The authors have no acknowledgements.

The study was approved by the ethical committee of the Medical University of Vienna and has been performed in accordance with the ethical standards found in the Declaration of Helsinki. An informed consent was signed by all patients and controls before the study.
1. Installation of the patient in the chair
<ol>
	<li>Perform the measurement binocularly. Install the patient in a stable chair with a backrest and a head fixation unit. The latter maintains the patient&#39;s head in a stable and defined position and consists of an elastic headband and a u-shaped headrest, which can be fixed to each other using an adhesive strap. Place the chair in a closable cabin allowing assessment of the SVV in the dark.</li>
	<li>Position the headrest in the desired inclination angle (0&#176;, &#177; 15&#176; or &#177; 30&#176;) by aligning it along the scale of a goniometer, which is attached to the chair&#39;s backrest. At the beginning of the experiment adjust the headrest at 0&#176; inclination at suboccipital height.</li>
	<li>Place the elastic headband on the patient&#39;s head and fix it with the screw on the back. Ensure that the headband in not positioned too low on the patient&#39;s forehead, so that it does not impair eye motility.</li>
	<li>Connect the adhesive straps &#8211; on the headband and on the headrest &#8211; with each other. This ensures an optimal fixation of the head to the headrest on the chair.</li>
</ol>
2. Installation of the SVV unit
<ol>
	<li>Mount the SVV unit by means of the fixation device on the chair in front of the patient (Figure 1a). The SVV unit consists of a LED light bar attached to a stick, allowing positioning in front of the patient. The position of the light bar can be adjusted in the roll plane through a connected potentiometer.</li>
	<li>Make sure that the SVV unit is firmly fixed and that the light bar is positioned exactly opposite to the patient&#39;s head and at the same level as the patient&#39;s eyes.</li>
	<li>Connect the SVV unit to the electrical connection underneath the chair.</li>
	<li>Place the potentiometer in the patient&#39;s left hand and instruct them on how to perform the SVV setting. While standing in front of the patient, adjust the position of the light bar again, if necessary, to ensure its position along the coronary plane.</li>
	<li>Read the SVV deviation from the true vertical on the goniometer on the back of the SVV unit. The goniometer contains an angle display of &#177;20&#176; at 2&#176; intervals and is equipped with an infrared camera placed 3 cm in front of the display, allowing continuous data acquisition in complete darkness (Figure 1b, 1c).</li>
	<li>Before continuing with the next step, check the visibility on the screen. The infrared-image of the angle display is transmitted to a screen outside of the cabin, ensuring that the patient&#39;s SVV estimates can be collected continuously without having to open the cabin door between tests, therefore preventing visual re-orientation.</li>
</ol>
3. Calibration under visual control
<ol>
	<li>Tilt the light bar 30&#176; to the right or left relative to the absolute vertical (which serves as start position before each SVV task) and ask the patient to adjust it to the vertical position under visual control. This serves to self-calibrate the patient and to check the visuomotor ability of the patient.</li>
	<li>If the patient confirms the displayed SVV position, compare it with the actual vertical.</li>
	<li>If the patient&#39;s setting deviates significantly from the actual vertical, check the orthograde position of the SVV unit again. A deviation of &#177;1&#176; is tolerable to confirm intact visuomotor function.</li>
</ol>
4. SVV setting in neutral head position
<ol>
	<li>Open the examination protocol for simultaneous entry of the SVV estimates. The protocol allows the documentation of the measurements during the experiment and randomly determines whether the SVV task is performed from the +30&#176; or -30&#176; starting position.</li>
	<li>Close the cabin door so that the patient is in complete darkness throughout the experiment. Check by intercom if the patient can understand the instructions well. Ask the patient now to tilt the light bar in the starting position: 30&#176; to the right or to the left (randomization according to the protocol, Figure 1d).</li>
	<li>After a waiting period of 15 s, instruct the patient to adjust the lightbar from the starting position until it reaches the subjective vertical. The patient is not under time pressure and can still correct the set position at any time. The patient confirms the setting verbally via the intercom system.</li>
	<li>Enter the tilt angle shown on the display in degrees in the protocol. Per definition, mark clockwise angle deviations with a plus, while mark counterclockwise deviations with a minus. In total, let the patient adjust the SVV in 6 passes, whereby the starting position of &#177;30&#176; is randomized.</li>
	<li>After completion of the trial in neutral head position, perform the test with head tilting in the roll plane. The tilt direction sequence (-30&#176;, -15&#176;, +15&#176; and +30&#176;) is also randomized for each patient.</li>
</ol>
5. SVV setting with head tilt
<ol>
	<li>Undo the initial head fixation by disconnecting the adhesive straps.</li>
	<li>Loosen the headrest and adapt the tilt position according to the protocol: 15&#176; or 30&#176; to the right or to the left. Make sure that the headrest is exactly aligned along the respective angle at the goniometer, which is attached to the chair&#39;s backrest. Fix the headrest in this position firmly.</li>
	<li>Fix the patient&#39;s head with the elastic headband to the headrest. Ensure that this head tilt is tolerable for the patient and adapt the height of the headrest if needed. Instruct the patient to maintain this head position during the trial.</li>
	<li>Close the cabin door and perform the trial as in the neutral head position.</li>
	<li>Upon completion of the trial, undo the head restraint and adjust the headrest according to the randomized head-tilt position given by the protocol.</li>
	<li>Close the cabin door again and perform the same procedures until all SVV settings in all head tilts have been recorded.</li>
</ol>

