Subjective Visual Vertical Perception Relates to Balance in Acute Stroke

Neuroanatomy of reduced distortion of body-centred spatial coding during body tilt in stroke patients

Awareness of the direction of the body's (longitudinal) axis is fundamental for action and perception. The perceived body axis orientation is strongly biased during body tilt; however, the neural substrates underlying this phenomenon remain largely unknown. Here, we tackled this issue using a neuropsychological approach in patients with hemispheric stroke. Thirty-seven stroke patients and 20 age-matched healthy controls adjusted a visual line with the perceived body longitudinal axis when the body was upright or laterally tilted by 10 degrees. The bias of the perceived body axis caused by body tilt, termed tilt-dependent error (TDE), was compared between the groups. The TDE was significantly smaller (i.e., less affected performance by body tilt) in the stroke group (15.9 ± 15.9°) than in the control group (25.7 ± 17.1°). Lesion subtraction analysis and Bayesian lesion-symptom inference revealed that the abnormally reduced TDEs were associated with lesions in the right occipitotemporal cortex, such as the superior and middle temporal gyri. Our findings contribute to a better understanding of the neuroanatomy of body-centred spatial coding during whole-body tilt.

Spatial neglect encompasses impaired verticality representation after right hemisphere stroke

Spatial neglect after right hemisphere stroke (RHS) was recently found to encompass lateropulsion, a deficit in body orientation with respect to gravity caused by altered brain processing of graviception. By analogy, we hypothesized that spatial neglect after RHS might encompass an altered representation of verticality. We also assumed a strong relation between body neglect and impaired postural vertical, both referring to the body. To tackle these issues, we performed contingency and correlation analyses between two domains of spatial neglect (body, extra-body) and two modalities of verticality perception (postural, visual) in 77 individuals (median age = 67) with a first-ever subacute RHS (1-3 months). All individuals with a transmodal (postural and visual) tilt in verticality perception (n = 26) had spatial neglect, but the reverse was not found. Correlation and multivariate analyses revealed that spatial neglect (and notably body neglect) was associated more with postural than visual vertical tilts. These findings indicate that after RHS, an impaired verticality representation results from a kind of graviceptive neglect, bearing first on somaesthetic graviception and second on vestibular graviception. They also suggest that the human brain uses not only a mosaic of 2D representations but also 3D maps involving a transmodal representation of verticality.

Association between spatial neglect and impaired verticality perception after stroke: A systematic review

BACKGROUND

Although most research on spatial neglect (SN) has focused on spatial perception deficits with regard to the lateral (left-right) axis, deficits of spatial perception with regard to the vertical (up-down) axis, such as disturbances in the perception of verticality (e.g., judgement of vertical orientations), have also been suggested.

OBJECTIVE

We aimed to systematically analyse reported associations between SN and characteristics of verticality perception while considering the time post-stroke.

METHODS

PubMed, Web of Science, Scopus, PubPsych and PsycArticles databases were searched on May 24, 2022 for articles written in English that evaluated the association between SN and verticality perception (i.e., the subjective visual vertical [SVV], subjective postural vertical [SPV] and subjective haptic vertical [SHV]) in adults after stroke. Left and right SN were considered and had to be assessed using standardized methods. Data were manually extracted, and risk of bias was assessed with the Newcastle-Ottawa Scale. The tilt of the line/chair relative to the gravitational vector and its direction, together with uncertainty (i.e., variability across measurements), were evaluated.

RESULTS

Thirteen studies were included (431 participants after stroke); at least 191 participants exhibited SN. Mainly the first 3 to 6 months post-stroke were evaluated. SN was associated with SVV misperception, which resulted in larger SVV tilts (mostly in the contralesional direction) and uncertainty in participants with than without SN. SVV tilt magnitudes ranged from a mean/median of -8.9° to -2.3° in SN participants and from -1.6° to 0.6° in non-SN participants, the latter falling within normative ranges. For SPV and SHV measurements, the magnitude of tilt and the uncertainty were insufficiently assessed or results were inconclusive.

CONCLUSIONS

SN was associated with larger SVV tilts and uncertainty, which suggests that SVV misperception is a key feature of SN. This observation highlights the importance of regular SVV assessment in people with SN in clinical practice.

PROSPERO

CRD42019127616.

Does electrical stimulation synchronized with ankle movements better improve ankle proprioception and gait kinematics in chronic stroke? A randomized controlled study

BACKGROUND:

Individuals with stroke have impaired sensorimotor function of ankle.

OBJECTIVE:

To investigate the effects of passive biaxial ankle movement training synchronized with electrical stimulation therapy (AMT-EST) on ankle proprioception, passive range of motion (pROM), and strength, balance, and gait of chronic stroke patients.

METHODS:

Thirty-five stroke patients were randomized. The experimental group received a total of 20 AMT-EST sessions. The control group received only EST. Primary outcome measures were ankle functions. Secondary outcome measures were clinical assessments of motor, balance, and gait-related functions. All assessments were compared before and after the intervention.

RESULTS:

The experimental group had significantly improved ankle dorsiflexor strength (p = 0.015) and ankle pROM during foot supination (p = 0.026) and pronation (p = 0.004) and clinical assessment (Fugl–Meyer Assessment of the lower extremities [FM-L], Berg Balance Scale, Timed Up and Go test, Fall Efficacy Scale, walking speed, and step length; all p < 0.05) values. The regression model predicting ankle proprioception showed significantly large effects (adjusted R² = 0.493; p < 0.01) of the combined FM-L score and time since stroke.

CONCLUSION:

Biaxial AMT-EST resulted in better ankle pROM and strength than conventional EST. Ankle proprioception was not significantly improved after AMT-EST and was predicted by the FM-L score and time since stroke.

Efficacy of sitting balance training with delayed visual feedback among patients with stroke: a randomized crossover clinical trial

[Purpose] This study aimed to determine the effect of delayed visual feedback on the center of pressure and sitting balance in patients with stroke. [Participants and Methods] This was a single-blinded, randomized crossover trial. The duration of each intervention in real-time visual feedback and delayed visual feedback conditions while sitting on the platform was five days. We measured the center of pressure, function in sitting test, and functional independence measure for physiotherapy assessment. [Results] Twenty patients with stroke were included in this study. The delayed visual feedback condition improved the center of pressure for lateral distance, function in sitting test, and functional independence measure. The lateral center of pressure deviation increased significantly after 500 ms of intervention. The function in sitting test evaluated the interaction between pre- and post-training, and these conditions revealed that timing and condition factors contributed to the improvement. Sitting balance training affected the functional independence measure. [Conclusion] Sensory-motor and cognitive learning was facilitated through balance training with delayed visual feedback, and the internal model was updated with the efference copy of error correction. Sensory-motor feedback to visual stimulation can improve postural control, balance, and activities of daily living.

