Influence of spatial orientation training in a centrifuge on the ability of fighter pilots to assess the bank angle during flight without visual references.

Without visual references, nonpilots exposed to coordinated flight turns underestimate the bank angle, because of discordant information of the roll-angular displacement from the otoliths, consistently signaling vertical position, versus the semicircular canals, enabling detection of the displacement. Pilots may also use their ability to perceive the G load and knowledge of the relation between load and angle to assess the bank angle. Our aim was to investigate whether the perception of bank angle can be improved by spatial orientation training in a centrifuge. Sixteen pilots/pilot students assessed their roll tilt, in complete darkness, during both real coordinated flight turns and gondola centrifugation, at roll tilts of 30° and 60°. The experiments were repeated after a 3-wk period, during which eight of the subjects performed nine training sessions in the centrifuge, comprising feedback on roll angle vs. G load, and on indicating requested angles. Before training, the subjects perceived in the aircraft and centrifuge, respectively: 37 (17)°, 38 (14)° during 60° turns and 19 (12)°, 20 (10)° during 30° turns. Training improved the perception of angle during the 60° [to 60 (7)°, 55 (10)°; P ≤ 0.04] but not the 30° [21 (10)°, 15 (9)°; P ≥ 0.30] turns; the improvement disappeared within 2 yr after training. Angle assessments did not change in the untrained group. The results suggest that it is possible to, in a centrifuge, train a pilot's ability to perceive large but not discrete-to-moderate roll-angular displacements. The transient training effect is attributable to improved capacity to perceive and translate G load into roll angle and/or to increased reliance on semicircular canal signals.NEW & NOTEWORTHY Spatial disorientation is a major problem in aviation. When performing coordinated flight turns without external visual cues (e.g., flying in clouds or darkness), the pilot underestimates the aircraft bank angle because the vestibular system provides unreliable information of roll tilt. The present study demonstrates that it is possible to, in a long-arm centrifuge, train a pilot's ability to perceive large but not discrete-to-moderate roll-angular displacements.

A study of otolith function in patients with orthostatic dizziness.

BACKGROUND: Orthostatic dizziness (OD) is the dizziness that occurs when moving from a sitting or a supine to a standing position. It is typically thought to be connected to orthostatic hypotension (OH). The otolithic control of respiratory and cardiovascular system through vestibulosympathetic reflex has been the focus of considerable recent interest. This study aimed to evaluate the relationship between the orthostatic dizziness and otolith organ function. METHODS: This study was carried on 50 adults aged from 18 to 50 years with normal peripheral hearing. Subjects were divided into two groups: controls (GI): 20 healthy adults and study group (GII): 30 patients who were complaining of OD. Patients were submitted to; blood pressure measurement in sitting and standing positions, combined vestibular-evoked myogenic potentials (VEMPs) and subjective visual vertical and horizontal tests (SVV) and (SVH). RESULTS: The study group showed abnormal absent cVEMP, oVEMP. There were also statistically significant differences of P13 and N23 latencies and (P13N23) amplitudes between the two groups in the left ears. Both groups differed significantly in SVH values deviated to the left side. Study group were further subdivided into ten patients with OH and 20 patients with OD without OH. The both study subgroups showed abnormal absent cVEMP, oVEMP and abnormal SVH. OH patients showed statistically significant differences of cVEMP waves P13, N23 latencies in the left ears when compared with the control. CONCLUSIONS: Otolith malfunction may be the cause of orthostatic dizziness (OD) in patients with and without orthostatic hypotension.

Mobile telephone use effects on perception of verticality.

Low-level radiofrequency (RF) signals may produce disorientation and nausea. In experiment I, we assessed mobile phone effects on graviception in nine symptomatic subjects after mobile telephone use and 21 controls. The mobile handset was strapped to each ear for 30 min in pulsed emission, continuous RF emission, or no emission test mode, respectively. The subjective visual vertical and horizontal (SVV/SVH) were tested from min 25 of exposure. There was no exposure effect; however, there was an ear effect, with the SVV/SVH being shifted to the opposite direction of the ear exposed. This could be due to thermal or RF effects or handset weight. In experiment II, we assessed the handset weight effect on 18 normal controls. After baseline SVV/SVH, the switched off handset was strapped to either ear; the SVV/SVH was repeated 25 min later. A significant ear effect was found. We compared the observed ear effect SVV/SVH change in the experiment II group to the continuous exposure ear effect change in the experiment I group, and the difference was not significant. The ear effect was attributed to a minor head tilt due to the handset weight, or proprioceptive stimulation of neck muscle affecting the perception of verticality.

