Human vestibular perceptual thresholds for pitch tilt are slightly worse than for roll tilt across a range of frequencies

Frequency dependence of human thresholds: both perceptual and vestibuloocular reflex thresholds

Although perceptual thresholds have been widely studied, vestibuloocular reflex (VOR) thresholds have received less attention, so the relationship between VOR and perceptual thresholds remains unclear. We compared the frequency dependence of human VOR thresholds to human perceptual thresholds for yaw head rotation in both upright ("yaw rotation") and supine ("yaw tilt") positions, using the same human subjects and motion device. VOR thresholds were generally a little smaller than perceptual thresholds. We also found that horizontal VOR thresholds for both yaw rotation about an Earth-vertical axis and yaw tilt (yaw rotation about an Earth-horizontal axis) were relatively constant across four frequencies (0.2, 0.5, 1, and 2 Hz), with little difference between yaw rotation and yaw tilt VOR thresholds. For yaw tilt stimuli, perceptual thresholds were slightly lower at the lowest frequency and nearly constant at all other (higher) frequencies. However, for yaw rotation, perceptual thresholds increased significantly at the lowest frequency (0.2 Hz). We conclude 1) that VOR thresholds were relatively constant across frequency for both yaw rotation and yaw tilt, 2) that the known contributions of velocity storage to the VOR likely yielded these VOR thresholds that were similar for yaw rotation and yaw tilt for all frequencies tested, and 3) that the integration of otolith and horizontal canal signals during yaw tilt when supine contributes to stable perceptual thresholds, especially relative to the low-frequency perceptual thresholds recorded during yaw rotation.NEW & NOTEWORTHY We describe for the first time that human VOR thresholds differ from human forced-choice perceptual thresholds, with the difference especially evident at frequencies below 0.5 Hz. We also report that VOR thresholds are relatively constant across frequency for both yaw rotation and yaw tilt. These findings are consistent with the idea that high-pass filtering in cortical pathways impacts cognitive decision-making.

Intra-individual consistency of vestibular perceptual thresholds

Vestibular perceptual thresholds quantify sensory noise associated with reliable perception of small self-motions. Previous studies have identified substantial variation between even healthy individuals' thresholds. However, it remains unclear if or how an individual's vestibular threshold varies over repeated measures across various time scales (repeated measurements on the same day, across days, weeks, or months). Here, we assessed yaw rotation and roll tilt thresholds in four individuals and compared this intra-individual variability to inter-individual variability of thresholds measured across a large age-matched cohort each measured only once. For analysis, we performed simulations of threshold measurements where there was no underlying variability (or it was manipulated) to compare to that observed empirically. We found remarkable consistency in vestibular thresholds within individuals, for both yaw rotation and roll tilt; this contrasts with substantial inter-individual differences. Thus, we conclude that vestibular perceptual thresholds are an innate characteristic, which validates pooling measures across sessions and potentially serves as a stable clinical diagnostic and/or biomarker.

An experimentally informed computational model of neurovestibular adaptation to altered gravity

Transitions to altered gravity environments result in acute sensorimotor impairment for astronauts, leading to serious mission and safety risks in the crucial first moments in a new setting. Our understanding of the time course and severity of impairment in the early stages of adaptation remains limited and confounded by unmonitored head movements, which are likely to impact the rate of adaptation. Here, we aimed to address this gap by using a human centrifuge to simulate the first hour of hypergravity (1.5g) exposure and the subsequent 1g readaptation period, with precisely controlled head tilt activity. We quantified head tilt overestimation via subjective visual vertical and found ∼30% tilt overestimation that did not decrease over the course of 1 h of exposure to the simulated gravity environment. These findings extended the floor of the vestibular adaptation window (with controlled vestibular cueing) to 1 h of exposure to altered gravity. We then used the empirical data to inform a computational model of neurovestibular adaptation to changes in the magnitude of gravity, which can offer insight into the adaptation process and, with further tuning, can be used to predict the temporal dynamics of vestibular-mediated misperceptions in altered gravity.

