Asynchronous Control of P300-Based Brain–Computer Interfaces Using Sample Entropy

Abstract

Brain–computer interfaces (BCI) have traditionally worked using synchronous paradigms. In recent years, much effort has been put into reaching asynchronous management, providing users with the ability to decide when a command should be selected. However, to the best of our knowledge, entropy metrics have not yet been explored. The present study has a twofold purpose: (i) to characterize both control and non-control states by examining the regularity of electroencephalography (EEG) signals; and (ii) to assess the efficacy of a scaled version of the sample entropy algorithm to provide asynchronous control for BCI systems. Ten healthy subjects participated in the study, who were asked to spell words through a visual oddball-based paradigm, attending (i.e., control) and ignoring (i.e., non-control) the stimuli. An optimization stage was performed for determining a common combination of hyperparameters for all subjects. Afterwards, these values were used to discern between both states using a linear classifier. Results show that control signals are more complex and irregular than non-control ones, reaching an average accuracy of 94.40 % in classification. In conclusion, the present study demonstrates that the proposed framework is useful in monitoring the attention of a user, and granting the asynchrony of the BCI system.

Correction: Martínez-Cagigal, V.; Santamaría-Vázquez, E.; Hornero, R. Asynchronous Control of P300-Based Brain–Computer Interfaces Using Sample Entropy. Entropy 2019, 21, 230

“…Figure 5 of the original paper contains errors [ 1 ]. However, the issue has no direct consequence on the manuscript, since the discussion and conclusions were made according to the corrected figure, which is shown below:…”

Toward Practical P300-based Brain–Computer Interfaces: Asynchrony, Channel Optimization and Assistive Applications

“…In this case, signals were band-pass filtered between 0.1-60 Hz and then, a 50 Hz notch filter was applied to remove the power interference. For the offline studies, finite impulse response (FIR) filters were used (Martínez-Cagigal et al, 2019b, 2020; for the online ones, infinite impulse response (IIR) filters were applied , 2019a.…”

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According to this non-chronological order, the first two papers were focused on the signal processing level, whereas the last two were aimed at providing assistive applications. The first paper (Martínez-Cagigal et al, 2019b) dealt with the need of supervision of current BCIs. Nowadays, most P300-based BCIs rely on synchronous paradigms, leading to a random selection of commands even when 1.1.

…”

“…Therefore, Appendix A includes the aforementioned manuscripts. Titles, authors, and abstracts of each one, as well as the journals in which they were published are shown below:Asynchronous control of P300-based Brain-Computer Interfaces using sample entropy (Martínez-Cagigal et al, 2019b).…”

“…Asynchronous control of P300-based Brain-Computer Interfaces using sample entropy (Martínez-Cagigal et al, 2019b).…”