We are grateful for the support provided by Carlo Prelz from the Technology Platform of the Human Sciences Faculty. We thank Noel Strahm for his contribution to the staircase implementation.

All data used for this manuscript were recorded after participants gave their informed consent and in line with the ethics approval of the Faculty of Human Sciences of the University of Bern [2020-04-00004].
1. Materials
<ol>
	<li>In order to estimate vestibular perception thresholds, ensure that there is access to a motion platform or a rotatory chair.</li>
	<li>Ensure that a control software for programming the motion profiles and interfacing the motion platform is present. 
	NOTE: PlatformCommander15,16, an open-source software package to interface the motion platform, was used in this study. PlatformCommander allows for defining sinusoidal acceleration profiles, which are often used to estimate vestibular thresholds.</li>
	<li>Ensure that a response device, for example, a game controller, is present for registering the participants&#39; responses.</li>
	<li>Motion platforms produce noise correlated with the movement intensity. Participants can use this auditory noise as an additional, unintended source of information during the estimation of vestibular perception thresholds. To mask the sound of the platform, present the participants with white noise via noise-canceling headphones during each trial.</li>
	<li>Blindfold the participants to eliminate the influence of visual motion cues.</li>
	<li>Decide on which estimation algorithm to use and define the respective parameters. If a staircase approach is used, define the starting point, the step size, the up-date, and termination rules. If the user does not know what values to choose, perform pilot measurements or consult the literature. Defaults are provided by the example scripts available online (https://gitlab.com/dr_e/2022-jovedemo). 
	NOTE: The starting point defines the peak velocity of the platform in the first trial. Determine suitable starting velocities by pilot testing or by consulting the threshold literature (for yaw thresholds, see Grabherr et al.5). The step size describes by how much the intensity changes between trials. The up-date rule describes whether and how the stimulation intensity is changed based on the participants&#39; responses. In the vestibular domain, a three-down/one-up staircase procedure is common. This means that the intensity is decreased after three consecutive correct answers but increased after each wrong answer. The termination criteria are usually defined by either a fixed number of trials or the number of intensity reversals. Intensity reversals are trials in which the response causes an intensity increase after one or more intensity decreases or vice versa. The provided script keeps track of the reversals, terminates the procedure, and automatically calculates the final threshold value.</li>
	<li>Decide for which frequency the threshold needs to be estimated. In the demonstration, 1 Hz was used. 
	NOTE: Vestibular thresholds are typically investigated for frequencies between 0.1 and 5 Hz, and thresholds are known to decrease as stimulation frequency increases3.</li>
	<li>Decide for which type of motion the threshold needs to be estimated. In the demonstration, yaw rotations are performed. 
	NOTE: Thresholds can be estimated for translations and rotations. Thresholds are most often estimated for the three main axes (naso-occipital, inter-aural, head-vertical) and the rotations around them (roll, pitch, yaw). The provided script only estimates one defined motion (direction, frequency) at a time. However, for estimating multiple thresholds, the script can be rerun with the same or different motion parameters (direction, frequency, rotation axes).</li>
	<li>Start every threshold estimation procedure with training, allowing the participant to familiarize themselves with the task. Use the script &#34;threshold-training.jl&#34; available online (see step 1.6) for this purpose. 
	NOTE: The training script presents a series of supra-threshold motion stimuli. The test script automatically controls the estimation procedure, handles the staircase algorithm updating, the stimulus intensity, the presentation of the motion stimulus, the presentation of auditory white noise during each motion stimulus, as well as the logging of all relevant data. During the training, ensure that the participant understands the task and provide guidance in case of uncertainties.</li>
</ol>
2. Instructions
<ol>
	<li>Explain the experimental procedure to the participant and obtain informed consent.</li>
	<li>Seat the participant on the chair mounted on the motion platform.</li>
	<li>Secure the participant using seat belts.</li>
	<li>Give the response buttons to the participant and explain how the keys are assigned to the responses.</li>
	<li>Blindfold the participant. Position the headphones on the participant&#39;s head.</li>
	<li>Apply a proper head fixation.</li>
	<li>Turn on the motion platform using the main, battery, and controller switch.</li>
	<li>Ensure that the area around the platform is clear and that no people can approach the moving platform during the test.</li>
	<li>Start the training procedure script by typing julia threshold-training.jl into the command line.</li>
	<li>Inform the participant about the engagement of the motion platform.</li>
	<li>Ensure a successful initialization of the session by checking the status displayed in the GUI of the server software (PlatformCommander). When successfully initialized, the status display will switch from Session Not Underway to Short Sequence. It will also display the IP address of the connected client and the time when the session was initialized. If the session is not successfully initialized after a few seconds, check the network connection between the client and the server. Ensure that the motion platform is switched on and that the controller is connected.</li>
	<li>Ensure that the participant understands the task, point out mistakes by the participant (e.g., when they push the wrong buttons), and respond to potential questions the participant may have.</li>
	<li>Inform the participant that the training procedure is finished, and the estimation procedure is about to start.</li>
	<li>Start the estimation procedure script by typing julia threshold-test.jl into the command line.</li>
	<li>Supervise the fully automated estimation procedure until the termination criteria are reached.</li>
	<li>Depending on the design, repeat the procedure starting at step 2.13 using different stimuli or terminate the procedure.</li>
	<li>Park the motion platform.</li>
	<li>Remove the head fixation, headphones, blinder, and buttons, and let the participant descend.</li>
	<li>Debrief the participant about the procedure and ask them about their experience to improve further experiments. 
	NOTE: The procedure can be paused and then restarted at any time, preferably not during the threshold estimation phase (steps 2.15-2.17).</li>
</ol>