Analysis of Verticality Perception in Older Adults With and Without Acute Stroke in Half-Lying Versus Sitting Positions

Currently, there is no research consensus regarding the influence of body position on verticality perception in acute stroke. In this study, we aimed to compare the influence of half-lying and sitting positions on measurements of the subjective visual vertical (SVV) and the subjective haptic vertical (SHV) of individuals in the acute stroke phase. In this cross-sectional study, we compared these positional experiences in two groups of participants: adults in the acute stroke phase and elderly individuals without stroke. Independent variables were stroke versus no-stroke groups, in half-lying versus sitting positions. Analyzed variables of related interest were cognition (Mini-Mental State Examination or MMSE), stroke severity (National Institutes of Health Stroke Scale or NIHSS), and trunk control (Trunk Impairment Scale or TIS). Dependent variables were visual and haptic verticality, as evaluated by SVV and SHV. There were observed differences in absolute SVV in sitting position between groups (p = 0.021), absolute SVV in half-lying position between groups (p = 0.033), absolute SHV in sitting position between groups (p = 0.003), absolute SHV in half-lying position between groups (p = 0.002), and constant SVV in half-lying position between groups (p = 0.007). In the stroke group there was a higher coefficient of variation of SVV and SHV in the half-lying position compared to sitting position. In the sitting position, we observed a very strong correlation between the TIS and absolute SHV (p = 0.008). We concluded that individuals in the acute phase of stroke had greater misperceptions of visual and haptic verticality than older adults without strokes and that individuals in the acute phase of stroke showed less variability in visual and haptic vertical perception in the sitting position than in the half-lying position. By implication, we should encourage the sitting position in the acute stroke phase and develop early strategies to increase the verticality perception.

Effects of Galvanic Vestibular Stimulation on Visual Verticality and Standing Posture Differ Based on the Polarity of the Stimulation and Hemispheric Lesion Side in Patients With Stroke

Introduction: There is growing evidence supporting the relationship of vertical misperception and poor balance control with asymmetrical standing posture in patients with stroke. Although the vestibular system has been shown to be responsible for vertical misperception and balance disorders, the effect of galvanic vestibular stimulation (GVS) on both vertical misperception and postural asymmetry after stroke remains elusive. The aim of this study was to investigate the effects of GVS on visual verticality and postural asymmetry after stroke and to clarify whether the effects differ depending on the polarity of the stimulation and hemispheric lesion side.

Methods: We measured the subjective visual vertical (SVV) and body weight distribution on each foot in an upright stance in 24 patients with a hemispheric stroke (10 with a left hemisphere lesion and 14 with a right hemisphere lesion) and nine age-matched healthy controls. During the measurements, bipolar GVS (1.5 mA) was applied over the bilateral mastoid processes in three stimulation conditions: contralesional-anodal and ipsilesional-cathodal vestibular stimulation, ipsilesional-anodal and contralesional-cathodal vestibular stimulation, and no stimulation. To examine whether GVS modulates visual verticality and standing posture, SVV and weight-bearing in the three conditions were analyzed.

Results: During no stimulation, the SVV deviated to the contralesional side in patients with a right hemisphere lesion, while more weight-bearing was observed on the ipsilesional limb than on the contralesional limb in both patient groups than in the controls. The SVV was modulated by reversing the polarity of GVS in all the groups when the cathodal stimulus side was either ipsilateral or contralateral to the lesion while the ipsilesional-cathodal vestibular stimulation reduced weight-bearing asymmetry in only the patients with a right hemisphere lesion.

Conclusions: These findings demonstrate that the effects of GVS on the SVV and standing posture differ depending on the polarity of GVS and the hemispheric lesion side. Patients with a right hemisphere lesion have difficulty maintaining their preferred standing posture under visual verticality modulation evoked by GVS. The application of GVS may clarify whether the vestibular system has neural redundancy after stroke to suppress any effects of the stimulation, including modulation of the visual verticality, on balance.

Ankle Proprioception Deficit Is the Strongest Factor Predicting Balance Impairment in Patients With Chronic Stroke

OBJECTIVE

To determine the main factor that predicts balance impairment in patients with chronic stroke.

DESIGN

Cross-sectional study.

SETTING

Inpatient rehabilitation hospital and research laboratory.

PARTICIPANTS

A total of 57 patients (42 men, 15 women; mean age 55.7±12.2 years) with chronic symptoms after stroke.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Primary outcomes were ankle functions, including strength, range of motion, and proprioception, and balance, including Berg Balance Scale score and Timed Up and Go test values. Secondary outcomes included gait kinematics, Fugl-Meyer Scale score, and Fall Efficacy Scale score.

RESULTS

According to the cutoff score <46 on the Berg Balance Scale and the Timed Up and Go test ≥13.5 seconds, 21 patients were classified as having a balance impairment (36.8%). Multivariable logistic regressions showed that ankle proprioception (odds ratio = 3.49; 95% confidence interval, 1.17-10.42) was a significant predictor when coupled with step length (odds ratio = 0.00; 95% confidence interval, 0.00-0.22). A cutoff score of 2.59 for the ankle proprioception value predicts balance impairment in patients with stroke (area under the curve 0.784).

CONCLUSION

Ankle proprioception can be used to predict balance impairment in patients with stroke.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Effects of prismatic adaptation on balance and postural disorders in patients with chronic right stroke: protocol for a multicentre double-blind randomised sham-controlled trial

INTRODUCTION

Patients with right stroke lesion have postural and balance disorders, including weight-bearing asymmetry, more pronounced than patients with left stroke lesion. Spatial cognition disorders post-stroke, such as misperceptions of subjective straight-ahead and subjective longitudinal body axis, are suspected to be involved in these postural and balance disorders. Prismatic adaptation has showed beneficial effects to reduce visuomotor disorders but also an expansion of effects on cognitive functions, including spatial cognition. Preliminary studies with a low level of evidence have suggested positive effects of prismatic adaptation on weight-bearing asymmetry and balance after stroke. The objective is to investigate the effects of this intervention on balance but also on postural disorders, subjective straight-ahead, longitudinal body axis and autonomy in patients with chronic right stroke lesion.

