Visual Vertical Orientation Research Articles

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.

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.

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.

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.

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.