Biology subjects

't Hart, B. M.

Publications and source records attributed to 't Hart, B. M..

At least 19 recordsLinked to original sources

bioRxiv2026

Vibrotactile stimulation on the upper back requires stronger vibration during goal-directed reaching but does not impede reaching performance

Vibrotactile stimulation is a promising method of biofeedback, with potential applications for ergonomic posture and balance, rehabilitation, and motor learning. These applications require balancing tactile perception with motor performance and cognitive workload. In this study, participants performed a detection task, a reaching task, and a concurrent reach-and-detect task, with vibrotactile signals delivered on the hand or upper back. Sensitivity to stimuli, motor performance, and cognitive workload were compared for each task. Sensitivity was suppressed during movement, but this suppression was greater on hand compared to the upper back. Movement time was slowed by vibration on the hand but not the upper back. Mental workload and task complexity increased for the reach-and-detect task compared to the individual tasks. We conclude that vibrotactile feedback devices worn on the upper back do not impede motor performance, with only minor tactile suppression. This could be overcome by presenting highly salient or personalized feedback.

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bioRxiv2026

Learning Environmental Dynamics: Building Internal Models of a Simulated External Force

Motor adaptation is typically studied using limb-based perturbations in highly constrained tasks. However, everyday actions require compensating for uncertain environmental dynamics impacting manipulated objects within redundant execution spaces, where multiple combinations of variables can achieve success. To investigate this, we designed a novel virtual reality task where participants launched a ball across a lateral water current to spatially distinct targets. Two experiments (2.0 m/s and 3.0 m/s) tested if classic adaptation signatures remain consistent across varying perturbation sizes. Results revealed three key signatures. First, participants exhibited robust error reduction to all targets during training. Second, between-subjects analyses revealed that this learning produced substantial, immediate transfer to untrained target locations. Finally, persistent motor aftereffects appeared upon perturbation removal, despite explicit cues indicating absence of the perturbation. Together, these results demonstrate that humans form internal models under altered projectile-environment dynamics, and that prior experience facilitates broad generalization across the workspace.

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bioRxiv2026

Rotation size drives heterogeneous explicit strategy development in motor adaptation

Humans rapidly adapt their movements to compensate for changes in the environment, yet how explicit movement strategies emerge during adaptation remains poorly understood. These strategies have traditionally been described by using a smooth, exponential learning curve, suggesting a relatively uniform pattern of strategy development across individuals (Taylor et al., 2014; McDougle et al., 2015). However, recent results suggest substantial variability in how individuals develop explicit aiming strategies, such as abrupt transitions (D'Amario et al., 2024; Townsend et al., 2026), or exploratory periods, or delayed stabilization of compensatory behaviour (Tsay et al., 2024), and some participants never developing a strategy. These findings raise the possibility that smooth group-averaged learning curves may obscure meaningful heterogeneity in individual strategy development. This study therefore examines whether explicit strategy development follows distinct individual-level patterns and whether these dynamics are influenced by perturbation size. Participants completed a visuomotor rotation reaching task where a cursor they controlled with their unseen, right hand was rotated around the home position using one of five perturbations (20, 30, 40, 50, and 60 degrees). Before each reach, participants reported their explicit strategy by aiming an arrow to indicate their planned hand movement direction. Based on previous findings, we hypothesized that participants would exhibit at least three distinct patterns of explicit strategy development emerged: 1) gradual/incremental, 2) stepwise, and 3) exploratory. Instead, participants were distributed along a continuum of strategy development profiles, with different regions along this continuum resembling these previous proposed patterns. Where learners fell along this continuum varied with perturbation magnitude, such that larger rotations associated with greater exploratory behaviour and proportion of strategy-use. Our findings reveal substantial heterogeneity in how explicit strategies emerge during visuomotor adaptation and suggest that smooth group-averaged learning curves may obscure important individual differences in learning dynamics. Notably, perturbation magnitude appears to systematically influence where individuals fall along this continuum, providing a potential mechanism for understanding how explicit strategies emerge and stabilize over time.

