Visual Vertical Research Articles

Lateropulsion After Hemispheric Stroke: A Form of Spatial Neglect Involving Graviception.

To test the hypothesis that lateropulsion is an entity expressing an impaired body orientation with respect to gravity in relation to a biased graviception and spatial neglect. Data from the DOBRAS cohort (ClinicalTrials.gov: NCT03203109) were collected 30 days after a first hemisphere stroke. Lateral body tilt, pushing, and resistance were assessed with the Scale for Contraversive Pushing. Among 220 individuals, 72% were upright and 28% showed lateropulsion (tilters [14%] less severe than pushers [14%]). The 3 signs had very high factor loadings (>0.90) on a same dimension, demonstrating that lateropulsion was effectively an entity comprising body tilt (cardinal sign), pushing, and resistance. The factorial analyses also showed that lateropulsion was inseparable from the visual vertical (VV), a criterion referring to vertical orientation (graviception). Contralesional VV biases were frequent (44%), with a magnitude related to lateropulsion severity: upright -0.6° (-2.9; 2.4), tilters -2.9° (-7; 0.8), and pushers -12.3° (-15.4; -8.5). Ipsilesional VV biases were less frequent and milder (p < 0.001). They did not deal with graviception, 84% being found in upright individuals. Multivariate, factorial, contingency, and prediction analyses congruently showed strong similarities between lateropulsion and spatial neglect, the latter encompassing the former. Lateropulsion (pusher syndrome) is a trinity constituted by body tilt, pushing, and resistance. It is a way to adjust the body orientation in the roll plane to a wrong reference of verticality. Referring to straight above, lateropulsion might correspond to a form of spatial neglect (referring to straight ahead), which would advocate for 3D maps in the human brain involving the internal model of verticality.

Novel characterization of subjective visual vertical in patients with unilateral spatial neglect

Visual vertical (VV), visually perceived direction of gravity, is widely measured to assess the vestibular function and visuospatial cognition. VV has been assessed by comparing orientation and variability of measured values separately between subject groups. However, changes in orientation and variability often differ in patients with unilateral spatial neglect (USN). Here, we developed a novel classification of VV that combines orientation and variability and characterized the effects of USN on VV.Forty-three subacute stroke patients with or without USN (USN+, n = 17; USN-, n = 26) and 33 age-matched controls were included in the study. In darkness, a luminous line, initially tilted at 30° either to the left or right, gradually rotated towards the vertical. The VV was defined as the deviation of the subjectively-perceived vertical from the true vertical. The new classification demonstrated that, while the majority of USN + patients (14/17) exhibited large variability, nine showed normal orientation and five showed greater contra-lesional deviation of orientation, suggesting different underlying mechanisms for orientation and variability. Further analyses revealed VV deviation to the initial tilt in all groups. However, the deviation in USN + was larger and more variable, indicating attentional disorders. Such characterization would contribute to individually specified clinical rehabilitation.

Modulating the internal model of verticality by virtual reality and body-weight support walking: A pilot study.

The study aimed at inducing a visual vertical (VV) bias by immersion in a virtual tilted room (VTR, visual cues), then testing the effect of 30% body-weight support walking (BWSW, somaesthetic cues) to correct this bias. We included 20 healthy participants (median age 54 years; 12 females) who wore the Oculus-Rift® Head Mounted Display to produce the virtual reality and generate the VV. VV (8 trials) was tested at baseline, then in 3 postural conditions (walking, sitting and BWSW), by 2 visual conditions (darkness and VTR), according to a pseudo-randomized blocked design. The VTR was tilted 18° clockwise. Data for 3 participants with virtual reality sickness were discarded, and those for 17 participants underwent non-parametric statistical analysis by 2 main criteria: VV and head orientation. The VTR induced a pronounced tilt of the vertical toward the tilted side under the baseline condition (median 11.4° [Q1-Q3 6.1-13.4]; P<0.01), with a large effect size (r=0.88). The effect was systematic, with great inter-individual variability (2-17°), and was similar under every postural condition (P<0.001), with a post-effect lasting 6min and suppressed under BWSW. In darkness, VV was more upright during BWSW than sitting (P<0.05), with a medium effect size (r=0.49). The VTR induced a slight head tilt of median 3.3° [2.8-5.9] toward the tilted side under every postural condition (P<0.001), with a large effect size (r=0.87). In darkness, the head was upright only at baseline and under BWSW. Being immersed in a tilted environment induces a powerful bias in verticality perception (11°). Contrary to our hypothesis, BWSW did not attenuate the effect induced by the VTR, probably because of the power of this effect. However, BWSW was the only postural condition able to suppress post-effects induced by the VTR, thereby leading to the head and VV oriented upright. BWSW may improve verticality representation, presumably by bringing augmented information about the direction of the Earth vertical. These findings represent an avenue for rehabilitation of patients with postural disorders caused by a wrong verticality representation. Technological improvements will be necessary to attenuate the virtual reality discomfort.

