{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T01:59:40Z","timestamp":1760234380899,"version":"build-2065373602"},"reference-count":25,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2021,4,28]],"date-time":"2021-04-28T00:00:00Z","timestamp":1619568000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>Inducing self-motion illusions referred as vection are critical for improving the sensation of walking in virtual environments (VE). Adding viewpoint oscillations to a constant forward velocity in VE is effective for improving vection strength under static conditions. However, the effects of oscillation frequency and amplitude on vection strength under treadmill walking conditions are still unclear. Besides, due to the visuomotor entrainment mechanism, these visual oscillations would affect gait patterns and be detrimental for achieving natural walking if not properly designed. This study was aimed at determining the optimal frequency and amplitude of vertical viewpoint oscillations for improving vection strength and reducing gait constraints. Seven subjects walked on a treadmill while watching a visual scene. The visual scene presented a constant forward velocity equal to the treadmill velocity with different vertical viewpoint oscillations added. Five oscillation patterns with different combinations of frequency and amplitude were tested. Subjects gave verbal ratings of vection strength. The mediolateral (M-L) center of pressure (CoP) complexity was calculated to indicate gait constraints. After the experiment, subjects were asked to give the best and the worst oscillation pattern based on their walking experience. The oscillation frequency and amplitude had strong positive correlations with vection strength. The M-L CoP complexity was reduced under oscillations with low frequency. The medium oscillation amplitude had greater M-L CoP complexity than the small and large amplitude. Besides, subjects preferred those oscillation patterns with large gait complexity. We suggested that the oscillation amplitude with largest M-L CoP complexity should first be chosen to reduce gait constraints. Then, increasing the oscillation frequency to improve vection strength until individual preference or the boundary of motion sickness. These findings provide important guidelines to promote the sensation of natural walking in VE.<\/jats:p>","DOI":"10.3390\/e23050541","type":"journal-article","created":{"date-parts":[[2021,4,28]],"date-time":"2021-04-28T10:41:58Z","timestamp":1619606518000},"page":"541","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Optimal Frequency and Amplitude of Vertical Viewpoint Oscillation for Improving Vection Strength and Reducing Neural Constrains on Gait"],"prefix":"10.3390","volume":"23","author":[{"given":"Wei","family":"Wang","sequence":"first","affiliation":[{"name":"Beijing Key Laboratory of Precision and Ultra-Precision Manufacturing Equipment and Control, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China"}]},{"given":"Kaiming","family":"Yang","sequence":"additional","affiliation":[{"name":"Beijing Key Laboratory of Precision and Ultra-Precision Manufacturing Equipment and Control, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China"}]},{"given":"Yu","family":"Zhu","sequence":"additional","affiliation":[{"name":"Beijing Key Laboratory of Precision and Ultra-Precision Manufacturing Equipment and Control, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China"}]}],"member":"1968","published-online":{"date-parts":[[2021,4,28]]},"reference":[{"key":"ref_1","first-page":"1","article-title":"The benefits of using a walking interface to navigate virtual environments","volume":"16","author":"Roy","year":"2009","journal-title":"ACM Trans. Comput. Hum. Interact."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"153","DOI":"10.1016\/j.apergo.2018.01.009","article-title":"Immersion of virtual reality for rehabilitation\u2014Review","volume":"69","author":"Tyler","year":"2018","journal-title":"Appl. Ergon."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1109\/MCG.2018.021951633","article-title":"An analysis of VR technology used in immersive simulations with a serious game perspective","volume":"38","author":"Menin","year":"2018","journal-title":"IEEE Comput. Graph. Appl."},{"unstructured":"Gibson, J.J. (1966). The Senses Considered as Perceptual Systems, Houghton Mifflin.","key":"ref_4"},{"unstructured":"Gibson, J.J. (1950). Perception of the Visual World, Houghton Mifflin.","key":"ref_5"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1068\/p2990","article-title":"Global-perspective jitter improves vection in central vision","volume":"29","author":"Stephen","year":"2000","journal-title":"Perception"},{"unstructured":"Anatole, L., Jean, M.B., Jean, M.H., and Donikian, S. (2006, January 25\u201329). Camera motions improve the sensation of walking in virtual environments. Proceedings of the IEEE Virtual Reality Conference, Alexandria, VA, USA.","key":"ref_7"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"951","DOI":"10.3357\/ASEM.2079.2007","article-title":"Vertical display oscillation effects on forward vection and simulator sickness","volume":"78","author":"Stephen","year":"2007","journal-title":"Aviat. Space Environ. Med."