Table 6.

Imagined speech classification methods summary (continuation).

References	Task	Methods	Brain area and waves	Performance
Cooney et al. (2020)	- Classification of /a/, /e/, /i/, /o/, and /u/	- CNN	- All areas	- Vowels: 35% best accuracy
	- Classification of “left,” “right,” “up,” “down,” “forward,” “backward” (in Spanish)	- ICA/LDA	−2–40 Hz bandpass	- Words: 30% best accuracy
Tamm et al. (2020)	Classification of five vowels and six words	- CNN	- F3, F4, C3, C4, P3, P4	−24% Average accuracy
		- Transfer learning
Chengaiyan et al. (2020)	Vowel classification	- RNN	- All areas	- RNN: 72% Average accuracy
		- DBN	−2–40 Hz bandpass	- DBN: 80% Average accuracy
Jiménez-Guarneros and Gómez-Gil (2021)	Short and long words classification	- SRDA	- All areas	- Short: 61% Average accuracy
				- Long: 63% Average accuracy