Internal model of verticality: Neuromodulation through body-weight support in a tilted virtual environment

The development of rehabilitation techniques modulating the sense of verticality is a major challenge in balance disorders related to lateropulsion or retropulsion (Stroke, Parkinson, etc.). Through this pilot study in healthy participants, we tested two techniques that are likely to modulate verticality perception: immersion in tilted virtual environment (visual cues) and walking with body weight support (somaesthesic cues). Among 20 recruited healthy participants, 12 were studied (53.3 ± 7 years old) for the following criteria: normal visual vertical (VV) in baseline, sensitive to an immersive virtual tilted room (VTR) without dizziness. Their VV (8 trials) was tested in 3 postural conditions (sitting, treadmill walking and treadmill walking with 30% of body weight suspended by a vertical cable (BWSW), combined with 2 visual conditions (darkness and VTR). VTR was produced by an Oculus Rift ® head mounted display (HMD), and tilted 18° clockwise. The study design aimed at introducing a VV bias through the VTR, then testing the immediate and after-effects of postural conditions. Data were analyzed with ANOVA. Regarding VV it was found a main effect of VTR (11.0 ± 4.4; F(1,10) = 158.5; P < 0.001), with an after-effect of several minutes recorded in darkness. It was also found a strong effect of the postural setting (F(2,20) = 5.4, P < 0.05). Post-hoc analysis showed that VV was 0.6° more vertical in the condition BWSW than in sitting ( P < 0.05). Being immerged in a tilted environment induces a powerful bias in verticality perception, stronger than that reported by studies using non-immersive tilted clues. Overall walking on a treadmill being supported by a vertical cable is a mean to recalibrate a biased vertical. This modulation of the internal model of verticality is likely due partly to a reweighting of somaesthesic input, and to an implicit direction of the Earth vertical given by the cable which supports the body. This might open an interesting track for the rehabilitation of patients with postural disorders due to a biased internal model of verticality.

Visual verticality perception after stroke: A systematic review of methodological approaches and suggestions for standardization

Introduction Visual vertical (VV) measurements are being increasingly used for routine clinical assessment of spatial cognition, to investigate otolithic vestibular function and identify altered verticality perception as a possible cause of postural disorders after stroke. The objective of this paper was to synthesize knowledge of assessment methods for testing VV after stroke. Material and methods This systematic review, following the PRISMA statement, involved a search for articles in MEDLINE via PubMED published up to November 2015 by using the search terms “visual vertical”, “verticality perception” and “stroke”. We included only case or group studies on VV perception after hemispheric, brainstem or cerebellar strokes. Two authors independently assessed data on patients’ and VV assessment characteristics, outcome measures, ranges of normality and psychometric properties. Results We assessed reports for 61 studies (1982 patients) of VV for hemispheric (n = 43), brainstem (n = 18) or cerebellar (n = 8) stroke. VV assessment procedures varied widely in paradigm, type of stimulus, patient posture, number of trials and outcome measures. However, some emerging guidelines recommend assessing VV in absolute darkness, with an even number of trials, from 6 to 10, with the body maintained upright (at least the trunk). Under these conditions, normal VV orientation (mean of VV estimates) can be considered from −2.5° to 2.5° and is highly reliable for use in clinical practice and research. A difference ≥ 2° between repeated measures for a given patient can be interpreted as a real change in VV perception. Myriad of protocols have been proposed, for which psychometric properties must be better analyzed. Discussion–conclusion This first review of VV assessment methods after stroke shows a great heterogeneity of procedures, settings and parameters, among which only some are eligible for standardization to limit measurement errors and better interpret the results.

