Biology subjects

Iturralde, P. A.

Publications and source records attributed to Iturralde, P. A..

6 recordsLinked to original sources

bioRxiv2026

Perceptual sensitivity supports online control, while perceptual errors drive motor memory formation during locomotor adaptation

1.To maintain stable locomotion, the nervous system must continually adapt, whether reacting to an unexpected perturbation, such as a trip on uneven terrain, or anticipating external demands, such as walking on snow, by forming and updating motor memories. Error-based learning is the dominant computational account of such adaptation, in which motor commands are updated to reduce prediction errors, that is, the mismatch between predicted and actual limb state. Yet this framework was largely defined in reduced, single-effector paradigms, where the sensory consequences of movement are isolated and the prediction error is directly observable. Whether the same principle governs whole-body, multi-segmental, multi-sensory behaviors such as walking has remained untested, owing in part to the challenge of identifying a behavioral proxy for prediction errors in this complex, dynamic setting. Here, we combined a split-belt treadmill paradigm with a novel method for quantifying perception of leg motion to address this open question. We found two perceptual contributions to locomotor adaptation: perceptual sensitivity predicted initial motor corrections during early adaptation, whereas perceptual errors (i.e., the mismatch between perceived and observed leg speed) predicted the magnitude of motor aftereffects during post-adaptation. Together, these findings demonstrate that locomotor adaptation is fundamentally constrained by perception of limb motion. Our results identify perceived limb motion as a behavioral proxy for prediction errors, establishing error-based learning, long characterized in reduced tasks, as a core computational principle underlying human locomotion. 2. SignificanceError-based learning is the dominant account of how the brain adapts movement, yet it was defined almost entirely in reduced laboratory tasks, such as cursor rotations, planar reaching, and saccades, where prediction errors are directly observable. Whether it governs whole-body behaviors such as walking has remained untested. Using a novel measure of leg-motion perception during split-belt walking, we show that two dimensions of perception contribute separably to adaptation. Perceptual sensitivity, a proxy for sensory uncertainty, relates to real-time motor corrections, consistent with Bayesian integration. Perceptual error, a proxy for the prediction error that underlies error-based learning, relates to motor memory formation. These findings establish leg-motion perception as a behavioral window onto the computations driving locomotor adaptation, providing a framework for understanding individual and clinical variability in motor behavior.

bioengineering↗

bioRxiv2025

Webers Law in walking: sensory scaling is observed in multi-sensory, dynamic tasks

We frequently adjust our behaviors in response to environmental changes. This behavioral flexibility requires adequate sensitivity to external stimuli to maintain optimal motor performance under evolving task demands. There is abundant empirical evidence that sensitivity scaling follows Webers Law. Webers Law states that the perception of a sensory stimulus is scaled by the magnitude of the background sensory context. However, Webers Law has so far been assessed only in uni-sensory static tasks, and it remains an open question whether this principle extends to multi-sensory, dynamic motor tasks. To address this question, we assessed somatosensory perception of relative leg motion (i.e., speed differences between right and left legs) in healthy young adults. We hypothesized that sensitivity to differences in leg speed would follow Webers Law. We estimated participants sensitivity to speed differences (sensory stimuli) using two-alternative forced choice (2AFC) tasks. Participants walked at a testing speed representing distinct sensory contexts: slow speed (low-intensity sensory context), comfortable speed (medium-intensity sensory context), and fast speed (high-intensity sensory context). All groups compared their assigned testing speed against a common reference speed. We found that sensitivity to speed differences followed Webers Law at both slow and fast non-habitual walking speeds, but this scaling differed when walking near the comfortable walking speed. Moreover, Webers Law scaling was reproduced by a drift-diffusion model that used only reaction times to quantify sensitivity, indicating that the evidence accumulation process described by the model can account for Webers Law scaling in multi-sensory, dynamic motor tasks, as well as in static, uni-sensory tasks. Author summaryAdapting motor behaviors to environmental changes requires precise sensory perception to maintain optimal performance. Webers Law, a fundamental principle of psychophysics, describes how sensory perception is scaled relative to background stimulus intensity to prevent sensory overload; however, its applicability to multi-sensory dynamic motor behaviors like locomotion remains unclear. Our results show that Webers Law partially explains how we perceive leg movement differences during walking. We found that sensitivity to speed differences scales following Webers Law when walking at non-habitual slow or fast speeds. However, near comfortable walking, people are actually more sensitive than at other speeds, departing from Webers Law. A drift-diffusion model replicated Webers Law scaling during walking, showing that the same mechanistic framework can explain the scaling of sensation in both static, uni-sensory tasks and dynamic, multi-sensory activities like walking.

bioengineering↗

bioRxiv2020

High-human acuity of speed asymmetry during walking

1Despite its central role in the proper functioning of the motor system, sensation has been less studied than motor output in sensorimotor adaptation paradigms. This deficit is probably due to the difficulty of measuring sensation: while motor output has easily observable consequences, sensation is by definition an internal variable of the motor system. In this study we asked how well can subjects estimate relevant environmental changes inducing motor adaptation. We addressed this question in the context of walking on a split-belt treadmill, which allows subjects to experience distinct belt speeds for each leg. We used a two-alternative forced-choice perceptual task (2AFC) in which subjects report which belt they thought to be moving slower. We characterized baseline accuracy in this task for healthy human subjects, and found 75% accuracy for 75 mm/s speed differences. Additionally, we used a drift-diffusion model of the task that could account for both accuracy and reaction times. We conclude that 2AFC tasks can be used to probe subjects estimates of the environment and that this approach opens an avenue for investigating perceptual deficits and its relation to motor impairments in clinical populations.

bioengineering↗

bioRxiv2019

Cerebral contribution to the execution, but not recalibration, of motor commands in a novel walking environment.