METHODS AND ANALYSIS

In this multicentre randomised double-blind sham-controlled trial, we will include 28 patients aged from 18 to 80 years, with a first right supratentorial stroke lesion at chronic stage (≥12 months) and having a bearing ≥60% of body weight on the right lower limb. Participants will be randomly assigned to the experimental group (performing pointing tasks while wearing glasses shifting optical axis of 10 degrees towards the right side) or to the control group (performing the same procedure while wearing neutral glasses without optical deviation). All participants will receive a 20 min daily session for 2 weeks in addition to conventional rehabilitation. The primary outcome will be the balance measured using the Berg Balance Scale. Secondary outcomes will include weight-bearing asymmetry and parameters of body sway during static posturographic assessments, as well as lateropulsion (measured using the Scale for Contraversive Pushing), subjective straight-ahead, longitudinal body axis and autonomy (measured using the Barthel Index).

ETHICS AND DISSEMINATION

The study has been approved by the ethical review board in France. Findings will be submitted to peer-reviewed journals relative to rehabilitation or stroke.

TRIAL REGISTRATION NUMBER

NCT03154138.

Gait Speed Modulations Are Proportional to Grades of Virtual Visual Slopes-A Virtual Reality Study

Gait is a complex mechanism relying on integration of several sensory inputs such as vestibular, proprioceptive, and visual cues to maintain stability while walking. Often humans adapt their gait to changes in surface inclinations, and this is typically achieved by modulating walking speed according to the inclination in order to counteract the gravitational forces, either uphill (exertion effect) or downhill (braking effect). The contribution of vision to these speed modulations is not fully understood. Here we assessed gait speed effects by parametrically manipulating the discrepancy between virtual visual inclination and the actual surface inclination (aka visual incongruence). Fifteen healthy participants walked in a large-scale virtual reality (VR) system on a self-paced treadmill synchronized with projected visual scenes. During walking they were randomly exposed to varying degrees of physical-visual incongruence inclinations (e.g., treadmill leveled & visual scene uphill) in a wide range of inclinations (−15° to +15°). We observed an approximately linear relation between the relative change in gait speed and the anticipated gravitational forces associated with the virtual inclinations. Mean relative gait speed increase of ~7%, ~11%, and ~17% were measured for virtual inclinations of +5°, +10°, and +15°, respectively (anticipated decelerating forces were proportional to sin[5°], sin[10°], sin[15°]). The same pattern was seen for downhill virtual inclinations with relative gait speed modulations of ~-10%, ~-16%, and ~-24% for inclinations of −5°, −10°, and −15°, respectively (in anticipation of accelerating forces). Furthermore, we observed that the magnitude of speed modulation following virtual inclination at ±10° was associated with subjective visual verticality misperception. In conclusion, visual cues modulate gait speed when surface inclinations change proportional to the anticipated effect of the gravitational force associated the inclinations. Our results emphasize the contribution of vision to locomotion in a dynamic environment and may enhance personalized rehabilitation strategies for gait speed modulations in neurological patients with gait impairments.

Visual and haptic verticality misperception and trunk control within 72 h after stroke

INTRODUCTION

Stroke patients often exhibit an altered perception of verticality, but there are no studies evaluating verticality perception in the first 72 h after stroke and its relationship with trunk control. Therefore, this study aimed to analyze visual and haptic verticality in the acute phase of stroke.

METHODS

This was a cross-sectional study conducted with two groups: (a) 13 individuals with stroke and (b) 12 healthy participants. We assessed verticality via the subjective visual vertical (SVV) and the subjective haptic vertical (SHV); and we measured trunk control with the Trunk Impairment Scale (TIS). We performed t-tests to compare the SVV and SHV between groups. Pearson correlation was performed between verticality tests with National Institutes of Health Stroke Scale (NIHSS) and the TIS.

RESULTS

Participants with recent stroke presented higher true and absolute SVV deviation values than did the control group. There was significant negative correlation between absolute (r = -0.57; p = 0.02) and true SVV (r = -0.54; p = 0.01) with TIS scores There was also significant positive correlation between absolute (r = 0.63; p = 0.009) and true SVV (r = 0.61; p = 0.003) with NIHSS. A significant negative correlation between NIHSS and TIS scores also was found (r = -0.80; p = 0.005).

CONCLUSION

Individuals with acute stroke presented larger variability in their perceptions of visual verticality than did healthy controls, and verticality perceptions were positively correlated with trunk impairment.

Vision Affects Gait Speed but not Patterns of Muscle Activation During Inclined Walking-A Virtual Reality Study

While walking, our locomotion is affected by and adapts to the environment based on vision- and body-based (vestibular and proprioception) cues. When transitioning to downhill walking, we modulate gait by braking to avoid uncontrolled acceleration, and when transitioning to uphill walking, we exert effort to avoid deceleration. In this study, we aimed to measure the influence of visual inputs on this behavior and on muscle activation. Specifically, we aimed to explore whether the gait speed modulations triggered by mere visual cues after transitioning to virtually inclined surface walking are accompanied by changes in muscle activation patterns typical to those triggered by veridical (gravitational) surface inclination transitions. We used an immersive virtual reality system equipped with a self-paced treadmill and projected visual scenes that allowed us to modulate physical-visual inclination congruence parametrically. Gait speed and leg muscle electromyography were measured in 12 healthy young adults. In addition, the magnitude of subjective visual verticality misperception (SVV) was measured by the rod and frame test. During virtual (non-veridical) inclination transitions, vision modulated gait speed by (i) slowing down to counteract the excepted gravitational "boost" in virtual downhill inclinations and (ii) speeding up to counteract the expected gravity resistance in virtual uphill inclinations. These gait speed modulations were reflected in muscle activation intensity changes and associated with SVV misperception. However, temporal patterns of muscle activation were not affected by virtual (visual) inclination transitions. Our results delineate the contribution of vision to locomotion and may lead to enhanced rehabilitation strategies for neurological disorders affecting movement.

The association between visuospatial neglect and balance and mobility post-stroke onset: A systematic review

BACKGROUND

Although previous narrative reviews have highlighted a potential association between visuospatial neglect (VSN) and balance disorders, to what extent different areas of balance and mobility could be affected is still unclear.

OBJECTIVES

This systematic review updates previous literature findings and systematically reviews sitting balance, standing balance and mobility outcomes.

METHODS

PubMed, Web of Science, ScienceDirect, Naric-Rehabdata, PEDro and the Cochrane Trials Library were systematically searched. Methodological quality was assessed by the National Heart, Lung, and Blood Institute Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. The association between VSN and sitting balance, standing balance and mobility (walking, stair climbing/descending and transfers) was investigated.

RESULTS

In total, 48 studies were included (4595 stroke survivors): at least 1319 (29%) showed symptoms of VSN. VSN was associated with less independence during sitting, with an asymmetric posture toward the affected body side. For standing balance, we revealed a significant negative association between VSN and mediolateral stability and weight shifting, whereas only activities of daily living-related VSN was associated with weight-bearing asymmetry during static stance. While walking, patients with VSN laterally deviated from their path. Results were inconclusive regarding other aspects of mobility. The association between VSN and balance/mobility seemed to decrease over time.

