{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T16:30:36Z","timestamp":1791217836011,"version":"4.1.0"},"reference-count":48,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2021,2,26]],"date-time":"2021-02-26T00:00:00Z","timestamp":1614297600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Hum. Neurosci."],"abstract":"<jats:p>CYBATHLON is an international championship where people with severe physical disabilities compete with the aid of state-of-the-art assistive technology. In one of the disciplines, the BCI Race, tetraplegic pilots compete in a computer game race by controlling an avatar with a brain-computer interface (BCI). This competition offers a perfect opportunity for BCI researchers to study long-term training effects in potential end-users, and to evaluate BCI performance in a realistic environment. In this work, we describe the BCI system designed by the team Mirage91 for participation in the CYBATHLON BCI Series 2019, as well as in the CYBATHLON 2020 Global Edition. Furthermore, we present the BCI\u2019s interface with the game and the main methodological strategies, along with a detailed evaluation of its performance over the course of the training period, which lasted 14 months. The developed system was a 4-class BCI relying on task-specific modulations of brain rhythms. We implemented inter-session transfer learning to reduce calibration time, and to reinforce the stability of the brain patterns. Additionally, in order to compensate for potential intra-session shifts in the features\u2019 distribution, normalization parameters were continuously adapted in an unsupervised fashion. Across the aforementioned 14 months, we recorded 26 game-based training sessions. Between the first eight sessions, and the final eight sessions leading up to the CYBATHLON 2020 Global Edition, the runtimes significantly improved from 255 \u00b1 23 s (mean \u00b1 std) to 225 \u00b1 22 s, respectively. Moreover, we observed a significant increase in the classifier\u2019s accuracy from 46 to 53%, driven by more distinguishable brain patterns. Compared to conventional single session, non-adaptive BCIs, the inter-session transfer learning and unsupervised intra-session adaptation techniques significantly improved the performance. This long-term study demonstrates that regular training helped the pilot to significantly increase the distance between task-specific patterns, which resulted in an improvement of performance, both with respect to class separability in the calibration data, and with respect to the game. Furthermore, it shows that our methodological approaches were beneficial in transferring the performance across sessions, and most importantly to the CYBATHLON competitions.<\/jats:p>","DOI":"10.3389\/fnhum.2021.635777","type":"journal-article","created":{"date-parts":[[2021,2,26]],"date-time":"2021-02-26T06:47:56Z","timestamp":1614322076000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":30,"title":["Long-Term Mutual Training for the CYBATHLON BCI Race With a Tetraplegic Pilot: A Case Study on Inter-Session Transfer and Intra-Session Adaptation"],"prefix":"10.3389","volume":"15","author":[{"given":"Lea","family":"Hehenberger","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Reinmar J.","family":"Kobler","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Catarina","family":"Lopes-Dias","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nitikorn","family":"Srisrisawang","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter","family":"Tumfart","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"John B.","family":"Uroko","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Paul R.","family":"Torke","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gernot R.","family":"M\u00fcller-Putz","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2021,2,26]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"103","DOI":"10.1016\/j.jneumeth.2015.01.033","article-title":"Performance variation in motor imagery brain\u2013computer interface: a brief review.","volume":"243","author":"Ahn","year":"2015","journal-title":"J. Neurosci. Methods"},{"key":"B2","doi-asserted-by":"publisher","DOI":"10.1109\/ijcnn.2008.4634130","article-title":"Filter bank common spatial pattern (FBCSP) in brain-computer interface","author":"Ang","year":"2008","journal-title":"Proceddings of the 2008 IEEE International Joint Conference on Neural Networks (IEEE World Congress on Computational Intelligence)"},{"key":"B3","doi-asserted-by":"publisher","DOI":"10.1109\/iembs.2009.5335381","article-title":"A clinical study of motor imagery-based brain-computer interface for upper limb robotic rehabilitation","author":"Ang","year":"2009","journal-title":"Proceedings of the 2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society"},{"key":"B4","doi-asserted-by":"publisher","first-page":"289","DOI":"10.1111\/j.2517-6161.1995.tb02031.x","article-title":"Controlling the false discovery rate: a practical and powerful approach to multiple testing.","volume":"57","author":"Benjamini","year":"1995","journal-title":"J. R. Stat. Soc. Ser. B Stat. Methodol."