Spatial anxiety contributes to the dizziness-related handicap of adults with peripheral vestibular disease.

In subjects with peripheral vestibular disease and controls, we assessed: 1. The relationship between spatial anxiety and perceived stress, and 2. The combined contribution of spatial anxiety, spatial perspective-taking, and individual cofactors to dizziness-related handicap. 309 adults participated in the study (153 with and 156 without peripheral vestibular disease), including patients with bilateral vestibular deficiency, unilateral deficiency (evolution <3 or ≥3 months), Meniere's disease, and Benign Paroxysmal Positional Vertigo. Assessments included: general health, personal habits, spatial anxiety (3-domains), perceived stress, spatial perspective-taking, dizziness-related handicap (3-domains), unsteadiness, sleep quality, motion sickness susceptibility, trait anxiety/depression, state anxiety, depersonalization/derealization. After bivariate analyses, analysis of covariance was performed (p ≤ 0.05). Spatial anxiety was related to unsteadiness and perceived stress, with an inverse relationship with trait anxiety (ANCoVA, adjusted R2 = 0.27-0.30, F = 17.945-20.086, p < 0.00001). Variability on perspective-taking was related to vestibular disease, trait and state anxiety, motion sickness susceptibility, and age (ANCoVA, adjusted R2 = 0.18, F = 5.834, p < 0.00001). All domains of spatial anxiety contributed to the Physical domain of dizziness-related handicap, while the Navigation domain contributed to the Functional domain of handicap. Handicap variability was also related to unsteadiness, spatial perspective-taking, quality of sleep, and trait anxiety/depression (ANCoVA, adjusted R2 = 0.66, F = 39.07, p < 0.00001). Spatial anxiety is related to perceived stress in adults both with and without vestibular disease, subjects with trait anxiety rated lower on spatial anxiety. State anxiety and acute stress could be helpful for recovery after peripheral vestibular lesion. Spatial anxiety and perspective-taking contribute to the Physical and Functional domains of dizziness-related handicap, possibly because it discourages behavior beneficial to adaptation.

Individual Cofactors and Multisensory Contributions to the Postural Sway of Adults with Diabetes.

To assess the interactions between individual cofactors and multisensory inputs on the postural sway of adults with type 2 diabetes and healthy subjects, 69 adults accepted to participate in the study (48 with/ 21 without diabetes). Assessments included neuro-otology (sinusoidal-rotation and unilateral-centrifugation), ophthalmology and physiatry evaluations, body mass index (BMI), physical activity, quadriceps strength, the ankle/brachial index and polypharmacy. Postural sway was recorded on hard/soft surface, either with eyes open/closed, or without/with 30° neck extension. The proportional differences from the baseline of each condition were analyzed using Multivariate and Multivariable analyses. Patients with polyneuropathy and no retinopathy showed visual dependence, while those with polyneuropathy and retinopathy showed adaptation. Across sensory challenges, the vestibulo-ocular gain at 1.28 Hz and the BMI were mainly related to changes in sway area, while the dynamic visual vertical was mainly related to changes in sway length. The ankle/brachial index was related to the effect of neck extension, with contributions from quadriceps strength/physical activity, polyneuropathy and polypharmacy. Across conditions, men showed less sway than women did. In conclusion, in adults with diabetes, sensory inputs and individual cofactors differently contribute to postural stability according to context. Rehabilitation programs for adults with diabetes may require an individualized approach.

Viewing Target Distance Influences the Vestibulo-Ocular Reflex Gain when Assessed Using the Video Head Impulse Test.

Gaze stabilization during head movements is provided by the vestibulo-ocular reflex (VOR). Clinical assessment of this reflex is performed using the video Head Impulse Test (vHIT). To date, the influence of different fixation distances on VOR gain using the vHIT has not been explored. We assessed the effect of target proximity on the horizontal VOR using the vHIT. Firstly, we assessed the VOR gain in 18 healthy subjects with 5 viewing target distances (150, 40, 30, 20, and 10 cm). The gain increased significantly as the viewing target distance decreased. A second experiment on 10 subjects was performed in darkness whilst the subjects were imagining targets at different distances. There were significant inverse relationships between gain and distance for both the real and the imaginary targets. There was a statistically significant difference between light and dark gains for the 20- and 40-cm distances, but not for the 150-cm distance. Theoretical VOR gains for different target distances were calculated and compared with those found in light and darkness. The increase in gain observed for near targets was lower than predicted by geometrical calculations, implying a physiological ceiling effect on the VOR. The VOR gain in the dark, as assessed with the vHIT, demonstrates an enhancement associated with a reduced target distance.

