The subjective visual horizontal for different body tilts in the roll plane: characterization of normal subjects

Statistical Considerations for Subjective Visual Vertical and Subjective Visual Horizontal Assessment in Normal Subjects

Objectives

Judgments of the subjective visual vertical (SVV) and subjective visual horizontal (SVH) while seated upright are commonly included in standard clinical test batteries for vestibular function. We examined SVV and SVH data from retrospective control to assess their statistical distributions and normative values for magnitudes of the preset effect, sex differences, and fixed-head versus head-free device platforms for assessment.

Methods

Retrospective clinical SVV and SVH data from 2 test platforms, Neuro-otologic Test Center (NOTC) and the Neurolign Dx 100 (I-Portal Portable Assessment System Nystagmograph) were analyzed statistically (SPSS and MATLAB software) for 408 healthy male and female civilians and military service members, aged 18-50 years.

Results

No prominent age-related effects were observed. The preset angle effects for both SVV and SVH, and their deviations from orthogonality, agree in magnitude with previous reports. Differences attributable to interactions with device type and sex are of small magnitude. Analyses confirmed that common clinical measure for SVV and SVH, the average of equal numbers of clockwise and counterclockwise preset trials, was not significantly affected by the test device or sex of the subject. Finally, distributional analyses failed to reject the hypothesis of underlying Gaussian distributions for the clinical metrics.

Conclusions

z scores based on these normative findings can be used for objective detection of outliers from normal functional limits in the clinic.

Evaluation of subjective vertical perception among stroke patients: a systematic review

BACKGROUND

Verticality misperception is relatively common among patients after stroke, and it may be evaluated in terms of (a) subjective visual vertical (SVV), (b) subjective haptic vertical (SHV) and (c) subjective postural vertical (SPV). To better understand these assessment methods, we conducted a systematic review of the methodological characteristics of different protocols for evaluating SVV, SHV and SPV among individuals after stroke.

OBJECTIVE

To standardize the methodological characteristics of protocols for evaluating verticality perception after stroke.

METHODS

We searched the following databases: PUBMED, regional BVS portal (MEDLINE, LILACS, IBECS, CUBMED, Psychology Index and LIS), CINAHL, SCOPUS, Web of Science, Science Direct, Cochrane Library and PEDro. Two review authors independently used the QUADAS method (Quality Assessment of Diagnostic Accuracy Studies) and extracted data.

RESULTS

We included 21 studies in the review: most (80.9%) used SVV, eight (38.1%) used SPV and four (19.0%) used SHV. We observed high variability in assessments of verticality perception, due to patient positions, devices used, numbers of repetitions and angle of inclination for starting the tests.

CONCLUSION

This systematic review was one of the first to explore all the methods of assessing verticality perception after stroke, and it provides crucial information on how to perform the tests, in order to guide future researchers/clinicians.

The Test-Retest Reliability of Subjective Visual Horizontal Testing: Comparisons between Solid and Dotted Line Images

The present study aimed to determine the test-retest reliability of subjective visual horizontal (SVH) testing when tested with solid and dotted line images. In this repeated measures study, 36 healthy young Malaysian adults (mean age=23.3±2.3 years, 17 males and 19 females) were enrolled. All of them were healthy and had no hearing, vestibular, balance, or vision problems. The SVH angles were recorded from each participant in an upright body position using a computerized device. They were asked to report their horizontality perception for solid and dotted line images (in the presence of a static black background). After 1 week, the SVH procedure was repeated. The test-retest reliability of SVH was found to be good for both solid line [intraclass correlation (ICC)=0.80] and dotted line (ICC=0.78). As revealed by Bland-Altman plots, for each visual image, the agreements of SVH between the two sessions were within the clinically accepted criteria (±2°). The SVH testing was found to be temporally reliable, which can be clinically beneficial. Both solid and dotted lines in the SVH testing are reliable to be used among young adults.

Altered Visual and Proprioceptive Spatial Perception in Individuals with Parkinson's Disease

