Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Use of Virtual Reality to Assess Dynamic Posturography and Sensory Organization: Instrument Validation Study

Use of Virtual Reality to Assess Dynamic Posturography and Sensory Organization: Instrument... Background: The Equitest system (Neurocom) is a computerized dynamic posturography device used by health care providers and clinical researchers to safely test an individual’s postural control. While the Equitest system has evaluative and rehabilitative value, it may be limited owing to its cost, lack of portability, and reliance on only sagittal plane movements. Virtual reality (VR) provides an opportunity to reduce these limitations by providing more mobile and cost-effective tools while also observing a wider array of postural characteristics. Objective: This study aimed to test the plausibility of using VR as a feasible alternative to the Equitest system for conducting a sensory organization test. Methods: A convenience sample of 20 college-aged healthy individuals participated in the study. Participants completed the sensory organization test using the Equitest system as well as using a VR environment while standing atop a force plate (Bertec Inc). The Equitest system measures the equilibrium index. During VR trials, the estimated equilibrium index, 95% ellipse area, path length, and anterior-posterior detrended fluctuation analysis scaling exponent alpha were calculated from center of pressure data. Pearson correlation coefficients were used to assess the relationship between the equilibrium index and center of pressure–derived balance measures. Intraclass correlations for absolute agreement and consistency were calculated to compare the equilibrium index and estimated equilibrium index. Results: Intraclass correlations demonstrated moderate consistency and absolute agreement (0.5 < intraclass correlation coefficient < 0.75) between the equilibrium index and estimated equilibrium index from the Equitest and VR sensory organization test (SOT), respectively, in four of six tested conditions. Additionally, weak to moderate correlations between force plate measurements and the equilibrium index were noted in several of the conditions. Conclusions: This research demonstrated the plausibility of using VR as an alternative method to conduct the SOT. Ongoing development and testing of virtual environments are necessary before employing the technology as a replacement to current clinical tests. (JMIR Serious Games 2020;8(4):e19580) doi: 10.2196/19580 KEYWORDS postural control; virtual reality; sensory organization test; intraclass correlations http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 1 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al drawbacks. When these technologies are combined, they greatly Introduction reduce the cost for a clinician to own testing equipment, as well as offer the opportunity to have a portable solution that could The Equitest system (Neurocom) is a computerized dynamic be taken into the field. Moreover, portable force plates present posturography device used by health care providers and clinical the possibility to record and assess a wider range of data, such researchers to safely test an individual’s postural control. as medial-lateral dynamics, and customize the outcomes to Implementing the sensory organization test (SOT) using the specific clinical goals. Likewise, VR headsets have continued Equitest system requires individuals to process and integrate to improve in quality and decrease in cost, and continued cues from the visual, vestibular, and proprioceptive systems. developments may lead to the ability to accurately track This test provides clinicians and researchers with an equilibrium movements in VR without additional hardware components score for each tested condition, a sensory analysis score, a such as force plates. strategy analysis, and a center of gravity (COG) alignment. While the Equitest system has evaluative and rehabilitative In keeping up with technological advancements, it is important value, it may be limited owing to its cost and lack of portability. to determine how new technologies can measure up to the “gold Moreover, the performance variables provided by the Equitest standards” they will eventually replace. Currently, VR is system are limited, representing gross outcome measures derived approaching this standard and is consistently shown to be a only from sagittal plane movement dynamics [1]. Recent valuable tool to conduct postural and motor control research. advances in technology provide opportunities to reduce these Previous research has found no difference between static balance limitations by providing more mobile and cost-effective tools in a physical environment versus a virtual environment [2]. while also observing a wider array of postural characteristics. Additionally, several scholars have supported the efficacy of The purpose of this research was to evaluate the validity of VR for use in balance assessments in a range of clinical using virtual reality (VR) and a force plate as an alternative to populations, such as those with concussion, stroke, Parkinson the Equitest system. disease, and high age [3-7]. Continuing in this trend, a large body of research has shown positive results in using VR to The SOT has been the dominant clinical test to assess sensory enhance training and rehabilitation for balance-related integration in the context of postural control for neurologic dysfunction [8-11]. Overall, VR has been demonstrated to disorders and deficits. With the wide use of clinical dynamic accurately assess balance in addition to providing a customizable posturography over the last 30 years, the Equitest system has means to enhance clinical outcomes. become widely accepted as the gold standard to assess postural stability and balance in several populations (eg, children, aging The purpose of this research was to compare the Equitest system adults, and military personnel) and clinical groups (eg, those to a VR balance assessment designed to mimic the SOT in a with concussion, vertigo, Parkinson disease, and Alzheimer young healthy population. It was hypothesized that the disease). By systematically disrupting the visual and equilibrium score would demonstrate high limits of agreement somatosensory information available to an individual, it is between the two testing conditions, supporting VR as a viable possible to distinguish someone’s reliance on the following option to decrease cost and increase the accessibility of postural three major sensory systems during balance tasks: the visual, assessment techniques. By illustrating the viability of VR to somatosensory, and vestibular systems. Conveniently, the emulate current clinical practices, future progress can focus on Equitest system provides an equilibrium score (indicating how improving and optimizing the implementation of VR in clinical little participants swayed) during each test, as well as