Vestibular contributions to linear motion perception

Vestibular contributions to linear motion (i.e., translation) perception mediated by the otoliths have yet to be fully characterized. To quantify the maximal extent that non-vestibular cues can contribute to translation perception, we assessed vestibular perceptual thresholds in two patients with complete bilateral vestibular ablation to compare to our data in 12 young (< 40 years), healthy controls. Vestibular thresholds were assessed for naso-occipital ("x-translation"), inter-aural ("y-translation"), and superior-inferior ("z-translation") translations in three body orientations (upright, supine, side-lying). Overall, in our patients with bilateral complete vestibular loss, thresholds were elevated ~ 2-45 times relative to healthy controls. No systematic differences in vestibular perceptual thresholds were noted between motions that differed only with respect to their orientation relative to the head (i.e., otoliths) in patients with bilateral vestibular loss. In addition, bilateral loss patients tended to show a larger impairment in the perception of earth-vertical translations (i.e., motion parallel to gravity) relative to earth-horizontal translations, which suggests increased contribution of the vestibular system for earth-vertical motions. However, differences were also noted between the two patients. Finally, with the exception of side-lying x-translations, no consistent effects of body orientation in our bilateral loss patients were seen independent from those resulting from changes in the plane of translation relative to gravity. Overall, our data confirm predominant vestibular contributions to whole-body direction-recognition translation tasks and provide fundamental insights into vestibular contributions to translation motion perception.

Human vestibular perceptual thresholds - A systematic review of passive motion perception

BACKGROUND

The vestibular system detects head accelerations within 6 degrees of freedom. How well this is accomplished is described by vestibular perceptual thresholds. They are a measure of perceptual performance based on the conscious evaluation of sensory information. This review provides an integrative synthesis of the vestibular perceptual thresholds reported in the literature. The focus lies on the estimation of thresholds in healthy participants, used devices and stimulus profiles. The dependence of these thresholds on the participants clinical status and age is also reviewed. Furthermore, thresholds from primate studies are discussed.

RESULTS

Thresholds have been measured for frequencies ranging from 0.05 to 5 Hz. They decrease with increasing frequency for five of the six main degrees of freedom (inter-aural, head-vertical, naso-occipital, yaw, pitch). No consistent pattern is evident for roll rotations. For a frequency range beyond 5 Hz, a U-shaped relationship is suggested by a qualitative comparison to primate data. Where enough data is available, increasing thresholds with age and higher thresholds in patients compared to healthy controls can be observed. No effects related to gender or handedness are reported.

SIGNIFICANCE

Vestibular thresholds are essential for next generation screening tools in the clinical domain, for the assessment of athletic performance, and workplace safety alike. Knowledge about vestibular perceptual thresholds contributes to basic and applied research in fields such as perception, cognition, learning, and healthy aging. This review provides normative values for vestibular thresholds. Gaps in current knowledge are highlighted and attention is drawn to specific issues for improving the inter-study comparability in the future.

Your Vestibular Thresholds May Be Lower Than You Think: Cognitive Biases in Vestibular Psychophysics

PURPOSE

Recently, there has been a surge of interest in measuring vestibular perceptual thresholds, which quantify the smallest motion that a subject can reliably perceive, to study physiology and pathophysiology. These thresholds are sensitive to age, pathology, and postural performance. Threshold tasks require decisions to be made in the presence of uncertainty. Since humans often rely on past information when making decisions in the presence of uncertainty, we hypothesized that (a) perceptual responses are affected by their preceding trial; (b) perceptual responses tend to be biased opposite of the "preceding response" because of cognitive biases but are not biased by the "preceding stimulus"; and (c) when fits do not account for this cognitive bias, thresholds are overestimated. To our knowledge, these hypotheses are unaddressed in vestibular and direction-recognition tasks.

CONCLUSIONS

Results in normal subjects supported each hypothesis. Subjects tended to respond opposite of their preceding response (not the preceding stimulus), indicating a cognitive bias, and this caused an overestimation of thresholds. Using an enhanced model (MATLAB code provided) that considered these effects, average thresholds were lower (5.5% for yaw, 7.1% for interaural). Since the results indicate that the magnitude of cognitive bias varies across subjects, this enhanced model can reduce measurement variability and potentially improve the efficiency of data collection.