<ol>
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The authors have no competing interests.

The presented protocol allows for a reliable and efficient estimation of vestibular perceptual thresholds. The protocol is suitable for threshold estimation along and around arbitrary axes and can be applied for all relevant stimulus frequencies (e.g., 0.1-5 Hz). Although we present data using a standard three-down/one-up adaptive staircase procedure, the protocol can also be used for other, more efficient estimation procedures12, including fixed intensity, transformed/weighted up/down, or Bayesian (e.g., Quest18) approaches. An exhaustive discussion of the available algorithms is beyond the scope of the presented manuscript, but an excellent comparison of theory, simulations, and actual data can be found elsewhere19. Efficient estimation procedures are of great relevance in the clinical context, where the time is limited, and research on faster assessments is currently conducted19,20.
A promising field of research is the identification of particular motion profiles and other clinically relevant parameters such as balance2,21. This line of research is important as it provides guidance on which axes and frequencies are most predictable for clinically relevant behavior and events, such as the risk of falling, thereby reducing the search space in a clinical context.
Once the equipment and software are available and work as intended, two factors are critical for reliable threshold estimation. First, the experimenter must ensure that the participant understands the task and stays vigilant throughout the entire procedure. For most stimuli (e.g., all translations), the instructions are clear and easy to follow. However, for pitch and roll rotations, the instruction to answer with left or right can be ambiguous, especially when the axis of rotation is placed at head level. In these cases, the body parts above the rotation axes (e.g., head) rotate in the opposite direction than the body parts below the rotation axes (e.g., feet). The terms left/right can be ambiguous, and it might be helpful to ask the participants to classify motions as clockwise or counterclockwise. It is important to explain and practice how the participant is expected to judge the motion stimuli. A sufficient number of test trials is particularly important when patients or older adults are investigated.
Second, it is important to choose a sufficient number of trials around the threshold. We recommend an adaptive termination criterion as the number of intensity reversals, instead of a fixed number of trials which has been used by others7,22. Additionally, using a predefined number of trials can become inefficient and bears the risk that the staircase does not converge when the start intensity is too far away from the threshold. In general, pilot experiments are required to select reasonable starting intensities and termination criteria.
Staircase algorithms aim to estimate a single point on the psychometric function23,24. Therefore, they provide limited information because response biases and the slope of the psychometric function cannot be derived from the estimated threshold. If such parameters are of interest, fixed intensities can be used to sample over a larger interval, allowing to fit the psychometric function. Although such a procedure is more time-consuming, it allows for more sophisticated analyses that can provide valuable insights14,25. Alternatively, adaptive slope-estimation algorithms can be used13.
An important aspect in the estimation of vestibular perception thresholds is the minimization of cues from other sensory systems. To achieve this, the noise generated by the platform is typically masked by white noise. The minimization of proprioceptive or tactile cues is more challenging1, and can only partly be achieved because acceleration requires a force acting on the body, which will inevitably induce extra-vestibular stimulation. However, cushions are often used to reduce tactile and proprioceptive signals. Likewise, the head fixation is required to ensure a constant orientation of the vestibular organs relative to the motion and to ensure that the motion profile performed by the head is the same as the one by the platform, without any filtering by the body that occurs under unrestricted motion conditions26.
At this point in time, vestibular perceptual thresholds are predominantly used in basic research. Studies showed that vestibular thresholds increase with age27,28, and they depend on direction20,28 and the frequency of motion5,29. More recently, perceptual thresholds were used to document the first evidence of perceptual learning in the vestibular domain14.
Studies comparing patients with vestibular disorders to healthy controls showed altered vestibular perceptual thresholds in line with their pathology. For example, thresholds were increased in patients with vestibular failure29,30,31, and a tendency to reduced thresholds or even a hypersensitivity was shown in patients with vestibular migraine31,32. These studies imply the potential for clinical applications, and a recent review4 discussed the applicability and usefulness of vestibular perceptual thresholds in a clinical diagnosis. One important aspect is that perceptual thresholds add unique properties to the doctor&#39;s toolbox. The standard procedures (HIT, VEMP, caloric irrigation) use direct pathways from the vestibular end-organs to the muscles of the eyes or cervix. Thereby, they do not offer the possibility of investigating the information chain to the neo-cortex. The estimation of vestibular perceptual thresholds, on the other hand, includes cognitive processes allowing to test the vestibular system from a different angle, which might be particularly interesting in the context of persistent postural-perceptual dizziness (PPPD). A shortcoming of the presented procedure is its inability to detect directional asymmetries, which has been reported by others33.
Vestibular perceptual thresholds are also of interest in the evaluation and monitoring of (therapeutic) interventions. Many studies use the risk of falling as an endpoint in the evaluation of treatment effectiveness. However, since a correlation between vestibular thresholds about the roll axis and risk of falling2 and performance during balance tasks34 has been demonstrated, thresholds could be used as a more reliable dependent variable, for example, to assess the outcome35 or optimal configuration of vestibular implants.

