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Review of Riemannian Distances and Divergences, Applied to SSVEP-based BCI

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Abstract

The firstgeneration of brain-computer interfaces (BCI) classifies multi-channel electroencephalographic (EEG) signals, enhanced by optimized spatial filters.The second generation directly classifies covariance matrices estimated on EEG signals, based on straightforward algorithms such as the minimum-distance-to-Riemannian-mean (MDRM). Classification results vary greatly depending on the chosen Riemannian distance or divergence, whose definitions and reference implementations are spread across a wide mathematical literature. This paper reviews all the Riemannian distances and divergences to process covariance matrices, with an implementation compatible with BCI constraints. The impact of using different metrics is assessed on a steady-state visually evoked potentials (SSVEP) dataset, evaluating centers of classes and classification accuracy. Riemannian approaches embed crucial properties to process EEG data. The Riemannian centers of classes outperform Euclidean ones both in offline and online setups. Some Riemannian distances and divergences have better performances in terms of classification accuracy, while others have appealing computational efficiency.

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Acknowledgments

This work has been done without any support of the ANR or the ERC.

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Correspondence to S. Chevallier.

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Conflict of interests

At the time this study was carried out, Emmanuel Kalunga was an employee of VASTech company, Stellenbosch, South Africa; and Quentin Barthélemy was an employee of Mensia Technologies S.A., Paris, France. Sylvain Chevallier and Eric Monacelli declare that they have no conflict of interest. This study was conducted by the authors without any specific funding or grant.

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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Chevallier, S., Kalunga, E.K., Barthélemy, Q. et al. Review of Riemannian Distances and Divergences, Applied to SSVEP-based BCI. Neuroinform 19, 93–106 (2021). https://doi.org/10.1007/s12021-020-09473-9

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