a sensory standards of care and applications to more populations of analysis score (indicating how much they relied on each system) interest. and strategy analysis (indicating the hip versus ankle strategy) for the battery of conditions. Methods While the Equitest system provides a quick evaluative tool for Participants clinicians and researchers, it is not without limitations. First, A convenience sample of 20 college-aged individuals (Table these outcome measures are derived solely from sagittal plane 1) was recruited to participate in this study. All participants movements and may not reflect a complete assessment of an were healthy individuals with no prior history of neurological individual’s postural control. Second, the costs associated with or physical injury or dysfunction. Upon arrival, participants the Equitest system may limit its availability in underserved provided informed consent. All procedures were approved by communities or during times immediately following an injury the institutional review board, and no adverse events were (such as a sports concussion). As an alternative to the Equitest encountered. system, it may be possible to combine more recent technologies, that is, portable force plates and VR, to ameliorate these Table 1. Participant demographics. Characteristic Male (n=7), mean (SE) Female (n=13), mean (SE) Age (years) 20.8 (0.4) 20.9 (0.37) Height (m) 1.79 (0.03) 1.66 (0.02) Weight (kg) 77.4 (5.58) 62.8 (3.33) http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 2 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al tracking (Figure 1). The “no tracking” option creates an Experimental Design experience where the objects viewed move with the user’s head After providing informed consent, participants completed a as if they are attached. The second option, which is common in SOT in two blocks, using the Equitest system and using VR. first-generation VR headsets, such as the Oculus DK1 and Blocks of tests were counterbalanced, and conditions within Google Daydream, is somewhat natural until users lean in a blocks were randomized. direction that moves their torso. The last of these most closely During the Equitest SOT, participants wore a harness that mimics reality. supported their weight in case they lost balance. Researchers Balance was tested in the following conditions in the VR helped participants into the harness so it fit comfortably and environment: in a completely dark environment, eyes open in safely. The conditions during the clinical test included (1) eyes an environment that mimics the clinical test (6DoF tracking), open on a stable surface, (2) eyes closed on a stable surface, (3) eyes open in an environment that mimics the surround of the eyes open with a sway-referenced surround, (4) eyes open on clinical test and moves and rotates with the participant’s head a sway-referenced surface, (5) eyes closed on a sway-referenced (no tracking), and eyes open in an environment that mimics the surface, and (6) eyes open with both a sway-referenced surround surround of the clinical test and moves forward and backward and surface. with the participant’s head but does not react to head rotation In the VR SOT, participants removed any glasses and wore a (head tracking only). Each condition was completed on a stable head-mounted display (HTC Vive, HTC). Participants adjusted surface and on a foam surface. the headset to ensure clarity in the virtual environment using a For each balance condition, in both the clinical test and the VR black screen with a textbox. To compare our VR SOT to existing test, participants completed two trials of 20 seconds. The order SOT research performed with real machines, we created a virtual of the trials was counterbalanced between the clinical test and scale model of the patterns used inside of the Equitest balance VR blocks, and the order of the conditions was randomized system. We placed this model in the center of a white virtual within the clinical test and VR blocks. In total, participants testing room (10 m × 9 m in size). These models and the testing completed 28 trials (six clinical testing conditions × two trials software were created using Unity 3D (v. 2018.2.10f1; Unity each, four VR testing conditions × two surface conditions × two Technologies). Our software allowed us to test users with the trials each) of 20 seconds of stationary balance. All participants following three different types of VR tracking: no tracking, provided written consent prior to beginning the experimental head rotation tracking only, and six degrees of freedom (6DoF) protocol. Figure 1. Effect of the head tracking condition in virtual reality on a user's view with translation or rotation of the head. 6DoF: six degrees of freedom. a score of 100 would be received, and if the participant exhibits Data Reduction 12.5° or greater sway (combined forward and backward), a The Equitest system calculated the equilibrium index (EI) during score of 0 would be received. During the VR conditions, each SOT condition [12], and it represents the extent to which participants completed the test on top of a portable force plate a participant sways forward or backward within a theoretical (Bertec Inc) that collected center of pressure (COP) data at 50 limit of 12.5° of displacement. If the participant has no sway, Hz. Custom MATLAB (Mathworks Inc) scripts were used to http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 3 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al detrend and filter the data (20-ms moving average filter) and analysis. In this manner, one trial each from SOT 3 and SOT 4 subsequently calculate the estimated equilibrium index (eEI), was removed, along with their VR condition pair. 95% ellipse area, path length, and anterior-posterior (AP) Statistical Analysis detrended fluctuation analysis scaling exponent alpha (DFA α) To assess the relationship between EI and eEI, intraclass from the COP data. The 95% ellipse area, path length, and AP correlations of consistency and absolute agreement were DFA α calculations are described elsewhere and represent calculated for similar conditions (Table 2). Intraclass correlation typical spatiotemporal characteristics of balance [13,14]. The coefficient (ICC) values were interpreted as poor (<0.5), eEI metric was derived based on the EI used by the Equitest moderate (0.5-0.75), good (0.5-0.9), and excellent (>0.9) system. To simplify this process, the forward and backward reliability [15]. Additionally, Pearson correlation coefficients sway angles were calculated as the inverse sine function of the were calculated to quantify the extent to which force plate anterior and posterior COP displacement, respectively, divided measurements were associated with the EI calculated by the by an estimated COG height (56% of the participant height). Equitest system within similar conditions. Correlation The first trial of each condition served as a familiarization coefficients were interpreted as