The human vestibular end-organ consists of five components, each optimized for detecting a specific component of the natural motion spectrum. The three semicircular canals are oriented roughly orthogonal to each other, which allows them to detect head rotations around three axes. The canals are accompanied by two macula organs for the registration of translational accelerations along the vertical axis or in the horizontal plane1. A functional decline or loss in each of the five components can lead to severe symptoms such as dizziness, vertigo, imbalance, and an increased risk of falling2. However, objectively assessing the function of all components separately is a laborious task and requires multiple assessments3. For example, the state of the horizontal canal is typically assessed through caloric irrigation and the head impulse test (HIT). The current gold standard for assessing the macula organs is vestibular evoked myogenic potentials (VEMPs). By combining multiple assessments, clinicians arrive at a more complete picture of the vestibular state from which they can derive diagnosis and treatment options.
A promising approach for quantifying vestibular performance is vestibular perceptual thresholds, which provide an objective, quantitative measure of the lowest self-motion intensity that can be reliably detected or discriminated by a participant. Even though perceptual threshold procedures are well established in some clinical disciplines (e.g., audiology), perceptual vestibular thresholds are not yet used for diagnostic purposes in the vestibular domain4. One reason for this is the non-availability of motion platforms and easy-to-use software. In principle, motion platforms and rotatory chairs can be used for threshold estimation. However, while six-degree-of-freedom (6DOF) motion platforms are suitable for estimating thresholds for various motion profiles, enabling the investigation of all five sub-components of the vestibular organ, rotatory chairs can only be used for accessing rotations in the horizontal (yaw) plane1,4.
Vestibular thresholds are typically estimated for translations along the three main axes (naso-occipital, inter-aural, head-vertical) and for rotations around them (yaw, pitch, roll), as visualized in Figure 1. Vestibular perceptual thresholds also depend on the stimulus frequency5. To account for this, motion profiles with a sinusoidal acceleration profile, consisting of a single frequency, are most often used for threshold estimation, but other profiles6,7,8 have also been used in the past.
Vestibular perceptual thresholds provide a tool for studying the interaction between vestibular sensation and higher cognitive processes. Thresholds, therefore, supplement clinical assessments such as the HIT, caloric irrigation, and vestibular evoked potentials, which rely on mechanisms (reflex arcs) bypassing the cortex. Additionally, vestibular perceptual thresholds estimated on a motion platform assess vestibular function in an ecologically valid setting9, rather than using artificial stimulation, which introduces multi-sensory conflicts1.
Due to the bidirectional nature of vestibular stimuli10, it is common to estimate vestibular discrimination rather than detection thresholds4. During a discrimination task, the participant perceives a stimulus and must decide which category it belongs to. For example, participants must decide in which direction they are moved (e.g., left/right). The theoretical framework for the threshold estimation is signal detection theory10,11. Discrimination thresholds can be estimated using various approaches, but in the vestibular domain, adaptive staircase procedures are the standard. In an adaptive staircase procedure, the intensity, typically the peak velocity, of the subsequent movement depends on the participants&#39; response (correct/incorrect) to the last stimulus/stimuli. Adaptive staircase procedures can be implemented in many ways12, but the most frequently used algorithm in vestibular research is x-down/y-up procedures with fixed step sizes. For example, in a three-down/one-up staircase, the stimulus intensity is reduced after the participant has given correct answers in three subsequent trials, but the intensity is increased whenever an incorrect answer has been provided (Figure 2). The exact selection of x and y in a x-down/y-up staircase enables one to target different threshold values (percentage of correct responses)13. A three-down/one-up staircase targets the intensity where participants correctly respond in 79.4% of the trials. Besides adaptive staircase procedures, other studies14 have used predefined, fixed intensities for threshold estimations. Using fixed intensities allows for estimating the whole psychometric function, which contains a lot more information than a single threshold value. However, fixed intensity procedures are time-consuming and less efficient when only a specific threshold value is of interest.
This article describes a protocol for estimating vestibular recognition thresholds using a 6DOF motion platform and an adaptive staircase procedure.