},{"key":"B5","doi-asserted-by":"publisher","first-page":"814","DOI":"10.1016\/j.neuroimage.2010.06.048","article-title":"Single-trial analysis and classification of ERP components \u2014 a tutorial.","volume":"56","author":"Blankertz","year":"2011","journal-title":"Neuroimage"},{"key":"B6","doi-asserted-by":"publisher","first-page":"41","DOI":"10.1109\/msp.2008.4408441","article-title":"Optimizing spatial filters for robust EEG single-trial analysis.","volume":"25","author":"Blankertz","year":"2008","journal-title":"IEEE Signal Process. Mag."},{"key":"B7","doi-asserted-by":"publisher","first-page":"433","DOI":"10.1163\/156856897x00357","article-title":"The psychophysics toolbox.","volume":"10","author":"Brainard","year":"1997","journal-title":"Spat. Vis."},{"key":"B8","doi-asserted-by":"publisher","first-page":"9","DOI":"10.1016\/j.jneumeth.2003.10.009","article-title":"EEGLAB: an open source toolbox for analysis of single-trial EEG dynamics including independent component analysis.","volume":"134","author":"Delorme","year":"2004","journal-title":"J. Neurosci. Methods"},{"key":"B9","doi-asserted-by":"publisher","first-page":"86","DOI":"10.1016\/j.ijpsycho.2012.01.014","article-title":"The effect of distinct mental strategies on classification performance for brain-computer interfaces.","volume":"84","author":"Friedrich","year":"2012","journal-title":"Int. J. Psychophysiol."},{"key":"B10","doi-asserted-by":"publisher","first-page":"43","DOI":"10.1016\/s1388-2457(01)00697-6","article-title":"Visualization of significant ERD\/ERS patterns in multichannel EEG and ECoG data.","volume":"113","author":"Graimann","year":"2002","journal-title":"Clin. Neurophysiol."},{"key":"B11","doi-asserted-by":"crossref","first-page":"49","DOI":"10.1109\/7333.918276","article-title":"Rapid prototyping of an EEG-based brain-computer interface (BCI).","volume":"9","author":"Guger","year":"2001","journal-title":"IEEE Trans. Neural Syst. Rehabil. Eng."},{"key":"B12","first-page":"5150","article-title":"HEAR to remove pops and drifts: the high-variance electrode artifact removal (HEAR) algorithm.","volume":"2019","author":"Kobler","year":"2019","journal-title":"Conf. Proc. IEEE Eng. Med. Biol. Soc."},{"key":"B13","doi-asserted-by":"crossref","first-page":"000469","DOI":"10.1109\/SMC.2016.7844284","article-title":"Restricted Boltzmann machines in sensory motor rhythm brain-computer interfacing: a study on inter-subject transfer and co-adaptation","author":"Kobler","year":"2016","journal-title":"Proceedings of the 2016 IEEE International Conference on Systems, Man, and Cybernetics (SMC)"},{"key":"B14","doi-asserted-by":"publisher","first-page":"1775","DOI":"10.1212\/01.wnl.0000158616.43002.6d","article-title":"Patients with ALS can use sensorimotor rhythms to operate a brain-computer interface.","volume":"64","author":"K\u00fcbler","year":"2005","journal-title":"Neurology"},{"key":"B15","doi-asserted-by":"publisher","first-page":"969","DOI":"10.1109\/jproc.2015.2419736","article-title":"Towards independence: a BCI telepresence robot for people with severe motor disabilities.","volume":"103","author":"Leeb","year":"2015","journal-title":"Proc. IEEE"},{"key":"B16","doi-asserted-by":"publisher","DOI":"10.1088\/1741-2552\/aab2f2","article-title":"A review of classification algorithms for EEG-based brain\u2013computer interfaces: a 10 year update.","volume":"15","author":"Lotte","year":"2018","journal-title":"J. Neural Eng."},{"key":"B17","doi-asserted-by":"publisher","DOI":"10.1109\/iww-bci.2015.7073024","article-title":"Towards improved BCI based on human learning principles","author":"Lotte","year":"2015","journal-title":"Proceedings of the 3rd International Winter Conference on Brain-Computer Interface"},{"key":"B18","doi-asserted-by":"publisher","DOI":"10.1088\/1741-2552\/aba162","article-title":"BCI for stroke rehabilitation: motor and beyond.","volume":"17","author":"Mane","year":"2020","journal-title":"J. Neural Eng."