Article

Stroboscopic Vision as a Dynamic Sensory Reweighting Alternative to the Sensory Organization Test

Authors:
  • Houston Methodist Research Institute
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Abstract

Context: The sensory organization test (SOT) is a standard for quantifying sensory dependence via sway-referenced conditions (sway-referenced support and sway-referenced vision [SRV]). However, the SOT is limited to expensive equipment. Thus, a practical version of the SOT is more commonly employed-the clinical test for sensory integration in balance; however, it fails to induce postural instability to the level of SRV. Objective: Determine if Stroboscopic vision (SV), characterized by intermittent visual blocking, may provide an alternative to the SRV for assessing postural stability. Design: Descriptive laboratory study. Setting: Research laboratory. Participants: Eighteen participants (9 males, 9 females; age = 22.1 [2.1] y, height = 169.8 [8.5] cm, weight = 66.5 [10.6] kg). Intervention: Participants completed the SOT conditions, and then repeated SOT conditions 2 and 5 with SV created by specialized eyewear. Main outcome measures: A repeated-measures analysis of variance was completed on the time-to-boundary metrics of center-of-pressure excursion in the anteroposterior and mediolateral directions in order to determine the difference between the full-vision, SV, and SRV conditions. Results: Postural stability with either SRV or SV was significantly worse than with full vision (P < .05), with no significant difference between SV and SRV (P > .05). Limits of agreement analysis revealed similar effects of SV and SRV except for unstable surface mediolateral time-to-boundary. Conclusions: In general, SV was found to induce a degree of postural instability similar to that induced by SRV, indicating that SV could be a portable and relatively inexpensive alternative for the assessment of sensory dependence and reweighting.

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... However, the 95% confidence intervals (CIs) associated with the betweencondition effect size crossed 0, suggesting that differences between full and stroboscopic vision conditions during dual-limb stance on a stable surface are inconclusive. 22 Furthermore, those with CAI have dual-limb balance deficits relative to uninjured controls, 23 but the impact of stroboscopic eyewear in those with a musculoskeletal condition is sparse. Confirming the effects of stroboscopic eyewear during a less challenging task (dual-limb stance) and in a heterogeneous sample would provide additional evidence of the utility of stroboscopic eyewear. ...
... Our sample size estimate was based off of previously published data comparing full vision to stroboscopic vision in double-limb stance while on a stable surface. 22 These data indicated that partial visual occlusion resulted in effect sizes 0.38 and 0.64 for frontal and sagittal plane postural control outcomes, respectively. We chose the more conservative effect estimate (0.38) and used an alpha of .05, ...
... Double-limb support was used because the protocol aligned with the larger investigation, and we aimed to build upon previous research that showed an inconclusive effect of stroboscopic vision on double-limb stance postural control while on a stable surface. 22 Similarly, the order of testing was fixed to accommodate specific requirements of the larger study. Participants did not complete any practice trials but were offered a familiarization period with the stroboscopic eyewear. ...
Article
Context: Prophylactic and rehabilitative balance training is needed to maximize postural control and develop appropriate sensory organization strategies. Partially occluding vision during functional exercise may promote appropriate sensory organization strategies, but little is known about the influence of partially occluded vision on postural control in those with and without a history of musculoskeletal injury. Objective: To determine the effect of increasing levels of visual occlusion on postural control in a heterogeneous sample of those with and without chronic ankle instability (CAI). The secondary objective was to explore postural control responses to increasing levels of visual occlusion among those with unilateral and bilateral CAI relative to uninjured controls. Design: Cross-sectional. Setting: Sports medicine research laboratory. Patients or other participants: Twenty-five participants with unilateral CAI, 10 with bilateral CAI, and 16 participants with no history of lower extremity injury. Main outcome measures: All participants completed four 3-minute postural control assessments in double-limb stance under the following 4 visual conditions: (1) eyes open, (2) low occlusion, (3) high occlusion, and (4) eyes closed. Low- and high-occlusion conditions were produced using stroboscopic eyewear. Postural control outcomes included time-to-boundary minima means in the anteroposterior (TTB-AP) and mediolateral directions (TTB-ML). Repeated-measures analysis of variances tested the effects of visual condition on TTB-AP and TTB-ML. Results: Postural control under the eyes-open condition was significantly better (ie, higher) than the limited visual occlusion and eyes-closed conditions (P < .001) for TTB-AP and TTB-ML. For TTB-AP only, partially occluded vision resulted in better postural control than the eyes-closed condition (P ≤ .003). Conclusions: Partial and complete visual occlusion impaired postural control during dual-limb stance in a heterogeneous sample of those with and without CAI. Stroboscopic eyewear appears to induce postural control impairments to the same extent as complete visual occlusion in the mediolateral direction.