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"562","DOI":"10.1068\/p7449","article-title":"Vection in depth during treadmill walking","volume":"42","author":"April","year":"2013","journal-title":"Perception"},{"doi-asserted-by":"crossref","unstructured":"So, R.H.Y., Wei, Y., and Chen, D.J.Z. (2017, January 24\u201327). Vection provoked by visual oscillation: Is frequency the major determining factor. Proceedings of the IEEE 6th Global Conference on Consumer Electronics, Nagoya, Japan.","key":"ref_10","DOI":"10.1109\/GCCE.2017.8229424"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1135","DOI":"10.1109\/TNSRE.2016.2603340","article-title":"Visuomotor entrainment and the frequency-dependent response of walking balance to perturbations","volume":"25","author":"Jason","year":"2017","journal-title":"IEEE Trans. Neural Syst. Rehabil. Eng."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1470","DOI":"10.1016\/j.jbiomech.2010.02.003","article-title":"Walking variability during continuous pseudo-random oscillations of the support surface and visual field","volume":"43","author":"Patricia","year":"2010","journal-title":"J. Biomech."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"322","DOI":"10.1177\/0142331219868924","article-title":"Speed adaptation and acceleration ripple suppression of treadmill user system using a virtual force moment balance model","volume":"42","author":"Wang","year":"2020","journal-title":"Trans. Inst. Meas. Control"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"109979","DOI":"10.1016\/j.jbiomech.2020.109979","article-title":"A comparison of variability and gait dynamics in spatiotemporal variables between different self-paced treadmill control modes","volume":"110","author":"Wang","year":"2020","journal-title":"J. Biomech."},{"key":"ref_15","first-page":"1","article-title":"The role of perceived speed in vection: Does perceived speed modulate the jitter and oscillation advantages?","volume":"9","author":"Deborah","year":"2014","journal-title":"PLoS ONE"},{"doi-asserted-by":"crossref","unstructured":"Stephen, P., and Bernhard, E.R. (2018). The search for instantaneous vection: An oscillating visual prime reduces vection onset latency. PLoS ONE, 13.","key":"ref_16","DOI":"10.1371\/journal.pone.0195886"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"21003","DOI":"10.1115\/1.4049964","article-title":"Walking speed estimation from a wearable insole pressure system embedded with an accelerometer using Bayesian neural network","volume":"4","author":"Wei","year":"2021","journal-title":"ASME J. Med. Diagn."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"903","DOI":"10.1098\/rspa.1998.0193","article-title":"The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis","volume":"454","author":"Norden","year":"1998","journal-title":"Proc. R. Soc. Lond. A"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1142\/S1793536909000047","article-title":"Ensemble empirical mode decomposition: A noise-assisted data analysis method","volume":"1","author":"Zhao","year":"2009","journal-title":"Advan. Adapt. Data Analy."},{"unstructured":"Flandrin, P., Goncalves, P., and Rilling, G. (2004, January 6\u201310). Detrending and denoising with empirical mode decomposition. Proceedings of the 12th European Signal Processing Conference, Vienna, Austria.","key":"ref_20"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"7926","DOI":"10.3390\/e17127849","article-title":"Multiscale entropy analysis of center of pressure dynamics in human postural control: Methodological considerations","volume":"17","author":"Brian","year":"2015","journal-title":"Entropy"},{"key":"ref_22","first-page":"42","article-title":"Approximate entropy detects the effect of a secondary cognitive task on postural control in healthy young adults: A methodological report","volume":"4","author":"James","year":"2009","journal-title":"J. NeuroEng. Rehabil."},{"doi-asserted-by":"crossref","unstructured":"Ben, Y.L., Fu, L.W., Chi, W.L., Xue, Y.Z., Xiao, L.W., and Yih, K.J. (2019). Complexity-Based Measures of Postural Sway during Walking at Different Speeds and Durations Using Multiscale Entropy. Entropy, 21.","key":"ref_23","DOI":"10.3390\/e21111128"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"109377","DOI":"10.1016\/j.jbiomech.2019.109377","article-title":"Complexity, symmetry and variability of forward and backward walking at different speeds and transfer effects on forward walking: Implications for neural control","volume":"97","author":"Gregory","year":"2019","journal-title":"J. Biomech."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1016\/j.physa.2003.08.022","article-title":"Multiscale entropy analysis of human gait dynamics","volume":"330","author":"Damasio","year":"2003","journal-title":"Physica A Statis. Mecha. Appl."}],"container-title":["Entropy"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1099-4300\/23\/5\/541\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:54:31Z","timestamp":1760162071000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1099-4300\/23\/5\/541"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,4,28]]},"references-count":25,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2021,5]]}},"alternative-id":["e23050541"],"URL":"https:\/\/doi.org\/10.3390\/e23050541","relation":{},"ISSN":["1099-4300"],"issn-type":[{"type":"electronic","value":"1099-4300"}],"subject":[],"published":{"date-parts":[[2021,4,28]]}}}