negligible (<0.3), weak (0.3-0.5), period, and only the final trial of each condition was used for moderate (0.5-0.7), strong (0.7-0.9), or very strong (>0.9) analysis. Data that were outside of three times the SD from the relationships between pairs of variables [16]. mean of its experimental condition were removed from the Table 2. Summary of all testing conditions, their abbreviations, and the quality of visual, somatosensory, and vestibular information available in the condition. Condition abbrevia- Equitest Virtual reality Information quality tion b c d e Eyes opened on a stable surface Stable virtual surround on a stable surface SOT 1 Vis –Som –Ves SOT 2 Eyes closed on a stable surface Blacked out environment on a stable sur- Som–Ves face SOT 3 Eyes opened with a sway-referenced surround Head-referenced virtual surround on a Vis–Som–Ves stable surface SOT 4 Eyes opened on a sway-referenced surface Stable virtual surround on a foam surface Vis–Som–Ves SOT 5 Eyes closed on a sway-referenced surface Blacked out environment on a foam sur- Som–Ves face SOT 6 Eyes opened with a sway-referenced surround and on a Head-referenced virtual surround on a Vis–Som–Ves sway-referenced surface foam surface In the column, normal text indicates accurate and italic text indicates inaccurate. SOT: sensory organization test. Vis: visual. Som: somatosensory. Ves: vestibular. (Figure 2). Visual inspection of the data indicated symmetry in Results most conditions and increased variability in the more challenging conditions (conditions 4-6). Data Presentation and Assessment of the Raw Data Boxplots of the data showing the median (thick line), IQR (box edges), and 95% CI (whiskers) for each condition were created http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 4 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Figure 2. Boxplots of all data collected in comparable SOT (light) and VR (dark) conditions. The median value (thick line), IQR (box edges), and 95% CI (whiskers) are indicated. SOT: sensory organization test; VR: virtual reality. 5 showed poor consistency and absolute agreement with similar Reliability of the eEI VR conditions. The Bland-Altman plots provide a visual Intraclass correlations between EI and eEI in similar conditions representation of agreement between two measurements by were evaluated and are presented alongside Bland-Altman plots plotting the absolute agreement or mean difference between in Figure 3 [17]. SOT conditions 1, 2, 3, and 6 demonstrated measurements on the vertical axis against the average of the moderate consistency and absolute agreement with their similar two measurements on the horizontal axis. VR condition counterparts. Meanwhile, SOT conditions 4 and http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 5 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Figure 3. Bland-Altman plots comparing the equilibrium index and estimated equilibrium index from the Equitest and VR SOT, respectively. The Pearson correlation coefficient (r), intraclass correlation coefficient for absolute agreement (ICCa), and intraclass correlation coefficient for consistency (ICCc) are provided. SOT: sensory organization test; VR: virtual reality. P=.005). Additionally, weak to moderate significant correlations Correlation of the EI With Force Plate Measurements were identified between EI and 95% ellipse area in conditions Pearson correlation coefficients were calculated between the 1 (r=−0.453, P=.045), 2 (r=−0.506, P=.02), and 6 (r=−0.500, Equitest EI and balance measures derived from COP data (Table P=.03) and AP DFA α in condition 1 (r=−0.511, P=.02). No 3). Weak to moderate significant correlations were identified other relevant correlations were identified between the Equitest between EI and eEI in SOT conditions 1 (r=0.454, P=.045), 2 EI and balance measurements derived from the COP data. (r=0.566, P=.009), 3 (r=0.652, P=.002), and 6 (r=0.597, http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 6 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Table 3. Pearson correlation coefficients between force plate measurements (columns) and the equilibrium index during each sensory organization test condition. a b Condition eEI 95% ellipse area Path length AP DFA α SOT 1 r 0.454 −0.453 −0.130 −0.511 P .045 .045 .59 .02 SOT 2 r 0.566 −0.506 −0.400 −0.041 P .009 .02 .08 .86 SOT 3 r 0.652 −0.329 −0.068 −0.234 P .002 .17 .78 .33 SOT 4 r 0.209 −0.143 −0.332 −0.007 P .39 .56 .16 .98 SOT 5 r 0.052 −0.242 −0.241 0.027 P .83 .30 .31 .91 SOT 6 r 0.597 −0.500 −0.334 −0.174 P .005 .03 .15 .46 eEI: estimated equilibrium index. AP DFA α: anterior-posterior detrended fluctuation analysis scaling exponent alpha. SOT: sensory organization test. measure aspects of how variability is structured in an individual Discussion plane. For example, 95% ellipse area quantifies the gross postural control behavior during quiet stance [18] and AP DFA This research has demonstrated the plausibility of using VR as α quantifies the structure of variability within an individual’s an alternative to the Equitest when conducting a SOT. Although AP sway trajectory (ie, how random or deterministic the data not a perfect replacement, eEI demonstrated reasonable is) [19], whereas EI evaluates how close an individual gets to correlations and ICCs with the clinical standard in several of a theoretical limit of stability [20]. The measures evaluated in the SOT conditions. Continued improvements to the VR testing this study were selected to represent a small array of postural environment need to be made to have more confidence in its control measurements, and future research should evaluate the use as a potential replacement. For example, the VR device may clinical utility of individual metrics. do a good job at mimicking the visual conditions of the SOT, but the foam mat might not equivocally disrupt somatosensory The recent surge in consumer-ready VR headsets has the information compared with the SOT. This is supported by seeing potential to greatly reduce the cost of conducting balance higher correlations between EI and eEI in the intact than assessments while also providing additional accessibility to inaccurate somatosensory conditions (conditions 1, 2, and 3 sites outside of the clinic, for example, on the sideline during versus conditions 4 and 5). Additionally, this study identified an athletic event. Likewise, using force plates opens access to a number of correlations between the Equitest system and typical raw, processed, and derived outcome measures that take balance measurements derived from COP data on a force plate. advantage of the full scope of postural dynamics and present Aside from eEI, 95% ellipse area and AP DFA α had some the opportunity to have more accurate information at the correlations with the clinical test. It is not surprising that these clinician’s disposal. In the future, it may even be possible to correlations were somewhat sparse as they distinctly measure accurately assess