... Since the current study is the first to measure the visual reliance via stroboscopic glasses during dynamic movements, the results could not be compared with previous studies. However, previous studies have consistently reported that visual contribution would be increased when the somatosensory system is disturbed during static postural control [2,7,16,17]. Therefore, this might indicate that stroboscopic glasses could alter visual reliance during dynamic movement as well as during simpler movements, such as one-legged postural control. ...
... One paper, recently published, reported that stroboscopic glasses can induce a degree of postural instability similar to that induced by the sensory organization test (SOT) [16]. The SOT is the gold standard for quantifying sensory dependence by utilizing swayreferenced conditions, but involves expensive equipment [17]. ...
Article
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Little is known about how disrupted vision affects visual reliance during postural control. postural control. Twenty-four physically active adults volunteered to participate in the study. Static postural control was quantified with center of pressure measures during a one-legged balance test with four different visual inputs (eyes-open (EO), high frequency of strobe vision (HSV), low frequency of strobe vision (LSV), and eyes-closed (EC)) and on two different surfaces (firm and foam). Dynamic postural control was calculated by the dynamic postural stability index and the Y-Balance test for three different visual inputs (EO, HSV, and LSV) and the two different surfaces. Romberg ratios (HSV/EO, LSV/EO, and EC/EO) were then calculated and used for statistical analysis to assess visual contribution during postural control. In the results, Romberg ratios were higher when people were on the foam surface than the firm surface in center of pressure total path in medial-lateral and anterior-posterior directions (p < 0.05, both directions). Similarly, Romberg ratios were higher on the foam surface than the firm surface in dynamic stability index in medial-lateral and anterior-posterior directions (p < 0.05, both directions). Stroboscopic glasses could alter visual reliance when the somatosensory system is disturbed by a foam pad during both static and dynamic postural control. Clinicians could use the glasses to manipulate visual reliance during dynamic balance training for patients with musculoskeletal injuries.
... In general, trained older subjects can improve their performance in stabilometer balance tests (Chiviacowsky et al., 2010;Allahverdipour et al., 2020). Recently, stroboscopic vision (or intermittent vision) has been proposed to improve stance control (Assländer et al., 2013;Kim et al., 2020). Continuous visual inflow is aliased by lenses of stroboscopic eyewear, which provides intermittent visual samples by alternating between clear and opaque states at a pre-set duty cycle and frequency. ...
Article
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Skill transfer from trained balance exercises is critical to reduce the rate of falls in older adults, who rely more on vision to control postural responses due to age-dependent sensory reweighting. With an electroencephalography (EEG) minimum spanning tree (MST) structure, the purpose of this study was to compare the organization of supraspinal neural networks of transfer effect after postural training using full and intermittent visual feedbacks for older adults. Thirty-two older adults were randomly assigned to the stroboscopic vision (SV) ( n = 16; age = 64.7 ± 3.0 years) and control (16; 66.3 ± 2.7 years) groups for balance training on a stabilometer (target task) with on-line visual feedback. Center-of-pressure characteristics and an MST-based connectome of the weighted phase-lag index during the bilateral stance on a foam surface (transfer task) were compared before and after stabilometer training. The results showed that both the SV and control groups showed improvements in postural stability in the trained task ( p < 0.001). However, unlike the control group ( p = 0.030), the SV group who received intermittent visual feedback during the stabilometer training failed to reduce the size of postural sway in the anteroposterior direction of the postural transfer task (unstable stance on the foam surface) in the post-test ( p = 0.694). In addition, network integration for the transfer task in the post-test was absent in the SV group ( p > 0.05). For the control group in the post-test, it manifested with training-related increases in leaf fraction in beta band ( p = 0.015) and maximum betweenness in alpha band ( p = 0.018), but a smaller diameter in alpha ( p = 0.006)/beta ( p = 0.021) bands and average eccentricity in alpha band ( p = 0.028). In conclusion, stabilometer training with stroboscopic vision impairs generalization of postural skill to unstable stance for older adults. Adequate visual information is a key mediating factor of supraspinal neural networks to carry over balance skill in older adults.