Visual verticality perception after stroke: A systematic review of methodological approaches and suggestions for standardization

Visual vertical (VV) measurements are being increasingly used for routine clinical assessment of spatial cognition, to investigate otolithic vestibular function and identify altered verticality perception as a possible cause of postural disorders after stroke. The objective of this paper was to synthesize knowledge of assessment methods for testing VV after stroke. This systematic review, following the PRISMA statement, involved a search for articles in Medline via PubMed published up to November 2015 by using the search terms “visual vertical”, “verticality perception” and “stroke”. We included only case or group studies on VV perception after hemispheric, brainstem or cerebellar strokes. Two authors independently assessed data on patients’ and VV assessment characteristics, outcome measures, ranges of normality and psychometric properties. We assessed reports for 61 studies (1982 patients) of VV for hemispheric ( n = 43), brainstem ( n = 18) or cerebellar ( n = 8) stroke. VV assessment procedures varied widely in paradigm, type of stimulus, patient posture, number of trials and outcome measures. However, some emerging guidelines recommend assessing VV in absolute darkness, with an even number of trials, from 6 to 10, with the body maintained upright (at least the trunk). Under these conditions, normal VV orientation (mean of VV estimates) can be considered from -2.5° to 2.5° and is highly reliable for use in clinical practice and research. A difference ≥ 2° between repeated measures for a given patient can be interpreted as a real change in VV perception. Myriad of protocols have been proposed, for which psychometric properties must be better analyzed. This first review of VV assessment methods after stroke shows a great heterogeneity of procedures, settings and parameters, among which only some are eligible for standardization to limit measurement errors and better interpret the results.

Assessing the visual vertical: how many trials are required?

BackgroundThe visual vertical (VV) consists of repeated adjustments of a luminous rod to the earth vertical. How many trials are required to reach consistency in this measure? This question has never been addressed despite the widespread clinical use of the measurement in stroke rehabilitation.MethodsVV perception was assessed (10 trials) in 117 patients undergoing rehabilitation after a first hemisphere stroke. The intraclass correlation coefficient (ICC) and standard error of measurement (SEM) were calculated for each patient category: with contralesional VV bias (n = 48), ipsilesional VV bias (n = 17) and normal VV (n = 52).ResultsFor patients with VV biases, 6 trials were required to reach high inter-trial reliability (contralesional: ICC = 0.9, SEM = 1.36°; ipsilesional: ICC = 0.896, SEM = 0.96°). For patients with normal VV, a minimum of 10 trials was required (ICC = 0.728, SEM = 1.13°). A set of 6 trials correctly classified 96 % of patients.ConclusionsIn the literature, 10 is the most frequently used number of trials used to assess VV orientation. Our study shows that 10 trials are required to adequately measure VV orientation in non-selected subacute stroke patients. For complex protocols imposing a decrease in the number of trials in each condition, 6 trials are needed to identify VV biases in most patients.

Maintaining trunk and head upright optimizes visual vertical measurement after stroke

Visual vertical (VV) measurement provides information about spatial cognition and is now part of postural disorders assessment [1] , [2] . Guidelines for clinical VV measurement after stroke remain to be established, especially regarding the orientation settings for patients who do not sit upright. We analyzed the need to control body orientation while patients estimate the VV. VV orientation and variability were assessed in 20 controls and 36 subacute patients undergoing rehabilitation after a first hemisphere stroke, in 3 setting: body not maintained (trunk and head free), partially maintained (trunk maintained, head free), or maintained (trunk and head). VV was analyzed as a function of trunk and head tilt, also quantified. Trunk and head orientations were independent. The ability to sit independently was affected by a tilted trunk. The setting had a strong effect on VV orientation and variability in patients with contralesional trunk tilt ( n = 11; trunk orientation –18.4 ± 11.7°). The contralesional VV bias was severe and consistent under partially maintained (–8.4 ± 5.2°) and maintained (–7.8 ± 3.5°) settings, whereas various individual behaviors reduced the mean bias under the non-maintained setting (–3.6 ± 9.3°, P < 0.05). VV variability was lower under the maintained (1.5 ± 0.2°) than non- (3.7 ± 0.4°, P < 0.001) and partially (3.6 ± 0.2°, P < 0.001) maintained settings. In contrast, setting had no effect in patients with satisfactory postural control in sitting. Subject setting improves VV measurement in stroke patients with postural disorders. Maintaining the trunk upright enhances the validity of VV orientation, and maintaining the head upright enhances the validity of within-subject variability. Measuring VV without any body maintaining is valid in patients with satisfactory balance abilities.