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The authors have nothing to disclose.

SVV is a method to ensure the sense of verticality. It results from the integration of several information. The vestibular system being of paramount importance in this perception, it has been shown that a lesion at any level of vestibular information pathway leads to SVV errors.
The measurement of SVV in the head upright position is now regarded as the clinical standard method for recording otolith function. However, this method is hampered by low sensitivity as SVV-deviations in darkness in healthy individuals are limited to &#177;2&#176; from the earth vertical14. Previous experimental studies have suggested that tilting the head in the frontal plane increases the sensitivity of the SVV test23. Several reports have been published on the effects of head tilts on SVV estimates in normal subjects, confirming a higher variability of the responses and thus possibly higher sensitivity in terms of graviceptive assessment in this paradigm. Whether this dynamic method definitely also increases the sensitivity in the detection of otolith function has still to be confirmed by direct method comparison. However, none of these previous experimental studies used a standardized protocol for applied head tilts, which ranged from 7&#176; up to 20&#176;, 30&#176;, 35&#176; or even 45&#176; in the roll plane24,25,26,27, thus making a comparison of results difficult.
The SVV paradigm at different head tilts has so far scarcely been applied in patients with central or peripheral vestibular disorders. Previous studies also used either different techniques in patients with peripheral lesions28,21 or applied different head tilts (i.e., 20&#176; or 25&#176;) in patients with central disorders like neglect or vestibular migraine29,30. These different procedures for the determination of the SVV make it reasonable to introduce a standardized test procedure in order to make test results more comparable.
The test protocol has several advantages compared to other test methods. First of all, it is characterized by a simpler applicability than the application of linear accelerations, centrifuges or whole body tilts for measuring otolith function in patients. While there are efforts to improve the quality of VEMPs in research and practice31,32, this clinically easy method still has a low sensitivity for the assessment of otolith impairment11. Thus, the easiest method to use in the clinical setting today is SVV measurement. The modified technique presented by us yields an increased variability of the responses and thus an increased information content by measuring under different head positions (Table 1), as previous data on normal subjects have also demonstrated23,27. Both our approaches of SVV assessment with head tilt and the bucket method represent feasible techniques of measurement of the otolith function. While the bucket test13 is a validated, easily performed bedside test accessible to everyone, our approach offers high sensitivity but still needs certain technical equipment. Zwergal et al. found an SVV deviation of 0.9&#176; &#177; 0.7&#176; for binocular measurements13. The validated technique of SVV assessment without head tilt resulted in an SVV median of 1.33 with 0 to 3.0 (95% CI) in the healthy cohort. With the approach of assessment with 15% head tilt, an SVV median of 1.66 with 0.34 to 5.34 (95% CI) was obtained.
The measurement in four different head tilt angles (i.e., &#177;15&#176; and &#177;30&#176; in the roll plane) is tolerable for patients and increases the robustness of the SVV responses in the test arrangement (Figure 2); the method is therefore also an ideal instrument for demonstrating the effect of interventions in a more sensitive way, as we were able to show in a Botox treatment study with cervical dystonia patients (Figure 3,4). Furthermore, the presented method can also be extended for experimental questions by the additional projection of a pattern rotating around the visual axis, so that the so-called dynamic SVV can be determined5.
In order to carry out the test method correctly, some points should be observed during the test procedure. For instruction and practice, as well as to check the patient&#39;s visuomotor abilities, we recommend that the patient makes the first SVV adjustments under visual control. It is also important that the cabin is always completely closed during the SVV settings so that the patient is actually in complete darkness, as any visual reference point can influence the settings. The order of the head positions should always be randomized, as should the start position of the lightbar before the respective SVV adjustment. Experiences from previous pilot tests showed that a continuous change of the head position, for example from -30&#176; to -15&#176;, to 0&#176;, +15&#176; and finally +30&#176;, leads to a directional bias in the SVV adjustments, apparently due to a learning effect. Previous studies have also shown that a prolonged retention of head tilt leads to an after-effect in SVV settings that falsifies the results27. Therefore, it is recommended not to allow too long a latency between head position changes.
Furthermore, the goniometer allows measurement of &#177;20&#176; at 2&#176; intervals. However, although the goniometer used shows 2&#176; intervals, the pointer used has a very high sensitivity and thus also enables the recording of numerical values between the intervals. This allows a visual resolution of 1&#176; without any problems when viewed on an external screen. The resolution of 1&#176; is also reflected in the representative test results shown.
Despite the simple handling of the method, it cannot or should not be used for some patient groups. These naturally include patients with severe visual impairments, with operative fixations in the area of the cervical spine, or patients who are cognitively or for other neurological reasons unable to adequately adjust the SVV. It is also not recommended for patients with cervical disc prolapse or severe cervical pain syndrome. Patients suffering from cervical dystonia can also only be examined to a limited extent with this method. However, previous studies from our laboratory show that these patients can still be examined as long as the head tilt does not exceed an angle of 30&#176; in the roll plane22.