Human movements are flexible as they continuously adapt to changes in the environment by updating planned actions and generating corrective movements. Planned actions are updated upon repeated exposure to predictable changes in the environment, whereas corrective responses serve to overcome unexpected environmental transitions. It has been shown that corrective muscle responses are tuned through sensorimotor adaptation induced by persistent exposure to a novel situation. Here, we asked whether cerebral structures contribute to this recalibration using stroke as a disease model. To this end, we characterized changes in muscle activity in stroke survivors and unimpaired individuals before, during, and after walking on a split-belt treadmill moving the legs at different speeds, which has been shown to induce recalibration of corrective responses in walking in healthy individuals. We found that the recalibration of corrective muscle activity was comparable between stroke survivors and controls, which was surprising given then known deficits in feedback responses post-stroke. Also, the intact recalibration in the group of stroke survivors contrasted the patients limited ability to adjust their muscle activity during steady state split-belt walking compared to controls. Our results suggest that the recalibration and execution of motor commands in new environments are partially dissociable: cerebral lesions interfere with the execution, but not the recalibration, of motor commands upon novel movement demands.

neuroscience↗

bioRxiv2018

Augmenting cognitive load during split-belt walking increases the generalization of motor memories across walking contexts

Cognitive load plays a role on the movement recalibration induced by sensorimotor adaptation, but little is known about its impact on the generalization of movements from trained to untrained situations. We hypothesized that altering cognitive load by distracting subjects during sensorimotor adaptation would facilitate the generalization of recalibrated movements beyond the training condition. We reasoned that awareness of the novel condition inducing adaptation could be used to consciously contextualize movements to that particular situation. To test this hypothesis, young adults adapted their gait on a split-belt treadmill (moving their legs at different speeds) while they observed visual information that either distracted them or made them aware of the speed difference between their feet. We assessed the adaptation and aftereffects of spatial and temporal gait features known to adapt and generalize differently when walking on the treadmill or overground. We found similar adaptation and aftereffects on the treadmill across all groups. In contrast, both groups with altered cognitive load (i.e., distraction and awareness groups) generalized their movements from the treadmill to overground more than controls, who walked without altered cognitive load. Of note, this effect was only observed in temporal gait features, which are less susceptible to online motor adjustments, and were eliminated upon experiencing large errors by briefly removing the split perturbation during adaptation (i.e., catch trial). Taken together, increasing cognitive demands during sensorimotor adaptation facilitates the generalization of movement recalibration, but this cognitive-mediated effect cannot eliminate the specificity of actions due to context-specific errors.

neuroscience↗

bioRxiv2018

The adaptation of muscle activity during split-belt walking reveals age-dependent decline of motor learning

Recent studies suggest that planned and corrective actions are recalibrated during some forms of motor adaptation. However, corrective (a.k.a., reactive) movements in human locomotion are thought to simply reflect sudden environmental changes independently from sensorimotor recalibration. Thus, we asked if corrective responses can indicate the motor systems adapted state following prolonged exposure to a novel walking situation inducing sensorimotor adaptation. We recorded electromyographic signals bilaterally on 15 leg muscles before, during, and after split-belts walking (i.e., novel walking situation), in which the legs move at different speeds. We exploited the rapid temporal dynamics of corrective responses upon introduction or removal of an unexpected speed transition to isolate them from the overall motor output. We found that corrective muscle activity was structurally different following short vs. long exposures to split-belts walking. Only after a long exposure, removal of the novel environment elicited corrective muscle patterns that matched those expected in response to a perturbation opposite to the one originally experienced. This indicated that individuals who recalibrated their motor system adopted split-belts environment as their new "normal" and transitioning back to the original walking environment causes subjects to react as if it was novel to them. Interestingly, this learning declined with age, but steady state modulation of muscle activity during split-belts walking did not, suggesting potentially different neural mechanisms underlying these motor patterns. Taken together, our results show that corrective motor commands reflect the adapted state of the motor system, which is less flexible as we age. Significance statementWe showed that corrective muscle activity elicited by sudden environmental transitions is revealing of the underlying recalibration process during sensorimotor adaptation. This allowed us to identify age-related decline in motor learning that was not discernible from kinematic measures conventionally used in motor adaptation studies. These findings suggest that older populations may have limited potential to correct their movements through error-based protocols simply given their age. Moreover, we describe the distinct motor patterns recruited during and after the split condition, informing our understanding of the therapeutic effect of this task. Therefore, our detailed EMG characterization provides valuable normative data of muscle activity that could be reinforced with repeated exposure of split-belts walking.

neuroscience↗