fig1

Figure 1. Overview of the speech generation process and silent speech interfaces. (A) Four stages of the speech generation process, following the process described in Ref. [31]. The figure that depicts stage 2 is adapted from Ref. [32], under CC BY 4.0 license; (B) Three categories of SSIs: epidermal, intraoral, and surgically embedded systems. These systems are classified by the level of physical intrusion into the human body. SSIs: Silent speech interfaces.