Impairment of otolith function can be caused by peripheral as well as by central vestibular conditions1. Peripheral vestibular causes include Meniere&#39;s disease, labyrinth infarction, as well as superior or inferior vestibular neuritis. Central otolith dysfunction can occur in lesions of central otolithic pathways from brain stem via thalamus2 to the vestibular cortex3. In addition, diminished otolith reflexes are also found in cerebellar disorders4. While a number of standardized methods, such as caloric testing or video-head impulse test, are available for the assessment of semicircular canal function, no standardized clinical measurement method exists for gravity estimation and verticality perception5.
Since the otoliths are responsible for the perception of linear acceleration, otolith function can in principle be measured by linear acceleration by recording the so-called translational vestibulo-ocular reflex (t-VOR). However, this requires the use of special and complex equipment such as a parallel swing or linear sleds4,6. For the assessment of unilateral saccular and utricular function a specific off-center centrifugation test has been developed, which could be used clinically in balance laboratories with a specific rotational chair system7. When displacing the head by 3.5&#8211;4 cm from the rotation axis, the eccentrically positioned utricle is stimulated unilaterally by a resultant centrifugal force. In this paradigm otolith function can be determined either by measuring the resulting eye torsion or the subjective visual vertical (SVV). This procedure, however, also requires sophisticated equipment and the method still shows limited sensitivities for both SVV and eye torsion assessment7. Otolith function can further be quantified through eye movement recordings. Assessment can be done in horizontal or linear acceleration, but also during head- or body tilt in the roll plane with application of 3-D videooculography. The latter allows determination of ocular torsion. The clinical application of this method is also limited due to its low sensitivity8. The perception of body verticality (i.e., the sensation that I feel my body aligned with the true vertical) can be assessed by means of the so-called subjective postural vertical. In this experimental task, patients are seated in a chair in a motorized gimbal and asked to indicate when they entered and exited the upright position, while being tilted 15 &#176; in the pitch or roll plane. The disadvantage of this technique is not only its elaborate experimental approach, but also that it measures both otolith and body proprioceptive signals9. Whether vestibular evoked myogenic potentials (VEMPs) are useful clinical screening tools for otolith function in various clinical disorders is still controversial10,11.
Visual tasks are currently the most frequently used clinical methods for measuring graviceptive function, which can be assessed through measurement of the subjective visual vertical (SVV)12. Seen from a precise physiological perspective, SVV is not a direct test of the otolith function alone, as the SVV is the result of a weighting between several sources of information (gravity, proprioceptive and also visual when they are available). However, for rapid clinical use, an easy application of this SVV task, the so-called bucket test, has been developed13 especially for the emergency setting, enabling immediate detection of acute disturbances of graviceptive perception. The more precise and standardized procedure consists of letting an observer align a light bar or rod with the estimated vertical. Tested in darkness in healthy individuals in an upright position, deviations are limited to &#177; 2&#176; from the earth vertical14. Using the SVV task, graviceptive function has so far been assessed in a variety of neurological conditions such as stroke15,16 or Parkinson&#8217;s disease17. Furthermore, impaired SVV-perception has also been reported in unilateral18,19 or bilateral vestibular lesions20, as well as in patients with benign paroxysmal positional nystagmus21.
We here present a modified SVV assessment method, which measures SVV estimates not only in head-upright position but also at &#177; 15&#176; and &#177; 30&#176; head tilts in the roll plane. This paradigm increases the information content for the detection of graviceptive deficits and for systematic tilts of the SVV.