CONCLUSIONS

Despite great heterogeneity in results, this study suggests that stroke survivors with VSN show specific deviations in posture and movement in the mediolateral direction. Although the association between VSN and balance/mobility has been extensively investigated, explanatory studies evaluating underlying mechanisms of the frequently present association are lacking. Future studies should address this by combining clinical and instrumented assessment of balance and gait performance, preferably longitudinally to investigate the associations over time.

Augmented Reality-Based Rehabilitation of Gait Impairments: Case Report

Background

Gait and balance impairments are common in neurological diseases, including stroke, and negatively affect patients’ quality of life. Improving balance and gait are among the main goals of rehabilitation. Rehabilitation is mainly performed in clinics, which lack context specificity; therefore, training in the patient’s home environment is preferable. In the last decade, developed rehabilitation technologies such as virtual reality and augmented reality (AR) have enabled gait and balance training outside clinics. Here, we propose a new method for gait rehabilitation in persons who have had a stroke in which mobile AR technology and a sensor-based motion capture system are combined to provide fine-grained feedback on gait performance in real time.

Objective

The aims of this study were (1) to investigate manipulation of the gait pattern of persons who have had a stroke based on virtual augmentation during overground walking compared to walking without AR performance feedback and (2) to investigate the usability of the AR system.

Methods

We developed the ARISE (Augmented Reality for gait Impairments after StrokE) system, in which we combined a development version of HoloLens 2 smart glasses (Microsoft Corporation) with a sensor-based motion capture system. One patient with chronic minor gait impairment poststroke completed clinical gait assessments and an AR parkour course with patient-centered performance gait feedback. The movement kinematics during gait as well as the usability and safety of the system were evaluated.

Results

The patient changed his gait pattern during AR parkour compared to the pattern observed during the clinical gait assessments. He recognized the virtual objects and ranked the usability of the ARISE system as excellent. In addition, the patient stated that the system would complement his standard gait therapy. Except for the symptom of exhilaration, no adverse events occurred.

Conclusions

This project provided the first evidence of gait adaptation during overground walking based on real-time feedback through visual and auditory augmentation. The system has potential to provide gait and balance rehabilitation outside the clinic. This initial investigation of AR rehabilitation may aid the development and investigation of new gait and balance therapies.

Immersive Virtual Reality in Stroke Patients as a New Approach for Reducing Postural Disabilities and Falls Risk: A Case Series

Stroke is a neurologic disorder considered the first cause of disability worldwide due to motor, cognitive, and sensorial sequels. Balance dysfunctions in stroke survivors increase the risk of falls and physiotherapeutic rehabilitation is essential to reduce it. Virtual reality (VR) seems to be an alternative to conventional physiotherapy (CT), providing virtual environments and multisensorial inputs to train balance in stroke patients. The aim of this study was to assess if immersive VR treatment is more effective than CT to improve balance after stroke. This study got the approval from the Ethics Committee of the University of Almeria. Three chronic ischemic stroke patients were selected. One patient who received 25 sessions of immersive VR intervention for two months was compared with another patient who received equivalent CT and a third patient with no intervention. Balance, gait, risk of falling, and vestibular and visual implications in the equilibrium were assessed. After the interventions, the two patients receiving any of the treatments showed an improvement in balance compared to the untreated patient. In comparison to CT, our results suggest a higher effect of immersive VR in the improvement of balance and a reduction of falls risk due to the active upright work during the VR intervention.

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.

Misperception of the subjective visual vertical in neurological patients with or without stroke: A meta-analysis

BACKGROUND

The interpretation of the verticality of the environment is crucial for a proper body balance. The subjective visual vertical test (SVV) is a widely used method to determine the visual perception of the verticality, whose alteration has been related with poor functional status.

OBJECTIVE

To analyze the visual perception of the verticality in neurological patients in comparison with healthy controls.

METHODS

We searched PubMed, Scopus, and Scielo from the start of the databases until October 2017 and manually searched the reference lists of studies comparing SVV values between neurological patients and controls. Standardized mean difference (SMD) and subgroup analysis were used to analyze differences between neurological patients and healthy subjects and between stroke and non-stroke patients, respectively.

RESULTS

A total of 1,916 subjects from 31 studies were included. Neurological patients misestimate the true vertical in comparison with controls (SMD = 1.05; 95% CI: 0.81, 1.28). The misperception of the verticality was higher in stroke patients (SMD = 1.35; 95% CI: 1.02, 1.68) than in patients with other neurological conditions (SMD = 0.48; 95% CI: 0.29, 0.68).

CONCLUSIONS

Neurological patients showed a misperception of the verticality, estimated using the SVV. The neurological pathology that most alters the SVV is stroke.

Sensory retraining of the leg after stroke: systematic review and meta-analysis

OBJECTIVE

This systematic review aimed to investigate the effects of interventions intended for retraining leg somatosensory function on somatosensory impairment, and secondary outcomes of balance and gait, after stroke.

DATA SOURCES

Databases searched from inception to 16 January 2019 included Cochrane Library, PubMed, MEDLINE, CINAHL, EMBASE, PEDro, PsycINFO, and Scopus. Reference lists of relevant publications were also manually searched.

REVIEW METHODS

All types of quantitative studies incorporating interventions that intended to improve somatosensory function in the leg post stroke were retrieved. The Quality Assessment Tool for Quantitative Studies was used for quality appraisal. Standardised mean differences were calculated and meta-analyses were performed using preconstructed Microsoft Excel spreadsheets.

RESULTS

The search yielded 16 studies, comprising 430 participants, using a diverse range of interventions. In total, 10 of the included studies were rated weak in quality, 6 were rated moderate, and none was rated strong. Study quality was predominantly affected by high risk of selection bias, lack of blinding, and the use of somatosensory measures that have not been psychometrically evaluated. A significant heterogeneous positive summary effect size (SES) was found for somatosensory outcomes (SES: 0.52; 95% confidence interval (CI): 0.04 to 1.01; I2 = 74.48%), which included joint position sense, light touch, and two-point discrimination. There was also a significant heterogeneous positive SES for Berg Balance Scale scores (SES: 0.62; 95% CI: 0.10 to 1.14; I2 = 59.05%). Gait SES, mainly of gait velocity, was not significant.

CONCLUSION

This review suggests that interventions used for retraining leg somatosensory impairment after stroke significantly improved somatosensory function and balance but not gait.