Predictors of clinical recovery from vestibular neuritis: a prospective study.

We sought to identify predictors of symptomatic recovery in vestibular neuritis. Forty VN patients were prospectively studied in the acute phase (median = 2 days) and 32 in the recovery phase (median = 10 weeks) with vestibulo-ocular reflex, vestibular-perceptual, and visual dependence tests and psychological questionnaires. Clinical outcome was Dizziness Handicap Inventory score at recovery phase. Acute visual dependency and autonomic arousal predicted outcome. Worse recovery was associated with a combination of increased visual dependence, autonomic arousal, anxiety/depression, and fear of bodily sensations, but not with vestibular variables. Findings highlight the importance of early identification of abnormal visual dependency and concurrent anxiety.

Biodynamic Hypothesis for the Frequency Tuning of Motion Sickness.

INTRODUCTION: Motion sickness is often provoked by oscillatory translational (linear) acceleration. For humans, motion frequencies around 0.2-0.3 Hz are the most provocative. A current explanation for this frequency band is that it spans a region of maximum ambiguity concerning the interpretation of vestibular signals. Below 0.2-0.3 Hz, linear accelerations are interpreted as 'tilt', whereas at higher frequencies accelerations are interpreted as 'translation', i.e., linear motion through space. This is termed the 'tilt-translation' hypothesis. However, the origin of this particular frequency range is unclear. We investigated whether the differential perceptions of oscillations at different frequencies derives from the biodynamics of active self-initiated whole body motion. METHODS: Video-films were taken of subjects running slaloms of various combinations of lengths/amplitudes to provoke a range of temporal frequencies of slalom (reciprocal of time to run a cycle). RESULTS: The usual tactic for cornering at frequencies <0.25 Hz was whole-body tilt, whereas >0.4 Hz lateropulsion of the legs with torso erect was observed. Between these frequencies subjects showed variable tactics, mixing components of both tilt and lateropulsion. CONCLUSIONS: This uncertainty in selecting the appropriate tactic for movement control around 0.2-0.3 Hz is the possible origin of 'tilt-translation' ambiguity. It also follows that externally imposed motion around these frequencies would challenge both perception and motor control, with the consequence of motion sickness.

Visually induced nausea causes characteristic changes in cerebral, autonomic and endocrine function in humans.

An integrated understanding of the physiological mechanisms involved in the genesis of nausea remains lacking. We aimed to describe the psychophysiological changes accompanying visually induced motion sickness, using a motion video, hypothesizing that differences would be evident between subjects who developed nausea in comparison to those who did not. A motion, or a control, stimulus was presented to 98 healthy subjects in a randomized crossover design. Validated questionnaires and a visual analogue scale (VAS) were used for the assessment of anxiety and nausea. Autonomic and electrogastrographic activity were measured at baseline and continuously thereafter. Plasma vasopressin and ghrelin were measured in response to the motion video. Subjects were stratified into quartiles based on VAS nausea scores, with the upper and lower quartiles considered to be nausea sensitive and resistant, respectively. Twenty-eight subjects were exposed to the motion video during functional neuroimaging. During the motion video, nausea-sensitive subjects had lower normogastria/tachygastria ratio and cardiac vagal tone but higher cardiac sympathetic index in comparison to the control video. Furthermore, nausea-sensitive subjects had decreased plasma ghrelin and demonstrated increased activity of the left anterior cingulate cortex. Nausea VAS scores correlated positively with plasma vasopressin and left inferior frontal and middle occipital gyri activity and correlated negatively with plasma ghrelin and brain activity in the right cerebellar tonsil, declive, culmen, lingual gyrus and cuneus. This study demonstrates that the subjective sensation of nausea is associated with objective changes in autonomic, endocrine and brain networks, and thus identifies potential objective biomarkers and targets for therapeutic interventions.

Pathophysiology and treatment of motion sickness.