Evaluating vestibular contributions to rotation and tilt perception

Vestibular perceptual thresholds provide insights into sensory function and have shown clinical and functional relevance. However, specific sensory contributions to tilt and rotation thresholds have been incompletely characterized. To address this limitation, tilt thresholds (i.e., rotations about earth-horizontal axes) were quantified to assess canal-otolith integration, and rotation thresholds (i.e., rotations about earth-vertical axes) were quantified to assess perception mediated predominantly by the canals. To determine the maximal extent to which non-vestibular sensory cues (e.g., tactile) can contribute to tilt and rotation thresholds, we tested two patients with completely absent vestibular function and compared their data to those obtained from two separate cohorts of young (≤ 40 years), healthy adults. As one primary finding, thresholds for all motions were elevated by approximately 2-35 times in the absence of vestibular function, thus, confirming predominant vestibular contributions to both rotation and tilt self-motion perception. For patients without vestibular function, rotation thresholds showed larger increases relative to healthy adults than tilt thresholds. This suggests that increased extra-vestibular (e.g., tactile or interoceptive) sensory cues may contribute more to the perception of tilt than rotation. In addition, an impact of stimulus frequency was noted, suggesting increased vestibular contributions relative to other sensory systems can be targeted on the basis of stimulus frequency.

Noise and vestibular perception of passive self-motion

Noise defined as random disturbances is ubiquitous in both the external environment and the nervous system. Depending on the context, noise can degrade or improve information processing and performance. In all cases, it contributes to neural systems dynamics. We review some effects of various sources of noise on the neural processing of self-motion signals at different stages of the vestibular pathways and the resulting perceptual responses. Hair cells in the inner ear reduce the impact of noise by means of mechanical and neural filtering. Hair cells synapse on regular and irregular afferents. Variability of discharge (noise) is low in regular afferents and high in irregular units. The high variability of irregular units provides information about the envelope of naturalistic head motion stimuli. A subset of neurons in the vestibular nuclei and thalamus are optimally tuned to noisy motion stimuli that reproduce the statistics of naturalistic head movements. In the thalamus, variability of neural discharge increases with increasing motion amplitude but saturates at high amplitudes, accounting for behavioral violation of Weber's law. In general, the precision of individual vestibular neurons in encoding head motion is worse than the perceptual precision measured behaviorally. However, the global precision predicted by neural population codes matches the high behavioral precision. The latter is estimated by means of psychometric functions for detection or discrimination of whole-body displacements. Vestibular motion thresholds (inverse of precision) reflect the contribution of intrinsic and extrinsic noise to perception. Vestibular motion thresholds tend to deteriorate progressively after the age of 40 years, possibly due to oxidative stress resulting from high discharge rates and metabolic loads of vestibular afferents. In the elderly, vestibular thresholds correlate with postural stability: the higher the threshold, the greater is the postural imbalance and risk of falling. Experimental application of optimal levels of either galvanic noise or whole-body oscillations can ameliorate vestibular function with a mechanism reminiscent of stochastic resonance. Assessment of vestibular thresholds is diagnostic in several types of vestibulopathies, and vestibular stimulation might be useful in vestibular rehabilitation.

Vestibular perceptual thresholds for rotation about the yaw, roll, and pitch axes

This effort seeks to further assess human perception of self-motion by quantifying and comparing earth-vertical rotational vestibular perceptual thresholds about the yaw, roll, and pitch axes. Early seminal works (Benson Aviat Space Environ Med 60:205-213, 1989) quantified thresholds for yaw, roll, and pitch rotations, using single-cycle sinusoids in angular acceleration with a frequency of 0.3 Hz (3.33 s motion duration) and found yaw thresholds to be significantly lower than roll and pitch thresholds (1.58-1.20 deg/s vs. 2.07 deg/s and 2.04 deg/s, respectively). Our current effort uses modern methods and definitions to reassess if rotational thresholds differ between these three axes of rotation in ten human subjects at 0.3 Hz and additionally across a range of frequencies: 0.1 Hz, 0.3 Hz, and 0.5 Hz. In contrast to the established findings of Benson et al., no statistically significant differences were found between the three rotational axes at 0.3 Hz. Further, no statistically significant differences were found at any of these frequencies. Instead, a consistent pattern was found for yaw, pitch, and roll of increasing thresholds with decreasing rotational frequency, consistent with the brain employing high-pass filter mechanisms for decision-making. We also fill a gap in the literature by extending the quantification of pitch rotation thresholds to 0.1 Hz. Finally, we assessed inter-individual trends between these three frequencies and across all three axes of rotation. In thoroughly considering methodological and other differences between the current and previous studies, we conclude yaw rotation thresholds do not differ from those in roll or pitch.