Sensory information and the perception of verticality in post-stroke patients. Another point of view in sensory reweighting strategies

INTRODUCTION

Perception of verticality is highly related to balance control in human. Head-on-body tilt <60° results in the E-effect, meaning that a tilt of the perceived vertical is observed contralateral to the head tilt in the frontal plane. Furthermore, somatosensory loss also impacts the accuracy of verticality perception. However, when several input sources are absent or biased, less options for sensory weighting and balance control occur. Therefore, this study aims to identify the E-effect and assess the effect of somatosensory loss on the extent of the E-effect.

METHODS

All patients with a first stroke admitted to a Belgian rehabilitation hospital were eligible for inclusion. Patients aged above 80 with other neurological and orthopaedic impairments as well as brainstem, cerebellar or multiple lesions were excluded. In addition, patients with visuospatial neglect and pusher behaviour were also excluded as this can affect verticality perception. The Rivermead Assessment of Somatosensory Performance (RASP), the Subjective Visual (SVV) and Subjective Postural (SPV) Vertical Test were administered.

RESULTS

In total, 37 patients were included in the analysis of which 24 patients completed both SVV and SPV assessment. Results show that the E-effect occurred in our sample of stroke survivors for both SVV and SPV. In addition, the presence of somatosensory loss will increase the E-effect in both SVV as SPV assessment. A significant difference in verticality perception was noted for both SVV and SPV between the group with no (SVV: 5.13°(6.92); SPV: 0.30°(1.85)) and highly severe (SVV: 10.54°(13.19); SPV: 5.96°(9.27)) sensory loss.

CONCLUSIONS

The E-effect occurs in stroke subjects and increases when patients experience somatosensory loss. This suggests that the lack of available afferent information impede estimation of verticality. Therefore, stroke survivors have fewer alternative input sources as a result of impairments, leading to fewer options about sensory reweighting strategies and balance recovery after perturbations.

Can pre-screening vestibulocerebellar involvement followed by targeted training improve the outcomes of balance in cerebellar ataxia?

Balance problems and frequent falls are common among clients with Cerebellar Ataxia (CA). CA is not a disease by itself but a collection of symptoms due to the involvement of cerebellum or its pathways. Presently the treatment for balance problems for CA is not standardized. Interventions available to improve balance are not specific to symptoms presentation. Functionally the cerebellum is divided into the spinocerebellum, vestibulocerebellum and corticocerebellum. Each functional zone has a distinct role in maintaining balance. Therefore, the presentation of symptoms will vary according to the functional zone involved. Pre-screening clients with CA for identifying the part of cerebellum involved will facilitate clinicians to provide tailor-made interventions for targeting specific symptoms for better outcomes. Pre-screening clients with CA according to the part of cerebellum involved is not in practice and our study will introduce this concept. We hypothesize pre-screening participants with spinocerebellar ataxia (SCA) for the involvement vestibulocerebellum followed by prescribing vestibulocerebellum targeted exercises will have better outcomes when compared to conventional balance training. We plan to conduct two related studies. In study 1 we will screen participants with CA for the involvement of vestibulocerebellum. In study 2, the effects of vestibulocerebellum targeted balance exercises on balance will be studied. We will assess the Subjective Visual Vertical (SVV) deviation and postural sway pattern to screen participants into people with and without vestibulocerebellar involvement. SVV deviation will be estimated using a computerized Subjective Visual Vertical (cSVV) device and postural sway pattern will be assessed using the limits of stability program of the Bertec© Balance system. The obtained SVV deviation scores will be used to derive at cut-off scores to discriminate clients with and without vestibulocerebellar involvement. The second study will test the treatment effects of conventional exercises plus vestibulocerebellum targeted exercises to improve balance by correcting SVV deviation in SCA with vestibulocerebellar involvement. The intervention is planned as 12 one-to-one sessions over three months period. Participants will be reassessed after the intervention and 3 months post-intervention. The findings of this cutting-edge research are extremely important to the clinicians, researchers and clients with SCA.

Is perception of visual verticality intact in patients with idiopathic cervical dystonia?

Idiopathic cervical dystonia (CD) is a focal dystonia characterized by an abnormal tilted or twisted head position. This abnormal head position could lead to a distorted perception of the visual vertical and spatial orientation. The aim of this cross-sectional study was to investigate whether the perception of the visual vertical is impaired in patients with CD. The subjective visual vertical test (SVV) was measured in 24 patients with CD and 30 controls. The SVV test is conducted in a completely darkened room. A laser bar is projected on an opposing white wall, which is deviated from the earth's gravitational vertical. Participants were seated with their head unrestrained and were instructed to position this bar vertically. The deviations in degrees (°) are corrected for the side of laterocollis in order to measure the E-effect. We found that patients were able to position the laser bar as equally close to the earth's gravitational vertical as controls (+ 0.67° SD ± 2.12 vs + 0.29° SD ± 1.08, p = 0.43). No E-effect was measured. Notwithstanding the abnormal position of the head, the perception of the visual vertical in patients with idiopathic CD is intact, possibly because of central neural compensatory mechanisms.

Disturbance of verticality perception and postural dysfunction in Parkinson's disease

OBJECTIVES

Verticality perception is known to be abnormal in Parkinson's disease (PD), but in which stage respective dysfunctions arise and how they relate to postural disorders remains to be settled. These issues were studied with respect to different dimensions of the subjective visual vertical (SVV) in relation to clinical parameters of postural control.

MATERIALS & METHODS

All participants had to orientate a luminous line at random planar orientations to a strictly vertical position using an automated operator system. The SVV was analyzed in 58 PD patients and 28 control subjects with respect to (i) the angle between true and subjective vertical (deviation) and (ii) the variability of this across five measurements (variability). Results were referred to the subjective upright head position (SUH), the disease stage, and clinical gait/balance features assessed by the MDS-UPDRS and the Tinetti test.

RESULTS

Parkinson's disease patients had significantly higher SVV deviation and variability than controls. With respect to disease stage, deviation developed before abnormal variability. SVV variability was associated with poor balance and gait performance, as well as postural instability. Deficits in SUH and SVV deviation were correlated and mostly unidirectional, but did not correspond to the side of motor symptom dominance.

CONCLUSIONS

Visual verticality perception in PD is deviated already in early stages, conceivably as a relatively static internal misrepresentation of object orientation. Variability about verticality perception emerges in more advanced stages and is associated with postural and balance abnormalities.