Difficulties in the integration of visual, vestibular, and somatosensory information in individuals with Parkinson's disease (PD) may alter perception of verticality. Accordingly, in this cross-sectional study, we analyzed PD patients' (n = 13) subjective visual vertical (SVV) and subjective haptic vertical (SHV) perceptions and compared them to those of healthy controls (n = 14). We compared SVV and SHV findings among participants with PD, healthy controls, and cutoff points of normality based on prior research literature, using the parametric nonpaired t test (at p < .05) and Cohen's d (at d > 0.8) to determine clinical relevance. We analyzed SVV with the bucket test and SHV with the rod rotations task in clockwise and counterclockwise directions. We calculated Pearson correlations to analyze the association between verticality tests and the most clinically affected body side. We calculated both the percentage of A-effect (expression of body tilt underestimation to the midline) and E-effect (expression of body tilt overestimation in the upright position). Individuals with PD showed greater variability in right SHV supination compared to the healthy control participants (p = .002). There was greater clinical relevance in right (as opposed to left) SVV (d = 0.83), right (as opposed to left) SHV pronation (d = 0.91), and left (as opposed to right) SHV pronation (d = 0.88). We observed a higher proportion of E-effect in individuals with PD. A significantly higher proportion of patients with PD, compared to patients in past literature, had right SHV pronation (p = .001), left SHV pronation (p = .023), right SHV supination (p = .001), left SHV supination (p = .046), and left SHV pronation (p = .046). Thus, subjective visual and proprioceptive perception of verticality is altered in patients with PD, compared to individuals without PD.

Assessment of Subjective Visual Vertical (SVV) Using the "Bucket Test" and the Virtual SVV System

OBJECTIVE

The purpose of this study was to describe the variability and test-retest reliability of a commercially available subjective visual vertical (SVV) system known as Virtual SVV (Interacoustics). In addition, the study aimed to compare the reliability of the Virtual system with a previously established bucket test of SVV.

STUDY DESIGN

Fifteen participants with normal hearing, normal middle ear function, and normal utricular function were included in the study. Each participant underwent static SVV testing using both the Virtual system and the bucket test. Subjects completed 2 testing sessions to determine test-retest reliability. For each test, data were collected with the head at 0°, tilted 45° to the right, and tilted 45° to the left.

SETTING

This study was conducted in a balance function laboratory embedded in a large, tertiary care otology clinic.

RESULTS

The mean SVV values obtained with the Virtual system were within 1°-2° from 0 with the head positioned at 0°, which is in agreement with many other studies of SVV with the head at 0° (Akin & Murnane, 2009; Halmagyi & Curthoys, 1999; Zwergal, Rettinger, Frenzel, Dieterich, & Strupp, 2009). Using the intraclass correlation coefficient, test-retest reliability of the Virtual system was excellent in the 45° left position and fair to good in the 45° right and 0° position. Test-retest reliability of the bucket test was poor in all head positions.

CONCLUSIONS

The Virtual system is a more reliable measure of static SVV than the bucket test. Therefore, the Virtual system could be utilized as a screening device for utricular dysfunction in busy clinical settings.

Otolith organ function according to subtype of benign paroxysmal positional vertigo

OBJECTIVES/HYPOTHESIS

The clinical features and treatment outcomes of benign paroxysmal positional vertigo (BPPV) are known to be different depending on the type of and involved canal. This difference could be due to differences in the functional change of the otolith organ.

STUDY DESIGN

Case series.

METHODS

Forty-nine patients were diagnosed to primary BPPV; 18 were categorized as posterior canal canalolithiasis (PC canalolithiasis), and 31 were categorized as horizontal canal (HC) BPPV with canalolithiasis or cupulolithiasis (HC canalolithiasis or HC cupulolithiasis). Diagnostic interventions to measure vestibular functions were performed such as electronystagmography (ENG), videonystagmography (VNG), and static and dynamic subjective visual vertical (SVV). BPPV was confirmed with nystagmus during positioning/positional test under ENG and VNG. Static SVV was recorded with a light-emitting diode (LED) bar located in front of the patients before eccentric rotation and dynamic SVV was recorded during eccentric rotation with the LED bar. SVV angles were read by the examiner and analyzed. The measured values were compared to those of normal controls and each other.

RESULTS

Dynamic SVV toward the lesion side in all subtypes of BPPV were significantly different from those of the controls; HC cupulolithiasis showed significantly lower values than those of PC canalolithiasis and HC canalolithiasis.

CONCLUSIONS

HC cupulolithiasis shows a lesser degree of utricular dysfunction compared with other subtypes. It could postulate the difference of pathophysiology between canalolithiasis and cupulolithiasis.

LEVEL OF EVIDENCE

4.

Gender and line size factors modulate the deviations of the subjective visual vertical induced by head tilt

Background

The subjective visual vertical (SVV, the visual estimation of gravitational direction) is commonly considered as an indicator of the sense of orientation. The present study examined the impact of two methodological factors (the angle size of the stimulus and the participant's gender) on deviations of the SVV caused by head tilt. Forty healthy participants (20 men and 20 women) were asked to make visual vertical adjustments of a light bar with their head held vertically or roll-tilted by 30° to the left or to the right. Line angle sizes of 0.95° and 18.92° were presented.