balance (and gait) using only the self-contained different characteristics of balance. The SOT measures only AP tracking of VR headsets. This research serves as a point from sway magnitude, while COP data can be used to calculate sway which we can merge motor control assessments with the magnitude in the frontal and sagittal planes combined or to accelerating advancements in consumer technologies. http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 7 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Conflicts of Interest None declared. References 1. Chiarovano E, Wang W, Rogers SJ, MacDougall HG, Curthoys IS, de Waele C. Balance in Virtual Reality: Effect of Age and Bilateral Vestibular Loss. Front Neurol 2017;8:5 [FREE Full text] [doi: 10.3389/fneur.2017.00005] [Medline: 28163693] 2. Robert MT, Ballaz L, Lemay M. The effect of viewing a virtual environment through a head-mounted display on balance. Gait Posture 2016 Jul;48:261-266. [doi: 10.1016/j.gaitpost.2016.06.010] [Medline: 27344394] 3. Lloréns R, Noé E, Colomer C, Alcañiz M. Effectiveness, usability, and cost-benefit of a virtual reality-based telerehabilitation program for balance recovery after stroke: a randomized controlled trial. Arch Phys Med Rehabil 2015 Mar;96(3):418-425.e2 [FREE Full text] [doi: 10.1016/j.apmr.2014.10.019] [Medline: 25448245] 4. Mirelman A, Maidan I, Deutsch JE. Virtual reality and motor imagery: promising tools for assessment and therapy in Parkinson's disease. Mov Disord 2013 Sep 15;28(11):1597-1608 [FREE Full text] [doi: 10.1002/mds.25670] [Medline: 24132848] 5. Morel M, Bideau B, Lardy J, Kulpa R. Advantages and limitations of virtual reality for balance assessment and rehabilitation. Neurophysiol Clin 2015 Nov;45(4-5):315-326 [FREE Full text] [doi: 10.1016/j.neucli.2015.09.007] [Medline: 26527045] 6. Saldana S, Marsh AP, Rejeski WJ, Haberl J, Wu P, Rosenthal S, et al. Assessing balance through the use of a low-cost head-mounted display in older adults: a pilot study. Clin Interv Aging 2017;12:1363-1370 [FREE Full text] [doi: 10.2147/CIA.S141251] [Medline: 28883717] 7. Wright WG, McDevitt J, Tierney R, Haran FJ, Appiah-Kubi KO, Dumont A. Assessing subacute mild traumatic brain injury with a portable virtual reality balance device. Disabil Rehabil 2017 Jul;39(15):1564-1572 [FREE Full text] [doi: 10.1080/09638288.2016.1226432] [Medline: 27718642] 8. de Rooij IJ, van de Port IG, Meijer JW. Effect of Virtual Reality Training on Balance and Gait Ability in Patients With Stroke: Systematic Review and Meta-Analysis. Phys Ther 2016 Dec;96(12):1905-1918 [FREE Full text] [doi: 10.2522/ptj.20160054] [Medline: 27174255] 9. Meyns P, Pans L, Plasmans K, Heyrman L, Desloovere K, Molenaers G. The Effect of Additional Virtual Reality Training on Balance in Children with Cerebral Palsy after Lower Limb Surgery: A Feasibility Study. Games Health J 2017 Feb;6(1):39-48 [FREE Full text] [doi: 10.1089/g4h.2016.0069] [Medline: 28051880] 10. Villiger M, Liviero J, Awai L, Stoop R, Pyk P, Clijsen R, et al. Home-Based Virtual Reality-Augmented Training Improves Lower Limb Muscle Strength, Balance, and Functional Mobility following Chronic Incomplete Spinal Cord Injury. Front Neurol 2017;8:635 [FREE Full text] [doi: 10.3389/fneur.2017.00635] [Medline: 29234302] 11. Yen CY, Lin KH, Hu MH, Wu RM, Lu TW, Lin CH. Effects of virtual reality-augmented balance training on sensory organization and attentional demand for postural control in people with Parkinson disease: a randomized controlled trial. Phys Ther 2011 Jun;91(6):862-874 [FREE Full text] [doi: 10.2522/ptj.20100050] [Medline: 21474638] 12. Nashner LM. EquiTest system operator’s manual, version 4.04. Clackamas, OR, USA: NeuroCom International, Inc; 1992. 13. Duarte M, Freitas SM. Revision of posturography based on force plate for balance evaluation. Rev Bras Fisioter 2010;14(3):183-192. [Medline: 20730361] 14. Peng CK, Havlin S, Stanley HE, Goldberger AL. Quantification of scaling exponents and crossover phenomena in nonstationary heartbeat time series. Chaos 1995;5(1):82-87. [doi: 10.1063/1.166141] [Medline: 11538314] 15. Koo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. Journal of Chiropractic Medicine 2016 Jun;15(2):155-163 [FREE Full text] [doi: 10.1016/j.jcm.2016.02.012] 16. Mukaka MM. Statistics corner: A guide to appropriate use of correlation coefficient in medical research. Malawi Med J 2012 Sep;24(3):69-71 [FREE Full text] [Medline: 23638278] 17. Bland J, Altman D. Measuring agreement in method comparison studies. Stat Methods Med Res 1999 Jun 01;8(2):135-160 [FREE Full text] [doi: 10.1191/096228099673819272] 18. Strang AJ, Haworth J, Hieronymus M, Walsh M, Smart LJ. Structural changes in postural sway lend insight into effects of balance training, vision, and support surface on postural control in a healthy population. Eur J Appl Physiol 2011 Jul;111(7):1485-1495 [FREE Full text] [doi: 10.1007/s00421-010-1770-6] [Medline: 21165641] 19. Rhea CK, Silver TA, Hong SL, Ryu JH, Studenka BE, Hughes CM, et al. Noise and complexity in human postural control: interpreting the different estimations of entropy. PLoS One 2011 Mar 17;6(3):e17696 [FREE Full text] [doi: 10.1371/journal.pone.0017696] [Medline: 21437281] 20. Chaudhry H, Findley T, Quigley KS, Bukiet B, Ji Z, Sims T, et al. Measures of postural stability. J Rehabil Res Dev 2004 Sep;41(5):713-720 [FREE Full text] [doi: 10.1682/jrrd.2003.09.0140] [Medline: 15558401] Abbreviations 6DoF: six degrees of freedom AP: anterior-posterior COG: center of gravity http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 8 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al COP: center of pressure DFA α: detrended fluctuation analysis scaling exponent alpha eEI: estimated equilibrium index EI: equilibrium index ICC: intraclass correlation coefficient SOT: sensory organization test VR: virtual reality Edited by N Zary; submitted 23.04.20; peer-reviewed by PC Wang; comments to author 04.07.20; revised version received 10.09.20; accepted 13.11.20; published 16.12.20 Please cite as: Wittstein MW, Crider A, Mastrocola S, Guerena Gonzalez M JMIR Serious Games 2020;8(4):e19580 URL: http://games.jmir.org/2020/4/e19580/ doi: 10.2196/19580 PMID: 33325830 ©Matthew William Wittstein, Anthony Crider, Samantha Mastrocola, Mariana Guerena Gonzalez. Originally published in JMIR Serious Games (http://games.jmir.org), 16.12.2020. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR Serious Games, is properly cited. The complete bibliographic information, a link to the original publication on http://games.jmir.org, as well as this copyright and license information must be included. http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 9 (page number not for citation purposes) XSL FO RenderX http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png JMIR Serious Games JMIR Publications

Use of Virtual Reality to Assess Dynamic Posturography and Sensory Organization: Instrument Validation Study

Loading next page...