The effects of aging on the subjective vertical in the frontal plane in healthy adults

[Purpose] To determine age-related differences in the subjective vertical in the frontal plane in healthy adults. [Subjects and Methods] The subjects were 26 healthy adults. For the subjective visual vertical (SVV), subjects were presented with a visual indicator in front of them that was rotated. For the subjective postural vertical-eyes open (SPV-EO) and subjective postural vertical (SPV), subjects sat in a seating device that was tilted right or left. The subjects gave a signal when they perceived true verticality. Each task was performed eight times. The items examined were the mean (tilt direction) and standard deviation (variability) of the eight trials, then the mean of four trials that started from the right or left side position. These items were compared between the young (age: 22–30 years [range]) and elderly (age: 60–74 years) groups. [Results] As for variability, the elderly group demonstrated significantly higher values of SPV-EO and SPV. As for the starting point effect, the elderly group demonstrated greater bias toward the starting direction than did the young group in SPV-EO and SPV in frontal plane. [Conclusion] The postural vertical was shown to change with age. Consideration of age-related changes and the starting point effect was indicated to be important.

Perception of Upright: Multisensory Convergence and the Role of Temporo-Parietal Cortex

We inherently maintain a stable perception of the world despite frequent changes in the head, eye, and body positions. Such "orientation constancy" is a prerequisite for coherent spatial perception and sensorimotor planning. As a multimodal sensory reference, perception of upright represents neural processes that subserve orientation constancy through integration of sensory information encoding the eye, head, and body positions. Although perception of upright is distinct from perception of body orientation, they share similar neural substrates within the cerebral cortical networks involved in perception of spatial orientation. These cortical networks, mainly within the temporo-parietal junction, are crucial for multisensory processing and integration that generate sensory reference frames for coherent perception of self-position and extrapersonal space transformations. In this review, we focus on these neural mechanisms and discuss (i) neurobehavioral aspects of orientation constancy, (ii) sensory models that address the neurophysiology underlying perception of upright, and (iii) the current evidence for the role of cerebral cortex in perception of upright and orientation constancy, including findings from the neurological disorders that affect cortical function.

Rod and frame test and posture under optokinetic stimulation used to explore two complementary aspects of the visual influence in postural control after stroke

BACKGROUND

Balance rehabilitation should consider individual comportments according to visual input (VI). Indeed, visual dependence (VD), defined as the predominance given to the VI whatever the circumstances, frequent after stroke it could disturb balance. Because the term VD is a bit restrictive and cannot be deduced from clinical tests, the term visual sensitivity (VS) is preferred here.

HYPOTHESIS

VI could have different influence depending on the task for a given individual.

METHODS

We retrospectively compared 2 VS tests routinely used: the rod and frame test (RFT) and optokinetic stimulation (OKS). In RFT, VS was defined by a misperception of the visual verticality induced by a tilted frame (VS RFT) and in OKS by tilted sitting posture induced by rotational OKS (VS OKS). We studied the relations between VS RFT and VS OKS.

RESULTS

We analysed data for 84 patients, mean age 55±10years, 45±30days after stroke. Scores for both tests were correlated with autonomy measured by the functional independence measure (r=-0.3, p=0.01 and r=-0.2, p=0.02). VS OKS score was also correlated with balance measured by the postural assessment scale for stroke (r=-0.3, p=0.03). VS RFT score was not correlated with VS OKS score (p=0.4, r=0.04).

DISCUSSION - CONCLUSION

A patient may display VS for one test without sensitivity for the other because these tests investigate different neural organisation - perception for RFT or action for OKS. Their relation to balance disorders should be further investigated to build individualized rehabilitation programs.

Ehlers-Danlos Syndrome, Hypermobility Type: Impact of Somatosensory Orthoses on Postural Control (A Pilot Study)

Elhers-Danlos syndrome (EDS) is the clinical manifestation of connective tissue disorders, and comprises several clinical forms with no specific symptoms and selective medical examinations which result in a delay in diagnosis of about 10 years. The EDS hypermobility type (hEDS) is characterized by generalized joint hypermobility, variable skin hyperextensibility and impaired proprioception. Since somatosensory processing and multisensory integration are crucial for both perception and action, we put forth the hypothesis that somatosensory deficits in hEDS patients may lead, among other clinical symptoms, to misperception of verticality and postural instability. Therefore, the purpose of this study was twofold: (i) to assess the impact of somatosensory deficit on subjective visual vertical (SVV) and postural stability; and (ii) to quantify the effect of wearing somatosensory orthoses (i.e., compressive garments and insoles) on postural stability. Six hEDS patients and six age- and gender-matched controls underwent a SVV (sitting, standing, lying on the right side) evaluation and a postural control evaluation on a force platform (Synapsys), with or without visual information (eyes open (EO)/eyes closed (EC)). These two latter conditions performed either without orthoses, or with compression garments (CG), or insoles, or both. Results showed that patients did not exhibit a substantial perceived tilt of the visual vertical in the direction of the body tilt (Aubert effect) as did the control subjects. Interestingly, such differential effects were only apparent when the rod was initially positioned to the left of the vertical axis (opposite the longitudinal body axis). In addition, patients showed greater postural instability (sway area) than the controls. The removal of vision exacerbated this instability, especially in the mediolateral (ML) direction. The wearing of orthoses improved postural stability, especially in the eyes-closed condition, with a particularly marked effect in the anteroposterior (AP) direction. Hence, this study suggests that hEDS is associated with changes in the relative contributions of somatosensory and vestibular inputs to verticality perception. Moreover, postural control impairment was offset, at least partially, by wearing somatosensory orthoses.

A disturbed processing of graviceptive pathways may be involved in the pathophysiology of balance disorders in patients with multiple sclerosis

The purpose of this study was to determine the relationship between perception of verticality and balance disorders in multiple sclerosis patients. We evaluated patients and healthy controls. Patients were divided into two groups according to their risk of fall, with or without risk of fall, measured by a Dynamic Gait Index scale. Graviceptive perception was assessed using the subjective visual vertical test. Patients with risk of fall showed worse perception than those without risk of fall, p < 0.001. Misperception of verticality was correlated with the dynamic gait index scores (p < 0.001), suggesting that the larger the error for verticality judgment, the greater risk for falling. Considering that the perception of verticality is essential for postural control, our results suggested that the disturbed processing of graviceptive pathways may be involved in the pathophysiology of balance disorders in these patients.

Usual dose of caffeine has a positive effect on somatosensory related postural stability in hemiparetic stroke patients

OBJECTIVE

To evaluate the effect of caffeine on balance control of hemiparetic stroke patients, we investigated the difference in postural stability before and after drinking coffee by observing changes in stability index (SI) from posturography.

METHODS

Thirty patients with history of stroke and 15 age-matched healthy subjects participated in this study. Effect of group factor (of the control and stroke groups) and treatment factor (pre- and post-drinking of coffee) on SI were tested in three conditions: with eyes opened, with eyes closed, and with a pillow support. The effects of these factors on visual deprivation and somatosensory change of subjects were also tested.