Results

The SVV tended to move in the direction of head tilt in women but away from the direction of head tilt in men. Moreover, the head-tilt effect was also modulated by the stimulus' angle size. The large angle size led to deviations in the direction of head-tilt, whereas the small angle size had the opposite effect.

Conclusions

Our results showed that gender and line angle size have an impact on the evaluation of the SVV. These findings must be taken into account in the growing body of research that uses the SVV paradigm in disease settings. Moreover, this methodological issue may explain (at least in part) the discrepancies found in the literature on the head-tilt effect.

Kinaesthetic and visual perceptions of orientations

In the present study we compare the kinaesthetic and visual perception of the vertical and horizontal orientations (subjective vertical and subjective horizontal) to determine whether the perception of cardinal orientations is amodal or modality-specific. The influence of methodological factors on the accuracy of perception is also investigated by varying the stimulus position as a function of its initial tilt (clockwise or counterclockwise) and its angle (22 degrees, 45 degrees, 67 degrees, and 90 degrees) in respect to its physical orientation. Ten participants estimated the vertical and horizontal orientations by repositioning a rod in the kinaesthetic condition or two luminous points, forming a 'virtual line' in the visual condition. Results within the visual modality replicated previous findings by showing that estimation of the physical orientations is very accurate regardless of the initial position of the virtual line. In contrast, the perception of orientation with the kinaesthetic modality was less accurate and systematically influenced by the angle between the initial position of the rod and the required orientation. The findings question the assumption that the subjective vertical is derived from an internal representation of gravity and highlight the necessity of taking into account methodological factors in studies on subjective orientations.

Subjective visual vertical during eccentric rotation in patients with vestibular neuritis

The subjective visual vertical (SVV) is a useful tool to evaluate clinical manifestations of vestibular loss, but there have been normal variations of the SVV within 1 degrees -3 degrees , and over time, the absolute deviated degrees of SVV tilts decreases. We investigated SVV values in patients with vestibular neuritis (VN) during eccentric rotation, the method used to assess utricular function during stimulation of one labyrinth. And we performed SVV in the resting state and during eccentric rotation to the lesion side and the healthy side of 15 patients with VN and 20 normal subjects. No difference in the resting state SVV values was observed between the VN patients and the control group, but there were significant differences in SVV values between these two groups during eccentric rotation. Therefore, SVV during eccentric rotation allowed us to obtain information about unilateral vestibular loss that could not be found by conventional SVV in patients with VN. Thus, SVV during eccentric rotation might be a good tool to diagnose unilateral vestibular loss.

Clinical use of subjective visual horizontal and vertical in patients of unilateral vestibular neuritis

OBJECTIVES

Subjective visual horizontal (SVH) and subjective visual vertical (SVV) used to assess otolith dysfunction and ipsilesional deviation of SVV and SVH in unilateral vestibular dysfunction is well known. The goal of this study was to investigate the clinical use of SVH/SVV and a dizziness scale in the clinical setting of acute unilateral vestibular neuritis.

METHODS

Thirty-five patients with unilateral vestibular neuritis were investigated. Every patient was diagnosed by physical examination and electronystagmography. Subjective visual horizontal and SVV were assessed during the acute or subacute period; the Dizziness Handicap Inventory (DHI) and Vestibular Disorder Activities of Daily Living Scale (VADL) were used for a self-dizziness scale at the same time. All patients underwent rehabilitation therapy. Subjective visual horizontal/SVV and DHI/VADL were assessed again approximately 4 weeks later. Postrehabilitation SVH/SVV and DHI/VADL data were compared with initial data.

RESULTS

Dizziness Handicap Inventory and VADL were improved after 4 weeks of rehabilitation, and the deviation toward ipsilesional side SVH and SVV was also improved.

CONCLUSION

These results demonstrate that SVH and SVV correlated with clinical dizziness symptoms in patients with acute unilateral vestibular neuritis. Therefore, SVH and SVV would be useful tools for the evaluation of clinical manifestations of unilateral vestibular neuritis.

