Experimental Brain Research

Stabilizing the upright posture of the trunk relies on vestibular and proprioceptive afference. Previous studies found that the feedback responses to sensory afference vary between postures and tasks. We investigated whether and how vestibular and proprioceptive afference contribute to trunk stabilization during different postural tasks, and during walking at different speeds. Twelve healthy adults performed tasks in a random order: sitting, standing on the right foot or both feet, and treadmill walking at five speeds: 0.8, 2.0, 3.2, 4.3 and 5.5 km/h, while exposed to unilateral muscle vibration on the right paraspinal muscles at the level of the second lumbar vertebra, or to a step-like electrical vestibular stimulation (EVS) with the anode behind the left ear. The mediolateral displacements of markers at the sixth thoracic level and sacrum in the global coordinate system were used to evaluate the responses to sensory stimulation. No significant responses to EVS at T6 and sacrum level were found in sitting and standing. Responses to muscle vibration were significant and differed between unipedal standing compared to sitting and bipedal standing. The latter suggests a different interpretation of the sensation of muscle lengthening in these postures. During walking, the magnitude of the responses to both stimuli increased from very slow speeds to moderate speeds. From moderate to higher speeds, responses to muscle vibration decreased, whereas responses to EVS plateaued. These findings suggest speed-dependent modulation of vestibular and proprioceptive contributions in trunk stabilization during walking. Summary statementBy applying electrical vestibular stimulation and muscle vibration, we found that how vestibular and proprioceptive signals are used for trunk stabilization differs between postural tasks and walking speeds.

Issuing a goal-directed action requires specifying the goal of the action as well as planning the hand trajectory to obtain it. Accumulating results suggest that planning a straight point-to-point trajectory is more efficient and likely to involve simpler optimization process compared to the planning of trajectories with more complex shapes (e.g., curved trajectories). We sought to find evidence for the qualitative difference between the two planning modes through the investigation of reaction times (RT) in a pointing task performed with the wrist. In experiment 1, 18 subjects performed delayed straight and curved via-point reaching movements to arrays of 2 or 8 targets. Both trajectory type and number of possible targets affected RT. In experiment 2 (N=14), we demonstrate a switching cost between the issuing of the two types of trajectories, irrespective of changes in target position. Unexpectedly, trajectory type did not affect RT in experiment 2, likely due to the lack of target pre-cuing in experiment 2. Our results suggest that the planning of curved and straight trajectories differ in their memory load during pre-planning and requires a time-consuming update of the motor commands when switching between straight and curved plans.

Dyad practice of complex motor skills, characterized by two learners alternating between physical and observational practice, can yield better motor outcomes and reduce practice time compared to physical practice alone. It is unknown if the superior effects of dyad practice on motor learning extend to proprioceptive learning. Forty-two healthy participants (18-35 years) were randomized into three groups (n=14 each): Dyad practice, physical practice with rest (PP-rest), and physical practice without rest (PP-no rest). Participants practiced a 2 degree-of-freedom gamified wrist movement task for 20 minutes using a custom-made wrist robotic device. Wrist position sense acuity was assessed before (baseline) and 24 hours after the end of training (retention), using the Just-noticeable-difference (JND) threshold and Uncertainty. Only the PP-no rest group exhibited significantly lower JND thresholds at retention compared to baseline (t(13)=2.44; p= 0.03, Hedges g=0.70). There were no differences in position sense Uncertainty within or between groups. Dyad practice may yield superior gains in motor performance, but this did not translate into comparable gains in proprioceptive acuity. A possible explanation for these findings is that the recruitment of explicit motor learning mechanisms during dyad motor skill practice does not enhance the implicit learning mechanisms underlying proprioceptive learning. HighlightsO_LIDyad practice (DP) may yield superior motor gains compared to physical practice C_LIO_LIDP does not yield superior proprioceptive gains compared to physical practice C_LIO_LIIntensive physical practice yields the largest gains in position sense acuity C_LI