<table><tbody><tr><td>6-DOF Motion Platform</td><td>MOOG</td><td>Models 170E122 or 170E131; Nov 12, 1999</td><td></td></tr><tr><td>Headphones</td><td>Sony</td><td>WH-100XM3</td><td></td></tr><tr><td>PlatformCommander</td><td>University of Bern</td><td>does not apply</td><td>Open Source control software: https://gitlab.com/KWM-PSY/platform-commander</td></tr><tr><td>Response Buttons</td><td>Logitech</td><td>G F310</td><td></td></tr></tbody></table>

estimating vestibular perceptual thresholds using a six-degree-of-freedom motion platform

Vestibular perceptual thresholds refer to the motion intensity required to enable a participant to detect or discriminate a motion based on vestibular input. Using passive motion profiles provided by six degree-of-motion platforms, vestibular perceptual thresholds can be estimated for any kind of motion and thereby target each of the sub-components of the vestibular end-organ. Assessments of vestibular thresholds are clinically relevant as they complement diagnostic tools such as caloric irrigation, the head impulse test (HIT), or vestibular evoked myogenic potentials (VEMPs), which only provide information on sub-components of the vestibular system, but none of them allow for assessing all components. There are several methods with different advantages and disadvantages for estimating vestibular perceptual thresholds. In this article, we present a protocol using an adaptive staircase algorithm and sinusoidal motion profiles for an efficient estimation procedure. Adaptive staircase algorithms consider the response history to determine the peak velocity of the next stimuli and are the most commonly used algorithms in the vestibular domain. We further discuss the impact of motion frequency on vestibular perceptual thresholds.

The result of the described procedure is a graph showing the used stimulus intensities over trials (Figure 2). The intensities should converge toward a constant value (Figure 2, dashed line). The adaptive staircase procedure links an acceleration intensity to the motion perception of the participant. The threshold is typically calculated by the test script (e.g., threshold-test.jl) as the mean value of all or a subset of the intensities presented at reversal trials. No further processing of the obtained value is necessary. Depending on the used update rule, different points on the psychometric function can be targeted. Using the three-down/one-up rule, the intensity at which the participant gives the correct response in 79.4% of the trials is estimated.
Figure 3 visualizes a failed threshold estimation. In the example, the termination criteria were set to 30 trials instead of a sufficient number of reversals. Due to the early mistake (trial 11), the estimation procedures resulted in a poor threshold estimation, which can be recognized by the fact that the staircase did not converge toward a value but kept a monotonic decrease until the end.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/63909/63909fig01.jpg" /> 
Figure 1: Visualization of the main axes and planes. The visualized axes and planes are typically used to describe motions related to head movements. Vestibular perceptual thresholds are most often estimated for the naso-occipital (NO), inter-aural (IA), and head-vertical (HV) axes, and for rotations around them which are referred to as yaw, pitch, or roll rotations. The figure was created using a freely available 3D head model17. <a href="https://www.jove.com/files/ftp_upload/63909/63909fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/63909/63909fig02.jpg" /> 
Figure 2: Visualization of a three-down/one-up staircase procedure. Intensity reversals are visualized in red. Triangles pointing up represent trials with correct responses, and triangles pointing down represent trials with incorrect responses. The dashed line represents the estimated threshold, which was calculated as the mean value of all eight reversal intensities. In the beginning, the update rule follows a one-down pattern until the first reversal (trial 6). This allows for a more efficient threshold estimation, particularly in cases where the start intensity is large compared to the unknown threshold. <a href="https://www.jove.com/files/ftp_upload/63909/63909fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/63909/63909fig03.jpg" /> 
Figure 3: Visualization of a failed threshold estimation. Due to the termination criteria (30 trials) and a selected start intensity relatively far away from the true threshold, the staircase function did not converge. A faster convergence toward the true threshold is hindered by an early, false response (trial 11). <a href="https://www.jove.com/files/ftp_upload/63909/63909fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Estimating Vestibular Perceptual Thresholds Using a Six-Degree-Of-Freedom Motion Platform at JoVE.com

Estimating Vestibular Perceptual Thresholds Using a Six-Degree-Of-Freedom Motion Platform

In this article, we describe the methods, procedures, and technologies required to estimate vestibular perceptual thresholds using a six-degree-of-freedom motion platform.

