Impact of Speller Size on a Visual P300 Brain-Computer Interface (BCI) System under Two Conditions of Constraint for Eye Movement

Table 4

Error performance (%, mean ± SE) results according to different layers of the matrix.

Layer	Overt attention				Covert attention
	Small	Medium	Large	Mean	Small	Medium	Large	Mean
Layer 1 (red)	2.8 ± 1.9	6.9 ± 4.3	16.7 ± 4.6	8.8 ± 4.1	50 ± 7.1	44.5 ± 8.5	66.7 ± 7.7	53.7 ± 6.7
Layer 2 (green)	2.1 ± 2.1	2.1 ± 2.1	12.5 ± 5.8	5.6 ± 3.5	49.3 ± 9.1	45.8 ± 10.6	70.8 ± 9.7	55.3 ± 7.8
Layer 3 (yellow)	4.2 ± 4.2	4.2 ± 4.2	20.8 ± 9.7	9.7 ± 5.5	29.2 ± 9.7	41.7 ± 8.3	33.3 ± 11.2	34.7 ± 3.7