Table 1.

Characteristics of papers investigating mental fatigue in SSVEP-based BCIs.

Number	Paper	Number of Subjects	Stimulation Frequency (HZ)	Number of Classes	Channels	Distance (cm)	Inter-Trial Interval (s)	Stimuli Durations (s)	Subjects’ Age	Subject’s Conditions	Stimulation’s Design	Cue’s Color	Objective Evaluation	Subjective Index
1	Chai et al. (2019)	8	8, 9, 10, 11, 12, 13, 14, 15	8	8 channels (PO8, PO4, PO7, PO3, POz, O1, Oz, and O2)	70	1.5	4	22–27 years old.	Normal visual acuity	Motion	Color ranges from white to black	Accuracy, ITR	Custom questionnaire (Bieger and Molina, 2010)
2	Zheng et al. (2020)	12	7.5	1	6 channels (PO3, PO4, POz, O1, O2, and Oz)	60	0.5	5	21–25 years old.	Normal visual acuity	Motion	Color ranges from white to black	SNR, SSVEP amplitude, $\alpha +\theta$	NASA-TLX
3	Seo et al. (2019)	54	12, 8.57, 6.67, 5.45	4	62 channels	60	4	4	24–35 years old.	Normal visual acuity	Flicker	white	$\alpha$, signal quality	Likert Scale
4	Xie et al. (2016)	9	8, 12, 13.33, 15	4	1 channel (Oz)	70	5	5	23–29 years old.	Normal visual acuity	Motion	Color ranges from white to black	$\alpha$, $\theta$, $\theta +\alpha$,$\theta /\alpha$, SSVEP amplitude, SNR	…
5	Dang et al. (2021)	8	6.67, 7.5, 8.75, 10, 12	5	8 channels (T5, P3, Pz, P4, T6, O1, Oz, and O2)	…	2	3	…	Normal visual acuity	Motion	Color ranges from white to black	Accuracy	Chalder Fatigue Scale (CFS) (Chalder et al., 1993)
6	Peng et al. (2021)	11	8, 10, 12, 15, 20, 30	6	1 channel (Oz)	50	3	3	21–29 years old.	Normal visual acuity	Flicker	white	$\alpha$, $\beta$, $\theta$, $\delta$, $\frac{\alpha +\theta }{\beta }$, $\alpha /\beta$, $\theta /\beta$, $\theta /\alpha$ $\theta +\alpha$, $\theta +\alpha +\beta$, SNR, sample entropy	Chalder Fatigue Scale (CFS)
7	Peng et al. (2019)	12	8, 10, 12, 15, 20, 30	6	1 channel (Oz)	50	3	3	21–29 years old.	Normal visual acuity	Flicker	white	$\alpha$, $\beta$, $\theta$, $\delta$, $\frac{\alpha +\theta }{\beta }$, $\alpha /\beta$, $\theta /\beta$, $\theta /\alpha$ $\theta +\alpha$, $\theta +\alpha +\beta$, SNR, MSE	Chalder Fatigue Scale (CFS)
8	Cao et al. (2014)	8	15	1	1 channel (Oz)	50	2	3	21–29 years old.	Normal visual acuity	Flicker	white	$\alpha$,$\left(\theta +\alpha \right)/\beta$, $\theta /\alpha$, SSVEP amplitude, SNR	Chalder Fatigue Scale (CFS)
		13	7–12	6
			13–18	6
9	Benda et al. (2018)	8	6.32, 7.06, 8, 9.23	4	8 channels (Pz, PO3, PO4, O1, O2, Oz, O9, and O10)	60	…	…	Average 28.13 years old.	Normal visual acuity	Flicker	white	$\alpha$, $\beta$, $\theta$, $\delta$,$\theta /\alpha$, $\frac{\alpha +\theta }{\beta }$	Chalder Fatigue Scale (CFS)
10	Keihani et al. (2018)	22	25, 30, 35	3	3 channels (Oz, O1, and O2)	75	2	6	23–30 years old.	Normal visual acuity	Flicker	White LED	Accuracy	Visual Analogue Scale (VAS) (Shahid et al., 2011)
11	Makri et al. (2015)	13	6.67, 7.5, 8.57, 10	4	4 channels (O1, O2, Oz and POz)	80	90	150	22–39 years old.	Normal visual acuity	Flicker	Checkerboard white and black, white square	$\alpha$, $\beta$, $\theta$, $\delta$-$\theta /\alpha$, $\frac{\alpha +\theta }{\beta }$, SSVEP amplitude	Chalder Fatigue Scale (CFS)
12	Palaniappan et al. (2018)	5	7	1	14 channels	…	…	…	25–26 years old.	Normal visual acuity	Flicker	…	$\beta$	…
13	Lee et al. (2018)	10	5.45, 6.67, 8.57	3	19 channels	50	5	6	24–32 years old.	Normal visual acuity	Flicker	white	band power at the target frequency, accuracy	simple questionnaire
14	Demir et al. (2019)	4	8,14, 28	3	128 channels	90	5	15	…	Normal visual acuity	Flicker	black and white checkerboards	PSDA, CCA, UF, BIFB	…
		4	6, 6.5, 7, 7.5, 8.2, 9.3, 10	7	3 channels			30
15	Chai et al. (2020)	14	8–15	8	8 channels (PO8, PO4, PO7, PO8, POz, O1, Oz, and O2)	70	3.5	5	Average 24.9 years old.	Normal visual acuity	Flicker and Motion	Blue, Green, Gray, White	Accuracy, SNR, $\frac{\alpha }{\theta }$	…
			38–45	8
			8–12.8	8