 
/lp/jmir-publications/use-of-virtual-reality-to-assess-dynamic-posturography-and-sensory-TnS0gEj0xk

References (22)

Publisher
JMIR Publications
Copyright
Copyright © The Author(s). Licensed under Creative Commons Attribution cc-by 4.0
ISSN
2291-9279
DOI
10.2196/19580
Publisher site
See Article on Publisher Site

Abstract

Background: The Equitest system (Neurocom) is a computerized dynamic posturography device used by health care providers and clinical researchers to safely test an individual’s postural control. While the Equitest system has evaluative and rehabilitative value, it may be limited owing to its cost, lack of portability, and reliance on only sagittal plane movements. Virtual reality (VR) provides an opportunity to reduce these limitations by providing more mobile and cost-effective tools while also observing a wider array of postural characteristics. Objective: This study aimed to test the plausibility of using VR as a feasible alternative to the Equitest system for conducting a sensory organization test. Methods: A convenience sample of 20 college-aged healthy individuals participated in the study. Participants completed the sensory organization test using the Equitest system as well as using a VR environment while standing atop a force plate (Bertec Inc). The Equitest system measures the equilibrium index. During VR trials, the estimated equilibrium index, 95% ellipse area, path length, and anterior-posterior detrended fluctuation analysis scaling exponent alpha were calculated from center of pressure data. Pearson correlation coefficients were used to assess the relationship between the equilibrium index and center of pressure–derived balance measures. Intraclass correlations for absolute agreement and consistency were calculated to compare the equilibrium index and estimated equilibrium index. Results: Intraclass correlations demonstrated moderate consistency and absolute agreement (0.5 < intraclass correlation coefficient < 0.75) between the equilibrium index and estimated equilibrium index from the Equitest and VR sensory organization test (SOT), respectively, in four of six tested conditions. Additionally, weak to moderate correlations between force plate measurements and the equilibrium index were noted in several of the conditions. Conclusions: This research demonstrated the plausibility of using VR as an alternative method to conduct the SOT. Ongoing development and testing of virtual environments are necessary before employing the technology as a replacement to current clinical tests. (JMIR Serious Games 2020;8(4):e19580) doi: 10.2196/19580 KEYWORDS postural control; virtual reality; sensory organization test; intraclass correlations http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 1 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al drawbacks. When these technologies are combined, they greatly Introduction reduce the cost for a clinician to own testing equipment, as well as offer the opportunity to have a portable solution that could The Equitest system (Neurocom) is a computerized dynamic be taken into the field. Moreover, portable force plates present posturography device used by health care providers and clinical the possibility to record and assess a wider range of data, such researchers to safely test an individual’s postural control. as medial-lateral dynamics, and customize the outcomes to Implementing the sensory organization test (SOT) using the specific clinical goals. Likewise, VR headsets have continued Equitest system requires individuals to process and integrate to improve in quality and decrease in cost, and continued cues from the visual, vestibular, and proprioceptive systems. developments may lead to the ability to accurately track This test provides clinicians and researchers with an equilibrium movements in VR without additional hardware components score for each tested condition, a sensory analysis score, a such as force plates. strategy analysis, and a center of gravity (COG) alignment. While the Equitest system has evaluative and rehabilitative In keeping up with technological advancements, it is important value, it may be limited owing to its cost and lack of portability. to determine how new technologies can measure up to the “gold Moreover, the performance variables provided by the Equitest standards” they will eventually replace. Currently, VR is system are limited, representing gross outcome measures derived approaching this standard and is consistently shown to be a only from sagittal plane movement dynamics [1]. Recent valuable tool to conduct postural and motor control research. advances in technology provide opportunities to reduce these Previous research has found no difference between static balance limitations by providing more mobile and cost-effective tools in a physical environment versus a virtual environment [2]. while also observing a wider array of postural characteristics. Additionally, several scholars have supported the efficacy of The purpose of this research was to evaluate the validity of VR for use in balance assessments in a range of clinical using virtual reality (VR) and a force plate as an alternative to populations, such as those with concussion, stroke, Parkinson the Equitest system. disease, and high age [3-7]. Continuing in this trend, a large body of research has shown positive results in using VR to The SOT has been the dominant clinical test to assess sensory enhance training and rehabilitation for balance-related integration in the context of postural control for neurologic dysfunction [8-11]. Overall, VR has been demonstrated to disorders and deficits. With the wide use of clinical dynamic accurately assess balance in addition to providing a customizable posturography over the last 30 years, the Equitest system has means to enhance clinical outcomes. become widely accepted as the gold standard to assess postural stability and balance in several populations (eg, children, aging The purpose of this research was to compare the Equitest system adults, and military personnel) and clinical groups (eg, those to a VR balance assessment designed to mimic the SOT in a with concussion, vertigo, Parkinson disease, and Alzheimer young healthy population. It was hypothesized that the disease). By systematically disrupting the visual and equilibrium score would demonstrate high limits of agreement somatosensory information available to an individual, it is between the two testing conditions, supporting VR as a viable possible to distinguish someone’s reliance on the following option to decrease cost and increase the accessibility of postural three major sensory systems during balance tasks: the visual, assessment techniques. By illustrating the viability of VR to somatosensory, and vestibular systems. Conveniently, the emulate current clinical practices, future progress can focus on Equitest system provides an equilibrium score (indicating how improving and optimizing the implementation of VR in clinical little