Vestibular perceptual thresholds refer to the motion intensity required to enable a participant to detect or discriminate a motion based on vestibular ...

estimating-vestibular-perceptual-thresholds-using-six-degree-freedom

Research

JoVE Journal

Behavior

3.0K Views.  University of Bern. Vestibulaire perceptuele drempels maken het mogelijk om alle vijf subcomponenten van het vestibulaire eindorgaan te testen. Ze kunnen worden gebruikt om klinische en fundamentele onderzoeksvragen aan te pakken. Vestibulaire waarnemingsdrempels, gemeten op bewegingsplatform, zijn gebaseerd op naturalistische bewegingsstimuli.Dit maakt de studie van multisensorische integratie en besluitvorming mogelijk. Vestibulaire perceptuele drempels kunnen worden gebruikt om te onderzoeken hoe de pe...

Video: Estimating Vestibular Perceptual Thresholds Using a Six-Degree-Of-Freedom Motion Platform

MPI CyberMotion Simulator: Implementation of a Novel Motion Simulator to Investigate Multisensory Path Integration in Three Dimensions

Path integration is a process in which self-motion is integrated over time to obtain an estimate of one's current position relative to a starting point 1. Humans can do path integration based exclusively on visual 2-3, auditory 4, or inertial cues 5. However, with multiple cues present, inertial cues - particularly kinaesthetic - seem to dominate 6-7. In the absence of vision, humans tend to overestimate short distances (&lt;5 m) and turning angles (&lt;30&deg;), but underestimate longer ones 5. Movement through physical space therefore does not seem to be accurately represented by the brain.
Extensive work has been done on evaluating path integration in the horizontal plane, but little is known about vertical movement (see 3 for virtual movement from vision alone). One reason for this is that traditional motion simulators have a small range of motion restricted mainly to the horizontal plane. Here we take advantage of a motion simulator 8-9 with a large range of motion to assess whether path integration is similar between horizontal and vertical planes. The relative contributions of inertial and visual cues for path navigation were also assessed.
16 observers sat upright in a seat mounted to the flange of a modified KUKA anthropomorphic robot arm. Sensory information was manipulated by providing visual (optic flow, limited lifetime star field), vestibular-kinaesthetic (passive self motion with eyes closed), or visual and vestibular-kinaesthetic motion cues. Movement trajectories in the horizontal, sagittal and frontal planes consisted of two segment lengths (1st: 0.4 m, 2nd: 1 m; &plusmn;0.24 m/s2 peak acceleration). The angle of the two segments was either 45&deg; or 90&deg;. Observers pointed back to their origin by moving an arrow that was superimposed on an avatar presented on the screen.
Observers were more likely to underestimate angle size for movement in the horizontal plane compared to the vertical planes. In the frontal plane observers were more likely to overestimate angle size while there was no such bias in the sagittal plane. Finally, observers responded slower when answering based on vestibular-kinaesthetic information alone. Human path integration based on vestibular-kinaesthetic information alone thus takes longer than when visual information is present. That pointing is consistent with underestimating and overestimating the angle one has moved through in the horizontal and vertical planes respectively, suggests that the neural representation of self-motion through space is non-symmetrical which may relate to the fact that humans experience movement mostly within the horizontal plane.

An efficient way to gain insight into how humans navigate themselves in three dimensions is described. The method takes advantage of a motion simulator capable of moving observers in ways unattainable by traditional simulators. Results confirm that movement in the horizontal plane is underestimated, while vertical movement is overestimated.

Path integration is a process in which self-motion is integrated over time to obtain an estimate of one's current position relative to a starting point 1. ...

Neuroscience

Three Dimensional Vestibular Ocular Reflex Testing Using a Six Degrees of Freedom Motion Platform

