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

Clinical Assessment of Subjective Visual and Haptic Vertical Norms in Healthy Adults

BACKGROUND AND OBJECTIVE

Accurate verticality perception is essential for daily life activities, such as correctly estimating object orientation in space. This study established normative data for the subjective visual vertical (SVV) and subjective haptic vertical (SHV) using the portable and self-constructable modified Bucket test and Rotating-Column test. Additionally, the contribution of age, sex, and starting position of the line/ column on SVV and SHV accuracy were evaluated.

METHOD

This study, part of the PRECISE project (ClinicalTrials.gov ID NCT05978596), was conducted following the STROBE guidelines. Healthy adults without visual/neurological/vestibular disorders were recruited. Subjective visual vertical and SHV accuracy were described in terms of constant errors (i.e., mean deviation from 0° [true vertical] respecting its direction), unsigned errors (i.e., mean deviation from 0° irrespective of direction), and variability (i.e., intra-individual standard deviation).

RESULTS

Sixty participants were evaluated (mean age: 41.14 [SD = 16.74] years). Subjective visual vertical constant errors between -2.82° and 2.90°, unsigned errors up to 2.15°, and variability up to 1.61° are considered normal. Subjective haptic vertical constant errors ranged from -6.94° to 8.18°, unsigned errors up to 6.66° and variability up to 4.25°. Higher ages led to higher SVV unsigned errors and variability. SHV variability was higher in females compared to males. Certain starting positions led to higher SVV and SHV constants and SVV unsigned errors.

DISCUSSION

Normative data are provided for affordable, self-constructable, and portable SVV and SHV tools. These norms are consistent with more sophisticated equipment and can be used to distinguish between normal and abnormal values.

Portable eye-tracking as a reliable assessment of oculomotor, cognitive and reaction time function: Normative data for 18-45 year old

Eye movements measured by high precision eye-tracking technology represent a sensitive, objective, and non-invasive method to probe functional neural pathways. Oculomotor tests (e.g., saccades and smooth pursuit), tests that involve cognitive processing (e.g., antisaccade and predictive saccade), and reaction time tests have increasingly been showing utility in the diagnosis and monitoring of mild traumatic brain injury (mTBI) in research settings. Currently, the adoption of these tests into clinical practice is hampered by a lack of a normative data set. The goal of this study was to construct a normative database to be used as a reference for comparing patients' results. Oculomotor, cognitive, and reaction time tests were administered to male and female volunteers, aged 18-45, who were free of any neurological, vestibular disorders, or other head injuries. Tests were delivered using either a rotatory chair equipped with video-oculography goggles (VOG) or a portable virtual reality-like VOG goggle device with incorporated infrared eye-tracking technology. Statistical analysis revealed no effects of age on test metrics when participant data were divided into pediatric (i.e.,18-21 years, following FDA criteria) and adult (i.e., 21-45 years) groups. Gender (self-reported) had an effect on auditory reaction time, with males being faster than females. Pooled data were used to construct a normative database using 95% reference intervals (RI) with 90% confidence intervals on the upper and lower limits of the RI. The availability of these RIs readily allows clinicians to identify specific metrics that are deficient, therefore aiding in rapid triage, informing and monitoring treatment and/or rehabilitation protocols, and aiding in the return to duty/activity decision. This database is FDA cleared for use in clinical practice (K192186).

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.

Subjective postural vertical in Parkinson's disease with lateral trunk flexion

BACKGROUND

Patients with Parkinson's disease (PD) and associated lateral trunk flexion (LTF) cannot accurately perceive their own verticality.

OBJECTIVE

We measured the subjective postural vertical in coronal plane (SPVc) angle on patients' ipsilateral and contralateral sides and combined to clarify the effects of SPVc on LTF. We also investigated effects of the SPVc angle on LTF severity.

METHODS

Thirty-nine patients (aged 74.1 ± 7.6 years) were divided between those with mild LTF (LTF angle < 10°, n = 34) and those with moderate to severe LTF (LTF angle ≥ 10°, n = 5) for comparison of the LTF angle, SPVc angle on both sides, inter-measurement variation in the SPVc angle, and the LTF to SPVc angle ratio (SPVc ratio).

RESULTS

We found significant positive correlation between LTF and the SPVc angle on the combined (r = .54, P = .001), ipsilateral (r = .51, P = .002), and contralateral (r = .50, P = .002) sides. We found significant negative correlation between the LTF angle and the SPVc ratio on the combined SPVc (r = -.82, P = .001), ipsilateral (r = -.69, P = .001), and contralateral (r = -.75, P = .001) sides and between the LTF and ipsilateral side coefficient of variation (r = -.34, P = .038). SPVc angles on ipsilateral and contralateral sides were significantly greater in cases of moderate to severe LTF than in cases of mild LTF (P < .01).

CONCLUSIONS

Subjective postural vertical in coronal plane assessment may be useful for assessing patients with PD and associated LTF.