Article
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Article
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Article
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Chapter
The upright stance position is inherently unstable since the smallest deviation from a perfect upright orientation produces forces due to gravity that accelerate the body toward the ground. Stability is achieved by generating appropriate joint torques that correct for deviations from a desired orientation with orientation changes detected by sensory systems (primarily somatosensory/proprioceptive, visual, and vestibular systems). Functionally, balance control can be viewed as a closed-loop feedback control system with the integration of different sources of sensory orientation information being one component of the overall system, but with the system's feedback nature placing constraints on the sensory integration process. Analysis of body sway evoked by balance perturbations allows for the measurement of “sensory weights” that represent the relative contributions of different sensory systems to an internal estimate of orientation that, in turn, is used to generate corrective actions. Experiments reveal that sensory weights are not fixed quantities, but vary as a function of environmental and experimental conditions as well as neurologic disorders that affect the quality of sensory information available from different sensory systems. Because environmental conditions can change rapidly, sensory reweighting must also occur rapidly enough to prevent instability due to an under- or overproduction of corrective action.
Chapter
For most individuals, balancing upright is a simple task that requires little effort. The inherent difficulties associated with standing balance are not revealed until a pathology or injury impairs its control. Fundamentally, standing upright requires us to balance our unstable whole-body load within a small base of support. Small movements of the upright body are detected by various sensory receptors, all encoding these movements through their own coordinate system with specific dynamics. The balance controller filters, processes, and integrates sensory cues of body motion to produce an error signal between predicted and actual sensory consequences of balance-related movements. Compensatory motor commands are generated in response to this error to maintain upright standing. In the present review, we first briefly describe the biomechanics and sensor dynamics of standing balance. We further review sensorimotor and perceptual approaches revealing operational principles of the balance system, along with computational approaches that explore control processes underlying upright stance. Finally, we present robotic tools that virtualize the sensory consequences, biomechanics, and/or environmental factors inherent to the standing balance task. Throughout, we emphasize works that combine sensorimotor, computational, and/or robotics approaches to highlight the task dependency, multisensory cue combinations, cortical-subcortical contributions, and internal representations underpinning balance control.
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Article
Purpose: To examine relationships among baseline demographics, symptom severity, computerized neurocognitive outcomes, and balance performance in collegiate athletes. Methods: Collegiate varsity athletes (N=207, age=19.3 ± 1.0 years) participating in an ongoing clinical research program who completed concussion baseline assessments including a demographic questionnaire, graded symptom checklist, neurocognitive assessment, and the Sensory Organization Test (SOT) were included in this study. The SOT composite equilibrium score (COMP) and three sensory ratio scores-vestibular (VEST), visual (VIS), and somatosensory (SOM)-were used to describe athletes' overall sensory organization and ability to utilize input from each sensory system to maintain balance. Separate stepwise multiple linear regression models were performed for each SOT outcome. Total symptom severity level and CNS Vital Signs domain scores served as predictor variables. Results: Stepwise regression models for COMP (R = 0.18, F4,201 = 11.29, P <0.001), VEST (R = 0.14, F4,201 = 8.16, P<0.001), and VIS (R = 0.10, F4,201 = 5.52, P <0.001) were all significant. Faster reaction times and higher executive function scores were associated with higher COMP and VEST scores in separate models. Those with faster reaction times also had significantly higher VIS scores. Conclusion: Reaction time and executive function demonstrated significant relationships with SOT balance performance. These cognitive processes may influence athletes' ability to organize and process higher order information and generate appropriate responses to changes in their environment, with respect to balance and injury risk. Future investigations should consider these relationships following injury and clinicians should be mindful of this relationship when considering concussion management strategies.