PURPOSE OF REVIEW: Motion sickness remains bothersome in conventional transport and is an emerging hazard in visual information technologies. Treatment remains unsatisfactory but advances in brain imaging, neurophysiology, and neuropharmacology may provide insights into more effective drug and behavioural management. We review these major developments. RECENT FINDINGS: Recent progress has been in identifying brain mechanisms and loci associated with motion sickness and nausea per se. The techniques have included conventional neurophysiology, pathway mapping, and functional MRI, implicating multiple brain regions including cortex, brainstem, and cerebellum. Understanding of the environmental and behavioural conditions provocative of and protective against motion sickness and how vestibular disease may sensitize to motion sickness has increased. The problem of nauseogenic information technology has emerged as a target for research, motivated by its ubiquitous applications. Increased understanding of the neurophysiology and brain regions associated with motion sickness may provide for more effective medication in the future. However, the polysymptomatic nature of motion sickness, high interindividual variability, and the extensive brain regions involved may preclude a single, decisive treatment. SUMMARY: Motion sickness is an emerging hazard in information technologies. Adaptation remains the most effective countermeasure together with established medications, notably scopolamine and antihistamines. Neuropharmacological investigations may provide more effective medication in the foreseeable future.

Vertigo and dizziness from environmental motion: visual vertigo, motion sickness, and drivers' disorientation.

The normal vestibular system may be adversely affected by environmental challenges which have characteristics that are unfamiliar or ambiguous in the patterns of sensory stimulation they provide. A disordered vestibular system lends susceptibility even to quotidian environmental experiences as the sufferer becomes dependent on potentially misleading, nonvestibular sensory stimuli. In both cases, the sequelae may be vertigo, incoordination, imbalance, and unpleasant autonomic responses. Common environmental motion conditions include visual vertigo, motion sickness, and motorists' disorientation. The core therapy for visual vertigo, motion sickness, and drivers' disorientation is progressive desensitization within a cognitive framework of reassurance and explanation, plus anxiolytic tactics and autogenic control of autonomic symptoms.

The awareness of body orientation modulates the perception of visual vertical.

It is established that the body position influences verticality perception. In contrast, the possible influence of the awareness of the body orientation on verticality perception has never been investigated. This hypothesis, explored in the present study, is supported by the role played by the parietal cortex and the insula in both body position awareness and verticality perception. Nine subjects were asked to estimate the direction of the visual vertical (VV) by 12 adjustments of a luminous line in three conditions: (1) a control condition (subjects were upright and aware of their position), (2) a condition of congruence between the lateral body tilt and the awareness of this tilt, and (3) a condition of dissociation of subjective and objective orientations (tilted subjects who felt upright). The dissociation between objective and subjective orientations was obtained by inducing experimentally a postural vertical (PV) bias through 5 min of lateral body tilt at 30° in darkness in a motorized flight simulator (mean 8.8° ± 4; min 6.2°; max 17.4°). VV orientation and variability were measured (expressed below in this order). As compared to the upright condition (0.3° ± 0.2; 0.8° ± 0.5), subjects showed similar VV orientation (0.1° ± 0.6; p=0.82) but an increased variability (1.4°±0.5; p<0.001) when tilted and aware of their tilt. In contrast, when they were tilted but felt upright, VV was biased in the direction of body tilt (2°±0.5; p<0.005) without increase of variability (0.9° ± 0.5; p=0.7). Our study reveals that the awareness of body orientation modulates verticality representation, which means that in addition to sensory integration, mental processes play also a role in the sense of verticality. We propose a novel model of verticality representation, based both on bottom-up and top-down processes.

Cognitive cues and visually induced motion sickness.