Tilt perception is different in the pitch and roll planes in human

Neurophysiological tests probing the vestibulo-ocular, colic and spinal pathways are the gold standard to evaluate the vestibular system in clinics. In contrast, vestibular perception is rarely tested despite its potential usefulness in professional training and for the longitudinal follow-up of professionals dealing with complex man-machine interfaces, such as aircraft pilots. This is explored here using a helicopter flight simulator to probe the vestibular perception of pilots. The vestibular perception of nine professional helicopter pilots was tested using a full flight helicopter simulator. The cabin was tilted six times in roll and six times in pitch (-15°, -10°, -5°, 5°, 10° and 15°) while the pilots had no visual cue. The velocities of the outbound displacement of the cabin were kept below the threshold of the semicircular canal perception. After the completion of each movement, the pilots were asked to put the cabin back in the horizontal plane (still without visual cues). The order of the 12 trials was randomized with two additional control trials where the cabin stayed in the horizontal plane but rotated in yaw (-10° and +10°). Pilots were significantly more precise in roll (average error in roll: 1.15 ± 0.67°) than in pitch (average error in pitch: 2.89 ± 1.06°) (Wilcoxon signed-rank test: p < 0.01). However, we did not find a significant difference either between left and right roll tilts (p = 0.51) or between forward and backward pitch tilts (p = 0.59). Furthermore, we found that the accuracies were significantly biased with respect to the initial tilt. The greater the initial tilt was, the less precise the pilots were, although maintaining the direction of the tilt, meaning that the error can be expressed as a vestibular error gain in the ability to perceive the modification in the orientation. This significant result was found in both roll (Friedman test: p < 0.01) and pitch (p < 0.001). However, the pitch trend error was more prominent (gain = 0.77 vs gain = 0.93) than roll. This study is a first step in the determination of the perceptive-motor profile of pilots, which could be of major use for their training and their longitudinal follow-up. A similar protocol may also be useful in clinics to monitor the aging process of the otolith system with a simplified testing device.

Impacts of Rotation Axis and Frequency on Vestibular Perceptual Thresholds

In an effort to characterize the factors influencing the perception of self-motion rotational cues, vestibular self-motion perceptual thresholds were measured in 14 subjects for rotations in the roll and pitch planes, as well as in the planes aligned with the anatomic orientation of the vertical semicircular canals (i.e., left anterior, right posterior; LARP, and right anterior, left posterior; RALP). To determine the multisensory influence of concurrent otolith cues, within each plane of motion, thresholds were measured at four discrete frequencies for rotations about earth-horizontal (i.e., tilts; EH) and earth-vertical axes (i.e., head positioned in the plane of the rotation; EV). We found that the perception of rotations, stimulating primarily the vertical canals, was consistent with the behavior of a high-pass filter for all planes of motion, with velocity thresholds increasing at lower frequencies of rotation. In contrast, tilt (i.e, EH rotation) velocity thresholds, stimulating both the canals and otoliths (i.e., multisensory integration), decreased at lower frequencies and were significantly lower than earth-vertical rotation thresholds at each frequency below 2 Hz. These data suggest that multisensory integration of otolithic gravity cues with semicircular canal rotation cues enhances perceptual precision for tilt motions at frequencies below 2 Hz. We also showed that rotation thresholds, at least partially, were dependent on the orientation of the rotation plane relative to the anatomical alignment of the vertical canals. Collectively these data provide the first comprehensive report of how frequency and axis of rotation influence perception of rotational self-motion cues stimulating the vertical canals.

Impact of Canal-Otolith Integration on Postural Control

Roll tilt vestibular perceptual thresholds, an assay of vestibular noise, have recently been shown to be associated with suboptimal balance performance in healthy older adults. However, despite the strength of this correlation, the use of a categorical (i.e., pass/fail) balance assessment limits insight into the impacts of vestibular noise on postural sway. As a result, an explanation for this correlation has yet to be determined. We hypothesized that the correlation between roll tilt vestibular thresholds and postural control reflects a shared influence of sensory noise. To address this hypothesis, we measured roll tilt perceptual thresholds at multiple frequencies (0.2 Hz, 0.5 Hz, 1 Hz) and compared each threshold to quantitative measures of quiet stance postural control in 33 healthy young adults (mean = 24.9 years, SD = 3.67). Our data showed a significant linear association between 0.5 Hz roll tilt thresholds and the root mean square distance (RMSD) of the center of pressure in the mediolateral (ML; β = 5.31, p = 0.002, 95% CI = 2.1-8.5) but not anteroposterior (AP; β = 5.13, p = 0.016, 95% CI = 1.03-9.23) direction (Bonferroni corrected α of 0.006). In contrast, vestibular thresholds measured at 0.2 Hz and 1 Hz did not show a significant correlation with ML or AP RMSD. In a multivariable regression model, controlling for both 0.2 Hz and 1 Hz thresholds, the significant effect of 0.5 Hz roll tilt thresholds persisted (β = 5.44, p = 0.029, CI = 0.60-10.28), suggesting that the effect cannot be explained by elements shared by vestibular thresholds measured at the three frequencies. These data suggest that vestibular noise is significantly associated with the temporospatial control of quiet stance in the mediolateral plane when visual and proprioceptive cues are degraded (i.e., eyes closed, standing on foam). Furthermore, the selective association of quiet-stance sway with 0.5 Hz roll tilt thresholds, but not thresholds measured at lower (0.2 Hz) or higher (1.0 Hz) frequencies, may reflect the influence of noise that results from the temporal integration of noisy canal and otolith cues.