participants swayed) during each test, as well as a sensory standards of care and applications to more populations of analysis score (indicating how much they relied on each system) interest. and strategy analysis (indicating the hip versus ankle strategy) for the battery of conditions. Methods While the Equitest system provides a quick evaluative tool for Participants clinicians and researchers, it is not without limitations. First, A convenience sample of 20 college-aged individuals (Table these outcome measures are derived solely from sagittal plane 1) was recruited to participate in this study. All participants movements and may not reflect a complete assessment of an were healthy individuals with no prior history of neurological individual’s postural control. Second, the costs associated with or physical injury or dysfunction. Upon arrival, participants the Equitest system may limit its availability in underserved provided informed consent. All procedures were approved by communities or during times immediately following an injury the institutional review board, and no adverse events were (such as a sports concussion). As an alternative to the Equitest encountered. system, it may be possible to combine more recent technologies, that is, portable force plates and VR, to ameliorate these Table 1. Participant demographics. Characteristic Male (n=7), mean (SE) Female (n=13), mean (SE) Age (years) 20.8 (0.4) 20.9 (0.37) Height (m) 1.79 (0.03) 1.66 (0.02) Weight (kg) 77.4 (5.58) 62.8 (3.33) http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 2 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al tracking (Figure 1). The “no tracking” option creates an Experimental Design experience where the objects viewed move with the user’s head After providing informed consent, participants completed a as if they are attached. The second option, which is common in SOT in two blocks, using the Equitest system and using VR. first-generation VR headsets, such as the Oculus DK1 and Blocks of tests were counterbalanced, and conditions within Google Daydream, is somewhat natural until users lean in a blocks were randomized. direction that moves their torso. The last of these most closely During the Equitest SOT, participants wore a harness that mimics reality. supported their weight in case they lost balance. Researchers Balance was tested in the following conditions in the VR helped participants into the harness so it fit comfortably and environment: in a completely dark environment, eyes open in safely. The conditions during the clinical test included (1) eyes an environment that mimics the clinical test (6DoF tracking), open on a stable surface, (2) eyes closed on a stable surface, (3) eyes open in an environment that mimics the surround of the eyes open with a sway-referenced surround, (4) eyes open on clinical test and moves and rotates with the participant’s head a sway-referenced surface, (5) eyes closed on a sway-referenced (no tracking), and eyes open in an environment that mimics the surface, and (6) eyes open with both a sway-referenced surround surround of the clinical test and moves forward and backward and surface. with the participant’s head but does not react to head rotation In the VR SOT, participants removed any glasses and wore a (head tracking only). Each condition was completed on a stable head-mounted display (HTC Vive, HTC). Participants adjusted surface and on a foam surface. the headset to ensure clarity in the virtual environment using a For each balance condition, in both the clinical test and the VR black screen with a textbox. To compare our VR SOT to existing test, participants completed two trials of 20 seconds. The order SOT research performed with real machines, we created a virtual of the trials was counterbalanced between the clinical test and scale model of the patterns used inside of the Equitest balance VR blocks, and the order of the conditions was randomized system. We placed this model in the center of a white virtual within the clinical test and VR blocks. In total, participants testing room (10 m × 9 m in size). These models and the testing completed 28 trials (six clinical testing conditions × two trials software were created using Unity 3D (v. 2018.2.10f1; Unity each, four VR testing conditions × two surface conditions × two Technologies). Our software allowed us to test users with the trials each) of 20 seconds of stationary balance. All participants following three different types of VR tracking: no tracking, provided written consent prior to beginning the experimental head rotation tracking only, and six degrees of freedom (6DoF) protocol. Figure 1. Effect of the head tracking condition in virtual reality on a user's view with translation or rotation of the head. 6DoF: six degrees of freedom. a score of 100 would be received, and if the participant exhibits Data Reduction 12.5° or greater sway (combined forward and backward), a The Equitest system calculated the equilibrium index (EI) during score of 0 would be received. During the VR conditions, each SOT condition [12], and it represents the extent to which participants completed the test on top of a portable force plate a participant sways forward or backward within a theoretical (Bertec Inc) that collected center of pressure (COP) data at 50 limit of 12.5° of displacement. If the participant has no sway, Hz. Custom MATLAB (Mathworks Inc) scripts were used to http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 3 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al detrend and filter the data (20-ms moving average filter) and analysis. In this manner, one trial each from SOT 3 and SOT 4 subsequently calculate the estimated equilibrium index (eEI), was removed, along with their VR condition pair. 95% ellipse area, path length, and anterior-posterior (AP) Statistical Analysis detrended fluctuation analysis scaling exponent alpha (DFA α) To assess the relationship between EI and eEI, intraclass from the COP data. The 95% ellipse area, path length, and AP correlations of consistency and absolute agreement were DFA α calculations are described elsewhere and represent calculated for similar conditions (Table 2). Intraclass correlation typical spatiotemporal characteristics of balance [13,14]. The coefficient (ICC) values were interpreted as poor (<0.5), eEI metric was derived based on the EI used by the Equitest moderate (0.5-0.75), good (0.5-0.9), and excellent (>0.9) system. To simplify this process, the forward and backward reliability [15]. Additionally, Pearson correlation coefficients sway angles were calculated as the inverse sine function of the were calculated to quantify the extent to which force plate anterior and posterior COP displacement, respectively, divided measurements were associated with the EI calculated by the by an estimated COG height (56% of the participant height). Equitest system within similar conditions. Correlation The first trial of each condition served as a familiarization coefficients were