fig4

Figure 4. EEG-based SSIs. (A) Working principle of EEG-based SSIs. The simplified EEG interface in the middle part of (A): Adapted from Ref. [91], under CC BY 4.0 license. EEG signals in the right part of (A): Adapted from Ref. [92], under CC BY 4.0 license; (B) SSIs enabled by scalp EEG and around-ear EEG. Scalp EEG: Adapted from Ref. [93], under CC BY 4.0 license. Around-ear EEG: Adapted from Ref. [94], under CC BY 4.0 license. EEG: Electroencephalography; SSIs: silent speech interfaces.