Electroencephalography Recording and Analysis

Continuous EEG was acquired using Neuroscan (Compumedics, Charlotte, United States) SynAmps2 64-channel amplifier and an Ag/AgCl Electro-Cap according to the standard international 10–20 system. A cephalic (forehead) location was used for the ground, and the left mastoid was chosen for reference. Vertical electrooculogram (EOG) was recorded from electrodes placed above and below the left eye. Horizontal EOG was recorded from electrodes placed at the left and right orbital rim. All interelectrode impedance was kept below 5 kΩ. The EEG signal was amplified with a band-pass filter from 0.01 to 100 Hz and digitized online at a sampling rate of 500 Hz.

The EEGLAB toolbox (Makeig et al., 2004) under the MATLAB environment was used for offline analysis. Data were re-referenced to the mean of the left and right mastoids and were digitally filtered from 0.1 to 30 Hz. Epochs were extracted from 0.2 s before to 1 s after the onset of the stimulus of interest. After baseline correction (-0.2 to 0 s), ocular artifacts were rejected by the independent component analysis. Trials with amplitudes exceeding ± 80 μV at any electrode were excluded from further analysis.

The ERP components analyzed included P2, FRN, P300, and LPP. Based on previous studies (Gehring and Willoughby, 2002; Yeung and Sanfey, 2004; Wu et al., 2012; Luo et al., 2015; Pornpattananangkul and Nusslock, 2015; Kwak et al., 2019) and topographical maps (refer to Figures 2, ​,3),3), the FC1, FCz, FC2, C1, Cz, and C2 electrodes were included in the calculations of the P2 component; for the FRN, one classical electrode, FCz, was included; for the P300, one classical electrode, Pz, was included; for the LPP, Cz, Cp1, Cpz, Cp2, P1, Pz, P2, and POz electrodes were included. We chose 230–270, 320–400, 350–450, and 500–800 ms after the onset of reward stimulus for analyzing P2, FRN, P300, and LPP. These time windows were selected according to visual inspection of waveforms and the classical definitions for these components.

(A) Grand-averaged event-related potentials (ERPs) at FC1, FCz, FC2, C1, Cz, and C2 electrodes for P200 with a comparison of the outcome under various feedback conditions. (B) Topographical voltage distributions of four conditions of interest in the time range of the P2 (230–270 ms).

(A) Grand-averaged ERPs at Cp1, Cpz, Cp2, P1, Pz, P2, Cz, and POz electrodes for late positive potential (LPP) with a comparison of the outcome under various feedback conditions. (B) Topographical voltage distributions of four conditions of interest in the time range of the LPP (500–800 ms).

Analysis of variance was conducted with three within-subject factors, namely, subjective evaluation (advantageous vs. disadvantageous), comparison direction (upward vs. downward), and electrode. Simple effect analysis was conducted when the interaction effect was significant. The Greenhouse–Geisser correction was used in all statistical analyses whenever appropriate. The Bonferroni correction was applied for multiple comparisons.