interpreted as negligible (<0.3), weak (0.3-0.5), period, and only the final trial of each condition was used for moderate (0.5-0.7), strong (0.7-0.9), or very strong (>0.9) analysis. Data that were outside of three times the SD from the relationships between pairs of variables [16]. mean of its experimental condition were removed from the Table 2. Summary of all testing conditions, their abbreviations, and the quality of visual, somatosensory, and vestibular information available in the condition. Condition abbrevia- Equitest Virtual reality Information quality tion b c d e Eyes opened on a stable surface Stable virtual surround on a stable surface SOT 1 Vis –Som –Ves SOT 2 Eyes closed on a stable surface Blacked out environment on a stable sur- Som–Ves face SOT 3 Eyes opened with a sway-referenced surround Head-referenced virtual surround on a Vis–Som–Ves stable surface SOT 4 Eyes opened on a sway-referenced surface Stable virtual surround on a foam surface Vis–Som–Ves SOT 5 Eyes closed on a sway-referenced surface Blacked out environment on a foam sur- Som–Ves face SOT 6 Eyes opened with a sway-referenced surround and on a Head-referenced virtual surround on a Vis–Som–Ves sway-referenced surface foam surface In the column, normal text indicates accurate and italic text indicates inaccurate. SOT: sensory organization test. Vis: visual. Som: somatosensory. Ves: vestibular. (Figure 2). Visual inspection of the data indicated symmetry in Results most conditions and increased variability in the more challenging conditions (conditions 4-6). Data Presentation and Assessment of the Raw Data Boxplots of the data showing the median (thick line), IQR (box edges), and 95% CI (whiskers) for each condition were created http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 4 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Figure 2. Boxplots of all data collected in comparable SOT (light) and VR (dark) conditions. The median value (thick line), IQR (box edges), and 95% CI (whiskers) are indicated. SOT: sensory organization test; VR: virtual reality. 5 showed poor consistency and absolute agreement with similar Reliability of the eEI VR conditions. The Bland-Altman plots provide a visual Intraclass correlations between EI and eEI in similar conditions representation of agreement between two measurements by were evaluated and are presented alongside Bland-Altman plots plotting the absolute agreement or mean difference between in Figure 3 [17]. SOT conditions 1, 2, 3, and 6 demonstrated measurements on the vertical axis against the average of the moderate consistency and absolute agreement with their similar two measurements on the horizontal axis. VR condition counterparts. Meanwhile, SOT conditions 4 and http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 5 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Figure 3. Bland-Altman plots comparing the equilibrium index and estimated equilibrium index from the Equitest and VR SOT, respectively. The Pearson correlation coefficient (r), intraclass correlation coefficient for absolute agreement (ICCa), and intraclass correlation coefficient for consistency (ICCc) are provided. SOT: sensory organization test; VR: virtual reality. P=.005). Additionally, weak to moderate significant correlations Correlation of the EI With Force Plate Measurements were identified between EI and 95% ellipse area in conditions Pearson correlation coefficients were calculated between the 1 (r=−0.453, P=.045), 2 (r=−0.506, P=.02), and 6 (r=−0.500, Equitest EI and balance measures derived from COP data (Table P=.03) and AP DFA α in condition 1 (r=−0.511, P=.02). No 3). Weak to moderate significant correlations were identified other relevant correlations were identified between the Equitest between EI and eEI in SOT conditions 1 (r=0.454, P=.045), 2 EI and balance measurements derived from the COP data. (r=0.566, P=.009), 3 (r=0.652, P=.002), and 6 (r=0.597, http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 6 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Table 3. Pearson correlation coefficients between force plate measurements (columns) and the equilibrium index during each sensory organization test condition. a b Condition eEI 95% ellipse area Path length AP DFA α SOT 1 r 0.454 −0.453 −0.130 −0.511 P .045 .045 .59 .02 SOT 2 r 0.566 −0.506 −0.400 −0.041 P .009 .02 .08 .86 SOT 3 r 0.652 −0.329 −0.068 −0.234 P .002 .17 .78 .33 SOT 4 r 0.209 −0.143 −0.332 −0.007 P .39 .56 .16 .98 SOT 5 r 0.052 −0.242 −0.241 0.027 P .83 .30 .31 .91 SOT 6 r 0.597 −0.500 −0.334 −0.174 P .005 .03 .15 .46 eEI: estimated equilibrium index. AP DFA α: anterior-posterior detrended fluctuation analysis scaling exponent alpha. SOT: sensory organization test. measure aspects of how variability is structured in an individual Discussion plane. For example, 95% ellipse area quantifies the gross postural control behavior during quiet stance [18] and AP DFA This research has demonstrated the plausibility of using VR as α quantifies the structure of variability within an individual’s an alternative to the Equitest when conducting a SOT. Although AP sway trajectory (ie, how random or deterministic the data not a perfect replacement, eEI demonstrated reasonable is) [19], whereas EI evaluates how close an individual gets to correlations and ICCs with the clinical standard in several of a theoretical limit of stability [20]. The measures evaluated in the SOT conditions. Continued improvements to the VR testing this study were selected to represent a small array of postural environment need to be made to have more confidence in its control measurements, and future research should evaluate the use as a potential replacement. For example, the VR device may clinical utility of individual metrics. do a good job at mimicking the visual conditions of the SOT, but the foam mat might not equivocally disrupt somatosensory The recent surge in consumer-ready VR headsets has the information compared with the SOT. This is supported by seeing potential to greatly reduce the cost of conducting balance higher correlations between EI and eEI in the intact than assessments while also providing additional accessibility to inaccurate somatosensory conditions (conditions 1, 2, and 3 sites outside of the clinic, for example, on the sideline during versus conditions 4 and 5). Additionally, this study identified an athletic event. Likewise, using force plates opens access to a number of correlations between the Equitest system and typical raw, processed, and derived outcome measures that take balance measurements derived from COP data on a force plate. advantage of the full scope of postural dynamics and present Aside from eEI, 95% ellipse area and AP DFA α had some the opportunity to have more accurate information at the correlations with the clinical test. It is not surprising that these clinician’s disposal. In the future, it may even be possible to correlations were somewhat sparse as they distinctly measure accurately assess