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bioRxiv2025

EEG Dynamics of Movement Preparation and Error Processing Distinguish Motor Adaptation From De Novo Learning

Previous research has distinguished behavioral mechanisms between motor adaptation and de novo learning. However, electroencephalography (EEG) markers dissociating them remain unclear. Here, participants (N = 32, 13 female) performed center-out reaching under a 30{degrees} fixed rotation (adaptation), mirror reversal (de novo learning), or random rotation (errors without learning), while we recorded EEG during movement preparation and post-movement feedback. We explored how perturbation type, training phase, and error magnitude shaped neural dynamics in both temporal and frequency domains. During preparation, the readiness potential (RP) showed opposite training-related modulation in the fixed and random rotations, suggesting increased reliance on updated internal models for adaptation. Mirror reversal training showed no RP change, likely reflecting reliance on effortful, explicit learning. Interestingly, we found that Lateralized Readiness Potentials (LRPs) reflected planned movement direction rather than effector-specific preparation. In the frequency domain, beta attenuation for large errors and alpha synchronization for small errors were more pronounced in the fixed rotation than in the mirror reversal, suggesting greater error-sensitivity during adaptation. During post-movement feedback, P3 amplitude decreased from early to late learning in the fixed and random rotations but remained stable in the mirror reversal, highlighting differences in cognitive demands across perturbations. A sustained late positivity emerged following small errors across perturbations, potentially indexing implicit learning. Random rotations also elicited distinct frontal and central beta modulation, likely reflecting disengagement due to task unpredictability. Together, we show that preparatory and feedback-related EEG signatures differ across perturbation types, revealing distinct neural mechanisms underlying motor adaptation and de novo learning. Significance statementUnderstanding how the brain supports skill acquisition and adaptation is critical for advancing theories and applications of motor learning. Although behavioral differences between motor adaptation and de novo learning are well established, the neural processes that distinguish them remain unclear. By comparing EEG activity during movement preparation and feedback-error processing across multiple perturbation types, we uncover distinct temporal and frequency domain signatures that uniquely characterize each learning process. Our findings show that adaptation engages neural dynamics consistent with updating internal models and error-processing, whereas de novo learning relies on explicit, cognitively demanding strategies that likely unfold over extended practice. These results provide a clear neural framework for distinguishing motor learning mechanisms.

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bioRxiv2025

Frame Effects Across Space and Time

When two probes are flashed at different times within a moving frame they can be perceived as dramatically separated from each other even though they are at the same location in the display. This effect suggests that we perceive object position relative to the surrounding frame even when it is moving (Ozkan et al., 2021). Here, 8 experiments reveal new properties of this frame effect. First, the influence of the frame on the perceived probe positions extends beyond its bounding contours by several degrees of visual angle, both in the direction of the frames motion and orthogonal to it. It is also undiminished when the probes and the frame are in different depth planes. However, the influence of the frames motion shows no extension in time - there is no effect on probes presented after the frame is removed and none retroactively before the frame appears either. The frame effect is also driven primarily by the displacement of the frame, not by its motion signals: the effect is stronger for moving bounded frames compared to moving, unbounded random-dot textures. When the bounded region has an internal texture that moves with or against the frames motion or remains static, it is the displacement of the frame that produces the perceived position shifts of the probes, while the effect of the internal motion is mostly suppressed. The frames influence is unaffected by whether the motion is self-initiated or not and does not reduce in strength across 2 hours of testing.

