c-VEP-based BCI for PIN pad task on a T9 layout

# Participants
Eleven 11 volunteers (2 woman, mean age 28) with normal or corrected-to-normal vision participated in this experiment in our laboratory. The participants did not report any of the exclusion criteria (epilepsy, neurological antecedents, being under psychoactive medication). The study was approved by the ethics committee of the University of Toulouse (CER approval number 2020-334) and carried in accordance with the declaration of Helsinki. Participants gave informed written consent, prior to the experiment. The consent form included a section to approve the online data sharing.

# Experimental protocol
We used the BrainProduct LiveAmp 32 active electrodes wet-EEG setup with a refresh rate of 500Hz to record the surface brain activity. The 32 electrodes followed the 10-20 international system.  The ground electrode was placed at the Fpz electrode location and all electrodes were referenced to FCz electrode. The electrodes impedance were brought below 20 $k\Omega$ prior to the recording. We used a single maximum length sequence with 11 different shifts to animate the stimulation for the different targets. The presentation was rendered on an LCD monitor: LG GN 750, 1027x768 pixels, 400 cd/m^2, and 60Hz refresh rate. EEG data and markers were synchronized during recording using Lab Streaming Layer.

Subjects were asked to follow cues on a T9 layout to emulate a PIN code typing task (11 classes problem). It was implemented in Python, using the Psychopy toolbox. The 11 stimuli were circles with radius of 150 pixels, with a margin of 250 pixels vertically and horizontally and the figure in the middle.
Fifteen 11-trial blocks were recorded for each subject. During a trial, one of the 11 targets was cued for 0.5s, followed by 2.2s of stimulation with a 0.7s inter-trial before next one. The cue sequence for each trial was pseudo-random and different for each block. After each block a pause was observed and subjects had to press space bar to continue.

# Pre-processing
No pre-processing was applied and data are neither sliced or epoched but it is possible to do it with the help of the markers.