Psychophysiological Recording and Analysis
Brain activity was recorded with electroencephalogram (EEG) using the
Biosemi Active-Two amplifier system (Biosemi, Amsterdam, the
Netherlands) from 64 Ag/AgCl active electrodes attached to an elastic
cap according to the 10/20 system. The Biosemi Active-Two system
includes two extra electrodes instead of a single ground electrode,
namely Common Mode Sense (CMS) and Driven Right Leg (DRL) which act as
online reference and ground. In addition, the electro-ocular activity
(EOG) was recorded with two flat type active electrodes that were placed
on the two outer canthi of both eyes to record horizontal eye activity
and two more were placed on the infraorbital and a supraorbital region
of the right eye to register eye vertical movements. The signal was
digitized at a 512 Hz sampling rate, and 24-bit analog-to-digital
conversion and threshold of impedance was kept below 30 kΩ.
SCR was recorded using the same Biosemi Active-Two amplifier system. Two
8 mm Ag/AgCl electrodes that contained 0.05M NaCl electrolyte medium.
The electrodes were attached to the second phalanx of the middle and
ring finger of the non-dominant hand after lightly cleaned with water.
Both EEG and SCR were analyzed offline with the software BrainVision
Analyzer 2.0 (BrainProducts Inc., Gilching, Germany). For the continuous
EEG recordings, data was filtered offline with 0.1 Hz low cutoff, 40 Hz
high cutoff, and 50 Hz notch filters. Ocular artifacts were detected and
corrected with Gratton-Cole artifact correction procedure (Gratton et
al., 1983). Afterwards, data was re-referenced to the average of all
electrodes and segmented into time windows of 500 ms pre-stimulus until
5500 ms after stimulus onset. Artifacts were rejected according to the
following criteria: 1) maximal amplitude allowed was 200 μV, 2) lowest
activity allowed in intervals was 0.5 μV (100 ms interval length), and
subsequently the remaining trials were averaged according to the
experimental conditions. The signal was then transformed into the
frequency domain using a Fast-Fourier-Transformation for the last 2000
ms of stimulus presentation in order to eliminate initial non-stationary
ssVEP components and to highlight ssVEP power which has shown to be more
sensitive to conditioning effects in the second half of CS presentation
(Miskovic & Keil, 2013; Moratti et al., 2006; Moratti & Keil, 2005).
Based on previous studies (Stegmann et al., 2020; Wieser et al., 2014)
and the topography (see Figure 2), the ssVEP signal was averaged across
electrodes Iz, Oz, O1, O2, and mean activity from these electrodes was
used in the statistical analyses.