RESULTS

Under all conditions, SI was higher in the stroke group than in the control group. Under eyes-open condition, the treatment factor was not statistically significant. Under eyes-closed condition, the interaction between group and treatment factor was statistically significant. After the subjects drank coffee, SI in the control group was increased. However, SI in the stroke group was decreased. Under pillow-supported condition, the interaction between group and treatment factor appeared marginally significant. For visual deprivation effect, the interaction between treatment and group factor was statistically significant. After caffeine consumption, the visual deprivation effect was increased in control group but decreased in the stroke group. For somatosensory change effect, the interaction between group and treatment factor was not statistically significant.

CONCLUSION

Postural stability of hemiparetic stroke patients related to somatosensory information was improved after intake of usual dose of caffeine.

The effects of visual and haptic vertical stimulation on standing balance in stroke patients

Objective

To explore the effect of visual and haptic vertical stimulation on standing balance in post-stroke patients.

Methods

Twenty-five post-stroke patients were recruited. We measured left/right standing pressure differences and the center of pressure (COP) parameters for each patient under three different conditions: no stimulation, visual, and haptic stimulated conditions. First, patients stood on a posturography platform with their eyes blindfolded. After a rest period, the patients stood on the same platform with their eyes fixed to a 1.5-m luminous rod, which was placed at a vertical position in front of the patients. After another rest period, the patients again stood touching a vertically placed long rod in their non-hemiplegic hand with their eyes blindfolded. We collected the signals from the feet in each condition and obtained the balance indices.

Results

Compared with the no stimulation condition, significant improvements were observed for most of the COP parameters including COP area, length, and velocity for both the visual and haptic vertical stimulation conditions (p<0.01). Additionally, when we compared visual and haptic vertical stimulation, visual vertical stimulation was superior to haptic stimulation for all COP parameters (p<0.01). Left/right standing pressure differences, increased, although patients bore more weight on their paretic side when vertical stimulation was applied (p>0.01).

Conclusion

Both visual and haptic vertical stimulation improved standing steadiness of post-stroke patients. Notably, visual vertical stimulation was more effective than haptic stimulation.

Integration of visual and haptic informations in the perception of the vertical in young and old healthy adults and right brain-damaged patients

OBJECTIVE

Multimodal perception raises the issue of sensory integration. The aim of this study is to assess whether the visuo-haptic subjective vertical could be predicted from the visual and haptic unimodal performances, according to a Bayesian model, which optimizes the reliability of the multimodal estimate. The limits of the model were assessed by evaluating the impact of aging, cerebral damage and spatial deficits.

METHOD

Young and older healthy participants, as well as patients with a right hemisphere lesion, suffering from spatial neglect or not, had to align a rod with the gravitational vertical in the visual, haptic and visuo-haptic modalities.

RESULTS

Visuo-haptic subjective vertical was correctly predicted by the model in healthy participants, as well as in patients in spite of different performances. An anticlockwise deviation of the subjective vertical was observed in the neglect group whatever the experimental conditions. By contrast, no deviation was observed in both non-neglect and healthy groups, for the visual and the visuo-haptic modalities. Nevertheless, the haptic subjective vertical was deviated, anticlockwise in the non-neglect patients and older healthy adults, and clockwise in the young healthy adults. Moreover, the variance was the smallest in the bimodal condition.

CONCLUSION

The integration of visual and haptic signals appeared to obey a Bayesian model optimizing the reliability of the multimodal estimate. This holds true despite of aging, brain damage or visuospatial disorders. Regarding the perception of the vertical, multisensory integration does not seem thus to depend only on right posterior cortical areas.

Software for subjective visual vertical assessment: an observational cross-sectional study

Spatial orientation in relation to the gravitational axis is significantly important for the maintenance of the posture, gait and for most of the human's motor activities. The subjective visual vertical exam evaluates the individual's perception of vertical orientation.

Objectives

The aims of this study were (1) to develop a virtual system to evaluate the subjective visual vertical exam, (2) to provide a simple tool to clinical practice and (3) to assess the subjective visual vertical values of h ealthy subjects using the new software. Study Design: observational cross-sectional study.

Methods

Thirty healthy volunteers performed the subjective visual vertical exam in both static and dynamic conditions. The exam consisted in adjusting a virtual line in the vertical position using the computer mouse. For the static condition, the virtual line was projected in a white background. For the dynamic condition, black circles rotated in clockwise or counterclockwise directions. Six measurements were taken and the mean deviations in relation to the real vertical calculated.

Results

The mean values of subjective visual vertical measurements were: static −0.372°; ± 1.21; dynamic clockwise 1.53° ± 1.80 and dynamic counterclockwise −1.11° ± 2.46.

Conclusion

This software showed to be practical and accurate to be used in clinical routines.

[Is the sense of verticality vestibular?]

The vestibular system constitutes an inertial sensor, which detects linear (otoliths) and angular (semicircular canals) accelerations of the head in the three dimensions. The otoliths are specialized in the detection of linear accelerations and can be used by the brain as a "plumb line" coding earth gravity acceleration (direction). This property of otolithic system suggested that the sense of verticality is supported by the vestibular system. The preeminence of vestibular involvement in the sense of verticality stated in the 1900s was progressively supplanted by the notion of internal models of verticality. The internal models of verticality involve rules and properties of integration of vestibular graviception, somaesthesic graviception, and vision. The construction of a mental representation of verticality was mainly modeled as a bottom-up organization integrating visual, somatosensory and vestibular information without any cognitive modulations. Recent studies reported that the construction of internal models of verticality is not an automatic multi-sensory integration process but corresponds to more complex mechanisms including top-down influences such as awareness of body orientation or spatial representations.

Influence of sensory loss on the perception of verticality in stroke patients

PURPOSE

The aim of this study was to investigate the relationship between somatosensory loss and perception of verticality in stroke patients suffering single-hemisphere lesions.

METHOD

Somatosensory loss was measured using the Rivermead Assessment for Somatosensory Performance (RASP). Perception of verticality was assessed with the Subjective Visual Vertical (SVV) and the Subjective Postural Vertical (SPV) tests. Absolute Values of SVV and SPV were used to analyze the amount of deviation in relation to somatosensory loss.

RESULTS

Thirty-two patients were included in the study (mean age = 45.91 SD = 31.88 years). Analysis showed that somatosensory loss was related to results of the SVV (r = -0.552, p = 0.001, Pearson Rank) and the SPV (r = -0.661, p < 0.001, Spearman Ï). Furthermore, results showed that both joint-related (SVV: r = -0.411, p = 0.019, Pearson Rank; SPV: r = -0.597, p = 0.001, Spearman Ï) and skin-related (SVV: r = -0.595, p < 0.001, Pearson Rank; SPV: r = -0.663, p < 0.001, Spearman Ï) somatosensory information is related to verticality perception.