The vestibular organ is a sensor that measures angular and linear accelerations with six degrees of freedom (6DF). Complete or partial defects in the vestibular organ results in mild to severe equilibrium problems, such as vertigo, dizziness, oscillopsia, gait unsteadiness nausea and/or vomiting. A good and frequently used measure to quantify gaze stabilization is the gain, which is defined as the magnitude of compensatory eye movements with respect to imposed head movements. To test vestibular function more fully one has to realize that 3D VOR ideally generates compensatory ocular rotations not only with a magnitude (gain) equal and opposite to the head rotation but also about an axis that is co-linear with the head rotation axis (alignment). Abnormal vestibular function thus results in changes in gain and changes in alignment of the 3D VOR response.
Here we describe a method to measure 3D VOR using whole body rotation on a 6DF motion platform. Although the method also allows testing translation VOR responses 1, we limit ourselves to a discussion of the method to measure 3D angular VOR. In addition, we restrict ourselves here to description of data collected in healthy subjects in response to angular sinusoidal and impulse stimulation.
Subjects are sitting upright and receive whole-body small amplitude sinusoidal and constant acceleration impulses. Sinusoidal stimuli (f = 1 Hz, A = 4&deg;) were delivered about the vertical axis and about axes in the horizontal plane varying between roll and pitch at increments of 22.5&deg; in azimuth. Impulses were delivered in yaw, roll and pitch and in the vertical canal planes. Eye movements were measured using the scleral search coil technique 2. Search coil signals were sampled at a frequency of 1 kHz.
The input-output ratio (gain) and misalignment (co-linearity) of the 3D VOR were calculated from the eye coil signals 3.
Gain and co-linearity of 3D VOR depended on the orientation of the stimulus axis. Systematic deviations were found in particular during horizontal axis stimulation. In the light the eye rotation axis was properly aligned with the stimulus axis at orientations 0&deg; and 90&deg; azimuth, but gradually deviated more and more towards 45&deg; azimuth.
The systematic deviations in misalignment for intermediate axes can be explained by a low gain for torsion (X-axis or roll-axis rotation) and a high gain for vertical eye movements (Y-axis or pitch-axis rotation (see Figure 2). Because intermediate axis stimulation leads a compensatory response based on vector summation of the individual eye rotation components, the net response axis will deviate because the gain for X- and Y-axis are different.
In darkness the gain of all eye rotation components had lower values. The result was that the misalignment in darkness and for impulses had different peaks and troughs than in the light: its minimum value was reached for pitch axis stimulation and its maximum for roll axis stimulation.
Case Presentation
Nine subjects participated in the experiment. All subjects gave their informed consent. The experimental procedure was approved by the Medical Ethics Committee of Erasmus University Medical Center and adhered to the Declaration of Helsinki for research involving human subjects.
Six subjects served as controls. Three subjects had a unilateral vestibular impairment due to a vestibular schwannoma. The age of control subjects (six males and three females) ranged from 22 to 55 years. None of the controls had visual or vestibular complaints due to neurological, cardio vascular and ophthalmic disorders.
The age of the patients with schwannoma varied between 44 and 64 years (two males and one female). All schwannoma subjects were under medical surveillance and/or had received treatment by a multidisciplinary team consisting of an othorhinolaryngologist and a neurosurgeon of the Erasmus University Medical Center. Tested patients all had a right side vestibular schwannoma and underwent a wait and watch policy (Table 1; subjects N1-N3) after being diagnosed with vestibular schwannoma. Their tumors had been stabile for over 8-10 years on magnetic resonance imaging.

A method is described to measure three-dimensional vestibulo ocular reflexes (3D VOR) in humans using a six degrees of freedom (6DF) motion simulator. The gain and misalignment of the 3D angular VOR provide a direct measure of the quality of vestibular function. Representative data on healthy subjects are provided

The vestibular organ is a sensor that measures angular and linear accelerations with six degrees of freedom (6DF). Complete or partial defects in the ...

A Vibrotactile Feedback Device for Seated Balance Assessment and Training

Postural perturbations, motion tracking, and sensory feedback are modern techniques used to challenge, assess, and train upright sitting, respectively. The goal of the developed protocol is to construct and operate a sitting platform that can be passively destabilized while an inertial measurement unit quantifies its motion and vibrating elements deliver tactile feedback to the user. Interchangeable seat attachments alter the stability level of the device to safely challenge sitting balance. A built-in microcontroller allows fine-tuning of the feedback parameters to augment sensory function. Posturographic measures, typical of balance assessment protocols, summarize the motion signals acquired during timed balance trials. No dynamic sitting protocol to date provides variable challenge, quantification, and sensory feedback free of laboratory constraints. Our results demonstrate that non-disabled users of the device exhibit significant changes in posturographic measures when balance difficulty is altered or vibrational feedback provided. The portable, versatile device has potential applications in rehabilitation (following skeletal, muscular, or neurological injury), training (for sports or spatial awareness), entertainment (via virtual or augmented reality), and research (of sitting-related disorders).

A sitting platform has been developed and assembled that passively destabilizes sitting posture in humans. During the user&#39;s stabilizing task, an inertial measurement unit records the device&#39;s motion, and vibrating elements deliver performance-based feedback to the seat. The portable, versatile device may be used in rehabilitation, assessment, and training paradigms.

Postural perturbations, motion tracking, and sensory feedback are modern techniques used to challenge, assess, and train upright sitting, respectively. ...

Assessing the Autonomic and Behavioral Effects of Passive Motion in Rats using Elevator Vertical Motion and Ferris-Wheel Rotation

The overall goal of this study is to assess the autonomic and behavioral effects of passive motion in rodents using the elevator vertical motion and Ferris-wheel rotation devices. These assays can help confirm the integrity and normal functioning of the autonomic nervous system. They are coupled to quantitative measures based on defecation counting, open-field examination, and balance beam crossing. The advantages of these assays are their simplicity, reproducibility, and quantitative behavioral measures. The limitations of these assays are that the autonomic reactions could be epiphenomena of non-vestibular disorders and that a functioning vestibular system is required. Examination of disorders such as motion sickness will be greatly aided by the detailed procedures of these assays.

Protocols are presented to assess the autonomic and behavioral effects of passive motion in rodents using elevator vertical motion and Ferris-wheel rotation.

