Biology subjects

Gonzalez-Rubio, M.

Publications and source records attributed to Gonzalez-Rubio, M..

4 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

Explicit control of step timing during split-beltwalking reveals interdependent recalibrationof movements in space and time

Split-belt treadmills that move the legs at different speeds are thought to update internal representations of the environment, such that this novel condition generates a new locomotor pattern with distinct spatio-temporal features compared to those of regular walking. It is unclear the degree to which such recalibration of movements in the spatial and temporal domains is interdependent. In this study, we explicitly altered subjects limb motion in either space or time during split-belt walking to determine its impact on the adaptation of the other domain. Interestingly, we observed that motor adaptation in the spatial domain was susceptible to altering the temporal domain, whereas motor adaptation in the temporal domain was resilient to modifying the spatial domain. This nonreciprocal relation suggests a hierarchical organization such that the control of timing in locomotion has an effect on the control of limb position. This is of translational interest because clinical populations often have a greater deficit in one domain compared to the other. Our results suggest that explicit changes to temporal deficits cannot occur without modifying the spatial control of the limb.

neuroscience↗