Assessments of Subjective Visual Gravity and Spontaneous Nystagmus in Patients With Vestibular Neuritis.

OBJECTIVE: This study aimed to assess the correlation between the spontaneous nystagmus (SN) and the subjective visual vertical/horizontal (SVV/SVH) among patients with vestibular neuritis (VN) at the different head positions. STUDY DESIGN: Case-control study. SETTING: Affiliated Sixth People's Hospital, Shanghai Jiao Tong University School of Medicine. METHODS: This study evaluated the SVV/SVH in both healthy subjects and patients with VN. These evaluations were performed in 5 different head positions: upright, 45° tilt to the left, 90° tilt to the left, 45° tilt to the right, and 90° tilt to the right. Additionally, the intensity of SN, as measured by slow-phase velocity, was recorded. RESULTS: In patients with VN, a significant correlation was observed between SN and SVV/SVH in an upright position. The intensity of SN was higher when the head was tilted 90° toward the affected side compared to other positions. The SVV/SVH displayed an ipsiversive shift, when the head was tilted toward both the lesion and unaffected sides, exhibiting a contraversive direction. Furthermore, the changes in position-induced SN were consistent with the displacements of SVV and SVH caused by head tilt. CONCLUSION: The presence of SN in patients with VN was observed to vary across different head position. These variations could potentially be attributed to the diverse activation patterns of the mechanical properties of otolith organs that are induced by head tilts.

Evaluation of subjective visual vertical and horizontal in patients with acoustic neuroma based on virtual reality.

Objective: To investigate potential differences in absolute deviation values of subjective visual vertical and horizontal between unilateral acoustic neuroma patients and healthy young adults under varying degrees of static head tilt, as well as the impact of proprioception on these values, with the aim of determining the effect of acoustic neuroma on gravity sensory pathway function in patients. Methods: We recruited 22 patients diagnosed with unilateral acoustic neuroma and 25 healthy young adults and employed virtual reality technology to assess the absolute deviation values of subjective visual vertical (SVV) and subjective visual horizontal (SVH) under eight different static tilted head positions (Head centered (0° tilt), PdP, Head tilt 15°, 30°, 45° to the left and right), then compare and analyze intergroup differences. Results: In the Head-centered position, both SVV and SVH absolute deviated values were significantly higher in the AN group compared to healthy young adults. The AN group exhibited significantly higher absolute deviation values of SVV compared to the healthy group when tilting their head 30° left and right. Additionally, when tilting their heads to the right at 15° and 45° the AN group showed significant increases in SVH absolute deviated values compared to healthy adults. The SVV and SVH absolute deviation values of LAN and SAN groups did not reach statistical significance. The results of the SVV test for PDP position did not show any significant differences among all groups. However, the SVH test revealed that the absolute deviation values of the LAN group was significantly higher than that of healthy individuals. Conclusion: Our study shows that the gravity sensing function of patients with unilateral acoustic neuroma is affected to different degrees, however, the degree of gravity sensing function damage of patients has little relationship with tumor size. When acoustic neuroma is larger than 2 cm, the effect of proprioception on patients' SVH outcome is noteworthy. So, we should pay attention to the postoperative follow-up of patients with acoustic neuroma and the evaluation of vestibular rehabilitation effect. Meanwhile, for patients opting for conservative treatment, it is imperative to monitor the dynamic changes in vestibular function and seize timely opportunities for intervention.

Subjective visual horizontal correlates better with ocular than with cervical vestibular evoked myogenic potentials.

OBJECTIVE: To examine the relationship between widely used otolith function tests: the Subjective Visual Horizontal (SVH) and Vestibular Evoked Myogenic Potentials (VEMP). METHODS: A retrospective analysis was performed on 301 patients who underwent SVH, ocular and cervical VEMP (oVEMP and cVEMP) tests on the same day. Correlations between the mean SVH tilt and amplitude asymmetry ratios for bone-conducted (BC) oVEMP and air-conducted (AC) cVEMP were examined. Diagnoses included vestibular neuritis, stroke, vestibular migraine, Meniere's disease, sudden sensorineural hearing loss (SSNHL) and vestibular schwannoma. RESULTS: SVH results were concordant with the oVEMP in 64% of cases and the cVEMP in 51%. Across all patients, SVH demonstrated a significant moderate correlation with BC oVEMP amplitude asymmetry ratios (r = 0.55, p < 0.001) and a weak correlation with AC cVEMP amplitude asymmetry ratios (r = 0.35, p < 0.001). A stronger correlation between SVH and oVEMPs was observed in patients with vestibular neuritis (r = 0.67, p < 0.001) and SSNHL (r = 0.76, p = 0.001). CONCLUSIONS: SVH correlates better with oVEMP than cVEMP symmetry. SIGNIFICANCE: This finding reinforces the hypothesis of a common utricular origin for both SVH and oVEMPs which is distinct from the saccular origin of cVEMPs.