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bioRxiv2025

Saturation, Task Error, and Feedback Timing Shape Early Implicit Adaptation

Motor adaptation is essential for maintaining coordination and precision in daily activities. Implicit motor adaptation--adaptation that occurs without conscious awareness--is thought to be primarily driven by sensory prediction errors. Here, we investigated how rapidly these unconscious changes in reaching behavior emerge as a function of error magnitude and the availability of task error signals. To this end, we employed a single-trial learning (STL) paradigm within a classical visuomotor rotation task. Participants made center-out reaching movements to either small (dot) or large (arc) targets while experiencing single perturbation trials with cursor rotations ranging from 1{degrees} to 90{degrees}, each followed by an aligned washout trial. By manipulating target size, we systematically modulated the presence of task error while holding sensory prediction error constant. We further compared these early implicit changes with those observed during standard prolonged adaptation to a fixed 20{degrees} rotation across >100 trials. Our results show that implicit adaptation emerges rapidly, even after a single exposure to small perturbations, and follows a saturating, fixed-rate response profile. Importantly, the magnitude of single-trial adaptation was greater when task error was present (small targets) compared with conditions in which only sensory prediction error was available (large targets). Moreover, STL-derived parameters moderately predicted the initial phase of adaptation during prolonged learning, suggesting that STL captures core dynamics of early implicit processes. These findings provide new insight into the mechanistic principles governing implicit motor adaptation. By identifying the parameters that drive early-stage error-based learning, this work refines current models of sensorimotor learning and highlights potential strategies for designing targeted training or rehabilitation protocols that leverage rapid adaptation processes to enhance motor performance and recovery.

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bioRxiv2025

Using Tools as Cues for Motor Adaptation in Virtual Reality

Humans are adept at using multiple tools, often switching between them even when each involves distinct and potentially conflicting motor demands. This study investigated how different features of a tool influence the formation of distinct motor memories during dual adaptation to opposing visuomotor perturbations. Using an immersive virtual reality (VR) setup, participants performed an aiming task in which they launched a ball toward a target using virtual tools, each consistently associated with a different visuomotor rotation. We manipulated tool features across three groups: one in which tools differed only in colour (Colour Control), one in which they differed in shape but involved similar movement patterns (Motor Congruent), and one in which they differed both in shape and in how they were operated--for example, a paddle-like forward swing to propel the ball versus a draw-and-release motion similar to a slingshot (Motor Incongruent). A fourth control group that adapted to a single perturbation with a single tool at a time was also included. Only the Motor Incongruent group demonstrated robust dual adaptation and clear aftereffects, comparable to those observed during single-tool learning. These results suggest that distinct modes of tool operation play a critical role in supporting the formation and retention of separate internal models during sensorimotor adaptation. New & NoteworthyHumans often switch between tools with conflicting motor demands. Using immersive virtual reality, we tested whether visual features or operational differences support dual adaptation to opposing visuomotor perturbations. Only when tools differed in both shape and mode of operation did participants show robust adaptation and aftereffects, comparable to single-tool learning. These findings highlight the critical role of movement-relevant cues in forming distinct motor memories for flexible tool use.

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bioRxiv2025

Tool and hand adaptation and localization in immersive virtual reality

The human brain readily adapts movements to achieve motor goals. Most visuomotor adaptation studies use planar reaching with a cursor, where misaligned feedback leads to compensatory adjustments, reach aftereffects, and shifts in perceived hand location. Whether these effects extend to more natural settings and tool use remains unclear. In the Hand Experiment, we showed that in immersive virtual reality (VR), adaptation to 30{degrees} and 60{degrees} visuomotor rotations produced robust reach aftereffects and the expected shifts in hand localization. In the Pen Experiment, we extended this paradigm to a familiar hand-held tool, assessing localization of both the tool tip and the hand. Adaptation with the pen induced comparable or greater recalibration effects than with the hand-cursor, including shifts in both perceived tool and hand position. These findings demonstrate that visuomotor adaptation in immersive VR generalizes beyond cursor-based tasks, revealing how the sensorimotor system recalibrates internal representations of both the body and tools in realistic 3D environments. Author summary for PLOS ONEThis study shows that when people adapt their movements in virtual reality, the brain recalibrates not only the sensed position of the hand but also of familiar tools, highlighting how we update body and tool representations in everyday-like environments.