BACKGROUND: The importance of cognitive processing of orientation cues in visually induced motion sickness and vection is often overlooked. Upright versus inverted visual scenes containing cues of different levels of salience were compared. METHODS: Panoramic scenes of 360 degrees were projected in the visual equivalent to the nauseogenic situation of rotating about an axis tilted from the vertical with a field of view of 84 degrees rotating at 0.2 Hz (72 degrees x s(-1)). Exposures were for 10 min or until moderate nausea developed. The design was counterbalanced repeated measures. Pilot Study: Subjects (N = 12) viewed visual conditions: a distant bland coastline scene as from an aircraft, tilted 30 degrees (Up); the same scene but inverted (Invert); and the scene morphed with no obvious orientation cues (Abstract). Main Experiment: Subjects (N = 22) viewed a city street scene containing numerous unambiguous and strong verticality cues under two conditions: upright (Up) and inverted (Invert), with 18 degrees tilt of rotational axis. RESULTS: Pilot Study: there were no significant differences between conditions in time (mean +/- SD min) to nausea endpoint (Up: 7.4 +/- 3.1; Invert: 7.1 +/- 3.1;Abstract: 7.8 +/- 2.4), nor for total symptom scores, nor for vection. Main Experiment: the upright scene was significantly more nauseogenic than the inverted, with shorter times to nausea endpoint (Up: 8.7 +/- 2.3; Invert: 9.2 +/- 2.2) and greater total symptom scores. Vection was marginally greater for Up than Invert. CONCLUSIONS: Salient and unambiguous higher order cognitive cues may modulate the development of motion sickness induced by optokinetic stimuli. There was no one-to-one correspondence between vection and motion sickness.

Off vertical axis rotation motion sickness and field dependence.

BACKGROUND: Our study probed the relationship between field dependence and the development of nausea in light and dark during whole-body, off vertical axis rotation (OVAR). METHODS: There were 24 subjects who underwent OVAR at 0.2 Hz, 18 degree tilt. Exposures were undertaken in both light and darkness in sessions spaced 5 d apart in balanced order design. During rotation, nausea was rated at 1-min intervals to a cut off at 20 min or a level of 'moderate nausea' was attained, at which point motion stopped. Before and after OVAR sessions field dependence was rated with the rod and frame test (RFT) with head upright or tilted 28 degree to induce a head-centric bias. RESULTS: Subjects tolerated OVAR longer in the light (mean 13.3 min +/- 6.8 SD) than in darkness (11.1 min +/- 7.2). Motion sickness susceptibility evaluated by questionnaire was inversely correlated with tolerance of OVAR in the light. There was a tendency for subjects who were visual field dependent to fare better with OVAR in the light than in darkness. Subjects whose RFT estimates with head tilted tended to incline the visual vertical to the direction of head tilt better tolerated OVAR in darkness. DISCUSSION: The results suggest that susceptibility, as evaluated by questionnaires probing motion sickness experiences in daily life, is influenced by visual factors. Assessments of sensitivity to reference frames for orientation, either visual or ego-centered, show promise for markers of motion sickness susceptibility according to the visual surround rather than to absolute levels of susceptibility to motion sickness.

Vestibular perceptual thresholds to angular rotation in acute unilateral vestibular paresis and with galvanic stimulation.

Studies of compensation of injury to the human vestibular system have, in the main, focused on the vestibular-ocular reflex. Probing vestibular perception allows more of the sensory pathway to be assessed. We present a novel paradigm for simultaneously testing vestibular perceptual and nystagmic thresholds to angular acceleration around an earth vertical axis. The perceptual thresholds can be modulated asymmetrically in normal subjects by DC galvanic stimulation with the head flexed in the roll plane, as expected from the main torsional plane of action of the galvanic stimulus. The perceptual and nystagmic thresholds were bilaterally elevated in acute vestibular neuritis, a unilateral condition, possibly due to central suppression of vestibular input. The degree of asymmetry in thresholds was small in comparison with the large caloric asymmetry present in the patients, indicating a relatively preserved capacity for near-threshold performance of the non-damaged labyrinth both in the "on" and "off" directions.

Respiratory vulnerability to vehicle buffeting.

OBJECTIVE: Buffeting in a jerky ride in a bus or ambulance normally provokes a sustained tachypnoea driven by vibration and sensory mechanisms including vestibular signals. Tachypnoea reinforces the torso against mechanical shocks but results in overbreathing, causing a mild fall in CO(2). However, normal CO(2) is rapidly restored by a reduction in depth of breathing. We test the hypothesis that vulnerable subjects, exemplified by elderly individuals and patients with vestibular disorders, may fail to adapt to buffeting. METHODS: Respiratory and cardiovascular functions were recorded from five elderly subjects, two patients with bilateral loss of vestibular function and five patients with 'BPPV,' while being exposed to 15-min buffeting in a flight simulator which simulated transport in an ambulance over rough pavement. Results were compared with published norms. RESULTS: Some subjects sustained overbreathing during motion, through either tachypnoea or deep breathing, causing a marked reduction in CO(2) levels (3/5, 2/2 avestibular, 4/5 elderly, 4/5 BPPV). Others failed to raise breathing frequency which would render them susceptible to mechanical shock (4/5 elderly, 1/2 avestibular). Overbreathing was particularly evident in three anxious subjects. INTERPRETATION: Overbreathing during buffeting could be caused by (1) resetting of CO(2) rest levels lower; (2) change in receptor sensitivity; (3) adjustment of central drive to breathing; and (4) stiffening of posture because of motion discomfort reduced the ability to modulate breathing. The buffeting experienced was moderately violent. More profound hypocapnia and mechanical shock are likely to result in vulnerable individuals failing to adapt to severe buffeting in transport on unpaved roads, in war zones or by sea ambulance.

