context--specifically, the configuration of targets in the workspace--shapes how we learn and what we learn during motor adaptation remains unknown. To investigate this, we conducted two reaching experiments in which participants experienced a visuomotor gain perturbation, with feedback scaled to 1.3x (Exp 1) or 0.7x (Exp 2) the actual movement distance. In both experiments, participants were assigned to either the Extent Group, which trained with targets of varying amplitudes in a single direction, or the Angular Group, which trained with targets of equal amplitude in different directions. We found marked differences in how the two groups learned: the Angular Group learned more implicitly than the Extent Group, as evidenced by larger post-perturbation aftereffects when participants were instructed to forgo re-aiming strategies. Just as striking were the differences in what the two groups learned: the Angular Group learned a translation rule, which generalized to new directions but not amplitudes, while the Extent Group learned the imposed gain rule, which generalized to new amplitudes but not directions. Together, these findings underscore the importance of training context in determining how and what we learn.

neuroscience↗

bioRxiv2025

Large Reaching Datasets Quantify the Impact of Age, Sex/Gender, and Experience on Motor Control

As we age, our movements become slower and less precise--but the extent of this decline remains unclear. To address this, we harmonized data from 2,185 participants across four published studies using a standard center-out reaching task. We found that older age was associated with a steady decline in reaction time (- 1.2 ms/year), movement time (-2.3 ms/year), and movement precision (-0.02{o}/year). Although the rate of decline did not differ by sex/gender, females consistently reacted more slowly (-8 ms), moved more slowly (-37 ms), and exhibited greater precision (+0.5{o}) across the adult lifespan. Notably, sex/gender differences attenuated after accounting for experiential factors such as video game use and the amount of sleep per day, whereas age remained a robust and consistent predictor of motor decline. Together, these findings provide a large-scale quantification of age, sex/gender, and experiential effects on motor control, offering a normative benchmark to inform future clinical interventions aimed at preserving motor function across the lifespan.

neuroscience↗

bioRxiv2024

Differential Aging Effects on Implicit and Explicit Sensorimotor Learning

Deterioration in motor control is a hallmark of aging, significantly contributing to a decline in quality of life. More controversial is the question of whether and how aging impacts sensorimotor learning. We hypothesized that the inconsistent picture observed in the current literature can be attributed to at least two factors. First, aging studies tend to be underpowered. Second, the learning assays used in these experiments tend to reflect, to varying degrees, the operation of multiple learning processes, making it difficult to make inferences across studies. We took a two-pronged approach to address these issues. We first performed a meta-analysis of the sensorimotor adaptation literature focusing on outcome measures that provide estimates of explicit and implicit components of adaptation. We then conducted two well-powered experiments to re-examine the effect of aging on sensorimotor adaptation, using behavioral tasks designed to isolate explicit and implicit processes. Convergently, both approaches revealed a striking dissociation: Older individuals exhibited a marked impairment in their ability to discover an explicit strategy to counteract a visuomotor perturbation. However, they exhibited enhanced implicit recalibration. We hypothesize that the effect of aging on explicit learning reflects an age-related decline in reasoning and problem solving, and the effect of aging on implicit learning reflects age-related changes in multisensory integration. Taken together, these findings deepen our understanding of the impact of aging on sensorimotor learning.

neuroscience↗

bioRxiv2024

Motor adaptation is reduced by symbolic compared to sensory feedback

Motor adaptation - the process of reducing motor errors through feedback and practice - is an essential feature of human competence, allowing us to move accurately in dynamic and novel environments. Adaptation typically results from sensory feedback, with most learning driven by visual and proprioceptive feedback that arises with the movement. In humans, motor adaptation can also be driven by symbolic feedback. In the present study, we examine how implicit and explicit components of motor adaptation are modulated by symbolic feedback. We conducted three reaching experiments involving over 400 human participants to compare sensory and symbolic feedback using a task in which both types of learning processes could be operative (Experiment 1) or tasks in which learning was expected to be limited to only an explicit process (Experiments 2 and 3). Adaptation with symbolic feedback was dominated by explicit strategy use, with minimal evidence of implicit recalibration. Even when matched in terms of information content, adaptation to rotational and mirror reversal perturbations was slower in response to symbolic feedback compared to sensory feedback. Our results suggest that the abstract and indirect nature of symbolic feedback disrupts strategic reasoning and/or refinement, deepening our understanding of how feedback type influences the mechanisms of sensorimotor learning.