Reliability study of the Visual Vertical in subacute stroke

Visual vertical (VV) has been being increasingly used as a routine clinical assessment to identify alteration of verticality perception as a possible cause of postural disorders after stroke. This study aims to determine if the reliability of VV is sufficient to support a wide clinical use in neuro-rehabilitation for stroke patients monitoring. We assessed the inter- and intra-raters reliability and the inter-trials reliability. In a first study, 20 subacute stroke patients in neuro-rehabilitation unit were tested after a first hemispheric stroke. To evaluate the inter-rater reliability, VV was assessed the same day by 2 examiners whose degrees of expertise differed. The second examiner repeated the test the next day in order to investigate intra-rater reliability. VV orientation (mean, primary criterion) and uncertainty (standard deviation, secondary criterion) were calculated over 10 trials. Their reliability was quantified by the intraclass correlation coefficient [ICC], Bland-Altman plots and the minimal detectable change (MDC). The concordance between two examiners was quantified by Cohen's kappa coefficients ( κ ). In a second study, inter-trials reliability was assessed in 117 subacute stroke patients by ICC and SEM. In study 1, regarding VV orientation, inter-and intra-rater reliability were excellent (ICC = 0.979 and 0.982). The Bland-Altman plots and the MDC revealed a difference inferior to 2° between two tests. The concordance between two assessments for the diagnosis of abnormal VV orientation was absolute for the same examiner ( κ = 1; P < 0.05) and excellent between two examiners ( κ = 0.92; P < 0.05). As for VV uncertainty the intra-rater reliability was satisfactory (ICC = 0.836) but the inter-rater reliability poor (ICC = 0.211). In study 2, a high inter-trials reliability required a minimum of 8 trials (ICC = 0.909; SEM = 1.18°) for patients with contralesional VV bias, whereas a minimum of 6 and 10 trials were required for patients with ipsilesional VV bias (ICC = 0.896; SEM = 0.96) and patients with normal VV perception (ICC = 0.728; SEM = 1.13) respectively. The orientation of the visual vertical is a highly reliable criterion, which may be used both in research and routine clinical practice. VV orientation can be adequately assessed with 6 to 10 trials in subacute stroke patients. Ten trials are recommended when comparison between sub-groups of patients having divers VV biased perception is intended.

Inter- and Intra-Rater Reliability of the Visual Vertical in Subacute Stroke.

Visual vertical (VV) has been used increasingly as a routine clinical assessment to identify alteration of verticality perception as a possible cause of postural disorders after stroke. This study aims to determine whether the reliability of VV is sufficient to support a wide clinical use in neurorehabilitation for monitoring of patients with stroke. Twenty patients with subacute stroke in neurorehabilitation unit were tested after a first and unique hemispheric stroke. To evaluate the inter-rater reliability, VV was assessed the same day by 2 examiners whose degrees of expertise differed. The second examiner repeated the test the next day to investigate intrarater reliability. VV orientation (mean, primary criterion) and uncertainty (SD, secondary criterion) were calculated for 10 trials. Their reliability was quantified by the intraclass correlation coefficient, Bland-Altman plots, and the minimal detectable change. The concordance between 2 examiners was quantified by Cohen's κ coefficients (κ). About VV orientation, inter- and intrarater reliability were excellent (intraclass correlation coefficient, 0.979 and 0.982). The Bland-Altman plots and the minimal detectable change revealed a difference inferior to 2° between 2 tests. The concordance between 2 assessments for the diagnosis of abnormal VV orientation was absolute for the same examiner (κ=1; P<0.05) and excellent between 2 examiners (κ=0.92; P<0.05). As for VV uncertainty the intrarater reliability was satisfactory (intraclass correlation coefficient, 0.836) but the inter-rater reliability was poor (intraclass correlation coefficient, 0.211). The orientation of the VV is a highly reliable criterion, which may be used both in research and in routine clinical practice.

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 5min 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.

Spatiotemporal dynamics of visual vertical judgments: early and late brain mechanisms as revealed by high-density electrical neuroimaging

Constructing and updating an internal model of verticality is fundamental for maintaining an erect posture and facilitating visuo-spatial processing. The judgment of the visual vertical (VV) has been intensively studied in psychophysical investigations and relies mainly on the integration of visual and vestibular signals, although a contribution of postural and somatosensory signals has been reported. Here we used high-density 192-channel evoked potential (EP) mapping and distributed source localization techniques to reveal the neural mechanisms of VV judgments. VV judgments (judging the orientation of visual lines with respect to the subjective vertical) were performed with and without a tilted visual frame. EP mapping revealed a sequence of neural processing steps (EP maps) of which two were specific for VV judgments. An early EP map, observed at ∼75–105 ms post-stimulus, was localized in right lateral temporo-occipital cortex. A later EP map (∼260–290 ms) was localized in bilateral temporo-occipital and parieto-occipital cortex. These data suggest that early VV-related neural processing involves the lateral and ventral visual stream and is related to visual processing concerning orientation, attention and comparison. The later, more dorsal, activation involves multimodal cortex subtending a constantly available and updated internal model of the vertical that we can refer to for the control of one's posture, actions, and visuo-spatial processing.