The effect of smoking nicotine tobacco versus smoking deprivation on motion sickness.

BACKGROUND: The experienced smoker maintains adequate nicotine levels by 'puff-by-puff self-control' which also avoids symptomatic nauseating effects of nicotine overdose. It is postulated that there is a varying 'dynamic threshold for nausea' into which motion sickness susceptibility provides an objective toxin-free probe. Hypotheses were that: (i) nicotine promotes motion sickness whereas deprivation protects; and (ii) pleasurable effects of nicotine protect against motion sickness whereas adverse effects of withdrawal have the opposite effect. METHODS: Twenty-six healthy habitual cigarette smokers (mean ± SD) 15.3 ± 7.6 cigs/day, were exposed to a provocative cross-coupled (coriolis) motion on a turntable, with sequences of 8 head movements every 30s. This continued to the point of moderate nausea. Subjects were tested after either ad-lib normal smoking (SMOKE) or after overnight deprivation (DEPRIV), according to a repeated measures design counter-balanced for order with 1-week interval between tests. RESULTS: Deprivation from recent smoking was confirmed by objective measures: exhaled carbon monoxide CO was lower (P<0.001) for DEPRIV (8.5 ± 5.6 ppm) versus SMOKE (16.0 ± 6.3 ppm); resting heart rate was lower (P<0.001) for DEPRIV (67.9 ± 8.4 bpm) versus SMOKE (74.3 ± 9.5 bpm). Mean ± SD sequences of head movements tolerated to achieve moderate nausea were more (P = 0.014) for DEPRIV (21.3 ± 9.9) versus SMOKE (18.3 ± 8.5). DISCUSSION: Tolerance to motion sickness was aided by short-term smoking deprivation, supporting Hypothesis (i) but not Hypothesis (ii). The effect was was approximately equivalent to half of the effect of an anti-motion sickness drug. Temporary nicotine withdrawal peri-operatively may explain why smokers have reduced risk for postoperative nausea and vomiting (PONV).

Slalom walking with prism disorientation: impact on verbal and spatial tasks.

BACKGROUND: Slalom walking wearing distorting prisms has been used to study multitasking during adaptation to spatial disorientation. We address the hypothesis that slalom-prism walking could interfere specifically with concurrent spatial tasks. METHODS: Subjects (16 men, 16 women) sat for 30 s then slalom walked through 5 aligned batons. This exercise was performed with normal vision and with prisms deviating gaze laterally by 15.50 Both conditions were done without any tasks, with a verbal task (matching the sex of male and female names uttered by male and female voices), and a spatial task (matching laterality of the words 'right' and 'left' delivered to the right or left ear). Conditions were balanced with instructions to perform rapidly and accurately. RESULTS: Time to walk the slalom was extended by the prisms from 16 s to 33 s, but unaffected by tasks. Slalom increased error rates on the spatial task by 8% above baseline, but verbal task errors remained unchanged. Prisms did not affect task errors. The rates of processing cognitive task items were slowed by approximately 0.5 s by slalom and by 1 s slalom walking with prisms. Prisms increased task reaction times by 340 ms during slalom. Contact with the poles occurred when multitasking, with men making three times more contacts than women. CONCLUSIONS: Slowing of all performance parameters is consistent with a 'bottleneck' caused by task multiplexing. Competition for spatial processing resources and confusion because of similar features may cause interference between the lateralized spatial task and slalom.

The social impact of dizziness in London and Siena.