neuroscience↗

bioRxiv2024

The Origin of Movement Biases During Reaching

Goal-directed movements can fail due to errors in our perceptual and motor systems. While these errors may arise from random noise within these sources, they also reflect systematic motor biases that vary with the location of the target. The origin of these systematic biases remains controversial. Drawing on data from an extensive array of reaching tasks conducted over the past 30 years, we evaluated the merits of various computational models regarding the origin of motor biases. Contrary to previous theories, we show that motor biases do not arise from systematic errors associated with the sensed hand position during motor planning or from the biomechanical constraints imposed during motor execution. Rather, motor biases are primarily caused by a misalignment between eye-centric and body-centric representations of position. This model can account for motor biases across a wide range of contexts, encompassing movements with the right versus left hand, finger versus hand movements, visible and occluded starting positions, as well as before and after sensorimotor adaptation.

neuroscience↗

bioRxiv2023

Implicit reward-based motor learning

Binary feedback, providing information solely about task success or failure, can be sufficient to drive motor learning. While binary feedback can induce explicit adjustments in movement strategy, it remains unclear if this type of feedback also induce implicit learning. We examined this question in a center-out reaching task by gradually moving an invisible reward zone away from a visual target to a final rotation of 7.5{degrees} or 25{degrees} in a between-group design. Participants received binary feedback, indicating if the movement intersected the reward zone. By the end of the training, both groups modified their reach angle by about 95% of the rotation. We quantified implicit learning by measuring performance in a subsequent no-feedback aftereffect phase, in which participants were told to forgo any adopted movement strategies and reach directly to the visual target. The results showed a small, but robust (2-3{degrees}) aftereffect in both groups, highlighting that binary feedback elicits implicit learning. Notably, for both groups, reaches to two flanking generalization targets were biased in the same direction as the aftereffect. This pattern is at odds with the hypothesis that implicit learning is a form of use-dependent learning. Rather, the results suggest that binary feedback can be sufficient to recalibrate a sensorimotor map.

neuroscience↗

bioRxiv2023

Perturbation Variability Does Not Influence Implicit Sensorimotor Adaptation

Cerebellar-dependent implicit adaptation has been regarded as a rigid process that automatically operates in response to movement errors in order to keep the sensorimotor system calibrated. This hypothesis has been challenged by recent evidence suggesting flexibility in this learning process. One compelling line of evidence comes from work suggesting that this form of learning is context-dependent, with the rate of learning modulated by error history. Specifically, learning was attenuated in the presence of perturbations exhibiting high variance compared to when the perturbation is fixed. However, these findings are confounded by the fact that the adaptation system corrects for errors of different magnitudes in a non-linear manner, with the adaptive response increasing in a proportional manner to small errors and saturating to large errors. Through simulations, we show that this non-linear motor correction function is sufficient to explain the effect of perturbation variance without referring to an experience-dependent change in error sensitivity. Moreover, by controlling the distribution of errors experienced during training, we provide empirical evidence showing that there is no measurable effect of perturbation variance on implicit adaptation. As such, we argue that the evidence to date remains consistent with the rigidity assumption.

neuroscience↗

bioRxiv2023

Implicit motor adaptation and perceived hand position without proprioception: A kinesthetic error may be derived from efferent signals

Implicit sensorimotor adaptation keeps our movements well-calibrated amid changes in the body and environment. We have recently postulated that implicit adaptation is driven by a perceptual error: the difference between the desired and perceived movement outcome. According to this perceptual re-alignment model, implicit adaptation ceases when the perceived movement outcome - a multimodal percept determined by a prior belief conveying the intended action, the motor command, and feedback from proprioception and vision - is aligned with the desired movement outcome. Here, we examined the role of proprioception in implicit motor adaptation and perceived movement outcome by examining individuals who lack proprioception. We used a modified visuomotor rotation task designed to isolate implicit adaptation and probe perceived outcome throughout the experiment. Surprisingly, implicit adaptation and perceived outcome were minimally impacted by deafferentation, posing a challenge to the perceptual re-alignment model of implicit adaptation.