Memories of pain can last a lifetime, preventing future injuries, but this comes at the expense of remembering other concurrent experiences. For acute pain this cost is outweighed by the benefits but when pain is chronic, pain memory benefits are limited and may even contribute to maintenance of the disorder. Here we investigated two hypotheses, (1) pain takes up slots in working memory or (2) pain induces arousal above optimum levels at high task difficulty, leading to a decrease in performance. To do this, we used the Sternberg Task of working memory, in which the participant plays repeated trials where they are shown different sets of numbers and then asked to identify whether a probe number was in the set or not. The Sternberg Task is ideal for testing the two hypotheses by looking at pain-related changes in accuracy and response time. There was a replication of the response time increase with set size, as well as the effect of older age on working memory and pain threshold. However, we saw no pain effect on either response time, accuracy, or the relationship between these parameters and set size with either chronic pain or an acute painful thermal stimulus. Together, this suggests that pain does not impair working memory in the Sternberg Task.

During reaching, arm choice depends on success and motor effort. Whether these factors influence leg choice for stepping behavior is unknown. Here, we conducted two experiments (1: proof-of-principle; 2: kinematic analysis) to explore whether limb selection for goal-directed stepping depends on success and/or effort under two Choice conditions: Free (choose either leg) and Constrained (no choice - only left leg). For both experiments, in which Free trials always preceded Constrained trials, we adapted the classic center-out target array in which right-leg dominant neurotypical adults stood in the middle of the array and stepped to pre-cued targets as accurately as possible. The Free condition reflected the preferred limb choice. We compared success, effort, and self-perceived difficulty between Free and Constrained trials, separately for three (Experiment 1) and two (Experiment 2) regions. Overall, in Free condition, participants uniformly selected the limb ipsilateral to lateral left and right targets and with slight leg dominance-based bias for central targets. Success (step accuracy and consistency/precision) did not depend on Choice condition, rather, performance improved over repeated trials. Effort (peak vertical foot lift and step path ratio) depended on Choice condition. Finally, independent of Choice condition, participants perceived posterior targets (particularly far targets) as the most difficult during non-dominant left steps. Present findings suggest that effort may influence leg choice to a greater degree than success for goal-directed stepping. Future work that probes these findings robustness in patients with unilateral paresis (intrinsic constraint) may advance our understanding of the motor decision processes for goal-directed mobility behaviors.

Previous work has shown that compared with young adults, older adults generalize their walking patterns more across environments that impose different motor demands (i.e., split-belt treadmill vs. overground). However, in this previous study, all participants walked at a speed that was more comfortable for older adults than young participants, which leads to the question of whether young adults would generalize more their walking patterns than older adults when exposed to faster speeds that are more comfortable for them. To address this question, we examined the interaction between healthy aging and walking speed on the generalization of a pattern learned on a split-belt treadmill (i.e., legs moving at different speeds) to overground. We hypothesized that walking speed during split-belt walking regulates the generalization of walking patterns in an age-specific manner. To this end, groups of young (<30 y/o) and older (65+ y/o) adults adapted their gait on a split-belt treadmill at either slower or faster walking speeds. We assessed the generalization of movements between the groups by quantifying their aftereffects during overground walking, where larger overground aftereffects represent more generalization, and zero aftereffects represent no generalization. We found an interaction between age and walking speed in the generalization of walking patterns. More specifically, older adults generalized more when adapted at slower speeds, whereas younger adults did so when adapted at faster speeds. These results suggest that comfortable walking speeds lead to more generalization of newly acquired motor patterns beyond the training contexts.