Although dizziness is a common presenting symptom in general and hospital practice, its social cost is not known. We assessed the social and work life impact of dizziness on patients in two contrasting European cities, Siena and London. First, we developed the 'Social life & Work Impact of Dizziness questionnaire' (SWID), which was validated by administering it to 43 patients with dizziness and 45 normal controls and by correlating the results with the EQ-5D (Europe quality of life) questionnaire. The SWID and EQ-5D scores were worse in patients than controls (p < 0.001) and the two correlated significantly (r = 0.50 p < 0.001). Then two hundred consecutive patients per city attending tertiary specialised 'dizzy patient' clinics, one in London led by a neurologist, one in Siena led by an ear, nose and throat specialist (ENT), were investigated with SWID. Amongst the 400 patients, 27% reported changing their jobs and 21% giving up work as a result of the dizziness. Over 50% of patients felt that their efficiency at work had dropped considerably. The mean number of days off work attributed to the dizziness in the previous 6 months was 7.15 days. Social life was disrupted in 57% of all 400 patients. Factor analysis identified that detrimental effects on work, travel, social and family life combine to create a single factor accounting for much of the overall impact of their dizziness. Significant differences in some measures of handicap between London and Siena emerged, with London patients often faring worse. Reasons for these location differences include, as expected, a higher proportion of neurological patients in London than in Siena. However, factors related to city demographics and social cohesion may also modulate the impact on quality of life and working practice. Regardless of inter-city differences, these findings highlight the high social and economic impact of dizziness.

Perceptual encoding of self-motion duration in human posterior parietal cortex.

It has been demonstrated previously that repetitive transcranial magnetic stimulation (rTMS) to right or left posterior parietal cortex (PPC) disrupts perceptual encoding of whole-body displacement during an angular path integration task using only vestibular cues for its completion. The effects of rTMS applied to right PPC (and left motor cortex as a control) during a vestibular-cued motion-reproduction task (i.e., not requiring path integration) were investigated in 5 subjects. Specifically, subjects were rotated in the dark on a motorized Bárány chair with raised cosine velocities of durations 1, 2, and 3 s and peak 30 degrees, 60 degrees, 90 degrees, and 120 degrees/s. Subjects were required to actively reproduce the motion profile after every rotation with a chair-bound joystick. It was found that rTMS applied to the right PPC during the passive (encoding) stimulus phase had no effect on angular velocity reproduction when compared to control (motor-cortex rTMS). In contrast, motion-duration reproduction was significantly worse with right PPC (versus control motor cortex) rTMS. The results imply that vestibular-derived cues of motion duration, but not velocity, are encoded in human PPC. It was inferred from these and previous data that human PPC is involved in human path integration and motion-duration perception, but not angular velocity self-motion perception.

Off-vertical axis rotation of the visual field and nauseogenicity.

BACKGROUND: Off-vertical axis rotation (OVAR) causes motion sickness which increases with angle of tilt and is most provocative around 0.2 Hz. The aim was to determine the tilt angle and frequency characteristics for visual OVAR, which is also known to be nauseogenic. METHODS: A computerized scene, as seen by a pilot at moderate altitude, rotated at different frequencies about an axis which could tilt as during OVAR. A concurrent visual detection task controlled attention. Exposures were for 10 min or until nausea developed. There were four experiments: Frequency tuning-visual motion at 0.05, 0.2, and 0.8 Hz, all at 18 degrees tilt of the axis of rotation (N = 14); gross visual tilt tuning-visual motion at 0, 45, and 90 degrees of tilt at 0.2 Hz (N = 12); fine visual tilt tuning -- 18, 36, 54, and 72 degrees tilts at 0.2 Hz (N = 24); and whole-body tilt of the participant at 0, 45, and 90 degrees, viewing rotation about a vertical axis at 0.2 Hz (N = 12). RESULTS: Nauseogenicity was significantly greater at 0.2 Hz than at lower or higher frequencies. Visual tilts 18 degrees to circa 45 degrees were significantly more nauseogenic. No differences were found between whole-body tilts. CONCLUSIONS: Nauseogenicity of visual OVAR peaks around 0.2 Hz, and increases with stimulus strength up to circa 45 degrees tilt, similar to real motion. With higher tilt angles, decreasing nauseogenicity suggests that the visual impact is partially quarantined because the motion would appear patently absurd and not a sensory conflict. Whole-body tilt may have failed to modulate nauseogenicity because of overriding somatosensory cues to Earth vertical.