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bioRxiv2025

Precision of reaches and proprioception in motor control and adaptation

How do precision of movement and proprioception influence motor control and adaptation? Several theories--such as the exploration-exploitation hypothesis--propose that variability plays a key role in motor performance and learning. However, empirical measures of motor and proprioceptive precision are often limited by small sample sizes, and proprioceptive estimates, especially those relying on efferent signals, are difficult to isolate and quantify. In this study, we leveraged a large dataset of 270 participants--including a subsample of older adults (ages 54- 84)--to assess the precision of hand movements and proprioceptive estimates, and to examine whether these factors predict individual differences in motor learning and adaptation. We found that baseline reach variance did not predict learning or changes in hand localization. Although active hand localization (which includes efferent contributions) was slightly more precise--showing an 8.6% reduction in variance--this suggests that unseen hand estimates rely primarily on proprioception. Neither motor nor sensory precision varied with age. However, reach aftereffects were modestly associated with proprioceptive precision before training and proprioceptive recalibration after training. No other measure of learning or variance was reliably associated. These findings suggest that reach aftereffects may partly reflect changes in hand proprioception, but overall, we identified no predictors of adaptation to a rotated visual cursor.

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bioRxiv2024

Implicit Adaptation is Fast, Robust and Independent from Explicit Adaptation

During classical visuomotor adaptation, the implicit process is believed to emerge rather slowly; however, recent evidence has found this may not be true. Here, we further quantify the time-course of implicit learning in response to diverse feedback types, rotation magnitudes, feedback timing delays, and the role of continuous aiming on implicit learning. We find that implicit learning unfolds at a higher rate than conventionally expected in all feedback conditions. Increasing rotation size not only raises asymptotes, but also generally heightens explicit awareness, with no discernible difference in implicit rates. Cursor-jump and terminal feedback, with or without delays, predominantly enhance explicit adaptation while slightly diminishing the extent or the speed of implicit adaptation. In a continuous aiming reports condition, there is no discernible impact on implicit adaptation, and implicit and explicit adaptation progress at indistinguishable speeds. Finally, investigating the assumed negative correlation as an indicator of additivity of implicit and explicit processes, we observe weak associations at best across conditions. Our observation of implicit learning early in training in all tested conditions signifies how fast and robust our innate adaptation system is.

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bioRxiv2024

Motor adaptation to environment changes predicting object behaviour can be flexible and implicit.

The human motor system can adapt to perturbations by updating existing models of motor control or by creating context-specific motor memories or strategies. We investigate if motor adaptation is context-informed when a perturbation is applied to either the throw direction of a ball, or the acceleration of the ball post-release during a virtual throw-to-target task. Using the visual slant of the task surface in an immersive virtual environment, we determine if the tendency for model updating is influenced by informative visual cues that predict perturbations to intended actions. Our findings reveal that perturbations resembling accelerations enabled flexible motor adaptation regardless of the presence of the slant cue. Perturbations in the throw direction conversely led to internal model updating. Additionally, visual slant properties of the task surface elicited implicit, slant-specific changes in performance. Our findings underscore the role of visual properties of both perturbations and environments in flexible motor learning.

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bioRxiv2023

Distinct learning, retention, and generalization in de novo learning

People correct for movement errors when acquiring new motor skills (de novo learning) or adapting well-known movements (motor adaptation). These two motor learning types should be distinct, as de novo learning establishes new control policies while adaptation modifies existing ones. Here, we distinguish between these two motor learning types, and assess de novo learning retention and generalization. In study 1, participants train with both 30{degrees} visuomotor rotation and mirror reversal perturbations, to compare adaptation and de novo learning respectively. We find no perturbation order effects, and that learning develops with similar rates and comparable asymptotes for both perturbations. Explicit instructions also provide an advantage during early learning in both perturbations. However, mirror reversal learning shows larger inter-participant variability. Furthermore, movement initiation is slower for the mirror perturbation, and we only observe reach aftereffects following rotation training. In study 2, we use a browser-based mirror reversal task to investigate learning retention and generalization to the untrained hand and across the workspace. Learning persists across three or more days, substantially transfers to the untrained hand, and to targets on both sides of the mirror axis. Our results show that behavioral mechanisms underlying motor skill acquisition are distinct from adapting well-known movements.