Motor skill learning involves multiple mechanisms, including use-dependent learning (UDL), reinforcement learning (RL), and error-based learning (EBL). These operate over different time scales and neural pathways, contributing uniquely to skill acquisition, consolidation, and transfer. Here we asked how these mechanisms support the acquisition of a spatially complex maze navigation task in five groups of healthy young adults. Groups received one of five types of feedback during training of their unseen dominant hand: UDL (no feedback), RL (binary success/failure feedback with a static threshold), RLA (binary feedback with an adaptive threshold), RLB (binary feedback with adaptive threshold and brief flash of cursor feedback), or EBL (continuous real-time cursor feedback). Skill, transfer, and proprioceptive acuity were assessed pre- and post- training using a speed-accuracy function (SAF) for each hand and a two-alternative forced-choice shape discrimination task. Results showed that UDL and RL groups exhibited no improvement post-training, while EBL, RLA, and RLB groups demonstrated accuracy improvements. EBL and RLB participants experienced a significant reduction in movement variability, with EBL showing a greater decrease compared to UDL. The left-hand SAF revealed improvements in accuracy across all groups except UDL. All groups showed reduced variability in the left hand, suggesting intermanual transfer, with EBL transferring more variability improvements than UDL. No significant proprioceptive changes were observed in any group. These findings provide new insights into motor skill learning, emphasizing that even minimal feedback can facilitate complex skill acquisition and transfer and has significant implications for studies where error-based learning may not be applicable. New and NoteworthyMinimal, adaptive binary feedback can effectively support the acquisition and transfer of spatially complex motor skills. While use-dependent and static reinforcement learning failed to enhance performance, adaptive reinforcement and error-based feedback significantly improved accuracy and reduced movement variability. Notably, these gains transferred to the untrained hand, highlighting the potential of reinforcement-based strategies in contexts where error-based learning is limited or unavailable, offering important implications for rehabilitation and motor training design.

This study investigated the muscle activity during the preparatory (anticipatory postural adjustment, APA), execution (online postural adjustments, OPA), and compensatory (compensatory postural adjustment, CPA) phases during standing with eyes opened or closed on an elevated platform. Eight healthy young women stood in the upright position, with eyes opened or closed, and did as-fast-as-they-could shoulder flexions on the ground and on 1-m-height-portable-elevated-platform. The surface EMG of trunk (lumbar extensor, and rectus abdominis) and lower limb (rectus femoris, biceps femoris, tibialis anterior and gastrocnemius lateralis) muscles during this task were recorded (1 kHz sampling frequency) and compared during these three phases. Analysis of variance was applied to compare the effects of height (floor and elevated platform), vision (open and closed), and postural adjustment (APA, OPA and CPA) into the activity of each muscle. These muscles were more active during OPA (p<0.0001) and less active during APA. On the elevated platform, these postural muscles presented more activty during APA (p<0.001). During the most stable condition (on the ground with eyes opened), muscle activity during APA and OPA was negatively correlated, and not correlated between OPA and CPA. Our results suggest postural control adapts to sensory, motor, and cognitive conditions. Therefore, the increased demand for postural control, generated due to the height of the support base, provokes the need for greater flexibility of postural synergies and causes a change in muscle activity. Summary StatementWe discuss how postural muscle activity behaves before and after a fast upper arms movement when someone stands on a elevated platform or on the ground.

In many motor learning tasks, the process of error reduction is mirrored in a process of effort reduction, where metabolic cost and or muscle co-contraction decrease gradually in tandem with error. Effort reduction may be incidental to the learning process, but high error movements can be more effortful and a drive to minimize effort costs could also play a role in motor learning. In this study, we focused on the effort requirements of the task, asking whether task (background) effort cost affects learning, aftereffects, or relearning in a split-belt walking task. We hypothesized that greater effort costs would amplify the need to reduce effort and accelerate learning. Alternatively, we hypothesized that greater effort requirement could compromise and slow the learning process. Participants in high, low, and control effort groups completed a split-belt walking task while wearing a weighted vest with 15% body mass, 5% body mass, or the vest only, and we assessed step length asymmetry throughout the protocol. Step length asymmetry changed similarly between groups, with similar rates and extent of learning and relearning and similar patterns of aftereffects when the split-belt perturbation was removed. We found no significant effect of task effort on the process of split-belt adaptation, suggesting that the brains response to gait asymmetry and ability to adapt to novel dynamics is relatively unchanged by background effort requirements of the task. NEW & NOTEWORTHYDespite the brains sensitivity to effort cost and willingness to adjust gait parameters to minimize cost, the process of split-belt adaptation was unaffected by increased effort requirements. This finding provides a foundation for further research into performance-dependent effort cost. Additionally, modest increases in effort should be further explored in rehabilitation applications where higher effort requirements may help build strength and fitness without impairing motor learning.