The overall goal of this study is to assess the autonomic and behavioral effects of passive motion in rodents using the elevator vertical motion and ...

Using Unidirectional Rotations to Improve Vestibular System Asymmetry in Patients with Vestibular Dysfunction

The vestibular system provides information about head movement and mediates reflexes that contribute to balance control and gaze stabilization during daily activities. Vestibular sensors are located in the inner ear on both sides of the head and project to the vestibular nuclei in the brainstem. Vestibular dysfunction is often due to an asymmetry between input from the two sides. This results in asymmetrical neural inputs from the two ears, which can produce an illusion of rotation, manifested as vertigo. The vestibular system has an impressive capacity for compensation, which serves to rebalance how asymmetrical information from the sensory end organs on both sides is processed at the central level. To promote compensation, various rehabilitation programs are used in the clinic; however, they primarily use exercises that improve multisensory integration. Recently, visual-vestibular training has also been used to improve the vestibulo-ocular reflex (VOR) in animals with compensated unilateral lesions. Here, a new method is introduced for rebalancing the vestibular activity on both sides in human subjects. This method consists of five unidirectional rotations in the dark (peak velocity of 320&#176;/s) toward the weaker side. The efficacy of this method was shown in a sequential, double-blinded clinical trial in 16 patients with VOR asymmetry (measured by the directional preponderance in response to sinusoidal rotations). In most cases, VOR asymmetry decreased after a single session, reached normal values within the first two sessions in one week, and the effects lasted up to 6 weeks. The rebalancing effect is due to both an increase in VOR response from the weaker side and a decrease in response from the stronger side. The findings suggest that unidirectional rotation can be used as a supervised rehabilitation method to reduce VOR asymmetry in patients with longstanding vestibular dysfunction.

A new rehabilitation method is presented for rebalancing the vestibular system in patients with asymmetric responses, which consists of unidirectional rotations toward the weaker side. By directly modifying the vestibular pathway rather than enhancing the multisensory aspects of compensation, asymmetry can be normalized within 1-2 sessions and show lasting effects.

The vestibular system provides information about head movement and mediates reflexes that contribute to balance control and gaze stabilization during ...

Controlled Rotation of Human Observers in a Virtual Reality Environment

The low cost and availability of Virtual Reality (VR) systems have supported a recent acceleration of research into perception and behavior under more naturalistic, multisensory, and immersive conditions. One area of research that has particularly benefited from the use of VR systems is multisensory integration, for example, the integration of visual and vestibular cues to give rise to a sense of self-motion. For this reason, an accessible method for the controlled physical rotation of an observer in a virtual environment represents a useful innovation. This paper presents a method for automating the rotation of an office swivel chair along with a method for integrating that motion into a VR experience. Using an example experiment, it is demonstrated that the physical motion, thus produced, is integrated with the visual experience of an observer in a way consistent with expectations; high integration when the motion is congruent with the visual stimulus and low integration when the motion is incongruent.

The controlled physical rotation of a human observer is desirable for certain experimental, recreational, and educational applications. This paper outlines a method for converting an office swivel chair into a medium for controlled physical rotation in a virtual reality environment.

The low cost and availability of Virtual Reality (VR) systems have supported a recent acceleration of research into perception and behavior under more ...

Implementing Vestibular Disorder Screening Tests

Screening People on Standing Balance with Romberg Testing and Walking Balance with Tandem Walking

The goal of this protocol is to inform readers about the exact procedures to use to perform two screening tests for vestibular disorders: tandem walking (TW) with eyes closed, also known as heel-toe walking, and the Clinical Test of Sensory Integration and Balance (CTSIB), which is also known as the modified Romberg. The study describes the steps for performing each test and each of the three CTSIB subtests so that the reader will be able to replicate the test conditions for use in the clinic, in the clinical laboratory, or in any other situation needing valid and reliable screening for balance skill which might be affected by changes in vestibular system function. The procedures detailed here can be easily administered and take less than 1 min per trial. References to published papers with normative data are provided. The representative results section includes examples of data collected with these screening tests.

Author Spotlight: Developing Low-Tech Balance Assessment Methods for Broad-Spectrum Healthcare Applications 

This article describes procedures for screening people for standing and walking balance impairments using two normed, rapid, low-tech balance tests.

The goal of this protocol is to inform readers about the exact procedures to use to perform two screening tests for vestibular disorders: tandem walking ...