neuroscience↗

bioRxiv2022

Cerebellar degeneration impairs strategy discovery but not strategy recall

The cerebellum is recognized to play a critical role in the automatic and implicit process by which movement errors are used to keep the sensorimotor system precisely calibrated. However, its role in other learning processes frequently engaged during sensorimotor adaptation tasks remains unclear. In the present study, we tested the performance of individuals with cerebellar degeneration on a variant of a visuomotor adaptation task in which learning requires the use of strategic re-aiming, a process that can nullify movement errors in a rapid and volitional manner. Our design allowed us to assess two components of this learning process, the discovery of an appropriate strategy and the recall of a learned strategy. Participants were exposed to a 60{degrees} visuomotor rotation twice, with the initial exposure block assessing strategy discovery and the re-exposure block assessing strategy recall. Compared to age-matched controls, individuals with cerebellar degeneration were slower to derive an appropriate aiming strategy in the initial Discovery block but exhibited similar recall of the aiming strategy during the Recall block. This dissociation underscores the multi-faceted contributions of the cerebellum to sensorimotor learning, highlighting one way in which this subcortical structure facilitates volitional action selection.

neuroscience↗

bioRxiv2022

Signatures of contextual interference in implicit sensorimotor adaptation

Contextual interference refers to the phenomenon whereby a blocked practice schedule results in faster acquisition but poorer retention of new motor skills compared to a random practice schedule. While contextual interference has been observed under a broad range of tasks, it remains unclear if this effect generalizes to the implicit and automatic recalibration of an overlearned motor skill. To address this question, we compared blocked and random practice schedules on a reaching task in which we used a feedback perturbation method that isolates implicit adaptation. The degree of implicit adaptation was quantified as the change in hand angle in the opposite direction of the perturbation, and retention was quantified as the percent of adaptation remaining after visual feedback was extinguished. In two experiments, participants tested under a random practice schedule exhibited slower implicit adaptation, but better retention compared to participants tested under a blocked practice schedule, the signature of contextual interference. These results indicate that contextual interference is not limited to the acquisition of new motor skills but also applies to the implicit adaptation of established motor skills.

neuroscience↗

bioRxiv2022

Implicit sensorimotor adaptation is preserved in Parkinson's Disease

Our ability to enact successful goal-directed actions involves multiple learning processes. Among these processes, implicit motor adaptation ensures that the sensorimotor system remains finely tuned in response to changes in the body and environment. Whether Parkinsons Disease (PD) impacts implicit motor adaptation remains a contentious area of research: whereas multiple reports show impaired performance in this population, many others show intact performance. While there are a range of methodological differences across studies, one critical issue is that performance in many of the studies may reflect a combination of implicit adaptation and strategic re-aiming. Here, we revisited this controversy using a visuomotor task designed to isolate implicit adaptation. In two experiments, we found that adaptation in response to a wide range of visual perturbations (3{degrees} - 45{degrees}) was similar in PD and matched control participants. Moreover, in a meta-analysis of previously published work, we found that the mean effect size contrasting PD and controls across 16 experiments was not significant. Together, these analyses indicate that implicit adaptation is preserved in PD, offering a fresh perspective on the role of the basal ganglia in sensorimotor learning. Significance statementAmong multiple motor learning processes, implicit adaptation ensures that our motor system remains exquisitely calibrated. Whether Parkinsons disease affects implicit motor adaptation has been a point of controversy. We revisited this issue using a visuomotor task designed to isolate implicit adaptation and found that individuals with PD and matched controls showed indistinguishable performance. A meta-analysis based on data from 16 previous experiments yielded a similar null result, strongly supporting the notion that implicit adaptation is preserved in PD.

neuroscience↗