A common clinical impression is that individuals with stroke tend to gaze downward while walking--focusing on the walking surface a short distance ahead for extended periods. However, this impression has not been formally verified, and thus, whether this is a true phenomenon--and, if so, what drives it--remains unknown. In this observational study, we examined the spatial and temporal aspects of walking gaze behavior in individuals with stroke and compared them to those of healthy controls. Our results indicate that individuals with stroke exhibit a greater tendency to gaze downward while walking compared to healthy controls. While the shorter look-ahead distances observed may be attributed to slower walking speeds, the prolonged duration of downward gazing (DWG) cannot be explained by speed alone. Instead, both the short look-ahead distance and prolonged DWG duration were associated with anxiety--particularly fear of falling--as well as impaired balance and gait control. Importantly, while participants reported consciously monitoring their stepping, this tendency was unrelated to DWG, suggesting that downward gaze is unlikely to serve this specific purpose. These findings suggest that anxiety related to walking instability may underlie both the slower walking speeds and the tendency for DWG. Having established the presence of the DWG phenomenon, we propose further investigation into its potential utility as a novel indicator of individuals self-assessed deficits in reactive and/or proactive balance and gait control.

Action cancellation - the ability to rapidly cancel an initiated movement in response to unexpected events - has been extensively studied in the upper limb using the stop signal task (SST). During gait, action cancellation is needed to stop and modify steps to avoid hazards and prevent falls. By adapting the SST to step initiation, this study investigated how the anticipatory postural adjustment (APA) and foot-lift phases of forward stepping were affected by action cancellation commands, and whether this changed with healthy ageing. The SST was performed in stepping, foot tap, and finger button conditions in 27 young (Mage = 28.7 years) and 29 healthy older adults (Mage = 70.1 years). Across conditions, older adults exhibited slower response speed compared to young adults and greater proactive slowing of responses when stop cues were anticipated. However, there was no significant difference in stopping speed between young and older adults. Stopping speed was fastest in the finger tap condition, and slowest in the step condition. When an APA was initiated in a step cancellation trial, the magnitude of the weight shift toward the step leg did not differ between successful and unsuccessful foot-lift cancellations. Foot-lift could be cancelled when stop cues were presented at similar phases of step preparation for young and older adults. These results suggest that the initial loading of the step leg is a ballistic process, however as weight is shifted toward the stance leg, action cancellation commands responding to external stimuli can decouple the APA and foot-lift step phases. Key PointsO_LIThe stop signal task (SST) - which allows an estimation of stopping speed independently of response speed - was applied to voluntary stepping in young and older adults. C_LIO_LIWhile response speed was slower for older than young adults, stopping speed was not significantly different between age groups in the upper limb, lower limb when seated, and during forward stepping. C_LIO_LIWhen stop cues were introduced, response speed slowed more in older than young adults, and more in the upper than the lower limb (i.e., Foot Tap and Step conditions). C_LIO_LIThe initial preparatory weight shift toward the stepping foot was not significantly different between successfully cancelled steps and normal steps, highlighting the ballistic nature of the early phase of step preparation. C_LIO_LIPrior to foot-lift, action cancellation commands could decouple the preparatory weight shift phase from foot-lift at similar stages of step initiation in young and healthy older adults. C_LI