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.

The value of vestibular graviceptive pathway evaluation in the diagnosis of unilateral peripheral vestibular dysfunction.

BACKGROUND: Evaluation of vestibular graviceptive pathway (VGP) in patients with unilateral peripheral vestibular dysfunction (UPVD) has received increasing attention from researchers. The study aimed to investigate the value of VGP evaluation in the diagnosis of UPVD. METHODS: Ninety-five UPVD patients were divided into attack and remission phase groups. VGP evaluation-related indicators, including subjective visual vertical (SVV), subjective visual horizontal (SVH), head tilt, ocular torsion (OT), and skew deviation (SD), were measured, and their correlations with cochleovestibular function test results were analyzed. The possible etiologies of contralesional VGP (c-VGP) were analyzed. RESULTS: Positive rates of SVV, SVH, OT, and SD were significantly higher, and the degrees of SVV, SVH, and OT were significantly greater in the attack phase group than the remission phase group. The sides with abnormal VGP evaluation results were correlated with the sides with hearing loss, abnormal caloric, and video head impulse test (vHIT) results. A total of 14 patients showed c-VGP, and possible etiologies included contralateral benign paroxysmal positional vertigo (n = 4), bilateral hearing loss (n = 8), bilateral vHIT gain reduction (n = 1), autoimmune diseases (n = 6), vascular risk factors (n = 6), lacunar infarction (n = 3), and endolymphatic hydrops (n = 3). CONCLUSIONS: Alterations in SVV, SVH, OT, and SD were noted in UPVD patients in different phases, which are presumed to be related to dynamic vestibular compensation; correlations between VGP evaluation results and cochleovestibular function test results indicate that VGP evaluation may be helpful for the diagnosis of the side affected in UPVD; the presence of c-VGP may be related to bilateral labyrinth lesions or endolymphatic hydrops on the affected side; and the involvement of autoimmune mechanisms also deserves attention.

Effect of age on virtual reality-assisted subjective visual vertical and subjective visual horizontal at different head-tilt angles.

OBJECTIVE: Subjective Visual Vertical (SVV) and Subjective Visual Horizontal (SVH) values may reflect bilateral utricle asymmetry. Bilateral utricle static tension balance can be used to evaluate bilateral otolith lesions and otolith-related central neuropathy. Few studies have examined Virtual Reality (VR)-assisted SVV and SVH values at various head-tilt angles across age groups. The present study aimed to determine the effects of age on VR-assisted SVV and SVH values at different head-tilt angles. METHODS: We divided 180 healthy subjects into 6 age groups (n = 30 in each group). VR-assisted SVV and SVH measurements were performed at 9 head-tilt angles (head held vertically, 0°; head tilted 30°, 45°, 60°, and 90° to the left/right) in the roll plane. RESULTS: SVV and SVH values significantly differed with head-tilt angle (p < 0.05). No significant difference was detected in the SVH and SVV values between different age groups (p = 0.632 and p = 0.810, respectively), and no interaction between the age group and the head-tilt angle was found for the SVH and SVV values (p = 0.670 and p = 0.084, respectively). CONCLUSION: These results suggest that age may have little effect on VR-assisted SVV and SVH at different head-tilt angles. Therefore, VR-assisted SVV and SVH can be evaluated as an effective, fast, and simple way to evaluate utricle function. LEVEL OF EVIDENCE: Level 4.

Virtual reality for the measurement of SVV and SVH during static head tilt in healthy adults: a novel vestibular test.