},{"key":"B19","doi-asserted-by":"publisher","first-page":"177","DOI":"10.1016\/j.jneumeth.2007.03.024","article-title":"Nonparametric statistical testing of EEG- and MEG-data.","volume":"164","author":"Maris","year":"2007","journal-title":"J. Neurosci. Methods"},{"key":"B20","doi-asserted-by":"publisher","first-page":"167","DOI":"10.1016\/j.neuroimage.2015.02.015","article-title":"Learning a common dictionary for subject-transfer decoding with resting calibration.","volume":"111","author":"Morioka","year":"2015","journal-title":"Neuroimage"},{"key":"B21","doi-asserted-by":"publisher","first-page":"1410","DOI":"10.1152\/jn.00918.2015","article-title":"Efficient neuroplasticity induction in chronic stroke patients by an associative brain-computer interface.","volume":"115","author":"Mrachacz-Kersting","year":"2016","journal-title":"J. Neurophysiol."},{"key":"B22","first-page":"5949","article-title":"Applying intuitive EEG-controlled grasp neuroprostheses in individuals with spinal cord injury: preliminary results from the MoreGrasp clinical feasibility study.","volume":"2019","author":"M\u00fcller-Putz","year":"2019","journal-title":"Conf. Proc. IEEE Eng. Med. Biol. Soc."},{"key":"B23","doi-asserted-by":"publisher","DOI":"10.3389\/fnins.2010.00034","article-title":"Temporal coding of brain patterns for direct limb control in humans.","volume":"4","author":"M\u00fcller-Putz","year":"2010","journal-title":"Front. Neurosci."},{"key":"B24","first-page":"3353","article-title":"Non-invasive control of neuroprostheses for the upper extremity: temporal coding of brain patterns.","volume":"2009","author":"M\u00fcller-Putz","year":"2009","journal-title":"Conf. Proc. IEEE Eng. Med. Biol. Soc."},{"key":"B25","doi-asserted-by":"publisher","first-page":"399","DOI":"10.1016\/s1388-2457(02)00387-5","article-title":"Clinical application of an EEG-based brain\u2013computer interface: a case study in a patient with severe motor impairment.","volume":"114","author":"Neuper","year":"2003","journal-title":"Clin. Neurophysiol."},{"key":"B26","doi-asserted-by":"publisher","first-page":"668","DOI":"10.1016\/j.cogbrainres.2005.08.014","article-title":"Imagery of motor actions: differential effects of kinesthetic and visual-motor mode of imagery in single-trial EEG.","volume":"25","author":"Neuper","year":"2005","journal-title":"Brain Res. Cogn. Brain Res."},{"key":"B27","doi-asserted-by":"publisher","first-page":"1","DOI":"10.1002\/hbm.1058","article-title":"Nonparametric permutation tests for functional neuroimaging: a primer with examples.","volume":"15","author":"Nichols","year":"2002","journal-title":"Hum. Brain Mapp."},{"key":"B28","doi-asserted-by":"publisher","DOI":"10.3389\/fnins.2017.00756","article-title":"Benchmarking brain-computer interfaces outside the laboratory: the cybathlon 2016.","volume":"11","author":"Novak","year":"2017","journal-title":"Front. Neurosci."},{"key":"B29","doi-asserted-by":"publisher","first-page":"437","DOI":"10.1163\/156856897x00366","article-title":"The videotoolbox software for visual psychophysics: transforming numbers into movies.","volume":"10","author":"Pelli","year":"1997","journal-title":"Spat. Vis."},{"key":"B30","doi-asserted-by":"publisher","first-page":"12","DOI":"10.1109\/msmc.2019.2958200","article-title":"Brain-machine interfaces: a tale of two learners.","volume":"6","author":"Perdikis","year":"2020","journal-title":"IEEE Syst. Man Cybernet. Mag."},{"key":"B31","doi-asserted-by":"publisher","DOI":"10.1088\/1741-2560\/13\/3\/036018","article-title":"Context-aware adaptive spelling in motor imagery BCI.","volume":"13","author":"Perdikis","year":"2016","journal-title":"J. Neural Eng."},{"key":"B32","doi-asserted-by":"publisher","DOI":"10.1371\/journal.pbio.2003787","article-title":"The cybathlon BCI race: successful longitudinal mutual learning with two tetraplegic users.","volume":"16","author":"Perdikis","year":"2018","journal-title":"PLoS Biol."},{"key":"B33","doi-asserted-by":"publisher","first-page":"211","DOI":"10.1016\/s0304-3940(00)01471-3","article-title":"Brain oscillations control hand orthosis in a tetraplegic.","volume":"292","author":"Pfurtscheller","year":"2000","journal-title":"Neurosci. Lett."},{"key":"B34","doi-asserted-by":"publisher","first-page":"248","DOI":"10.1007\/bfb0100491","article-title":"EEG-based brain-computer interface using subject-specific spatial filters","author":"Pfurtscheller","year":"1999","journal-title":"Engineering Applications of Bio-Inspired Artificial Neural Networks. IWANN 1999. Lecture Notes in Computer Science"},{"key":"B35","doi-asserted-by":"publisher","first-page":"1842","DOI":"10.1016\/s1388-2457(99)00141-8","article-title":"Event-related EEG\/MEG synchronization and desynchronization: basic principles.","volume":"110","author":"Pfurtscheller","year":"1999","journal-title":"Clin. Neurophysiol."