Otolith Function Assessed with the Subjective Postural Horizontal and Standardised Stance and Gait Tasks

If otolith function is essential to maintain upright standing while moving along slanted or uneven surfaces, subjects with an otolith deficit should have difficulty judging whether the inclination of the surface on which they are standing is tilted or not. We tested this judgement and compared it with the ability to control trunk sway during standardised stance and gait tests. Thirteen patients with unilateral vestibular nerve neurectomy at least 6 months prior to testing and 39 age-matched controls were asked to move a dynamic posturography platform on which they were standing back to their subjective 'horizontal' position after the platform had been slowly tilted at 0.4 degrees/s to 5 degrees in 8 different directions. Normal subjects left the platform deviated in pitch (forwards-backwards) at about 0.7 degrees on describing the platform as levelled off for all directions of tilt. Patients showed larger deviations of about 1.3 degrees in pitch with significant differences for forward right tilt (1.58+/-0.73 degrees compared to 0.73+/-0.11 degrees for normals; mean and SEM) and for forward left. Roll (lateral) deviations were about 0.4 degrees for normals and 0.5 degrees larger for the patients (for example, for backward left, 1.13+/-0.24 degrees compared to 0.4+/-0.07 degrees in normals). Except for a tendency towards greater deviations to the lesion side of patients with eyes closed, no differences were noted between tests under eyes open and closed conditions. However, for backward and roll tilts patients needed to steady themselves first by grasping a handrail when tested with eyes closed. Stance tests on foam showed increases in roll and pitch trunk sway with respect to controls. Patients had significantly larger trunk roll sway deviations during 1-legged stance tests and during gait trials. For stance trials, the patients lost their balance control prior to the end of the standard 20-second recording time. We conclude that a unilateral loss of otolith inputs due to nerve resection permanently impairs the ability to judge whether the support surface is horizontal, and leads to excessive trunk sway when standing on a compliant surface as well as excessive trunk roll sway during gait.

Perception of the head transversal plane and the subjective horizontal during gondola centrifugation

The subjective visual horizontal (SVH) and the subjective head transversal plane (STP) were measured by means of an adjustable luminous line in darkness during centrifuging. Subjects (N = 10) were seated upright, facing forward in a swing-out gondola. After acceleration of the centrifuge to 2G (vectorial sum of the earth's gravity and the centrifugal force; gondola inclination 60 degrees), subjects had to set the line either so that it was perceived as gravitoinertially horizontal (SVH) or so that it was perceived as parallel with the transversal ("horizontal") plane of the head (STP). Initially after acceleration, the SVH was tilted with respect to the gravitoinertial horizontal of the gondola (M = 16.6 degrees). This tilt was compensatory with respect to the gondola inclination. However, the STP was tilted in the opposite direction (M = 12.4 degrees), which might suggest a vestibular-induced distortion of the mental representation of one's own body. Similar results were obtained when measuring the subjective visual vertical (SVV) and the subjective midsagittal plane (SSP) in 5 subjects. The perceived roll angle (obtained as SVH-STP or SVV-SSP) was considerably larger than had previously been reported. Time constants for exponential decay of the tilt of the SVH or SVV were often 2-3 min, indicating a memory for semicircular canal information on changes in head orientation--a position-storage mechanism.

Suppression of the E-effect during the subjective visual vertical test

The subjective visual vertical was measured in 38 healthy subjects. The head was alternately roll-tilted to the right and to the left, and the start position of the light bar was alternately set clockwise and counterclockwise. When the head is tilted less than 60-70 degrees a deviation of the subjective visual vertical in the opposite direction to the head tilt is expected. This phenomenon has been reported in various studies as the E-effect. The present study demonstrates however that the E-effect is suppressed if the start position of the light bar is presented relatively parallel to the length axis of the tilted head.

Neck muscle vibration alters visually perceived roll in normals

The objective of this study was to determine whether vibration of dorsal neck muscles or of the mastoid bone or of both modified the perception of visual orientation in the head roll-tilt plane in normal subjects. Measurements of the subjective visual vertical (SVV) were obtained from 26 normal human subjects. Subjects reported the SVV in the upright and in the left and right 30 degrees static head roll-tilt positions. Subjects then reported the SVV while vibration was applied to the left or right dorsal neck or left or right mastoid. Both head position and vibration independently modified settings of the SVV. In head-tilted positions, vibration of the upper dorsal neck muscles (on the side of the head opposite to the head tilt) caused a significantly greater shift of the SVV in the opposite direction of head roll-tilt compared to vibration of the lower dorsal neck muscles or of the mastoid. These results support a role for cervical somatosensory information in perception of visual orientation in the roll plane. Our findings may help explain the differences observed in visual orientation perception in normal subjects between head alone and whole-body roll-tilt. Finally, vibration of neck muscles in the head roll-tilted plane may be a useful method to test cervical somatosensory function possibly by increasing their response to external stimulation.