<table><tbody><tr><td>Adjustable plastic goniometer board 7,87&quot; x 7,87&quot;, (marked tilt angles of 0&amp;deg;, 15&amp;deg; and 30&amp;deg; )</td><td>self-produced</td><td>6</td><td>for fixation at the backrest and for adjustment of neckrest along the given tilt angles (0&amp;deg;,15&amp;deg;,30&amp;deg;)</td></tr><tr><td>Elastic head band with adjustable screw on the back</td><td>Micromedical Technologies Inc</td><td>4</td><td>modified with attached adhesive strap</td></tr><tr><td>HD LCD display, 1366 x 768p resolution, 19&quot;</td><td>Philips</td><td>5</td><td>for monitoring SVV-adjustments outside the cabin (infrared camera recording)</td></tr><tr><td>Subjective Visual Vertical Set including infrared video camera (black/white, resolution 0,25&amp;deg;)</td><td>Micromedical Technologies Inc</td><td>2</td><td></td></tr><tr><td>Sytem 2000 (Rotational Vestibular Chair System with Centrifuge)</td><td>Micromedical Technologies Inc., 10 Kemp Dr., Chatham, IL 62629-9769 United States</td><td>1</td><td></td></tr><tr><td>Tiltable headrest&amp;nbsp;</td><td>Micromedical Technologies Inc</td><td>3</td><td>modified with attached adhesive strap</td></tr></tbody></table>

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.