},{"key":"B36","doi-asserted-by":"publisher","first-page":"1123","DOI":"10.1109\/5.939829","article-title":"Motor imagery and direct brain-computer communication.","volume":"89","author":"Pfurtscheller","year":"2001","journal-title":"Proc. IEEE"},{"key":"B37","doi-asserted-by":"publisher","first-page":"441","DOI":"10.1109\/86.895946","article-title":"Optimal spatial filtering of single trial EEG during imagined hand movement.","volume":"8","author":"Ramoser","year":"2000","journal-title":"IEEE Trans. Rehabil. Eng."},{"key":"B38","doi-asserted-by":"crossref","DOI":"10.1186\/s12984-016-0157-2","article-title":"The cybathlon promotes the development of assistive technology for people with physical disabilities.","volume":"13","author":"Riener","year":"2016","journal-title":"J. Neuroeng. Rehabil."},{"key":"B39","doi-asserted-by":"publisher","first-page":"380","DOI":"10.1109\/tnsre.2016.2645681","article-title":"Long-term stable control of motor-imagery BCI by a locked-in user through adaptive assistance.","volume":"25","author":"Saeedi","year":"2017","journal-title":"IEEE Trans. Neural Syst. Rehabil. Eng."},{"key":"B40","doi-asserted-by":"publisher","first-page":"50","DOI":"10.1109\/rbme.2013.2290621","article-title":"Divergence-based framework for common spatial patterns algorithms.","volume":"7","author":"Samek","year":"2014","journal-title":"IEEE Rev. Biomed. Eng."},{"key":"B41","doi-asserted-by":"crossref","DOI":"10.2202\/1544-6115.1175","article-title":"A shrinkage approach to large-scale covariance matrix estimation and implications for functional genomics.","volume":"4","author":"Sch\u00e4fer","year":"2005","journal-title":"Stat. Appl. Genet. Mol. Biol."},{"key":"B42","doi-asserted-by":"crossref","DOI":"10.1186\/s12984-017-0344-9","article-title":"Cybathlon experiences of the Graz BCI racing team Mirage91 in the brain-computer interface discipline.","volume":"14","author":"Statthaler","year":"2017","journal-title":"J. Neuroeng. Rehabil."},{"key":"B43","first-page":"2579","article-title":"Visualizing data using t-SNE.","volume":"9","author":"van der Maaten","year":"2008","journal-title":"J. Mach. Learn. Res."},{"key":"B44","doi-asserted-by":"publisher","first-page":"587","DOI":"10.1109\/tbme.2010.2093133","article-title":"Toward unsupervised adaptation of LDA for brain-computer interfaces.","volume":"58","author":"Vidaurre","year":"","journal-title":"IEEE Trans. Biomed. Eng."},{"key":"B45","doi-asserted-by":"publisher","DOI":"10.1088\/1741-2560\/8\/2\/025009","article-title":"Co-adaptive calibration to improve BCI efficiency.","volume":"8","author":"Vidaurre","year":"","journal-title":"J. Neural Eng."},{"key":"B46","doi-asserted-by":"crossref","first-page":"767","DOI":"10.1016\/S1388-2457(02)00057-3","article-title":"Brain-computer interfaces for communication and control.","volume":"113","author":"Wolpaw","year":"2002","journal-title":"Clin. Neurophysiol."},{"key":"B47","doi-asserted-by":"publisher","first-page":"17849","DOI":"10.1073\/pnas.0403504101","article-title":"Control of a two-dimensional movement signal by a noninvasive brain-computer interface in humans.","volume":"101","author":"Wolpaw","year":"2004","journal-title":"Proc. Natl. Acad. Sci. U.S.A."},{"key":"B48","doi-asserted-by":"publisher","first-page":"1107","DOI":"10.1109\/tbme.2017.2742541","article-title":"Transfer learning: a Riemannian geometry framework with applications to brain-computer interfaces.","volume":"65","author":"Zanini","year":"2018","journal-title":"IEEE Trans. Biomed. Eng."}],"container-title":["Frontiers in Human Neuroscience"],"original-title":[],"link":[{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fnhum.2021.635777\/full","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2021,2,26]],"date-time":"2021-02-26T06:48:04Z","timestamp":1614322084000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fnhum.2021.635777\/full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,2,26]]},"references-count":48,"alternative-id":["10.3389\/fnhum.2021.635777"],"URL":"https:\/\/doi.org\/10.3389\/fnhum.2021.635777","relation":{},"ISSN":["1662-5161"],"issn-type":[{"value":"1662-5161","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,2,26]]},"article-number":"635777"}}