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bioRxiv2022

Motor adaptation does not differ when a perturbation is introduced abruptly or gradually

People continuously adapt their movements to ever-changing circumstances, and particularly in skills training and rehabilitation, it is crucial that we understand how to optimize implicit adaptation in order for these processes to require as little conscious effort as possible. Although it is generally assumed that the way to do this is by introducing perturbations gradually, the literature is ambivalent on the effectiveness of this approach. Here we test whether there are differences in motor performance when adapting to an abrupt compared to a ramped visuomotor rotation. Using a within-subjects design, we test this question under 3 different rotation sizes: 30{degrees}, 45{degrees}, and 60{degrees}, as well as in 3 different populations: younger adults, older adults, and patients with mild cerebellar ataxia. We find no significant differences in either the behavioural outcomes, or model fits, between abrupt and gradual learning across any of the different conditions. Neither age, nor cerebellar ataxia had any significant effect on motor adaptation either. These findings together indicate that motor adaptation is not modulated by introducing a perturbation abruptly compared to gradually, and is also unaffected by age or mild cerebellar ataxia.

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bioRxiv2022

Adapting to visuomotor rotations in stepped increments increases implicit motor learning

Human motor adaptation relies on both explicit conscious strategies and implicit unconscious updating of internal models to correct motor errors. Implicit adaptation is powerful, requiring less preparation time before executing adapted movements, but recent work suggests it is limited to some absolute magnitude regardless of the size of a visuomotor perturbation when the perturbation is introduced abruptly. It is commonly assumed that gradually introducing a perturbation should lead to improved implicit learning beyond this limit, but outcomes are conflicting. We tested whether introducing a perturbation in two distinct gradual methods can overcome the apparent limit and explain past conflicting findings. We found that gradually introducing a perturbation in a stepped manner, where participants were given time to adapt to each partial step before being introduced to a larger partial step, led to [~]80% higher implicit aftereffects of learning, but introducing it in a ramped manner, where participants adapted larger rotations on each subsequent reach, did not. Our results clearly show that gradual introduction of a perturbation can lead to substantially larger implicit adaptation, as well as identify the type of introduction that is necessary to do so.

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bioRxiv2022

Measures of Implicit and Explicit Adaptation Do Not Linearly Add

Moving effectively is essential for any animal. Thus, many different kinds of brain processes likely contribute to learning and adapting movement. How these contributions are combined is unknown. Nevertheless, the field of motor adaptation has been working under the assumption that measures of explicit and implicit motor adaptation can simply be added in total adaptation. While this has been tested, we show that these tests were insufficient. We put this additivity assumption to the test in various ways, and find that measures of implicit and explicit adaptation are not additive. This means that future studies should measure both implicit and explicit adaptation directly. It also challenges us to disentangle how various motor adaptation processes do combine when producing movements, and may have implications for our understanding of other kinds of learning as well. (data and code: https://osf.io/dh86e)

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bioRxiv2022

Rapid motor adaptation to bounce perturbations in online Pong game is independent from the visual tilt of the bouncing surface

