Brainamp amplifier

EEG was recorded using 64 sintered Ag/AgCl electrodes which were distributed on the electrode cap (Easycap) according to the international 10% system (Klem et al., 1999 (link)). The FCz electrode served as reference (re-used after offline average referencing) and the AFz electrode served as ground. Impedance at each electrode was kept below 5 kΩ. Two additional electrodes were used to record vertical and horizontal eye movements. One was placed under the lower eye lid and the other 1 cm lateral to the right eye. EEG data were digitized using a 64 channel BrainAmp amplifier¹ with a sampling rate of 1000 Hz and recorded with the BrainVision recorder software¹.

The EEG was recorded from 32 Ag-AgCl preamplified electrodes mounted on the actiCap and with a brainAmp amplifier (Brainvision, Morrisville). The recording reference was FCz and the acquisition rate was 500 Hz. All the EEG processing was performed in the NeuroRT software (Mensia, Renne). The following steps were performed in this order for the online preprocessing of the data: down-sampling to 256 Hz, bandpass filtering with an infinite impulse response filter at 1–50 Hz, notch filtering at 60 Hz, blink removal through blind source separation, re-referencing to the common average reference, and artifact detection by computing the Riemannian distance between the covariance matrix and the online mean. The data was then filtered to keep only the upper alpha band (10.5–13 Hz) and squared. Only data from P3 and P4 was kept in accordance with Ewing (Ewing et al., 2016 (link)). Finally, each 0.5 s epoch was divided by the average of the 1-min calibration period to normalize the data. This value, which ranged from 0.008 to 6.87, was then sent to the adaptation system to be used in the decision rule-based process.