BACKGROUND AND OBJECTIVE: Few previous studies have used virtual-reality (VR) technology to measure subjective visual vertical (SVV) and subjective visual horizontal (SVH) during static head tilt (0°, 30°, 45°, 60° and 90°). We propose a novel vestibular test for measuring the normal range of SVV and SVH during static head tilt in healthy adults. METHODS: Eighty healthy adults were included in the study. SVV and SVH were calculated in nine head positions. RESULTS: With head tilt 90° to the right, SVV skewed to the right, and SVH skewed upward. With head tilt 90° to the left, SVV skewed to the left, and SVH skewed downward. SVV was asymmetrical only at a head tilt of 90°. SVV and SVH were similar at all degrees of head tilt, except for 30° to the right, 45° to the left, and 0°. CONCLUSIONS: VR measurements showed that SVV and SVH differed at various degrees of static head tilt. The standardized protocol proposed here may be used to establish a reference range for utricle function when evaluating acute, unilateral vestibular lesions.

Dynamic changes of otolith organ function before and after repositioning in patients with benign paroxysmal positional vertigo detected by virtual reality auxiliary technology: A cohort study.

Objectives: To dynamically investigate otolith function in patients with benign paroxysmal positional vertigo (BPPV) before, after, and 1 month after repositioning, and explore the possible compensation mechanisms. Methods: Thirty-six patients confirmed with BPPV (canal lithiasis) treated in our hospital between August 2020 and March 2021, as well as 36 health controls matched for age and gender (normal control group, NC group) were enrolled. For NC group, the virtual reality (VR) auxiliary static subjective visual vertical (SVV), subjective visual horizontal (SVH), and SVV of dynamic unilateral centrifugation (DUC), were measured at inclusion. For the BPPV group, visual analog scale (VAS) was used to assess the vertigo degree, while static SVV, SVH, and DUC were performed before, after, and 1 month after repositioning. First, we compare the deviations of SVV0/SVH0° when the subject's head is in the positive position, and SVV of DUC between BPPV and NC groups before repositioning, after which we compared the deviations in SVV45, SVV90, SVH45, SVH90°, and SVV of DUC between the affected and unaffected sides before repositioning. Finally, paired t-test was used to compare the VAS score, deviations in static SVV0, SVV45, SVV90, SVH0, SVH45, and SVH90°, and deviations in SVV of DUC before, after, and 1 month after repositioning. (Here, 0, 45, and 90° refer to the angle which the center axis of head deviates from the gravity line.). Results: SVV0 SVH0°, and SVV of DUC at 120 and 180°/s 0 significantly differed between BPPV and NC group before repositioning. The deviations in SVV45, SVV90, SVH45, SVH90°, and SVV of DUC at 120°/s-2 and 180°/s-4.5 did not significantly differ between bilateral sides in BPPV patients before repositioning. The deviation in SVH90° was significantly lower after repositioning than before. The deviation in SVH45° was significantly higher 1 month after repositioning than before. The deviation angle of SVV of DUC at 180°/s-0 was significantly lower after repositioning than before. The vertigo VAS score of patient with BPPV continued to decrease after repositioning. Conclusion: Before repositioning, the otolithic organ function of BPPV patients was obviously impaired, with no significant difference between the healthy and affected ear. After repositioning, there was a transient recovery of otolithic organ dysfunction followed by a sustained decline to similar levels to before repositioning.

The influence of type of visual image and gender on the perception of horizontality: a subjective visual horizontal (SVH) study.

BACKGROUND: The graviceptive otolith function can be measured using subjective visual horizontal (SVH) testing. Nevertheless, more research efforts are required to understand the essential variables affecting SVH. OBJECTIVE: The aim of the present study was to determine the effects of type of visual image and gender on subjective visual horizontal (SVH) perception among healthy adults. MATERIALS AND METHODS: In this comparative study, 50 healthy young adults were enrolled. While in an upright body position, they were required to report their perception of horizontality for two types of visual images (solid line and arrow pattern) using a computerized SVH device. RESULTS: The arrow pattern produced significantly bigger SVH angles than the solid line (p < .001). In contrast, no significant influence of gender was found on SVH results (p = .743), Based on the statistical outcomes, the preliminary normative data for SVH were established. CONCLUSIONS AND SIGNIFICANCE: The arrow pattern (a more complex visual image) produced bigger SVH deviations than the simple solid line image. In contrast, the horizontality perception does not appear to be affected by gender. The preliminary normative SVH data gathered from the present study can be beneficial for clinical and future research applications.

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.

Contralesional subjective visual horizontal predicts endolymphatic hydrops.