Motor adaptation describes the ability of the motor system to counteract repeated perturbations in order to reduce movement errors. Most research in the field investigated adaptation in response to perturbations affecting the moving hand. Fewer studies looked at the effect of a perturbation applied to the movement target, however they used simplistic visual stimuli. In this study, we examined motor adaptation to perturbations affecting the motion of dynamic targets. In addition, we asked whether external visual cues in the environment could facilitate this process. To do so, participants were asked to play an online version of the Pong game in which they intercepted a ball bouncing off a wall using a paddle. A perturbation was applied to alter the post-bounce trajectory of the ball and the wall orientation was manipulated to be consistent or not with the ball trajectory. The "trained tilt" group (n = 34) adapted to the consistent condition and the "trained horizontal" group (n = 36) adapted to the inconsistent condition. In case participants optimally integrate external visual cues, the "trained tilt" group is expected to exhibit faster and/or more complete adaptation than the "trained horizontal" group. We found that the perturbation reduced interception accuracy. Participants showed large interception errors when the perturbation was introduced, followed by rapid error decrease and aftereffects (errors in the opposite direction) once the perturbation was removed. Although both experimental groups showed these typical markers of motor adaptation, we did not find differences in interception success rates or errors between the "trained tilt" and "trained horizontal" groups. Our results demonstrate that participants quickly adapted to the dynamics of the pong ball. However, the visual tilt of the bouncing surface did not enhance their performance. The present study highlights the ability of the motor system to adapt to external perturbations applied to a moving target in a more dynamical environment and in online settings. These findings underline the prospects of further research on sensorimotor adaptation to unexpected changes in the environment using more naturalistic and complex real-world or virtual reality tasks as well as gamified paradigms.

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bioRxiv2022

Exploring the frame effect

Probes flashed within a moving frame are dramatically displaced (Ozkan et al, 2021; Wong &Mack, 1981). The effect is much larger than that seen on static or moving probes (induced motion, Duncker, 1929; Wallach et al, 1978). These flashed probes are often perceived with the separation they have in frame coordinates -- a 100% effect. Here we explore this frame effect on flashed tests with several versions of the standard stimulus. We find that the frame effect holds for smoothly or abruptly displacing frames, even when the frame changed shape or orientation between the endpoints of its travel. The path could be non-linear, even circular. The effect was driven by perceived not physical motion. When there were competing overlapping frames, the effect was determined by which frame was attended. There were a number of constraints that limited the effect. A static anchor near the flashes suppressed the effect but an extended static texture did not. If the probes were continuous rather than flashed, the effect was abolished. The observational reports of 30 online participants suggest that the frame effect is robust to many variations in its shape and path and leads to a perception of flashed tests in their locations relative to the frame as if the frame were stationary. Our results highlight the role of frame continuity and of the grouping of the flashes with the frame in generating the frame effect.

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bioRxiv2022

Reduced feedback barely slows down proprioceptive recalibration

Introducing altered visual feedback of the hand results in quick adaptation of reaching movements. And while this may be partly due to explicit strategies, our lab has shown that implicit changes like reach aftereffects and shift in estimates of the unseen hand, can also emerge and even saturate within a few training trials. The goal of the current study is to determine whether these rapid changes in unseen hand position that occur during classical visuomotor adaptation are diminished or slowed when feedback during training is reduced. We reduced feedback by either providing visual feedback only at the end of the reach (terminal feedback) or constraining hand movements to reduce efferent contribution (exposure). We measured changes as participants completed reaches with a 30{degrees} rotation, a -30{degrees} rotation and clamped visual feedback, with these two "impoverished" training conditions, along with classical visuomotor adaptation training, while continuously estimating their felt hand position. Classic continuous-cursor training produced exemplary learning curves and rapid and robust shifts in felt hand position. Training with terminal feedback slightly reduced the initial rate of change in overall adaptation and but not the magnitude of shifts in felt hand position. Finally using a robot to constrain and deviate hand movement direction, called exposure training, only delayed saturation of proprioceptive changes by a single trial and these changes were slightly smaller than those during classical training. Taken together, adaptation and shifts in felt hand position are a rapid and robust responses to sensory mismatches and are only slightly modulated when feedback is reduced. This means that, given a visuo-proprioceptive mismatch, the resulting shift in sense of limb position can contribute to movements from the start of adaptation.

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