SVV assessment was performed using a rotational chair system (Figure 1a) comprising a tiltable headrest and an adjustable LED light bar. The SVV adjustments were recorded via an infrared camera from a goniometer display on the back of the lightbar (Figure 1b). The devices used and the test protocol correspond exactly to the test methods presented here.
SVV measurement was performed in 13 healthy individuals at a mean age of 52.8 years. Gender distribution was 69.2% females and 30.8% males. They had no history of vestibular disorders and exhibited normal results in vestibular- and ocular motor function tests, which included assessment of spontaneous eye movements or spontaneous nystagmus, assessment of gaze-evoked nystagmus (at &#177;25&#176;), horizontal and vertical saccades (&#177;5-20&#176;), smooth pursuit eye movements (at 0.1, 0.2 and 0.4 Hz), VOR-gain examination with sinusoidal rotational chair test (at 0.04, 0.08 and 0.32 Hz) and test of VOR-suppression (at 0.04 Hz). The absolute tilt of the SVV from the actual vertical at 0&#176; head position was assessed (Figure 2) and showed an SVV median of 1.33 (95% CI 0 to 3.00), which correlates with values reported in the literature.
At a head tilt of 15&#176; an SVV median of 1.66 was achieved (95% CI, 0.34 to 5.34; Figure 2) and measurements of the SVV at a head tilt of 30&#176; yielded an SVV median of 5.33 (95% CI, 0.17 to 9.84; Figure 2). In conclusion, increased deviation and variability of the SVV was observed with higher head tilt angles, correlating with a higher information content for detecting graviceptive impairment in a dynamic setting.
The method was also used to analyze SVV tilts in patients suffering from cervical dystonia (CD). In total, 32 patients were tested. The patient group had a median age of 59.0 years and consisted of 36.7% males and 63.3% females. They exhibited a median habitual head deviation of either 10.0&#176; clockwise or 8.5&#176; counterclockwise. Assessment of the SVV at the patient&#8217;s habitual head posture revealed major deviations from the actual vertical with a median of 2.65&#176; (95% CI, 0.17 to 7.83; Figure 3, second bar). In comparison to healthy individuals at their habitual head posture (approximately 0&#176; head tilt), the patient&#8217;s response was significantly impaired with a median difference of &#8211; 1.34&#176; (95% CI, -2.5 to -0.33, p=0.017; Figure 3, first bar).
The method was subsequently also used in a follow-up examination in order to assess possible treatment effects. Patients suffering from cervical dystonia were treated with botulinum toxin (BoNT) in order to improve the head posture into an upright position. Three weeks after injection of BoNT, the patients&#8217; SVV estimates in habitual head position (Figure 3) and at 30&#176; head tilt (Figure 4) did not differ anymore from those of controls. A detailed discussion and interpretation of these results can be found in a preceding paper22.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60418/60418fig1.jpg" /> 
Figure 1: Experimental setup. (a) A rotational chair system is used for SVV assessment, equipped with a tiltable headrest and an adjustable LED light bar. (b) The goniometer on the back of the lightbar covers a total measuring width of &#177;20&#176; at 2&#176; intervals. The SVV adjustments are recorded via an infrared camera (black box in front of the goniometer display), allowing data acquisition from outside the cabin. SVV was assessed in an upright sitting position in a completely dark cylindrical cabin with a diameter of 2 meters. In front of the participants, at a distance of 50 cm, there was a dim light bar, 2 mm wide and 10 cm long, which could be rotated about its midpoint by means of an electronic motor and a remote control device, so that a coaxial rotation around the middle eye of the test subject was guaranteed. All participants adjusted the bar six times from randomized starting positions at &#177;30&#176; (relative to the absolute vertical) for parallel alignment with the perceived gravitational vertical. The six estimates were averaged for further analysis. (c) The headrest can be tilted 15&#176; or 30&#176; to the right or to the left. Through an adhesive strap on the headband and the headrest, the patient&#8217;s head can be firmly fixed in the desired position. (d) Schematic map of the arrangement of the experimental setup. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/60418/60418fig1large.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/60418/60418fig2v2.jpg" /> 
Figure 2: SVV tilts in healthy individuals. Absolute SVV tilt in degree assessed at head tilts of 0&#176;, 15&#176; and 30&#176; in healthy individuals. Increase of the SVV tilt was observed with higher head tilt angles. With permission from Elsevier (This figure has been modified from Platho-Elwischger et al. 201722). <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/60418/60418fig2v2large.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/60418/60418fig3v2.jpg" /> 
Figure 3: SVV tilts in patients suffering from cervical dystonia upon injection of botulinum toxin. Absolute SVV tilt in degree assessed in healthy controls, patients suffering from cervical dystonia at baseline (CD baseline) and three weeks after injection of botulinum toxin (CD week 3) at habitual head posture. SVV deviations of CD patients at baseline were significantly increased compared to controls (p=0.017), but not after botulinum toxin injection (CD week 3). With permission from Elsevier (This figure has been modified from Platho-Elwischger et al. 201722). <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/60418/60418fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/60418/60418fig4v2.jpg" /> 
Figure 4: SVV tilt in CD patients and controls during head tilt. Absolute SVV tilt during 0&#176; (A), 15&#176;(B) and 30&#176; (C) head tilt in controls, CD patients at baseline (CD baseline) and three weeks after injection of botulinum toxin (CD week 3). SVV estimations of CD patients at baseline with 30&#176; head tilt showed significantly increased deviations compared to controls, which was not the case after botox therapy (CD week 3). With permission from Elsevier (This figure has been modified from Platho-Elwischger et al. 201722). <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/60418/60418fig4v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1">
	<tbody>
		<tr>
			<td rowspan="2">Patients</td>
			<td rowspan="2">N</td>
			<td rowspan="2">Head tilt</td>
			<td rowspan="2">SVV median (95% CI)</td>
			<td colspan="2">Within group differences</td>
		</tr>
		<tr>
			<td>Mean difference (95% CI)</td>
			<td>p-Values</td>
		</tr>
		<tr>
			<td rowspan="3">Controls</td>
			<td rowspan="3">13</td>
			<td>0&#176;</td>
			<td>1.33 (0 to 3.00)</td>
			<td>0&#176; vs. 15&#176;: &#8722; 0.85&#176; (&#8722; 2.1 to 0.36)</td>
			<td>0.1525</td>
		</tr>
		<tr>
			<td>15&#176;</td>
			<td>1.66 (0.34 to 5.34)</td>
			<td>15 vs. 30&#176;: &#8722; 2.31&#176; (&#8722; 3.72 to &#8722; 0.90)</td>
			<td>0.0039*</td>
		</tr>
		<tr>
			<td>30&#176;</td>
			<td>5.33 (0.17 to 9.84)</td>
			<td>0&#176; vs. 30&#176;: &#8722; 3.17&#176; (&#8722; 5.39 to &#8722; 0.94)</td>
			<td>0.009*</td>
		</tr>
	</tbody>
</table>
Table 1: Descriptive data of absolute SVV tilt and differences within head-positions in healthy individuals. SVV was measured in degree (&#176;). Statistically significant values (p&#60;0.05) are marked with *. CI: confidence interval; N: number of patients; SVV: subjective visual vertical. With permission from Elsevier (This table has been modified from Platho-Elwischger et al. 201722).