Background: The subjective visual horizontal (SVH) is a test of utricular function that assesses conjugate ocular torsion which is a component of the ocular tilt reaction (OTR). In unilateral destructive peripheral vestibular lesions, the OTR and so the SVH tilt is usually ipsiversive.Aims/objective: Our study aimed to profile the causes of a contraversive SVH tilt in patients with a confirmed unilateral peripheral vestibular deficit.Materials and methods: The clinical records, nystagmus and vestibular investigation characteristics of 52 patients with a unilateral canal paresis (CP) on caloric of ≥30%, a contraversive SVH tilt of ≥4 degrees and at least one pure tone audiometry were retrospectively analysed.Results: The most common diagnosis of patients (n = 39) with a contraversive SVH and ipsilesional CP was endolymphatic hydrops: 35 (67.3%) had Meniere's disease (MD) and 4 (7.7%) had delayed endolymphatic hydrops (DEH). The remaining 13 (25%) of cases had other peripheral aetiologies or an unknown diagnosis. 16 (30.8%) patients had ictal spontaneous nystagmus at the time of SVH or caloric testing.Conclusions and significance: A contraversive SVH with unilateral CP suggests endolymphatic hydrops.

Vestibular evoked myogenic potentials in practice: Methods, pitfalls and clinical applications.

Vestibular evoked myogenic potentials (VEMPs) are a useful and increasingly popular component of the neuro-otology test battery. These otolith-dependent reflexes are produced by stimulating the ears with air-conducted sound or skull vibration and recorded from surface electrodes placed over the neck (cervical VEMPs) and eye muscles (ocular VEMPs). VEMP abnormalities have been reported in various diseases of the ear and vestibular system, and VEMPs have a clear role in the diagnosis of superior semicircular canal dehiscence. However there is significant variability in the methods used to stimulate the otoliths and record the reflexes. This review discusses VEMP methodology and provides a detailed theoretical background for the techniques that are typically used. The review also outlines the common pitfalls in VEMP recording and the clinical applications of VEMPs.

Mastoid Vibration Reduces Ipsilesional Shift of Subjective Visual Horizontal in Patients with Acute Stage of Unilateral Vestibulopathy.

BACKGROUND AND OBJECTIVES: To investigate effect of the vibration on subjective visual horizontal (SVH) in patients with acute stage of unilateral vestibulopathy. SUBJECTS AND METHODS: Twenty-five unilateral vestibulopathy patients which analyzed into 42 cases at different time points and suffered from spinning vertigo for more than 24 hours without hearing loss and neurologic abnormality were enrolled. Thirteen subjects with spontaneous nystagmus (>3 degree/sec; averaged symptom onset <1 week) at the time of SVH measurement were classified into the acute unilateral vestibulopathy group (aVU). The other 29 subjects without spontaneous nystagmus were classified into the compensated vestibulopathy group (cVU). SVH was performed with vibration at either mastoid or sterocleidomastoid muscle. RESULTS: In the analysis of overall subjects, vibration did not significantly change the degree of shift of SVH. However, analyzed by group, the shift of SVH with vibration at ipsilesional mastoid was significantly decreased than baseline in aVU (p<0.05). The shift of SVH with vibration at contralesional mastoid was significantly increased than baseline in cVU (p=0.05). CONCLUSIONS: The shift of SVH due to vibration in acute stage of unilateral vestibulopathy showed reduction of the shift, while in compensated stage it showed increase of the shift.

Effect of age on virtual reality-assisted subjective visual vertical and subjective visual horizontal at different head-tilt angles

Abstract Objective: Subjective Visual Vertical (SVV) and Subjective Visual Horizontal (SVH) values may reflect bilateral utricle asymmetry. Bilateral utricle static tension balance can be used to evaluate bilateral otolith lesions and otolith-related central neuropathy. Few studies have examined Virtual Reality (VR)-assisted SVV and SVH values at various head-tilt angles across age groups. The present study aimed to determine the effects of age on VR-assisted SVV and SVH values at different head-tilt angles. Methods: We divided 180 healthy subjects into 6 age groups (n = 30 in each group). VR-assisted SVV and SVH measurements were performed at 9 head-tilt angles (head held vertically, 0°; head tilted 30°, 45°, 60°, and 90° to the left/right) in the roll plane. Results: SVV and SVH values significantly differed with head-tilt angle (p < 0.05). No significant difference was detected in the SVH and SVV values between different age groups (p = 0.632 and p = 0.810, respectively), and no interaction between the age group and the head-tilt angle was found for the SVH and SVV values (p = 0.670 and p = 0.084, respectively). Conclusion: These results suggest that age may have little effect on VR-assisted SVV and SVH at different head-tilt angles. Therefore, VR-assisted SVV and SVH can be evaluated as an effective, fast, and simple way to evaluate utricle function. Level of Evidence: Level 4.