The Effect of Noisy Galvanic Vestibular Stimulation on Learning of Functional Mobility and Manual Control Nulling Sensorimotor Tasks

Galvanic vestibular stimulation (GVS) is a non-invasive method of electrically stimulating the vestibular system. We investigated whether the application of GVS can alter the learning of new functional mobility and manual control tasks and whether learning can be retained following GVS application. In a between-subjects experiment design, 36 healthy subjects performed repeated trials, capturing the learning of either (a) a functional mobility task, navigating an obstacle course on a compliant surface with degraded visual cues or (b) a manual control task, using a joystick to null self-roll tilt against a pseudo-random disturbance while seated in the dark. In the “learning” phase of trials, bilateral, bipolar GVS was applied continuously. The GVS waveform also differed between subjects in each task group: (1) white noisy galvanic vestibular stimulation (nGVS) at 0.3 mA (2) high-level random GVS at 0.7 mA (selected from pilot testing as destabilizing, but not painful), or (3) with the absence of stimulation (i.e., sham). Following the “learning” trials, all subjects were blindly transitioned to sham GVS, upon which they immediately completed another series of trials to assess any aftereffects. In the functional mobility task, we found nGVS significantly improved task learning (p = 0.03, mean learning metric 171% more than the sham group). Further, improvements in learning the functional mobility task with nGVS were retained, even once the GVS application was stopped. The benefits in learning with nGVS were not observed in the manual control task. High level GVS tended to inhibit learning in both tasks, but not significantly so. Even once the high-level stimulation was stopped, the impaired performance remained. Improvements in learning with nGVS may be due to increased information throughput resulting from stochastic resonance. The benefit of nGVS for functional mobility, but not manual control nulling, may be due to the multisensory (e.g., visual and proprioceptive), strategic, motor coordination, or spatial awareness aspects of the former task. Learning improvements with nGVS have the potential to benefit individuals who perform functional mobility tasks, such as astronauts, firefighters, high performance athletes, and soldiers.

Predicting individual acclimation to the cross-coupled illusion for artificial gravity

BACKGROUND

The cross-coupled (CC) illusion and associated motion sickness limits the tolerability of fast-spin-rate centrifugation for artificial gravity implementation. Humans acclimate to the CC illusion through repeated exposure; however, substantial inter-individual differences in acclimation exist, which remain poorly understood. To address this, we investigated several potential predictors of individual acclimation to the CC illusion.

METHODS

Eleven subjects were exposed to the CC illusion for up to 50 25-minute acclimation sessions. The metric of acclimation rate was calculated as the slope of each subject's linear increase in spin rate across sessions. As potential predictors of acclimation rate, we gathered age, gender, demographics, and activity history, and measured subjects' vestibular perceptual thresholds in the yaw, pitch, and roll rotation axes.

RESULTS

We found a significant, negative correlation (p = 0.025) between subjects' acclimation rate and roll threshold, suggesting lower thresholds yielded faster acclimation. Additionally, a leave-one-out cross-validation analysis indicated that roll thresholds are predictive of acclimation rates. Correlations between acclimation and other measures were not found but were difficult to assess within our sample.

CONCLUSIONS

The ability to predict individual differences in CC illusion acclimation rate using roll thresholds is critical to optimizing acclimation training, improving the feasibility of fast-rotation, short-radius centrifugation for artificial gravity.