Watch this Scientific Journal Video about Assessment of Static Graviceptive Perception in the Roll-Plane using the Subjective Visual Vertical Paradigm at JoVE.com

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

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 ...

assessment-static-graviceptive-perception-roll-plane-using-subjective

Universidad San Sebastian

Research

JoVE Journal

Medicine

5.7K Views.  Medical University Vienna, Austria. The perception of gravity is commonly determined by the subjective visual vertical in the head upright position. The additional assessment at head tilts of ± 15° and ± 30° in the roll plane ensures increased information content for the detection of impaired graviceptive perception.

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

Measuring Sensitivity to Viewpoint Change with and without Stereoscopic Cues

The speed and accuracy of object recognition is compromised by a change in viewpoint; demonstrating that human observers are sensitive to this transformation. Here we discuss a novel method for simulating the appearance of an object that has undergone a rotation-in-depth, and include an exposition of the differences between perspective and orthographic projections. Next we describe a method by which human sensitivity to rotation-in-depth can be measured. Finally we discuss an apparatus for creating a vivid percept of a 3-dimensional rotation-in-depth; the Wheatstone Eight Mirror Stereoscope. By doing so, we reveal a means by which to evaluate the role of stereoscopic cues in the discrimination of viewpoint rotated shapes and objects.

We discuss a novel method forviewpoint-rotation of visual stimuli, and demonstrate using a mirror stereoscopethe three-dimensional percept of rotation-in-depth. The technique can be used to investigate the role of stereoscopic cues in encoding viewpoint-rotated figures.

The speed and accuracy of object recognition is compromised by a change in viewpoint; demonstrating that human observers are sensitive to this ...

Behavior

Methods to Explore the Influence of Top-down Visual Processes on Motor Behavior

Kinesthetic awareness is important to successfully navigate the environment. When we interact with our daily surroundings, some aspects of movement are deliberately planned, while others spontaneously occur below conscious awareness. The deliberate component of this dichotomy has been studied extensively in several contexts, while the spontaneous component remains largely under-explored. Moreover, how perceptual processes modulate these movement classes is still unclear. In particular, a currently debated issue is whether the visuomotor system is governed by the spatial percept produced by a visual illusion or whether it is not affected by the illusion and is governed instead by the veridical percept. Bistable percepts such as 3D depth inversion illusions (DIIs) provide an excellent context to study such interactions and balance, particularly when used in combination with reach-to-grasp movements. In this study, a methodology is developed that uses a DII to clarify the role of top-down processes on motor action, particularly exploring how reaches toward a target on a DII are affected in both deliberate and spontaneous movement domains.

It is unclear how top-down signals from the ventral visual stream affect movement. We developed a paradigm to test motor behavior towards a target on a 3D depth inversion illusion. Significant differences are reported in both deliberate, goal-directed movements and automatic actions under illusory and veridical viewing conditions.

Kinesthetic awareness is important to successfully navigate the environment. When we interact with our daily surroundings, some aspects of movement are ...