CONCLUSIONS

This study provides evidence that perception of verticality is related to somatosensory loss, which means that somatosensory loss will lead to a larger amount of deviation of SVV and SPV in relation to the gravitational vector. Furthermore, it is interesting to note that both SVV and SPV are influenced by somatosensory loss.

IMPLICATIONS FOR REHABILITATION

• Somatosensory information is related to both visual and postural aspects of verticality perception. • Both joint- and cutaneous-related modalities of sensory information are related to perception of verticality. • Sensory training could be important in the recovery of verticality perception.

Semi-automatic measurement of visual verticality perception in humans reveals a new category of visual field dependency

Previous assessment of verticality by means of rod and rod and frame tests indicated that human subjects can be more (field dependent) or less (field independent) influenced by a frame placed around a tilted rod. In the present study we propose a new approach to these tests. The judgment of visual verticality (rod test) was evaluated in 50 young subjects (28 males, ranging in age from 20 to 27 years) by randomly projecting a luminous rod tilted between -18 and +18° (negative values indicating left tilts) onto a tangent screen. In the rod and frame test the rod was displayed within a luminous fixed frame tilted at +18 or -18°. Subjects were instructed to verbally indicate the rod's inclination direction (forced choice). Visual dependency was estimated by means of a Visual Index calculated from rod and rod and frame test values. Based on this index, volunteers were classified as field dependent, intermediate and field independent. A fourth category was created within the field-independent subjects for whom the amount of correct guesses in the rod and frame test exceeded that of the rod test, thus indicating improved performance when a surrounding frame was present. In conclusion, the combined use of subjective visual vertical and the rod and frame test provides a specific and reliable form of evaluation of verticality in healthy subjects and might be of use to probe changes in brain function after central or peripheral lesions.

Visual field dependence influences balance in patients with stroke

To compare the occurrence of visual field independence/dependence in healthy subjects with patients who are post-stroke using the Rod and Frame Test, and determine whether increased visual dependence is reflected in their postural responses when immersed in a moving visual environment. Eight older and twelve young adults, and twelve patients with cortical or sub-cortical stroke, were asked to align a rod enclosed in a tilted frame to vertical and horizontal. Angular deviations of rod position were calculated and compared. Center-of-mass (COM) of the body was calculated for two patients and two young adults standing in the dark and in an immersive virtual environment to examine their postural responses. Balance of the patients did not appear different from healthy subjects when standing in the dark suggesting they were not dependent on the presence of vision, but more rapid and larger COM displacements emerged in the patients when immersed in a moving visual scene. Patients also exhibited greater errors when aligning the rod compared to both healthy groups. Thus, patients with stroke may be more dependent on visual inputs when they are present, and have more difficulty resolving conflict between the visual and somatosensory cues compared to healthy young or older subjects. This impaired conflict resolution may underlie the rapid instability observed in patients when they were placed in a moving visual environment.

Ageing of the postural vertical

A postural vertical (PV) tilted backward has been put forward as a reason explaining the backward disequilibrium often observed in elderly fallers. This raises the question of a possible ageing process of the PV involving a backward tilt of verticality perception increasing with age. We have explored this hypothesis by measuring PV in pitch using the wheel paradigm in 87 healthy subjects aged from 20 to 97 years. The possibility that this physiological ageing accelerated in the second part of life was also analysed. Two indices were calculated: the mean orientation (PV-orient) and the dispersion (PV-uncert). The correlation between age and PV-orient was r = -0.2 (p < 0.05). Added to the fact that PV was twice as shifted backward in the 38 seniors over 50 years (-1.15 degrees +/- 1.40 degrees ) as in the 49 young adults under 50 years (-0.45 degrees +/- 0.97 degrees ; t = 2.75, p < 0.01), this indicates the existence of a physiological ageing process on the direction perceived as vertical by the whole body, with a slight backward shift of PV throughout the life span. The correlation between age and PV-uncert was r = 0.35 (p < 0.001) in all subjects and r = 0.59 (p < 0.001) in seniors. This indicates that subjects get less and less accurate in their perception of the postural vertical with age, especially very old subjects who show great uncertainty in determining with their body the direction of the vertical. Taken together, these findings indicate that the internal model of verticality is less robust in elderly people. This may play a part in their postural decline.

From line to dots: an improved computerised rod and frame system for testing subjective visual vertical and horizontal

Background

Perception of subjective visual vertical (SVV) and horizontal (SVH) has traditionally been measured by rotating a mechanical rod either with or without a frame present. The computerised rod and frame (CRAF) system has previously only been used to measure SVV. We have expanded the use of this system by testing its feasibility to measure SVH. This was done by comparing two groups of subjects (n = 103) randomly assigned to be tested for SVV or SVH.

Findings

Preliminary results showed a higher than expected percentage of individuals with SVH errors < 0.5°. This was attributed to additional visual cues provided by the changing appearance of the rod as it approached the horizontal. A solution to this problem was sought by replacing the rod by two dots to mark its ends. In a second investigation 30 subjects were tested using both the "rod as line" and "rod as dots" presentation. Bland and Altman analysis showed no difference between the rod and dots presentations in the measurement of SVV, but confirmed a fixed error of -0.93° between rods and dots for SVH. Changing the rod from a line to dots in the computer system resulted in errors for both SVV and SVH that were comparable to previous studies using manual systems.

Conclusions

The computerized rod and frame system may be improved by replacement of the line with two dots. This reduces clues provided to the subject by the appearance of the rod on the screen.

Is backward disequilibrium in the elderly caused by an abnormal perception of verticality? A pilot study

OBJECTIVE

We hypothesised that backward disequilibrium (BD), defined by a posterior position of the centre of mass with respect to the base of support, could be caused by a backward tilt in the perception of verticality.

METHODS

The relationship between BD, the perception of verticality, and the history of falls in 25 subjects aged 84.5+/-7.4 years was analysed. An original ordinal scale, the BD scale (BDS), was used to quantify BD. Postural (PV) and haptic verticals (HV) were measured in sagittal plane.

RESULTS

BDS scores closely correlated with the number of falls (r = 0.81, p =10(-5)). The more the PV was tilted backward, the greater the BDS scores (r = -0.95, p<10(-6)), with a huge backward tilt of about 15 degrees in 4 subjects with severe BD. In these subjects, the tilt in perception of verticality was transmodal since a severe backward HV tilt was also found.

CONCLUSIONS

This transmodality suggested high-order cognitive disruption in the construction of the subjective vertical used in postural control by subjects showing BD, which confirmed our hypothesis.

SIGNIFICANCE

This study clearly shows that perception and action with respect to gravity are closely related and brings a new insight about fall mechanisms in the elderly.