Psychological Symptoms and Spatial Orientation During the First 3 Months After Acute Unilateral Vestibular Lesion

We undertook this study to assess the correlation between the results of simple tests of spatial orientation and the occurrence of common psychological symptoms during the first 3 months after an acute, unilateral, peripheral, vestibular lesion. Ten vestibular patients were selected and accepted to participate in the study. During a 3-month follow-up, we recorded the static visual vertical (VV), the estimation error of reorientation in the yaw plane and the responses to a standardized questionnaire of balance symptoms, the Dizziness Handicap Inventory (DHI), the depersonalization/derealization inventory by Cox and Swinson (DD), the Dissociative Experiences Scale (DES), the 12-item General Health Questionnaire (GHQ-12), the Zung Instrument for Anxiety Disorders and the Hamilton Depression Rating Scale. At week 1, all patients showed a VV >2° and failed to reorient themselves effectively. They reported several balance symptoms and handicap as well as DD symptoms, including attention/concentration difficulties; 80% of the patients had a Hamilton score ≥8. At this time the balance symptom score correlated with the DHI. After 3 months, all scores decreased. Multiple regression analysis of the differences from baseline showed that the DD score difference was related to the difference on the balance score, the reorientation error and the DHI score (p <0.01). No other linear relationships were observed (p >0.5). During the acute phase of a unilateral, peripheral, vestibular lesion, patients may show poor spatial orientation concurrent with DD symptoms including attention/concentration difficulties, and somatic depression symptoms. After vestibular rehabilitation, DD symptoms decrease as the spatial orientation improves, even if somatic symptoms of depression persist.

Evolution of Subjective Visual Vertical Perturbation After Stroke

Objective. The perception of visual verticality is often perturbed after stroke and might be an underlying component of imbalance. The aim of this study was to describe the evolution of visual vertical (VV) perturbation and to investigate the factors affecting it. Methods. Thirty patients with hemiplegia after a single hemispheric stroke (17 left lesioned [LL] and 13 right lesioned [RL]) were studied. Visual verticality was tested within 45 days of stroke, and then at 3 and 6 months. Subjects sat in a dark room and adjusted a luminous rod to the vertical position. The differences between patients’ adjustments and vertical were calculated. The effects on VV evolution of the side, size, type, and location of the lesion were tested. Results. Sixty percent of the recent stroke patients had an initial inaccurate perception of verticality, and 39% of these patients recovered during the 1st 3 months after stroke. The evolution of VV tilt depended on the side of the lesion (P = 0.01), with better recovery in LL patients. None of the other factors studied affected VV normalization. Conclusions. The poorer recovery of vertical perception after right-side stroke might be due to the predominant role of the right hemisphere in spatial cognition, and might be involved in the poorer recovery of balance after stroke in RL patients.

Perception of spatial orientation in spasmodic torticollis. Part 2: The visual vertical.

Twenty-nine patients with idiopathic spasmodic torticollis (ST) and matched normal control subjects were asked to align a target line to perceived earth vertical [visual vertical (VV)]. Settings were made against a whole-field random-dot background that was either stationary or rotating around the line of sight, and subjects performed the task upright and lying horizontally on their sides. Normal subjects were tested both head upright and after assuming a voluntary head tilt. Patients with ST set the VV close to true upright with a minimal deviation toward tilt of the head in contrast to normal subjects assuming a head tilt who set the VV in the opposite direction to the head tilt (Müller "E" effect). Settings against the spinning disk were biased in the direction of rotation similarly for both subject groups. Settings made against static or spinning disk performed when subjects lay horizontally were tilted in the direction of recumbence (Aubert "A" effect) similarly for both subject groups. When attempting to set the target line parallel to the long axis of the face, patients with head tilt set the line to upright, whereas normal subjects correctly estimated their tilts. One hypothesis offered to explain these results is that the patients referenced only their upright trunk for vertical and did not make use of neck proprioceptive or vestibular signals of head tilt so that all settings were made as if the trunk and head were upright. Alternatively, patients may have used only otolith signals as the reference for upright, and these are recalibrated in ST patients with head tilt. The pathological deviation becomes accepted as upright posture, and VVs and facial orientation are estimated as if the head were upright. In either case the findings indicate abnormal processing of the perception of visual verticality in ST patients.