How to Study Placebo Responses in Motion Sickness with a Rotation Chair Paradigm in Healthy Participants

Placebo responses occur in every medical intervention when patients or participants expect to receive an effective treatment to relieve symptoms. However, underlying mechanisms of placebo responses are not fully understood. It has repeatedly been shown that placebo responses are associated with changes in neural activity but for many conditions it is unclear whether they also affect the target organ, such as the stomach in motion sickness. Therefore, we present a methodology for the multivariate assessment of placebo responses by subjective, behavioral and objective measures in motion sickness with a rotation chair paradigm. The physiological correlate of motion sickness is a shift in gastric myoelectrical activity towards tachygastria that can be recorded with electrogastrography. The presented study applied the so-called balanced placebo design (BPD) to investigate the effects of ginger compared to placebo and the effects of expectations by verbal information. However, the study revealed no significant main or interactional effects of ginger (as a drug) or information on outcome measures but showed interactions when sex of participants and experimenters are taken into considerations. We discuss limitations of the presented study and report modifications that were used in subsequent studies demonstrating placebo responses when rotation speed was lowered. In general, future placebo studies have to identify the appropriate target organ for the studied placebo responses and to apply the specific methods to assess the physiological correlates.

An experimental rotation chair paradigm is used to investigate whether a placebo intervention on motion sickness affects subjective outcome measures only or also affects behavioral and objective measures in a balanced placebo design.

Placebo responses occur in every medical intervention when patients or participants expect to receive an effective treatment to relieve symptoms. However, ...

Visualization Method for Proprioceptive Drift on a 2D Plane Using Support Vector Machine

Proprioceptive drift, which is a perceptual shift in body-part position from the unseen real body to a visible body-like image, has been measured as the behavioral correlate for the sense of ownership. Previously, the estimation of proprioceptive drift was limited to one spatial dimension, such as height, width, or depth. As the hand can move freely in 3D, measuring proprioceptive drift in only one dimension is not sufficient for the estimation of the drift in real life situations. In this article, we provide a novel method to estimate proprioceptive drift on a 2D plane using the mirror illusion by combining an objective behavioral measurement (hand position tracking) and subjective, phenomenological assessment (subjective assessment of hand position and questionnaire) with a sophisticated machine learning approach. This technique permits not only an investigation of the underlying mechanisms of the sense of ownership and agency but also assists in the rehabilitation of a missing or paralyzed limb and in the design rules of real-time control systems with a self-body-like usability, in which the operator controls the system as if it were part of his/her own body.

This article describes a novel method to estimate proprioceptive drift on a 2D plane using the mirror illusion and combining a psychophysical procedure with an analysis using machine learning.

Proprioceptive drift, which is a perceptual shift in body-part position from the unseen real body to a visible body-like image, has been measured as the ...

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 ...

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 ...

Computerized Dynamic Posturography for Postural Control Assessment in Patients with Intermittent Claudication

Computerized dynamic posturography with the EquiTest is an objective technique for measuring postural strategies under challenging static and dynamic conditions. As part of a diagnostic assessment, the early detection of postural deficits is important so that appropriate and targeted interventions can be prescribed. The Sensory Organization Test (SOT) on the EquiTest determines an individual&#39;s use of the sensory systems (somatosensory, visual, and vestibular) that are responsible for postural control. Somatosensory and visual input are altered by the calibrated sway-referenced support surface and visual surround, which move in the anterior-posterior direction in response to the individual&#39;s postural sway. This creates a conflicting sensory experience. The Motor Control Test (MCT) challenges postural control by creating unexpected postural disturbances in the form of backwards and forwards translations. The translations are graded in magnitude and the time to recover from the perturbation is computed.
Intermittent claudication, the most common symptom of peripheral arterial disease, is characterized by a cramping pain in the lower limbs and caused by muscle ischemia secondary to reduced blood flow to working muscles during physical exertion. Claudicants often display poor balance, making them susceptible to falls and activity avoidance. The Ankle Brachial Pressure Index (ABPI) is a noninvasive method for indicating the presence of peripheral arterial disease and intermittent claudication, a common symptom in the lower extremities. ABPI is measured as the highest systolic pressure from either the dorsalis pedis or posterior tibial artery divided by the highest brachial artery systolic pressure from either arm. This paper will focus on the use of computerized dynamic posturography in the assessment of balance in claudicants.

Individuals with intermittent claudication exhibit poor balance compared to healthy controls. Computerized dynamic posturography is an objective method for measuring an individual's postural responses to balance disturbances. This provides an objective reflection of the person&#x2019;s ability to respond to situations under which sensory stimuli are altered and unexpected perturbations occur.

Computerized dynamic posturography with the EquiTest is an objective technique for measuring postural strategies under challenging static and dynamic ...

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 ...

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.

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 ...