Algorithm 2 The OSS method for SSVEP-BCI

Input:    Individual calibration data with subject-specific channels: ${\widehat{\mathit{X}}}_{e,1}\in {\mathbb{R}}^{N_{c1}\times N_s{N}_f \times { N}_t }$ Process: Obtaining eigenvalues by TRCA and descending sort ${\lambda }_1$ > ${\lambda }_2$> …> ${\lambda }_M$    For $m$ ← 1 to M:

Do compute ${\mu }_1\left(m\right)$ $, {\mu }_2\left(m\right)$ $\mathrm{by} \left(18\right) \mathrm{and} {\sigma }^2\left(m\right)$ by (19)        compute  $l\left(m\right)$ by (20) $N_{sp}$ $\mathrm{index}\left(\max \right\{ l\left(m\right)$})

Output: the number of optimal task-related subspaces $N_{sp}$