COMPASS: Computations for Orientation and Motion Perception in Altered Sensorimotor States

Reliable perception of self-motion and orientation requires the central nervous system (CNS) to adapt to changing environments, stimuli, and sensory organ function. The proposed computations required of neural systems for this adaptation process remain conceptual, limiting our understanding and ability to quantitatively predict adaptation and mitigate any resulting impairment prior to completing adaptation. Here, we have implemented a computational model of the internal calculations involved in the orientation perception system’s adaptation to changes in the magnitude of gravity. In summary, we propose that the CNS considers parallel, alternative hypotheses of the parameter of interest (in this case, the CNS’s internal estimate of the magnitude of gravity) and uses the associated sensory conflict signals (i.e., difference between sensory measurements and the expectation of them) to sequentially update the posterior probability of each hypothesis using Bayes rule. Over time, an updated central estimate of the internal magnitude of gravity emerges from the posterior probability distribution, which is then used to process sensory information and produce perceptions of self-motion and orientation. We have implemented these hypotheses in a computational model and performed various simulations to demonstrate quantitative model predictions of adaptation of the orientation perception system to changes in the magnitude of gravity, similar to those experienced by astronauts during space exploration missions. These model predictions serve as quantitative hypotheses to inspire future experimental assessments.

Vestibular Precision at the Level of Perception, Eye Movements, Posture, and Neurons

Precision and accuracy are two fundamental properties of any system, including the nervous system. Reduced precision (i.e., imprecision) results from the presence of neural noise at each level of sensory, motor, and perceptual processing. This review has three objectives: (1) to show the importance of studying vestibular precision, and specifically that studying accuracy without studying precision ignores fundamental aspects of the vestibular system; (2) to synthesize key hypotheses about precision in vestibular perception, the vestibulo-ocular reflex, posture, and neurons; and (3) to show that groups of studies that are thoughts to be distinct (e.g., perceptual thresholds, subjective visual vertical variability, neuronal variability) are actually "two sides of the same coin" - because the methods used allow results to be related to the standard deviation of a Gaussian distribution describing the underlying neural noise. Vestibular precision varies with age, stimulus amplitude, stimulus frequency, body orientation, motion direction, pathology, medication, and electrical/mechanical vestibular stimulation, but does not vary with sex. The brain optimizes precision during integration of vestibular cues with visual, auditory, and/or somatosensory cues. Since a common concern with precision metrics is time required for testing, we describe approaches to optimize data collection and provide evidence that fatigue and session effects are minimal. Finally, we summarize how precision is an individual trait that is correlated with clinical outcomes in patients as well as with performance in functional tasks like balance. These findings highlight the importance of studying vestibular precision and accuracy, and that knowledge gaps remain.

The role of vestibular cues in postural sway

Controlling posture requires continuous sensory feedback about body motion and orientation, including from the vestibular organs. Little is known about the role of tilt vs. translation vs. rotation vestibular cues. We examined whether intersubject differences in vestibular function were correlated with intersubject differences in postural control. Vestibular function was assayed using vestibular direction-recognition perceptual thresholds, which determine the smallest motion that can be reliably perceived by a subject seated on a motorized platform in the dark. In study A, we measured thresholds for lateral translation, vertical translation, yaw rotation, and head-centered roll tilts. In study B, we measured thresholds for roll, pitch, and left anterior-right posterior and right anterior-left posterior tilts. Center-of-pressure (CoP) sway was measured in sensory organization tests (study A) and Romberg tests (study B). We found a strong positive relationship between CoP sway and lateral translation thresholds but not CoP sway and other thresholds. This finding suggests that the vestibular encoding of lateral translation may contribute substantially to balance control. Since thresholds assay sensory noise, our results support the hypothesis that vestibular noise contributes to spontaneous postural sway. Specifically, we found that lateral translation thresholds explained more of the variation in postural sway in postural test conditions with altered proprioceptive cues (vs. a solid surface), consistent with postural sway being more dependent on vestibular noise when the vestibular contribution to balance is higher. These results have potential implications for vestibular implants, balance prostheses, and physical therapy exercises.NEW & NOTEWORTHY Vestibular feedback is important for postural control, but little is known about the role of tilt cues vs. translation cues vs. rotation cues. We studied healthy human subjects with no known vestibular pathology or symptoms. Our findings showed that vestibular encoding of lateral translation correlated with medial-lateral postural sway, consistent with lateral translation cues contributing to balance control. This adds support to the hypothesis that vestibular noise contributes to spontaneous postural sway.