Perception of postural verticality in roll and pitch while sitting and standing in healthy subjects

Misperception of body verticality in neurological disorders: A systematic review and meta-analysis

INTRODUCTION

The internal representation of verticality could be disturbed when a lesion in the central nervous system (CNS) affects the centers where information from the vestibular, visual, and/or somatosensory systems, increasing the risk of falling.

OBJECTIVE

The aim was to evaluate the vestibular and somatosensory contribution to the verticality pattern in patients with stroke and other neurological disorders.

METHODS

A literature search was performed in PubMed, Scopus, Web of Science, and CINAHL databases. Cross-sectional, case-control, and cohort studies comparing body verticality in patients with stroke or CNS diseases (CNSD) versus healthy controls were selected. Subjective postural vertical (SPV) in roll and pitch planes was used as the primary variable.

RESULTS

Ten studies reporting data from 390 subjects were included. The overall effect for CNSD patients showed a misperception of body verticality in roll (standardized mean difference [SMD] = 1.05; 95% confidence interval [CI] .84-1.25) and pitch planes (SMD = 1.03; 95% CI .51-1.55). In subgroup analyses, a high effect was observed in the perception of SPV both in roll and pitch planes in stroke (p = .002) and other CNSD (p < .001).

CONCLUSION

These findings suggest a potential misperception of SPV in patients with stroke and other neurological disturbances. Patients with CNSD could present an alteration of vestibular and somatosensory contribution to verticality construction, particularly stroke patients with pusher syndrome (PS), followed by those with PS combined with hemineglect.

Tilt perception is different in the pitch and roll planes in human

Neurophysiological tests probing the vestibulo-ocular, colic and spinal pathways are the gold standard to evaluate the vestibular system in clinics. In contrast, vestibular perception is rarely tested despite its potential usefulness in professional training and for the longitudinal follow-up of professionals dealing with complex man-machine interfaces, such as aircraft pilots. This is explored here using a helicopter flight simulator to probe the vestibular perception of pilots. The vestibular perception of nine professional helicopter pilots was tested using a full flight helicopter simulator. The cabin was tilted six times in roll and six times in pitch (-15°, -10°, -5°, 5°, 10° and 15°) while the pilots had no visual cue. The velocities of the outbound displacement of the cabin were kept below the threshold of the semicircular canal perception. After the completion of each movement, the pilots were asked to put the cabin back in the horizontal plane (still without visual cues). The order of the 12 trials was randomized with two additional control trials where the cabin stayed in the horizontal plane but rotated in yaw (-10° and +10°). Pilots were significantly more precise in roll (average error in roll: 1.15 ± 0.67°) than in pitch (average error in pitch: 2.89 ± 1.06°) (Wilcoxon signed-rank test: p < 0.01). However, we did not find a significant difference either between left and right roll tilts (p = 0.51) or between forward and backward pitch tilts (p = 0.59). Furthermore, we found that the accuracies were significantly biased with respect to the initial tilt. The greater the initial tilt was, the less precise the pilots were, although maintaining the direction of the tilt, meaning that the error can be expressed as a vestibular error gain in the ability to perceive the modification in the orientation. This significant result was found in both roll (Friedman test: p < 0.01) and pitch (p < 0.001). However, the pitch trend error was more prominent (gain = 0.77 vs gain = 0.93) than roll. This study is a first step in the determination of the perceptive-motor profile of pilots, which could be of major use for their training and their longitudinal follow-up. A similar protocol may also be useful in clinics to monitor the aging process of the otolith system with a simplified testing device.

Efficacy of lateral truncal tilt training with a wedge on postural vertical and activities of daily living in recovery phase after stroke: A randomized crossover trial

BACKGROUND: The subjective postural vertical (SPV) is affected by training that requires participants to maintain balance; training to achieve sitting balance may also help SPV recovery and activities of daily living (ADLs). OBJECTIVE: This study aimed to assess the medium-term effects of balance training on the postural vertical (PV) and ADLs in patients with stroke. METHODS: Thirty-three patients with stroke were enrolled in this randomized crossover trial. The outcomes were SPV, SPV with eyes opened (SPV-EO), and the Functional Independent Measure (FIM) after the 14-day intervention of experimental or control training. Experimental training consisted of a maximum lateral truncal tilt to the paretic side at 0.25 Hz with or without a 10° wedge, repeated 60 times. Repeated-measures two-way analysis of variance was performed with two factors: intervention and the intervention period. RESULTS: There was no interaction between the control condition and the PV, but there was interaction between the intervention period and using a wedge for SPV variability errors. FIM showed an interaction between the intervention period and the use of a wedge. CONCLUSIONS: Balance training while sitting with a wedge significantly improved the SPV and FIM. This improved cognition and perception, which facilitate difficult dynamic tasks in ADLs.

Comparison of two methods based on one psychophysical paradigm to measure the subjective postural vertical in standing

The perception of verticality can be altered with age or due to neurological diseases. Different procedures have been described to measure the subjective postural vertical (SPV). A deviation from the earth vertical was either described as a single position or as a sector defined by two positions representing the edges of the perceived verticality. In this study, for the first time, we investigated if these two methods produce equal values, and consequently can be merged to set normative values. SPV in standing was tested in 24 healthy young adults (28.4 (5.2) years of age, 12 women). Each participant performed both methods in the sagittal and the frontal plane. Absolute and constant error values were found to be similar for both methods in both planes with a mean difference of less than 0.3° (p > 0.148). The mean width of the SPV sector was 3.9° (0.9°) in the sagittal and 3.7° (1.4°) in the frontal plane, ranging in the mean from -5.5° to 8.1° in the sagittal and -5.3° to 4.3° in the frontal plane. SPV values significantly differed in range between both methods in both planes with a mean difference of more than 3.1° (p<0.002). Results show that both methods, SPVposition and SPVsector, produce equal error values when applied with otherwise similar methodological settings and can therefore be used alternatively or within the same meta-analysis. The SPVsector, however, led to wider range values and was less frequently rated as the preferred method to represent the participants' subjective verticality.

New Mobile Device to Measure Verticality Perception: Results in Young Subjects with Headaches

The subjective visual vertical (SVV) test has been frequently used to measure vestibular contribution to the perception of verticality. Recently, mobile devices have been used to efficiently perform this measurement. The aim of this study was to analyze the perception of verticality in subjects with migraines and headaches. A cross-sectional study was conducted that included 28 patients with migraine, 74 with tension-type headache (TTH), and 93 healthy subjects. The SVV test was used through a new virtual reality system. The mean absolute error (MAE) of degrees deviation was also measured to qualify subjects as positive when it was greater than 2.5°. No differences in the prevalence of misperception in verticality was found among healthy subjects (31.18%), migraineurs (21.43%), or those with TTH (33.78%) (p = 0.480). The MAE was not significantly different between the three groups (migraine = 1.36°, TTH = 1.61°, and healthy = 1.68°) (F = 1.097, p = 0.336, and η2 = 0.011). The perception of verticality could not be explained by any variable usually related to headaches. No significant differences exist in the vestibular contribution to the perception of verticality between patients with headaches and healthy subjects. New tests measuring visual and somatosensory contribution should be used to analyze the link between the perception of verticality and headaches.