Fig 1.
Comparison of mental load between the evoked EEG and ongoing EEG in both of flickering SSVEP-BCI and motion-reversal SSMVEP-BCI tasks for individual subjects.
The mean values and SD of the ratio index θ/α of individual subjects within SSVEP-BCI and SSMVEP-BCI tasks were calculated. All statistics were assessed by unbalanced one-way ANOVA, *** p < 0.001 between evoked EEG and ongoing EEG, ** p < 0.01 between evoked EEG and ongoing EEG.
Fig 2.
Comparison of the mean values and SD of mental load score between flickering SSVEP-BCI and motion-reversal SSMVEP-BCI task conditions over subjects.
The mean values and SD of the normalized power indices α and θ and ratio index θ/α were calculated from evoked EEG over nine subjects. Horizontal axis: SSVEP—flickering SSVEP-BCI task condition; SSMVEP—motion-reversal SSMVEP-BCI task condition. All statistics were assessed by one-way ANOVA, *** p < 0.001 between evoked EEG in SSVEP-BCI and SSMVEP-BCI tasks.
Fig 3.
Grand-averaged SSVEP and SSMVEP spectra at fatigue level 1 and level 4 states over nine subjects.
(A) Grand-averaged SSVEP spectrum. (B) Grand-averaged SSMVEP spectrum. Fatigue level 1: spectral power calculated from the first five epochs of each run in SSVEP-BCI and SSMVEP-BCI tasks; Fatigue level 4: spectral power calculated from the last five epochs of each run.
Fig 4.
Comparison of SSVEP and SSMVEP amplitudes between four different fatigue levels for individual subjects.
All statistics were assessed by one-way ANOVA, *** p < 0.001 between four different fatigue levels in both of SSVEP-BCI and SSMVEP-BCI tasks, ** p < 0.01 between four different fatigue levels, * p < 0.05 between four different fatigue levels.
Fig 5.
Comparison of SSVEP and SSMVEP SNRs between four different fatigue levels for individual subjects.
All statistics were assessed by one-way ANOVA, *** p < 0.001 between four different fatigue levels in both of SSVEP-BCI and SSMVEP-BCI tasks, ** p < 0.01 between four different fatigue levels, * p < 0.05 between four different fatigue levels.
Table 1.
Statistical summary of the amplitude variations under fatigue level 1 and 4 for individual subjects.
Table 2.
Statistical summary of the SNR variations under fatigue level 1 and 4 for individual subjects.
Fig 6.
Comparison of the mean values and SD of fatigue score between fatigue level 1 and 4 in both of flickering SSVEP-BCI and motion-reversal SSMVEP-BCI conditions over subjects.
(A) Comparison of fatigue between fatigue level 1 and 4 in SSVEP-BCI condition. (B) Comparison of fatigue between fatigue level 1 and 4 in SSMVEP-BCI condition. The mean values and SD of the normalized power indices α, θ and θ + α were calculated from ongoing EEG over nine subjects. Horizontal axis: Level 1—fatigue level 1 state; Level 4—fatigue level 4 state. All statistics were assessed by one-way ANOVA, *** p < 0.001 between ongoing EEG in SSVEP-BCI and SSMVEP-BCI conditions, * p < 0.05 between ongoing EEG in SSVEP-BCI and SSMVEP-BCI conditions.