A Human-machine-interface Integrating Low-cost Sensors with a Neuromuscular Electrical Stimulation System for Post-stroke Balance Rehabilitation

A stroke is caused when an artery carrying blood from heart to an area in the brain bursts or a clot obstructs the blood flow to brain thereby preventing delivery of oxygen and nutrients. About half of the stroke survivors are left with some degree of disability. Innovative methodologies for restorative neurorehabilitation are urgently required to reduce long-term disability. The ability of the nervous system to reorganize its structure, function and connections as a response to intrinsic or extrinsic stimuli is called neuroplasticity. Neuroplasticity is involved in post-stroke functional disturbances, but also in rehabilitation. Beneficial neuroplastic changes may be facilitated with non-invasive electrotherapy, such as neuromuscular electrical stimulation (NMES) and sensory electrical stimulation (SES). NMES involves coordinated electrical stimulation of motor nerves and muscles to activate them with continuous short pulses of electrical current while SES involves stimulation of sensory nerves with electrical current resulting in sensations that vary from barely perceivable to highly unpleasant. Here, active cortical participation in rehabilitation procedures may be facilitated by driving the non-invasive electrotherapy with biosignals (electromyogram (EMG), electroencephalogram (EEG), electrooculogram (EOG)) that represent simultaneous active perception and volitional effort. To achieve this in a resource-poor setting, e.g., in low- and middle-income countries, we present a low-cost human-machine-interface (HMI) by leveraging recent advances in off-the-shelf video game sensor technology. In this paper, we discuss the open-source software interface that integrates low-cost off-the-shelf sensors for visual-auditory biofeedback with non-invasive electrotherapy to assist postural control during balance rehabilitation. We demonstrate the proof-of-concept on healthy volunteers.

A novel low-cost human-machine interface for interactive post-stroke balance rehabilitation system is presented in this article. The system integrates off-the-shelf low-cost sensors towards volitionally driven electrotherapy paradigm. The proof-of-concept software interface is demonstrated on healthy volunteers.

A stroke is caused when an artery carrying blood from heart to an area in the brain bursts or a clot obstructs the blood flow to brain thereby preventing ...

Evaluating Postural Control and Lower-extremity Muscle Activation in Individuals with Chronic Ankle Instability

Computerized dynamic posturography (CDP) is an objective technique for the evaluation of postural stability under static and dynamic conditions and perturbation. CDP is based on the inverted pendulum model that traces the interrelationship between the center of pressure and the center of gravity. CDP can be used to analyze the proportions of vision, proprioception, and vestibular sensation to maintain postural stability. The following characters define chronic ankle instability (CAI): persistent ankle pain, swelling, the feeling of &#8220;giving way,&#8221; and self-reported disability. Postural stability and fibular muscle activation level in individuals with CAI decreased due to lateral ankle ligament complex injuries. Few studies have used CDP to explore the postural stability of individuals with CAI. Studies that investigate postural stability and related muscle activation by using synchronized CDP with surface electromyography are lacking. This CDP protocol includes a sensory organization test (SOT), a motor control test (MCT), and an adaption test (ADT), as well as tests that measure unilateral stance (US) and limit of stability (LOS). The surface electromyography system is synchronized with CDP to collect data on lower limb muscle activation during measurement. This protocol presents a novel approach for evaluating the coordination of the visual, somatosensory, and vestibular systems and related muscle activation to maintain postural stability. Moreover, it provides new insights into the neuromuscular control of individuals with CAI when coping with real complex environments.

Individuals with chronic ankle instability (CAI) exhibit postural control deficiency and delayed muscle activation of lower extremities. Computerized dynamic posturography combined with surface electromyography provides insights into the coordination of the visual, somatosensory, and vestibular systems with muscle activation regulation to maintain postural stability in individuals with CAI.

Computerized dynamic posturography (CDP) is an objective technique for the evaluation of postural stability under static and dynamic conditions and ...

Assessment of Static Graviceptive Perception in the Roll-Plane using the Subjective Visual Vertical Paradigm

Vestibular disorders are among the most common syndromes in medicine. In recent years, new vestibular diagnostic systems have been introduced that allow the examination of all semicircular canals in the clinical setting. Assessment methods of the otolithic system, which is responsible for the perception of linear acceleration and perception of gravity, are far less in clinical use. There are several experimental approaches for measuring the perception of gravity. The most frequently used method is the determination of the subjective visual vertical. This is usually measured with the head in an upright position. We present here an assessment method for testing otolith function in the roll plane. The subjective visual vertical is measured in the head upright position as well as with head inclination of &#177; 15&#176; and &#177; 30&#176; in the roll plane. This extended functional paradigm is an easy-to-perform clinical test of otolith function and ensures increased information content for the detection of impaired graviceptive perception.

The perception of gravity is commonly determined by the subjective visual vertical in the head upright position. The additional assessment at head tilts of &#177; 15&#176; and &#177; 30&#176; in the roll plane ensures increased information content for the detection of impaired graviceptive perception.

Vestibular disorders are among the most common syndromes in medicine. In recent years, new vestibular diagnostic systems have been introduced that allow ...

Estimating Vestibular Perceptual Thresholds Using a Six-Degree-Of-Freedom Motion Platform

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