balance (and gait) using only the self-contained different characteristics of balance. The SOT measures only AP tracking of VR headsets. This research serves as a point from sway magnitude, while COP data can be used to calculate sway which we can merge motor control assessments with the magnitude in the frontal and sagittal planes combined or to accelerating advancements in consumer technologies. http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 7 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al Conflicts of Interest None declared. References 1. Chiarovano E, Wang W, Rogers SJ, MacDougall HG, Curthoys IS, de Waele C. Balance in Virtual Reality: Effect of Age and Bilateral Vestibular Loss. Front Neurol 2017;8:5 [FREE Full text] [doi: 10.3389/fneur.2017.00005] [Medline: 28163693] 2. Robert MT, Ballaz L, Lemay M. The effect of viewing a virtual environment through a head-mounted display on balance. Gait Posture 2016 Jul;48:261-266. [doi: 10.1016/j.gaitpost.2016.06.010] [Medline: 27344394] 3. Lloréns R, Noé E, Colomer C, Alcañiz M. Effectiveness, usability, and cost-benefit of a virtual reality-based telerehabilitation program for balance recovery after stroke: a randomized controlled trial. Arch Phys Med Rehabil 2015 Mar;96(3):418-425.e2 [FREE Full text] [doi: 10.1016/j.apmr.2014.10.019] [Medline: 25448245] 4. Mirelman A, Maidan I, Deutsch JE. Virtual reality and motor imagery: promising tools for assessment and therapy in Parkinson's disease. Mov Disord 2013 Sep 15;28(11):1597-1608 [FREE Full text] [doi: 10.1002/mds.25670] [Medline: 24132848] 5. Morel M, Bideau B, Lardy J, Kulpa R. Advantages and limitations of virtual reality for balance assessment and rehabilitation. Neurophysiol Clin 2015 Nov;45(4-5):315-326 [FREE Full text] [doi: 10.1016/j.neucli.2015.09.007] [Medline: 26527045] 6. Saldana S, Marsh AP, Rejeski WJ, Haberl J, Wu P, Rosenthal S, et al. Assessing balance through the use of a low-cost head-mounted display in older adults: a pilot study. Clin Interv Aging 2017;12:1363-1370 [FREE Full text] [doi: 10.2147/CIA.S141251] [Medline: 28883717] 7. Wright WG, McDevitt J, Tierney R, Haran FJ, Appiah-Kubi KO, Dumont A. Assessing subacute mild traumatic brain injury with a portable virtual reality balance device. Disabil Rehabil 2017 Jul;39(15):1564-1572 [FREE Full text] [doi: 10.1080/09638288.2016.1226432] [Medline: 27718642] 8. de Rooij IJ, van de Port IG, Meijer JW. Effect of Virtual Reality Training on Balance and Gait Ability in Patients With Stroke: Systematic Review and Meta-Analysis. Phys Ther 2016 Dec;96(12):1905-1918 [FREE Full text] [doi: 10.2522/ptj.20160054] [Medline: 27174255] 9. Meyns P, Pans L, Plasmans K, Heyrman L, Desloovere K, Molenaers G. The Effect of Additional Virtual Reality Training on Balance in Children with Cerebral Palsy after Lower Limb Surgery: A Feasibility Study. Games Health J 2017 Feb;6(1):39-48 [FREE Full text] [doi: 10.1089/g4h.2016.0069] [Medline: 28051880] 10. Villiger M, Liviero J, Awai L, Stoop R, Pyk P, Clijsen R, et al. Home-Based Virtual Reality-Augmented Training Improves Lower Limb Muscle Strength, Balance, and Functional Mobility following Chronic Incomplete Spinal Cord Injury. Front Neurol 2017;8:635 [FREE Full text] [doi: 10.3389/fneur.2017.00635] [Medline: 29234302] 11. Yen CY, Lin KH, Hu MH, Wu RM, Lu TW, Lin CH. Effects of virtual reality-augmented balance training on sensory organization and attentional demand for postural control in people with Parkinson disease: a randomized controlled trial. Phys Ther 2011 Jun;91(6):862-874 [FREE Full text] [doi: 10.2522/ptj.20100050] [Medline: 21474638] 12. Nashner LM. EquiTest system operator’s manual, version 4.04. Clackamas, OR, USA: NeuroCom International, Inc; 1992. 13. Duarte M, Freitas SM. Revision of posturography based on force plate for balance evaluation. Rev Bras Fisioter 2010;14(3):183-192. [Medline: 20730361] 14. Peng CK, Havlin S, Stanley HE, Goldberger AL. Quantification of scaling exponents and crossover phenomena in nonstationary heartbeat time series. Chaos 1995;5(1):82-87. [doi: 10.1063/1.166141] [Medline: 11538314] 15. Koo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. Journal of Chiropractic Medicine 2016 Jun;15(2):155-163 [FREE Full text] [doi: 10.1016/j.jcm.2016.02.012] 16. Mukaka MM. Statistics corner: A guide to appropriate use of correlation coefficient in medical research. Malawi Med J 2012 Sep;24(3):69-71 [FREE Full text] [Medline: 23638278] 17. Bland J, Altman D. Measuring agreement in method comparison studies. Stat Methods Med Res 1999 Jun 01;8(2):135-160 [FREE Full text] [doi: 10.1191/096228099673819272] 18. Strang AJ, Haworth J, Hieronymus M, Walsh M, Smart LJ. Structural changes in postural sway lend insight into effects of balance training, vision, and support surface on postural control in a healthy population. Eur J Appl Physiol 2011 Jul;111(7):1485-1495 [FREE Full text] [doi: 10.1007/s00421-010-1770-6] [Medline: 21165641] 19. Rhea CK, Silver TA, Hong SL, Ryu JH, Studenka BE, Hughes CM, et al. Noise and complexity in human postural control: interpreting the different estimations of entropy. PLoS One 2011 Mar 17;6(3):e17696 [FREE Full text] [doi: 10.1371/journal.pone.0017696] [Medline: 21437281] 20. Chaudhry H, Findley T, Quigley KS, Bukiet B, Ji Z, Sims T, et al. Measures of postural stability. J Rehabil Res Dev 2004 Sep;41(5):713-720 [FREE Full text] [doi: 10.1682/jrrd.2003.09.0140] [Medline: 15558401] Abbreviations 6DoF: six degrees of freedom AP: anterior-posterior COG: center of gravity http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 8 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Wittstein et al COP: center of pressure DFA α: detrended fluctuation analysis scaling exponent alpha eEI: estimated equilibrium index EI: equilibrium index ICC: intraclass correlation coefficient SOT: sensory organization test VR: virtual reality Edited by N Zary; submitted 23.04.20; peer-reviewed by PC Wang; comments to author 04.07.20; revised version received 10.09.20; accepted 13.11.20; published 16.12.20 Please cite as: Wittstein MW, Crider A, Mastrocola S, Guerena Gonzalez M JMIR Serious Games 2020;8(4):e19580 URL: http://games.jmir.org/2020/4/e19580/ doi: 10.2196/19580 PMID: 33325830 ©Matthew William Wittstein, Anthony Crider, Samantha Mastrocola, Mariana Guerena Gonzalez. Originally published in JMIR Serious Games (http://games.jmir.org), 16.12.2020. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR Serious Games, is properly cited. The complete bibliographic information, a link to the original publication on http://games.jmir.org, as well as this copyright and license information must be included. http://games.jmir.org/2020/4/e19580/ JMIR Serious Games 2020 | vol. 8 | iss. 4 | e19580 | p. 9 (page number not for citation purposes) XSL FO RenderX

Journal

JMIR Serious GamesJMIR Publications

Published: Dec 16, 2020

Keywords: postural control; virtual reality; sensory organization test; intraclass correlations

There are no references for this article.