Starting position effects in the measurement of the postural vertical for pusher behavior

Pusher behavior (PB) is a severe lateral postural disorder that involves a disturbed subjective postural vertical (SPV) in the frontal plane. SPV is measured by determining the mean value and standard deviation of several trials beginning on both the contralesional- and ipsilesional-tilted positions. However, the postural representation, when passively tilted to the contralesional versus ipsilesional position, is different between patients with and without PB. Therefore, we hypothesized that SPV dependence on the starting position will be influenced by PB. For 53 patients with hemispheric stroke enrolled, SPV was measured using a non-motorized vertical board with eyes closed. The mean value (tilt direction) and standard deviation (variability) were calculated in four trials, each from two positions, with the patient tilted to the contralesional position (SPV-CL condition) and then to the ipsilesional position (SPV-IL condition). Patients were categorized into the non-pusher (n = 29) and pusher (n = 24) groups. In the SPV-CL trials, the tilt direction was significantly tilted contralesionally for the pusher group (- 6.3° ± 1.6°) compared with that for the non-pusher group (- 2.2° ± 1.8°; p < 0.001), with no significant difference in variability between the groups. In the SPV-IL trials, the tilt direction was not significantly different between the groups, but the variability was significantly higher in the pusher group (4.8° ± 2.0°) than in the non-pusher group (2.2° ± 1.3°; p < 0.001). The dependence of tilt direction and variability of SPV on the starting position in patients with PB differed from those noted in patients without PB. These results may help explain this abnormal posture and optimize neurological rehabilitation strategies for PB.

Young and Older Adults Differ in Integration of Sensory Cues for Vertical Perception

Introduction

The subjective visual vertical (SVV) measures the perception of a person's spatial orientation relative to gravity. Weighted central integration of vestibular, visual, and proprioceptive inputs is essential for SVV perception. Without any visual references and minimal proprioceptive contribution, the static SVV reflects balance of the otolith organs. Normal aging is associated with bilateral and progressive decline in otolith organ function, but age-dependent effects on SVV are inconclusive. Studies on sensory reweighting for visual vertical and multisensory integration strategies reveal age-dependent differences, but most studies have included elderly participants in comparison to younger adults. The aim of this study was to compare young adults with older adults, an age group younger than the elderly.

Methods

Thirty-three young and 28 older adults (50–65 years old) adjusted a tilted line accurately to their perceived vertical. The rod's final position from true vertical was recorded as tilt error in degrees. For otolithic balance, visual vertical was recorded in the dark without any visual references. The rod and frame task (RFT) with tilted disorienting visual frames was used for creating visuovestibular conflict. We adopted Nyborg's analysis method to derive the rod and frame effect (RFE) and trial-to-trial variability measures. Rod alignment times were also analyzed.

Results

There was no age difference in signed tilts of SVV without visual reference. There was an age effect on RFE and on overall trial-to-trial variability of rod tilt, with older adults displaying larger frame effects and greater variability in rod tilts. Alignment times were longer in the tilted-frame conditions for both groups and in the older adults compared to their younger counterparts. The association between tilt accuracy and tilt precision was significant for older adults only during visuovestibular conflict, revealing an increase in RFE with an increase in tilt variability. Correlation of σ_SVV, which represents vestibular input precision, with RFE yielded exactly the same contribution of σ_SVV to the variance in RFE for both age groups.

Conclusions

Older adults have balanced otolithic input in an upright position. Increased reliance on visual cues may begin at ages younger than what is considered elderly. Increased alignment times for older adults may create a broader time window for integration of relevant and irrelevant sensory information, thus enhancing their multisensory integration. In parallel with the elderly, older adults may differ from young adults in their integration of sensory cues for visual vertical perception.

Normative data for human postural vertical: A systematic review and meta-analysis

Perception of verticality is required for normal daily function, yet the typical human detection error range has not been well characterized. Vertical misperception has been correlated with poor postural control and functionality in patients after stroke and after vestibular disorders. Until now, all the published studies that assessed Subjective Postural Vertical (SPV) in the seated position used small groups to establish a reference value. However, this sample size does not represent the healthy population for comparison with conditions resulting in pathological vertical. Therefore, the primary objective was to conduct a systematic review with meta-analyses of Subjective Postural Vertical (SPV) data in seated position in healthy adults to establish the reference value with a representative sample. The secondary objective was to investigate the methodological characteristics of different assessment protocols of SPV described in the literature. A systematic literature search was conducted using Medline, EMBASE, and Cochrane libraries. Mean and standard deviation of SPV in frontal and sagittal planes were considered as effect size measures. Sixteen of 129 identified studies met eligibility criteria for our systematic review (n = 337 subjects in the frontal plane; n = 187 subjects in sagittal plane). The meta-analyses measure was estimated using the pooled mean as the estimator and its respective error. Mean reference values were 0.12°±1.49° for the frontal plane and 0.02°±1.82° for the sagittal plane. There was a small variability of the results and this systematic review resulted in representative values for SPV. The critical analysis of the studies and observed homogeneity in the sample suggests that the methodological differences used in the studies did not influence SPV assessment of directional bias in healthy subjects. These data can serve as a reference for clinical studies in disorders of verticality.