We examined the influence of mental fatigue on static balance control in healthy young adults to gain greater clarity about this issue than provided in previous research. Based on the prevailing assumption in pertinent literature, we hypothesized that mental fatigue leads to a reduced cognitive regulation of quiet upright standing, as reflected in center of pressure (COP) excursions. More specifically, we hypothesized that the influence of mental fatigue on balance control depends on the attentional effort required by the balance tasks being performed. To test these hypotheses, 44 young adults (24 women and 20 men) were quasi-randomly assigned to either an experimental group that was mentally fatigued (using the TloadDback-task with individualized settings) or a control group (who watched a documentary). Before and after the intervention the participants performed six balance tasks that differed in (attentional) control requirements, while their COP was being recorded. From these time-series sway variability, mean speed, and sample entropy were calculated and analyzed statistically. Additionally, mental fatigue was assessed using VAS scales. Statistical analyses confirmed that the balance tasks differed in control characteristics and that mental fatigue was elevated in the experimental group, but not in the control group. Nevertheless, no significant main effects of mental fatigue were found on any of the COP measures of interest, except for some non-robust and difficult to interpret interaction effects involving the factor group. These results suggest that, in young adults, postural control in static balance tasks is largely automatic and unaffected by mental fatigue.

The occurrence of an error when performing a motor sequence causes an immediate reduction in speed on subsequent trials, which is referred to as post-error slowing. However, understanding how post-error slowing changes with practice has been difficult because it requires extended practice on a novel sequence task. To address this issue, we examined post-error slowing in a novel glove-based typing task that participants performed for 15 consecutive days. Speed and accuracy improved from the early to middle stages of practice, but did not show any further improvements between middle and late stage of practice. However, when we analyzed the response to errors, we found that participants decreased both the magnitude and duration of post-error slowing with practice, even after there were no detectable improvements in overall task performance. These results indicate that learning not only improves overall task performance but also modifies the ability to respond to errors.

Why do some cortically blind (CB) drivers who are missing vision from a quadrant or hemifield have trouble maintaining a central lane position, while others do not? A recent driving study in virtual reality showed that most patients with right-sided visual field deficits (right CB) perform similarly to controls, while most of those with left CB demonstrated a unique pattern of steering biases (Giguere et al., 2025). In this study, we tested the hypothesis that these biases could result from loss of visual information falling on the blind field. The steering and gaze behavior of 24 subjects with normal vision (mean age: 19.8 years, SD: 1.44) were recorded in a virtual reality steering task while gaze-contingent occluding masks were imposed on a quadrant of their visual field. The central five degrees of vision were spared to mimic the sparing present in most CB patients. Turn direction (left/right), turn radius (two non-constant radii), and occlusion quadrant (one of four quadrants or no occlusion) were randomized between trials. We found that the pattern of steering biases observed in CB drivers were not replicated when visually-healthy drivers were subjected to gaze-contingent masks, and we conclude that it may be a mistake to characterize the effects of cortical blindness on steering behavior as consistent with a simple omission of visual information. This insight has the potential to guide future research on CB adaptation to their visual impairments and possible interventions to improve their steering performance.

Combined action observation and motor imagery (AOMI) facilitates corticospinal excitability (CSE). This study used single-pulse transcranial magnetic stimulation (TMS) to explore changes in CSE for coordinative AOMI of a single-leg sit-to-stand (SL-STS) movement. Twenty-one healthy adults completed two testing sessions, where they engaged with baseline (BL), action observation (AO), and motor imagery (MI) control conditions, and three experimental conditions where they observed a slow-paced SL-STS while simultaneously imagining a slow- (AOMIHICO), medium- (AOMIMOCO), or fast-paced (AOMILOCO) SL-STS. A TMS pulse was delivered to the right leg representation of the left primary motor cortex at three stimulation timepoints aligned with peak EMG activity of the knee extensor muscle group for the slow-paced (T3), medium-paced (T2), and fast-paced (T1) SL-STS during each condition. Motor evoked potential (MEP) amplitudes were recorded from the knee extensor muscle group as a marker of CSE for all stimulation timepoints and conditions. A main effect for experimental condition was reported for all stimulation timepoints. MEP amplitudes were significantly greater for AOMIHICO at T1 and T3, and AOMIMOCO and AOMILOCO at all stimulation timepoints, when compared with control conditions. This study provides neurophysiological evidence supporting the use of coordinative AOMI as an alternative method for movement (re)learning.