Human vestibular memory studied via measurement of the subjective horizontal during gondola centrifugation

Measurements of the subjective visual horizontal (SVH) were made in a large swing-out gondola centrifuge. Rotation of the centrifuge was anti-clockwise, as seen from above. Test subjects were seated upright in the gondola, facing forwards. In front of the subject, at a straight-ahead eye-level position, there was a narrow luminous line, which could be rotated, by remote control, about the visual axis. At gravitoinertial force levels of 1.1-1.3G the subjects were asked to indicate, by repeatedly setting the line in darkness, what they perceived as horizontal (the SVH). During gondola centrifugation, the head and body length axis is always parallel with the resultant gravitoinertial force vector (vectorial sum of earth gravity force and the centrifugal force) i.e., the horizontal plane of the head or body does not change with respect to the gravitoinertial horizontal. Hence, the otolith organs, as well as the somatosensory system, continually signal upright position. However, the swing-out of the gondola during acceleration of the centrifuge (25 degrees at 1.1G) is a roll (frontal plane) change-in-position stimulus to the vertical semicircular canals, thus creating an otolith-semicircular canal conflict. After acceleration of the centrifuge, the SVH was initially tilted up to 20 degrees to the right relative to the gravitoinertial horizontal. Since there was no roll-tilt stimulus to gravity receptors, this SVH tilt must be related to stimulation of the semicircular canals. However, it decayed much more slowly than any known effects of angular-velocity stimulation of the semicircular canals. The decay was bi-phasic with two time constants, the smaller in the region of 1-2 min, the other being too large to be reliably estimated on the basis of data collected during only 10 min. This persistence of the SVH tilt suggests a memory for angular changes in roll head position detected by the semicircular canals-a position-storage mechanism. Further, the SVH seems to be dependent on two different mechanisms related to semicircular canal stimulation.

Visually perceived vertical and visually perceived horizontal are not orthogonal

The authors examined the difference in errors made by eight subjects in setting a bar of light in an otherwise darkened room to either visually perceived vertical (VPV) or visually perceived horizontal (VPH) during maintained roll-tilted positions around the naso-occipital axis. Two viewing distances were examined, 25 and 60 cm. Subjects were tested at roll-tilt angles of 10 degrees intervals from upright to body horizontal (both left ear down (LED) and right ear down (RED)) in a randomized fashion. Settings were made only after a 1 min delay at each tilt angle to allow for decay of the semicircular canal signal. Chair rotation speed was 2 degrees/s with subjects being re-tested using 1/2 degree/s (at 25 cm) to determine the effect of rotation speed. Average errors for vertical versus horizontal were significantly different from each other (P < 0.01) at both the 25 and 60 cm viewing distances. The errors follow a complex function, with VPH showing smaller errors than VPV for large roll-tilts, while the opposite was true for medium-sized roll-tilts. This was true at both chair velocities. That is, VPV and VPH are not orthogonal to one another under the conditions examined. There are large differences between individuals but each individual showed a repeatable pattern. The average extent of non-orthogonality was found to be as high as 7 degrees at some large roll-tilt angles. These findings raise questions about the appropriateness of comparing the results of studies using the different tasks VPV and VPH. Factors that might contribute to this effect are discussed, including somatosensory input and ocular counterrolling (OCR).

The subjective horizontal at different angles of roll-tilt in patients with unilateral vestibular impairment

The subjective visual horizontal is mainly dependent on the otolithic system. A group of 11 patients with sudden unilateral vestibular impairment were asked to set a dimly illuminated bar according to their subjective horizontal when they were seated upright and tilted 10, 20, and 30 degrees to the right and left in a completely darkened room (Bias test). The patients were examined within 1 week, after 3 and 6 weeks, and 9 patients consented to the 11-week follow-up. The results were compared with ENG examinations. In the acute stage of the disease all patients, when they were in upright position, set the light bar tilted towards the affected side. At roll tilt to the affected side, 9 of the 11 patients set the light bar in the same direction as their body tilt (undercorrection). At a tilt to the unaffected side 6 of the 11 patients made an undercorrection. For the group of patients the magnitude of undercorrection was larger at tilt to the affected side than to the unaffected side. The patients' ability to correctly align the light bar with the true horizontal gradually improved but was found normal in both upright and tilted positions in only three of the nine patients at the last follow-up. In four of the six patients who still demonstrated pathologic results, these were met only in tilted positions. No significant correlation was found between the intensity of spontaneous nystagmus or the degree of caloric side difference and the deviation in setting of the light bar in upright or tilted positions. The large asymmetric perceptual responses at tilt found at onset might be explained by the two-directional organisation of the utricle.