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Article
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Article
Purpose: The underlying cause of balance impairments in chronic ankle instability (CAI) patients remains unknown but an altered utilization of sensory information has been hypothesized as a potential cause. The purpose of this systematic review with meta-analysis was to determine if CAI patients utilize somatosensory information to the same extent as uninjured controls during static single limb stance. Method: We searched PubMed, CINAHL, SPORTDiscus, and Scopus databases from origin to March 2016 using the combination of key words including: postural control, postural stability, single limb stance, single leg stance, single leg balance, single limb balance, time-to-boundary, or TTB. Eligible studies had to include instrumented single leg stance with both eyes open (EO) and closed (EC) in healthy, CAI, or both groups as well as report time-to-boundary (TTB) means and standard deviations (SD). Results: A total of 11 articles were identified. Effect sizes using EC to EO standardized mean differences (SMD) and 95% confidence intervals (CI) were calculated for all studies that were included in this investigation. Similarly, pooled estimates for each TTB outcome were compared between the CAI and uninjured control groups. The 95% CI of the mediolateral (ML) TTB mean (Control: -1.50 (-1.71 to -1.29), CAI: -2.04 (-2.31 to -1.77)), anterioposterior (AP) mean (Control: -2.19 (-2.43 to -1.96), CAI: -2.82 (-3.13 to -2.52)), and AP SD (Control: -1.81 (-2.03 to -1.58), CAI: -2.50 (-2.79 to -2.22)) did not overlap, indicating significant differences between two groups. Conclusion: On the basis of our systematic review with meta-analysis, it appears that CAI patients do not utilize somatosensory information to the same extent as uninjured controls and instead upregulate the use of visual information during single limb stance.
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To determine whether there was a difference in the timed scores on a modified version of the Clinical Test of Sensory Interaction and Balance (CTSIB) with the feet apart versus feet together and to correlate modified CTSIB scores with Sensory Organization Test (SOT) scores. Prospective correlational study. Outpatient clinic. Thirty patients (mean age, 58+/-17 y) with vestibular dysfunction who were undergoing vestibular therapy. Subjects completed the modified CTSIB with their feet together and feet apart at the end of a vestibular therapy session. Subjects also completed the SOT on the same day. Modified CTSIB scores (feet together, feet apart) and SOT scores. Modified CTSIB scores were slightly lower when performed with feet together as compared with feet apart. However, no statistically significant difference existed between scores on the modified CTSIB with feet together versus feet apart using the Wilcoxon signed-rank test (P<.05). The modified CTSIB correlated more strongly with SOT scores when performed with feet together than with feet apart using the Spearman rho. Scores on the modified CTSIB performed with the feet together did not differ from scores on the modified CTSIB performed with the feet apart. In persons with vestibular disorders, the CTSIB done with the feet together correlated more closely with the SOT.
Article
A novel approach to quantifying postural stability in single leg stance is assessment of time-to-boundary (TTB) of center of pressure (COP) excursions. TTB measures estimate the time required for the COP to reach the boundary of the base of support if it were to continue on its instantaneous trajectory and velocity, thus quantifying the spatiotemporal characteristics of postural control. Our purposes were to examine: (a) the intrasession reliability of TTB and traditional COP-based measures of postural control, and (b) the correlations between these measures. Twenty-four young women completed three 10-second trials of single-limb quiet standing on each limb. Traditional measures included mean velocity, standard deviation, and range of mediolateral (ML) and anterior-posterior (AP) COP excursions. TTB variables were the absolute minimum, mean of minimum samples, and standard deviation of minimum samples in the ML and AP directions. The intrasession reliability of TTB measures was comparable to traditional COP based measures. Correlations between TTB and traditional COP based measures were weaker than those within each category of measures, indicating that TTB measures capture different aspects of postural control than traditional measures. TTB measures provide a unique method of assessing spatiotemporal characteristics of postural control during single limb stance.