BackgroundAvoidance of movements is an important factor in chronic pain. Previous experiments have investigated the involved learning mechanisms by pairing movements with painful stimuli but, usually, other visuospatial cues are concurrently presented during learning. Therefore, participants might primarily avoid these visuospatial rather than the movement-related cues, potentially invalidating related interpretations of pain-induced movement avoidance. Here, we separated kinesthetic from visuospatial cues to investigate their respective contribution to avoidance learning. MethodsParticipants used a hand-held robotic manipulandum and, during an acquisition phase, received painful stimuli when performing center-out movements. Pain stimuli could be avoided by choosing a curved rather than direct movement trajectories. To distinguish the contribution of kinesthetic vs. visuospatial cues we used two generalization contexts: either participants executed novel movements passing through the same location at which pain had previously been presented in the acquisition phase; or they executed the same pain-associated movements after having been reseated, so that the hand did not pass through the pain-associated location. ResultsAvoidance generalization was comparable in both contexts, and remarkably, highly correlated between them. Our findings suggest that both visuospatial and kinesthetic cues available during acquisition were associated with pain and led to avoidance. ConclusionsOur research corroborates the fear-avoidance pain model and previous studies findings that pain can become associated with movements. However, our study indicates that visuospatial cues also play a critical role. Future studies should distinguish movement-related and space-related associations in pain learning. SignificanceChronic pain is a significant health issue typically attributed to maladaptive learning of pain-movement associations and movement avoidance. We demonstrate that visual cues can play a similarly important role as movement cues in pain learning. This aspect has not previously been considered and has likely confounded previous research findings.

Dexterous manipulation may be guided by explicit information about object property. Such a manipulation requires fine modulation of digit position and forces using explicit cues. Young adults can form arbitrary cue-object property associations for accurate modulation of digit position and forces. Aging, in contrast, might alter this conditional learning. Older adults are impaired in accurately modulating their digit forces using explicit cues about object property. However, it is not known whether older adults can use explicit cues about object property to modulate digit position. In this study, we instructed ten healthy older and ten young adults to learn a manipulation task using arbitrary color cues about object center of mass location. Subjects were required to exert clockwise, counterclockwise, or no torque on the object according to the color cue and lift the object while minimizing its tilt across sixty trials. Older adults produced larger torque error during the conditional learning trials than young adults. This resulted in a significantly slower rate of learning in older adults. Older, but not young adults, failed to modulate their digit position and forces using the color cues. Similar aging-related differences were not observed while learning the task using implicit knowledge about object property. Our findings suggest that aging impairs the ability to use explicit cues about object property to modulate both digit position and forces for dexterous manipulation. We discuss our findings in relation to age-related changes in the processes and the neural network for conditional learning.

The central nervous system (CNS) is thought to use motor strategies that minimize several criteria, such as end-point variability or effort, to plan optimal motor patterns. In the case of vertical arm movements, a large body of literature demonstrated that the brain uses a motor strategy that takes advantage of the mechanical effects of gravity to minimize muscle effort. Results from other studies suggested that the relative importance of each criterion may vary according to the tasks constraints. For example, it could be hypothesized that reduced end-point variability driven by high accuracy demands is detrimental to effort minimization. The present study probes this specific hypothesis using the framework of gravity-related effort minimization. We asked twenty young healthy participants to perform vertical arm reaching movements towards targets whose size varied across conditions. We recorded the arm kinematics and electromyographic activities of the anterior deltoid to study two well-known motor signatures of the gravity-related optimization process; i.e., directional asymmetries on velocity profiles and negative epochs on phasic muscular activities. The results showed that both indices were reduced as target size decreased, demonstrating that the gravity-related optimization process was reduced under high accuracy constraints. This phenomenon is consistent with the use of a trade-off strategy between effort and end-point variability. More generally, it suggests that the CNS is able to appropriately modulate the relative importance of varied motor costs when facing varying task demands.

