## 2 Methods
### BCI Paradigm Design: Visual and Auditory Stimuli
#### 2.4.2 BCI Versions and Iterations  
The different interfaces tested were developed according to the patient's needs for basic communication, with the goal of providing a small lexicon. The interfaces were designed iteratively, aiming to overcome the challenges posed by the lack of eye movement and aiming to simplify the interface and increase the patient's attention and engagement. Table 3 lists the iterations of the developed BCIs. In the following section, we describe the several iterations and their rationale (videos for each interface are available at [[https://home.isr.uc.pt/~gpires/videos/BCI4](https://home.isr.uc.pt/~gpires/videos/BCI4) ALL/videos.html]([https://home.isr.uc.pt/~gpires/videos/BCI4](https://home.isr.uc.pt/~gpires/videos/BCI4) ALL/videos.html) (accessed on 11 March 2024), except for the familiar faces' interface due to privacy reasons). \begin{table}
\begin{tabular}{c l l l} \hline \hline
**Iteration** & **Interface** & **Visual Stimulation** & **Audio Stimulation** \\ \hline
1 & Va & Arrow layout with words ON in green & - \\ \hline
2 & AVA & Arrow layout with words ON in green & Spoken words \\
2 & AVNa & Arrow layout with words ON in green & 4 spoken words and 3 white noise \\ \hline
3 & Vsf & Standard face in small central layout & - \\
3 & **Vff** & Familiar faces in small central layout & - \\
3 & AVsf & Standard face in small central layout & Spoken words \\
3 & **AVff** & Familiar faces in small central layout & Spoken words \\ \hline
4 & AVNsf & Standard face in small central layout & 4 spoken words and 3 white noise \\
4 & AVNff & Familiar faces in small central layout & 4 spoken words and 3 white noise \\ \hline
5 & **Vsf** & Standard face in grid layout & - \\
5 & **Vff** & Familiar faces in grid layout & - \\
5 & AVsf & Standard face in grid layout & Spoken words \\
5 & **AVff** & Familiar faces in grid layout & Spoken words \\
5 & AVNsf & Standard face in grid layout & 4 spoken words and 3 white noise \\ \hline
6 & **Vsf** & Standard face in grid layout with & - \\  & & & \\
6 & **Vff** & 'SIM/’NAO’ on the same side & - \\
6 & **AVsf** & Standard face in grid layout with & - \\  & & & \\
6 & **AVsf** & 'SIM/’NAO’ on the same side & Spoken words \\
6 & **AVff** & Familiar face in grid layout with & \\  & & & \\
6 & **AVNsf** & Standard face in grid layout with & 4 spoken words and 3 white noise \\ \hline
7 & **AVNw** & Words in grid layout with ‘SIM/’NAO’ & 4 spoken words and 3 white noise \\  & & on the same side, words ON in green & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Iterative design of the BCI interfaces (interfaces highlighted in bold were tested online with the patient). As a starting point, we used the visual interface tested in [7], adjusted to seven Portuguese text words ('Sim', 'Nao', Tosse', 'Ajuda', 'TV', 'Sono', and 'Stop') associated to arrow symbols. The stimuli were highlighted by switching color from gray to green. The symbols were positioned close together to be within the patient's foveal region. Given the poor ERP results obtained with this interface obtained in the first sessions, we decided to replace the text/arrow symbols with larger images covering the entire range of the screen. At the flash time, the text word was replaced by an image of an emotionally neutral person. The rationale of using faces as stimuli was to trigger ERPs related to face detection and processing and to increase task engagement [21; 22; 23]. Given the improvements in ERPs and in performance, we replaced the standard face with 7 images of the family, expecting to further improve task engagement and enhance ERPs. Given the vision impairments in CLIS patients related to the absence of gaze movements and eye dryness, auditory stimuli were added to the previous interfaces. The auditory stimuli were the 7 spoken words. Purely auditory interfaces and hybrid visuo-auditory interfaces were created.