The ability to differentiate between self-motion and motion in the environment is an important factor for maintaining upright balance control. Visual motion can elicit the sensation of a fall by cueing a false position sense. While there is evidence supporting the role of central vision and fall risk, including measures of contrast sensitivity, depth perception, and size of the visual field, the relationship between motion detection thresholds and balance control remains unknown. The aim of this study is to explore the relationship between thresholds for visual motion detection (VMDTs) of the environment and measures of visual sensitivity to balance disturbances in the environment while walking. Thirty young adults (18-35 years) and thirty older adults (55-79 years) participated in a counter-balanced study where they 1) walked on a self-paced treadmill within a virtual environment that delivered frontal plane multi-sine visual disturbances at three amplitudes (6{degrees}, 10{degrees}, and 15{degrees}), and 2) performed 100 trials of a two-alternative forced choice (2AFC) task in which they discriminated between a counterclockwise ("left") and clockwise ("right") rotation of a visual scene under three conditions (standing, standing with optic flow, and walking). Visual sensitivity was measured using frequency response functions of the center of mass displacement relative to the screen tilt (cm/deg) while VMDTs were measured by fitting a psychometric curve to the responses of the 2AFC task. We found significant positive correlations between measures of visual sensitivity and VMDTs for 7 out of the 9 conditions in young adults, and nonsignificant positive correlations between the two measures in older adults. VMDTs were overall higher in older adults, although not significantly in the standing condition, indicating more motion in the environment is required for older adults to consciously perceive it. VMDTs also tended to increase from standing, standing with optic flow, and walking, although not significantly between the standing and standing with optic flow conditions for both populations. We interpret the positive correlations between the two measures as an indication that individuals with lower motion detection thresholds can more accurately differentiate between self-motion and motion in the environment, resulting in lower responses from visual disturbances in the environment.

Visual, vestibular, proprioceptive and cutaneous sensory information is important for posture control during quiet stance. When the reliability of one source of sensory information used to detect self-motion for posture control is reduced, there may be a reweighting of inputs within and/or across the remaining sensory systems determining self-motion for postural control. Muscle vibration, which creates an illusion of muscle stretch and a compensatory movement to shorten the vibrated muscle, may be used to determine the weighting of muscle spindle Ia proprioception for posture control. The objective of this study was to determine the effect of vision occlusion on triceps surae muscle Ia proprioceptive weighting for postural control during quiet stance, utilizing 80 Hz muscle vibration and a quantitative measure of the bodys anterior to posterior ground center of pressure response to triceps surae muscle vibration in freely standing subjects. Subjects (N = 41; mean(standard deviation), 19.6(2.0) years) were examined as they stood with eyes open or eyes closed. Ground center of pressure was measured during quiet standing with, and without, bilateral vibration of the triceps surae muscles. The mean backward center of pressure shift induced by triceps surae vibration was significantly greater during the eyes closed condition compared to eyes open (eyes closed: -4.93(1.62) centimeters; eyes open: -3.21(1.33) centimeters; p = 6.85E-10; Cohens d = 1.29). Thirty-seven subjects increased, and two subjects decreased, their vibration induced center of pressure backward shift in the eyes closed condition compared to eyes open, although the magnitude of the change varied. Results support the idea that for most subjects, during an eyes closed stance there is an increased triceps surae muscle Ia proprioceptive weighting for postural control, due to the need for posture control to depend more on non-visual feedback.